CONTROLLED SYNTHESIS AND CHARACTERIZATION OF BRANCHED,
FUNCTIONALIZED, AND CYCLIC POLYMERS
A Dissertation
Presented to
The Graduate Faculty of The University of Akron
In Partial Fullfillment
of the Requirements for the Degree
Doctor of Philosophy
Vijay Chavan
August, 2011 CONTROLLED SYNTHESIS AND CHARACTERIZATION OF BRANCHED,
FUNCTIONALIZED, AND CYCLIC POLYMERS
Vijay Chavan
Dissertation
Approved: Accepted:
Advisor Department Chair Dr. Roderic P. Quirk Dr. Ali Dhinojwala
Committee Chair Dean of the College Dr. Mark D. Foster Dr. Stephen Z.D. Cheng
Committee Member Dean of the Graduate School Dr. Judit E. Puskas Dr. George R. Newkome
Committee Member Date Dr. Chrys Wesdemiotis
Committee Member Dr. Kevin Cavicchi
ii ABSTRACT
A variety of methods were used to make polymers with different architecture and functionalities. The linking chemistry of vinyldimethylchlorosilane (VDMCS) with poly(styryl)lithium (Mn = 1,700-3,000 g/mol) was studied. The average degree of
branching varied from 7.5 to 9.4 with an increase in concentration of VDMCS (1.2 to 5.2
eq). The intrinsic viscosities and melt viscosities (at 160 oC) of the star polymers were
found to be less than half of that of the corresponding linear polystyrenes.
α-Pyrrolidine-functionalized polystyrene (Mn = 2,700 g/mol, Mw/Mn = 1.03, 92.5%) was
successfully synthesized from α-chloromethyldimethylsilane-functionalized polystyrene
(Mn = 2,600 g/mol, Mw/Mn = 1.02) based on NMR spectroscopy, MALDI-TOF and ESI
mass spectrometry.
The stability of silyl hydride groups under atom transfer radical polymerization
conditions was proven by copolymerizing methyl methacrylate and (4-
vinylphenyl)dimethylsilane (VPDS). Tapered block copolymers of isoprene, VPDS, and
styrene with narrow molecular weight distributions (1.04 and 1.05) were synthesized via
anionic polymerization.
Evidence regarding the topology of cyclic polybutadienes was obtained by Atomic
Force Microscopy of grafted polymers obtained by grafting an excess of silyl hydride-
functionalized polystyrene (Mn = 8,300 g/mol, Mw/Mn =1.01) onto cyclic polybutadiene
(Mn=88,000 g/mol, Mw/Mn = 2.0).
iii The reactivity of polyisobutylene carbocations was compared with respect to
competitive electrophilic addition to a vinyl group versus silyl hydride transfer by
investigating the reaction with VPDS. Based on GPC results, and 1H and 13C NMR spectroscopy, no evidence for any vinyl group addition was observed.
A successful attempt was made to prepare electrospun fibers from fluoro- functionalized styrene-butadiene elastomers. The water contact angle of these surfaces was found to be 162.8o ± 3.8o for the fibrous mat of the fluorinated polymers as compared
to 151.2o ± 2.4o for the analogous fibrous mat of the non-fluorinated polymers.
In-chain functionalization of tapered styrene butadiene rubber using
chloromethydimethylsilane was quantitatively done via a hydrosilation reaction.
Pyrrolidine-functionalized styrene butadiene rubber was obtained in 71% yield after
reacting pyrrolidine with chloromethyldimethylsilane-functionalized styrene butadiene rubber.
In-chain, silyl hydride-functionalized, deuterated polystyrene (Mn = 2,100 g/mol,
Mw/Mn = 1.01) was functionalized with allyl cyanide in the presence of Karstedt’s catalyst to obtain in-chain cyano-functionalized, deuterated polystyrene (45% based on the mass of in-chain, cyano-functionalized deuterated polystyrene obtained).
iv TABLE OF CONTENTS
Page
LIST OF TABLES…………………………………………………………………..…..xii
LIST OF FIGURES………………………………………………………………….….xiii
LIST OF SCHEMES…………………………………………………………….………xx
CHAPTER
1. INTRODUCTION
1.1.Controlled synthesis of star polystyrene by living anionic polymerization……....1
1.1.1. Living anionic polymerization..…….…...……….………………………..1
1.1.2. Monomers…………………..………………………………..…………....2
1.1.3. Organolithium compounds ……...…………..……………….……………3
1.1.4. Structure of organolithium compounds in polar and non-polar solvents.....3
1.1.5. Ion pairs and free ions……………….….…………………………………6
1.1.6. Advantages of anionic polymerization……..……………………………..7
1.1.6.1.Ability to target calculated molecular weight ……...…………...…….8
1.1.6.2. Ability to obtain polymers with narrow (≤1.1) molecular weight
distribution (MWD)………………………………………………..…8
1.1.6.3. Synthesis of block copolymers……..………………………………...9
1.1.6.4. Ability to obtain chain-end and in-chain functionalized polymers...... 9
1.2. Synthesis of star-branched polymers using anionic polymerization…..……...... 16
1.3. Functionalized polymers via combination of hydrosilation and atom transfer
v radical polymerization.……………..…...……………………………....……...18
1.3.1. Atom transfer radical polymerization (ATRP)..……….……..……………18
1.3.2. Functionalization of polymers using atrom transfer radical polymerization
…………………………………………………………………………...…22
1.4. Synthesis of tapered block copolymers of isoprene, styrene, and (4-
vinylphenyl)dimethylsilane (VPDS) by anionic polymerization…….……….....24
1.5. Synthesis of cyclic polymers by ring opening metathesis polymerization ...... 25
1.5.1. Ring-opening metathesis polymerization (ROMP)……..………….………..25
1.5.2. Synthesis of cyclic polymers……………………..………………………….30
1.6. Preference for reduction over electrophilic addition in cationic polymerization..32
1.6.1. Cationic polymerization……………...………………………………………32
1.7. Superhydrophobic surfaces from fluoropolymers using electrospinning …….…38
1.7.1. Electrospinning….…...………………………………………………..……..38
1.7.1.1. Solvent………………...…………………………………………………39
1.7.1.2. Viscosity………………...…………………………………...…………..39
1.7.1.3. Glass transition temperature (Tg)…………...………………...………….40
1.7.1.4. Conductivity…………….………………………………….………….…40
1.7.1.5. Feed rate…………...……………………….….…………….……….…..41
1.7.1.6. Temperature………..………..…………………..………….……………41
1.7.1.7. Collector………………….…………………….……..……….…………41
1.7.1.8. Distance between collector and tip………………………………………41
1.7.2. Superhydrophobic surfaces (SHS)……………….…….…………….………42
II. EXPERIMENTAL ……………………………………………..…………………….44
vi 2.1. High vacuum techniques……………...………………………………………….44
2.2. Dry box techniques…………...…………………………...………………….….45
2.3. Compounds used as received………...……….………………………………….45
2.4. Compounds purified by stirring over calcium hydride and distilling under
vacuum……………………...…………………………………………………...47
2.5. Purification of other chemicals ……………………...……….………………….48
2.5.1. Styrene……………...………………………………..………………………48
2.5.2. Benzene..………………………………………………………….…….……48
2.5.3. sec-Butyllithium……………...………………………………………………48
2.5.4. Tetrahydrofuran (THF)………………...…………...………………………..49
2.5.5. Isobutylene and methyl chloride…...………………….....…………………..49
2.6. Synthesis of reagents and polymers …………………………..……………...…..49
2.6.1. Star polymer synthesis….…………...………………………..…………………49
2.6.2. Synthesis of 4-pentyllithium………………………………………………...…..51
2.6.3. Synthesis of α-4-pentynylpolystyrene (PS-V)……………………………...…...51
2.6.4. Functionalization of α-4-pentynylpolystyrene using chloromethyldimethylsilane
(PS-Cl)………………………………………………………………………….52
2.6.5. Functionalization of chloro-functionalized polystyrene with pyrrolidine
(PS-N)…………………………………………………..………………………52
2.6.6. Synthesis of (4-vinylphenyl)dimethylsilane (VPDS)……………………….…..52
2.6.7. Synthesis of propargyl 2-bromoisobutyrate (PGBIB)……….……………….....53
2.6.8. Atom transfer radical polymerization of methyl methacrylate and
(4-vinylphenyl)dimethylsilane using of propargyl 2-bromoisobutyrate as an
vii Initiator (B3P65).……………………………………………………...………53
2.6.9. Atom transfer radical polymerization of methyl methacrylate and
(4-vinylphenyl)dimethylsilane using ethyl α-bromoisobutyrate as an initiator
(B3P84)...... 54
2.6.10. Functionalization of B3P84 with allyl alcohol……………………………...…54
2.6.11. Synthesis of tapered block copolymer of isoprene and mixtures of styrene and
(4-vinylphenyl)dimethylsilane………………………………..……………..……55
2.6.12. Synthesis of N-mesitylimidazole……………………….………..…………….55
2.6.13. Synthesis of 1H-Imidazolium,1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl)-
bromide……………………….…………………………………….………..….56
2.6.14. Synthesis of rutheniumdichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)
(tricyclohexylphosphine) ………………………...………………..…………...56
2.6.15. Synthesis of rutheniumdichloro[1-heptanyl-7-ylidene[3-(2,4,6-trimethylphenyl)
1H-imidazol-1-yl-2(3H)-ylidene]](tricyclohexylphosphine)(cyclic catalyst)….56
2.6.16. Synthesis of cyclic polybutadiene………………………………….….…….....57
2.6.17. Synthesis of silyl hydride-functional polystyrene (PSSiH)……………....……57
2.6.18. Grafting of cyclic polybutadiene by silyl hydride-functionalized polystyrene..57
2.6.19. Synthesis of 2-chloro-2,4,4-trimethylpentane (TMPCl)…………………...…..58
2.6.20. Cationic polymerization of isobutylene and reaction with
(4-vinylphenyl)dimethylsilane……………………………………..……………59
2.6.21. Synthesis of tridecafluoro-1H,1H,2H,2H-octyldimethylsilane (TDFS)…...…..60
2.6.22. Fluoro Functionalization of styrene butadiene rubber C1205…………...... …..60
viii 2.6.23. Synthesis of chloromethyldimethylsilane-functionalized styrene butadiene
rubber………………………………………………………………….………61
2.6.24. Synthesis of pyrrolidine-functionalized styrene butadiene rubber………….....61
2.6.25. Synthesis of in-chain, silyl hydride-functionalized, deuterated polystyrene…..61
2.6.26. Purification of silyl hydride-functionalized, deuterated polystyrene…………..62
2.6.27. Synthesis of cyano-functionalized, deuterated polystyrene……………………62
2.7. Electrospinning……………………………………………………………...………62
2.8. Characterization techniques ………………………………………………...………63
2.8.1. Column chromatography………………………………………………..…...…..63
2.8.2. Thin-layer chromatography (TLC)……………………………..…………..…....63
2.8.3. FT-IR spectroscopy………………………………………………………….…...63
2.8.4. NMR spectroscopy…………………………………………………………….....64
2.8.5. Gel permeation chromatography (GPC)……………………………………...….64
2.8.6. MALDI-TOF mass spectrometry………………………………..………...……..65
2.8.7. Electrospray ionization mass spectrometry (ESI) ……………..……….....……..66
2.8.8. Melt viscosity…………………………………………………………..….……..66
2.8.9. Contact angle measurements………………………………………………..……66
2.8.10. Scanning electron microscopy…………………………....……………....…….66
2.8.11. Atomic force microscopy (AFM)……………………………….……………...67
