Preparation, Characterisation and Properties of Siloxane Copolymers

Y OF

o z') n

of Preparation, characterisation and Properties siloxane copolymers and Dispersions

t GÊUEE

A Thesis Submitted Towards the Degree of

Doctor of PhilosoPhY

Michael Shields B.Sc. (Hons)

IVERSITYOFAD E

School of ChemistrY and PhYsics The UniversitY of Adelaide ) October 2003 CONTENTS

vll Acknowledgements

viii Statement

ix Abstract

xi Abbreviations

1 CHAPTER 1 INTRODUCTION

1 1.1 Introduction to Siloxane Polymer Chemistry 1 and Copolymers 1.1.1 Poly(dimethylsiloxane) Polymers 2 1.1.1.1 CYclic PoIY(DMS) J l.I.l.2 Siloxane Polymer Preparation 5 1.1.1.3 Ring-opening Polymerisation 1 1.1.1.4 OrganofunctionalPoly(DMS) 8 1.1.1.5 Preparation of Functional Silanes 9 1.1.1.6 Heterofunctional Condensation 9 Lt.2 The Michael Addition Reactions 11 l.l.2.I Michael Additions with Amines t2 1.1.2.2 Michael Addition with Thiols 13 1.1.3 Characterisation Methods 13 1.1.3.1 NuclearMagneticResonanceSpectroscopy I6 1.1.3.2 GelPermeationChromatography 18 1.1.3.3 ViscositYMeasurements 20 T.1.4 Aims for the SYnthetic AsPect

22 t.2 Introduction to Siloxane Polymer Colloids 22 1.2.1 Emulsions and Latexes 23 t.z.lJ EmulsionPolYmerisation 26 1.2.1.2 The Electrical Double Layer 29 1.2.r.3 Brownian Motion and Coagulation 30 r.2.1.4 DLVO Theory 30 t.2.1.5 InterParticle Attraction 31 t.2.r.6 Electrostatic RePulsion JJ t.2.1.1 Flocculation of Particles 35 1.2.1.8 Steric Stabilisation 37 t.2.2 Colloidal Characteris ations 37 r.2.2.r Electrophoretic Mobility Measurements 39 t.2.2.2 TurbiditY Measurements 40 1.2.2.3 MicroscoPY 42 t.2.3 Aims for the Polymer Colloids Research 42 1.2.4 Thesis Outline

44 CHAPTER 2 THE PREPARATION AND CHARACTERISATION OF SILOXANE COPOLYMERS

44 2.r Introduction and Aims 46 2.2 Literature Review 4l 2.3 Experimental Section 41 2.3.1 Materials 48 2.3.2 CoPolYmerisation Reactions 48 2.3.2.I Experimental for Scheme 2'3 48 2.3.2.2 Preparation of Potassium Silanolate (4) 48 2.3.2.3 Experimental for Scheme 2'4 48 2.3.2.4 Experimental for Scheme 2'5 48 2.3.3 CoPolYmer Characterisations 48 2.3.3.1 NuclearMagneticResonanceSpectroscopy 49 2.3.3.2 ColumnSeParation 49 2.3.3.3 ViscositYMeasurements 49 2.3.3.4 GelPermeationChromatography 50 2.4 Results and Discussion Amine Functional 50 2.4.r Preparation and Characterisation of Poly(DMS ) using Heterocondensation

1l Amine Functional 55 2.4.2 Preparation and Characterisation of Poly(DMS) using Potassium Silanolate Functional 58 2.4.3 Preparation and Characterisation of Thiol Poly(DMS) using Trifluoromethanesuffonic Acid 64 2.5 Conclusions

65 CHAPTER 3 THE MICHAEL ADDITION

65 3.1 Introduction and Aims 66 3.2 Literature Review 69 3.3 Experimental Section 69 3.3.1 Materials 69 3.3.2 Michael Additions 10 3.3.2.1 Experimental for Scheme 3'2 l0 Experimental for Scheme 3'4 3.3.2.2 ,71 3.3.2.3 Experimental for Scheme 3'5 7I 3.3.2.4 Experimental for Scheme 3'8 ]I 3.3.2.5 Experimental for Scheme 3'11 l2 3.3.2.6 Experimental for Scheme 3'12 l2 3.3.2.7 Experimental for Scheme 3'13 13 3.3.3 Characterisations 13 3.3.3.1 NuclearMagneticResonanceSpectroscopy 13 3.3.3.2 Gel Permeation Chromatography l3 3.4 Results and Discussion 13 3.4.r Michael Additions using Propylamine 71 3.4.2 Michael Additions using 3-Aminopropyl MethYldiethoxYsilane 80 Poly(EG) Acrylate 3.4.3 Michael Additions using Methoxy 83 3.4.4 InvestigationofProticSolventsforMichaelAdditionsusing Amine Function Silanes Silane 89 3.4.5 Michael Additions using Thiol Functional 93 Michael Additions using 3.4.6 Investigation of Protic solvents for Thiol Functional Silanes

rll 95 Functional Poly(DMS) 3.4.7 Michael Additions of Amine 98 Functional Poly(DMS) 3.4.8 Michael Additions with Thiol 103 3.5 Conclusions

105 CHAPTER4ASTUDYOFPOLYSIOXANEDISPERSION STABILITY WITH AMINE AND POLY(ETHYLENEGLYCOL)

105 Introduction and Aims 4.1 rc] 4.2 Literature Review 109 4.3 Experimental 109 4.3.1 Materials 110 4.3.2 PreParation of DisPersions 110 4.3.2.1 Preparation of Poly(DMS) Emulsions 110 4.3.2.2 PreparationofPoly(DMS-MS)Dispersions 110 4.3.2.3 PreparationofPoIy(DMS-MS)/AMDispersions 111 4.3.3 PhYsical Measurements 111 4.3.3.1 OPtical MicroscoPY 111 4.3.2.2 TurbiditYMeasurements 111 4.3.3.3 NuclearMagneticResonance Spectroscopy r12 4.3.3.4 ElectrophoreticMobilityMeasurements 112 Results and Discussion 4.4 lt2 Dispersions 4.4.1 Studies of Poly(dimethylsiloxane) rt2 4,4,1.|lnvestigationofthePoly(DMS)Dispersion.withoptical MicroscoPY Nuclear 114 4.4.1.2 Investigation of the poly(DMS) Dispersion with Magnetic Resonance spectroscopy 116 4.4.I.3 lnvestigation of the Poly(DMS) Dispersion with ElectroPhoretic Measurements 118 4.4.2 Studiesof(Dimethylsiloxane-g-methylsiloxane)Dispersions r20 4.4.3 Studies of Non-dialysed Poly(dimethylsiloxane-g- methylsiloxane) Dispersions at Elevated Temperature t22 4.4.4 StudiesofPoly(dimethylsiloxane-g-methylsiloxane)/Amine Macromonomers DisPersion

lv Dispersions t23 4.4.4.r Effect of the AM on the Poly(DMS-MS) using Optical MicroscoPY of the 125 4.4.4.2 Nuclear Magnetic Resonance Spectroscopy PoIy(DMS-MS)/AM DisPersed Phase Dispersion t21 4.4.4.3 Effect of AM on the Poly(DMS-MS) Stability and r29 4.4.4.4 Effect of Low pH on the Poly(DMS-MS) Poly(DMS -MS )/AM DisPersions Poly(DMS-MS) 132 4.4.4.5 The Effect of Added Electrolyte on the and Po1y(DMS-MSYAM DisPersions the Poly(DMS- 135 4.4.4.1 The Application of DLVO Theory for MS) Dispersions 139 4.5 Conclusions

142 CHAPTER s STABILITY OF POLYI3-(DIMETHOXYMETIIYL)- To LATEXES I-PROPANETHIOL] DISPERSIONS: FROM EMULSIONS

t42 5.1 Introduction and Aims t43 5.2 Literature Review Gelation t43 5.2.r Siloxane Dispersion Preparation and Additions t44 5.2.2 Water or dispersion based Michael r45 5.3 Experimental t45 5.3.1 Materials t46 5.3.2 PreParation of DisPersions t46 5.3.2.1 Preparation of the Poly(DMST) Dispersion r46 5,3.2.2PreparationofthePo1y(DMST)/IVIPEGMaDispersion r46 s.3.3 PhYsical Measurements t46 5.3.3.1 Previous Techniques 141 5.3.3.2 Scanning Electron Microscopy 141 5.4 Results and Discussion t41 5.4.1 Studies of the Poly(DMST) Dispersions 141 5.4.1.1 Stability of the poly(DMST) Dispersions during SYnthesis

v 151 5.4.r.2 Characterisation of the Poly(DMST) Dispersions on the Poly(DMST) r54 5.4.1.3 The Application of DLVO Theory Dispersion t51 5.4.r.4 Gelation of the Poly(DMST) Dispersion Dispersion 159 5.4.2 Studies of the PoIy(DMST)/\4PEGMa 160 5.4.2.t Optical Microscopy Studies of the Poly(DMST)/ MPEGMa DisPersion 163 5.4.2.2 Evidence for Chemisorption of MPEGMa Dispersion 165 5.4.2.3 Stability of the PoIy(DMST)/\4PEGMa and Structure Determination 165 5.4.3 MPEGMa Layet Thicknes s and 161 5.4.4 Effect of Electrolyte on the Poly(DMST) Po1y(DMST)/MPEGMa DisPersions Dispersion Stability r70 5.4.5 Poly(DMST) and PoIy(DMST)/NIPEGMa at Low PH t73 5.4.6 Investigation of Solid Particles Po1y(DMST)/MPEGMa fl4 5.4.7 Investigation of Small Particles in t76 5.5 Conclusions

r79 CHAPTER 6 CONCLUSIONS AND FUTURE \ryORK

of Amine and Thiol 119 6.1 The Preparation and Michael Additions Functional Copolymers of Poly(DMS) using Amine or Thiol 180 6.2 Investigation of Polysiloxane Dispersions Groups attached to Poly(EG) through a Michael Addition 181 6.3 Final Comments r82 6.4 Future'Work

184 References

188 Appendix

v1 Acknowledgements

the completion of my I wish to thank everyone that participated in my project and and Dr Geoff crisp who thesis. Firstly to my supervisors, Dr Brian Saunders throughout the provided me with excellent ideas, feedback and encouragement reading my draft and course of the project. Andrew Koh for his guidance, the students of the viewpoints in the laboratory. The academic staff and The members of chemistry department for their helpfulness and approachability' especially Phil Clements the technical staff who keep the department running, Microscopy for usage and who provided valuable assistance with NMR. Adelaide assistance with electron microscopy'

Pty Ltd for useful advice I also wish to thank Geoffrey Swincer and Flexichem and scholarshiP funding.

and my best friends Finally I would like to thank my parents for all round support Baulderstone for Ian Mclntosh, Michael cherry and my girlfriend Melissa keeping me sane during the project'

v11 Statement

for any other award in This work contains no material which has been accepted contains no material previously any university and, to the best of my knowledge, reference has been published or written by another person, except where due made in the text.

in the University Library' I give consent to this copy of the thesis, hen deposited being available for loan and photocopyin '

v111 Abstract

(poly(DMS)) Amine and thiol funcrional copolymers of poly(dimethylsiloxane) mechanism' The were prepared using an alkoxy silane via a heterocondensation by nuclear magnetic amine functional poly(DMS) copolymers were characterised random configuration resonance (NMR) spectroscopy. The copolymers were of when using potassium silanolate as a catalyst and of block copolymer functional poly(DMS) configuration when using sodium hydroxide. The thiol acid and the (random arrangement) was prepared using trifluoromethanasulfonic (GPC) and properties were investigated using gel permeation chromatography viscosity measurements.

attack on an A Michael Addition, which is a reaction consisting of a nucleophilic a methacrylate or electrophilic acceptor, was performed. The reaction between and verified by acrylate and the nucleophilic amine or thiol group was achieved (poly(EG)) NMR specrroscopy. The acceptors contained a poly(ethyleneglycol) functional poly(DMS) was chain, which provided hydrophilic grafting. The amine to yield a tertiary amine' able to react with two equivalents of poly(EG) acrylate

or thiol The efficiency of the Michael Additions was tested using amine reaction times functional silane monomers with NMR spectroscopy. The fastest alcohols were used as (typically < 1 day) occurred for the thiols and when primary the protic solvents. Howevel, there was a trans-esterification reaction between chain. Tertiary butanol solvent and the ester, resulting in the loss of the poly(EG) to the hydroxyl was the best protic solvent employed due to the hindered access when the group. The Michael Additions also proceeded significantly faster hydroxyl end group' methoxy end group of poly(EG) was used instead of the which inhibited the This was attributed to hydrogen bonding with the nucleophile, nucleophilic attack on the acrylate'

Siloxane dispersions wele prepared using surfactant-free precipitation triethoxymethylsilane polycondensation of dimethoxydimethylsilane (DMDES), (DMST) in (TEMS) with DMDES or 3-(dimethoxymethylsilyl)-1-propanethiol

1X In the absence of heat' the aqueous ethanol solutions under alkaline conditions' 2 pm and were stable siloxane dispersions exhibited average particle sizes - during the time investigated (i'e', several weeks)'

diethoxymethylsilane and The Michael Addition product between 3-Aminopropyl identified and shown to be two equivalents of methoxy poly(EG) acrylate was particles using zeta (Ç) potential incorporated at the surface of the polysiloxane optical microscopy and turbidity measurements and NMR spectroscopy. Using chains exhibited improved measurements, the dispersion with surface poly(EG) concentrations (0 0'1 M stability acfoss pïz - 5 and at increased electrolyte - was postulated to exist NaCl). The structure of the poly(EG) chains at the surface thickness, which was estimated by the as a brush configuration with > 2 nmlayer exhibited greater stability concentration of poly(EG) measured. The dispersion stabilisation and thus than that which would be expected from electrostatic supported the presence of steric stabilisation'

for an extended time' the When the siloxane dispersions were prepared at 60oC indicated by the insolubility of samples exhibited gelation behaviour. This was behaviour was attributed to ring- the dispersed phase in the solvents tested. This siloxane oligomers' opening of cyclic and enhanced polymerisation of the cross-linking' followed by the entanglement of polymer chains causing

dispersion and the success of The Michael Addition was performed on the DMST spectroscopy. The absence of the reaction was confirmed by extraction and NMR and turbidity measurements' gelation was investigated using optical microscopy provided steric stabilisation' This was attributed to the poly(EG) chains, which the layer thickness of the The ( potential measurements were used to determine poly(EG)groupsatthesurface.Analysisofthepoly(EG)concentrationafter structure with a layer dialysis suggested the copolymer existed as a brush electron microscopy (SEM)' thickness of ca.10 nm. When observed by scanning exhibited hexagonal close the particles at the lower end of the partiole distribution Michael Addition packing. This could be due to secondary nucleation after the occurred.

X ABBREVIATIONS

Symbols

Att Hamaker constant of Phase 1

Azz Hamaker constant of Phase 2 A"¡ Effective Hamaker constant

a Droplet or Particle radius D Siloxane group containing two oxygens D" Gyration diameter

di Particle diameter of length i

dp Resolving Power

du Volume averaged particle diameter diameter du"n' Critical volume averaged particle E Applied field strength

e Electron charge k Boltzmann constant H Two-particle separation distance

Ho Applied magnetic fiel

h Planck's constant I Ionic strength t Intensity of incident light Ir Intensity of transmitted light L Repeating unit length Length M Siloxane group containing one oxygen Mi Molar mass of grouP i Mn Number averaged molar mass Mp Peak molar mass M* Weight averaged molar mass mw Molecular weight mass in Ni Number of polymer chains with molar group i

n Number of rePeating units

x1 size group i 1ì¡ Number of Particles in no Refractive index

P Pressure constant (logarithim) PKu Acid dissociation particles q Number of molecules in unit volume of RI Refractive index f Capillary radius T Temperature in Kelvin T" Glass transition temPerature t Time U Mobility V Particle velocity Vn Two-particle attractive interaction energy

Vmin Minimum for the two-particle interaction Vn Two-particle repulsive interaction energy

V,o, Two-particle total interaction energy

V Velocity

v Frequency V/ srability ratio

wtVo Weight Percentage

z ElectrolYte charge number

Greek Symbols

O( PolarisabilitY

õ Hydrodynamic laYer thicknes s

õ' NMR chemical shift Distance of the Stern plane from the surface ^ AA lnterfacial area change

AE Change in energY

AH Enthalpy of a reaction

AGfor Free energy for emulsion formation

AS Change in entroPY

xlr t Relative permittivitY ( = tn eo ) v MagnetogYric ratio Interfacial tension between phase o and B TCTP n Viscosity 1/r Double laYer thickness

). Wavelength

vo Bulk particle concentration

p Density o Half life of the number of particles

x Turbidity

at the Stern V¿ Potential Plane at the true surface Vo Potential Iç Zetapotential

Compounds and Abbreviations

L Hydroxy-terminated PoIY(DMS )

2 1,3 -diaminopentyl methyldimethoxysilane poly(DMS 3 Amine-functionalised copolymer of )

4 Potassium silanolate

5 Methyl-terminated PoIY(DMS)

6 3 -Aminoproyl methyldiethoxysilane of poly(DMS 7 Amine-functionalised copolymer )

1 -propanethiol I 3 -(Trimethoxysilyl)-

1 -propanethiol 9 3 -(Dimethoxymethylsilyl)- poly(DMS) 10 Thiol-functionalised copolymer of poly(DMS) L1 Thiol-functionalised copolymer of

12 Propylamine

13 Methyl methacrylate

14 Methyl acrylate (mw 15 Methoxy poly(ethyleneglycol) methacrylate = 41s) t6 Product of the reaction between 12 andl3

xil1 and14 17 Product of the reaction between 12 and1-.S 18 Product of the reaction between t2 (mw 375) L9 Poly(ethyleneglycol) acrylate = (mw 1000) 20 Poly(ethyleneglycol) acrylate = 2I Product of the reaction between 6 andl4 )1 Product of the reaction between 6 and 19 and20 23 Product of the reaction between 6 (mw 454) 24 Methoxy poly(ethyleneglycol) acrylate = and one 25 Product of the reaction between 6 equivalent of 24 and two 26 Product of the reaction between 6 equivalents of 24 6 and 24 27 Cyclic product of the reaction between and24 in 28 Products of the reaction between 6 propanol and 24 in tertiaty 29 Products of the reaction between 6 butanol (mw 30 Methoxy poly(ethyleneglycol) Methacrylate =

1 100) and L3 3L Product of the reaction between 9 and 15 32 Product of the reaction between 9 and 30 33 Product of the reaction between 9

34 Product of the reaction between 3 and24

35 Product of the reaction between 7 and24 and 15 36 Product of the reaction between L0 and 30 37 Product of the reaction between 10 and 15 38 Product of the reaction between L1 and 30 39 Product of the reaction between 11

acac AcetYl acetonate COSY Correlated spectroscopy CV Coefficient of variation DMDES DimethYldiethoxYsilane DMST 3-(Dimethoxymethylsilyl)- 1 -propanethiol GPC Gel permeation chromatograPhY

X1V (30) MPEGMA Methoxy poly(ethyleneglycol) methacrylate NMR Nuclear magnetic resonance o/w Oil-in-water PCS Photon Correlation SPectroscoPY Poly(DMS) Poly(dimethYlsiloxane) Poly(DMST) Poly((methylsilyl)- 1 -propanethiol) Poly(EG) Poly(ethyleneglYcol) ppm Parts per million PZC Point of zero charge TEMS TriethoxymethYl silane TIIF Tetrahydrofuran TMS Tetrametþlsilane SEM Scanning electron microscoPY TFOH Trifluoromethanesuffonic acid wo Water-in-oil CHAPTER 1 INTRODUCTION

into two sections' The first The background and introduction to this project is divided with one-phase section deals with siloxane polymer chemistry and is concerned polymer colloids and is synthetic reactions. The second section deals with siloxane concerned with two phase dispersions'

1.1 Introduction to Siloxane Polymer Chemistry

1.1..1PoIy(dimethylsiloxane)PolymersandCopolymers

number of beneficial Poly(dimethylsiloxane) or poly(DMS) polymers exhibit alatge Surface properties of attributes that are not exhibited by regular organic polymers. wetting, high water poly(DMS) include a low surface tension, good lubrication, good glass transition temperature repellence and a soft feel. Bulk properties include a low chemical (150 K), high dietectric constant and high compressibility' Beneficial resistance' low properties include low reactivity, low toxicity, high oxidative I environme ntalhazatdand low fire hazard'

flexibility of the The origin of many of these properties lies in the strength and partial ionic character which siloxane bond. The siloxane bond (-si-o-) exhibits a comparatively long si-o imparts thermal and oxidative stability. For poly(DMS), the polymers, reduce excluded volume and Si-C bond lengths compared to typical organic chain segments'1 interactions between methyl groups of neighbouring

may contain between The various structures containing silicon and oxygen linkages units for poly(DMS) contain one to four oxygen atoms per silicon atom. The repeat nomenclature (Figure 1' 1)' two oxygen atoms attached per silicon and is given the D

1 I I CH¡ o

"i' I 1 I Si o- si-cHj Si Si -o_ -o- -o- -o- I - I I I o CH¡ CH¡ CH:

I T a M D

various functional Sroups Figure L.L Structures and nomenclatufe for the containing silicon and oxygen linkages'

and the end group is M (mono- The repeat unit for poly(DMS) is D (di-oxygen) then T (tri-oxygen) or Q oxygen). If the polymer was prepared with a cross-linker, (quaternary-oxygen)isgivenforthegroupwherethecross-linkerislocated.

1.1.1.1 CYclic PoIY(DMS)

poly(DMS) can leaffange to produce a Under the influence of strong acids or bases, ionic character of the si-o bond distribution of ring and chain molecules. The partial depending on the conditions is able to be cleaved by either acids or bases and cyclic poty(DMS) contains two employed the oligomers may form cyclic species.l nomenclature' The value of the oxygen atoms per silicon and is also given the D repeating siloxane units in the cyclic subscript (e.g., D¡) indicates the number of (Figure 1.2). CH¡

CH¡

CH: o

o I / CH¡ \.r, CH¡ \", CH¡

D3 D¿ poly(DMS)' Figure 1.2 Structure and nomenclature for selected cyclic

strain energies' only poly(DMS) rings are able to form because they have very low size are strainless or almost Ds has a minor strain while Da and rings of greater

2 depolymerisation strainless.l'2 Cyclic siloxanes aÍe generated by backbiting cyclics can also form depending on the end-to-end chain distance of the oligomers' a result, siloxane polymerisations as a result of chain cleavage of linear polymer. As frequently generate mixtures of cyclic and linear species'1

I.l.l,2 Siloxane Polymer Preparation

polymerisation of silane or siloxane Siloxane polymers are typically prepared by the route' The process of preparing oligomers and generally follow an anionic or cationic of bi-functional siloxane polymers is performed either by the polycondensation polymerisation of cyclic silanes (homo- or heterocondensation) or ring-opening oligomers.

silanols and the elimination The homocondensation reaction involves the addition of support a favourable of water. Studies performed by Wilczek and Chojnowski3 was reported to be reaction. The condensation of trimethyl silanol in dichloromethane reaction is shown in Scheme l '1' an exothermic reaction (AH = -21 kJmol-t;. Th"

CH. CH

I Scheme 1.1 I I H:o 2 C}l,\ ei- OH + CH: Si si- cH3 + -o- I CH: CH: CH¡

the Studies performed by Guibergia-Pierron and Sauvet4 investigated silanol monomers and homocondensation reaction between phenyl functionalised reported an activation energy of -70 kJmol-l'

consist of an average For the preparation of polymers, bifunctional silanes which afe required for functionality of two Si-oH groups per monomer or oligomef propagation (Scheme 1.2).

CH 3 CH 3 CH 3 I -nH2O I I HO Si o OH n HO- Si -si Scheme L.2 -oH t -= CH CHs CH¡ 3 n-1

J hydrolysis reaction can hinder The reaction is an equilibrium process and the reverse can drive the the polymerisation. The removal of water during the process Principle which states that if an condensation reaction.5 This follows Le Chatelier's will adjust to offset the equilibrium is disturbed, the components of the equilibrium disturbance.6

are typically employed so In the industry, monomers such as dimethyldichlorosilane process (Scheme 1'3)'l hydrolysis and polycondensation can occur in a one-pot

CH. CH CH3 CH 3 I -nH2O I Scheme L.3 2nH2O I Si _o- OH ncl- Si-Cl -----+ HO S i-oH HO I I - CH¡ CH: CH¡ CH: t_ n-1

by forming the The presence of a strong base can catalyse the silanol condensation silanolate ion (Scheme 1'4).1 CH¡ CH¡ II si-o K' + Hzo Si-OH + KOH =- I CH: CH: Scheme 1.4 CH¡ CH¡ CH¡

I + __ HO_Si_O_ S F_OH I,O_ Si-O K + I CH: CH: CH¡

+ KOH

the silanolate on the silanol' The propagation stage involves a nucleophilic attack by

determining the The experiments using monomers such as trimethylsilanol in reaction cannot be used to thermodynamics and kinetics relating to the condensation polymers' The latter are more interpret the end capping reactions for the poly(DMS) Further complications in stable and more hydrophobic than silanol monomers'l concerns the ability for understanding the end capping reactions of poly(DMS) Chojnowski et al'1 investigated siloxane bonds to break and rearrange in equilibrium.

4 in basic media and reported the polycondensation of oligodimethylsiloxane-cr-ú>diols the presence of disproportionation (Scheme 1'5)' 'i" 'i" 1.5 i' Si H HO Si Scheme 2HO Si ------* HO +

I I CH CH¡ CH¡ n+1 n -1

from smallef Different size oligodimethylsiloxane-cr-o>diols can be prepared oligomers. Sharaf and Marks performed chain extensions using and 2-ethylhexanoate oligodimethylsiloxane-cr-c*diols with diethoxydimethylsilane mass from 700 gmol-l to 22000 gmol-l as a catalyst and reported an increase in molar examined the chain extension using gel permeation chromatography. Clarson et al9 of 2- of oligodimethylsiloxane-cr-odiols and reported the concentrations those which favoured ethylhexanoate that favoured chain extension and important consideration as the heterocondensation with alkoxy silane. This is an initiator can govern the relationship between heterocondensation and the possibility for homocondensation. If heterocondensation is desired than homocondensation must be eliminated'

1.1.1.3 Ring'opening Polymerisation

is by ring-opening Another common synthetic method of preparing poly(DMS) is thermodynamically polymerisation of cyclic siloxane' Ring-opening polymerisation and cyclic forms of the controlled and consists of an equilibrium between linear between the ring- siloxane. Since there is no net change in the number of bonds there is a negligible change in opening or ring-forming of cyclic and linear polymer, t strained and has a subsequent enthalpy. The exception is D3, which is slightly Since D¿ and greater size cyclics increase in enthalpy (15 kJmol-l) for ring-opening.lo by an entropic consideration' have very minor or no strain, ring-opening is controlled freedom of the open This is attributed to the increase in the number of degrees of chain structure

5 1949 when Hyde11 Anionic polymerisation of cyclic siloxanes was first discussed in linear polymers' The noticed that strong bases transformed cyclic oligomers into siloxane bond favours D¿ over observed reaction order for base-catalysed cleavage of polymerisation' The first linear which can be taken advantage of in an equilibrium base produces a silanolate end- step is the initiation, where the presence of a strong curve lepresents the Si-O- group via cleavage of the Si-O bond (Scheme 1.6;.1 The

repeat units (e.g', Da). +-\ K O-Si Scheme 1.6 KOH + + Ho-

This is followed by a propagation step (Scheme 1'7) + K +- K Scheme 1.7 + i-o-si

HO-

a trimethyl functionalised The silanolate end groups can then be neutralised using (Scheme 1'8)' silane such as hexamethyldisiloxane (MM)

CH¡

si-o--L K i-o-si-cH3

I CH¡ + Scheme L.E + ----+ CH¡ 'f" 'T' k o-si-cH3 CH¡ -si-o-si-cH3 I CH¡ CH¡ CH¡ MM

6 acid and water' While The silanol functionality can also be generated using a strong linear over D4' an the acid catalysed polymerisation favours chain cleavage of (much the equilibrium involving equilibrium between cyclic and linear species like (Scheme 1'9)' potassium silanolate) has been reported3 for this reaction

HA + +

Scheme 1.9

\ A Si HT_Si

Hzo + HO-- Si

is D¿ and is easily The most commonly employed cycl\cr2 in siloxane chemistry by 2esi NMR formed and distinguished from other chains or linear oligomers used prepare siloxane spectroscopy. Ring-opening polymerisation can be to other than methyl groups' copolymers using cyclics that contain substituents

l.l.l.4 Organofunctional Poly(DMS)

such as surface For many applications such as hair and skin care, the properties copolymers can be adhesion for poly(DMS) are insufficient. Organofunctional amine groups' copolymers of prepared with various functional groups such as polar processors for many y"*''t' amine have been used for fabric treatments by the textile poly(DMS) polymer used on Addition of a small proportion of amine groups on the fabrics can be wool prevents shrinkage during wash cycles.14 Polyester/cotton is achieved by the improved using a soil-releasing hydrophilic siloxane. This (poly(Ec)), carboxylic incorporation of polar groups such as poly(ethyleneglycol) 15 acids or quaternarY amines'

7 polymer is low, the When the concentration of added reactive groups in the the characteristics of poly(DMS), organofunctional siloxane generally retains most of group' The proportion is while gaining the new interaction from the added functional 'When less than 5 mol7o'1 the considered low when the functional group represents new characteristics proportion of added reactive groups is high (> 5 mo|Vo), entirely for the copolymer may be exhibited'1

and the organofunctional The most common linkage between the polymer backbone group (X) is the propyl group (Figure 1'3)'

T S i-CIJ2-C¡¿z-CHz-x

Figure 1.3 Structure of the propyl spacer'

stability to the repeat unit and The three-carbon spacef confers thermal and hydrolytic allowstheorganicgroup(X)tobespatiallydistinctsuchthatreactantaccessisless hindered by the backbone.l

1.1.L.5 Preparation of Functional Silanes

polymers, the desired functional In order to prepare the organofunctional poly(DMS) hydrosilylation of a silane group can be first incorporated using the anti-Markovnikov

monom"rt6 (Scheme 1. 10).

OCH3

CH¡ + CH2:CH-CH2-NH2 -si-H Scheme 1.10 ocH3 OCH 3

+ cH: si- c}l2- CIF'z- CH2-NH2 - ocH3

8 for the organic The anti-Markovnikov reaction provides the three-carbon spacer project' The silyl alkoxy group, which is to be either a amine or thiol group in this producing a copolymer via the groups remain unreacted and become the active site in heterocondensation. l.l.l,6 Heterofunctional Condensation

various other silicon functional The silanol group can produce a siloxane linkage with Si-H, (with R being groups. Examples of this include si-cl, si-ocoR, si-oR, si-NR, with silanol or an alkyl or aryl group). The species can undergo condensation as it allows a greater oligodimethylsiloxane-cx-odiols.l This is particularly useful rangeofmonomeltypestobeincorporatedintothepoly(DMS)backbone.

alkoxy groups are used Heterofunctional condensations involving three or four silyl in the technology of with oligodimethylsiloxane-cr-r+diols to produce cross-linking employed are cold vulcanized elastomers. The cross-linking agentslT typically

Si(OCH3)4, MeSi(OCH3)3 or PhSi(OCH3)3'

t.I.z The Michael Addition Reactions

this project' The Michael The Michael Additionls is a key reaction for the work in Addition involves the reaction between a nucleophile and an Cr'B-unsaturated is to be used in this project to acceptor. The addition can combine two reactants and silanes' The Michael further extend the grafting of the copolymers or modified thiols' alcohols or Addition can occuf for a variety of nucleophiles including amines, double or triple bond carbanions. The Michael acceptor may contain a conjugated listed in Table 1' 1' with an ester, aldehyde, nitrile or nitro group such as those

9 Table 1.1 List of possible nucleophiles and acceptors for Michael Additions'le Nucleophiles Michael AccePtors RNH2 CHz=CHCHO RNHR CH=CHCOzR RSH CH=CCOzR (RCO)2COII CHz=CHC--N RCOCH2COR CHz=CHNOz

The bold font rePresents the nucleophilic grouP

extend the grafting of polymers In order to understand the use of Michael Additions to of the reaction mechanism is or in modifying silane macromonomers, the knowledge electrophile centre' the required. unlike a direct 1,2 addition of the nucleophile to an is stabilized via the Michael Addition involves the conjugate or 1,4 addition that enolate ion intermediate (Figure 1'4)'

4 o ll I I C Nu <---+> C C C-Nu -\ L- C 2 1 - - - I I

Figure 1.4 Mechanism for the formation of an enolate ion intermediate'le

required to polarize The presence of the carbonyl group (or nitrile, nitro) is therefore of the nucleophile to the the carbon-carbon double bond. The net result is the addition unaffected' The formation carbon-carbon double bond, with the carbonyl group itself the formation of the oc-Nu of the intermediate requires the loss of the ncc bond and requited 12 kcal / bond. Thomas and Kollman20 calculated that this intermediate - reported low activation mol for the reaction between methane thiol and acrolein. They structure using ab Initio energy between the ion-dipole complex and the transition molecular orbital studies.

the thermodynamics Despite a dependence on the type of solvent or steric hindrances, by examination of the bond often favour a conjugate addition' This can be illustrated

energies between a primary amine and methyl acrylate'2l

10 RNH2 + cHz:cH-co2cH3 ------+ RNH z-clglz-cozcH¡ -cH 640 kJmol I ENg - 390 kJmotl + ECC(¡) - 250kJmot1 Erotal - 4l5kJmotl 695 kJmoì-1 ECN - 280 kJmotl + ECtt - Etotal - acrylate' E represents Figure L.5 Reaction between a primary amine and methyl thebondenergyforthebondstobebrokenandbondsformed.

the total energy input subtracted Given the enthalpy of the reaction (AH) is equal to to an exothermic by the total energy output, AH = - 55 kJmol-1, which corresponds reaction.

this project are concerned with The various Michael Additions that are included in two types of nucleophiles, the amine and the thiol'

l.l.2.I Michael Additions with Amines

can be either negatively charged or In a Michael Addition the attacking nucleophile to a hydrogen atom that can neutral. If it is neutral, the nucleophile is usually attached amines contain a lone pair of subsequently be eliminated.le As primary or secondary Since amines are basic electrons they can act as nucleophiles in the neutral form' attack would be favourable they behave as poor leaving groups and the nucleophilic of amines is usually irreversible over the elimination reaction. The Michael Addition Michael Addition without under these conditions. Examples2l of amines undergoing 1'13' the addition of abase is shown in Schemes 1'11to

CH,

I CH¡ cH:- cH2- NH2 + CJjr:ç- C}lz-

o Scheme 1.1L -100 0c, 40 hr

88Vo

11 cH¡-cH2-NH2 + CH2: CH-C:N Scheme 1.12

H2O,5 hr,2o oC, t hr, 100 oC

907o CH: CHz- NH C}{z- CH2 N - -C: - 21 to produce tertiary amines: Secondary amines can also undergo Michael Additions CH¡

I __ I CH¡-CH2- NH2 + CHz Ç-Ç-o-cH3

lt o

methanol, 3 daYs, 20 oC Scheme 1..13 l'tvo

ll c}l2-cH- C -o-cH3 cH¡- cHz- <.::

1.1.2.2 Michael Addition with Thiols

amine or alcohol group The thiol group (S-H) is more acidic than the coresponding Since sulfur is a larger and therefofe acts as a nucleophile in the anion form only' away from the nucleus and atom than nitrogen, the outermost electrons are further better nucleophile compared to thus held more loosely which makes a sulfur anion a 10 (cf. pK" 40 for amines)'22 an amine.2'Not" that the pKu of alkyl thiols is - -

to rapidly produce high Michael Additions involving thiols have been reported23 o yields (Scheme l.I4). il CH3- SH + HC- c- o CH¡ - Scheme 1.14 o

ll cDcl3 21oC I hr CH¡- s-c o lO0Vo -CH¡ H

t2 1.L.3 Characterisation Methods

characterised by nuclear The copolymers to be prepared in this project are to be the presence and proportion of magnetic resonance (NMR) spectroscopy to determine end group analysis and the the modified groups, the size of the polymer chains by (GPC) and proporlion of cyclic oligomers present. Gel permeation chromatography of the polymers estimated viscosity measurements are to be used to support the size by end group analYsis'

1.L.3.1 Nuclear Magnetic Resonance Spectroscopy

(i'e', non-zero spin NMR spectroscopy requires atoms with spin angular momentum with positive spin states). When an external magnetic field is applied, the nuclei (cr-spin state) and those of orient themselves in the direction of the applied field 6 direction (p-spin state) (Figure negative spin state orient themselves in the opposite

1.6).

B state

o( state

No magneric field Magneric field applied I nuclei exposed to a Figure 1.6 Schematic representation of the spin states of magnetic field'

applied to the nuclei orientated When electromagnetic radiation of a specific energy is the radiation' flip spin and by the magnetic field the nuclei of the 0( state will absorb the energy difference between the enter the p state. The energy difference is equal to

13 and forth in resonance with the two states (AF). The spins continue to flip back 6 states results in an NMR signal' electromagnetic radiation. The resonance between

the better the resolution of the The greater the energy difference (AE) between states is related to the strength of the NMR spectrum. The energy difference between states applied magnetic field (H"): h^y (1.1) AE= hv = 2n Hn

is the frequency and the where h = Planck's constant (6.63 x 10-3a Js), v lis properties of a particular nucleus' magnetogyric ratio, which depends on the magnetic is equal to26'15 x 107 rad T-1 s-l' In the case of the proton, the magnetogyric ratio given field strength with a given The energy diff-erence is therefore, constant for a lH, t3c, ,nsi; ratio.6 nuclei (i.e., which has a characteristic magnetogyric

from the applied magnetic The presence of other nuclei can partly shield a nucleus magnetic field by field. The nuclear magnetic moments interact with the local electronic currents)' electronic orbital angular momentum (i.e., circulation of surrounding atoms a given Therefore, depending on the chemical nature of the dense environment the shift is resonance frequency may be shifted. For an electron This is known as the upfield and a less dense environment the shift is downfield' (pp-).,4 chemical shift (õ,) and is measured in parts per million

(r.2) shift in Hz from the tetramethYlsilane (TMS ) standard ô'= spectrometer ln

lH and in NMR is upfield since TMS is usually employed as a reference compound as carbon is more electronegative the protons are in an electron dense environment the reference compound and the than silicon.6 In'nsi NMR TMS is also employed as from TMS' chemical shifts typically can be either upfield or downfield

a non-zero spin' Its low 2esi is the only natural occurring isotope of silicon with 13c, where high concentrations and long abundance (4.lvo)places it in the group with resonances' The problem of low experiments are required in order to resolve the

t4 day Fourier Transform (FT- abundance nuclei is partially overcome with modern the data are NMR). RF pulses excite all the nuclei simultaneously and tnsi also possess long mathematically transformed to a Spectrum. However, delays between excitation and relaxation times f'or spins that would cause significant concentration of a relaxation. This can be overcome with the addition of a small serves to replace other paramagnetic relaxation agent such as cr(acac)3. This dipole-dipole relaxation interactions with the highly efficient electron-nuclear 25 interaction, thereby decreasing the relaxation time'

for linear and cyclic Examples of chemical shifts for different silicon environments poly(DMS)arelistedinTableir}andothervarioussilanesarelistedinTablel'3'

Table 1.2 cyclic poly(DMS)'2s 'nsi NMR shifts for linear and M D(1st) D(2nd) D(3rd) D(4th) Compound (ppm) (ppm) (ppm) (ppm) (ppm) MM 6.19 MDM 6;70 -2r.50 MDzM 6.80 -22.00 MD:M 6.90 -21.80 -22.60 MD¿M 7.00 -2t.80 -23.40 -22.30 MDsM 7.00 -21.80 -22.40 7.00 -21.80 -22.30 -22.20 -22.33 -22.29 MDzM 7.00 -2r.89 -22.49 D3 cYclic -9.r2 Da cyclic -19.51 D5 cyclic -2r.93 D6 cyclic -22.48

Table 1.3

'nsi NMR shifts for various silanes.25 rsi shift Compound chemical shift Compound "tt"-ical(ppm) 0.0 zO -10.5 -18.25 ioH -r2.6 -J.J S 29.87 CH¡ -44.2 SiH¿ -91.90 CH OCH

15 can be A two dimensional experiment called cosY (correlated spectroscopy) Two identical chemical shift performed in order to detect spin-spin coupled protons. spectrum on the axes are plotted orthogonally with the traditional one-dimensional coupled are shown by cross diagonal of the plot. All peaks that are mutually spin-spin Th" advantage of peaks which are symmetrically placed about the diagon ul'26 determination by identifying detecting spin-spin coupled protons allows structural functional groups that are in close proximity'

1.L.3.2 Gel Permeation Chromatography

siloxane copolymers' GPC The synthesis in this project involves the preparation of Much of the can be used to characterise the molar mass of the copolymers' the cross-linking of pioneering work was performed by Moore2T who investigated a GPC column' The GPC column is styrene with divinyl benzene in the preparation of and provide a fange of molar able to separate the polymer into different chain lengths in terms of molar mass masses. The distribution of molar masses is characterised

averages (Figure 1.1).tt

M Mn

Ø Ø(t

è\ña

l\{olar mass

distribution cufve' Figure L.7 Schematic representation of a typical molar mass mass' peak molar mass and Note that Mn, Mp and M* *à tn" number uu"tug" molar the weight avel'age molar mass respectively'

molecules at a given molar mass The Mn and M* relate to the number (NJ of polymer (Mi) by:

I6 t NiMi (1.3) Mn INi

(1.4) M*

diffusional broadening of the However, both the Mn and M* are subject to error from larger molecules, the longer the peak.2s Since smaller molecules diffuse faster than peak can occul' The peak retention time the greater the error or broadening of the of molecules at a single molar molar mass (Mp) is defined as the largest mole fraction a GPC chromatograph and is a mass and can be represented by the maximum peak in rigorous treatment of useful quantity to compare various polymers without a broadening elTor.

pump, injection valve, a sefles The essential components to Gpc include the solvent (Figure 1'8)' The columns of columns packed with beads of porous gel and a detector high-pressufe pumps are required to are uniformly and tightly packed and generally pumps offer pulse-free force solvent through the column. High quality solvent the requirement of recording constant volumetric flow rates and are essential in

accurate elution times.28 injection valve

detector

pump recorder

waste solvent GPC columns

Figure L.8 Schematic illustration of a GPC apparatus'

t] into a solvent stream' which GPC involves the injection of a dilute polymer solution polymer molecules are able to flows through columns of porous gel. The smallest so have a relatively long flow path pass through most of the pofes in the beads and are excluded from all but the through the column. However, the largest polymers path' 28 largest of the pores and have a relatively short flow

is required to measure As solvent continuously flows through the column a detector each moment during the the relative concentration of solute in the solvent at red can be used to measure experiment. Detectors such as ultra violet or infra refractometer (RI) measures the adsorption from the polymer. The differential and pure solvent.2s The refractive difference in refractive index between the eluant polystyrene are easily distinguished and index of toluene, poly(dimethylsiloxane) and

have values of 1'496, 1.400 and 7'5g2,respectively'29

organic solvents are rigid porous The GPC column packing most commonly used with surface treated silica gel' Styragel is a beads of either cross-linked polystyrene or divinyl benzene with a small commonly used gel, it is a copolymer of styrene and

degree of cross linking (i.e-,ZVo)'

Mn and M' values for all types Since samples with narrow polydispersity of specific are used as a universal of polymers are not available, polymers such as polystyrene for a range of polystyrene standards' calibration. One can measure the retention times from those retention times' then estimate the molar mass for different polymers

1.1.3.3 ViscositY Measurements

that the polymer flows at different The applications for various polymers may require viscosity is an important measulement rates ranging from rapid flow to no flow. The polymer chains increases the flow in quantifying the rate of flow. As the size of the be used to estimate the rate decreases. Viscosity measurements can therefore, viscosity averaged molar mass of a polymer'31

18 u-tube viscometer Viscosity measurements can be performed using an Ostwald for flow within a given (Figure 1.9) with a known sample reference. The duration viscometer is directly proportional to the viscosity'

viscometer' The left bulb Figure 1.9 Schematic illustration of an ostwald u-tube bulb. is |tre reservoir bulb and the right bulb is the measuring

lower etched marks and is The viscometer contains a measuring bulb with upper and is forced through the tube attached directly above a thin capillary tube. The liquid for the liquid to flow back into the reservoir bulb under pressure and the time required viscosity of the liquid' into the measuring bulb is recorded' Depending upon the (r) can be used' viscometers of different capillary thickness with radius

rate of shearing force per The flow of a liquid is described as Newtonian when the parallel planes' At the middle of unit area is proportional to the gradient between two amount of shear and maximum the capillary tube the liquid experiences the minimum amount of shear velocity (v) while at the walls the liquid experiences maximum

(Figure 1.10).31

dv/dr

V ? within the Figure 1.10 Schematic representation of the variation of shear viscometer caPillary tube.

t9 and can be The polymers to be investigated in this work are not in solutions flow, the viscosity of the considered Newtonian. Under the conditions of Newtonian the Poiseuille equation:28 liquid can be related to the radius of the capillary tube by (1.s) V noP t 8n/

of the capillary, r is the radius where v is the volume of liquid, t is time, I is the length and is the viscosity of the capillary P is the pressure difference across the capillary 1 that determines the volumetric flow rate'

is also proportional to the Since the pressure that drives the liquid though the capillary (n) and a reference sample density (p), the viscosity between an unknown sample

(r'¡,") can be calculated using:31 (1.6)

and reference liquids' where t and t."¡ is the duration time for the unknown respectively

1.1.4 Aims for the Synthetic Aspect

Theaimsforthesyntheticaspectsofthisprojectaretwofold:

amine or thiol 1) To prepare and characterise siloxane copolymers containing functional groups. with the amine and 2) The Michael Addition of poly(EG) acceptor molecules thiol functional silane monomefs and siloxane copolymers'

contain silyl alkoxy groups that Objective one is concerned with silane monomers that with poly(DMS)' The should be able to undergo a series of condensation reactions must not interfere with the monomefs will contain an amine or thiol group which with new functionality' The incorporation into poly(DMS) but provide the copolymer

20 and type of functional groups aim is to get a greater understanding of the proportions backbone' that can be covalently attached to the poly(DMS)

poly(EG) groups onto Objective two is concerned with the addition of a hydrophilic which contains a c[' B an amine or thiol group using an acceptor functionality greater understanding of the unsaturated functional group. The aim is to get a hydrophilic groups to the efficiency of the Michael Addition and its usage in attaching the possible side reactions or silane and siloxane species, as well as investigating applications in the industry' For conditions that limit the reaction for the potential a softener the hydrophobic nature example, when poty(DMS) is applied to textiles as the surface' This causes of the polymer prevents the discharge of electrons from fibre materials' The electrostatic attraction with dust and other undesirable adsorption of water' which incorporation of hydrophilic chains may allow the electrons from the surface and provides ionic conductance and allows the discharge of other material'3O The covalent subsequently reduces the electrostatic attraction to term survival against fteatment attachment of the hydrophilic group may ensule long

and wear of the textile

2l r.2 Introduction to siloxane Polymer colloids

of siloxane emulsions and The second part of the project involves the investigation latexesandtheresultsanddiscussionarecoveredinChapter4and5.

1.2.1 Emulsions and Latexes

(e'g', water and oil)' The two An emulsion is a dispprsion of two immiscible liquids phase and continuous phase' For an oil- phases are designated by the terms dispersed form in a water phase' If the in-water emulsion the oil is dispersed in the droplet (cf' droplets) then the term latex dispersed phase consists of solid polymer particles focus on emulsions' dispersion (cf. emulsion) is used. The discussion will

every day life' some of the many Emulsions in various forms are encountered in industry (milk, butter)' when the examples of emulsions can be found in the food an O/IV emulsion (e'g'' milk) and dispersed phase is oil, the emulsion is regarded as is used (e'g', butter)' Applications when the dispersed phase is water, the term WO droplets), pharmaceutical can be found in the cleaning industry (removal of oil creams) and the textile industry (drug detivery), cosmetic industry (lotions and industry (coatings).3r

liquids requires energy due to the The formation of an emulsion from two distinct one of the liquids in the other' large increase in interfacial area arising from dispersing be represented3l as: The free energy (ÂGror*) for emulsion formation can (r.7) AGro., = '¡,"Þ^A - TAS

the interfacial tension' T is the where AA is the change in interfacial area, fB it change in entropy' The entropic term temperature in absolute Kelvin and AS is the in interfacial area that is the favours emulsion fbrmation, however, it is the change <100 nm' Since AGro.,n of all dominant term31 unless the droplet size is very small and stability is colloids is positive, emulsions are thermodynamically unstable kineticallY controlled.

22 all directions' However' Molecules in bulk solution are subjected to attraction in forces resulting in a net molecules at an interface experience unbalanced attractive phase' This force results force in the direction normal to the surface towards the bulk

c)¿ and p and is measured in in an interfacial tension (fÞ) ¡etween the two liquids,

N/m.31

the formation of an emulsion' The Decreasing fp decreases AG¡o.. thus favouring molecules (e'g', interfacial tension can be decreased by addition of amphipathic interface' which provide surfactants and certain types of polymers) at the the hydrophilic portion and intermolecular bonding between the aqueous phase and between the oil phase and the hydrophobic portion'

the two phases with mechanical Emulsions are frequently prepared by dispersion of of inhomogeneites in the shearing. The emulsions tend to be polydispersed because mixers can break up local shear. Equipment such as homogenisers and laboratory larger droplets giving rise to a less polydispersed emulsion'3r

of two phases' They The emulsions in this project aIe not prepared by emulsification single phase' The general term for are prepafed by a chemical reaction with an initial this process is called emulsion polymerisation'

1,.2.1.1 Emulsion Polymerisation

with an initial soluble This project involves the preparation of an emulsion starting and colloidal monomer. The mechanism of both chemical (condensation reactions) for understanding the (droplet nucleation) are expected to be important considerations

properties of the final emulsion.

either soluble in the solvent Emulsion polymerisation requires that the monomers are for the polymerisation must or partially soluble (e.g., styrene in water). The catalyst polymerisation which be soluble in the solvent otherwise the system is a suspended The two main type of resembles that of a bulk phase polymerisation reaction' Free-radical emulsion polymerisation pfocesses are free-radical and ionic'

23 remains active during polymefisations involve the formation of a radical which polymerisation involves the propagation until termination with another radical. Ionic As termination does formation of a positive (cationic) or negative (anionic) charge' the number of active sites is not occur between two like charges the potential for considerably larger than that of the free-radical p'o"ess't'

of monomer to a If the propagation for ionic polymerisations occurs by addition polymerisation and polymer chains growing chain, the mechanism is known as living monomels to react the grow fast. If propagation allows for the ability for any two In step growth polymerisation mechanism is known as step growth polymerisation. reaction of the initial the growth of polymer chains is typically slower but the monomer concentration is rapid'28

of the emulsion is In this project the chemical reaction present in the preparation follows the step growth expected to consist of a condensation reaction, which absence of any stabilising mechanism. The emulsion is also to be prepared in the

surfactant.

the oligomels can When the solubility of the newly formed oligomers decreases' bonding' As the arrange in micelles to experience favourable intermolecular primary droplets or particles can oligomers or aggregates grow in size, nucleation into to form larger droplets' occur. The precipitated droplets can adsorb more monomers polar (due to ion-dipole Given the absence of surfactant, an ionic group that is of the dispersion is obtained interactions) will reside at the phase interface. Stability and provide a significant if enough charge groups can form at the interface droplets would eventually form two electrostatic potential, otherwise the precipitating nuclei or droplets occurs distinct separated phases. Aggregation of monomer swollen electrostatic stabilisat ion'32 to increase the size of the droplets to provide adequate

potential for nuclei to adsorb As the surface area of the dispersed phase increases, the state in the emulsion polymerisation at the interfäce increases. This leads to a steady intermediates with primary when the rate of capture and flocculation of participating Generally the faster the droplets equals the rate of nucleation of primary droplets'

24 the final distribution' polymerisation reaches this steady state the less polydispersed secondary nucleation) leads to a This is because continued nucleation (also known as the dispersed phase also favours broader distribution. The increasing surface area of droplets'32 polymerisation at the surface relative to the interior of the

the surface as a result of the If sufficient electrostatic stabilisation can be achieved at added stabiliser' Some of the polymerisation process, no surfactant is required as an performed by Goodwin ol33'34 early surfactant-free emulsion polymerisation was 't the preparation of polystyrene using the free-radical process. The procedure involved latex particles using sulphate radicals'

precipitation The preparation of poly(DMS) dispersions using surfactant-free The term surfactant- polycondensationhas been reported by various authors.3s'36'37'38 surfactant and in these cases the free indicates that the emulsion contains no added from the charged groups on the emulsion is controlled by electrostatic stabilisation oligomers that can oligomers. Precipitation rcferc to the formation of non-soluble that of a suspended undergo continued polymerisation. This stage resembles polymerisation the polymerisation reaction, however, in classical suspended polycondensation refers to the monomers would start in the suspended form. Finally the active site for method of polymerisation involved and the formation of propagation is shown in Scheme 1'15'

CHs CH¡

I ___+ + CH3CH2OH cH3cH20- Si-OCH2CH3 + H2O CH3CH2O-si-OH

CH: CH¡ Scheme 1.15

oH-

CH¡

cH3cH2O-si-o- + H2O

CH¡

poly(DMS) from silyl alkoxy The surfactant-free precipitation polycondensation of This is different to normal functional groups therefore, requires water as a reactant'

25 the suspension medium does not emulsion or precipitation polymerisation in which play a direct role in the reaction'

1.2.1.2 The Electrical Double Layer

into contact with a polar Most surfaces acquire an electric charge when brought ionisation, ion adsorption or ion medium (e.g., water). This may occur as a result of of nearby ions of the polar dissolution. The surface charges influence the distribution Due to thermal motion the medium so that counter-ions ale attracted to the surface' double layer (Figure 1' 11)'31 excess of counter-ions (cf. co-ions) forms an electric

,/S tern plane

charged surface in water Figure 1.LL Schematic replesentation of a negatively (water molecules not dePicted)'

of two regions' an inner region The electric double layer can be regarded as consisting ions subjected to electrical of adsorbed ions and an outer diffuse region containing forces and random thermal motion'

that are attached to the surface The inner region consists of specifically adsorbed ions 'Waals are strong enough to overcome by electrostatic and/or van der forces that was proposed by Stern (1924) to thermal agitation. The thickness of the inner region

26 as the Stern plane' The potential at be the length of a hydrated ion radius and is known (Vo).'t the Stern plane is refe*ed to as the surface potential

the potential decreases The outer region contains an excess of counter-ions and plane (Figure l'12)'31 exponentially as a function of distance from the Stern

v" P^ plane

V¿

1/r

distance

potential as a function distance Figure L.L2 Schematic representation of electrical ir"; charged surface with specifically adsorbed counter-ions' "

in the magnitude of the potential The representation in Figure 1.12 illustrates a change Stern plane (ry6)' The thickness that is possible between the true surface (vo) and the or Debye length (1/r), is of the outer region, also known as the double layer thickness electrical potential decreases to a defined as the distance which the magnitude of the is dependent upon the ionic value of l/e (i.e., -0.37) of the value of ryo. The thickness

strength, permittivity and ion type'3l

The The value of l{,a can be estimated from electrophoretic measurements' between the surface ions electrophoretic behaviour depends on the potential of shear Experimentally the shear plane that are fixed and that of the solution which are free. and outer region extending represents a rapid change in viscosity between the inner the charged ions at the surface' from the surface. Since some solvent will be bound to away from the Stern plane' the plane of shear is typically located at a small distance

27 as the zetaporential (€). If neutral The potential measured at the shear plane is known the Stern plane is not shifted, but the macromolecules are adsorbed at the surface then 3t 1'13)' shear plane is displaced from the surface (Figure

surface stern plane shear plane neutral macromolecule ^{!rûS -

(a) O) region of the double layer Figure 1.13 Schematic repfesentation of the inner plane, with (a) no adsorbed indicating the location of t|e Stern plane and shear macromonomers and (b) adsorbed macro nolecules'

a low ionic strength the value for the In the absence of adsorbed macromolecules and the ( potential'" Sinc" the magnitude surface potential can be assumed to be equal to from the Stern plane a shift in the of the potential decreases as a function of distance will thus decrease the ( potential' shear plane by the adsorption of macromolecules

potential was less for surfaces Fleer et øl3e showed that the magnitude of the ( of AgI sol was measured with containing adsorbed macromolecules. The ( potential a pH fange between 3 and 13' and without the adsorption of poly(vinylalcohol) at at the shear plane (with a The ( potential for a charged, bare, particle ((1) measured to the surface potential (VJ by: distance, A, from the droplet surface) was related

r ZeCtì ¡Ze{ol (1.8) tanh L-oof = e-*o tanhL-OOtJ

charge number' Boltzmann where z, €, k,'I' are the electron charge' electrolyte potential of the particle covered by a constant and tempelature, respectively. The ( surface potential at the new layer of uncharged surfactant ((z) was related to the

28 by the hydrodynamic thickness distance of the surface of shear (ô) which was defined of the surfactant laYer

zeÇz 'ì ( ze!o\ r ^ (1.e) ¡¿¡¡ [;-Of = e-Ko tanh L-a¿1 J

an uncharged adsorbed layer The change in the ( potential due to the adsorption of thickness (õ). This was therefore can provide the determination of the layer thickness in the layer of non- performed by Barnes and prestidge'6 in determining the ionic surfactant on the.surface of poly(DMS) droplets.

1.2.L.3 Brownian Motion and Coagulation

is that regardless of the particle A fundamental characteristic for suspended particles energy. The average size there will be the same average translational kinetic gravity is 1'5 kT' The motion of translational kinetic enefgy fbr any particle ignoring result of random collisions individual particles is continually changing direction as a random motion is known as with the molecules of the suspending medium. The Since aGro'- > 0 in Brownian motion and is more evident for smaller particles' dispersion is Equation 1.1, the presence of droplets of particles in a motion as well as systematic thermodynamically unstable. Therefore, Brownian collisions between motion (i.e., gravity) contributes to the motion that favours possess no means of kinetic particles which may lead to coagulation. If the particles and the stability ratioal iw; stabilisation then every collision resurts in coagulation40

equals 1:

(1.10) \{= unit time Number of collisions that result in aggtegation per

the potential barrier in The stability ratio is a measure of the effectiveness of dispersion exhibits a method of preventing the particles from coagulation. When a decreases' The kinetic stabilisation (e.g., electrostatic) then the rate of coagulation in that direction by pfesence of a barrier decreases the probabitity of movement 40 individual Brownian events

29 a dilute sol and investigated Verwey and Overb e"k42 e*amined the coagulation for corelated to stability ratios of interparticle energy maxima of 15 kT and25 kT that time for the sol' the presence of 10s and 10e, respectively. Given a rapid coagulation can significantly increase the a maximum of moderate magnitude compared to kT coagulation time (i.e., to several months)'

1.2.1.4 DLVO TheorY

can be investigated by The dispersion stability in the presence of stabilising barriers independently DLVO theory. Deryagin and Landau43 and Verway and Overbeekaa lyophobic sols' The theory developed a quantitative theory for the stability of place when two particles involved calculations of the energy changes that take forces' The repulsion is approach one another due to repulsive and attractive the attraction due to van der generally due to overlap of electric double layers and of colloid systems to interpret Waals forces. DLVO theory can be applied to a range srability.3l

by the sum of the attractive The total two-particle interaction enelgy (v1o¡) is given (Va)andrepulsive(Vn)interactionintheabsenceofstericstabilisation: (1.11) Vtot=V¡+Vn

1.2.1.5 Interparticle Attraction

from the observation of Attractive forces between non-polar molecules are evident These attractive forces were liquid phases for non-polar compounds (i.e., benzene)' the polarisation of one first explained by London (1930) and are attributed to a second molecule' and vice molecule by fluctuations in the charge distribution in gives rise to an induced-dipole- versa. Because of this correlation, the attraction is proportional to the inverse sixth induced-dipole interaction. The interaction energy for an assembly of molecules power of separation between the molecules. However, additive' Therefore' the the interaction between interparticle molecule pairs is long ranged compared to London interaction energy between colloid particles is individual molecules.ao

30 (Vn) between two identical particles of radii Hamaker45 derived the interaction energy

ø separated bY a distance H:31 ot!l t 1 (1.t2) v.r=- -* . t+2lnx(x+2)l LL'|t n trG.Ð 1"-*1'¡t (x+ 1)2J where (x =WZa)

and is related to the individual Hamaker and A"¡is the effèctive Hamaker constant (Azz) by constants of the solvent (Arr) and the particles (1.13) A"ff = (A,l/t -Arr"t)' (cr) of the atoms or The Hamaker constants are dependent on the polarisability

molecules where:46 (1.14) 3- hrúr&q' ¡\l^.. I -+

particles' v is a characteristic And q is the number of molecules in unit volume of frequencyidentifiedwiththatcorrespondingtothefirstionisationpotentialandhis energies at larger planck,s constant. It is also noted that the values for the attractive true value' This is due to the separation (H > 10 nm) may be larger than the the theory ignores the finite time for the retardation effect, where at larger separations I particles'3 propagation of electromagnetic radiation between

1.2.1.6 Electrostatic RePulsion

electrical double layer can cause As two charged surfaces approach, the overlap of the region' This causes an a build up of counter-ions and co-ions in the interparticle from the continuous phase into the increase in ionic osmotic pressufe forcing water The repulsive (vn) interaction is interparticle region and thus separating the particles'

represented bY:31

3zrsak2r2nf exp[-rH] VR= ez22 (1.1s)

where ze\ta 'y= 4kT

31 reciprocal of r' r[o is the surface and the double layer thickness is equal to the or dielectric constant' potential (Stern plane) and e is the relative permittivity

increasing particle separation Generally vn decreases in an exponential fashion with the same sign of the potential' (H) and will be positive (repulsion) for particles with using Equations 1'12 The total interaction energy (v¡o¡) can therefore, be calculated (H) (see Figure 1'14)' and 1.15 as a function of separation distance

V¡ Energy barrier to coagu lation

Vrot ÞD q) c)

é,)

V¡

Secondary minimum the primary nnnlmum Interpa.rticle distance

Va' repulsive energy Figure 1.L4 Schematic representation of the attractive energy identical particles as a function of vn and total interaction energY v,o, between two interparticle distance'

minimum state where they are Particles of a dispersion may enter the secondary as flocculation' The flocculation of separated by a liquid film. This process is known are able to entef the primary particles is reversible (i.e., they redisperse).a0 If particles between particles is minimum than coagulation can occur where the contact irreversible.

32 1.2.1.7 Flocculation of Particles

can have significant effects changes in the particle size and the double layer thickness with a subsequent affect on on the ability fbr particles to enter a secondary minimum minimum (sometimes the stability of the dispersion. Flocculation in the secondary as a reversible process' von called weak flocculation) has been well established supported the secondary minimum Bwzagha7 performed the initial experiments that into the secondary state. The equilibrium that exists for the entrance/departure that is not minimum has an entropic contribution from the particle concentration

considered in DLVO theory.a8

of flocculation and is The depth of the secondary minimum determines the degree the particles' For larger particles' dependent on the ( potential , l/R, eand the size of movement due to thermal systematic motion such as sedimentation and solvent 4e of increasing the particle gradients increases the collision frequ"ncy. The effect (Figure 1'15)' radius is shown using DLVO theory for latex particles3r

70 60 50 3 40

èo I q) 30 q) c, 20 9 10 ¡i q) 0 a -10

-20 (b) -30 10 0 2 4 6 I InterParticle distance H (nm)

10-20 J, €R = 78, ( = 15 mV, I= 0.1 M, T = =2x10-6m.

JJ of the secondary minimum' The increase in the particle size increases the magnitude in particle size also increases which presumably enhances flocculation. The increase decreases the possibility for the magnitude of the energy barrier or maximum which to an increase in the coagulation. Therefore, increasing the particle size contributes flocculation trend onlY'

flocculation' An increase rn Increasing the ionic strength of the medium also favours electrical double layer' electrolyte concentration decreases the length of the layer will cause the potential Additional counter-ions in the diffuse part of the double is often referred to as to decrease over a shorter distance. This phenomenon total interaction energy between compression of the double layer. The effect on the particles is shown in Figure 1'16'

3 20

èo 0) 10 q) 6)

c) 0 cÉ é) (a) 1 0

-20 (b)

-30 10 0 2 46 I Interparticte distance H (nm)

ct of ionic strength on the V1o1 using sed for this examPle were secondary minimum on the Ç=l5mV,a=1x10-6m, (b) I 0'2 M' T =298 K and either (a) I = 0.1 M or =

of the secondary minimum and The increase in ionic strength increases the magnitude The increase in ionic strength decreases the interparticle separation of the minimum' strength for an aqueous medium also decreases the maximum. Therefore, the ionic

34 the tendency for both when increased (addition of electrolyte) will increase examined the effect flocculation and coagulation. Litton and Olson50 quantitatively of pure water' The of particle detachment of a flocculated system with the addition and dissipated the particle decrease in ionic strength removed the secondary minimum flocs

1.2.1.8 Steric Stabilisation

several different possible Steric stabilisation is a term that is used to describe In a two-phase system' stabilising mechanisms involving adsorbed macromolecules' portions tend to reside at the macromolecules containing hydrophilic and hydrophobic preferred phases, e'g., hydrophilic interface with the respective components in their

segments have preference to the aqueous phase'

may interpenetrate and give When the particles collide, the adsorbed macromolecules macromolecule segments' If the rise to localised increases in the concentration of the the adsorbed medium is a good solvent for the hydrophilic moieties of the solvent and repulsion macromolecules, then strong interactions occur with 40 occurs.

An increase in osmotic Steric stabilisation occurs through an osmotic mechanism' to chain overlap) causes solvent pfessure in the region between the particles (i.e., due extent of the stabilisation to diffuse between the particles thus separating them. The anchored in the continuous will be dependent upon the configuration of the chains the stabilisation will be phase. If the chains are orientated as a brush configuration 51 long ranged compared to if they are coiled

stabilisation is with non-ionrc The most extensively studied method of utilising steric was shown by Ottewill and surfactants containing ethyleneglycol repeat units' It on the 'Walkersl that poly(EG) and hydrocarbon chain macromolecules adsorbed surfaceofpolystyrenelatexparticlesprovidedenhancedstability.