2.8.12. Differential scanning calorimetry (DSC)…………………….………………....67
III. RESULTS AND DISCUSSION …………………………………………………….68
3.1. Synthesis of star polymers using anionic polymerization……………..……………68
3.2. Synthesis of amine-functionalized polystyrene...…………………………………..78
ix 3.3. Synthesis of in-chain functionalized polymers using atom transfer radical
polymerization and hydrosilation ………………………………...……...……...….93
3.3.1. Synthesis of propargyl 2-bromoisobutyrate initiator…………………………...93
3.3.2. Synthesis of (4-vinylphenyl)dimethylsilane……………………………………95
3.3.3. Synthesis of copolymer of methyl methacrylate and
(4-vinylphenyl)dimethylsilane using propargyl 2-bromoisobutyrate as an
initiator (B3P65).……………………...... …………………………..97
3.3.4. Synthesis of copolymer of methyl methacrylate and
(4-vinylphenyl)dimethylsilane using ethyl-α-bromoisobutyrate as an
initiator (B3P84)……………………….………………...…………………...104
3.3.5. Synthesis of B3P84 allyl alcohol…………………………...…………………108
3.4. Copolymerization of isoprene, styrene, and (4-vinylphenyl)dimethylsilane..…..…111
3.5. Synthesis of cyclic polybutadiene using ring-opening metathesis
polymerization …………………………………………………………..…………121
3.5.1. Synthesis of N-mesitylimidazole…………………..……………...……….….121
3.5.2. Synthesis of 1H-imidazolium, 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl)
bromide ………………………..….…………………………………..………122
3.5.3. Synthesis of ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)
(tricyclohexylphosphine)…………………………………………………..…124
3.5.4. Synthesis of ruthenium dichloro[1-heptanyl-7-ylidene[3-(2,4,6-trimethylphenyl)-
1H-imidazol-1-yl-2(3H)-ylidene]](tricyclohexylphosphine)……….………....126
3.5.5. Synthesis and characterization of cyclic polybutadiene……. ………………..129
x 3.5.6. Synthesis and characterization of cyclic polybutadiene grafted with
silyl-hydride functionalized polystyrene………………………...…………..…132
3.6. Carbocationic polymerization ……………………………………...……………...140
3.6.1. Synthesis of 2-chloro-2,4,4-trimethylpentane ……………………...…………140
3.6.2. Reaction of polyisobutylene carbocations with (4-vinylphenyl)-
Dimethylsilane…………………………………………………………...…....141
3.7. Synthesis of superhydrophobic surfaces by electrospinning……………………....148
3.7.1. Synthesis of tridecafluoro-1H,1H,2H,2H-octyldimethylsilane (TDFS)………148
3.7.2. Fluoro functionalization of styrene butadiene rubber C1205…………...... ….150
3.7.3. Electrospinning and characterization of electrospun fibers……………….…..156
3.8. Synthesis of pyrrolidine-functionalized styrene butadiene rubber…………….…..162
3.9. Synthesis of in-chain, cyano-functionalized, deuterated polystyrene…………...…166
IV. CONCLUSIONS……………………………………………………………….…..182
REFERENCES……….……………………………………………….………………..187
APPENDICES…..……………………………………………………………………...201
APPENDIX A…..………………………………………………………………...201
APPENDIX B…..…………….…………………………………………………...206
APPENDIX C…..………………………………………………………………...207
APPENDIX D…..………………………………………………………………...209
xi LIST OF TABLES
Table Page
1.1. Monomers that can be anionically polymerized……………….……..…………..…..2
1.2. Degree of association (N) of organolithium compounds in polar and
non-polar solvents ………..……………………………………………………….…5
1.3. Polymerizable and non-polymerizable monomers for ROMP………..………...…...28
1.4. Electrical conductivities of some common solvents………………...…………..…..40
3.1. Molecular weight data of base polystyrene (bPS) and polystyrene reacted
with VDMCS (vPS)………………………………………….…...………….….…..70
3.2. Intrinsic viscosity data of linear polystyrene (LPS) and polystyrene reacted
with VDMCS (vPS)……………………..……………..…………………...……….71
3.3. Observed and calculated MALDI-TOF peaks for B3P65…………………….....…103
3.4. Molecular weight data for copolymers of isoprene, styrene, and
(4-vinylphenyl)dimethylsilane (65LowSi and 65HighSi polymers)……………….114
3.5. Molecular weight data of cyclic polybutadiene and grafted cyclic
polybutadiene ……………….……………………………….………………..…..135
3.6. Molecular weight data of base polyisobutylene and polyisobutylene reacted
with (4-vinylphenyl)dimethylsilane (PIBCl and PIBVPDS)…………..……….….142
xii LIST OF FIGURES
Figure Page
1.1. Winstein’s spectrum………………………………………………………….……….7
1.2. Monomers that can be polymerized using atom transfer radical
polymerization……………………………...……………..………..………………20
1.3. Initiators used for atom transfer radical polymerization..………….………………..22
1.4. Representative list of monomers that can undergo cationic polymerization………..35
1.5. Initiator/coinitiator systems for various monomers. …………………...………...…36
1.6. Electrospinning apparatus ……………...………………………………………..….39
2.1. Assembly of the vacuum line. …………………………………………………..…..45
2.2. Design of reactor for making star polymer via anionic polymerization...... ….51
2.3. Design of reactor for synthesis of
2-chloro-2,4,4-trimethylpentane ……………………...………..…………………...59
3.1. GPC chromatograms of base polystyrene and polystyrene reacted with 1.5
equivalents of VDMCS in benzene at 30 oC for 12 hrs and 3 days ………...……..69
3.2. 1H NMR spectrum of star polymer …………...………………………………….…75
3.3. 29Si NMR spectrum of star polystyrene ……………...……………………………..76
3.4. Melt viscosities of linear and star polystyrenes. ………...…………………………77
3.5. GPC chromatograms of vinyl-functionalized (PS-V),
chloro-functionalized (PS-Cl), and pyrrolidine-functionalized
(PS-N) polystyrenes………………………………………………………………80
xiii 3.6. 1H NMR spectrum of vinyl-functionalized polystyrene (PS-V)……………...……..81
3.7. 1H NMR spectrum of chloro-functionalized polystyrene (PS-Cl)…………………..82
3.8. 1H NMR spectrum of pyrrolidine-functionalized polystyrene (PS-N)………...……83
3.9. 13C NMR spectrum of vinyl-functionalized polystyrene……………………...…….84
3.10. 13C NMR spectrum of chloro-functionalized polystyrene (PS-Cl)………………...85
3.11. 13C NMR spectrum of pyrrolidine-functionalized polystyrene (PS-Cl)………...…85
3.12. MALDI-TOF mass spectrum of vinyl-functionalized polystyrene (PS-V)………..87
3.13. MALDI-TOF mass spectrum of vinyl-functionalized polystyrene (PS-V)
expanded in the region m/z = 2300-2600…………...……………………………..87
3.14. MALDI-TOF mass spectrum of chloro-functionalized polystyrene
(PS-Cl)…………………..………………………………………………………...89
3.15. MALDI-TOF mass spectrum of chloro-functionalized polystyrene (PS-Cl)
expanded in the region m/z = 2600-2800……………...…………………………..90
3.16. ESI mass spectrum of pyrrolidine-functionalized polystyrene (PS-N)…………….91
3.17. ESI mass spectrum of pyrrolidine-functionalized polystyrene (PS-N)
expanded in the region m/z = 2600-2800……………...…………………………..92
3.18. 1H NMR spectrum of propargyl 2-bromoisobutyrate.……………………....…...... 94
3.19. 13C NMR spectrum of propargyl 2-bromoisobutyrate …………………..…….….95
3.20. 1H NMR spectrum of (4-vinylphenyl)dimethylsilane.……………………....……..96
3.21. 13C NMR spectrum of (4-vinylphenyl)dimethylsilane………...………………..…97
3.22. GPC of polymer B3P65 (RI signal)…………………………...……....………..….99
3.23. 1H NMR spectrum of polymer B3P65…………………….……………………...100
3.24. FTIR spectrum of polymer B3P65.…………………..………….……….....…….101
xiv 3.25. Complete MALDI-TOF mass spectrum of polymer B3P65...………….…….…..102
3.26. Assignment labels of individual MALDI-TOF mass spectral
peaks of B3P65 in the region m/z =1550-1630.……………..………………...... 102
3.27. Labeling of individual MALDI-TOFF mass spectral peaks of
B3P65 in the region m/z = 1630-1700.………………………………….…….…103
3.28. GPC chromatogram (RI signal) of polymer B3P84.…………………….………..105
3.29. 1H NMR spectrum of polymer B3P84.………………………...…..…………..…107
3.30. FTIR Spectrum of B3P84……………………...……………………………..…..108
3.31. GPC chromatograms of B3P84 and B3P84allyl alcohol..……………...….……..109
3.32. 1H NMR spectrum of B3P84 allyl alcohol.. ……………...……………………...110
3.33. FT-IR spectrum of B3P84 allyl alcohol…………………………….….……...….111
3.34. GPC chromatogram of the copolymer of isoprene, styrene, and (4-
vinylphenyl)dimethylsilane (65LowSi).………………………...……..……...…113
3.35. GPC chromatogram of the copolymer of isoprene, styrene, and (4-
vinylphenyl)dimethylsilane (65HighSi)……………………...……………....…..114
3.36. 1H NMR spectrum of 65LowSi polymer.……………………...…………………115
3.37. 1H NMR spectrum of 65HighSi polymer……………………..…………………..116
3.38. 29Si NMR spectrum of 65LowSi polymer..…………...………………………….118
3.39. 29Si NMR spectrum of 65HighSi polymer………………………………………..118
3.40. 29Si NMR spectrum of (4-vinylphenyl)dimethylsilane…………………………...119
3.41. FT-IR spectrum of 65LowSi polymer…………………………………………….120
3.42. FT-IR spectrum of 65HighSi polymer……………………………………………120
3.43. 1H NMR spectrum of N-mesitylimidazole…………………...…………………..122
xv 3.44. 1H NMR of 1H-imidazolium, 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl)
bromide ……………………...... …………………………………………..123
3.45. 1H NMR spectrum of ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-
(2,4,6-trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)
(tricyclohexylphosphine)(linear catalyst)……………...…………….………….125
3.46. 31P NMR spectrum of ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-
(2,4,6-trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)
(tricyclohexylphosphine)(linear catalyst)………...…………………….……….126
3.47. 1H NMR spectrum of ruthenium dichloro[1-heptanyl-7-ylidene[3-(2,4,6-
trimethylphenyl)-1H-imidazol-1-yl-2(3H)ylidene]]
(tricyclohexylphosphine) (cyclic catalyst)…………………………………..…...128
3.48. 31P NMR spectrum of ruthenium dichloro[1-heptanyl-7-ylidene[3-(2,4,6-
trimethylphenyl)-1H-imidazol-1-yl-2(3H)ylidene]]
(tricyclohexylphosphine) (cyclic catalyst)………………………………...……..129
3.49. Log molecular weight and RI signal versus elution time for cyclic
and linear polybutadiene………………………………..…………………..…….132
3.50. Intrinsic viscosity versus molecular weight for cyclic and linear
polybutadienes……………………………………………………………..…..…132
3.51. GPC chromatogram of silyl hydride-functionalized polystyrene
(PS-SiH)…………………...……………………………………………………..133
3.52. 1H NMR spectrum of silyl hydride-functionalized polystyrene
(PS-SiH)…………...………………………………………………………..……134
3.53. FT-IR spectrum of silyl hydride-functionalized polystyrene (PS-SiH)………..…134
xvi 3.54. GPC chromatograms of cyclic polybutadiene, linear silyl hydride-
functionalized polystyrene, and grafted cyclic polybutadiene…………...…..…..136
3.55. AFM image of cyclic polybutadiene grafted with PS-SiH…………...……….....138