35 barrier requires knowledge of the The extent for an absorbed layer to provide a steric the thickness can be represented by the layer thickness. Given a freely rotating chain, gyration diameter and is given by:52

(1.16) Dg = L (2n13)1t2

n is the number of units in the chain' where L denotes the length of the repeat unit and chain or brushlike orientation Equation 1.16 indicatés that having a mofe constrained of the adsorbed polymers would increase the layer thickness'28

steric stabilisation, there exists a when adsorbed macromolecules provide favourable combined layer thickness steeply increasing osmotic gradient at the corresponding interaction energy vs' interparticle between the two surfaces. The effect on the total

separation curve is depicted in Figure 1'17

F 20 (b) è0! é) 10 q) q)

I 0 cÉ¡r (a) 0) -10

-20

-30 0 2 4 6 I 10 InterParticle distance H (nm)

on the interaction Figure 1.L7 Representation of the effect of steric stabilisation barrier (b) is a schematic energy curve (a) used in Figure 1.16. The steric separation'31 representation of J;;p gradieñt at a given interparticle "

36 may make it virtually impossible for The presence of a steric barrier from a surfactant given the presence of a secondary particles to enter the primary minimum. However, part dependent on the location minimum, the prevention of flocculation would be in 2ô > H minimum) then the of the steric barrier (i.e., twice the layer thickness). If lsecondary then flocculation may steric layer may prevent flocculation. If 2ô < H (secondary minimum) minimum (V.in) is sufficiently great be favoured if the energy depth of the secondary (i.e., >1 kT)

1.2.2 Colloidal Characterisations

allows the properties and molecular The characterisation of polymers and copolymers prepared in this project are and bulk relationships to be understood. The dispersions to determine the to be characterised by electrophoretic mobility measurements Turbidity measurements and magnitude and sign of the particles surface potential' analyse the stability of the microscopy (optical and electron) are to be used to functional groups of the compounds dispersions and NMR is to be used to identify the

making uP the disPersed Phase'

1.2.2.1 Electrophoretic Mobility Measurements

plus attached material relative Electrophoresis is the movement of a charged surface mobility of the particles of a to a stationary liquid by an applied electric field' The apparatús' The appalatus dispersion can be analysed using a microelectrophoresis on each end' The cell is consists of a cylindrical cell attached to two electrodes water and is illuminated by a submersed in a temperature-controlled container of microscope' The lamp. The particles aIe then visually observed using an attached Brothers Mk II instrument (Figure apparatus to be used in this project is the Rank

1 .1 8).

3l mlcroscope objective { wlre

strengthening water rod

pump outlet

pump inlet

observation tube lamp Pt black heating rod electrode

cell and water bath Figure 1.1,8 Schematic representation of microelectrophoresis of the Rank Brothers Mk tr apparatus'

with or against the field is measured At a fixed applied voltage, the particle movement to mobility (u) as a function of distance and time and subsequently converted according3l to: (1.17) V lJ= E

strength, which is equal to the where V is the velocity (m/s) and E is the applied field applied voltage against the inter-electrode distance'

solvent (e.g., oH- ions from Since the cell walls will be charged in the presence of flow is the movement of water), there exists electro-osmotic flow. Electro-osmotic electric field' This causes liquid relative to a stationary charged surface by an applied return flow of liquid at the a flow of liquid near the cell walls and a compensating are performed at a calibrated centre of the tube.3l Therefore, mobility measurements plane' where the position ayay from the cell walls' This is known as the stationary

38 and the resulting motion is the electro-osmotic flow and the return flow cancel out true electroPhoretic mobilitY'

(u) according to the The ( porential (() can be calculated from the mobility 3l Smoluchowski equation:

k_ (1.18) fJ= Tl

of the continuous phase' The where 4 is the viscosity and e is the permittivity the surfaces of contact are flat' Smoluchowski equation requires the assumption that (i.e., Ka >> 1) then this assumption is If the droplets or particles are of sufficient size reasonable.3l

1.2.2.2 TurbiditY Measurements

investigate dispersion Turbidity measurements are to be used in this project to dispersed phase is such that it destabilisation. The size of the particles making up the the electric field associated with scatters visible light. Light scattering results ftom of the electron clouds of the the incident light, which induces periodic oscillations and atoms. Light is scattered in all directions and may involve constructive where the turbidity (t) of a destructive interf'erences. The result is a turbid solution, material is defined by the expression:31

t-tL) Åt e' (1.19)

and incident light, respectively and where It and Io are the intensities of the transmitted L is the length of the samPle'

density (oD) of a sample due A spectrophotometer can be used to measure the optical The optical density is to the reduction of light transmitted through the sample' to show that light is scattered numerically equivalent to absorbance' The term is used is related to the turbidity by46: and not absorbed by the particles. The optical density

39 2.303 0D L_ L (1.20)

then the turbidity decreases' If a dispersion is subjected to creaming or sedimentation due to The rate of sedimentation or creaming can be considerably enhanced to be used in this coalescence or aggregation.53 Changes in turbidity are a method project to interpret stability changes of the dispersion'

1.2.2.3 MicroscoPY

measurements Optical microscopy can provide real images of a dispersion' Indirect outliers' A computer can such as dynamic light scattering are subject to averaging or distribution as well as amplify images from optical microscopy and provide a particle

providing a visual record of the dispersion'

from a There are a number of ways of choosing an average particle diameter (d') conventionally distribution. For dispersions the volume averaged diameter is

used and is given bY:53

du = (¡I ni di3 )'/3 (t.2t)

where ni is the number of particles in group i with size di'

size of every counted In order to produce a size distribution for the dispersion, the polydispersity or the particle is grouped in 100 nm size increments. The extent of the of variation broadening of the distribution can be calculated using the coefficient (CV):ao

100xo (1.22) CV= ã-

where o = fT (d)'lt'' (1.23)

40 and I nidi I tt'di' d= æ (r.24) In' In'

limited by the The magnification obtained from the light microscope is however, of light ()') according to:a0 resolving power (dp), which is limited by the wavelength (1.2s) ¡. dp no sinO

20 is the angle subtended by where no is the refractive index of the medium (air) and the resolution of optical the microscope objective at the focal plane. Therefore, size (i'e" 500 nm)' microscopy is limited to a lower limit for particle or droplet

using electron microscopy' Greater magnification and resolution can be achieved order of 0'01 nm and are Electron beams can be produced with wavelengths of the equivalent of lenses' The focused by electric or magnetic fields, which act as the they hit a particle will be electrons are fired at the sample and depending on whether of approximately 5 nm for represented as either black or white with a resolution limit The electron beams of SEM the scanning electron microscopy (SEM) technique.3t secondary low velocity electrons are deflected across the surface of the sample. The fall on to a sensitive detector' that are emitted are drawn towards a collector grid and of surfaces and structures The mechanism allows the examination of the fine detail with three dimensional characterisitics'40

the continuous phase) and The limitations of the technique are that water (i.e., from from the sample' Therefore' any volatiles in a vacuum environment will be removed or coagulation' the layout of the particles can be altered by induced flocculation

microscopy techniques are Throughout the course of the project, optical and electron to be used for characterisations of the dispersions'

4l t.2.3AimsforthePolymerColloidsResearch

project include The aims for the polymer colloids research in this

poly(DMS) and modified A greater understanding of the mechanism by which the and to investigate the poly(DMS) dispersions become unstable after prolonged storage macromolecules are to factors controlling the stability of the dispersions' Hydrophilic the stability under conditions be incorporated at the surface of the particles to improve of altered pH and electrolyte levels'

afe to be investigated on the Changes in the structure of the adsorbed polymer chains Stabilising poly(EG) chains siloxane droplets as a function of time and temperature. the surface of the thiol are to be covalently grafted via a Michael Addition to stability' functional siloxane particle in an effort to improve the dispersion

1.2.4 Thesis Outline

functional copolymers of Chapter 2 involves the preparation of amine and thiol the molar mass are poly(DMS). The functional proportions of the copolymers and GPC' characterised using NMR, viscosity measurements and

Addition using template Chapter 3 involves the investigation of the Michael and solvent on the rate of the molecules and the effect of the reactant sizes, types of the copolymers reaction. This chapter also investigates the Michael Addition

synthesised in chaPter 2.

involves the preparation of chapter 4 is the first of the colloids chapters and initially of a functional silane known polysiloxane dispersions, followed by the incorporation the dispersions is investigated prepared in chapter 3. The effect on the stability of optical microscopy' under low pH and high electrolyte conditions using electrophoretic mobility and turbidity measurements'

42 chapter 5 involves the preparation of a dispersion using 3-(Dimethoxymethylsilyl)-1- a two-phase Michael propanethiol at an elevated temperature. This then involves stability of the dispersions is Addition at the surface of the particles. The effect on the investigated.

for the synthetic and chapter 6 is the Iast chapter and contains the final conclusions colloidalaspectsoftheworkaswellsuggestedfuturework.

43 CHAPTER2THEPREPARATIONAND CHARACTERISATION OF SILOXANE COPOLYMERS

2.1 Introduction and Aims

reaction with Siloxane copolymers can be prepared by the heterocondensation This can be performed hydroxyl terminated siloxane polymers and alkoxy silanes' potassium silanolate'1 using various base or acid catalysts including the catalyst,

groups can undergo a The functional silanes that contain two active alkoxy silyl groups.t This will produce a heterocondensation with silanol or silyl hydroxyl end poly(DMS) copolymer with amine functional grafting groups'

hydroxyl at the ends of the The addition of a base catalyst should convert the silyl the silyl alkoxy site of polymer into the active oxygen anion for nucleophilic attack at polymer presumably will limit the modified silane. However, the length of the initial is the case' the final the extent of the incorporation of modified silane' If this Alternatively, potassium copolymer would be arranged as a block copolymer. Potassium silanolate can act as an silanolate as a catalyst can break the siloxane bond. chain scrambling of ion pair aggregate,which can cleave the siloxane bond and cause 1 linear polymer (Figure 2.1) ot ring-opening polymerisation'

Si '.\/.''o si- -S¡.'-

Figure 2.1 Schematic representation of chain scrambling.l

44 poly(DMS) has been confirmed The ability for an alkali metal cation to associate with interaction was more by 23Na NMR and it was reported that the chain scrambling 54 to short chains' significant for polymers or larger oligomers compared

the resulting copolymer would If chain cleavage of the poly(DMS) backbone occurs' number of end groups should not presumably be arranged randomly. Additionally the limit the proportion of functional silane that can be incorporated'

thiol groups with an acid Poly(DMS) copolymers can also be prepared containing for the incorporation catalyst.l An acid catalyst would presumably be more effective more acidic (typical thio122 of thiol silanes compared to amine silanes since thiols are pKu - 10).

strong interactions with the Strong acids such as CF¡SO¡H are able to undergo has the ability to cleave the siloxane bond.ss Like potassium silanolate, CF¡S9¡H to prepare a random poly(DMS) backbone.22 This suggests that it would be possible incorporated thiol functional copolymer arïangement with a significant proportion of silane

copolymers of The aim of this work is to prepare amine and thiol functionalised copolymers poly(DMS) at low and high functional proportions. organofunctional poly(DMS) as mentioned in have a range of additional advanta8es over regular investigate the ability for the Chapter 1. However, the purpose for this work is to to be prepared functional silanes to be incorporated in a linear chain' The copolymefs the amine or thiol as a can then become precursors for further reactions using of the nucleophilic group. The goal is to get a greater understanding be able to apply it later for heterocondensation reaction for poly(DMS) and also to two-phase disPersion reactions'

45 2.2 Literature Review

of Studies by Chu et o156 investigated the heterocondensation environment for nonamethyltetrasiloxane-1-ol in order to simulate the oli godimethylsiloxane-cr,rudiols (Scheme 2' 1 )' CH¡ CH3 (CHr)'Si(OCH¡)+-n Scheme 2.1 I Si(CHr).(OCH¡)s-n CH¡ S CH: si-o

CHs CHs Ja J were Using acidic conditions two mechanisms involving heterocondensations alkoxysilane to form aî considered; first, the acid catalyst reacted with the cyclic transition state intermediate that reacted with the silanol; or secondly, a the silanol' The rate of the occurred between the acid catalyst, alkoxysilane and 0, with more silyl alkoxy groups reaction was enhanced in the series n = 3 ) 2 > I > being due to the increased favouring the condensation. This was rationalized as state' Chmieleck a et al57 electron withdrawing capability in stabili zing thetransition observed similar trends for base catalysis'

been reported to alter the The effects of substituents on the silane monomers have inu"'tigated the molar condensation and cyclisation rates. Wright and Semly"ntt 4 ot 5 siloxane groups' The cyclisation equilibrium constants for cyclics containing H < cH¡ < cHccH2 < rate of cyclic formation increased in the substituent trend, increases there CH3CH2CH2. This was rationalized as the size of the substituent that could be would be a decrease in the number of low-energy conformations

adopted by the corresponding linear chlin'

between an amlne Guibergia-Pierron et ala investigated the heterocondensation The reaction did not functional alkoxy silane and an oligodimethylsiloxane-cr,o>diol' was favoured over the proceed without a base catalyst and the heterocondensation the heterocondensation was an homocondensation reaction. The authors reported that distribution of branching efficient method to synthesize silicon resins with a regular points.

46 between two alkoxy silanes was Ogasawara et al59 reported that the condensation formation of the silanol possible with the addition of water, because of the a heterocondensation functionality (Schem e 2.2). Water could therefore hinder reaction by the addition of two alkoxy silanes' Scheme 2.2 R3SiOCH3 + HzO R3SiOH + CHiOH -> poly(DMS) copolymer using a Spinu and McGrath60 produced an amine functional reaction' they employed a silanolate catalyst. ln contrast to a heterocondensation During the course of the cyclic monomers (Da) with an amine functional cyclic' conversion of cyclics to reaction, linear polymer was formed due to the favourable equilibrium between JÙvo linear. Depending upon the conditions employed, a stable

andgOVo linear was achieved'

61 poly(DMS) and ring- patnode and wilcock proposed that chain scrambling of 62 Chojnowski and'Wilczek opening of Da could be performed using sulphuric acid' the rate of the reaction by have reported that addition of water greatly increases regenerating the acid.

2.3 Experimental Section 2.3.r Materials

Wacker-Chemie. Da, |,3- Hydroxyl-terminated poly(DMS) (1) was supplied by poly(DMS) (5) and diaminopentyl methyldimethoxysilane (2), methyl-terminated Pty Ltd' 3-Aminoproyl thiol-functional poly(DMS) (L0) were supplied by Flexichem 3- methyldiethoxysilane (6) was supplied by Fluka Chemika' (Dimethoxymethylsilyl)-1-propanethiol(9)wassuppliedbyAldrichChemical acid (TfOH) were supplied Company Inc. Acetic acid and trifluoromethanasuffonic hydroxide were by B.D.H Chemicals Pty Ltd. sodium hydroxide and potassium suppliedbyAPSFinechem.Methanol,l,3-propanediolandsilicagel(230-400 grade' Polystyrene standards mesh) were supplied by Merck and water was of MilliQ gmol l) were supplied by (Mp = 2025,3550, 4800, 10000, 20500, 34500 and 50000 obtained without any further the Waters CorPoration All chemicals were used as purification.

41 2.3.2 Copolymerisation Reactions 2.3.2.1 Experimental for Scheme 2.3

round bottom flask Z (0.25 g) was combined with 1 (8.0 g, mw - 3100 gmolt; in a oC (0'016 g) in methanol (0'07 and heated to 55 under nitrogen. Sodium hydroxide observed' After 20 g) was added to the mixture and the changes in viscosity were (0'006 g)' minutes the reaction was quenched with glacial acetic acid

2.3.2.2 Preparation of Potassium Silanolate (4)

to 110oC D4(2.0 g) was mixed with KOH (0.63 g) and toluene (5 rnl) and heated next day. Fresh samples overnight in a round bottom flask and used immediately the of potassium silanolate were prepared as required'

2,3.2.3 Experimentat for Scheme 2'4

flask under S (10.0 g, mw - 6300 gmol-l¡ was mixed with 6 (3.0 g) in a round bottom oC for 48 hours' The nitrogen. 4 (2.6 g) was added and the mixture was heated to 75 pressure (2 mm Hg)' ethanol produced in the reaction was removed under reduced

2.3.2.4 Experimental for Scheme 2'5

TfOH, 5 and 9' 11 L0 (mw - 8500 gmol-l) was prepared by Flexichem Pty Ltd using the procedure employed (mw - 3800 gmol-t; *a, prepared using TfOH, 5 and 9 using by Flexich"-.u'

2.3.3 Copolymer Characterisations

2.3.3.1 Nuclear Magnetic Resonance Spectroscopy

lH NMR polymer samples were dissolved in CDCI¡ for analysis by and 'nsi 300 MHz (tÐ' spectroscopy using a Gemini-300 spectrometer operating at chromium(Itr) Tetramethylsilane (TMS) was used as the reference and

48 the 2esi NMR acetylacetonate (Cr(acac)3) was used as the relaxation agent for experiments

2.3.3.2 Column SeParation

An individual sample of 1,2,3, 5, 6 or 7 (1.0 g) was dissolved in dichloromethane hour using (5.0 ml) and passed through 100 g of silica gel (230-400 Mesh) for t removed under reduced dichloromethane. The dichloromethane in the eluant was lH spectroscopy. pressure and the residue (if any) was examined by NMR

2.3.3.3 ViscositY Measurements

1L) wele measured using The viscosities of the undiluted polymers (1, 3, 5, 7, l0 or (relative) was an Ostwald u-tube capillary viscometer at 22oC. The viscosity required 1 minute and referenced against 1,3 propanediol (120 centistokes)'64 which averaged molar mass of the 30 seconds to pass through the viscometer' The viscosity poly(DMS) and polymers was estimated using a known calibration between linear viscosity 6'7

2.3,3.4 Gel Permeation Chromatography

were 50 - 100 mg samples of copolymers L0, 1L, or the polystyrene standards passed through the columns' dissolved in toluene (1 ml) eluant, which had previously contained 2 columns 20.0 pl of the solution was injected into the instrument, which columns were 500 Å and supplied by the Waters Corporation. The porosities of the flow rate and the 10,000 ,Å.r Toluene was used as the solvent at a 1 ml/min a refractive index components were detected by refractive index differences using was not available for this detector. Unfortunately a more sophisticated GPC apparatus to digital project. Improvisations for GPC included the conversion of analog charts of the polystyrene and normalising the baseline drift. Additionally the broadening value or a molar mass standard peaks suggested a weight averaged molar mass distribution would be less useful.

49 2.4 Results and Discussio 2.4.1 preparation and Characterisation of Amine Functional Poly(DMS) using Heterocondensation

an amine containing In order to produce an amine functionalised poly(DMS) chain, homocondensation reaction silane was required. Silanols are extremely sensitive to a g.65'66 The amino functional with acidic or basic impurities during storage and handlin groups that were reactive to a silane, therefore, contained two active silyl alkoxy I condensation reaction,'but stable towards trace impurities.

The reaction between hydroxyl-terminated poly(DMS) (1) and l,3,diaminopentyl according to the methyldimethoxysilane (2) was performed using a base catalyst because following mechanism (scheme 2.3). Acids were considered less suitable protonated the they facilitate the homocondensation of the silanol and presumably amme group.

CH. 3

I H3CO ocHs Si H + -si-

I CH¡ n I 2 I NH

(CHùz

a,I', CH. NaOH I CH3OH D¿ CHJOH Si o-si + +

I CH (CHz)¡ v

3 (CHùz

NHz

and2. scheme 2.3 Proposed mechanism for the reaction between I

50 to be prepared, knowledge of the In attempt to understand the nature of the copolymer average molar mass for the size of the initial poly(DMS) polymer is essential. The first involved measuring the polymer chains of 1 was estimated by two methods. The the molar mass for linear relative viscosity of 1 which was - 40 centistokes' using a viscosity averaged poly(DMS) and known viscosity measurements (Figure 2.2),67 molar mass was estimated at -3100 gmol-l'

1000000 a a o 1 00000 a (h (¡) a t a 10000 ct) a

e) 1000 a 9 oo O ct) 100 a I a o a 10 a

1 1000 10000 100000 1000000 Molar rnass (grmt-l)

viscosity averaged molar Figure 2.2 Calibration between the_viscositY^rutd the mÃs for linear poly(DMS) reported by Gelest Inc'"'

NMR spectrum of 1 The second method involved integrating the signals in the'nsi with the silicon (Appendix: Figure A1). The resonance at -10.6 ppm was consistent integration of the signal at environment attached to a hydroxyl group.25 The area of -10.6ppmsuggestedanaverageof-4}repeatsiloxanegroupscorrespondingtoan

average molar mass of - 32OO gmol-l'

of the tnsi NMR spectroscopy (Figure 2.3) was used to analyse the composition products from the reaction between I and 2 in Scheme2'3'

51 cH3 o- cl13 ji l. D cItr-si-R jlr I cH3 4 iL ln cI!-si-cE ii I __l t D¿ l" cIú-si -19 -20 -2t -22 -23 -R CIü CHr CE: CH¡ CII, l" - - - -NII- - -NH, CIú -Sr -R D I o C 3 TMS B

ppm -15 -20 -25 0 -5 10

tesi Figure 2.3 NMR spectrum of the products of scheme 2.3.

approximately 5Vo of the The formation of a new resonance at -I9 ppm suggested that known to rearrange to linear polymer was converted to Da cyclic. Poly(DMS) is influence of strong acids produce a distribution of ring and chain molecules under the - 686970 or bases.

that either a homo or The absence of the resonance at -10.6 ppm indicated Guibergia-Pierron and heterocondensation of the initial polymer had occured' the heterocondensation Sauveta suggested that in the presence of a base catalyst' favourable than between PhMe2SiOH and PhMe2SiOMe was 10 times more homocondensation of PhMezSiOH'

a homocondensation via It was also considered a possibility that 2 could undergo with more of 2 to produce hydrolysis of the silyl alkoxy group which could then react 2esi the NMR shifts for oligomers or cyclics.se Spinu and McGrath60 huve measured mass spectfoscopy' cyclic products of 2 and confirmed the molecular identity from and 5 produced NMR Cyclics of the precursor 2 containing repeat units of 3, 4 'nsi no corresponding shifts of -16, -20 and -23 ppm, respectively. There were of 2, even though bulky resonances in the spectrum at these shifts to imply cyclisation

52 due to increased entlopy substituents (cf. Da) have been shown to favour cyclisation effects.ss'60

2'3 showed The lH NMR spectrum (Figure 2.4) fot the products of Scheme of functionalised amine (y = resonances that integrated to the anticipated proportion ratios or 2 and I' 1) to dimethyl (x = 35) corresponding to the starting

H \ /- çII3 AI I CIIs Si- R - A

CH3 A A I A CHI Sr cHl 51-O

I cH3 A A 4 cH3

v o

A I D¿ CII] Si R 3 E

I H GBD o cI{3 H c B R= NII' cH, cH, Clt NH- cH, cE - BCDETCT- - - - -

1.0 ppm 0.0 60 5.0 4.0 3.0 20

tH Figure 2.4 NMR specrrum of the products of Scheme 2.3

lH revealed the presence of Based on the integration atT (0.47o), the NMR specÚum I57o of 2 a quantity of methoxy groups (3.5 ppm), which indicates approximately of 2 remained (two methoxy groups) was present. This suggested that either some polymer chains' However' unreacted or was present at the termination sites of the not observed in the NMR since the resonance for the silicon of 2 (- -2 ppm) was 'esi (one methoxy group) was in the spectrum (Figure 2.3), this suggested that 3o7o of 2 groups) was termination position and the remaining lo%o of 2 (no methoxy chain length by a factor of 7' incorporated within the polymer, increasing the average

53 2esi spectrum (Figure 2'3) was The area of the resonance at -1.2.3 ppm in the NMR polymer' Lrlx et al71 noted consistent with3oäo of 2 atthe termination position of the in this region' It is similar fesonances comparing hydroxyl and ethoxy termination tesi shifts for silicon attached to noted that literature values vary for NMR spectra electron withdrawing amine hydroxyl groups at the end of chains' The effect of the This affect was also group can cause a downfield shift for the silicon environment' presence of 2 in the termination observed by Spinu and McGrath,60 supporting the total silicon position. The fesonance comprised approximately 0.77o of the repeat units' Since the environment, indicating an average chain length of -285 consistent with the increase in average length of L was estimated at - 42, this was chain length bY a factor of 7'

molar mass of -20'000 An average chain length of -285 corresponds to an average of 3 measured at gmol-l. This was roughly consistent with the relative viscosity gmol-l using an approximation of -1000 centistokes which corresponds to -28,0000 However' it is molar mass for poly(DMS) of known viscosity measurements'24 by the pfesence of a small important to consider that the viscosity may be altered is determined for linear proportion of cyclic species. Additionally the molar mass groups' Grafting groups poly(DMS) whereas the copolymer contains grafting amine melt polymers.T2 Since the have been known to cause deviations in the viscosity of of the viscosity grafting groups are small and the proportion is low, the estimation

averaged molar mass seems reasonable for this comparison'

if 2had covalently An experiment was performed in order to investigate empirically 2 wete dissolved in an organic bonded to the polymer. The starting materials L and and eluted with more solvent' solvent and were passed through a silica gel column no 2 based on the absence of The total eluant contained -95Vo of the mass of L and lH Primary and secondary amines CH2 groups in the NMR spectrum of the residue. silica, thus preventing 2 from are capable of forming strong hydrogen bonds with 2'3 were dissolved in the passing through the column.tn When the products of Scheme using the same quantity of solvent same organic solvent and passed through a column if no polymer component there were no non-volatile residues in the eluant' Therefore, to the polymer' of L was present it suggested that 2 was covalently attached

54 sites of the polymer the length of Since the amine was incorporated at the termination In addition' employing 1 limited the proportion of amine that could be incorporated' Decreasing the size of more of 2hadno affect, as it did not react (results not shown)' Siloxane bond 1 would presumably promote cyclisation or homocondensation'a amine content for the copolymer' cleavage was employed in order to produce higher

Amine Functional Poly(DMS) 2.4.2 preparation and characterisation of using Potassium Silanolate

bond in methyl terminated Potassium silanolate (4) was used to break the siloxane poly(DMS)(5)'Themethylendgroupwasusedtodecreasethepolymerisation 5 was measured at 110 between different chains. The initial relative viscosity of molar mass of 6300 gmol-l centistokes, which corresponded to an estimated average 2esi of 5 (Appendix: from known viscosity measurements.6T The NMR spectrum at the upfield position of Figure 4.2) revealed the termination osi(cH3)3 lesonance termination resonance was 37o +7.1 ppm. The area of integration represented by the chain length of 61 siloxane of the total silicon environment suggesting an average - gmol-1 which was groups. This corresponded to an average molar mass of -5000

consistent with the measured viscosity'

siloxane bond and allow a higher The advantage of using 4 was its ability to break the The potassium cation was proportion of amine to be incorporated within the polymer. more reactive than the sodium employed, as Morton and Bostick6s reported it to be alkali metal cation to cation at chain cleavage due to the varying ability for the bond cleavage and chain associate with poly(DMS). The active Si-O K* sites from g'oup''tu The scheme scrambling should presumably react with the silyl alkoxy and D+ according to the following consisted of 4, 5 and 6 to produce the products 7 proposed mechanism (Scheme 2'4)'

55 cH. 'ì" t. I -! 'K Si OK CH Si

+ I I CHr CH¡ CH 3 n m 5 4

cH. CH: CH. CH. cH. Chain I l. I Scrambling I t. ! + CH¡ Si Si K' K CF + -si I I CH¡ CH¡ CH¡ CH¡ n-n m n

"i" cH3cH2 -O-Si-O-CHzCH¡ (CH)¡

6 NHz

CH" rì" "ìu' l. + CH¡ Si o-si-cH3 + cH3cH2oK

I I CH¡ CH¡ (CH): CH¡ + D4 X v

I NHz 7

between 4, 5 and 6' scheme 2.4 Proposed mechanism for the reaction

silanolate catalyst with The method employed by Spinu and McGrath60 used the cleaved, the active Si-O K* remained amine functional cyclic. For each siloxane bond the active site would form the in the polymef. However, with the silyl alkoxy group, be less efficient compared to SiO-K+ for RO K* (R = CH3CH2) species, which would was requifed to react all further chain cleavage. Additional 4 (cf. Spinu and McGrath) Figure 2'5)' of 6 for the preparation of 7 (tH NMR spectrum in

56 c1I3 A

I A sr-

cH3 I CHj A AlÀ CI! -Sr-CI1 x D¿ ol'cDf, cll. cH, cH, cll - - -NI{, CE B -si - v7 D

A lo cE cÌt -si- I cH, ¡,

20 1.0 ppm 0.0 6.0 5.0 40 3.0

tH Figure 2.5 NMR Spectrum of the products of Scheme 2.4

lH that the proportion of The resonances in the NMR spectrum suggested expected for the incorporated amine to dimethyl was x = 3'5 to Y = 1' The resonances reacted' The high silyl alkoxy group of 6 were absent, suggesting that all of 6 had NMR spectrum portion of amine in 7 was now evident in the resonances of the 'nsi ppm, compared to (Figure 2.6), which revealed a larger area for the resonance -22'5 that given bY 3.

crr3 cIr3 I D l" o ClTr-Si-CI! I crl3 4 ln crrs x -si-cIú D¿ I l* B cr! si - cH, cTIl- c]f2 NII2 - - - o v tcI cI[ B I -CI¿ -5¡ I -23.O '7 -21.O -21.5 -22.O -22.5

D c TMS

ppm -25 -5 -10 -15 -20

,nsi Figure 2.6 NMR spectrum of the products of Scheme 2.4

51 1 to 3'5' which was The integration of the resonances at -22.5 ppm and -21ppmwas tH NMR spectrum of the products of Scheme 2'4' identical to that observed in the I the smaller resonance at The resonance at -19 ppm was consistent with Da cyclic and According to Spinu and McGrath60 a resonance -20 ppm may be a cyclic form of 6. functionalised cyclic of 4 siloxane units' Howevet' of -20 ppm indicated an amine of a Iesonance at this accounted for only 2vo of the total silicon content. The absence that the silyl alkoxy 3.5 ppm (Figure 2.5) and-10 to -13 ppm (Figure 2.6) suggested

òite of 6 was not present at the terminal sites'

l7o) had significantly The resonance from the termination group (+ 7.I ppm the average estimated decreased as 4 and 6 have been incorporated in 5, extending viscosity also increased chain length from -67 to -200 averatIe repeat units' The grafting amine from 110 centistokes to 900 centistokes. Since the proportion of measurements groups is large the estimation of the molar mass from the viscosity

becomes less useful.

ft is also noted that it is possible for water to hydrolyse 6 and cause through a silica gel homocondensation. However, when the copolymer was passed eluant' This suggested a column, no significant quantity of 4 or 5 was observed in the covalent attachment between 4 and 5 with 6'

2.4.3PreparationandCharacterizationofThiotFunctionalised Poly(DMS) using Trifluoromethanasuffonic Acid

for the preparation of The anionic polymerisation mechanism could not be employed from the acidic thiol thiol functionalised poly(DMS) because of the side reactions possible using group (cf. amine groups). However, cationic polymerisation was (Scheme 2'5)' TfoH and water according to the following mechanism

58 CH. CHr rl" 'ï" l" '1" 'a I TfOH H- Si si- CH¡ CH¡ Si _ si_ CH: ------> -si I I CH¡ n' CH¡ CH¡ CH¡ n CHz + 5 CH. CH¡ 'ï" "ï" Hzo t" I Si si_ CH: Si si- CH¡ - TfOH I I CH¡ CH¡ CH¡ n-n' CH¡ n-n'

1'"' R= OCH¡ 8 R- Si-(CH2)¡-SH R= CH¡ 9 ocH3

'f' CH¡ R 'r' I I + CH3OH CH¡ Si Si si- CH¡ -si l + D+ CH¡ CH CH¡ x v SH

R = OCH¡ 10

R= CH¡ 11

between 5' TfOH and I or 9' Scheme 2.5 Proposed mechanism for the leaction

varying the initial The proportion of thiol functionality (y) could be adjusted by Pty Ltd and quantity of I or 9 employed. copolymer L0 was supplied by Flexichem approximately 1:70 for 8 reported to have been prepared with I at a low quantity of the and 5, respectively. Presumably the additional methoxy group enhanced 2esi spectroscopy revealed heterocondensation reaction.s6 Analysis of 10 by NMR group (+1 ppm)' which that l.4vo of the silicon content was in the termination groups and suggested coffesponded to an estimated avefage of -140 repeat siloxane

an average molar mass of -10,000 gmol-l (Figure 2'7)'

59 CIT3 cH3 D l. D¿ cI!-si-cE 10 I cE3 4 lo cE -Si -cE

l" SH 611r 6- Si Cft CH, ClI, - - - - - l' B D C cIL cE -si - I cH3

-20 ppn -25 -10 -15 0 -5

products of Scheme 2'5 using monomer 8 Figure 2.7 'esi NMR spectrum of the

8 (1 methoxy group) The resonance at -11 ppm was consistent with the incorporated (3 methoxy groups) with an area consistent with a l:70 proportion. Unreacted I 2esi 40 ppm and terminal reacted I (2 would produce a NMR shift at approximately - the proportion of thiol methoxy groups) at approximately - 2 ppm' Since two units of I functionalised silane was !:70, this indicated an average of groups was further investigated incorporated per chain. The proportion of methoxy tH by NMR spectroscopy (Figure 2'8)

A cII3 cHg n I D¿ Al 51- (J CH3-Si- cH3 CH3 A 4 Alo CTI'-Si-eH3 x .lBcDI SH CI{u O- Si CE CII?- CI1, - - - - o E A B A l" l0 D C cII3 F -si -cE I cIT3 A

2.0 1.0 ppm 0.0 5.0 4.0 30 tH 2'5 using monomer 8' Figure 2.8 NMR spectrum of the products of Scheme

60 rH functional groups (y = 1) to The NMR spectrum revealed the proportion of thiol dimethyl(x=¡})integratingbetweenAandB.Additionally,therewas approximate|y3ovoofthesilylmethoxygroup(F)presentthatcorrespondedtol methoxy group from the initial S compound'

which corresponded to The relative viscosity of 10 was measured at 180 centistokes, viscosity measurements for linear an avefage molar mass of 8,500 gmol-l from known 2esi from the NMR poly(DMS¡.67 This was consistent with the molar mass estimation is useful only as a guide due termination group. However, the estimated molar mass Since the proportion of to the presence of small grafting groups and cyclic material' the molar mass was grafting (si-cH2-cHz-cHz-SH) was low the estimation of

reasonable

mass of 10' A series of GPC was employed to investigate the average molar were first performed (Figure 2'9)' polystyrene standards of known molar mass values

4.8 4.6 4.4 4.2 g4 a ào I 3.8 O 3.6 o 3.4 3.2 Ja 17.0 18.0 74.0 15.0 16.0 elution tirre (min)

a function of elution time Figure 2.9 GPC calibration for polystyrene standards as (Mp)' agãinst the logarithm of the peak molar mass

the measured The known polystyrene molar mass peaks when plotted against to estimate the molar mass' retention times provided a gradient which could be used

based on the retention time'

6l a polystyrene based The peak retention time for 10 was 15.9 minutes suggesting consistent with the viscosity molar mass peak of 12,000 gmol-l which was relatively 1)' 2esi end group analysis (10,000 gmol measurements (8,500 gmol-l) and NMR

functional silane 9 was The preparation of 11 using a higher portion of thiol increased significantly and an undertaken. The viscosity of 11 during the reaction the average chain length' The final arbitrary proportion of Mz was added to decrease incorporation of Mz in the backbone' viscosity of 50 centistokes indicated successful of the products of ,osi NMR spectroscopy was used to examine the composition

Scheme 2.5 using 9 (Figure 2'lO)'

CH¡ cH3 l. si-o D cE -si-R CH¡ 4 A lr CI+-Sr-CI! X D¿ l* cttr-5¡-ç1tr-cH? -sH v TMS D B IIC C cE Si-R 11 - I I I ¡UÚrf3

-15 -20 ppm -25 -5 -10 10 5 0

,nsi of Scheme 2.5 using 9' Figure 2.10 NMR spectrum of the products

with methyl termination The 2esi NMR spectrum revealed a lesonance consistent length of 38 siloxane groups' (5.27o, C) which coffesponded to an average chain - the Mz addition (unreacted Mz is This was consistent with the chain shortening from pressure during workup)' volatile and was presumably all removed under reduced 2esi of D¿ cyclic at ppm (3Vo) and The NMR spectrum also revealed the presence -19

62 presence of the propyl thiol the downfield resonance at -23.3 ppm suggested the of the silicon group attached to the silicon. This was justified since the resonance downfield from the environment near the amino functionalised portion in 7 was also a 0'3 ppm downfield backbone (and additionally the silane 9 was measured as having silicon near the thiol shift compared to the silane 2)' Therefore, the resonance for the between A portion would presumably be further downfield. The area of integration rH performed to confirm the and B in Figure 2.10 was 1:10. The NMR of LL was proportion of x and Y (Figure 2.lI)'

A cH3 A cI{3 s1-l A I cE si-R I cHs A - 4 D¿ Alo cE-si-cE A X

I AIBCD E C4-si-cE-cII: cÛ C B v D E 11

ppm 0.0 5.0 4.0 3.0 20 1.0

lH Figure 2.1-L NMR spectrum for the products of Scheme 2.5 using 9

rH between y and x' The NMR spectrum (Figure 2.11) suggested a 1:10 proportion groups had reacted' The spectrum also indicated that all of the functional methoxy (Figure 2.10)' The coinciding with the absence of resonances at -11 ppm to -13 ppm molar mass of 3000 gmol-t chain length of 38 repeat units corresponded to an average a value of 3800 gmol-l with a measured viscosity of 50 centistokes which suggested - rH the NMR integrations and based on linear poly(DMS).6t Th" effor associated with the slight the viscosity interpretation would be significant enough to explain of LL revealed a difference in the calculated molar mass values. The GPC analysis I' mass of 1500 gmol retention time of 17.8 minutes and a polystyrene average molar

63 are useful as a The estimated molar mass from the viscosity and GPC measurements guide due to the presence of the thiopropyl grafting on the backbone.