3.56. 1H NMR spectrum of 2-chloro-2,4,4-trimethylpentane…………………………..141
3.57. GPC chromatograms of PIBCl and PIBVPDS as a function of elution
volume using a) RI detector b) light scattering detector response ………………142
3.58. 1H NMR spectrum of PIBCl……………...………………………………………143
3.59. 1H NMR spectrum of PIBVPDS………………………………………………….144
3.60. 13C NMR spectrum of PIBCl…………...……………………………..…………145
3.61. 13C NMR spectrum of PIBVPDS…………………………………………………146
3.62. 1H NMR spectrrum of TDFS...... 149
3.63. FT-IR spectrum of TDFS…………………………………………………………149
3.64. 1H NMR spectrum of C1205……………………………………………………...151
3.65. 1H NMR spectrum of C1205Fluoro………………………………………………153
3.66. 19F NMR spectrum of C1205Fluoro………………...…..………………………..154
3.67. FT-IR spectrum of C1205Fluoro………………...……………………………….155
3.68. GPC chromatograms of C1205 and C1205Fluoro……………..…………………156
3.69. DSC curves of C1205 and C1205Fluoro…………...………………………...…..156
3.70. SEM image of electrospun C1205 fiber…………....…………………………..…158
3.71. SEM image of C1205Fluoro electrospun fiber…………………………………...158
3.72. Contact angle picture of spun coated film of C1205………………………...……159
3.73. Contact angle picture of electrospun mat of C1205……………….……………...160
3.74. Contact angle picture of spun coated film of C1205Fluoro………………………161
xvii 3.75. Contact angle picture of electrospun mat of C1205Fluoro………………...……..161
3.76. 1H NMR spectrum of chloromethyldimethylsilane-functionalized styrene
butadiene rubber……………………...…………………………………………..164
3.77. 1H NMR spectrum of pyrrolidine-functionalized styrene butadiene rubber……...164
3.78. GPC chromatograms of styrene butadiene rubber (C1205) and
chloromethyldimethylsilane-functionalized styrene butadiene rubber
(C1205-Cl)…………………………...…………………………………………..165
3.79. GPC chromatograms of crude (B4P64 crude) and purified silyl hydride-
functionalized (B4P64 pure) deuterated polystyrene……………...……………..168
3.80. 1H NMR spectrum of crude, in-chain, silyl hydride-functionalized,
deuterated polystyrene………………………………………...………………....169
3.81. 1H NMR spectrum of purified, silyl hydride-functionalized, deuterated
polystyrene………………………...……………………………………………..170
3.82 FT-IR spectrum of crude, silyl hydride-functionalized, deuterated
polystyrene…………………...…………………………………………………...171
3.83. FT-IR spectrum of purified, silyl hydride-functionalized, deuterated
polystyrene………………………..……………………………………………...172
3.84. GPC chromatograms of pure, in-chain, silyl hydride- (B4P64 pure) and
cyano-(B4P65 CN) functionalized, deuterated polystyrene………………...…...174
3.85. 1H NMR spectrum of in-chain, cyano-functionalized, deuterated
polystyrene…………………………...…………………………………………..175
3.86. 13C NMR spectrum of in-chain, silyl hydride-functionalized, deuterated
polystyrene………………...……………………………………………………..176
xviii 3.87. 13C NMR spectrum of in-chain cyano-functionalized deuterated
polystyrene…………..…………………………………………………………...177
3.88. FTIR spectrum of in-chain, cyano-functionalized, deuterated
polystyrene………………………..……………………………………………...177
3.89. MALDI-TOF mass spectrum of in-chain, silyl hydride-functionalized,
deuterated polystyrene…………………...………………………………………179
3.90. MALDI-TOF mass spectrum of in-chain, silyl hydride-functionalized,
deuterated polystyrene expanded in the region m/z 2100-2400…………….……179
3.91. MALDI-TOF mass spectrum of cyano-functionalized, deuterated
polystyrene…………………..…………………………………………………...180
3.92. MALDI-TOF mass spectrum of cyano-functionalized, deuterated
polystyrene expanded in the region m/z 2200-2400………..…………………....181
xix LIST OF SCHEMES
Scheme Page
1.1. Synthesis of chain-end functionalized polymers…………………….……………...15
1.2. Synthesis of in-chain functionalized polymers ………………..…………………....15
1.3. Mechanism of atom transfer radical polymerization………………….………...…..19
1.4. Hydroxy functionalization of
poly(styrene-b-(4-vinylphenyl)dimethylsilane)……………………….……………24
1.5. Reaction mechanism of ring-opening metathesis polymerization………………..…27
1.6. Intermolecular and intramolecular chain transfer in ring-opening
metathesis polymerization……………….…..……………………………………..29
1.7. Cyclization and grafting of block copolymer by anionic
polymerization ………………….……….……………………………………...….32
1.8. Mechanistic steps in non-proton-initiated cationic polymerization…...………….....34
3.1. Formation of star polymer using VDMCS as a linking agent……………..………...73
3.2. Anionic synthesis of star polymers using divinylbenzene as a linking
agent………………………………..……………………………………………….74
3.3. Synthesis of amine functionalized polystyrene………………..……….. …………..79
3.4. Synthesis of (4-vinylphenyl)dimethylsilane………………..………………………..95
3.5. Atom transfer radical polymerization mechanism……………..……………………99
3.6. Cyclization of ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)
xx (tricyclohexylphosphine)……………………………….………………………...127
3.7. Expected structure of diblock copolymer synthesized from isobutylene and
(4-vinylphenyl)dimethylsilane………………………………….…………………140
3.8. Mechanism of reaction between (4-vinylphenyl)dimethylsilane and
polyisobutylcarbenium ion………………………….……………………………..147
3.9. In-chain amino functionalization of styrene butadiene rubber……………….……163
3.10. Synthesis of in-chain, silyl hydride-functionalized, deuterated
polystyrene…………………………….……...... 167
3.11. Synthesis of in-chain cyano-functionalized deuterated polystyrene…………..….173
xxi CHAPTER I
INTRODUCTION
Many useful polymers can be made using chain polymerization reactions such as radical polymerization, controlled radical polymerization, anionic polymerization, cationic polymerization, and ring-opening metathesis polymerization. These polymerization techniques can also be used to change the architecture and the type of functional groups on the polymers which in turn affect their physical properties.
In this research, a variety of these methods were utilized to synthesize and characterize new functional polymers f, and macrocyclic polymers (ring-opening metathesis polymerization). Functional polymers were typically synthesized by hydrosilation reaction between vinyl-functionalized polymers and hydrosilanes with different functional groups. In case of fluoro-functionalized styrene butadiene rubber synthesized by hydrosilation reaction, an application to synthesize a superhydrophobic surface was presented.
1.1 Controlled synthesis of star polystyrene by living anionic polymerization
1.1.1 Living anionic polymerization
Living anionic polymerization is a chain growth polymerization which occurs without chain termination or transfer. After the discovery of “living anionic polymerization” by
Szwarc and coworkers1,2 tremendous work has been done in this field. Since at the end of monomer consumption chains can be still active, well-defined functionalized, block, and
1 star polymers can be synthesized by using anionic polymerization.3 The number average molecular weight of the polymer chain in living anionic polymerization is simply determined by the ratio of grams of monomers added to the moles of initiator. Anionic polymerization has been extensively used to prepare diblock and triblock copolymers which have a wide range of commercial applications.3, 4 Living anionic polymerization is one of the best methods available to prepare monomodal, narrow molecular weight distribution (≤1.1) polymers at complete monomer conversion. Various important aspects of anionic polymerization are described in the following sections.3
1.1.2. Monomers
Many different monomers can be polymerized using anionic polymerization.
Polymerizability of any vinyl monomer via anionic methods depends on the ability of the substituents on the double bond to stabilize the negative charge. These substituents should also not react with the growing anionic chain. Thus, functional groups with acidic hydrogens such as primary and secondary amines, hydroxy, carboxyl, and acetylene present problems in anionic polymerization of vinyl monomers since they react with the initiators and the growing polymeric anions. These groups must be protected in order to carry out a successful anionic polymerization. Substituents which help in delocalizing the negative charge facilitate anionic polymerization of vinyl monomers. Examples of such substituents are aromatic rings, cyano, sulfoxide, carbonyl, carboxyl, sulfone, and nitro groups. Various monomers that can be anionically polymerized are listed in Table 1.1.
Table 1.1. Monomers that can be anionically polymerized.3
Vinyl Monomers Others
Styrene Epoxide
2 Dienes (butadiene, isoprene, and 1,3-cyclohexadiene) Aldehyde
Vinyl pyridines Lactone
Alkyl methacrylates and acrylates Lactam
Methacrylonitrile Siloxane
Alkyl cyanoacrylates
Certain cyclic monomers can also be polymerized using anionic polymerization. These
include ethylene oxide, propylene oxide, ε-caprolactone, propylene sulfide, hexa-
methylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and caprolactam.3
1.1.3. Organolithium compounds
Organolithium compounds are generally used as initiators for anionic polymerization because of their ability to give polymers with a wide molecular weight range and narrow molecular weight distribution. It is important to study organolithium compounds because their structure and aggregation behavior determines the molecular weight distribution and stereochemistry of polymers. Organolithium compounds possess both the characteristics of covalent and ionic bonds.3 They are readily soluble in hydrocarbon solvents as
opposed to other organoalkali metal compounds, which are generally only soluble in
polar solvents.3 Lithium is unique among all the alkali metals because of its highest
electron affinity, electronegativity, smallest covalent and ionic radii, and availability of
relatively low-lying, unoccupied p-orbitals. 3
1.1.4. Structures of organolithium compounds in polar and non-polar solvents
Most alkyllithium compounds are soluble in hydrocarbon solvents such as benzene, cyclohexane, toluene, hexane, and heptane due to their aggregation behavior in these
3 solvents.3, 5 However, there are some alkyllithium compounds such as methyllithium,
vinyllithium, allyllithium, and phenyllithium that are insoluble in hydrocarbon solvents.