2.5 Conclusions

was carried out using The preparation of an amine functional poly(DMS) copolymer and hydroxyl- heterocondensation reaction between an amine functional silane results suggested a terminated poly(DMS) and sodium hydroxide catalyst. The times and successful covalent ïncorporation with a chain size increase by 7 with amine and corresponding increase in the viscosity' The strong interaction

surfaces excluded the polymer from GPC analysis'

due to the presence of The preparation consisted of a relatively simple mechanism and a block copolymer' silyl alkoxy end groups the polymer presumably was arranged as silanolate as a The proportion of amine groups was increased by using potassium copolymer catalyst. The amine content achieved was ten times greater than the first The mechanism and the high proportion lead to a noticeable yellow colouring' poly(DMS) with the alkoxy consisted of random incorporation or chain scrambling of

silane.

The thiol functional copolymer (10) prepared using trimethoxysilyl-1-propanethiol was deduced by the and poly(DMS). The extent and position of thiol incorporation results suggested the chemical shifts f-or o, l, 2 or 3 silyl methoxy groups. The and a 1 to 70 copolymer contained approximately 2 functional groups per chain proportion of thiol groups.

cationic mechanism' The thiol proportion was able to be increased using the same 2esi the thiol groups The NMR spectrum revealed a new resonance which suggested viscosity during the were incorporated within the chain. The change in the progressive conditions allowing reaction revealed the successful splicing of M2 under acidic also exhibited no control over the final viscosity and molar mass. The copolymer coloration and the initial thiol odour was completely removed.

64 CHAPTER 3 THE MICHAELADDITION

3.1 Introduction and Aims

other functional The addition of Michael acceptors can be a means of incorporating group can behave as a groups onto a donor molecule or polymer. An amine or thiol acrylate as the nucleophile and form a covalent linkage with a methacrylate or which contains functional acceptor molecule. Employing a methacrylate or acrylate the donor molecule' substituents, those substituents can be incorporated on to

poly(EG) chains grafted on the since poly(DMS) is hydrophobic, the incorporation of This should provide polymer would increase the hydrophilic nature of the polymer' potential for interfacial new characteristics such as solubility in polar solvents and the (Figure 3'1)' properties due to the hydrophobic and hydrophilic components

o-c_o cH2 CH¡ -cH2 - I CH3 Si CH, - -CH3 X I o CHz

I I CH¡ Si Cle^z- CHz- CH2 - -NH v o

Figure 3.1. Poly(DMS) attached to poly(EG) via amine linkage'

in Figure 3'2' Commercially available examples of suitable acceptors are shown

65 CH¡ o H o

il cH2-ç-c-o cH2-.ç-c-o CH2--ç-TÎ C-O rl--l +_. r+--, CHz CHz CHz

I (b) (c) I (a) CHz CHz CHz

I I oI o o -n -n -n +CH¡ +CH¡ including: (a) methyl Figure 3.2 Structures of various hydrophilic acceptors poly(EG)methacrylate,(b)methylpoly(EG)acrylateand(c)poly(EG)acrylate'Note: n is the number of repeat ethyleneglycol units'

reaction for various The aim of this work is to characterise the Michael Addition determine the best reaction template molecules involving amine and thiol donors and either a primary conditions. The copolymels prepared in Chapter 2, which contain to react with a hydrophilic amine (3 and 7) or thiol group (10 and 1L) was allowed between two functional acceptor. The desired result requires the covalent attachment hindered due to the access groups on relatively large macromolecules, which may be greater understanding of the to those functional groups. The goal is to achieve a solvent and temperature Michael Addition reactions, including the effect of a catalyst, to graft hydrophilic on the reaction. In addition, a mechanism is to be proposed groups on to the poly(DMS) backbone'

3.2 Literature Review

market compared to A greater variety of methacrylates is available in the commercial huve reported that acrylates. However, studies by Klee et aI73 and Rosenthal et oI74 compared to those with p acrylates show enhanced reactivity as Michael acceptols methacrylates was carbon substituents. The reason for the reduced reactivity for attributed to steric hindrance at the double bond site'

66 Michael Additions' Largemacromolecules have also been shown to undergo efficient eight primary amines to Yonetake ,t ol15 converted a macromolecule that contained (Figure 3.3)' tertiary amines using large acceptor macromolecules

R R

I N-CH2 CHz-CH2- N

-C¡12- I R R R'

CH 2-clFrz- cH2-N-R'

ft = -CHz -CH2 -CHz CH2 CHz- N-R' -CHz- R' o

il R C -cHz-cH2- -(CHz)ro prepared by Figure 3.3 Michael Addition product of a large macromolecule Yonetake et al.t)

Cossu et al76 Hindered secondary amines can also undergo Michael Additions' to produce a tertiary reported the reaction between an alkyne and a hindered amine amine (Figure 3.4)

C}Iz CHz

I I C}{z CHz N o

-c -o-cH3 prepared by cossu e/ Figure 3.4 Michael Addition product of a hindered amine al.,'76

67 in the absence of a Despite the ability for amines to undergo Michael Additions the reaction' catalyst, literature examples utilize various catalysts to enhance ions77 and weak bases Catalysts include strong bases such as hydroxide or alkoxide catalysts are used so they such as tertiary phosphines.T8 Generally non-nucleophilic Lewis acids,79 metal do not react with the acceptor. Examples include "n'y*"''to'81 83 irridation. complexesS2 undother approaches involve microwave

more Michael Additions involving thiols have been reported to be considerably examined peptides reactive than the corresponding amine. Studies by Or et al84 selectivity for the Michael containing both thiol and primary amines with complete Additions at the sulphur site (Scheme 3'1)'

o o o

il il NH2 cH-c-NH-CH-C-OH

-C-c I cH2oH SH o

+ CHr:çg O-CH3 -C-

NHz

NH: I + o (CH,)+ o o

il I NHt C CH -NH-c- -c-NH-CH-C-OH -g- I cH2oH o S

I cHz o

CHz-C-ril O-CHj

scheme 3.L Selective Michael Addition prepared by or et al.8a

68 performed at low Michael Additions involving thiols have also been successfully high reactivity of the temperatures (-40 and -70oC), which is consistent with the sulphur anionic nucleoPhile.ss

resemble the species There are also some examples in the patent literature that closer reactions using used in this project. Takanashi et al86 performed Michael Addition The patent claimed to amines, including primary amines attached to alkoxy silanes' also performed produce tertiary amines using two acrylate species' Lo and ZiemelisST to siloxane polymers experiments using amine groups, in this case they were attached claimed the reactions and they were reacted with acryl functional compounds' They Wolter et al88 used were able to produce acrylamide-functional organopolysiloxanes. conduct thiopropyl groups attached to alkoxy functional silanes and claimed to Michael Additions with both acrylate and methacrylate species'

3.3 Experimental Section

3.3.1 Materials

3- 3-Aminopropyl diethoxymethylsilane (6) was supplied by Fluka chemika' (Dimethoxymerhylsilyl)-1-propanethiol (9), propylamine (12), methyl methacrylate gmol.1) (13), methyl acrylate (14), methoxy poly(EG) methacrylate (15; mw = 4]5 gmol-r;, methoxy and (30; mw = 1100 gmol-t), pgly(EG) acrylare (19; mw = 315 were poly(EG) acrylate (24; mw = 454 gmol-r) and diazabicyclo[5'4'0]undec-7-ene (20;111'¡¿ 1000 supplied by Aldrich chemical company Inc. Poly(EG) acrylate = butoxide and gmol l; was supplied ABCR. Chlorobenzene, potassium tertiary butanol and methanol were supplied by Merck. Dichloromethane, ethanol, tertiary was supplied by propanol were supplied by chem Supply Pty Ltd and triethylamine the manufacturer' APS Fine Chem. All compounds were used as received from

69 3.3.2 Michael Additions

3.3.2.1 Experimental for Scheme 3.2

g, 100 mmol), 14 (5'82 g, 2 g (33.8 mmol) of 12 was combined with either 13 (3'38 chlorobeîzeîe (20 ml) in a 100 mmol) or 15 (32.I 9,68 mmol) and were added to oC and any round bottom flask. After 4 days at 50 under reflux, the chlorobeîzene 90 oC I 2 mmHg' unreacted L3 or 14 was removed under vacuum at approximately methyl esterl 5.4 g (>957o yield) of [Propanoic acid, 2-methyl-3-(propylammino)-, dimethyl ester] (16) and 7.8 g (>95 Vo yield of [Propionic acid, 3,3'-(propylimino)di-, Preobrazhenskii et (17) was prepared. 16 and 17 were also produced by Michelse and prepared, unreacted L5 was non-volatile a190 ."spectively. 34 g (\OVo yield) of 18 was tH (3H' s), 2'85 (1H, d d), and remained in the product. NMR of 16 (CDC13) õ 3.7 (3H' 17 (CDCI3) õ 3'65 2.6 (4F^,m), 1.5 (2H, m),1.25 (l]H,br s), 1' 17 (3H, d)' 0'9 t)' (CDCI3) ô 6'15 (1H' s)' (6H, s), 2.15 (4]H,t),2.4 (6H, m), 142 (z]H,m)' 0'9 (3H' t)' 18 5.55(1H,s),4.25(2H,m),3.6("2H[n-13]m),3'31(3H's)'2'5-2'9(5H'm)'1'96 (3H, s), I.5 (z[,m), 1'16 (3H, d),0'88 (3H, Ð'

3,3.2.2 Experimental for Scheme 3'4

(4'28 g, l1'4 2 g of 6 (11.4 mmol) was combined with either 14 (I g,11.4 mmol),19 oc at 50 underreflux mmol) or20 (11.4 9,11.4 mmol). Reactions were performed oC). (20 ml) were (except the reaction with dichloromethane at 43 The solvents ranged from 3 days to 7 chlorobenzene, dichloromethane or toluene. Reaction times oC / 2 mmHg days. The solvents were removed under vacuum at approximately 90 oC were attempted (except dichloromethane, 40 / 2 mmHg)' Additional experiments oC reaction temperature with 1 molar equivalent of 15 in methanol (20 ml) or at 100 or with 0.02 g of either potassium tertiary butoxide, diazabicyclo[5'4.0]undec-J-ene or triethylamine. 3 g (>95Vo yield) of [B-Alanine, N-[3-[1,3,3,3-tetramethyl-1- esterl (21)' 6.19 g (>957o yield of [(trimethylsilyl)oxy] disoloxanyllpropyll-, methyl Yokota'9l 22 andl3.5 g of 23 were prepared. 2L was also prepared by Nakamura and (zlJ,t),2'4] lH NMR of 22 (CDCI3) õ4.2 (z[,br s),3.65 ("2H [n - I3l, m),2'85 (2H' 3'65 ("2H (4H, m), 1.5 (2H, m), 0.6 (2H, t),0.12 (3H, s), 23 (CDC13) õ 4'25 t)' (zlF,.,br s), 0'5 (Z}J'br s)' 0'15 (3H' s)' ln - 43f,m),2.4-3.0 (7H, m), I.5

lo 3.3.2.3 Experimental for Scheme 3'5

2go16(lllmmol)wascombinedwith24(5.l8g,11.4mmolor10'359,22'8 oC heated to 43 under reflux mmol) in dichloromethane (20 ml). The reactions wele under vacuum at for 1 and 18 days respectively. The solvent was removed oC yield) of 25 and l2'4 g (807o yield) of approximarely 40 I 2 mmHg. 7.11 g (957o tH s), 3.6 ("2H [n 13], m), 3'3 26 was prepared. NMR of 26 (cDcb) õ 4.2 (2[,br - (2H't)'O'12 (3H' s)''nsi NMR (3H, s), 2.5-2.8(6H, m), l'5 (2H,m),1'2(3H' t)' O'51 of 26 (CDCI3) d -4.8 (s), -20'2 (s)'

3.3.2.4 Experimental for Scheme 3'8

(10.35 g,22'8 mmol) in either propanol 2 g of 6 (1l.4mmo1) was combined with 24 performed at either 22 or 50oC (20 ml) or tertiary butanol (20 ml). The reactions wefe oc vacuum at approximately 90 I 2 under reflux. The solvents were removed under mmHg.Propanolwasremovedbypriordilutionwithchlorobenzene(dilutionmixture lH (CDC13) of 28 in propanol' õ 4'3 (2H' t)' of 2O:1 chloroben zenelpropanol). NMR (6H' m)' 1'6 (m)' 1'3 (3H' t)' 0'9 4.05 (t), 3.65 ('2iH[n - 13], m),3'4 (3H, s)' 2'4-2'9 s)' 3'65 ("2H 13]' m)'3'4 (m), 0.6 (2H,t),0.15 (3H, s)' 29 (CDCI3) õ 4'2 (zR'br [n - (2H' br s)' 0'15 (3H' s)' (3H, s), 2.4-2.9 (6H, m), 1.5 (2[,br s), 1'3 (s)' 0'5

3.3.2.5 Experimental for Scheme 3'11'

1gof9(5.5mmol)wascombinedwitheither13(1.6g,!6.5mmol),15(2'6g,5'5 All reactions were performed mmol) or 30 (6.1 g, 5.5 mmol) in a round bottom flask' uC tertiary butanol as a solvent (30"C)' at 22 (room temperature) except those using propanol, methanol or tertiary butanol' Solvents were either dichloromethane, toluene, reactions were catalysed by 5vo Reaction times ranged from t hour to 6 days. All solvents were removed under molar equivalents of potassium tertiary butoxide. The oC and methanol' 40 vacuum at approximately 90 / zmmHg (except dichloromethane by first diluting with oC I 2 mmHg). ln some experiments, propanol was removed chlorobenzene(20:1)'1'5g(gTvoyield)ofPropanoicacid,3-tt3- (31) was prepiled (31 (dimethoxymethylsilyl)propyllthiol-2-methyl-, methyl ester

7l 32 in dichloromethane was also prepared by Boutevi n et al.e2¡. 3.55 g (9OVo yield) of (95Vo yield) of 33 was (95Vo yieldin propanol, gTvo yield tertiary butanol) and I .12 g rH (2H, t),3'65 ("2H also prepared. NMR of 32 (CDCI:) in dichloromethane, õ 4.25 (5H, m), l'65 (2H' 1'3 (3H' d)' 0'65 [n - 13], m), 3.5 (3H, s), 3'4 (3H, s),2'4-2'9 Ð' ("2H 13], (2H,t),0.15 (3H, s). 32 (CDC13) in tertiary butanol, õ 4'25 (2H,t),3,65 [n - m),3.4(3H,s),2.5-2.9(5H,m),L6(z]H,brs),1'35(3H'd)'0'6(zH'brs)'0'15(3H' s).33(CDCI3)õ4'25(2H,t),3.65(^z:H[n-43]'m)'3'4(3H's)'2'5-2'9(5H'm)'1'6 (2[,br s), 1.25 (3H, d), 0'6 (2E,br s),0'15 (3H, s)'

3.3.2.6 Experimental for Scheme 3'12

or 2 molar copolymers 3 and 7 (Chapter 2) were used without further purification' I a round bottom flask' equivalents of 24 per amine were combined with 3 ot 7 (3 g) in oC ethanol or All reactions were performed at 50 under reflux in chlorobenzene, The solvents tertiary butanol (20 ml) with reaction times between 3 and 14 days' oC (except ethanol at 50 were femoved under vacuum at appfoxlmately 90 / 2 mmHg oC /2mmHg). tH NMR (CDCI3) of 34,õ4.25 (2H,t),3.7 (^2H [n - 13], m)' 3,6 (3H, s),3.4(3H,s),2.5-2.95(10H,m),1"7(brs),1'55(2Hbrs)'0'55(2H'brs)'0'1(large (6H' m)' s). 35(CDCI3) õ4'25 (2H,t),3.65 (^2H [n - 13], m)'3'4 (3H' s)' 2'4-2'95 7.5 (2[,br s), 1.25 (s), 0.5 (2E,bt s), 0'1 (large s)'

3.3.2.7 Experimental for Scheme 3'13

1 molar copolymers L0 and LL (Chapter 2) were used without further purification. L0 or 11 (3 g) in a equivalent of 15 or 30 per thiol proportion was combined with oC (except when using round bottom flask. All reactions were performed at 22 oC)' propanol or tertiary butanol, which was at 30 The solvents were either THF' 1 day' All reactions tertiary butanol (20 ml) with reaction times between t hour and The solvents were catalysed by 5vo molar equivalents of potassium tertiary butoxide. oc were removed under vacuum at approximately 90 I 2 mmHg. In some (20:1)' lH experiments, propanol was removed by prior dilution with chlorobenzene NMR(CDCI3)of37,õ4.25(2H,t),3'65(^2Hln-431'm)'3'4(3H's)'2'5-2'9(5H' m),1.65(2H,brs),1-25(3H,d),0.6(2[,brs),0'1(larges)'38(CDC13)ô4'3(2H'

12 (5H' l'6 (z['br s)' 1'25 (3H' d)' 0'9 t),3.1("2H [n - 13], m),3.4 (3H, s), 2'5-2'9 m)' ("2H 431' m)' 3'4 (t), 0.6 (2l,bt s), 0.1 (large s)' 39 (CDCI3) õ 4'3 (2H' t)' 3'65 [n - 0'1 (large s)' (3H, s), 2.4-2.9 (5H, m), 1.6 (ziH,t),1'25 (3H, d)' 0'6 (zIJ' t)'

3.3.3 Characterisations 3.3.3.1 Nuclear Magnetic Resonance Spectroscopy

in CDCI3 and analysed by All starting materials and resulting residues were dissolved tH COSY NMR tH NMR spectroscopy and in certain cases 'nsi NMR or Gemini-300 spectrometer spectroscopy was employed. The instrument was a 1H). (TMS) was used as the reference operating at 300 MHz (for Tetramethylsilane as the relaxation agent for the and chromium(Itr) acetylacetonate Cr(acac)3 was used 'nsi NMR.

3.3.4,2 Gel Permeation Chromatography

describedtn2'3'3'4 under 50 - 100 mg samples of 37 or 39 were used as previously the same conditions

3.4 Results and Discussion

3.4.1 Michael Additions using Propylamine

In order to investigate the potential for Michael Additions between large trialled' As indicated in macromolecules, smaller template molecules were initially 15 at 50 oc in Scheme 3.2, propylamine (12) was reacted with 1.3, 14 or chlorobenzene for four daYs'

13 o

_c_c_o_cHjil __-___+ CH3-CH2-CH2-NH2 + CHz 16

13 12 CH¡ o cH3-cH2-cH2-NH2 + cHz-cH ------+ 17 -o-cH3 14 t2 o

CHj ------+ l$ CH3-CH2-CH2-NH2 + CH.-C'l -X-"1cH,-cH,-o+ 15 t2 CHr

Scheme 3.2 Michael Additions of propylamine'

of the expected product (Table In each case the Michael Addition Save a good yield 3.1)

Table 3.1 Reactions of Scheme 3.2

Yield/product Donor Acceptor Temp Solvent Time oc days >957o t2 13 50 Chlorobenzene 4 t6 lequiv 3equiv t2 t4 50 Chlorobenzene 4 >957o ô t7 lequiv J 4 >807o 12 15 50 Chlorobenzene lequiv 2equiv L8

e*cest L3 was removed For the preparation of 16 (previously prepared by Michelsn;, lH used to confirm the identity of under reduced pressure and NMR spectroscopy was the product (Figure 3.5).

74 D H

ABC I CII' Cnr CIfx N - - El- E2 I H- tl H F G I C CITts 16 H B l (1 U C,8,, G F tì H E f) I

I clrs H

1.0 ppn 6.0 5.0 4U 30 2.0

tH Figure 3.5 NMR spectrum of addition product 16

1H ppm (F) of the methyl The NMR revealed the formation of a 3H doublet at 1.17 the carbon with a group initially from the methacrylate. This was now adjacent to new resonances at 2'6 lone hydrogen (G) providing a doublet resonance. There were proximity to a - 2.g ppm (E and G), which were consistent for protons with close presumably would nitrogen group. Since the hydrogens at E are diastereotopic, there (suggested as 2.6 ppm and2.9 be different chemical shifts for each of the E hydrogens (5 - 6 ppm) ppm). There was also an absence of signals for the vinyl hydrogens expected from the starting material (13)'

the product was The reaction of L2 with excess of 14 was also performed and tH analysed by NMR spectroscopy (Figure 3'6)'

15 CE

I CII:

I CE

B c I cI! cH, cH, N - - - I CIå D 17 E B A I F cE T

I o o/ J t F

ppn 2.0 1.0 6.0 5.0 4.0 30

tH Figure 3.6 NMR spectrum of addition product L7

(previously prepared by The reaction between 12 and excess L4 produced 17 preobrazhenskii et ale), which was a tertiary amine that contained two ester groups tH that from two equivalents of 14. This was indicated by the NMR spectrum (E) integrating for four exhibited new resonances at 2.4 ppm (D) and 2.8 ppm at the 5-6 ppm region' hydrogens each. There was also an absence of vinyl resonances there was no characteristic Since acrylates (cf, methacrylates) contain a B hydrogen methyl doublet at I-I7 ppm in the final product'

the same conditions' The two reactions (12 with 13 or 14) were performed using of the Michael However, the reaction with 14 proceeded to react with two equivalents of L3 was reactive' acceptor to produce a tertiary amine whereas only one equivalent that acrylates This experimental result was in good agreement with other reportsl3'14 were more reactive than methacrylates as Michael acceptors.

the initial templates, the size Since the Michael Additions proceeded in good yield for reacted with 12 of the acceptor molecule employed was increased' 15 successfully on tH NMR Appendix: with a reasonable yield of 18 (807o secondary amine based Figure A3).

16 3.4.2 Michael Additions using 3-Aminopropyl Methyldiethoxysilane

a Michael Addition The reaction of 6 with 1.3 yielded no products consistent with (Scheme 3.3).

cH2-cH3

oI cH, o

I Scheme 3.3 CH:- + CH2 :!_[ -o-cH3 >+ -cH2-cH2-NH2 13 o 6

cH2 -cH3

simplest amines as the This suggested that methacrylates might only react with the attempts size around the nitrogen is greater in 6 compared with 12' Unsuccessful (up 100oC)' using were made to react 6 with L3 or L5 at increased temperatures to tertiary protic solvents and the addition of various bases (including potassium the use of butoxide, diazabicyclo[5.4.0]undec-7-ene or triethylamine)' However, since the pK" of a bases such as tertiary butoxide can be reasoned to be ineffective the equilibrium primary amine would be -40 (cf. pK" of tertiary butanol - lg),t' so anion' would not favour the formation of a significant quantity of amide

including 14' 19 and 20 By way of contrast, 6 did react readily with various acrylates, (Scheme 3.4 and T able 3'2)

't1 cH2-cH3

oI o

I CH:- + CH2:CH -cH2-cH2-NH2 -R 6 Acrylate

CH, CHz-CH¡ -ç¡¡¡ oI o

I ----+ CH¡ CH2-CH2 -CIJ2-CH2--NH- -o-R

cH2 -cH3 reactant Product ft= t4 2l -CH: cH2-cH2-o t9 ,,, Ï' cH2-cH2-o L" 20 23 )rz

Scheme 3.4 Michael Addition between 6 and various acrylates

Table 3.2 Reactions of Scheme 3.4

Donor Acceptor Temp Solvent Time Yield/product oc days >95Vo 6 1,4 50 Chlorobenzene J 2t 1 equiv 1 equiv >95Vo 6 19 43 Dichloromethane 7 22 1 equiv 1 equiv >lO7o 6 20 50 Toluene 1 23 1 equiv 1 equiv

Nakamura and The reaction between 6 and L4 produced 21' (previously prepared by Yokotael) at an efficient rate. However, upon increasing the size of the acceptor 6 and L9 molecule the reaction became significantly slower' The reaction between

78 six days to reach proceeded to produce 5OVo of 22 after one day, but required a further lH g|vo completion based upon NMR spectroscopy (Figure 3.7).

IJ ocHrclrs H

A ItcD I clfs N

-si-cHr-cHr-cHr- I I c112 T ocHrcII3

I CH, 1) HI c:oI o/

-f-CH,

C B lu G D,F cw) H

I f O ^:1 H

ppm 6.0 50 4.0 3.0 20 l0

lH Figure 3.7 NMR spectrum of addition ptodact22'

large resonance (H) The integration for the repeating cHzcHzo is now evident by the (H) the group located at the at - 3.6 ppm. It is noted the final upfield cH2 $roup is end of the chain (i.e', -CHzOH)'

ethoxy resonance There was a noticeable reduction in the integration area for the or reacted (indicated by J). This suggested that up to 35Vo of 22had either hydrolysed or cyclic species' further with other molecules of 22 to form dimers, linear chains' from previous reports Due to the bulky nature of the propylamine group, it was likely unlikely that this side that cyclic formation would be dominant.60 However, it was Addition itself' It is reaction would have any direct conflicting effect on the Michael site would now be noted that any post-Michael Addition reactions at the ethoxy groups (I and J) complicated. The reduction in the integration area for these ethoxy (or to would require hydrolysis, followed by heterocondensation homocondensation) and form cyclics. Chmielecka et al51 observed the formation of the Si-O- anion Water presumably attributed this to trace water in the previously dried solvent. Additionally would be present due to the hydrophilic nature of the poly(EG) chains' the hydroxyl termination may contribute to the silyl ethoxy hydrolysis'

19 but was not employed Mass spectroscopy was considered for further characterization parent ion' This was attributed to as the instrument recorded species larger than the t'C because of the poor polymerisation type reactions. NMR was also not employed of the macromolecule' resolution of the key functional groups relative to the size

undergo double Michael In order to determine the propensity for these acrylates to were employed with Additions to produce a tertiary amine, two equivalents of 1'9 for the formation of a reaction times of up to three weeks. However, no evidence tH mixture' tertiary amine was observed in the NMR spectrum of the a significantly larger acceptof The single Michael Addition could be achieved using (20) produced successful molecule. The reaction involving the long chain poly(EG) (Appendix: Figure A4)' It was addition of j|To of 23 after seven days in toluene also reduced for this reaction' noted the integrated area of the side ethoxy groups were

Acrylate 3.4.3 Michael Additions using Methoxy Poly(EG)

was significantly enhanced The reactions of 6 with 24 (Scheme 3.5 and Table 3.3) L9 and24 is that the latter compared to that of 6 and 19. The only difference between chain' contains a methyl group at the end of the poly(EG)

80 cH2-cH1

oI +

I CH¡ o -cH2-cH2-NH2 cHz- cH2- o CH¡ CHz :cH-[-"+ t cH2 6 A -cH3 cH2-cH3

oI ----+ I CH¡ si- cH2-cH2-cHz-N - I o

I cH2 -cH3 o

R. = CHz- ClHz- cH2 o CH¡ - r

Rt H25 R'=R26

Scheme 3.5 Michael Additions between 6 and24'

Table 3.3 Reactions of Scheme 3.5

Yield/product Donor Acceptor Temp Solvent Time OC days >957o 6 24 45 Dichloromethane 1 25 1 equiv 1 ulv 18 907o 6 24 45 Dichloromethane 26 1 equiv 2 equiv

amine (25) after one The reaction with one equivalent of 24 proútced 957o secondary day(spectrumnotshown).Changingtheendgroupofthepoly(EG)chainfrom from 7 days to 1 day' It hydroxyl to methoxy increased the rate of the single addition of 19 and the amine group is believed that hydrogen bonding between the end group of 6 interfered with the Michael Addition'

81 tertiary amine 26' which After extended duration (18 days) a large proportion of the (lH NMR spectrum: Figure contained two poly(EG) chains per amine was formed the reaction 3.8). The duration for this reaction was not improved by increasing oC temperature up to 100 in chlorobenzene'

IJ cTr cH, - G,I A BcD cllj c\-cú-cHr- \R

I cII, cE - R= o D,E H c$ cI{:- cHr- cE clI3 - T G - H F

26 G C J

ppm 0.0 3.0 2.0 1.0 6.0 5.0 40 tH Figure 3.8 NMR spectrum of 26'

of close proximity to The integration for 26 indicated the presence of ten hydrogens time also increased the nitrogen or carbonyl (D,E,F). The effect of the long reaction The progress of the formation of rate of the side reactions of the silyl ethoxy groups. groups (Figure 3'9)' tertiary amine is shown with the decrease in silyl ethoxy

100 100

80 80

60 L (d 60 o t)F o F 40 H 40 ñ èa 20 20

0 0 0246 8 10 t2 14 16 18 Time (days)

in the diethoxy Figure The yield progress of 26 formation (r) and reduction 3.9 tU ,"r-onur." (r) (from NtUf spectroscopy) as a function of time.

82 of time during the course The silyl ethoxy Ïesonances decreased steadily as a function tnsi NMR spectroscopy was of the reaction. As a result of the silyl ethoxy reaction, performed to determine the products formed (Figure 3'10)'

Clt, ç4 - llr ctt, cII, o]-"* T - - )a cH!- R t cÊ, ciü o]-.* -cII -cH,-cIIe \.,r, cH,-c- o I - ll L - - _lt

I CH, cI+ 26- 27 27

15 -2O ppm -25 l0 5 -5 -10

Figure 3.L0 'esi NMR spectrum of 26 and27

2esi revealed a resonance at The resonances in the NMR spectrum (Figure 3.10) -5 2esi with the NMR ppm for the unreacted silyl diethoxy (26), which was consistent (27) was consistent for 6 (not shown). The second resonance at -20.2 ppm for cyclic groups and a propylamine with the 'nsi NMR of cyclic containing four siloxane substituent.60

of cyclic species evidently The increased size of the donor anime due to the formation course of the reaction' did not decrease the rate of the tertiary addition over the

Additions using Amine 3.4.4 Investigation of Protic solvents for Michael Functional Silanes

rate of tertiary amme Employing methanol as a solvent increased the appalent Since the transition formation to a reaction time of three days (tH NMR Figure 4.5). reactants, the effect of a protic state for a Michael Addition is more charged than the the transition state and the solvent should provide a stronger interaction between state will thus solvent. Decreasing the energy gap between reactants and transition

83 a marked increase in the increase the rate of the reaction. Rahman et al93 noted in protic solvents' reaction rate when using primary amines as nucleophiles

also enhanced the reaction of As well as enhancing the Michael Addition, methanol (J) were removed during the course the silyl ethoxy groups. TOVo ofthe ethoxy groups stabilized by protic of the reaction. The formation of Si-O- anion might be more An alternative solvents such as methanol to form cyclic or linear oligomers' in Scheme 3'6' explanationga could be exchange with solvent as suggested

I I + cH3- oH -si-o-cH2-cH3I I

I Scheme 3.6 I . + CH3-CHz- oH --l -Si-O-CH3 ->- I possible reaction' A process The effect of the protic solvent can also lead to another the poly(EG) chain' known as trans-esterficationle where the alcohol can replace its effect does remove while this process does not affect the Michael Addition linkage

the poly(EG) chain from the amine (Scheme 3'7)'

OCH ,CH H (ï)

I N CHz- CHz- C CH¡ Si C}Jz C]Hz- C."z - - - - - I CHz OCH ,CH

cH3 I -o CH 2

I +o -7 CH¡ OCH zCH 3 H It_ I cH, Si cH2- cHz- cHz- N-CH2- CHs -6-O-CH3 - - il I o ocH2cH3

+ o cIJz- cHz- -7

scheme 3.7 Proposed mechanism for trans-esterfication.