The rate of initiation of anionic polymerization is presumably determined by the degree
of association (N) of these organolithium compounds. Associated anions will hinder the
process of initiation. A higher degree of association results in slower initiation while a
lower degree of association results in faster initiation. The rate of initiation is important
in anionic polymerization because it is the main factor affecting the molecular weight
distribution. If the initiation is slower than propagation then chain initiation will be
slower than chain growth. This will result in chains of different lengths and thus the
resulting polymer will have a broader molecular weight distribution.
Various factors such as the structure of organolithium compounds, its concentration,
solvent, and temperature affect the degree of association. Degree of association is
determined by studying colligative properties such as freezing point depression,
isopiestic, boiling point elevation, and vapor pressure depression.3 Relatively bulkier
alkyl groups reduce the degree of association. For example, straight chain organolithium compounds such as n-butyllithium and ethyllithium exist as hexamers in hydrocarbon solution.3 In the case of sec-butyllithium and t-butyllithium, tetrameric aggregation is
observed.3 Higher temperature reduces the degree of association while lower temperature increases the degree of association in hydrocarbon solvents.3 For example, 2-
methylbutyllithium exists as hexameric aggregates in pentane at 30 oC while at lower
temperature (-12 oC) it exists predominantly as heptamers (N = 7.6).3 Higher concentrations of an organolithium compound in a solvent generally increase the degree of association whereas lower concentrations reduce the degree of association. For
4 instance, 2-methylbutyllithium exists as trimers (N= 3.2) at a lower concentration of
0.048 M and as hexamers at 0.89 M in pentane at 30 oC.3
The degree of association changes dramatically when the solvent is changed from non-
polar to polar. In general, more polar solvents lower the average degree of association
compared to hydrocarbon solutions. For example, n-butyllithium exists as hexameric
aggregates in benzene but as dimeric aggregates (N = 2.4) in tetrahydrofuran (THF).3 sec-
Butyllithium, which exists predominantly as tetramers in benzene, has a degree of association of 1.1 in THF.3 The degree of association decreases with decreasing
temperature in polar solvents. This reduction in degree of association occurs since
dissociation of ions is an exothermic process in polar solvents. Lowering temperature will
thermodynamically favor the dissociation process due to the increase in dielectric
constant.6 Table 1.2 shows the degree of association of three important organolithium
compounds and their degree of association in polar and non-polar solvents. Polymeric
organolithium compounds such as poly(styryl)lithium and poly(dienyl)lithium exist as
dimers and tetramers, respectively, in non-polar solvents such as benzene.3, 7, 8,9
Table 1.2. Degree of association (N) of organolithium compounds in polar and non-polar
solvents.3
Organolithium compound N in non-polar solvents3 N in polar solvents3
n-Butyllithium 6.3 (benzene) 4 (diethyl ether)
6.2 (cyclohexane) 2.4 (THF, -108 oC) sec-Butyllithium 4 (benzene) 1.1 (THF, -108 oC)
4 (cyclohexane) t-Butyllithium 4 (benzene) 1.1 (THF, -108 oC)
4 (hexane)
5 However, they quickly dissociate (N =1) when sufficient quantities of THF are added.3
Polar solvents help convert contact ion pairs into solvent-separated pairs by charge separation and cation solvation.3 The degree of cation solvation in polar media depends
on the size of cation. Smaller cations such as lithium are easily solvated compared to bulkier cations such as cesium and sodium. Thus, the largest fraction of solvent-separated ion pairs is observed in case of lithium as a counterion.3
1.1.5. Ion pairs and free ions
Based on Coulomb’s law shown in equation 1, the attractive force between two
oppositely charged ions is directly proportional to the amount of charge on each ion and
inversely proportional to the square of the distance between these two ions.
2 E = [z1 x z2] / 4π D x r . (1)
z1, z2 = amount of charge on each of the two point charges (Coulomb, C)
E = electrostatic force (Newton, N) of attraction between the two ions with charges z1 and
z2.
r = distance between the two charges (meter, m)
D = dielectric constant of the medium around the charges (C2/Nm2).
It can be seen that, as the distance between ions increases, the electrostatic force of
attraction decreases and vice versa. At a certain distance between these two charges, the
electrostatic interaction energy equals the average kinetic energy (3/2 x RT = 0.98 kcal
o /mol at 25 C). This distance is called the critical distance (rc). When the interionic
distance is below rc, ions exist as contact ion pairs, whereas above rc they exist as free
ions. Rearranging equation 1 provides equation 2.
rc = √([z1 x z2] / 4π x D x E) (2)
6 Thus, rc will vary inversely with the dielectric constant of a solvent (D). For solvents with
high D (polar) such as water (D = 78.5), rc is 3.6 Å. For solvents with lower D (non-polar solvents) such as benzene (D = 2.3), rc is 120 Å. Depending on the distance between
them, ion pairs fall under two main categories. First, is the contact ion pair where the ions
are in direct contact with each other. Second is solvent-separated or loose ion pair where
the ions are separated by a sheath of solvent. There are many factors such as type of
counterion and carbanion, solvent, and temperature that will determine whether the ions
are contact pairs or solvent-separated. This consideration is important because the rate of
initiation and rate of propagation during anionic polymerization will depend on the nature
of the ion pairs in the solution. Contact ion pairs tend to be less reactive whereas solvent
separated ion pairs are more reactive. The nature of the reactive species in case of
organolithium compounds can be explained based on Winstein’s diagram as shown in
Figure 1.1.3 In case of non-polar solvents, contact ion pairs are observed whereas polar
solvents favor solvent-separated ion pairs.
- + - + - + (RMt)n n RMt R ,Mt R // Mt R + Mt Contact Ion Solvent-Separated Aggregated Dissociated Free Ions Pair Ion Pair
k [M] k [M] k1 [M] k2 [M] k3 [M] 4 5
Figure 1.1. Winstein’s diagram.
All of the above ions will have their own propagation rate constants which will make the overall propagation kinetics complicated.
1.1. 6. Advantages of anionic polymerization
7 There are many advantages of using living anionic polymerization for polymer synthesis as listed below.
1.1.6.1. Ability to control molecular weight
The calculated number average molecular weight of polymers synthesized by living anionic polymerization corresponds to the ratio of the mass of the monomer in grams and the moles of initiator. Based on this simple relationship, accurate molecular weights can be targeted in anionic polymerization provided that reactive impurities (e.g. air, water, and acidic compounds) are removed. In the case of difunctional-initiators (organolithium compounds), the number average molecular weight per block corresponds to the ratio of the mass of monomer and twice the moles of added initiator. A wide range of molecular weights from 1,000 g/mol to > 1 million g/mol can be obtained by anionic polymerization.
1.1.6.2. Ability to obtain polymers with narrow (≤ 1.1) molecular weight distribution
(MWD)
Molecular weight distribution is the ratio of the weight average molecular weight and the number average molecular weight. Polymers with narrow MWD have more equivalent polymer chains than polymers with broad MWD. For a living polymerization, MWD
3 depends on degree of polymerization (Xn) as shown in equation 3.
2 MWD = Mw /Mn = 1 + [Xn /(Xn + 1) ] (3)
For Xn >> 1, Xn + 1 ≈ Xn , hence,
MWD = Mw/ Mn = 1 + 1/Xn (4)
8 Thus, as the degree of polymerization increases, the MWD is expected to decrease for a living polymerization as shown in equation 4. Living anionic polymerization is one of the
best methods used to prepare polymers with narrow MWD (≤1.1) at complete monomer
conversion. Broad molecular weight can also be obtained deliberately to ease polymer
processing by using less reactive initiators, a mixture of initiators, or continuous addition
of initiator to the reactor. Less reactive initiators or continuous addition of initiators will
ensure that chain growth occurs faster than initiation. Thus, chains of varying lengths are
obtained which leads to a broad MWD.
1.1.6.3. Synthesis of block copolymers
Block copolymers can combine the properties of the two different types of polymers or
show completely different properties from the individual polymer blocks. For example,
polystyrene is a stiff material (high tensile strength) in the form of a homopolymer.
Polybutadiene on the other hand is very elastic (low modulus, high strain) but not stiff.
Block copolymers of polystyrene and polybutadiene, however, are tough (high tensile
strength and high strain depending on the percentage of polybutadiene). Since polymer
chains are still living at the end of anionic polymerization, consecutive addition of a
second or third monomer can take place to yield well-defined block copolymers with
narrow molecular weight distributions. Narrow MWD is important for thermoplastic
elastomers where elasticity is achieved by physical phase separation of the different
blocks of polymers. Without narrow MWD, optimum physical properties are difficult to
obtain.
1.1.6.4. Ability to obtain chain-end and in-chain functionalized polymers
9 Since the polymer chains remain active after all of the monomer is consumed in living anionic polymerization, electrophilic reagents can be reacted with the anions to obtain chain-end functionalized polymers as shown in equation 5.
PLi + X-Y P-X + Y Li
Anion Electrophilic Functional Reagent Polymer (5)
However, the reaction of anions with electrophilic reagents is usually not quantitative.
Some of the examples of chain-end functionalized polymers via anionic
polymerization can be summarized as follows.
When poly(styryl)lithium compounds were treated with carbon dioxide, only 60% of
the desired carboxylated polystyrene was obtained.3 The remaining 40% of the
product included a dimer (28%) and a trimer (12%) as shown in equation 6.
1) CO2 PSLi PS-COOH + PS-CO-PS + (PS)3COH + 2) H3O (6)
This problem can be solved by addition of 1,1-diphenylethylene (DPE) prior to
carbonation process. Using DPE end-capping prior to carbonation, the desired
product (-COOH functionalized polystyrene) was obtained in more than 98% yield.3
When DPE was used before carbonation process, dimers and trimers were not formed
because of the bulky nature of the diphenylmethyllithium chain end which prevents
chain coupling. High degrees of carbonation can also be obtained when just 1-2
equivalents of Lewis bases such as N,N,N’,N’-tetramethylethylenediamine (TMEDA)
(quantitative yield in hydrocarbon solvent) were used.3 More than 90% of carbonated
10 polystyrene was obtained when poly(styryl)lithium dissolved in a THF/benzene
mixture (0.5% by vol of THF) was poured onto solid carbon dioxide.