84 methoxide and poly(EG) The trans-esterfication process is reversible given the the methanol was in excess the alkoxide have similar leaving group tendencies. since of poly(EG) alkoxide'6 trans-esterfication process presumably favours the removal an ester, using methanol Brackenrid ge olgs investigated the trans-esterfication of "t tH in the NMR spectrum' and reported the formation of a singlet (3H) at 3'82 ppm for the compound' This also corresponds to the 3H singlet at 3.18 ppm observed tH be identified in NMR methyl propanoate.nu Ho*"uer, this resonance cannot overlaps (Appendix Figure spectrum as the resonances responsible from the poly(EG) As).

with the silyl In order to determine the extent of trans-esterfication and exchange solvent (scheme 3'8)' ethoxy side groups, propanol was employed as the protic cH2-cH3

oI +

I CH¡ CH2-CH2-CH2-NH2 O - CH: CHz cP'z- cH2-o -o ï CH2 6 24 -CH3 R

propanol I CH¡ Si CH2 CH2- CHz - - - -N I Rt R 28

R o- cH2 - -cH3 _o-CHz-cHz-cH:-o_si o

il R' CHz-CH2 cH2 -cHr-o - -C o ll CHz CI/'z - -CHz-C-O- -CH2 -CH¡

to produce a mixture scheme 3.g Michael Addition between 6 and 24 inpropanol of products labelled as 28.

85 lH NMR spectroscopy The reaction between 6 and 24 inpropanol was analysed by the spectrum' (Figure 3.11) and new products were observed from analysis of

I ßcD CH¡ si

I R 28 G'P A H I 40E R -o-cH] 21Cc D,J si C,F,O -o- E rc 336/t LN M K/- I B -6-ç¡1. -CHr-CHl l.n, - J- -.r, -!-{.n, -.+-1. 5ûc/c

JK NOP cH, CH, - -CH: -CHr-CHr 50c,

2.O 1.0 0.0 .s 6.0 5.5 5.0 4.5 3.5 3.0 2.5 1.5 ppm

lH as 28' Figure 3.L1 NMR spectrum of the various products labelled

(e'g', 0'9 ppm)' The The lH NMR fevealed the presence of propyl resonances at to the double bond of propyl resonances cannot be attributed to addition of the alcohol the new lesonances the acrylate. This is due to the chemical shifts associated with between2-3ppmfromtheaminelinkage(-N-CH2CHz-COù'Ifthelinkagewas the O-CHz group oxygen based (-O-CH2CH z-COù the new resonance triplets for (3'73ppm) and .,r/ould appeaf at greater than 3 ppm as seen by Bellouard et df1

Houghton and SouthbYes ll.z5PPm;'

to an exchange of The propanol resonances (E, F, G) in Figure 3.11 can be attributed were removed' alcohols at the silyl ethoxy site (Scheme 3'9) as excess volatiles

+ CH3-CH2-CH2-OH -si-o-cH2-cH3 Scheme 3.9 cHz-cH3 + cH3-cHr- oH

-S -si-o-cHz-

86 ppm and when the oxygen The o-cH2 unit in pure propanol gives a fesonance at 3.6 ppm (tetrapropyl orthosilicatee6)' is connected to silicon the shift is approxim ately 3'7 giues a lesonance at 4'05 However, the COz-CHz unit in an ester (propyl proponiaten6¡ trans-esterfication in ppm. It was this resonance (N) that indicated the extent of the Figure 3.11.

with 5ovo of the poly(EG) The final products (28) consisted of >95Vo tertiary amine the silyl ethoxy side groups lost due to trans-esterfication. Approximately one third of of the resonances G' were exchanged with propanol estimated by the integration area as ethoxy and the P and N. The integration area of I indicated, 40Vo remained produce cyclic and/or remaining portion presumably underwent condensation to oligomers (Si-O-Si).

trans-esterfication reaction The rate difference between the Michael Addition and the and temperatures' The was compared by examining the reaction at various durations prior to solvent removal to samples were diluted in a 20:1 aprotic solvent mixture solvent removal process' The decrease the trans-esterfication that occurred during the results are listed in Table 3.4.

Table 3.4 Michael Additions of 6 and two equivalents of 24 in propanol'

oC Trans-esterfication solvent Temp Time Tertiary amine (hours) formed -57o Propanol 50 1 -lOVo

Propanol 50 24 -907o -50Vo -35Vo Propanol 22 168 -80Vo

rate of the Michael The trans-esterfication process competes effectively with the propanol is used as Addition at elevated temperatures and at longer durations when not be achieved under the solvent. The fbrmation of tertiary amine, therefore, could It was noted that these conditions without undergoing significant trans-esterification' equivalent of 24 to produce the propanol solvent was useful for the addition with 1 (<57o)' secondary amine (25) after one hour with minimal trans-esterfication

87 that could increase Tertiary butanol was investigated as an alternative protic solvent was a hindered (bulky) alcohol the rate of the Michael Addition, since tertiary butanol would be retarded on a steric it was hypothesised that the trans-esterfication plocess basis. The results of the experiments are shown in Table 3.5.

Table 3.5 butanol' Michael Additions of 6 and two equivalents of 24 in fertiary

Trans-esterfication Solvent Temp Time Michael Addition Days or solvent exchange <2Vo Tertiary butanol 50 I lTVo Tertiary butanol 50 4 35Vo -57o Tertiary butanol 50 t2 957o -77o

the rate of the Michael The results indicated that tertiary butanol does not enhance reaction did yield Addition to the same extent as the primary alcohols' However, the The products (29) of the tertiary amine slightly faster than that of the aprotic solvents' tH (Figure 3'12)' the reaction after l}days was analysed by NMR

o H r llrl [ .r 15- cH, o-l- cH, cE o cIT' R cH, ö- -l D - - - - - r_: D L I B Cl 93- 1 00% iú cT{^ cH. CH' N - - I o - - I I R HI il tq cIIx cIIz ô-a)- - - - EF 0t% 5% Ì-,/ -o-cl{x ,CH, o- c'-cHr G \ 0-'7% - 'cH, I D,H o 88-95% --asi Ç B - J,E K G

ppm 0.0 6.0 5.0 4.0 3.0 20 1.0

tH labelled as 29 Figure 3.1,2 NMR spectrum of the mixture of products

88 the lH NMR (Figure 3'12)' There rwas a minor tertiary butoxy Iesonance observed in the lesonance This may be attributed to trans-esterfication (0-1vo) or alternatively groups (O-17o). It was also could be a result of butanol exchange with the side ethoxy less than 5Vo were noted that most of the ethoxy groups were absent indicating with two present. The majority of the product underwent a Michael Addition equivalents of 24 producing a yield of 88-95Vo'

3.4.5 Michael Additions using Thiol Functional Silane

required a base unlike amines, the Michael Additions employing a thiol nucleophile basic and could act as a catalyst or no product was formed. The amine was quite they were converted to an neutral nucleophile. However, since the thiols were acidic (cf. tertiary butanol and anion using a base. The pKu of primary thiols is -10 -19)22 in the presence of tertiary therefore, would favour the formation of the sulphur anion reaction would be butoxide, thus increasing its nucleophilicity. In addition, the group and unlikely to proceed without a base because a thiol is a good leaving (Scheme 3'10)' therefore would not favour the formation of the sulphur cation

o y'-- _-L * c-o-Ril R-t R R_S-H + CHz -CH,LCH Scheme 3.10

R = alkyl groups

(9) and various Michael Additions using 3-(dimethoxymethylsilyl)-1-propanethiol methacrylates were performed according to Scheme 3'11'

89 OCH¡ o il I Si cH, cIJz- cþz sH + CH,:C-C-O-R'l cH¡ - - - - I I ocHl 9 CH¡

ocH3 o potassium tertiary ll butoxide l S- CH2-CH-C-O- R CH¡ Si CH2 CHz- CHz- - - I I OCH CH¡ -

reactant product R- cH¡ 13 31 -

15 32

30 33

Scheme 3.L1, Michael Additions of 9 and various methacrylates'

anion occulred faster It was experimentally determined that reactions of the sulphur the analogous amines (Table and proceeded readily at room temperature compared to 3.6).

Table 3.6 Reactions of Scheme 3'11'

Time Yield/product Donor Acceptor Temp Solvent Catalyst OC (days)

tertiary 1 9'7Vo 9 13 22 Dichloro- Potassium 3L l equiv 3 equiv methane butoxide 1 >907o 9 15 22 Dichloro- Potassium terÍary 32 1 equiv 1 equiv methane butoxide 6 >957o 9 30 22 Toluene Potassium tertiary 33 1 equiv 1 equiv butoxide

90 Michael The methacryIates, which wefe generally unsuccessful in undergoing of the high Additions with amines, could now be employed with thiols because spectroscopy and nucleophilicity of the sulfur anion' As with the amine series, mass poor resolution trc NMR were not employed because of polymerisation reactions and 9 and 13 produced of the key functional groups respectively. The reaction between The reaction 31 (spectrum not shown and previously prepared by Boutevin et ale2¡' upon the lH NMR between 9 and 14 produced 32 rapidly in good yield based spectrum of the isolated product (Figure 3'13)'

J ocE ¡lBcDI fq ^1-¡ú v¿r2 \ -5t-uEì-wr2lElx: -q r H vvf!l -c-H G H-C-CÍ{3 F

I 32 o

CH, }I D,E F CH, B I H c o G -i H l---r r ctr3 E

2.0 1.0 ppm 0.0 60 50 40 3.0

lH Figure 3.L3 NMR spectrum of addition product 32'

(F) group was characteristic of The new doublet observed at l.2ppm from the methyl Bianchi and Cestiee in a successful addition involving a methacrylate as observed by thioacetic acid' The new an analogous reaction involving methyl methacrylate and seen in Figure 3'5 with resonances at 2.5 to 2.9 ppm were consistent with the linkage tH employed to identify the hydrogens of E being diastereotopic. COSY NMR was protons on nearby the specific proton assignment by examining the coupling between carbons (Figure 3'14).

9I J 0.0 oclrs ppm I Sa DCB lA CE si- cE T-atr- c*r- 0.5 - B I @ Er H-C-H E2 I

I 1.0 G H-C-CH3 F I F I (1 :C¡ 1.5 C

2.0 CE o H o I CE 2.5 I o ^:7 3.0 CEI E, I 3.5 H

4.0

H 4.5 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 ppm

tH Figure 3.L4 COSY NMR spectrum of addition product 32.

lH resonances at 2'5 ppm The COSY NMR spectrum indicated coupling between the the diastereotopic protons and 2.8 ppm which was consistent with coupling between doublet at 1.2 ppm (F) and Er and E2. There was also coupling observed between the the close proximity the resonances at 2.7 ppm (G). The observed coupling confirms of the functional groups and the success of the Michael Addition.

92 heating' However, The reaction of 9 with 15 proceeded rapidly to completion without significantly slower when a larger poly(EG) length (30) was used the reaction was lH that toluene was (20Vo afterthree days). Based on NMR spectroscopy, it was found yield of 33 after six the most efficient of the aprotic solvents tested producing >95Vo was the best aprotic days (Appendix: Figure A6). It was not clear why toluene solvent for this reaction.

of Thiol 3.4.6 Investigation of Protic solvents for Michael Additions Functional Silanes

after one day using a protic The reaction between 9 and 30 was achieved in good yield trans- solvent, however, trans-esterfication was also evident. The extent of and tertiary butanol' esterfication was investigated using 9 and 15 in propanol

greater than that Since the reactivity of thiols in Michael Additions was considerably in as little as one hour at of amines, the additions using propanol could be achieved room temperature (Table 3.7).

Table 3.7 tertiary butoxide Reactions of Scheme 3.11 using protic solvents and potassium are independent of catalyst. The yield of the Michael Àddition and trans-esterfication one another.

Trans- Solvent Duration \ilorkup Michael Addition yield esterfication Propanol t hour 60oC 2mmlHg >95Vo -607o Propanol t hour 60"C 2mml}Jgu >95Vo -3OVo Tertiary butanol 1 day 60oC 2mml}lg >907o -O7o u chlorobenzene dilution (20:1) prior to solvent removal.

were performed at The additions between 9 and 15 utilizing propanol as a solvent by heating attributed room temperature, howevef, the process of removing the solvent removal, when the to extensive trans-esterification of the product. Prior to solvent was diluted with aprotic solvent (2O:1), the extent of the trans-esterfication solution tH (Table and NMR was consequently decreased during the heating stage 3"7 reaction using tertiary spectrum, Appendix: Figure A7). The product (32) from the

93 day of reaction even butanol as the solvent exhibited no trans-esterfication after one 3.15)' with heating to remove the solvent (lH NMR spectrum: Figure

J ocHl ¡, IlBcD cH1-si-cH,-cHì-cH'ì-'l ocH3I Er H- H E4 GH- F 32 c-o o ,-l--t CH. lH cH"

I F o D,EI A #'CH¡IH G Ez C B I

2.0 1.5 1.0 0.5 0.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 ppm

tH as the solvent' Figure 3.15 NMR spectrum of 32ptepated with tertiary butanol

butoxy group would If trans-esterfication was present in the product, the tertiary that the reaction produce a singlet (CH¡) at 1.45 ppm' These results confirmed trans-esterfication in the between 9 and 15 in tertiary butanol did not produce any product under these conditions.

the silyl methoxy The presence of protic solvents also increased the reactions of NMR spectrum groups producing cyclic and linear species identified in the 'nsi (Figure 3.16).

94 (a)

(b)

ppm -10 -15 -20 -25 0 -5

t'Si of 9 and 15 in (a) Figure 3.L6 NMR spectrum of the product from the reaction tertiary butanol and (b) dichloromethane'

product silyl groups When dichloromethane was employed as a solvent, 53Vo of the hydrolysed to produce remained unchanged as dimethoxy groups (-2.4 ppm) and 4lvo the si-oH functionality (-I2.2 ppm). HoweveI, there was no evidence of (< -15 when tertiary condensation observed to produce the si-o-si linkage ppm)' cycl\c (D+ size) and butanol was employed as a solvent the product contained 5OVo ppm, respectively' The formation of 50Vo linear (or > D¿ size ring) at -20.5 and -22.4 influences the cyclic is consistent with the presence of bulky substituents which equilibrium shift from linear to cyclic'17

3.4.7 Michael Additions of Amine Functional Poly(DMS)

silane v/ith the conditions for Michael Addition established for the substituted the prepared copolymers monomers, the Michael Additions were then performed on groups and were from chapter 2. Copolymers 3 and 7 contained primary amine suitable for reactions with acrylates (Scheme 3'I2)'

95 R

I CH3 Si R = CH2-CHz- CH2-NH-CH2 - -CH3 o -CHz-NHz x- 35 y - I R,= CH3 Si CHi Si - -R - -CH3 X 3

CH¡ -si-R v CH2 CH2 NH2 R' R = -CH2- o -

x- 3.5 y - I Rt= CH: CH¡ -si- I CH¡ 7 o H,--c'.¡--olct, CH2-- CH- [-"+.-L )-t 24

3+24 ____> 34 7 +24 ----+ 35

Scheme 3.L2 Michael Addition between 3 or 7 with24'

poly(EG) grafting would Since Poly(DMS) is a hydrophobic polymer, the addition of properties of the final reduce the extent of the hydrophobic nature and change the are listed in polymer. The reactions involving the amine functionalised copolymers Table 3.8.

Table 3.8 Reactions of Scheme 3'12'

Trans- Donor Acceptor Temp Solvent Time Yield/ OC (days) product esterfTcation >907o N/A 3 24 50 Chlorobenzene J I equiv 34 7 24 50 Ethanol 4 >9OVo -50-7OVo 2 equiv 35 -107o 7 24 50 Tertiary 14 -lj%o 2 equiv butanol 35

96 to produce a faster Since the methyl terminated poly(EG) previously was shown The lH NMR spectrum for Michael Addition, 24 wasused as the Michael acceptor. poly(DMS) (3) and 24 the products of the reaction between the amine functionalised is shown in Figure 3'17.

R: I O- CH: CH, CH, CIf¡ NH- CII, CH, l{H-R - - I - BT:-DEIGE- - - -\t CH3 -Si-R 1{ .U-[-"+cu,1.* cII3 vI3 -"+î

A .{ I cI{3 s

v o .rl CIIr Si -R - I, CH¡ D,RG,H,I K B

2.0 10 0.0 ppm 60 5.0 4.0 3.0 lH Figure 3.1.7 NMR specrrum of the addition product 34.

produce the new The copolymer (3) underwent a Michael Addition with 24 to lH spectrum indicated an copolymer 34 tbatcontained poly(EG) groups. The NMR new resonances (H' I) at 2'5 absence of vinyl resonances ftom24 and the formation of to 3.0 ppm.

7 and two equivalents The formation of 35 involved the reaction between copolymer 7 contained considerably of 24 toproduce the tertiary amine product. The copolymer hydrophilicity of the more amine chains than copolymer 3, which increased the copolymer allowing solvation in various protic solvents'

produced a product containing The reaction of 7 with two equivalents of 24 inethanol lH (Figure However' as with tertiary amines as indicated by NMR spectroscopy A'8)' the products' Since the model reactions, there was significant trans-esterfication in

91 reactions the presence there were no silyl ethoxy groups in 7 compared to the model trans-esterfication' of a cH¡ resonance at L2ppm was indicative of

the addition between 7 When tertiary butanol was employed as a solvent the rate of lH However, based on the and two equivalents of 24 was decreased (cf. ethanol). after 14 days (Figure 3'18)' NMR spectrum, -7O7o conversion to 35 was achieved

crrs

ctrl CIT

clrr ct{3 - -

"lBcD C$ cn s, - cÉ, cH, - - - o -lìR,

ClIr"lA SL- CH1 35 - I cr! A A R- O Ts E,D EFìl I õ _cH] cH, cI! --l- cE -cIIr-"-"ï - -o )_r' 6O0/" R o ll / cI{' EC G c B _ cft2 _ cf{, 6¡¡, I II -l-6-6' \cs. to%"

2.O 1.0 ppm 0.0 6.0 5.0 4.0 3.0 tH Figure 3.L8 NMR spectmm of addition products 35'

rate of addition The use of tertiary butanol as a solvent while providing a slower less trans- compared to that of the primary alcohols, pfoduced significantly tH I1Vo 1ofüary esterfication. The NMR spectmm indicated that approximately was thus butoxy (1.3 ppm) remained after solvent removal' Tertiary butanol for amine functional considered the best solvent for the double Michael Addition addition' poly(DMS), while aprotic solvents would be more suitable for a single

3.4.8 Michael Additions of Thiol Functional Poly(DMS)

with the methacrylates' The previous Michael Additions using 9 were able to react in Michael The copolymers 10 and L1 (Scheme 3.13) were then investigated Additions with the same methacrylates'

98 CH¡ R- OCH3 x-70 Y-l CH3 Si - -CH. 10

R- CH¡ x- l0 y - I CH3 Si - -CHj X 11

R- Si -CH2 -CH2-CH2-SH v o o z=7 15 :CH-C- cH2 CH: I CHz z=22 30 CH¡ Si CH¡ -cHr-o t I CH:, CH¡ 10+ 15 ----+ 36 10+ 30 ____+ 37

11 + 15 _-----> 38 11 + 30 ____-* 39

1'5 or 30 scheme 3.13 Michael Additions of L0 or L1 with methacrylates

potassium tertiary butoxide The Michael Additions using 10 or 1L were catalysed by

and the additions using 10 are shown in Table 3'9'

Table 3.9

Reactions of Scheme 3.13 with copolymer L0'

product Trans- Donor Acceptor Temp Solvent Time Yield/ oc (days) esterfïcation

36 N/A L0 L5 22 THF 1 -90Vo/ 37 N/A 10 30 22 THF 1 -9OVol

in an aprotic solvent after The Michael Additions of 10 with 15 and 30 were achieved based on the integration area 1 day at 22oC. The yields for the reactions were -907o tH Figure A'9 for the reaction of resonances from NMR spectroscopy (Appendix: between 10 and 30).

99 would have on the molar GPC was used to investigate what effect further grafting was measured at an elution time mass estimation technique. The GPC analysis of L0 based on polystyrene of 15.9 minutes for the molar mass peak (12000 gmol-l 37 was 14'9 minutes standards: Figure 2.9). Howevet, the elution time for shape through extended corresponding to 36000 gmol-l. Presumably changing the coils to permeate the grafting of the polymer decreased the ability of the polymer at which the polymer would pores of the GPC column. This would increase the rate the molar mass' It is also pass through the column and give a false exaggeration of and thus prevented the noted that both 37 and 30 were solids at room temperature of viscosity measufements measurement of viscosity. This supported the inaccuracy exhibited longer grafted in determining molar mass averages when the polymer chains.

(L1) was reacted with L5 The copolymer containing a larger number of thiol groups solvents and and 30 and catalysed by potassium tertiary butoxide in various conditions (Table 3' 10).

Table 3.10

Reactions of Scheme 3.13 with copolymer L1'

product Trans- Donor Acceptor Temp Solvent Time Yield/ OC (days) esterfÏcation >95Vo N/A 11 30 22 Toluene 1 39 o4 >957o -507o 11 15 22 Propanol 38 a .04 >95Vo -77o 11 15 22 Propanol 38

1 >95Vo 07o 11 30 30 Tertiary butanol 39

u chlorobenzene dilution (20:1) prior to solvent removal

Addition between 11 and The most efficient aprotic solvent reported for the Michael NUR spectrum 30 was toluene with potassium tertiary butoxide catalyst 1lU Appendix:FigureA.10).ThiswasanalogoustotheMichaelAdditionofl0with30. upon increasing the Apparently dichloromethane became a less suitable solvent poly(EG)chainlengthfrom-7to-21(15and30'respectively)'

100 Addition of 11 with 15 the when the protic solvent propanol was used for the Michael the enhanced effect of a reaction required only I hour. This was consistent with product of 1L and L5 in protic solvent seen using 9. The trans-esterfication of the by diluting the protic solvent propanol was considerable (507o conversion). However, with an apfotic solvent prior to solvent removal the extent of trans-esterfication tH (Figure 3'19)' significantly decrease dto -17o based on the NMR spectrum

A CH¡

CHr- Sj- R

CHì-Si -CH¡ 'o ----|-_--_--tnl B c D G CHr-5¡ cH. cH. CH-R - - -cH1-s tl H CH¡ EzF 38 F

CH¡ EI A D, C,I B o L ErG f _-J/- il HfJ ç :..-a)

-c -o-cH.-cHr'l c( -cHl R= ll r * lL "L-' J- cu, -ll-oJ-cn,ics.' -o l? 919c J H

'l' rr,,l",,l 20 15 10 05 ppm 6.0 5.5 5.0 4.5 4.0 35 30 25

tH Figure 3.19 NMR spectrum of addition products 38'

heating the solution the since the Michael Addition for 1L could be achieved without the solvent undef reduced only requirement f'or raising the temperature was to remove propanol during this pressure. Therefore, upon dilution (20:1) the availability of the extent of the trans- heating stage decreased with a coffesponding decrease in esterfication.

Addition of 12 with 31 When tertiary butanol was employed as a solvent the Michael required no prior proceeded in high yield after one day at 30oc. The experiment due to dilution for solvent removal, as there was no evidenca for trans-esterfication

101 The resulting the relatively short duration (cf. copolymer 7 required 14 days)' rH (Figure 3.20)' product was analysed by and COSY NMR spectroscopy

F H I D, EI A

G B H E4 C

A cE 0.0 -si-R H -lr ppm Clfî-Ciü -f "tr- Al A -o Jzz A CIf¡ Si v¡ÈÆ 0.5 - - B CE-si-clü-cE-cH,DolBcl 1.0 o @ F cIl¿ 39 1.5 -si -R c I cII3 C A 2.0

2.5 fGl

I Æ G E 3.0 @r 3.5 H

4.0 H

4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 ppm

tH Figure 3.20 NMR and COSY spectra of addition product 39.

r02 Michael Addition indicated The lH NMR and COSY spectra supported a successful E and G at2'5 to 2'9 ppm' by the new doublet (F) at 1.2 ppm and the new resonances TheCosYspectrumalsorevealedthediastereotopiccouplingbetweentheEprotons in Figure 3.14' and the coupling between F and G as seen previously

3.s Conclusions

towards the smaller The rate and extent of the Michael Additions was favourable investigated that was able molecules such as propylamine which was the only amine to react with the methacrylates employed'

methyl acrylate while only one Propylamine was able to react with two equivalents of indicated that the acrylates were equivalent of methyl methacrylate was reactive. This to the methacrylates' This better electrophiles for the Michael Addition compared substituent at the carbon' presumably was due to steric interference of the methyl B

to the acrylate increased the The presence of the bulky ethylene glycol chain attached was further increased for time required fbr a single Michael Addition. This duration for different chain lengths the larger poly(Ec) chains. The success of the reaction the most efficient aprotic solvent for was dependent on the solvent used with toluene would require further the longest chains. The reason for this is unclear and investigation.

on the Michael Addition' The The end group of the poly(EG) chain had an influence relative to the hydroxyl end' methoxy end significantly increased the rate of reaction Thehydroxylgroupoftheacceptormayhavehydrogenbondedwithamine rate using the methoxy end decreasing the access of the vinyl group' The increased allowed the double Michael Addition to be performed'

the silyl alkoxy groups in the The longer the reaction proceeded the greater the extent This made it preferable amine and thiol were removed producing cyclic or oligomers' the Michael Addition' to synthesi ze thecopolymers before carrying out

103 the thiols compared In each case the Michael Addition was significantly faster for anion allowed the with the amines. The enhanced nucleophilicity of the sulphur Michael Additions to be conducted at room temperature conditions.

for both thiol and The presence of protic solvents enhanced the Michael Addition was stabilised by the protic amines reactants, presumably since the transitional state groups and also solvent. The protic solvents enhanced the loss of the silyl alkoxy reduced with the thiol reactions caused a trans-esterfication process. This process was removal heating stage' by diluting the solvent with aprotic solvent during the solvent itself' trans- However, since the amines required heating during the reaction esterfication could not be reduced in this way'

of the Michael Addition Tertiary butanol was the most efficient solvent; while the rate of the trans-esterfication was not as rapid as the primary alcohol solvents, the extent preferred solvent for was significantly reduced. Tertiary butanol was therefore the both copolymers'

the formation of The addition of hydrophilic poly(EG) to the copolymers lead to the copolymer required polymers that were solid at room temperature and therefore, gentle heating to exhibit flow.

ro4 CHAPTER 4 ASTUDY OF POLYSIOXANE DISPERSION STABILITY WITHAMINEAND POLY(ETHYLENEGLYCOL)

4.1 Introduction and Aims

Modified poly(DMS) emulsions have a range of application in various industries' groups are poly(DMS) emulsions such as those with amine or poly(EG) functional applicationsl02' personal care used for textile coating,100'tot pup", coating, home care emulsion form is that it and laundry products.lOt Th. advantage of using the the adsorption of provides a delivery mechanism for the polymer. This allows low viscosity conditions' hydrophobic polymers to a surface under water soluble and on the material'lO4 In the case of textiles, this method prevents oil staining

of poly(DMS) Poly(DMS) emulsions can either be prepared by mechanical shearing precipitation in water with added surfactant or through the surfactant-free monomers can be polycondensation method.3s The polycondensation of silane (Figure achieved using dimethoxydimethylsilane (DMDES) 4'l)'

CH¡ CH¡

H,O /ì _------)> cH3cH2O + CH 3CH2OH cHsCH2O -si -ocH2cH3 NH4OH -si-o- CH¡ CH¡ Solubilised monomer DMDES o-H CH¡ CH¡ CH¡ CH¡

I I I Si cH3cH2O Si CH3CH2O CH¡CHzO - -o-si-o- - -OCH2CH3\-/ l -si-o- I CH¡ CH: CH¡ CH: Poly(DMS) oligorner

in water'35 Figure 4.L Mechanism for the polycondensation of DMDES

105 begins' The After the formation of the poly(DMS) oligomers, droplet formation particle formation by the free- mechanism for droplet formation is similar in part to The essential difference is radical emulsion polymerisation mechanism using styrene' the condensation that the oligomer and polymerisation process is controlled by The oligomers can either reaction shown in Figure 4.1 (cf. chain polymerisation)' can lead to form micelles or continue growing into polymer chains. Both processes growing droplets to adsorb the nucleation of small droplets. It is also possible for

oligomer from solution (Figure 4'2)'t0t

assoclate

into micelles

polymerise

nucleation

adsorption of oligomer at surface droplet droplet of growth

growth mechanism Figure 4.2 Schematic illustration of the droplet nucleation and believed to be operative for the poly(DMS) emulsions'

regarded as having a low The initial droplets formed by the nucleation process can be rapid coagulation' This stability constant (w) in Equation 1.10 and may undergo charge density that occurs until the new droplets attain a radius with a surface the charge density of the provides a sufficiently large W to prevent coagulation' As increases' For droplet surface increases the electrostatic barrier against coagulation

106 the magnitude of the classical surfactant-free emulsion polymerisation of styrene, on the ionic strength of radius required to achieve adequate stabilisation is dependent of charged end the medium, the surface charge on the droplet and the number

105 groups

the previous work The aim of the work described in this chapter is to first investigate of the poly(DMS) emulsions prepared by surfactant-free precipitation and the polycondensation process. Details include the stability of the dispersions approaches to effect of a cross-linker monomer. Subsequent work will detail silanes' providing additional stabilisation using amine and poly(EG) functional The effects of the prepared as described in chapter 3 using Michael Additions' of the dispersions are incorporation of the modified silane monomer on the properties structural property insights also to be determined. The work should provide improved for these dispersions'

4.2 Literature Review

first reported by Obey The preparation of monodisperse poly(DMS) emulsions was process by Goodwin and Vincent.3s The mechanism was analogous to the free-radical by Stobe' ut o1106 involving et al33,1os using a surfactant free system and that reported particles' The work by the hydrolysis of tetraethoxysilane to produce colloidal silica water or solutions of water Obey and Vincent3s involved the solvation of DMDES in a slow iricrease in turbidity and ethanol. Addition of ammonium hydroxide caused by GPC, mass due to droplet formation. The dispersed material was characterised presence of a high spectrometry and NMR spectroscopy. They reported the were formed by proportion of cyclic oligomers as well as linear oligomers' Cyclics of the dilute intramolecular condensations (backbiting), which was a consequence orientations with additional conditions employed. Increased dilution provided chain with another monomer degrees of freedom. The probability of a chain end reacting increased'l The (cf. its own chain end) decreased as the monomer concentration was and electrophoretic workers characterised their emulsions using optical microscopy surface and a mobility measurements. The results revealed a negatively charged to 5 pm' depending monodisperse droplet distribution with an average diameter of I

107 Large droplets on the propoftions of ethanol and ammonium hydroxide employed' as increased were generally favoured by higher ammonium hydroxide concentrations charge was attributed to ionic strength increased the rate of coalescence' The negative that migrated to the the ionic terminal groups of the poly(DMS) oligomer chains an electrostatic liquid/liquid interface. The formation of this negative charge provided barrier to flocculation'3s

for polymerisation to that proposed by Gunzbourg et a1101 employed a related method The process involved ring- Obey and Vincent3s except starting with a cyclic siloxane. A key difference opening polymerisation with hydroxide followed by condensation' particles' because the was that surfãctant was required to stabilise the forming It should be polymerisation reaction involved chain or living-end polymerisation' groups for electrostatic stabilisation noted that this method consists of fewer ionic end compared to step growth condensation'

surfactants as poly(DMS) emulsions were also studied by Anderson et a1.38 They used to the particles but adsorbed additional stabilisers. These surfactants were not grafted at the interface and consisted of block copolymers poly(ethyleneoxide)- poly(propyleneoxide)-poly(ethyleneoxide)(PEo-PPo-PEo).Theirresultsrevealed the droplets' This that the presence of surfactants decreased the avelage size of formation by steric observation was attributed to early stability during droplet providing enough electrostatic stabilisation when the droplet size was insufficient in stabilisation.

the same method as Barnes and Prestidg"'u prepared poly(DMS) emulsions using of block copolymer reported by Obey and Vincent.3s They investigated the addition They were able to adsorption at the droplet interface to provide steric stabilisation. difference in ( potential calculate the layer thickness of PEO-PPO-PEO using the the shear plane' Due to the corresponding to the adsorbed layer affect on displacing droplets, the PEO interpenetration of the PPO segment inside the poly(DMS) phase' The interpenetration segments were able to extend further into the continuous layer structure and thickness' mechanism was proposed to significantly influence the electrostatic stabilisation 'when the pH of the emulsion was lowered to a point where

108 flocculated' However' was insufficient, the droplets without the adsorbed copolymer flocculate and the the emulsion droplets with the adsorbed copolymer did not contribution from the emulsion remained stable. This supported a steric stabilisation

adsorbed layer and the determined thickness'

monomers on the preparation Goller et aI31 investigated the affect of trialkoxy silane Triethoxymethylsilane of the siloxane emulsion as described by obey and Vincent.3s cross-linking (TEMS) contains three active sites for polymerisation which allowed the proportion of cyclic between linear chains. The purpose of this was to decrease 'When exclusively used' material which was formed when the DMDES monomer was dispersed phase was the initial proportion of cross-linker was sufficiently high the particles) or microgels (swollen suggested to be either as solid particles (i'e., latex

cross-linked PolYmer).

using a reaction between the Matisons et alr08 modified the surface of silica particles chlorine functional silane' surface silyl hydroxide and either an alkoxy, acetoxy or to manipulate the refractive The purpose of the work was to treat the silica in order group' index. The work utilised many functional groups including the aminopropyl of the aminopropyl The work in this chapter continues on this by the incorporation group attached to two poly(EG) groups'

4.3 Experimental 4.3.r Materials

(TEMS) were Dimethoxydimethylsilane (DMDES) and triethoxymethylsilane (28Vo), sodium supplied by Aldrich chemical company Inc. Aqueous ammonia HCI was supplied hydroxide and sodium chloride were supplied by APS Finechem' of "MilliQ grade"' All by BDH Chemicals. water used to prepare the emulsions was chemicals were used as received'

109 4.3.2 Preparation of DisPersions

4.3.2.1 Preparation of Poly(DMS) Emulsions

water (82 g) and DMDES (3 g) was placed in a poly(vinylchloride) container with magnetic stining bat ror 24 ethanol (5 g) and sealed. The solution was stirred using a Then aqueous ammonia houfs, allowing for the DMDES to dissolve in the solution' the first hour and stiffing (10 g, 28Vo) was added. The solution became turbid within dialysed in dialysis tubing in was continued for a further 24 hours. The emulsion was with - 4I of water. The dialysis duration was for 5 days and involved 10 changes molar mass water. The dialysis tubing was supplied by Sigma and had a molecular purified by five cut-off of 12,000 gmol-l. The dialysis tubing was previously

successive stages of soaking in boiling water fot 20 minutes'

4.3.2.2 Preparation of Poly(DMS-MS) Dispersions

(poly(DMS- The procedure used to prepare poly(dimethylsiloxane-g-methylsiloxane) dispersions as MS)) dispersions was the same as that used to prepare poly(DMS) of the dispersed phase described above. However, proportions of 5, 20, and 50 wtvo involving the of TEMS were initially employed in place of DMDES. Experiments flask with a fitted effect of heating were performed using a 100 ml round bottom (2'4 and TEMS reflux condenser. The initial dispersed phase consisted of DMDES Ð oC weeks' (0.6 g) and the solution/emulsion was heated at 60 for several

4.3.2.3PreparationofPoIy(DMS.MS)/AMDispersions

The procedure used to prepare the poly(dimethylsiloxane-8-methylsiloxane)/amine same as used to prepare macfomonomers (poly(DMS-MSyAM) dispersions was the initial quantities were the poly(DMS-MS) dispersion as described above. However, lH (AM)' The DMDES (2.13 g),TEMS (0.6 g) and,2 g of the amine macromonomers 2esi Figures 3'8 and 3'10, and NMR and structures of the AM used are shown in container was to reduce respectively. The advantage of using a poly(vinylchloride) with a glass surface' amine adsorption on the container walls that may be apparent

110 4.3.3 Physical Measurements

4.3.3.1 Optical MicroscoPY

connected to Optical microscopy was carried out using an Olympus CH30 microscope was analysed using a COHU CCD camera and a computer. The droplet distribution as a standard to scion Image Beta 3B software system. A micrometer slide was used involved thresholding determine the pixel length for a known distance. The analysis groups of diameter sizes the image and converting the pixel area of each particle into that provided the (100 nm increments) using a specially constructed Excel spreadsheet was 1 distribution. The minimum droplet diameter that could be measured accurately the pm since using an objective lens that gave greater magnification decreased size was measured sharpness of the droplet image. The volume avelage droplet was calculated using according to Equation l.2l and the coefficient of variation Equations 1.22 and 1.24.