Hydroxy-functionalized polymers were quantitatively obtained by anionic
polymerization by simple addition of 2-3 equivalents of ethylene oxide prior to
quenching the reaction by methanol as shown in equation 7.3 Under proper reaction
conditions, no oligomerization of ethylene oxide was observed because of the high
degree of aggregation of lithium alkoxides.3, 10
O
1) 3
PSLi PS-CH2CH2OH
2) CH3OH (7)
Synthesis of amine-functionalized polymers requires protection and deprotection
steps because of acidic protons present on primary or secondary amines as shown in
equation 8. Even after protecting and deprotecting steps, quantitative yields are not
guaranteed. For example, when PSLi was reacted with 1-2 equivalents of N-
(benzylidine)trimethylsilylamine, the desired amine product was obtained in 69-90%
yield.3 The remaining products contained acetophenone-type functionalized polymers
(12%) and dimers (19%).3
H PS + H3O PSLi + N Si NH2
(8)
11 Sulfonated polymers can be obtained by treating polymeric organolithium
compounds with sultones. However, the yields of functionalized polymers from such reactions are not very high (30-53%). The yield was increased to 93% when the anion
was reacted with DPE prior to treatment with sultones in presence of a mixture of
THF and benzene (15% THF by volume) as shown in equation 9.3
O
SO2 PSLi + PSCH2CH2CH2SO3 Li
1)
CH2CH2CH2SO3 Li PSLi PS
2) O SO2
(9)
Aldehyde-functionalized polymers were prepared in quantitative yields when PSLi was reacted with 4-morpholinecarboxaldehyde in benzene followed by termination of the reaction by methanol.3 Side reactions such as dimer formation were avoided
because of the formation of a stable tetrahedral α-amino alkoxide intermediate (A) as
shown in equation 10.
12 OLi CH3OH PSLi + ONCHO PS N O PS-CHO
A (10)
Trialkoxysilyl-functionalized polymers were synthesized in quantitative yields when
PSLi was treated with p-(chloromethylphenyl)trimethoxysilane in THF at -78 oC as shown in equation 11.
OMe OMe
Si OMe PSLi + Si OMe -78 oC PS OMe Cl OMe THF (11)
Since direct treatment of polymeric organolithium compounds with electrophilic reagents often give incomplete functionalization and side products, development of better ways to functionalize polymers via anionic polymerization was essential. This was achieved in our group recently via a clever two-step method of functionalization.
The first step involved treatment of active polymeric anions with chlorodimethylsilane to yield silyl hydride functionalized polymers. It was then treated with various commercially available alkenes via hydrosilation reactions to obtain functionalized polymers as shown in Scheme 1.1 for poly(styryl)lithium.
Using this method many different kinds of functional groups such as hydroxy, amine, acetate, fluoro, alkoxy, and cyanide were incorporated onto polymer chain end in quantitative yields.11-18 The presence of chain-end functional groups usually affects
the surface and interfacial properties of polymers.19 To change bulk properties of
polymers, functional groups have to be incorporated into the repeating units within
the polymer chain. This method of functionalization is called in-chain
13 functionalization. Recently our group has reported a new efficient way of in-chain
functionalization.12, 20, 21 Dynamic and dielectric properties of in-chain and end-chain
functionalized polymers have also been studied.22, 23 Quantitative in-chain
functionalization of polystyrene12 shown in Scheme 1.2 was achieved first by
quenching excess of living PSLi chains with dichloromethylsilane. This reaction
yielded polymers having silyl hydride groups at the center of this chain. The excess of
living PSLi chains were treated with ethylene oxide and terminated with methanol to yield hydroxy-functionalized polystyrene. The mixture was then purified by column
chromatography using silica gel where the polar hydroxy-functionalized polystyrene
was easily separated from non-polar, in-chain silyl hydride functionalized
polystyrene. Purified silyl hydride, in-chain functionalized polystyrene was then
reacted with allyl cyanide to give in-chain, cyano-functionalized polystyrene in
quantitative yield.12
14 2 eq Cl Si H CH3
PSLi PS Si H o 30 C, C6H6 0 30 C, C6H6 CH3
Si CN PS
CN
OH
Si F Si OH PS PS Si H (CF2)6 PS F
(CF2)6
NH2
Si NH2 PS
Scheme 1.1. Synthesis of chain-end functionalized polymers.
PS Si PS + 0.1 PSLi + LiCl 2.1 eq PSLi + Cl Si Cl
H H
1) 2) CH3OH O
PS Si PS + 0.1 PSCH2CH2OH
H
PS Si PS + CN PS Si PS
H Karstedt's catalyst, o Toluene,90 C, 14 da CN
Scheme 1.2. Synthesis of in-chain functionalized polymers.
15 1.2. Synthesis of star-branched polymers using anionic polymerization
Star polymers are known to behave differently than their corresponding linear analogues.24 Well-defined star polymers have previously been synthesized by anionic polymerization.3, 25-30 The physical properties of these star polymers, such as intrinsic viscosity and melt viscosity, can be much lower than their linear counterparts leading to their easy processing.24, 31, 32 Different methods have been used in past to synthesize star polymers. Many of these methods include convergent or divergent dendritic approaches, use of linking agents, and use of condensing agents. The dendritic approach is cumbersome in that it requires higher control over the reaction, multiple steps, and frequent purification stages.33 In the case of linking agents such as chlorosilanes, a fixed degree of branching is obtained depending on the structure of the linking agent and the number of displacable atoms. Linking agents can sometimes also yield a mixture of products depending on the steric hindrance of the reactive carbanionic chain end groups.
For example, when poly(styryl)lithium anion was reacted with tetrachlorosilane, a mixture of three-arm and four-arm star polymers was obtained.34
Condensing agents35, 36 such as vinylchlorosilanes, however, could prove much more helpful in preparation of star structures due to variability in the degree of branching depending on their concentration. The vinyl group on vinyl chlorosilanes is capable of neucleophilic addition and oligomerization while the halogen atom can undergo nucleophilic substitution leading to the formation of star polymer.
The reaction of organolithium compounds with vinylchlorosilanes can sometimes be quite complicated. Instead of getting a vinyl-functionalized alkyl group, there have been reports of cyclization when the size of anion is a major factor as shown in equation 12.37
16 Hexane H 2 Si 2 Li + Room Temp. Si Cl Si
(12)
The concentration of vinyldimethylchlorosilane (VDMCS) is another aspect that can decide the end product of reaction with a poly(styryl) anion. A higher concentration of
VDMCS can lead to vinyl-functionalized polystyrene as reported by Chaumont et al.38, whereas a low concentration of chlorosilanes can lead to a branched38 polymer structure.
Many attempts have so far been made to synthesize branched and star polymers using anionic polymerization by using vinyl chlorosilanes as linking agnets.39-42 These attempts,
however, have many drawbacks. First, most of these polymers42 were synthesized at
much lower temperature, such as -78 oC, which is rarely practical from commercial point
of view. Second, the solvent used in these polymerization techniques (tetrahydrofuran)
can cause termination of poly(styryl) anions leading to non-functional polymers.3
Problems such as high polydispersity indices, low degree of branching, and lack of intrinsic and melt viscosity data were associated with some of the studies.42
The use of vinyldimethylchlorosilane (VDMCS) as a condensing agent to obtain star
polystyrene via anionic polymerization was investigated in this study. An attempt was made to synthesize star polymers using industrially attractive conditions such as room
temperature, only a few equivalents of linking agent (VDMCS), no purification steps, and
a few hours of reaction. Different properties that influence processing of polymers such as
17 intrinsic viscosity and melt viscosity were studied. These properties were then compared with the linear analogues of star polystyrenes.
1.3. Functionalized polymers via combination of hydrosilation and atom transfer radical polymerization.
1.3.1. Atom transfer radical polymerization (ATRP)
Various living polymerization methods such as anionic3, cationic43, 44, and ring opening metathesis45 polymerization occur without chain termination or chain transfer. Similar to living polymerization methods, new methods of radical polymerizations were developed and termed as reversible-deactivation radical polymerization.46 In these methods chain termination is a minor reaction and molecular weight linearly increases with monomer conversion. A good agreement between calculated and observed molecular weight can be achieved with a possibility of narrow molecular weight distribution at low conversions.
The mechanism of atom transfer radical polymerization is shown in Scheme 1.3., where a metal halide and ligand complex act as chain activating (MtX/L, at lower oxidation state of metal hallide) and deactivating (MtX2/L, at higher oxidation state of metal halide) agents.47 Initiation is achieved by breaking a weaker carbon halogen bond of an initiator to form a radical. This radical then attacks the monomer and starts growing a molecular chain. The growing radical is deactivated by metal halide (higher oxidation state) and activated back by metal halide (lower oxidation state) continuously. The radicals can also couple or disproportionate (i.e., terminate) to give a dead polymer chain. Molecular weight distribution can be controlled depending on the relative rates of activation and deactivation. Narrow molecular weight distribution is achieved when rate constant of deactivation is higher than rate constant of propagation.47 Catalysts which cause faster
18 deactivation of growing chains will lower the polydispersities of the polymers obtained
via atom transfer radical polymerization.47
Initiation MtX/L . R-X R + MtX2/L R-(M) [M] 2n+2 Termination
n[M] . . R-M R-(M)n-M + MtX2/L R(M)n-M-X + MtX/L Propagation
Scheme 1.3. Mechanism of atom transfer radical polymerization.
Many kinds of monomers such as styrenes, acrylates and methacrylates, acrylonitrile, methacrylamides, and isoprene can be polymerized using atom transfer radical polymerization.47 Substituents on these monomers have the ability to stabilize the
growing radical which leads to formation of polymers. Figure 1.2 shows the range of
monomers that can be polymerized using atom transfer radical polymerization.
19 Styrenes
X
X= Br, Cl, F, OMe, OAc, CF3 Acrylates
O O O O O
O O O O O
OH O
Methacrylates
O O O O O O O O O O
Other O
C O CN
NH2
N
Figure 1.2. Monomers that can be polymerized using atom transfer radical polymerization.47
Initiators for atom transfer radical polymerization generally have halide groups such as bromide and chloride attached to them due to the low bond energy of C-Br (263 KJ/mol)
20 and C-Cl bonds (309 KJ/mol).48 Initiators generally have aryl, allyl or carbonyl groups on
them to stabilize the radical. Figure 1.3 summarizes the list of various initiators with
attached bromine or chlorine atoms. Various halogenated alkanes, α-haloketones, α-
haloesters, α-halonitriles, and sulfonyl halides have been used as initiators for atom
transfer radical polymerization.47 Generally copper-based metal halides are used as metal halide catalysts because of their low cost and compatibility with various monomers.47
Ligands are used in atom transfer radical polymerization to dissolve the metal halides in organic solvents. Nitrogen-functionalized ligands are commonly used due to their ability to complex with metal halides such as copper bromide and copper chloride.47 The size of
the ligand used in atom transfer radical polymerization will affect the efficiency of
catalysts.47 Relatively bulkier ligands reduce the efficiency of catalysts.47 A higher
activity of catalysts is generally observed for bridged and cyclic ligands.47
21 X Br
Br O O
O X O O
O
X = Cl, Br
O O O Br Br HO Br O O O O
O N
S Cl O O
O S Cl S Cl
O O
Figure 1.3. Initiators used for atom transfer radical polymerization.47
1.3.2. Functionalization of polymers using atom transfer radical polymerization.
Functionalization is an important process that can alter the physical and chemical properties of polymers. Functionalized polymers have many applications such as biomaterials, organic catalysis, surfactants, lubricants, fuel additives, compatibilizing agents, optoelectronics, microanalytical devices, electronics, and chemical sensors.49-51
Many attempts regarding synthesis of functional polymers via atom transfer radical polymerization have been reported.52-65 These include use of functional initiators, block
22 copolymerization, terminating the growing polymer chain with a functional group, as
well as chemical and plasma surface modification. Of the many polymers that have been
studied, PMMA was chosen in this research because of its wide range of applications 66-
68,51 and the ability to polymerize MMA using various polymerization techniques. PMMA
has been modified with many functional groups by various methods in the past.69-73
For instance, protected amine- and hydroxy-functionalized organolithium initiators were used to prepare functionalized PMMA.70 Functionalized PMMA prepared
accordingly had a very narrow molecular weight distribution and good agreement
between calculated and observed molecular weight. The protecting group was hydrolyzed
to yield quantitative functionalization. Amine-functionalized PMMA was also prepared
by reaction of N-lithiodiaminopropane with PMMA.74, 75 A similar procedure was used to
make amine functionalized PMMA for use in fabrication of microanalytical devices. 67
Hydroxyl- and amine-functionalized PMMA was synthesized by group transfer polymerization for use as compatibilizing agents and surfactants.73 The functionalization was achieved by terminating silyl ketene acetal ended PMMA with benzaldehyde and N-
trimethylsilylbenzaldimine, respectively.
Polymerization of methyl methacrylate (MMA) has been carried out using different
combinations of initiators, catalysts and ligands via atom transfer radical polymerization.
47, 76-78 To introduce functional groups on PMMA, modified initiators were used for atom
transfer radical polymerization.71, 72 Our group has already reported copolymerization of
(4-vinylphenyl)dimethylsilane with styrene using anionic polymerization and its
functionalization. 15, 79 The functionalization was carried out using a hydrosilation
reaction, which was studied in detail in the past.11, 12, 80, 81 Copolymerization of (4-
23 vinylphenyl)dimethylsilane and MMA using atom transfer radical polymerization was
investigated in this study. A general, easy, and quantitative method of functionalizing this
polymer was also devised.
1.4. Synthesis of tapered block copolymers of isoprene, styrene and (4-vinylphenyl)-
dimethylsilane by anionic polymerization.
Copolymerization of styrene and (4-vinylphenyl)dimethylsilane has been studied
before.79 Quirk and coworkers79 copolymerized styrene and (4-
vinylphenyl)dimethylsilane in cyclohexane at room temperature. The reactivity ratios of
(4-vinylphenyl)dimethylsilane and styrene were found to be 1.74 and 0.16,79 respectively.
Block copolymers of styrene and (4-vinylphenyl)dimethylsilane were also synthesized by anionic polymerization using sec-butyllithium as an initiator in THF at -78 oC.82 The silyl
hydride groups on these polymers were later converted to hydroxysilyl groups by
oxidation using dimethyldioxirane as shown in Scheme 1.4.82
OO H H n 0 oC, acetone m n m
Si Si
H OH
Scheme 1.4. Hydroxy functionalization of poly(styrene-b-(4-vinylphenyl)dimethylsilane).
24 Triblock copolymers of styrene and (4-vinylphenyl)dimethylsilane have also been made
by using di-initiators such as potassium napthalenide in THF at -78 oC. 83 Most of these efforts were dedicated to making hard block segmented polymers with monomers such as styrene. Polyisoprene is an important polymer for various industrial applications such as synthetic rubber in tires, sealants, adhesives, dampeners, hoses, gloves, and textiles.84
Synthetic rubber (polyisoprene based) is usually compounded with fillers85 such as silica
(SiO2), carbon black, calcium carbonate, and talc (hydrated magnesium silicate,
85 Mg3Si4O11.(OH)2). Of these fillers, silica is very important since it has high resistance
to heat and chemicals, a low thermal expansion coefficient, excellent thermal
conductivity, and transparency.85 These properties can thus be imparted to the rubber
after compounding, provided that the dispersion of silica in rubber is uniform. There have
been many reports of improving the dispersion of silica in rubber. Here, copolymerization
of (4-vinylphenyl)dimethylsilane in presence of isoprene and styrene was studied. A
successful attempt was made to synthesize these tapered block copolymers using sec- buyllithium as an initiator in hydrocarbon solvents such as benzene at room temperature.
These polymers can be useful for synthesizing in-chain functionalized polymers which affect the bulk properties of polymeric materials.
1.5. Synthesis of cyclic polymers by ring opening metathesis polymerization (ROMP).
1.5.1. Ring-Opening Metathesis Polymerization (ROMP)
The word metathesis was derived from two Greek words meta (change) and tithemi
(place). 86 In English, metathesis indicates transportation of sounds or letters in a word. In
the field of chemistry, metathesis implies interchange of carbon atoms between two
double bonds. Olefin (double bond) metathesis can be categorized into three important
25 groups namely exchange metathesis, ring-opening metathesis polymerization (ROMP),
and ring-closing metathesis. Further discussion focuses mainly on ROMP. ROMP is a reversible, step-growth polymerization process of converting cyclic monomers into polymers. 45 Equilibrium in ROMP is determined by various reactions conditions such as monomer concentration, monomer to catalyst ratio, temperature, solvent, and nature of catalyst. The driving force behind ROMP is the free energy change (ΔG) caused by release in ring strain of the cyclic monomer. If ΔG is negative, polymerization of monomer will readily occur. When ΔG values are positive, polymerization of monomer will not occur. Some examples of polymerizable and non-polymerizable monomers are listed in Table 1.3.
In ROMP the polymer chain retains the double bond from the monomer. As shown in equation 13 this behavior is different compared to ionic or radical polymerizations where sigma bonds are formed from the double bonds in monomers. The mechanism of ROMP is shown in Scheme 1.5. Initiation occurs by coordination of a transition metal alkylidine
with a cyclic monomer. Cycloaddition of the metal complex and the cyclic monomer
takes place to form a four-membered metallocyclobutane intermediate. It then yields a
metal complex similar to the original metal alkylidine complex with addition of one unit
of monomer.
ROMP
(13)
26 Initiation
R L Mt n + LnMt R LnMt Mt
R Ln R
Propagation
R R
LnMt LnMt
n
R
LnMt
n+1
Termination
R R + X-Y Y LnMt
n+1 n+1
+ XMtLn
Scheme 1.5. Reaction mechanism of ring opening metathesis polymerization (ROMP).
27 Table 1.3. Polymerizable and Non-polymerizable monomers for ROMP.87
Polymerizable Monomers Non-polymerizable monomers
X
Y
Si
Similar steps (reversible addition as well as chain transfer) are then repeated during
propagation. Termination takes places by addition of terminating agents which
selectively eliminate the metal complex from the polymer chain.
Since ROMP is a reversible process, elimination of monomer or oligomer from the
polymer chain can also take place. This process is called chain transfer or backbiting.45
Chain transfer can take place between two polymer chains or within the same polymer chain as shown in Scheme 1.6.
28 Intermolecular chain transfer R
LnMt
n+1 LnMt
R n+1
R R
X
+
LnMt MtLn
Y
Intramolecular chain transfer
LnMt
* *
R n
+
R
LnMt
M
Scheme 1.6. Intermolecular and intramolecular chain transfer in ring opening metathesis polymerization (ROMP).
29 When it takes place between two chains, the molecular weight of individual chains either
changes or remains the same. During intramolecular chain transfer the molecular weight decreases after elimination of cyclic oligomer.
1.5.2. Synthesis of cyclic polymers.
The synthesis of cyclic polymers has enticed scientists for many years. One of the
driving forces behind the studies of cyclic polymers is their unusual properties compared
to linear polymers. Cyclic polymers have lower melt viscosity, lower solution viscosity 88
and better heat resistance.89-91 Many attempts have been made to synthesize cyclic polymers.90-96 One of the major breakthroughs regarding synthesis of cyclic polymers
came in 2002, when Grubbs and coworkers 97 synthesized cyclic polyoctenamer with one
residual double bond per repeating unit using a ruthenium-based catalyst. A year later98 they succeeded in synthesizing cyclic polybutadiene (CyPBD) using the same ruthenium- based catalyst. They used cyclododecatriene (CDT) in place of 1,5-cyclooctadiene (COD) for polybutadiene synthesis due to inherent contamination of COD monomer with 4- vinylcyclohexane.98 Linear polymer impurities were found when COD was used. Both of these attempts based their conclusions for formation of cyclic polymers on increased SEC
elution volumes, reduced intrinsic viscosities, lower radii of gyration compared to the
corresponding linear polymers as well as MALDI-TOF analysis of low molecular weight
polymers. Though Jones reagent (an oxidizing agent consisting of mixture of chromic
trioxide and dilute sulfuric acid) was used to eliminate the possible linear structure in the
case of cyclic polyethylene (obtained after hydrogenation of cyclic polyoctenamer), no
such test was used to prove the cyclic nature of cyclic polybutadiene. The work reported
herein focused on further documenting the cyclic nature of this polybutadiene formed
30 using the Grubb’s catalyst procedure. A new method of decorating cyclic ring by silyl hydride-functionalized polystyrene via hydrosilation was achieved. For this purpose, the work of Deffieux and coworkers 99 was of interest. The authors decorated the cyclic
polymer by displacing the chlorine atoms on the backbone with poly(styryl)lithium
anions as shown in Scheme 1.7. Various ways were analyzed to achieve grafting on
CyPBD to observe the cyclic rings using AFM. The presence of double bonds on CyPBD suggested that hydrosilation reaction could be effectively used to achieve grafting on
CyPBD.100 Polybutadiene has been grafted with chlorodimethylsilane via hydrosilation in
the past.100 In this research silyl hydride functionalized polystyrene was grafted onto
CyPBD to prove its cyclic nature with the aid of AFM.
31 A B C
O
a b c O O O O
Cl OH Cl
O
Cl
O A C
b O a B O O c O nPSLi
Cl O
O
Scheme 1.7. Cyclization and grafting of block copolymer by anionic polymerization.
1.6. Preference for reduction over electrophilic addition in cationic polymerization
1.6.1. Cationic polymerization
One of the earliest example of cationic polymerization dates back to the year 1789 when
Watson and coworkers101 carried out protonic acid-initiated polymerization of β-pinene
and isobutylene. It was later followed by one of the key milestones set by R.M.
32 Thomas101 when isobutylene was polymerized to obtain high molecular weight polymer and was also copolymerized with small quantities of isoprene. This product, butyl rubber, has excellent gas barrier properties. In addition, butyl rubber is also known for its
excellent chemical and UV resistance.