4.3.3.2 TurbiditY Measurements

(Cary Turbidity measufements were carried out using a UV-visible spectrophotometer approximately 300BIO). The cells used consisted of a 1 cm path length and contained 3 ml of liquid. The incident wavelength of 400 nm was used for all turbidity measurements

4.3.3.3 Nuclear Magnetic Resonance Spectroscopy

so the aqueous The emulsion was mixed with CHzCl2 and sufficient HCI was added After shaking the phase pH was less than 4 to ensure phase separation would occul' the organic phase solution and standing overnight, the C]HzClz was femoved from in CDCIr for analysis by under reduced pressure. The resulting residue was dissolved rnsi operating at 300 MHz tH or NMR spectroscopy using a Gemini-30O spectrometer the 2esi NMR (tI{). Tetramethylsilane (TMS) was used as the reference and for was used to counter experiment, 0.01 M of chromium (Itr) acetylacetonate Cr(acac)3 2esi the slow relaxation time of the excited state'

111 4.3.3.4 Electrophoretic Mobility Measurements

emulsions after dialysis at Electrophoretic mobility measurements were performed on The instrument used various pH levels using sodium hydroxide or hydrochloric acid' Considerable care was was the Rank Brothers Microelectrophoresis apparatus MK tr' on the stationary plane of taken to ensure the mobility measufements were performed ( potential was calculated the cell. The background electrolyte was 10-4 M KCI' The 1'18)' In this from the mobility data using the Smoluchowski equation (Equation Smoluchowski work the values for ra were larger than 40 and so the use of the

equation to calculate the ( was considered reasonable'31

4.4 Results and Discussion 4.4.1 Studies of polY(DMS) Emulsions

performed The preparation of an emulsion containing poly(DMS) droplets was a 3 wtVo dispersed according to the technique employed by Obey and Vincent3s using phase. The emulsion was first analysed by optical microscopy.

optical 4.4.1.r Investigation of the Poly(DMS) Dispersion with Microscopy

higher dispersed phase The emulsion was characterised by optical microscopy using on the average droplet than used by the model conditions elsewhere.3s'37 The effect was taken after one day size and distribution was investigated. The micrograph below of moderate stirring (Figure 4'3).

t12 t * è P'" t, {Þ ç i * 4 a tl + ü * þ t '4 I * * IA * t rb , tù + j t tô * * f ,* âí '* } * sì ( * *.. * 4 s tt*ü * $'t* * 3 t ü t "'tt t r¡ & s { Y' , t * t * g * - 4* ö 4 Í t * .v n * ç 4 ¡¡ t * i Ë * * * .* ** * ¡ È å à* t *, f 4 ,* ll 9c¿ 1# .40 pm * .à

prepared using Figure 4.3 optical micrograph of the poly(DMS) emulsion DMDES.

Figure 4.3 was The average diameter and droplet size distribution of the emulsion in analysed and appears in Figure 4.4'

8 Ø U) 6 C) 4 ñ 2

0 1.0 2.0 3.0 4.0 diameter (pm)

Figure 4.4 Droplet distribution of the poly(DMS) emulsion after one day

113 pm for the emulsion The volume average droplet diameter was measured at -1.9 Obey and Vincent3s for prepared with 3 wt% DMDES. The emulsions prepared by produced an the same ammonium hydroxide concentration at I wtTo monomer they reported an increase average droplet size < 1 pm. In agreement with this work, spectroscopy in droplet size at greater monomer concentrations via photon correlation (PCS). They noted that the technique was increasingly unreliable in measuring dropletsizes> 1Pm.

to be characterised as The emulsions prepared by Obey and Vincent35 were also said pm ,monodisperse'. Using Equation s 1.22 and I.24 and ignoring the presence of < 1 7o our system' droplets the coefficient of variation was calculated as - 36 for of variationa0 is less Typically a system is regarded as monodisperse if the coefficient the increased fhan \}To,which was not satisfied in this case. The results suggested droplets and the initiat monomer proportion increased the volume average size of the longer polydispersity. The increased polydispersity may have resulted from a DMDES' nucleation period due to an increase in the concentration of

Nuclear Magnetic 4.4.1.2 Investigation of the Poly(DMS) Dispersion with Resonance SPectroscoPY

phase the emulsion In order to analyse the structures making up the poly(DMS) the pH of the emulsion' required phase separation. This was achieved by lowering could be which enhanced coalescence and phase separation. As phase s-eparation was dependent upon the achieved in this manner it indicated the emulsion stability at low pH' negatively charged electrostatic stabilisation, which presumably decreased 2esi and analysed by NMR A sample of the dispersed phase was dissolved in CDCI3 spectroscopy (Figure 4.5).

t14 C ltt/ \l'si \t l\ Þl bl o c¡/,,\ \ /./-t \ o-si/

lB D B R- si- R

I n n= 0,7,2,3,4,5 erÈ,

R= CIICII¡OH or OH or O C B D A

-e5 ppÍr 0 *5 -tI -l$

phase Figure 4.5 'esi NMR spectrum of the isolated poly(DMS)

products' The analysis The resonances in Figure 4.5 represent a range of different monomer DMDES' using literature examples3s'2s suggested the absence of the initial not shown)' The which would have been located at - - 4 ppm (2esi NMR of DMDES Da at ppm (c)' resonances indicated the presence of D3 at -8'2 ppm (A)' cyclic -19'0 of the silyl ethoxy group' the end groups at -l l ppm (B) which could either consist The resonances at hydrolysed silyl hydroxyl group or the silyl oxygen anion' -21 repeat unit ppm (D) were consistent with linear oligomers or cyclics with a siloxane the resonances at' of greater than 4. Due to the high proportion of end gfoups, -21 cyclics cannot ppm would be consistent with linear oligomers, however, larger sized the resonances was be discounted. The pefcentage of each species present from shown in Table 4'1' compared with those reported by obey and vincent35 and

115 Table 4.1

Isolated Obey and Obey and poly(DMS)" Vincentb Vincent" 27o DMDES - -4 07o 0Vo lVo Dr --9 lVo 0Vo 39 Vo End - -11 to -13 30 Vo lI Vo 58 Vo 14 Vo D+ - -19 to -19.5 34 7o 44 7o Linear or Dn (n >4) - -2I pPm 29 Vo 31 7o u This work, the sample was prepared with 3 wt70 DMDES and 5 wtvo ethanol' t S^"-*pfr *ás prepared with 5 *ì7o OMDES and 40 wt%o ethanol'3s " Sample was prepared with 3SwIToDMDES and 55 wtTo ethanol'35

prepared by obey Despite the higher DMDES and ethanol content for the emulsions the NMR spectra and Vincent,3s the resonances for the functional groups from 'nsi present' Each reveal a qualitative consistency in the type of functional groups as linear material' dispersion contained a substantial proportion of cyclic, as well

Electrophoretic 4.4.L.3 Investigation of the Poly(DMS) Dispersion with Measurements

would be At high pH conditions the silyl end groups shown in the'esi NMR spectrum groups at the surface of the deprotonated if the PH > pKu. The existence of Si-O- by an droplets would provide electrostatic stabilisation. This was investigated The change in ( electrophoresis experiment that analysed the mobility of the droplets' to previous reports' potential as a function of pH is shown in Figure 4'6 and compared

116 20 o 0 I A A -zo o o tã co ra A A ,-¡ -40 ot A o 9o -60 T T

-80 0 2 4 6 810t2 pH

emulsion in a 1x10-a Figure 4.6 ( potential as a function of pH for the poly(DMS) ge36 for a 2 M KCI solution (r). Literature values incîuded ur" by Éu*., and Prestid The ( pglentials were wtTo DMDES emulsion solution' in a 1x10-'M KNO¡ measured after dialysis apparatus DMDES emulsion dilure solution (a). T for a 1 wtTo The ( potentials measured after dialysis prepared in I 7o ammonia solution. ^were solution (o)' u.ing phase analysis light scattering technique in a lx10-3 M KCI

the pH was lowered' As anticipated, the magnitude of the ( potential decreased as the negative charges at This was because protons present at low pH began to counter the surface:

---r R3SioH + HzO (4.1) R3SiO + HrO+

4 and at lower pH values The point of zero charge (PZC) was at the pH between 3 and good agreement with the the shear plane exhibited a positive charge. TlnePZC was in equal to the pKu for measurements by Teare.l0e The PZC can be regarded as being silanol according to the Henderson-Hasselbalch equation:6 t&sioH PKu pH+ log t&sio l (4.2)

pH if [R3Sio- ] t&SiOH then PKa

tn l alTlo,Sonnefeldll and The result is consistent with the pKu values reported by Ong et

Chaiyavat et a1112 of 4.5,4'0 and 4'O - 4'3, respectively'

4.4.2 Studies of Poly(dimethylsiloxane'g'methylsiloxane) Dispersions

with DMDES in the Preliminary studies were performed using hydrophilic monomers groups caused preparation of dispersions. However, the incorporation of hydrophilic such as dissolution of the siloxane. The presence of a cross-linker the solubility of triethoxymethylsilane (TEMS) was used as a method for decreasing the dispersed phase by producing branching oligomers'

reported a Experiments by Goller et al31 employing a I wtTo poly(DMS) dispersion TEMS/DMDES equalled change from liquid droplets to solid particles as the ratio of groups' one. This was attributed to the extensive grafting from the additional Si-O- but yielded Also the addition of cross-linker at a ratio < 1 did not form solid particles droplets of a smaller size.

cross-linker propottion The effect of the particle size was investigated as a function of for the 3 wtTo total dispersed phase Figure 4'7)'

2.0 t.6

F t.2 ¿ 0.8

0.4

0.0 01020304050 7o crosslinker

(DMDES) incorporated into Figure 4.7 Effect of the proportion of cross-linker particle size uÌii,g' optical pJfypfrrfs-VfS; dispersion å" ìn" .average line represents the data from^measut:l Goller et al'' for the -ióror"opy after 1 Ouy. fn" dotted I wtVo poìypfrrfs-MS) dispersion measured using PCS'

118 Goller et al'37 The The result of added cross-linker was consistent with the results of proportion of general shift to a larger particle size was consistent with the higher comparisons for the dispersed phase as observed in Figure 4.4 assuming reasonable particle size as a different measuring techniques can be made. The decrease in et al31 to be function of increasing TEMS proportion was suggested by Goller for particle growth due attributed to an enhanced rate of production of nucleation sites since an increase in to reduced solubility of the cross-linked oligomers. Additionally, the density as Goller the proportion of cross-linked oligomers significantly increased minor increase in et aI37 observed for > 50% cross-linker and solid particles' A a decrease in the density for cross-linker at lower proportions may contribute to particle size for a given mass'

the dispersion could Goller et al31 proposed that above 50 7o crosslinker proportion as cross-linked latex be characterised as a microgel. Microgels can be regarded prepared withZovo particles that are swollen in a good solvent.ll3'tto Th" dispersions in the form of DMDES in this work may be regarded as cross-linked coils of polymer of microgels' For the a liquid or solid particle or may exhibit (in part) the properties the general terms purpose of this work, when cross-linkef monomels wefe used respectively' dispersion and particle are used instead of emulsion and droplet,

rwere relatively unstable long The dispersions prepared with or without cross-linker only DMDES and term. After a period of - 4 weeks, the dispersions prepared with the dispersed phase' the dispersions with 2o7o TEMS exhibited phase separation of could be extended to As suggested by Obey and Vincent3s the dispersion lifetime pH of the dispersion was several months by dialysing the dispersion with water' The removal from the measured during dialysis to examine the extent of hydroxide continuous phase (Figure 4.8).

119 t2

8 ä6l+l

0 5 0 1 23 4 Time (days)

of dialysis time' Figure 4.8 pH of the poly(DMS-MS) dispersion as a function

monomer from the In eliminating the ammonium hydroxide and presumably soluble Since the continuous phase, the continued growth of droplets decreased' a negative electrophoretic measurements indicated that the droplets exhibited remove the unwanted potential at pH 6, this suggested dialysis with water was able to droplets to oH- from the continuous phase while leaving the surface charge on the maintain stabilitY.

4.4.3 studies of Non-dialysed Poly(dimethylsiloxane'g' methylsiloxane) Dispersions at Elevated Temperature

at elevated The destabilisation of the non-dialysed dispersion was also investigated oC was investigated by temperature. The progress of the dispersion heated at 60 4'9)' particle size and turbidity measurements as a function of time Figure

r20 1 7 6 P 0.8 5 é) tn ¿ 4 d ^J tiLT Ë 0.6 2 z

1 o.4 0 5 6 1 2 34 Time (days)

(l) as a function Figure 4.9 Volume averaged particle diameter (.) llld turbidity of time for the poly(DMS-tUJ) ¿ltp"tsion heated at 60oC'

extended heating ttme' The dispersion exhibited a decrease in the turbidity during the layer that was found This was attributed to the tbrmation of a clear immiscible liquid increase in the particle above the dispersion. Howevel, since there was no significant micrograph of the size, the method of destabilisation was complicated. The optical is shown in Figure 4'10' comparison between the early dispersion and late dispersion (b)

.-rrit,-

during heating Figure 4.L0 optical micrographs of the poly(DMS-MS) dispersion oC at 60 after (a) 1 day and (b) 6 daYs

t2r in the number of The optical micrographs in Figure 4.10 illustrate the decrease that as large particles particles without an increase in the particle size. This suggests form very large aggregates that or aggregates form they increased in size rapidly to was taken to keep the are no longer representative of the continuous phase. care therefore, particles from dispersion continually mixed in order to break up flocs' irreversibly aggregated (i'e'' aggregates not observed by optical microscopy were instability of this coagulated). The possible explanation for the higher temperature by the experiments of obey and type may be an acceleration of a process experienced occurred by enhanced Vincent3s during prolonged storage. This may have is further examined later polymerisation or cross-linking and this type of mechanism

in Chapter 5.

4.4.4StudiesofPoly(dimethylsiloxane.g.methytsiloxane)/ Amine Macromonomers DisPersion

poly(EG) to the siloxane groups In order to achieve chemisorption of the hydrophilic silane was employed' The at the surface of the particle, the modified amine functional macromonomers (AM) used components of the dispersed phase including the amine

are shown in Figure 4.1 1.

ocH2CH3 ocH2cH3. ocH2CH3 o l-" l I CH¡ S¡-CH¡ CH¡- Si-OCH2CH3 CH¡- qi-R CH¡ - -si-R J.",.", J"",.". JcH2cHr AM Cyclic DMDES TEMS Monomer - 0.00082 moles - 0.00041 mole¡ 0.016 moles 0.0038 moles o

ft= cH., cH2 Hz t"' ,/ - -[-"¡ " -"", -o ] cH2- cH2- cH2-N - \.n, cuz-i-"+ CHz-."",-o] tt, - o

including the Figure 4.LL Initial monomers for the poly(DMS-MS)/AM dispersion number of moles of each component'

t22 interface' The three possible destinations for the AM are either at the liquid-liquid nature of the AM inside the particle or in the continuous phase. Given the hydrophilic particles' At it is unlikely that they would reside in the interior of the poly(DMS-MS) (chemisorption) or the liquid-liquid interface the AM can be covalently bonded physisorption physisorbed. The cyclic component may ring open and undergo either (1:16 mole fraction to or chemisorption. However, a relatively high proportion of AM the cyclic material DMS-TMS) is initially added and presumably the majority of This would still leave a would be removed from the continuous phase during dialysis. fraction to DMS-TMS) significant portion of the monomer component (1:24 mole the particle' available for chemisorption or physisorption at the surface of

4.4.4.1 Effect of the AM on the PoIy(DMS-TMS) Dispersions using Optical MicroscoPY

rwere The poly(DMS-MS) and poly(DMS-MS)/AM dispersions compared after dialysis by optical microscopy (Figure 4' 12)

dispersion and (b) Figure 4.12 Optical micrographs of the (a) poly(DMS-MS) poly(DMS -MS YAM disPersion.

t23 the presence of the The micrographs indicate that the bulk of the particles prepared in particles as well' The AM are smaller (difficult to see) with some noticeably larger (Figure distribution of the range in particle size was analysed for both dispersions 4.t3).

T2 I

rt) 10 U) tr t 8 I C) I I

Èa 6 tr b\ tr ot 4

2 I tr ¡rrE tr 0 1.0 2.O 3.0 4.0 5.0 diamter (pm)

poly(DMS- Figure 4.L3 Particle distribution of poly(DMS-MS) dispersion (r) and pm' VfSynVf dispersion (r). The minimum particle size counted was 1

the bulk The poly(DMS-MSyAM dispersion exhibited a smaller particle size for the optical particles. Despite a I pm measurement lower limit, (difficult to see from particle diameter (- micrographs in Figure 4.12) thete was a similar volume average result is speculative as it was assumed there was 1.6 ¡rm) for both dispersions. This minor contribution from the lower end of the particle sizes for the comparison. was 0'2 pm However, the number avelage diameter for the poly(DMS-MS)/AM The coefficient of smaller than poly(DMS-MS) suggesting a broader distribution. 59Vo variation calculated using Equations 1.22 and 124 was approximately 40Vo and for poly(DMS-MS) and poly(DMS-MS)/AM, respectively'

stabilisation of the The decrease in particle size may be attributed to improved were growing particles during the preparation' This could be achieved if AM species phase' Partial present at the interface between the siloxane species and the continuous

t24 and reduce the steric stabilisation could then contribute to the overall stabilisation the adsorption of required charge density at the particle surface for a given size.3l If polydispersity AM is inhomogeneous, it could also explain the increase in the observed.

4.4.4.2 Nuclear Magnetic Resonance spectroscopy of the Poly(DMS- MS)/AM DisPersed Phase

from the continuous Assuming the dialysis of the dispersions removed the free AM the interior of the phase and that the AM would be too hydrophilic to be present in poly(DMS-MS) particles the amount of AM present after dialysis presumably There would presumably corresponded to the amount at the surface of the particles. performing the be some desorption of amine over time,40 which was minimizedby phase was separation procedure immediately after dialysis. This dispersed tH investigated using NMR spectroscopy (Figure 4'I4)'

c R l¡, ocIlcllr l" -s1-cItr -si-oH I

t CHt cE-o ' -cHr- J "Ë,-,S,-" H A -J-""",-I \"* cH¡

B C,I J c,H D,F

2.0 ppm 0'0 6.0 5.0 4.0 3.0 1.0

tH dispersion containing Figure 4.1-4 NMR of the isolated dispersed phase of the the AM.

and the resonance at By taking a comparison between the resonance at J from the AM A for silyl methyl a crude approximation of a l:10 mole fraction can be made

r25 component of the AM was between AM and DMS-TMS. Since the initial monomer lost during I:24 IoDMS-TMS it implies that approximately 66Vo of the monomer was dialysis.

the volume of Given an average particle radius of 800 nm from optical microscopy, the total mass of the each particle would be 2 x 10-18 m3. Taking into consideration particles would be DMDESÆEMS dispersed phase (- 2.13 g) the total number of radius 800 nm the approximately 1.3 x 1012. Also using the average particle of the total surface area surface area of one particle would be 8 x !O-r2 m2. Therefore, for all the particles in a 100 ml dispersion is approximately 10 m2.

performed and Solid content studies by heating aliquots of the dispersion were The proportion of confirmed that DMDES and TEMS were not removed by dialysis' tH (Figure 4.14) would be AM that survived dialysis taken from the NMR spectrum Therefore' the 1:70 of the initial mole proportion of DMDESÆEMS employed' The total number of moles of AM (i.e., at the surface) was - 2.8 x 10-a moles' lO20' For a number of AM molecules (using Avogadro's number) is thus l'l x the particles covered by maximum coverage at the particle surface the surface area of of the AM that contributes to each AM is - 6.1 x 10-20 m2. The cross-sectional radius result was based on the the surface area on the particle is therefore - 0.14 nm. This area for a average particte size, which does not consider the total surface an approximation for polydispersed system. Therefore, the cross-sectional radius is this system.

Equation 1'16 would be Given the radius of a macromolecule randomly coiled using that the almost 1 nm in size, the small cross-sectional radius estimated suggests poly(EG) chains may be brush orientated (Figure 4'15)'

126 particle' Figure 4.L5 Schematic illustration of brush structule at the surface of a

multiple layers may Alternatively if the surface consists of randomly coiled AM then structure or multiple be present to account for the additional content. Either a brush chains to provide steric layers would presumably enhance the ability for the poly(EG) stabilisation.

4.4.4.3 Effect of AM on the Poly(DMS'MS) Dispersion stability

Vincent3s exhibited a The stability of the poly(DMS) emulsions prepared by Obey and work the stability of the stable droplet size proceeding dialysis with water. For this in stability poly(DMS-MSyAM dispersion was investigated to identify any reduction and due to the presence of the AM. The particle size for the poly(DMS-MS) (Figure poly(DMS-MSyAM dispersions were investigated by optical microscopy 4.t6).

r21 2.0

1.8

r.6 ¿ 7.4

t.2

1.0 0 4 8 12 Time (days)

proceeding Figure 4.L6 Volume avelage particle diameter as a function of time diilysis for the poly(DMS-vr5l f¡l and poly(DMS-MS)/AM (¡) dispersions.

as stable as the The stability of the poly(DMS-MS)/AM dispersion was comparatively not affect the poly(DMS-MS) dispersion. Therefore, the presence of the AM does of some larger stability of the dispersion during the time tested despite the presence particles observed in Figure 4.12.

interface, the stability In order to investigate the effect of adsorbed AM at the particle of the dispersions were

1) Investigated atlow pH conditions; and 2) Investigated at elevated electrolyte concentrations

with water to ensure All stability experiments were performed proceeding the dialysis not interfere with the that the ammonium hydroxide present prior to dialysis would pre-dialysis experiment lowering of the pH or addition of electrolyte experiments. The was not suitable as excess such as the elevated temperature experiment (Figure 4.9) AM contributed to destabilisation.

t28 4.4.4.4 Effect of Low pH on the Poly(DMS-MS) and Polv(DMS-MSyAM Dispersions

The effect of pH on the electrophoretic properties was investigated using as a function of electrophoretic measurements. The measurements were performed equation pH and converted to ( potentials (Figute 4.I7) using the Smoluchowski (Equation 1.18).

100 80 60 40 20

q) 0 -20 È \J¡ -40 -60 -80 2 4 6 8 pH

(n) and poly(DMS- Figure 4.1-7 ( potential as a function of pH for poly(DMS-MS) MS)/AM (r).

poly(DMS-MS)/AM The ( potential measurements indicated that the particles of the the poly(DMS-MS) dispersion at pH - 4 became highly positively charged. Since (< 20 mV) the potential dispersion exhibited particles with a small positive potential of-80mVmustbecausedbytheprotonatedtertiaryamine.

literatureuo is 10' The pKu for a simple tertiary amine such as triethylamine from the - Tertiary amines are This indicates that when pH < pKu then I R¡N* ] > [ R:N ]. potential at the generally very basic and readily accept a proton.6a Therefore' the ( anions while in the surface of the particles at pH > 4 must be dominated by the become protonated at presence of the cationic amine. Presumably when the anions pH - 4,the cationic amine becomes the dominant source of charge.

129 dispersion Furthermore, the ( potential for the particles of the poly(DMS-MS)/AM poly(DMS-MS) (pH > 5) exhibited a lower in magnitude value compared to the the cationic amine dispersion. This is presumably caused by the contribution from of the particle may group. Alternatively a layer of uncharged poly(EG) on the surface Since the potential decreases cause the shear plane to be displaced from the surface' shear plane would exponentially from the Stern plane, the displacement of the the difference in the ( decrease the ( potential.36,3e Freer et ar3e determined that could be used to estimate potential due to the presence of an uncharged polymer layer charge density is the layer thickness. However, the theory requires that the surface with the AM constant. since the poly(DMS-MSyAM dispersion was prepared charge density is initially present and is itself charged, the assumption that the surface constant cannot be made.

after one day at the The stability of the dispersions at low pH values was investigated microscopy (Figure 4'18) altered pH condition. The stability was examined by optical

and turbidity measurements (Figure 4'I9)'

1.2

P 0.8 q) U) d 0.6 ¡r z 0.4 0.2

0 5432 pH

the poly(DMS-MS) Figure 4.18 function of pH for were dialysed and the (n) and poly( The dispersions turbiditywas of HCI'

130 8 7 6 5 tsL ,<3 2

1 0 5432 pH

poly(DMS-MS) Figure 4.L9 Volume function of pH for the dialysed and the (ri and poly(DMS-MS The dispersions were particle iir" *ut measu on of HCI'

the The results in Figures 4.18 and 4.19 revealed that at low pH conditions and an poly(DMS-MS) dispersion exhibited a decrease in turbidity (phase separation) in stability was increase in the particle size (presumably coalescence)' The reduction < Friberg et allrs presumably related to the low magnitude of the ( potential at pH 5. with ( potentials reported particle instability for electrostatically stabilized dispersions exhibited little of less than 30 mv in magnitude. The poly(DMS-MSyAM dispersion with the high positive ( change in turbidity and particle diameter. This was consistent presumably potential at pH < 5. Therefore, the dispersion (only at low pH) was steric stabilisation stabilised by cationic electrostatic stabilisation and possibly also flocculation and from the poly(EG) groups. This provided a strong barrier against

coalescence.

of time The dispersions were further investigated at lower pH value as a function

131 8 7 6 5 I 4 3 2

1 0 0 2 46 8 10 Time (days)

pH 3 for poly(DMS- Figure 4.20 Volume average diameter as a function of time at MS) (¡) and poIY(DMS-MSYAM (r)'

pH 3 presumably The poly(DMS-MSyAM dispersion was unchanged over time at steric contribution' The due to the strong cationic electrostatic attraction and possibly day was poly(DMS-MS) exhibited an increase in particle size and by the third be made. essentially phase separated and no size determinations could

4.4.4.5 The Effect of Electrolyte on the Poly(DMS-MS) and Poly(DMS- MSYAM DisPersions

to examine the The dispersions were investigated at raised electrolyte concentration the dispersions were steric contribution to the AM at the surface. The stability of analysed by optical microscopy and turbidity measurements'

t32 1.2

0.8 P o ü) 0.6

Cd H ! 0.4 z 0.2

0 0 o.o2 0.04 0.06 0.08 0.1 NaCl (mol/l)

for Figure 4.21 Turbidity measurements as a function of NaCl concentration pJfpVfS-MSyAM 1i) and poly(DMS-MS) (r) dispersions. The dispersions were NaCl. àiuiyr"O and then the turbidity *u. *"utured at one day after addition of

¿ 6 t-l 4

0 0 o.o2 0.04 0.06 0.08 0.1 NaCl (moUl)

for ßigure 4.22 Volume average diameter as a function of NaCl concentration piyprras-Ms) (r) and polylDMS-MSyAM (n) dispersions. The dispersions were of NaCl' äiuíyr"O and then the particle size was measured at one day after addition

The results in Figures 4.2I and 4.22 reveal that the poly(DMS-MS) dispersions increase exhibited a significant decrease in turbidity and increase in particle size. An layer in electrolyte concentration would decrease the length of the electrical double resulting in decreased electrostatic stabilisation. Therefore, this would favour a flocculation and coalescence process. Particle coalescence would increase the average particle diameter as observed'

133 to the effect of The poly(DMS-MS)/AM dispersion exhibited a greater resistance and the extent of the added electrolyte, both in the concentration of NaCl required may be attributed to a change in turbidity and particle size. The enhanced stability concentrations steric contribution from the AM. However, an increase in electrolyte for steric can also dehydrate the poly(EG) chains and reduce their effectiveness tu reduced stability observed stabilisation.t Thi, would be consistent with some of the at higher electrolyte concentrations (e'g', at 0'1 M)'

period of time' The The effect of elevated electrolyte was also investigated over a function of particle poly(DMS-MS) and poly(DMS-MS)iAM were investigated as a

size over time at 0.04 M concentration of NaCl'

a ¿ J 2

0 0 2 4 6 Time (days)

an electrolyte Figure 4.23 Volume average diameter as a function of time at poly(DMS-MSyAM (¡) concentration of 0'04 M fãr poly(DMS-MS) (r) and dispersions.

particle size in the The poly(DMS-MS) dispersion exhibited an initial increase in the the dispersion was first three days due to the presence of 0.04 M NaCl' However' stabilisation relatively stable for the proceeding days. Presumably the electrostatic The poly(DMS-MS)/AM was srill present at 0.04 M NaCl but in a reduced capacity' time at 0'04M NaCt dispersion exhibited very little change in the particle size over supporting a steric stabilisation contribution'

134 4.4.4.7 The Application of DLVO Theory for the Poly(DMS'MS) Dispersions

To further investigate the stability behaviour of the poly(DMS-MS) dispersions' and DLVO theory was employed to investigate the tendency for particles to approach and The flocculate or coagulate across a range of electrolyte concentrations pH' from the effective Hamaker constant of the dispersions (2.8 x 10-21 ¡ was calculated for individual Hamaker constants using Equation 1.13. The Hamaker constant for the hydrocarbons" wus used for the dispersed phase (6 x 10-20 J) and waferr2l 20 energies were continuous phase (3.7 x 10 ¡. The total particle-particle interaction 1'15 and Va' the calculated from Vp, the interparticle repulsion term, in Equation interaction interparticle attractive term, in Equation 1.12. The total interparticle energy curve is shown inF\gure 4.24.

1100 900 F 700 J¿ \ 500 Ë 300 100 -100 020406080 H (nm) Figure 4.24 Two particle interacti for dispersion as a function of separation s u 8'3 *"i"' Aerr = 2.8x10-21 J, e = 75, Ç = 31 M. For clarity the graph in the inset is an of secondary minimum.

dispersion As expected the interaction energy curve for the dialysed poly(DMS-MS) small at neutral pH without added NaCl exhibited a strong maximum and a very consistent with the secondary minimum at large separation. The theory is generally 4.16. observed stability for the dialysed dispersion shown in Figure

reduction when rhe pH was lowered to 3, the poly(DMS-MS) dispersion exhibited a stability in the magnitude of the ( potential (Figure 4.17) and reduced dispersion

135 (Figure 4.20). However, the poly(DMS-MS)/AM dispersion exhibited a large in ( positive ( potential and the dispersion remained stable. The effect of the change 4.25. potential for the two-particle interaction cuIves is shown \nFigute

4000 3500 3000 F 2500 \-\¿ 2000 o 1500 1000 500 0 -500 0 20 40 60 80 H (nm)

poly(DMS-MS) Figure 4.25 Two parri for the for the calculation dispersions as a function s used and I 0'001 M at -8 mV *"i", Aerr = 2.8x10-21J, e = (r) for poly(DMS) or +78 mV (¡) for poly

conditions at pH The two particle interaction in Figure 4.25 tepresents the dispersion high ( 3 for the poly(DMS-MS) and poly(DMS-MSyAM dispersions at low and 'When the potential magnitudes, respectively. the ( potential is low in magnitude other maximum and presence of the maximum is reduced to 25 kT. Relative to the potential and the total taking into consideration the sensitivity between the surface which was observed in interaction energy, this supports coagulation and coalescence, large maximum Figure 4.20. The poly(DMS-MSyAM dispersion exhibited a very which was consistent with the observed stability at pH 3 over time'

In order to calculate the two particle interaction at an elevated electrolyte of the double layer concentration, new ( potentials were required since compression The ( potential for the can cause a decrease in the magnitude of the ( potential.3l poly(DMS-MS) and poly(DMS-MS)/AM dispersions at 0.04 M background ionic strength electrolye were -2I and -15 mV, respectively. The effect of the raised

136 shown tn and lower ( potentials on the two-particle interaction energy curve is

Figures 4.26 and 4.21 .

2æ

150

3 100 * 9o 50

-50 0 5 10 15 20 H (nm)

Figure 4.26 Two Parti n dispersions as a function weie: A"n = 2.8x10-21 J, e a 21 mV (r) for poty(DMS-MS) or -15 mV ( )

Fi 10 J¿ 5

-5

-10 0510 15 20 H (nm)

ßigure 4.27 Expanded y-axis from Figure 4'26'

the values for the Due to the uncertainty of the value of the Hamaker constants, the maximum maxima and secondary minima are useful as a guide only' However, 10-3 M in for poly(DMS) at an ionic strength of 0.04 M was 180 kT (cf' 980 kT at 1 x from Figure 4.24). The maxima 980 kT and 180 kT are essentially indistinguishable maxima are over- each other and support a stable dispersion' Presumably the

r31 'the trend' for estimated by the theory. The decreased maximum does suppoft since the poly(DMS- increased probability for coagulation in the primary minimum with the MS) at 0.04 M dispersion was experimentally unstable. This was consistent of time. The existence observed increase in particle size in Figure 4.23 as a function phase separating (which did of a maximum was also consistent with the dispersion not because of the occur with low pH conditions). The maxima may be overestimated which can distortion of the particles. This causes flattening of the surface curvatuLe

increase the van der Waals attraction at close interparticle distances'117'118

poly(DMS- Additionally the presence of a secondary minimum (Figure 4.27) for the for coagulation or MS) dispersion (-4 kT) favours flocculation which is the precursor by examining DLVO coalescence. The pfesence of secondary minima was supported Bagchillg theory at various electrolyte concentrations that may exist in error' to be -5'5 kT' reported a theoretical depth for instability at the secondary minimum secondary minimum that Hesselink et a1120 also reported a depth of < -5 kT for the exhibited extensive fl occulation.

poly(DMS- The poly(DMS-MSyAM dispersion exhibited a lower maximum then in the MS). Assuming the maxima are overestimated the trend favours coagulation stability was primary minimum relative to poly(DMS-MS). Howevet, since improved stabilisation (i.e., observed for poly(DMS-MSyAM it suppofts an additional type of steric stabilisation).

an adsorbed A monolayer of random coils of poly(EG) from the AM would produce structure (Figure layer -0.9 nm using Equation 1.16. However, given a brush type typical bond 4.15) with bonds stretched at a given bond angle such as 109'5" and layers between two lengths,2a the layer could extend to - 2.6 nm. The combined separation (Figure approaching particles may then provide a strong barrier at 5'2 nm 4.28).

138 200

150 I roo o 50

-50 0 5 10 15 20 H (nm)

Figure 4.28 Two particle interaction cufves for poly(DMS-MSyAM dispersion as a fuiction of separation (H) with a steric barrier at 5.2 nm (dotted line)' The parameters a 8'3 10-7 m used for the calculation were: Aerr = 2'8xlO-21J, e = J5' T = 298K' = x and I = 0.04 M and at -15 mV.

reaching The large barrier at - 5.2 pm (maximum unknown) should prevent particles the primary minimum and coagulating. This was consistent with the improved stability for the poly(DMS-MSyAM dispersion a concentration of 0.04 M NaCl'

4.5 Conclusions

poly(DMS) emulsion droplets that were prepared exhibited a larger droplet size and size distribution, than that reported by Obey and Vincent3s for a smaller dispersed duration phase content. The increased proportion of DMDES may have increased the when nucleation occurred producing a larger range of droplet sizes.

The characteristics of the poly(DMS) dispersed phase was also consistent with the portion of Obey and Vincent35 emulsion. 'esi NMR spectroscopy revealed a large cyclic and small oligomers with either Si-O- or Si-OH end groups' The Si-O- end groups at the surface of the droplets provided the electrostatic stabilisation for the emulsion. This was investigated by electrophoresis measurements, which confirmed a pH was significant negative ( potential at the surface of the droplets' When the

r39 the reported lowered the negative end gfoups became protonated at approximately pKu value for the Si-OH group.

(TEMS) in The average particle size was reduced by the incotporation of cross-linker an enhanced rate of accordance with the work by Goller et al37 . This was attributed to of the production of nucleation sites for particle growth due to reduced solubility cross-linked oligomers or alternatively an increase in density may have also contributed to a decrease in the particle size for a given mass.

during A significant drawback for these dispersions is the inherent instability reported prolonged storage. Dialysis of the dispersions with water removed the ammonium the long hydroxide which presumably prevented further particle growth and improved term stability in accordance with the reports by Obey and Vincent'3s For the the dispersion prepared with the amine macromonomels, dialysis also allowed removal of excess macromonomers. The stability of the poly(DMS-MS) dispersion polymerisation without dialysis was tested by prolonged heating to enhance the rate of or cross-linking in the dispersed phase. However, the system was complicated as growth particles would rapidly form into a phase separated layer without an obvious in the particle sizes'

at low The dialysed poly(DMS-MS) dispersions were unstable and phase separated pH pH. \ù/hen the AM was incorporated the dispersions maintained stability at lower to the values and at pH 3 over a period of time. This was primarily attributed when the protonated amine which provided a cationic electrostatic stabilisation anionic charge was absent. The experimental results could be generally explained poly(DMS- using DLVO theory at the conditions of a pH 3 continuous phase' The while the MS) dispersion exhibited a significantly reduced maximum to coagulation poly(DMS-MsyAMdispersionexhibitedaVerylargemaximum.

The The dispersions were also subjected to elevated electrolyte concentrations' poly(DMS-MS) dispersion exhibited an increase in particle size as the concentration to shield the of electrolyte was increased. This was attributed to the ability for the ions DLVO electrostatic repulsion between particles and compress the double layer' significant theory suggested that at 0.04 M ionic strength there still existed a

r40 small maximum. V/hile only a partial breakdown of the dispersion would suggest a maximum, the maximum determined was quite large and presumably over-estimated theory supported a by rhe theory. For the poly(DMS-MS)/AM dispersion, the DLVO revealed a decreasing trend for the maximum. Since the experimental evidence poly(EG) chains resistance to the effect of added electrolyte, this suggested that the may have provided some steric contribution to the stabilisation assuming the to become magnitude of the maximum was over-estimated. The dispersion did start can unstable at higher electrolyte levels. Presumably the effect of electrolytes dehydrate the poly(EG) groups and reduce the effectiveness.

would be more In order for the poly(EG) chains to provide a steric contribution it likely that the chains were orientated in a brush structure (> 2 nm)' This assumption tH surface by was consistent with the proportion of macromonomer estimated at the NMR spectroscopy and the corresponding cross-sectional radius the macromonomer

acquired at the Particle surface'

t4t CHAPTER s sTABrLrrY oF POLY[3- (DTMETHOXYMETHYLSILYL)' L - PROPANETHIOL] DISPERSIONS: FROM EMULSIONS TO LATEXES

5.1 Introduction and Aims

containing modified An alternative to the preparation of a poly(DMS) dispersion referred to as silanes involves the preparation of a new type of dispersion previously referred poly(DMST). 3-(Dimethoxymethylsilyl)-1-propanethiol (DMST, alkoxy groups (Si-oCH¡) as to as 9 in chapters , 2 and 3) contains the same silyl a thiol group' which DMDES for a heterocondensation reaction. DMST also contains via a Michael Addition' can be used to incorporate poly(EG) methacrylate monomers in chapter 3 (sections The synthetic pathway is believed to be similar to that discussed 3.4.5 and3.4.6).

to hydrolyse and undergo Under alkaline and aqueous conditions, DMST is believed cyclic oligomers analogous condensation reactions to produce immiscible linear and products are expected to to that achieved with DMDES (Figure 5.1). The immiscible group should form the nucleate into particles (presumably droptets). The thiol sulphur anion since the pKu for primary thiols22 is -10'

CH¡ CH¡ CH¡ CH I NH4oH I + -----> si-o si-o- I cH3o si-ocH3 S - I water/ethanol I (cHz): 60oc (CHz)¡ I (cHz): (CHz)¡

I I I S S' S H n I

DMST Linear Oligomer Cyclic

Figure 5.1 Hydrolysis and condensation of DMST

r42 with water and The sulphur anion will be hydrophilic due to ion-dipole interactions the interface' In the thus the particles would be expected to exhibit sulphur anions at act as work that follows it is proposed that the sulphur anions at the interface such as MPEGMa nucleophiles for a Michael Addition with poly(EG) methacrylates (previously referued to as 30)'

of The aims for this parr of the work involve the grafting of poly(EG) chains In contrast polysiloxane particles in order to achieve a sterically stabilised dispersion. be performed during the to chapter 4, it is proposed that the Michael Addition is to prepared at elevated formation of the dispersion. The dispersions are to be Michael Additions and temperatures (cf. chapter 4) in order to enhance the rate of the to linear)' the extent of siloxane polymerisation (i.e., conversion of cyclic

the By performing stability experiments, the structure of the dispersion during of polycondensation reaction can be determined' This allows a greater understanding for preparing siloxane the mechanism of the dispersion instability and a methodology dispersions with improved stability.

5.2 Literature Review gelation 5.2.1 Siloxane dispersion preparation and

growth mechanism The preparation of poly(DMST) is new. It is proposed that the and Vincent'35 For resembles that for poly(DMS) dispersion prepared by Obey linear poly(DMS) the nucleation of droplets occurred as the immiscible cyclic and was that the nuclei oligomers are formed. The mechanism proposed by the workers, and adsorption of formed were colloidally unstable and droplet growth by aggregation was high enough to monomer and oligomer occurred until the surface charge density provide electrostatic stabilisation from surface Si-O- groups' An important instability was evident observation reported for the siloxane emulsion was that the and/or gel after several months of storage. This was attributed to coalescence formation.3s

r43 the emulsion Gel formation was reported by Barrere et a1121 whom investigated and Vincent3s they polymerisation of D+. Contrary to the emulsions prepared by Obey alt21 reported an prepared their dispersions at elevated temperatures' Barrere et emulsion stability and ostwald-type ripening of the dispersion that resulted in reduced gelation. The range of sizes of the particles was 10-100 nm'

monomer (TEMS) for the Goller et al37 investigated the effect of added cross-linking 'when the poly(DMS) emulsion prepared by the obey and vincent3-s process' making up the dispersions were prepared with greater than 50 wt%o of TEMS using transmission dispersed phase, the particles were characterised as solid-like cross-linker allowed electron microscopy. This was because the high proportion of microgel extensive non-linear network formation between oligomers causing solid formation. The dispersions became unstable with the formation of white sediment.

s.2.2 Water or dispersion based Michael Additions

are favoured for protic water is a good solvent for Michael Additions as the additions Michael Addition of solvents (Chapter 3). Moghaddam et a1122 reported a rapid However' the work amines in the presence of neutral water and microwave irridation' the dispersed in this chapter requires the addition to occur at the interface between

phase and the continuous Phase'

water of a two-phase Toda et alr23 p.rformed successful Michael Additions in acceptol was suspension. Contrary to the mechanism of this work the Michael as a chalcone and exhibited a present as the dispersed phase. The acceptol was known of either amine (e'g', carbon-carbon double bond. The donor nucleophiles consisted were stabilised by the methylamine) or thiols (e.g., phenylthiol). The suspensions was also added for the surfactant hexadecyltrimethylammonium bromide and Kzco¡ thiol addition. The work was reported to provide a novel method of producing exhibit pollution efficient Michael Additions without organic solvent, which can problems.

144 a dispersion' Hayashi et a1124 also reported a successful Michael Addition within oC and Amine functionalised silica (nucleophile) was dispersed in methanol at 30 5.1)' addition at the interface with a methacrylate was achieved (Scheme

CHz: c-R O-o-si-(CH2)3-NH2 + Silica-NHz CH¡

(D-o- si- (cHz)¡- NH- cH2 -cH-R CH¡

CH R- I CH: -c-o -(cHùz-o-c-o-o il o o CH¡

spheres.r2a Scheme 5.1 Michael Addition grafting on amine functional silica

The reaction provided the first step in the alteration of the hydrophobic/hydrophilic involving nature of the surface of the silica spheres. Similar Michael Additions the preparation dispersions were performed by Fujiki et a1.125 The study investigated with methyl of amine functionalised silica and subsequently the Michael Addition oC. acrylate in methanol at 50

5.3 Experimental

5.3.L Materials

poly(EG) 3-(Dimethoxymerhylsilyl)-1-propanethiol (DMST) and methoxy 1100 gmol-l) methacrylate (MPEGMa) (with a number average molecular weight of (0'88 gcm-3)' were supplied by Aldrich Chemical Company Inc' Aqueous ammonia sodium hydroxide and sodium chloride were supplied by APS Finechem' Hydrochloric acid was supplied by BDH Chemicals. Ethanol and dichloromethane

r45 grade' These were supplied by Chem Supply Pty Ltd. Water was of "MilliQ" chemicals were used without further purification' 5.3.2 PreParation of DisPersions 5.3.2.I Preparation of the Poly(DMST) Dispersion

(26'5 DMST (1 g) was dissolved in an aqueous solution of ethanol (20 Ð and water e) in a round bottom flask with a magnetic stining bar. Once dissolved, aqueous heated to 60oC' The ammonia solution (2.5 Ð was added and the solution was were left stirring solution became turbid within 30 - 45 minutes. The dispersions time intervals for overnight at 60oc. samples of the dispersions were taken at regular prepared using DMDES analysis during the preparation. Separate experiments were oc dispersions were (0.5 g) and DMST (0.5 g) at 60 and DMST (1 g) at 23oC. Both was supplied by dialysed with 10 changes of water over 5 days' The dialysis tubing Sigma and had a molar mass cut-off of 12,000 gmol-l'

5.3.2.2 Preparation of the poly(DMST)/MPEGMa Dispersion

with MPEGMa The procedure used for preparing stabilised poly(DMST) dispersions MPEGMa was was the same as described above with the exception that 0'2 g of The dispersions were added t hour after the addition of aqueous ammonia solution. The investigated within 24 hours after the addition of the ammonia solution' days and the dispersions were also dialysed with 10 changes of watef over 5 dispersion stability was investigated'

5.3.3 Physical Measurements

5.3.3.1 Previous Techniques

(4'3'3'2)' NMR The optical microscopy technique (4.3'3.1), turbidity measuremenrs (4'3'3'4) were spectroscopy Ø.3.3.3) and electrophoretic mobility measurements performed according to the methods previously mentioned'

t46 5.3.3.2 Scanning Electron Microscopy

scanning electron Scanning electron microscopy was performed using a Philips xL30 water was microscope. A drop of the dispersions was pipetted onto the cell and the Au/Pd and allowed to evaporate overnight. The cells were then sputter coated with exposed in a vacuum.

5.4 Results and Discussion 5.4.r Studies of the Poly(DMST) Dispersions

Prior to the investigation of the Michael Addition the poly(DMST) dispersion was resulting from characterised fully in order to act as a control to interpret any benefit the Michael Addition.

5.4.1.1 Stability of the Poly(DMST) Dispersions during Synthesis

particle size was To assess the effect of heating on the dispersion stability, the data the examined periodically during the preparation. Optical microscopy for poly(DMST) dispersion was obtained and the images are shown in Figure 5'3'

147 ð i* e "ç L|. l* t -; e { {ry} t {c} "ç a fx ÈO , to" ü5 ø ,¡* t"o ö a o a ttt' d'È e 6 {tt , '' 'É! o* .o t * d o+ ' I ." l"'- r "' "& "t' o,i ",1râ o e .þ .rÐ ç d ).,. r f t 0 0 È ü rÞ- r ì û t0t ú 0çr pas ., ã Q" * o a o (r CI Cøo o o ñ & q f .ïat # L'-**: dú a ,*s ..ô löû ü ''" 'in ; cå tü ,, " üçi {t ^* I *I_* (l r, r* s w þ * d l* ö '{t *fj Õ, ün' ,r e s € 0 'l:.''.| ö Ç ü q "s$ '' .ù 1 bo - ü "3 à å Gr ê eÈ * * "o o *.,ô, I t1 ô t å û a *. .' ü.û Ë 'bo ¡i .çih cï d .llì¡tm , .s ç 6 !h* _.t ! : * *â t û ^ .!

heating at 60oc for (a) t hour, (b) 2 hours and (c) 1 day The Figure 5.2 optical micrographs of the poly(DMST) dispersion after in the bottom right corner of (c)' micrographs were taken at the same magnification and the scale appears

Þ oo first two hours of It was evident that the poly(DMST) dispersion was stable during the particles' preparation since the optical micrograph revealed a distribution of isolated micrographs at Despite that the majority of the particles appear to be isolated for the possibly one and two hours, there appears to be some minor aggregation present, oC flocculation. After one day of continued heating at 60 latge aggregates were evident. This was a reduction in the dispersion stability.

In order to investigate the origin of the stability change, the particle size was (Figure 5.3)' measured during the preparation using optical microscopy

6.0

5.0 4.0

3.0

2.0

1.0 0.0 0 2 4 6 time ( hours)

Figure 5.3 Variation of the volume average particle diameter of the dispersed addition poly(DMST) particles with time during synthesis. The time is relative to the oC of NH+OH. The dispersion was maintained at 60 throughout the synthesis'

diameter size The dispersion exhibited an increase in particle size until a critical pm, constant size (du"d) of - 5 pm was reached. Once the particles reached - 5 the larger aggregates measured was representative of the dispersed phase, as significantly the sediment were formed as a suspended or sedimented phase. The formation of than 5 pm in phase suggested rapid and extensive aggregation of particles greater - size. There was no evidence of coalescence for the 5 pm particles.

t49 after one day of The examination of the aggregates of the poly(DMST) dispersion was tested in preparation suggested a gel structure. The solubility of the aggregates and dimethyl sulfoxide' various solvents including dichloromethane, ethanol, toluene NMR could therefore' In all cases the material was insoluble suggesting a gel' 'nsi gelation' The observations not be used to investigate the aggregates and the cause of i'e', when chains are consistent with the conversion of cyclic to linear polymer' a chain network. entangle in one another they result in the formation of

was reported to form a ln the work by Obey and Vincent35 the poly(DMS) dispersion the base from gel after extended storage, specifically when not dialysed to remove of cyclic to solution. Assuming that the gel formation was related to the conversion by an increase in linear and/or extended polymerisation than this could be accelerated by the poly(DMST) temperature. ln this case of the present work, the gel formed oC the Obey and dispersion heated at 60 may represent the accelerated form of Vincent emulsion'3s

that may resemble the Alternatively the sulphur groups may provide cross-linking (>507o) TEMS' 3a-'ere et dispersion prepared by Goller et al31 for high portion of polymerisation of D¿' alr2r also reported gelation through heating of the dispersion was not This was attributed to ostwald ripening. However, ostwald ripening larger than those significant in this work because the particles were considerably

observed to undergo Ostwald ripening'121

The first The dispersion instability observed exhibited two distinct processes' and the second involved the initial growth of the particles from - 2 trtm to - 5 ¡rm leading to the process involved the subsequent gelation. The probable explanation the number of newly initial increase in particle size was presumably a decrease in growingparticlespresentduringtheearlyStagesofthesynthesis.

150 gelation The possible explanations leading to aggregation and the subsequent considered are either:

as cyclic, which decreases 1) The adsorption of species from solution such the surface charge density (cf. species with Si-o- groups). Therefore, decreasing the electrostatic stabilisation between particles causes aggregation.

larger than kT 2) A secondary minimum is present with a depth significantly which can cause particle flocculation'

discussions' The mode of stability is to be investigated in the following

5.4.1.2 characterisation of the Poly(DMST) Dispersions

were shown by obey Siloxane emulsions prepared from monomers such as DMDES material' The investigation by and Vincent35 to produce significant quantity of cyclic particle swelling Goodwin et al3afor surfactant free emulsion polymerisation revealed to have relevance here if or uptake of non-ionic material. This mechanism is thought in Figure 5'2(c)' A the adsorption of cyclics contributed to the instability observed would be useful' knowledge of cyclic proportions present for poly(DMST) dispersion of the dispersion The dispersed phase was therefofe extracted at the initial stages 2esi (Figure 5.4). preparation and analysed by NMR spectroscopy

151 I D I E l" R Si S si-R'

R I I I R R R S t- C R n o .R - cHz or CH2 -cIJz-cH2-s- \l l" -CH2 -CH2-SH o R si-R' R/ \o- S1 R'= OCH3 or OH or O I \R R

E D B C I /* A S I I o

'1""1""1" "1""1""1" I Ilrrrrlrrrrlr¡"1"" I 1""1""1"' I -20 ppm 10 0 -10

the poly(DMST) Figure 5.4 'nsi NMR spectrum of the dispersed phase of section 5'3'2'I diJpersion after t hour of réaction using the conditions described in (TMS = Oppm).

cyclic with The resonances in Figure 5.4 ate consistent with the presence of siloxane fepeat approximat ely l5Vo (B) and l47o (C) consistent with three and four 1 ppm upfield units, respectively. The resonances for the cyclics were approximately Figure 5'4 and from compared to the resonances of the poly(DMS) cyclics shown in thiopropyl the literatu re.'S,tt The change in shift was presumably due to the previously been substituent group as similar substituents (e.g., aminopropyl) have 2esi proportion of cyclic at shown to cause upfield shifts in the NMR spectrum.60 The system the early stages of preparation was consistent with the siloxane emulsion 397o of the prepared by obey and vincent.35 The end groups (A and D) represented 4 repeat total silicon and 32Vo (E) was consistent with linear or cyclic greater than tnsi NMR units. This is because cyclics containing 5 repeat units or greater produce

r52 the proportion of end resonances at the same chemical shift as linear oligomer. Given oligomer' groups at D, the resonances at E presumably represented linear

by Si-O- groups (also These dispersions are believed to be electrostatically stabilised investigated to confirm sulphur anions) and the surface charge of the particles was groups would this. Therefore, the uptake of cyclic which contains no Si-O value may be presumably decrease the surface charge density and at a critical measurements on responsible for the decreased stabilisation. Electrophoretic mobility ( potentials the poly(DMST) dispersed phase were performed and converted to (Equation 1'18) was (Figure 5.5) to test the hypothesis. The Smoluchowski equation equation was considered used to conveft mobility into ( potential. The Smoluchowski significantly larger than valid for these measurements because the product of ra was

-90 -80 -70 -60 -50 a L, -40 -30 -20 -10 0 0 2 4 6 time (hours)

dispersion as a Figure 5.5 Variation of the ( potential for the poly(DMST) electrolyte function of time during preparation ãt OO"C at high pH with a background of 1 x 10-4 M KCl. The curve is a guide for the eye'

of the ( during The results shown in Figure 5.5 reveal an increase in the magnitude charge synthesis. This is being interpreted as being due to an increase in surface potentials:31 density according to the Poisson-Boltzmann distribution at low

153 oo ÊK{o (s.1)

double layer where oo is the charge density, e is the permittivity, K is related to the ( potential is thickness and l|/o is the surface potential. Therefore, assuming that the the an approximate of the surface potential an increase in the ( potential increases surface charge densitY.

swelling with Given a decreased contribution to charge without the Si-O- groups, of cyclics is cyclics would be expected to decrease in ( potential. Therefore, swelling less likely the cause for instability.

of charged material' The increase in the ( potential may be attributed to the adsorption The adsorption of small charged oligomers may increase the number of charged increase groups at the surface relative to the increase in the particle size. This would an already the surface charge density and the ( potential. It is noted that given be unlikely negatively charged surface, the adsorption of further negative species may

and further analysis would be required'

Dispersion 5.4.1.3 The Application of DVLO Theory on the Poly(DMST)

Another possible explanation for the poly(DMST) instability observed during resulting preparation is flocculation in a secondary minimum' The ionic strength pH was from NH+OH is difficult to calculate in an ethanol/water solvent' The calculate ionic measured at 10.3; however, the reliability of using this pH value to pH electrode' The strength is in question due to liquid junction potentials across the in pK6 for ammonia in dioxane-water solutions is 8.75 (cf., 4.75 for ammonia was used to water;.126 The pH value for ammonia in pure water was 11.8 and

estimate the ionic strength of 0.006 M using: (s.2) pH = - log [H*] and tOH-l tH.l = 10-14

The ionic strength (I) was assumed to be equal to [OH-]

154 DLVO theory can be used to investigate the likelihood of a significant secondary minimum. The solution permittivity (e : 66) was estimated from contribution between the individual permittivity of water and ethanol:

tlsolution) = €lwater) Qwater + Êlethanol) Oethanol (s.3) where 0water + Qethanol I

lO-20 J' which The Hamaker constant reported by Vincentt" fo, water (411) was 3'l x be the was used in this woik. The Hamaker constant for poly(DMS) was taken to 20 Hamaker constant for hydrocarbons3l 16 x 10 ¡. The effective Hamaker constant potential of 70 mV was was therefo re -2.8 x 10-21 J from Equation 1.21. An average ( pH Since used since it was the measured ( potential of the dispersion after 1 day at 7' spheres can be used' H << a the Equation 1. 12 for the interparticle attraction between This was combined with the equation for the repulsion term (Equation 1'15) to particle produce curves for the total interparticle interaction energy (vtot) at different

sizes (Figures 5.6 and 5.7).

7000 +5 6000 *4 5000 F 4000 -x-3 \-v E 3000 - t-2 2000 <-1 1000 0 -1000 0 10 20 30 40 50 H (nm)

Figure 5.6 Two particle interaction curves for poly(DMST) dispersion at various purtl.t. sizes (pm) as a function of separation (H). The parametels used for the and I 0'006 M' calculation were: Aerr = 2.8xl}-21 J, e = 66, Ç =70 mV' T = 333 K = The particle sizes considered are shown in the graph in pm'

155 The theory predicts that an increase in the particle size increases the energy maxlmum and improves stability to coagulation in the primary minimum. However, upon further inspection there is an opposite effect on the secondary minimum (Figure 5.7)'

4 +1pm a J -t- 2 ¡tm 2 -3lrm --¡ 4llm F 1 __* 5 pm =.s 0 -1 n

-3 20 25 30 3s 40 45 s0 H (nm)

Figure 5.7 Two particle interaction curve for poly(DMST) indicating the seãondary minimums. Not" that the data was taken from that shown in Figure 5.6.

It is noted that the depths of the secondary minima is critically dependent on the ionic strength which unfortunately required estimation for this work. However, the analysis using DLVO theory revealed the presence of secondary minima. The depth of the secondary minimum (V*in) as a function of the particle size is shown in Figure 5.8.

-0.5

F -1 ,y .E -1.5

a -2.

-2.5

-J- 0.0 1.0 2.0 3.0 4.0 5.0 Particle size (Pm)

Figure 5.8 Secondary minimum depths (V,"inlkT) as a function of particle size using the parameters in Figure 5.6.

156 depth of the The theory suggests that upon increasing the size of the particles, the attraction at secondary minimum increases due to an increase in the van der Waals for a larger separation distances.3l With a 1.5 kT average translational kinetic energy become particle,a0 the interparticle interaction supports flocculation once particles greater than 2 pm. It is important to note that this theory considers two-particle situation where interaction only. The real system is complicated by a many particle entropy maY be imPortant.

5.4.1.4 Gelation of the Poly(DMST) Dispersion

forms gel The important question to address was why the poly(DMST) dispersion suggested that aggregates during continual heating at 60oc. The DLVO analysis maxima flocculation was possible at particle sizes 2-5 pm in diameter. However, the in Figure 5.6 suggested that coalescence would be unlikely to follow flocculation' nature (i'e', Since the particles during the early stages of preparation were liquid in by DLVO droplets) they may be susceptible to deformation, which is not considered called theory. DeformationllT of a particle can be characterised by a bell shaped form

a dimple (Figure 5.9).

flocculation H*40nm --

H>100nm particle deformation and coagulation

2r (r: film radius)

Figure 5.9 Schematic illustration of the proposed particle deformation'

r57 contact and the The approach of two deforming particles produces a thin film between of this film may film length increases with the extent of deformation' The radius to the electrostatic greatly enhance the affect of the van der waals attraction relative the closest two repulsion. When two identical particles begin to overcome repulsion' surface curve that are surface points experience attraction, while the points on the there is a greatet further away experience repulsion. If the parlicles are deformed then distance'118 surface area that can experience attraction at a given separation

of the many Additional possibilities that may lead to coagulation can be a result formation of floc particle effect. Two-particle interaction theory does not consider the deformation'll8 The structures and volume restrictions that could occur and cause is possible flocculated particles therefore, may come closer together if deformation (Figure 5.10).

(a) (þ)

between (a) Figure 5.1,0 Schematic illustration of the proposed transformation flocculated hard spheres and (b) aggregates of deformed particles'

in the The particles of poly(DMST) have sufficient kinetic energy to flocculate separations) allows the secondary minimum. The close approach (30 - 40 nm exhibit sufficierit formation of floc structures that at a critical size (- 5 p*) may deformation allowing the maximum to be overcome'

158 to increases in Alternatively, aggregated particles arranged in flocs may be susceptible solution' For particle size from adsorption of polymer chains or monomers from the a 30 nm outer example, a particle with a diameter of 5 pm in order to encompass Vo increase in the region would need to increase in size to 5.06 pm. Therefore, a 3'6 are already particle volume would be sufficient to force coagulation once particles flocculated (Figure 5' 1 1).

Adsorption of r' polymer/monomer from þsolution

------+

30-40 nm separation 0-40 nm separation (b) (a)

between (a) Figure 5.11 Schematic illustration of the proposed transformation of particles reversibly flocculated and (b) partial coagulation caused by adsorption polymer or monomer'

particles Either of these processes may be contributing to coagulation of flocculated which produces the observed gelation'

5.4.2 Studies of the PoIy(DMSTyIIPEGMa Dispersion

dispersion If flocculation, coagulation or coalescence is operative for the poly(DMST) The proposal for it should be possible to avoid this by providing steric stabilisation' the the addition of MPEGMa is to prevent an increase in particle size during added dispersion preparation. Poly(DMS) dispersions with non-ionic surfactants smaller size38 before the preparation have been shown to produce particles of a 1800 nm to 50 nm).

159 of the The objective fbr the addition of MPEGMa during the early formation of the particle poly(DMST) dispersion was to leact the sulphur anion at the surface (chemisorption) via a Michael Addition. This should result in a covalent attachment of the hydrophilic poly(EG) groups (Figure 5'12)'

CHz //////////// //////////// ll CH¡ _____--+ I I + S S -c I Q:Q I CHz -+-o CH¡ I -cH CHz Q:Q I CHz r t-23 o I ocH3 I CHz

MPEGMA I CHz 23 ocH3

MPEGMa at the Figure 5.L2 Proposed mechanism for the Michael Addition of particle surface.

5.4.2.1 optical Microscopy studies of the PoIy(DMST)/NIPEGMa Dispersion

Thepoly(DMsTyMPEGMadispersionwasanalysedbyopticalmicroscopyduring function of preparation. The volume-average particle diameter was calculated as a time and compared to the poly(DMST) dispersion (Figure 5.13).

160 5 o o a a 4 o J^ o o o o -¡- o o Ë 2

0 0246 Time (days)

of poly(DMST) (') Figure 5.L3 Variation of the volume-averaged particle diameter at 60 (o). and poly(DMSTyMPEGMa particles during preparation "c

in particle The poly(DMST)/\4PEGMa dispersion exhibited only a minor increase The dispersion was size compared to poly(DMST) which exhibited a large increase' oC microscopy further investigated after one day of preparation at 60 by optical (Figure 5.14).

dispersion after I Figure 5.L4 optical micrograph for the poly(DMSTyMPEGMa day at 60oC.