The key steps in non-protonic cationic polymerization are shown in Scheme 1.8.43
Initiation consists of two steps. The first step involves generation of cation from the initiator (cationogen) which is also described as ionization. The initiation step is completed when the generated cation reacts with monomer. This process is called cationation. Propagation proceeds when successive addition of monomer units takes place. Chains can be terminated by deliberate addition of nucleophiles which leads to polymer chains with halogen or other functional groups. The choice of cationogen, metal catalyst (coinitiator), solvent, and temperature are critical to achieve controlled cationic polymerization. 101
33 Ion generation
R-X + MtXn R MtXn+1
Cationation
R MtXn+1 + R MtXn+1 R' R' Propagation
R + n CH-CH MtX MtXn+1 R n+1
R' R' R' n R'
Chain Transfer to nucleophilic agent X R + Y-X R MtX MtXn+1 + n+1 Y n R' R' n R' R'
Chain Transfer to monomer
R R MtXn+1 MtXn+1 + +
n n R' R' R' R' R' R'
Termination
X R R MtXn+1 + MtXn
n n R' R' R' R'
Scheme 1.8. Mechanistic steps in non-protonic-initiated cationic polymerization.
Various kinds of monomers can undergo cationic polymerization depending on their
ability to stabilize the positive charge on cation. 101 Monomers having electron donating and electron delocalizing groups can be polymerized using cationic polymerization.
34 Figure 1.4 shows a representative list of various monomers that can undergo cationic
polymerization. Other monomers that can undergo cationic polymerization belong to the
styrene or vinyl ether families.
Cl
O N
O
O O O O
Figure 1.4. Representative list of monomers that can undergo cationic polymerization.
There have been many kinds of initiators used for cationic polymerization. The choice of
initiator and coinitiator as a pair is necessary. This is because some initiators act as cationogen only in presence of certain coinitiators. Figure 1.5 lists several
initiator/coinitiator systems with respective monomers used for cationic
polymerization.101
35 Initiator Monomer Coinitiator
Isobutylene Cl TiCl4
Cl Cl BCl3
2,4,6-Trimethylstyrene OAc BCl3
p-Chlorostyrene Cl TiCl4
Isobutyl vinyl ether HI I2
Cl Styrene SnCl4
SnCl CH3SO3H 4
Figure 1.5. Initiator/coinitiator systems for various monomers.
One of the most common monomers which can only be polymerized using cationic polymerization is isobutylene. Polyisobutylene and butyl rubber (copolymer with 1-3%
36 isoprene) has found many applications in fields such as tubeless tires, inner liners, electrical insulators, adhesives, sealants, additives, gaskets, moisture barriers, gloves and polymeric coatings on coronary stent. 101-106 These applications are the result of the many
interesting physical and chemical properties of these polymers such as high resistance to
heat, chemicals, excellent gas barrier properties, dielectric properties, high damping
ability, resistance to moisture, ozone, and UV.43, 105-107 Functionalization of
polyisobutylene is an important step that alters its properties. Functionalization can be
achieved by either post polymerization treatment of PIB108 or addition of chain transfer
agents such as trimethylallysilane (transfer of allyl group), and hydride donors such as
1,4-cyclohexadiene, 2,5-heptadiene, 3-propylcyclopentene, 1,3,5-cycloheptatriene, tributylsilane, and triethylsilane to living PIB cation. 109
One of the earliest examples of hydride transfer from hydrosilane to a carbenium ion dates back to 1947. 110 It was found that n-hexyl chloride and n-pentyl chloride were
converted to their respective alkanes when reacted with triethylsilane in the presence of
AlCl3 as a Lewis acid. Later, many examples of hydride transfer were reported which
focused on kinetics, thermodynamics and stereochemistry of the reaction between
carbenium ions and hydrosilanes.111-119 The reactivity of hydrosilanes towards hydride
transfer depends on their substituents. The order of reactivity shows the following trend
(equation 14):120
Et3SiH > nOct3SiH > Et2SiH2 >Ph2SiH2 > Ph3SiH > PhSiH3 (14)
Triethylhydrosilane was found to be a better hydride donor compared to other
hydrosilanes because of the presence of electron donating ethyl groups and the smaller
size of ethyl groups as compared to phenyl groups. At very low temperature (-70 oC) the
37 relative rate of hydride transfer towards bis(p-anisyl)carbenium ion was found to show
the following order (equation 15):121
HSiMe2Ph > HSiMe3 > HSiMePh2 > HSiPh3 (15)
Relative rate 18.0 7.70 2.71 1
This result was important in our case since (4-vinylphenyl)dimethylsilane resembles the
121 structure of HSiMe2Ph and it was shown by authors that the substituent on the phenyl
ring had little effect on the rate of hydride transfer. Recent reports by the Faust group 122,
123 demonstrated that hydride transfer occurred from tributylsilane to the polyisobutyl
carbenium ion. (4-Vinylphenyl)dimethylsilane has been previously polymerized via
anionic polymerization showing the stability of the –SiH bond under anionic
polymerization conditions. The stability of the –SiH headgroup in cationic conditions had
been demonstrated in presence of a Lewis acid such as trimethylaluminum by Kennedy
and coworkers.124, 125 In this research the affinity of polyisobutyl carbenium ion (PIBC)
towards electrophilic addition to a vinyl group versus reaction with silyl hydride group at
the same time was compared.
1.7. Superhydrophobic surfaces from fluoropolymers using electrospinning
1.7.1. Electrospinning
Electrospinning is a process of making thin fibers from an electrically charged jet of
polymer solution.126 Many interesting reviews have been written which give detailed
descriptions of electrospinning.127-133 The assembly for electrospining is shown in Figure
1.6. A syringe attached to a high voltage power supply is filled with polymer solution. A
collector is kept at a desired distance from tip of the syringe at a distance d. Flow of the
polymer solution in the syringe can be controlled by a syringe pump.
38 Collector
Syringe
High voltage supply
Figure 1.6. Electrospinning apparatus.126
After application of sufficient amount of voltage, the drop of polymer solution at the tip
is drawn into thin jets and the resulting fibers are deposited on the collector. The collector
can be a fixed surface or a revolving cylinder for a continuous electrospinning process.126
For a successful electrospinning process, the following parameters must be optimized.126
1.7.1.1. Solvent
A proper choice for a solvent is critical. A solvent with too a high boiling point would not be evaporated from the jet during its flight. This residual solvent may flow after deposition or cause the fibers to stick on the collector. A solvent with too a low boiling point will evaporate too fast and may cause clogging of the jet. Hence a solvent with optimum volatility should be chosen which evaporates from fibers before they reach the collector.
1.7.1.2. Viscosity
39 The viscosity of the polymer solution should not be too high. A high viscosity will
require higher voltage to initiate electrospinning and can cause an increase in the fiber
diameter. A viscosity which is too low will result in free draining of the solution from the tip.
1.7.1.3. Glass transition temperature (Tg)
Polymers with Tg higher than room temperature should be chosen. This is because
polymers with Tg lower than room temperature will flow after deposition on the collector
and give a sticky or coated mat of fibers. These polymers, however, can be covalently
bonded to polymers having Tg higher than room temperature to give electrospun fibers
with uniform diameter.
1.7.1.4. Conductivity
The conductivity of solvents is important in electrospinning. Solvents with higher
conductivity will be easily attracted to the oppositely charged electrode. Thus, a polymer solution having a solvent of higher conductivity will be easily attracted to the oppositely charged electrode leading to fibers with lower diameters. Solvents with lower conductivity will be difficult to attract to the oppositely charged electrode. Thus, a polymer solution having a solvent with lower conductivity will be difficult to stretch leading to fibers with higher diameters.126 Table 1.4 shows the conductivities of various
solvents used for electrospinning.
Table 1.4. Electrical conductivities of some common solvents.126
Solvent Conductivity (mS/m)
Dimethylformamide (DMF) 1.090
Distilled water 0.447
40 Methanol 0.1207
1,2-Dichloroethane 0.034
Acetone 0.0202
Ethanol 0.0054
1.7.1.5. Feed rate
The feed rate of the polymer solution determines the size of the fiber. A sufficient feed
rate is required to initiate electrospinning. Once initiated, increasing flow rate increases
the thickness of the electrospun fiber.
1.7.1.6. Temperature
A higher temperature will reduce the viscosity of the polymer solution and will yield
fibers with lower diameters. Care should be taken to prevent thermal degradation or
crosslinking when increasing the solution temperature.
1.7.1.7. Collector
The collector for the fibers can be conducting or non-conducting. A non-conducting collector such as glass, wood or plastic will not be able to dissipate the charges from the polymer jets. This will cause the potential of the collector to rise and reduce the potential difference between tip and collector. Thus the rate of fiber deposition will slowly decrease. A conducting collector will be able to ground the incoming charged jet. This will help in maintaining a constant potential difference between the collector and tip.
Thus, uniform deposition of fibers will take place when a conducting collector such as
aluminum foil is used.
1.7.1.8. Distance between collector and tip
41 The distance between collector and tip (d) has a complex effect on fiber diameter. The
strength of electric field increases with decreasing d. Thus bead formation can take place due to instability of polymer jet. Reducing d also reduces the time available for solvent to evaporate. This residual solvent then can cause fusion of fibers.
Increasing d will give enough time for solvent to evaporate and thus can prevent fiber fusion. It, however, reduces the electrostatic force between the tip and collector. Reduced electrostatic force can cause insufficient extension of polymer jet producing thicker fibers.
1.7.2. Superhydrophobic surfaces (SHS)
Superhydrophobic surfaces are hydrophobic surfaces with contact angles (WCA) greater than 150o.134 Due to their superhydrophobicity, these surfaces are water repellent and self-cleaning. Superhydrophobicity of a surface depends on two main factors.135 The first
factor is the surface chemistry. Fluorous groups, in general, are known to impart
hydrophobicity due to their low surface energy. The second factor is the surface
roughness. Thinner surfaces with large surface areas are known to have higher water
contact angles. Inspiration for making SHS can be taken from nature. The silver ragwort
plant, for example, has superhydrophobic leaves.134 A closer look (SEM image) at these
surfaces reveals the presence of a fibrous structure with an average diameter of 6 μm.
Electrospinning can produce fibers ranging from a few nanometers to several micrometers. Thus, it can be used to make fibrous assemblies which, in turn, can act as hydrophobic surfaces depending on their structures and diameters.
Many groups have synthesized superhydrophobic surfaces using electrospinning of polymer solutions.134 The type of polymers used for making SHS can be categorized as
42 non-fluorinated and fluorinated hydrophobic polymers. Examples of non-fluorinated
hydrophobic polymers include polystyrene (WCA 156o-160o) 134, 136, poly(styrene-b-
dimethylsiloxane) (WCA 163o) 134, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
(WCA 158o)134, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (WCA 158o)137, a blend of polystyrene and polyaniline (WCA 166o)137, a blend of polyaniline and
polyacrylonitrile (WCA 164o)138, nylon-6 (WCA 168o)139, poly(3-hydroxybutyrate-co-3-
hydroxyvalerate) (WCA 158o)140, poly(methyl methacrylate)-graft-
poly(dimethylsiloxane) (WCA 160o)141, poly(methyl methacrylate)-graft-polyhedral oligomeric silesquioxanes (POSS) (WCA 165o)142. Examples of fluorinated hydrophobic
polymers include poly(2,3,4,5,6-pentafluorostyrene) (PPFS) (WCA 160o)134, poly(tetrafluoroethylene-co-vinylidene fluoride-co-propylene) and PTFE particles (WCA
161o)143, poly(vinylidene fluoride) (WCA 156o)144, and polystyrene-block-
poly(perfluorooctylethyl methacrylate) (WCA 150o).145 Most of the literature associated
with superhydrophobic fibers deals with polymers with hard segments having a glass
transition temperature higher than room temperature. Very few attempts have been made to synthesize superhydrophobic surfaces from elastomers (Tg lower than room
temperature) such as styrene butadiene rubber and polyisoprene.146 Therefore it was of
interest to study fluorinated elastomers for making superhydrophobic surfaces via
electrospinning.