161 the The optical micrograph of the poly(DMST)/MPEGMa dispersion suggested and the particle presence of some minor flocculation. The volume avefage diameter (Figuer 5'15)' distribution was calculated using particle size analysis software

6 ta

U) Ø a a G a a 0()4 'a a aa oit a ñ a a 2 a.tt t'-,' a 0 1.0 2.0 3.0 4.0 5.0 6.0 diameter (pm)

Figure 5.L5 Particle size distribution after 1 day for poly(DMST)/IvIPEGMa dispersion prePared at 60oC'

calculated The volume average diameter for the poly (DMST)/MPEGMa dispersion using Equations 1'22 using Equation 1.21 was - 2.8 pm. The coefficient of variation and 1.24 was 4O7o for particles above 1 [rm. The average particle size and after polydispersity after one day was similar to that of the poly(DMST) dispersion preparation, MPEGMa was one hour. Since MPEGMa was added one hour into the time' therefore, responsible for the maintained stability after this

using greater The presence of smaller sub-micron particles were evident when

magnification (Figure 5. 1 6)'

r62 ,# &

& 5Fm

with MPEGMa at Figure 5.L6 Optical micrograph of^the poly(DMST) dispersion higher magnification after 1 day at 60oC'

without added These particles were not evident for the poly(DMST) dispersion addition of MpEGMa and may be attributed to a secondary nucleation process after MPEGMa. This involves the formation of secondary droplets that can contain formation' poly(EG) chains at the surface during the early stage of their droplet

5.4.2.2 Evidence for Chemisorption of MPEGMa

poly(DMST), a sample of In order to assess the Michael Addition of MPEGMa onto conditions and the dispersed phase was separated from the dispersion using acidic of base in order dissolved in CDCI¡. Michael Additions of thiols require the presence to assume that to produce the sulphur anion (chapter 3) and therefore it is reasonable no further reaction occurred during the separation procedure' Additionally the of water poly(DMST) dispersion for this analysis was first dialysed with 10 changes with MPEGMa' to remove free DMST or dissolved oligomers that may have reacted lH The NMR spectrum of the sample is shown in Figure 5' 17'

t63 o

A I B CD s cH3 S, cH2- cH2- CIt2- - -R A I o

o H I -]I E! H c B R= [-"t*, _cH2 D -ç9, -olcur) _r, I cH3 G J E G F

2.0 ppm 0.0 7.0 6.0 5.0 4.0 3.0 1.0

tH Figure 5.17 NMR spectrum of the dispersed phase of poly(DMST) prepared with added MPEGMa.

of The lH NMR spectrum revealed five major resonances from the polymerisation DMST (4, B, C, D, J). This was expected since a smaller proportion of MPEGMa and not the interior was added (cf. DMST) as the addition was required at the surface that can be of the particles. Resonances H and I correspond to the poly(EG) chain tH E, F, G confirm determined with a NMR spectrum of MPEGMa. The resonances Chapter 3 the covalent linkage between the sulphur and MPEGMa as discussed in (Figure 3.13) and reported elsewhere.ee

rH at 60oC' The NMR was performed on the dispersion after one day of preparation rapidly However, the Michael Additions at the particle surfaces may have occurred proceeded at or since a similar one-phase reaction in propanol at room temperatule

less than one hour (Table 3.7).

tH trans- Additionally the NMR spectrum supports the absence of significant MPEGMa due esterfication (Chapter 3-Scheme 3.7) between ethanol and the ester of 3.11. to a lack of a signal at 4.O ppm as previously shown in Figure

r64 5.4.2.3 stability of the PoIy(DMST)/NIPEGMa Dispersion

a week The poly(DMSTyMPEGMa dispersion also exhibited some sediment after the resembling that of the poly(DMST) dispersion. However, the quantity of was increased' sediment phase was reduced and the time required for its formation Additionally the particles making up the sediment phase could be redispersed' The poly(DMST) dispersed phase could not be redispersed as a gel was formed' Therefore, the particles in the sediment of the poly(DMST)/l\4PEGMa dispersion The were flocculated and those of the poly(DMST) dispersion were coagulated' while the separation of flocculated particles is reversible (secondary minimum) particles of coagulates is not (primary minimum)'

growth up The presence of poly(EG) chains at the particle surface prevented particle few hours of to 5 pm, which was observed for the poly (DMST) dispersion in the first preparation. It is suggested that the poly(EG) layer prevented flocculated particles coming closer together (i.e., to coagulate)'

s.4.3 MPEGMa Layer Thickness and structure Determination

In order to further investigate the origin of the improved stability of was required' poly(DMST)/l\4PEGMa, a knowledge of the poly(EG) layer thickness approximation of Given the average number of repeat ethylene glycol units was 23, an coiled then the the layer thickness can be made. If the poly(EG) chains are randomly if the approximate layer thickness given by Equation 1.16 is - 1.8 nm' However, the layer chains adopt a brush like structure and are anchored from the surface and bond thickness could reach - 8.5 nm given an arbitrary bond angle of 109'5o length of 0.15 nm for C-C and C-O.24

area The same procedure from chapter 4 can be used to estimate to cross-sectional 10-6 m gives a volume available for the poly(EG) chains. The average radius of l'4 x in 50 g stock was 1 x of l.2x 10-17 m' pe, particle. The total dispersed phase volume 1010' The surface 10-6 m3. Therefore, the number of particles is approximately 8'7 x If the poly(EG) area of a particle ts 2.5 x 10-11 m2 giving a total surface area of 2 m2.

165 chain was oriented in a brush at 110o bond angles the cross-sectional radius from simple geometry is 0.0415 nm (theoretical). This corresponds to a cross-sectional area cover this of 5.4 x 10-21 m2. The number of poly(EG) chains required to completely and area is 4 x l}2o molecules which corresponds to a ratio of 8:1 between DMST lH MpEGMa. The proporrion of DMST to MPEGMa calculated from the NMR (Figure 5.17) of the dispersed phase after dialysis was 14:1. There was slightly less MpEGMa available for ideal coverage but the calculation suggests there was radius sufficient MpEGMa available for a brush structure or close to. The theoretical of the for coverage probably underestimates the true value due to the close proximity functional groups through out the macromolecule. It also important to note that even to the with sufficient room for the poly(EG) to lie flat, the chains could still extend in continuous phase because of favourable intermolecular interactions with water.

The layer thickness can be estimated with the use of ( potential calculations' Electrophoretic mobilities measurements of the poly(DMST) and poly(DMST)/\4pEGMa dispersions were performed to determine the effect of the of pH adsorbed layer on the ( potential. The mobilities were measured as a function

and were converted to ( potentials (Figure 5.18) using the Smoluchowski equation (Equation 1.18).

20 E--- 0

-20

5 -40 Cd I -60 o \, -80

-100 2.0 4.0 6.0 8.0 10.0 pH

Figure 5.18 Ç potential vs. pH for the poly(DMST) (¡) and poly(DMST)/ MPEGMa (r) dispersions as a function of pH'

r66 The effect on the ( potential was a decrease in magnitude for both positive and presumably negative potentials in the presence of poly(EG). The layer thickness was plane responsible for the reduction in the ( potential by the displacement of the shear the double assuming the adsorbed layer does not affect the charge density profile of layer.

The Equations 1.8 and 1.9 used by Fleer et alse for the determination of the layer be used to thickness for an uncharged surfactant adsorbed at a dispersion interface can 4Å with (r estimate the layer thickness attributed from the poly(EG)' A A value36 of the calculation. The estimation for or -94 mV and Ç2 or -60 mv were used for high pH ô value suggested a l0 nm layer thickness. The ( potential values obtained at the were used in order to minimise the effect of experimental error associated with mobility measurements. The estimated layer thickness at other pH values ranged from 5-20 nm. The layer thickness corresponds to a brush adoption and not that of would random coils. Given a 10 nm layer thickness, two approaching particles experience respective poly(EG) chains at - 2O nm interparticle separation'

Figure 5.7 shows that V.in for 2 pm to 5 pm size particles for the poly(DMST) of the dispersion would be at a considerable distance (35 - 40 nm) from the surface particle. Therefore, it would be unlikely that the added MPEGMa could provide a barrier for flocculation at this separation distance' This was consistent with of the experimental observation of reversible sedimentation observed during storage particles of the dispersion after. Some minor flocculation was also evident in the optical micrographs in Figure 5.14. However, the effect of the poly(EG) layer presumably prevented flocculated particles coming closer than - 20 nm.

5.4.4 Effþct of Added Electrolyte on the Poly(DMST) and Poly(DMST)/ MPEGMa Dispersions

In order to further investigate the stability of the dispersions, the addition of added stability electrolyte was employed. Turbidity measurements were used to examine the of the dispersion at various electrolyte concentrations (Figure 5.19).

r67 t.20

1.00

P 0.80 é) çh 0.60 cÉ L 0.40 z 0.20

0.00 0.0 0.2 0.4 0.6 0'8 1'0 NaCl concentration (mol/l)

Nacl Figure 5.19 Variation of the normalised turbidity as a function of added (r) dispersions' concentrarion for the poly(DMST) (r) and poly(DMSTyMPEGMa on a The turbidity was meàro."d one day after addition of electrolyte and stored after 24 hours rotating frame. Since the poly(DMST) dispersion was already unstable experiments' at 60 "õ the dispersion wai heated for only 2 hours for those

A visual observation of the poly(DMST) dispersions at elevated electrolyte is known that an concentration revealed the presence of sediment layers' While it case, the aggregation process can cause an increase in turbidity,4O in this The samples were sedimentation (as a result of aggregation) was the dominant factor' ovet the 24 continually rotated after addition of electrolyte to limit the sedimentation prior to the hour period. This also allowed the redispersal of sedimented flocs contribute to the measurement while sedimented coagulants (i'e., gel) would not turbidity.

became unstable The results of Figure 5.19 suggest that the poly(DMST) dispersion NaCl the due to a considerable reduction in the electrostatic stability. At 0.2 M gel that resembled the dispersion was completely separated. The sediment formed a noted that when this gel formed with prolonged heating of the dispersion. It should be oC of sodium dispersion which was subjected to two hours at 60 in the absence added electrolyte chloride, remained stable after one day. Therefore, the addition of poly(DMST) was directly responsible for the observed loss of stability for the

168 only a dispersion. The poly(DMST)/MPEGMa dispersion maintained stability with

partial decrease in turbidity observed.

by The addition of added electrolyte would further enhance the extent of flocculation also increasing the depth of the secondary minimum. However, added electrolyte will closer compress the double layer and bring the new secondary minimum to a interparticle range. At such distances the adsorbed layer should provide a steric are not barrier against flocculation in the deeper minimum given the poly(EG) chains significantly compressed due to hydration'

The poly(DMST) dispersions at higher ronlc strength concentrations were investigated using DLVO theory figure 5'20)

? 10 I Ò F ì -v 0 \ -.- 0.05M .9 -10 -o 0.1M -20 -)+0.2M {-1M -30 0 10 20 30 40 H (nm)

Figure 5.20 Two particle interaction curves for the poly(DMST) dispersion at for the u*iou, ionic strengt|s as a function of separation (H). The parameters used a 1 x 106 calculation *"r"',i* =;.s.io-ti J, r* = à6, ç =70 mv, T = 298K and = m. The dotted line represents the steric barrier'

to kT. since The secondary minima in Figure 5.20 ate significant in depth compared the poly(DMST)/MpEGMa dispersion maintained stability at elevated electrolyte greater than concentration, this supports the presence of a steric barrier at a distance by the the new secondary minima depths. Therefore, â V-in at 2O nm is unaffected a function addition of electrolyte to the dispersion. The partial decrease in turbidity as moieties of electrolyte concentration may be related to dehydration of the hydrophilic

r69 reduce õ and of the poly(EG) chains at igh electrolyte concentration. This would Thompson and increase the V.in. A decrease in stability was also observed by with pryde116 who investigated the effect of poly(EG) adsorption on latex particles

increasing temPerature.

at Low pH 5.4.5 poly(DMST) and PoIy(DMST)/NIPEGMa Dispersion Stability

relation to the In order to further investigate the extent of steric contribution in (i.e'' Si-O-), electrostatic contribution that is directly attributed by the anionic charges oxygen was the dispersion stability was measured at low pH where the silyl protonated.

3 using 0'l M HCI' The pH of the poly(DMST)/lvIPEGMa dispersion was reduced to pH and the ( At this pH an aliquot of the dispersion was diluted in a solution of equal that potential was measured at - 5 mV. The low ( potential magnitude suggested The turbidity of insignificant electrostatic stabilisation would be present at this pH' investigating the the poly(DMSTyMPEGMa dispersion was used as the method of (Figure 5'21)' For a dispersion stability and was measured at regular time intervals prepared using a 1:1 comparison study, the poly(DMST-co-DMS) dispersion was were dialysed mole ratio of DMDES and DMST. This was because the dispersions was too for this experiment (cf. that in Figure 5'19) and the poly(DMST) dispersion unstable for dialYsis'

110 t.2

P 0.8 q) (t) 0.6

, 0.4 z 0.2

0 0 100 200 300 400 500 Time (hours)

Figure 5.2L Variation of the normalised turbidity for the poly(DMST) dispersion t with MPEGMa (o) and poly(DMST-co-DMS) (o) at pH 3 after a period of dialysis' = 0 corresPonds to the addition of acid'

the turbidity once The poly(DMST-co-DMS) dispersion exhibited a rapid reduction in layer after the pH was lowered. Almost all of the dispersion had formed a sediment pH 3 only 20 minures. The results for the poly(DMST)/MPEGMa dispersion at the ( potential suggested a partial reduction in stability only. As the magnitude of represented by a decrease decreased the electrostatic stabilisation decreased. This is in the repulsion term (V."0) and a corresponding decrease in the enelgy maximum' DLVO theory was applied using the ionic strength at pH 3, which was approximately 0.001 M (Figure 5.22).

r7l 10

5 F +ot -5

-10 0 10 20 30 40 50 H (nm)

poly(DMST) Figure 5.22 Two particle interaction curves for the dialysed the calculation diJpersion with addeå MPEGMa at pH 3. The parameters used for '75,Ç=5 M anda= 1x 106 were: Aerr= 2.8x 10-21 J, tp = mV' T =298K' I=0'001 m.

alter the magnitude The precise ( potential is difficult to determine and its value can a tentative explanation' of the maximum, so the curve in Figure 5.22 is useful only as ratio The ( potential accuracy is in question because of the low potential to error favorable exhibited for ( potentials low in magnitude. However, an energetically 5 maximum particle-particle interaction is appalent at a 5 mV ( potential with a kT particles present. without a steric barrier at - 20 nm from the adsorbed layers the by would presumably coagulate and possibly coalesce. Coalescence was observed in order to Obey and Vincent35 who used low pH conditions to separate emulsions

analyze the dispersed phase by NMR spectroscopy'

18 days it can be Since the dispersions relative turbidity decreased only by 4ovo aftet slight decrease in suggestecl that some limited steric stabilisation was present' The active as there turbidity also suggests the presence of electrostatic stabilisation was the system is was no change in turbidity for the dispersion at neutral pH' Therefore, proposed to be electrosterically stabilised'

112 5.4.6 Investigation of Solid Particles

the dispersion when the poly(DMST) dispersion was prepared at room temperature i'e., the exhibited similar characteristics as the Obey and Vincent35 dispersion, instability produced liquid dispersed phase contained mostly cyclics and dispersion phase was less phase separation (presumably as a result of coalescence)' The liquid (i.e., removal of dense than water giving a thin film at the surface after dialysis dispersion was heated to 60 ethanol from the continuous phase). However, when the tested (such as oC the dispersed phase became insoluble in all organic solvents was not possible' ethanol, dichloromethane and toluene), so NMR investigation consequence of Presumably the insolubility was due to extensive gelation as a The dispersion polymerisation within each particle (and possibly between particles)' the dispersed instability produced a sediment layer, indicating a higher density of can be seen phase than water. An example of increased density upon polymerisation of 10' with poly(DMS), polymer viscosities (as a result of increased polymer length) I gmol and 1.09 gmol-1, 1000 and 30,000 mpa exhibit densities2s of 0.931gmol-l,0.97 a change from respectively. An increase in density of the separated phase suggested droplets to that of latex particles'

the average oligomer It is proposed that during heating of the poly(DMST) dispersion, and polycondensation' molar mass was increased due to ring-opening polymerisation polymer or oligomer chains Gelation may then be caused by the entanglement of the is widely accepted for within the particles. Entanglement of flexible polymer chains melt polymers or high concentrated solutionsl28'12e and for poly(DMS) poly-"rr.tto't3t

exhibited sedimentation Since the parricles of the poly(DMST)il\4PEGMa dispersion of (in pure water), this suggested that this dispersion also exhibited a conversion cyclic to linear during heating. However, as the particles of the the poly(DMST)/MPEGMa dispersion were not coagulated (only flocculated), reactions' conversion to a particle nature was not attributed from interparticle

cross-linking An alternative explanation for the gelation may be attributed to covalent undergo a nucleophilic between polymer chains. Given the silyl oxygen anions can

113 anion to covalently attack at the silicon site it may also be possible for the sulphur bond to other silicon sites since the sulphur anion is a strong nucleophile'

5.4.7 Investigation of Small Particles in PoIy(DMST)/NIPEGMa

phase was A qualitative analysis of the presence of small particles in the dispersed were dried by conducted using scanning electron microscopy (SEM)' The dispersions was analysed by placement inside a vacuum. The poly(DMST)/l\4PEGMa dispersion SEM and the image is shown in Figure 5'23'

5Ém

added Figure 5.23 SEM image for the poly(DMST) dispersion prepared with MPEGMa at 6OOC.

The poly(DMST)/\4PEGMa dispersion exhibited extensive flocculation or for However, coagulation for the larger particles under the vacuum conditions SEM. The at high magnification the presence of small spherical particles was detected' particles were generally arranged in hexagonal close packing, which is a characteristic formed once the for monodisperse particles.l3t Pr"ru-ably these particles were than the MPEGMa was added by a secondary nucleation process as they were smaller

174 bulk particles. As new particles began to form the addition of MPEGMa at the surface presumably provided stability via steric stabilisation at a lower particle size since a critical size for charge density was not required for stability.

The presence of these small particles that were not distorted or phase separated rù/ere supported a solid state for the particles. Similar observations reported by Goller et al37 where SEM was used to distinguish the presence of microgels in replace of droplets. However, in a vacuum without a continuous phase the particles of > 1 pm of the poly(DMST) dispersions experienced significant aggregation preventing accurate interpretations for those particles.

115 5.5 Conclusions

poly(DMST)/IvIPEGMa The comparison between the progress of poly(DMST) and of time (Figure 5'24) dispersions with one day of heating is illustrated as a function

Poly(DMST) Poly(DMST)/MPEGMa t=0

+ HlO + CHTCH2OH + NH4OH DMST + H,O + CHTCH,OH + NH4OH DMST one Phase one Phase

t< I hr aao a a a a a a a a particle a particle a a a a a fomation a a formation a a a tta a a '

t= I hr size increasing due to insufficient oo ooa size increasing electrostatic a a due to insufficient ù stabilization a a electrostatic àà o o stabilizatio0 Michael Addition of MPEGMa

t=2hr size continùes to iÈ with less i increase t** -d newly formed +f.Þ f oo o particles formed ùù ùù secondary o nucleation o critical size reached MPEGMa stabilisers of small o (5Ëm) the particles particles with MPEGMA rapid coagulation and,/ no further size increase t> 2hr or coalescence possible cause: o flocculation flocculation then possible but not particle deformation o coagulation ì.e., and/or floc particle growth at >20 nm from adsorPtion of o J particle separation

t= I day oC T 60 oC causes T = 60 causes = i extended polymerisation or extended PolYmerisation à o crosslinking ù crosslinking o à dropìet ) latex Particle o o droplet ) latex Particle i sedimenlation + rùù flocculation < 5 Pm disPersed possible onlY droplets à

t>2days i sediment ù ù gentle phase (gel) shaking s¡' i------> *.þ f ß*ù ù

the poly(DMST) and Figure 5.24 Illustrative representation of the progress of poly(DMST)/l\4PEGMa dispersions'

176 of the obey In rhe first hour (Figure 5.24) the poly(DMST) dispersion resembled that chapter The and Vincent3s poly(DMS) dispersion and the dispersions prepared in 4. solution became turbid as a result of particle formation due to the reaction between monomers to produce oligomeric and cyclic material'

oc particle size After one hour at 60 the poly(DMST) dispersion exhibited an average to 5'0 pm. The of approxim ately 2.2 pm and by two hours the particle size increased or S- groups increase in size allowed sufficient surface charge density from the Si-o- there were to provide electrostatic stabilisation. However, when MPEGMa was added provided steric no significant further increases in particle size as the poly(EG) chains (from stabilisation. Also, as new particles in the presence of MPEGMa formed size' secondary nucleation) they were able to remain stable at a much smaller

and The 5 pm particles of the poly(DMST) dispersion wele unstable to coagulation during gel formed after one day. Since the ( potential of the poly(DMST) dispersion the preparation increased, the adsorption of cyclic (swelling) was considered less likely to be the method of reducing the electrostatic stabilisation. Also, Ostwald the particles ripening was considered insignificant due to the relatively large size of DLVO involved and so the eventual instability was first attributed to flocculation. the particles theory supported the presence of a secondary minimum, which allowed However, to approach to within 30-40 nm for a two identical particle interaction. to undergo despite very large maxima required for particles to approach close enough stage and coagulation, it is suggested that the particles are liquid in nature at this significant for susceptible to deformation. This phenomenon is considered to be very not large droplets (5 pm) and may also be amplified by a many particle interaction

considered by DLVO theory.

DMST The results suggested a successful Michael Addition between MPEGMa and at the surface, with sufficient proportion of MPEGMa for brush coverage' The when MPEGMa displacement of the shear plane due to a reduction in the ( potential was at the surface also supported a brush structure as the layer thickness was nm' estimated at 10 nm, which was consistent with the theoretical length of 8'5

t]1 with reversible After one day the presence of MPEGMa provided a stable dispersion gelation flocculation only. while the poly(DMST) dispersion experienced extensive a solid nature with no steric stabilisation. The particles of both dispersions exhibited of gel, increase closer resembling that of latex particles. This included the formation during the SEM in the dispersed phase density and the survival of small particles polymerisation by the experiment. This presumably can be attributed to continued chains. higher temperature employed and entanglement of the polymer

at reduced electrolyte The poly(DMST)/IvIPEGMa dispersion was further investigated decreased. A minor and low pH conditions where the electrostatic stabilisation is for the dispersion' decrease in stability supported an electrosteric mechanism

178 CHAPTER 6 CONCLUSIONSAND FUTUREWORK

6.1 The Preparation and Michael Additions of Amine and Thiol Functional Copolymers of Poly(DMS)

Amine and thiol functional poly(DMS) copolymers wele prepared using the For the heterocondensation mechanism with a base or acid catalyst, respectively. to produce a random amine, the results suggested that potassium silanolate was able while sodium incorporation of functional silane within the poly(DMS) backbone' the backbone hydroxide produced a block copolymer. Random incorporation within The ability for the was also achieved for the thiol functional poly(DMS) using TfOH' of end-stopper. acid to cleave the backbone was further evident by the incorporation

Michael Additions The amine and thiols were shown to be excellent nucleophiles for tested were shown to using a range of template molecules and silanes. All the thiols Michael be stronger nucleophiles (cf. amines) and exhibited the most efficient of the donor or Addition. The duration for the Michael Addition increased as the size influenced the reaction' acceptor increased. The end-group of the poly(EG) chain also and hindered The hydroxyl group presumably hydrogen bonded with the nucleophile group cannot the reaction by reducing the access to the vinyl group. The methoxy faster' hydrogen bond to the nucleophile and the reaction was significantly

For the The effect of the solvent also influenced the Michael Addition reaction. aprotic solvents, dichloromethane or chlorobenzene was generally sufficient' For all However, for the much larger poly(EG) chains, toluene was more efficient' the aprotic the Michael Additions, the protic solvents were significantly better than the charged solvents, which can presumably be attributed to the stabilisation of transition state. The consequence of using a protic solvent was the trans-esterification reduced using tertiary between the solvent and the ester of the acceptor. This was butanol which contains hindered access to the alcohol group'

n9 functional copolymers The Michael Additions wefe performed on the thiol and amine of poly(DMS). While the patent literaturel0o'133'134 nu. examples of attaching the Michael poly(EG) chains to a poly(DMS) chain to increase the hydrophilicity' a novel method of attachment' Addition of a poly(EG) macromolecule provided

Thiol 6.2 Investigation of Polysiloxane Dispersions using Amine or Groups Attached to Poly(EG) through a Michael Addition

in a mannef that was The poly(DMS) and poly(DMS-MS) dispersions were plepared The greater similar to that of Obey and Vincent3s and Goller et a1,31 respectively' produced particles of a larger size dispersed phase proportion employed in this project a longer nucleation time and greater distribution. This was presumably attributed to

since there was more monomer present'

and then the For the amine work, the Michael Addition was performed beforehand While for the thiol' product was added to the reagents for preparing the dispersion' occurred after the the dispersion was prepared with DMST and the Michael Addition formation of the disPersion.

performed at room Studies of the poly(DMS-MS) dispersion were predominately dispersion became unstable to temperature and were relatively stable. However, the level was increased due to a aggregation when the pH was decreased or the electrolyte containing the reduction in the electrostatic stabilisation. However, the dispersion steric stabilisation' poly(EG) groups attached via the amine, remained stable due to to be oriented as a brush The structure of the poly(EG) at the surface was suggested provided further insights structure with a layer thickness > 2 nm. The synthetic work incorporation into the mechanisms for the dispersed phase chemistry' The successful a similar of the amine f'unctional silane in the poly(DMS) backbone, supports following the same incorporation in the poly(DMS) oligomer in a dispersion phase for the AM grafting heterocondensation mechanism. This may support chemisorption on the poly(DMS-MS) surface.

180 gloups at the DMST was a useful monomer to prepare a dispersion with sulphur prepared with DMDES' surface while being analogous to the poly(DMS) dispersion of the linear In this work the dispersion was prepared at 60oC. Thus the proportion a dispersion polymer relative to cyclic increased. This had the effect of producing was prepared at 60oc' susceptible to gelation. when the poly(DMS-MS) dispersion For the gelation was also observed suggesting a tempelature dependent effect' was achieved poly(DMST) dispersion, a two-phase Michael Addition with MPEGMa Layer resulting in steric stabilisation and enhanced stability against gelation' that the displacement of thickness measurements from microelectrophoresis suggested were indicative of a the shear plane and the proportion of poly(EG) after dialysis poly(EG) chain allowed the brush structure - 10 nm in thickness. The presence of the nucleation that formation of smaller and presumably solid particles from secondary could only be observed bY SEM.

new characteristics The results have produced a novel siloxane based dispersion with phase that not previously seen with polysiloxane dispersions , i.e-, a solid dispersed entangled)' In presumably resembles that of latex particles (longer polymer chains the addition, because poly(EG) was shown to be covalently attached for to poly(DMST)/\,fPEGMa dispersion, the dispersion would be less susceptible cannot be desorption. while the chemisorption of AM to poly(DMS-MS) can be distinguished distinguished fiom physisorption, the poly(DMST) dispersion

and the success of the Michael Addition confirms chemisorption'

6.3 Final Comments

preparing copolymers The work in this project describes two complementary ways of demonstrated the of siloxane, the bulk/solution and in the dispersion. This work has poly(DMS) for both use of Michael Additions to incorporate poly(EG) chains onto of procedures. It is suggested that surfactant-free precipitation polycondensation oligomers of siloxane copolymers can be used for textile coatings if small size poly(DMS) are acceptable. If longer chains and cross-linked copolymers are more control over desirable then heating the dispersion is fecommended' However, if

181 by a the poly(DMS) copolymers is required then bulk polymerisation followed solution Michael Addition is recommended'

6.4 Future Work

and that of the The Michael Addition of the amines to produce secondary amines the thiols could be achieved in excellent yields and in short times' However' especially formation of the double addition to amine requires further optimisation, best solvent that did not when the donors amines are on a poly(DMS) backbone. The the use of a produce significant trans-esterification was tertiary butanol' Ideally, activation primary alcohol is more suitable, however, the difference in the reaction further investigation' energy for the Michael Addition and trans-esterification requires

polymer typically When small poly(EG) chains are covalently attached to the liquid may be the polymers become solid at room temperature. Further investigation a liquid polymer is required to identify the strong intermolecular forces involved if required with similar hydrophilic groups covalently attached.

poly(DMST) is Further work is required on the structure of the gel observed when temperature heated during the preparation. It was proposed that the increased also leads to increased the extent of the polymerisation. However, whether this linkage is still in entanglement of chains or there is exists cross-linking via sulphur include solid question. Further experimental techniques to help resolve this issue may

state NMR or atomic force microscopy'

dispersion As very small particles could be formed for the poly(DMST)/\4PEGMa particles during through secondary nucleation it should be possible to produce these would be to vary the the initial nucleation period. Future experiments suggested, to the dispersion' If proportion of DMST and to vary the time the MPEGMa is added occur in the the MpEGMa is added too soon then the Michael Addition may If MPEGMa continuous phase and so the poly(EG) would not reside at the interface. can produce the small is added too late, then presumably only secondary nucleation particles.

t82 The DLVO theory used in this project does not consider particle deformation and was suggested to be primarily responsible for the coagulation behaviour observed despite the theoretical maxima. Therefore, the DLVO theory that was used was a tentative argument only to allow trends between systems to be established. Further depth of DLVO theory such as theoretical work which incorporates droplet deformation would be required to gain more interpretation from theory. Ivanov et all7'rr8 have reported

on a range of extra-DLVO forces and Ninha*t3t hu, reported on the limitations of DLVO theory.

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187 APPENDIX

OH IrB cII3 Si- cI+ -

IIA cE -Si-cH3 X

-20 -21

CIT¡ CITts B

ppm -10 -15 -20 -25 5 0 -5

Figure 4.L 'nsi NMR spectrum of 1-

TMS lo cE -si-cII3 A

B CE CE

nDm -)5 5 -10

Figure 4.2 'nsi NMR spectrum of 5

188 ¡ H cEj ÀBC D ll r c ]H cH, cl{l- cE clrr cE, cH¡ - "-o-f - -o+cEI-t 18 F

JCr! O G lH 'lll c.E, cl{r -1, cn' -o )-¡ 15

G H D.F.C E

6.0 5.0 4.0 3.0 2.0 1.0 ppm 0.0 tH Figure 4.3 NMR spectrum of product 18 and reactant L5 (which was non- volatile and remained in the product).

IJ CH?-CH1

A B CD E CH¡ cH2-cH2 -NH-R A G I 23 cH2 cHr -

R= o F CH,- cHr-of H D,E,F -cH.- )zz C B

G J

rlIr I I I ppm 6.5 6.0 5.0 4.5 40 35 30 25 20 15 10 05 0.0

tH Figure A..4 NMR spectrum of 23

189 3.0 2.0 1.0 ppm 0.0 6.0 5.0 40

tH Figure 4.5 NMR spectrum of the product of the reaction between 6 and 24 ín methanol

J ocHs A BCD cII3 S

-si-c]q-cHr-cH¡- I ocEI CIT, E GH CIL F 33 J H,J cIrz lu CH, oI G,E,D + -zz CITT I F A H j jÀ

60 50 4.0 3.0 2.0 1.0 ppm 0.0

tH Figure .4..6 NMR spectrum of 33

190 o R IJ L lM À I EC D clL _o_+_cH. 7gj/o cttl Si c112 _) -cE -cE "* - -1 - -Cltr -c4-s-Rr I -[-"f I cI{3 K R R L,H o rrll NOP EFG c-o- cHr-cI{¡- ^rl 30v¡ _o_cIú 66o/o -eE -cE- I R H clr3 K 3t% _o_si ) K

G,P

M J,I,D C,Eo A B LNE

1.0 ppm 00 6.0 50 40 30 20

- tH Figure 4.7 NMR spectrum of the products for the reaction between 9 and 15 in propanol and chlorob enzene

o -ln x rc clll'll cH' cH¡ --]_cn -c-o-f L - -o t_ 40% o lt CÉ, "l-A' G E cll IJ -$i-gH, x cHl c- o-c- cE- cE - 60% I ¡. lBcD H CII3 CH, CH, CII¡ -Si - - o - -NR, v A o F,E,D A' I A cH3 _sr_ cI{3 J B cII, A C

6.0 50 4.0 30 20 1.0 ppm 0.0 tH Figure A'.8 NMR spectrum of the products for the reaction between 7 and24in ethanol

191 A cIIs nr Â I A R=H o CH:-Sr- clT3 -1 r G r H _cH_ ll cE -]-crr -t -CIå -o ) I I -rr' H cIr3

E1 ¡' H rlBcD CI{3 ...... _ O-....._ Si CH, CI\ CH, 5¡ - - - - J D,E, o v C F B G cHå"lA CE H E, -Sj - I cIr3 À

2.0 0.0 6.0 5.0 4.0 3.0 L0 ppm

tH Figure 4.9 NMR spectmm of the products for the reaction between 10 and 30

A Er R= CH¡ HOrll Hll I A lcll I CH¡ c I cHz-cH2-"Ï:i, -si-cHl trlt-cH-c-o L H CH3

A A E2F CH3-5¡-CH.

A lucD cHr- si cH, CH2-cHz - - -SR A v water

A A CH: D,EI -Si-CHl I G CH¡ F A Ez H I C B

2.5 2.O 1.0 0.5 0.0 6.5 .0 5.5 5.0 4.5 4.0 3.5 3.0 1.5 ppm

tH Figure A.L0 NMR spectrum of the products for the reaction between 11 and 30

r92

Shields, M., Crisp, G., & Saunders, B. R. (2003). A study of poly[3- (dimethoxymethylsilyl)-1-propanethiol] dispersion stability: from emulsions to latexes. Physical Chemistry Chemical Physics, 5(7), 1426-1432.

NOTE:

This publication is included in the print copy

of the thesis held in the University of Adelaide Library.

It is also available online to authorised users at:

http://dx.doi.org/10.1039/B210568C