43 CHAPTER II
EXPERIMENTAL
2.1. High vacuum techniques
The assembly of the high vacuum line used in this research is shown in Figure 2.1. The
line consisted of two manifolds connected by glass tubes. The lower manifold consisted
of four glass arms (A, B, C, and D) with female 24/40 joints attached at the bottom.
Flasks and reactors with male 24/40 joints were attached to these arms by using high
vacuum grease. Arm P was used for attaching all glass reactors to the line. Arm Q was
used for creating positive pressure from a dry nitrogen cylinder when addition of air- and
moisture-sensitive reagents was desired. The upper manifold was connected to a cold
trap. The flow to the cold trap was controlled by the top Rotaflow® stopcock. The cold
trap was cooled by liquid nitrogen to collect volatile solvents and reagents. High vacuum
was achieved by use of an oil diffusion pump containing Dow-Corning® silicone oil.
Evacuation of the vacuum line was achieved by an Edwards vacuum pump. Oil inside the pump was replaced at least every three months to maintain the quality of vacuum. A
Tesla coil was used for determining the quality of the vacuum. The tip of the Tesla coil was placed on the upper part of the cold trap. The absence of a discharge was an indication of high vacuum (pressure less than 10-4 torr).147 A noisy discharge indicated
the presence of gases inside the vacuum line.
44 Rotaflow®
Diffusion pump
Q Extra A P D dry N2 BC Liquid N2
Vacuum pump
Figure 2.1. Assembly of the vacuum line.
2.2. Dry box techniques
A Vacuum Atmospheres drybox (Model HE-193 and MBraun LabMaster 130) was used to carry out air- and water-sensitive reactions. Argon was circulated through a Vacuum
Atmospheres Omni Train inert gas purification system to maintain inert conditions. The oxygen level inside the drybox was checked using a (Cp2TiCl2)2ZnCl2 complex indicator
dissolved in toluene. 148 An oxygen concentration of >5 ppm was indicated by a change
from green to brown color.148 Periodic filling with argon and degassing was done until
the indicator maintained its green color. Glassware was previously heated to 130 oC before putting it into the antechamber of the drybox. The glassware in the antechamber was cooled by vacuum pumping for 2 h.
2.3. Compounds used as received.
The following compounds were used as received:
(Tridecafluoro-1H,1H,2H,2H-octyl)dimethylchlorosilane (95%, Gelest)
2,4,4-Trimethyl-1-pentene (TMP) (99%, Aldrich)
45 2,4,6-Trimethylaniline (98%, Alfa Aesar)
2,6-Di-tert-butylpyridine (DtBP) (97%, TCI America)
2,6-Bis(1,1-dimethylethyl)-4-methylphenol (BHT, 99%, Aldrich)
2,2’-Bipyridine (98%, Aldrich)
4-Chlorostyrene (98%, Synquest Lab)
8-Bromo-1-octene (97%, Aldrich)
Allyl alcohol (99%, Acros)
Benzylidene-bis(tricyclohexylphosphine)dichlororuthenium (Grubbs catalyst 1st
generation, Sigma-Aldrich)
Calcium hydride (95%, Alfa Aesar)
Copper bromide (CuBr) (Aldrich, 99.999%)
Cyclohexane (99%, EMD)
Dibutylmagnesium (15% by weight in heptane, FMC, Lithium Division)
Diethyl ether (99%, EMD)
Ethyl α-bromoisobutyrate (EBIB) (Aldrich, 98%)
Formaldehyde (37% in H2O, Aldrich)
Glyoxal (30% in H2O, Aldrich)
Karstedt’s catalyst (Platinum divinyltetramethyldisiloxane complex, 2.1-2.4% Pt by wt.
in xylene, Gelest)
Linear polybutadiene (Polymer laboratory, Department of Polymer Science, The
University of Akron, Mn = 52,000 g/mol, Mw = 69,000 g/mol, Mw/Mn = 1.46, please see
Appendix for more details)
Lithium aluminum hydride (95%, Aldrich)
46 Lithium metal (FMC, 98% stabilized with Na)
Magnesium turnings (98%, Aldrich)
N,N,N′,N′′,N′′-Pentamethyldiethylenetriamine (PMDETA) (99%, Aldrich)
N,N-Dimethylacetamide (DMA) (99.5%, Aldrich)
Phosphoric acid (85% in H2O, Aldrich)
Potassium t-butoxide (99%, Sigma Aldrich)
Potassium-t-bromide (99.99%, Aldrich)
Sodium Chloride (99%, Fisher)
Styrene-butadiene rubber (C1205) (Repsol, Spain; Mn = 68,600 g/mol, Mw = 69,700
g/mol, Mw/Mn = 1.02, 77.6% polybutadiene by wt)
Sulfuric acid (98%, VWR)
Titanium tetrachloride (99.9%, Aldrich)
2.4. Compounds purified by stirring over calcium hydride and distilling under vacuum
The following compounds were stirred over calcium hydride for 12 h. These compounds were subjected to three freeze-pump-thaw cycles before distilling into dry ampoules under high vacuum.
1,5,9-Cyclododecatriene (98%, Alfa Aesar)
5-Bromo-1-pentene (95%, Aldrich)
Chloromethyldimethylsilane (95%, Gelest)
Deuterated styrene (98%, Cambridge Isotope Laboratories)
Dichloromethylsilane (98%, Aldrich)
Dimethylchlorosilane (DMCS) (98%, Aldrich)
Ethylene oxide (99%, Aldrich)
47 Heptane (99%, EMD)
Methanol (99%, VWR)
Methyl methacrylate (MMA) (99%, Aldrich)
Methylcyclohexane (MeCx) (99%, Aldrich)
Pyrrolidine (99%, Aldrich)
Vinyldimethylchlorosilane (VDMCS) (97%, Aldrich)
Toluene (99%, EMD)
2.5. Purification of other chemicals
2.5.1. Styrene
Styrene (99%, ACS grade, EMD, NJ) was stirred and degassed over calcium hydride in a flask attached to the vacuum line. It was then distilled into a flask which contained 1,10-
phenanthroline (~40 mg) and 1 mL of dibutylmagnesium (neat). A maroon colored solution was obtained. This solution was subjected to three freeze-degas-thaw cycles.
Styrene was distilled from the above flask into graduated ampoules prior to use.
2.5.2. Benzene
Benzene (EMD, ACS grade) was first stirred in a flask over calcium hydride for 12 h
with periodic freeze-pump-thaw cycles on the vacuum line. It was then distilled into a dry round-bottomed flask having a Rotaflow® stopcock. Dry nitrogen was passed through
this flask and a mixture of sec-butyllithium and styrene was added to this flask before
distilling benzene into the flask. The colorless solution changed its color to bright orange.
The flask was subjected to three freeze-pump-thaw cycles. Fresh benzene was distilled
from this flask as required.
2.5.3. sec-Butyllithium
48 sec-Butyllithium (FMC, 1.5M in cyclohexane) was used as received. The molarity of the
initiator was determined by the double titration method using 0.1N HCl and allyl
bromide.149
2.5.4. Tetrahydrofuran (THF) (99.9%, EMD)
THF was stirred in a flask on the vacuum line with crushed calcium hydride powder for
12 h. It was cooled with a dry ice and isopropyl alcohol mixture. After degassing, the solvent was brought to room temperature using a warm water bath. It was then distilled into a flask containing freshly cut sodium pieces and benzophenone. A bright blue colored solution was obtained. The flask was stored under a positive pressure by dry nitrogen. Fresh THF was distilled under vacuum from this flask as required.
2.5.5. Isobutylene (Exxon) and methyl chloride (LANXESS) were dried by passing through a column containing CaCl2/BaO before collecting in a measuring cylinder at -70
oC.
2.6. Synthesis of reagents and polymers
2.6.1 Star polymer synthesis
The design of the reactor for the star polymer synthesis is shown in Figure 2.2. The reactor was made by sealing ampoules onto a round-bottomed flask. The ampoules had spiral seals and glass-coated iron hammers next to them. Glass-coated iron hammers were held next to ampoules by securing magnet bars on the outside glass with tape. Side ampoules were used for collecting a base sample and a sample after 12 h of reaction. A side arm on round-bottomed flask was used for injecting sec-butyllithium (3.2 mL, 1.68 M in cyclohexane, 5.4 mmol) under a positive, dry nitrogen flow. The side arm was then sealed with a flame and the entire reactor was evacuated using high vacuum. Benzene
49 (150 mL) was then distilled into this flask, frozen, and degassed. The reactor was then sealed off from the vacuum line. The frozen solvent was then thawed using a warm water bath. Reaction was initiated by breaking the styrene ampoule (10.8 g, 103 mmol) first.
After 12 h of reaction, a base sample (3 mL solution) of the homopolymer was removed in the side ampoule by heat sealing with a flame. This side ampoule was flame-sealed from the reactor after freezing the sample solution using a dry ice and isopropyl alcohol bath.
The solution in the reactor was thawed by using warm water bath. The seal next to
VDMCS ampoule (1.6 g, 13.5 mmol) was broken after the solution was warmed to the room temperature. The color of solution changed from bright orange to light yellow and eventually became colorless. A sample of reaction was taken after 12 h. The final reaction mixture was quenched with degassed methanol at the end of three days. The polymer was obtained by precipitating the above solution dropwise into methanol. The polymer (8.9 g,
82.4%) was obtained after drying under vacuum for 24 h at room temperature.
Vacuum Styrene VDMCS Methanol Methanol
Methanol
Inlet for Ampoule for initiator Ampoule for base sample base sample after linking after 12 h
Solution
50 Figure 2.2. Design of reactor for making star polymer via anionic polymerization.
2.6.2. Synthesis of 4-pentenyllithium150
To a reactor similar to the one shown in Figure 2.2, diethyl ether (20 mL) and 5-bromo-
1-pentene (6.4 mL, 54 mmol) ampoules were attached. The flask was evacuated under vacuum and closed using a Rotaflow® stopcock. This entire reactor was then moved into the dry box to add lithium (3.74 g, 54 mmol). The reactor was removed from the dry box
and was attached to vacuum line. After degassing under vacuum, the reactor was cooled
to 0 oC. The seals next to the ampoules were broken and the reaction mixture was stirred
at 0 oC for 24 h. The reactor was again taken inside drybox. The product, 4-
pentenyllithium was filtered using a coarse glass frit and diluted using dry heptane (50
mL). 4-Pentenyllithium was obtained in 70% yield (0.74 M by double titration149). The initiator (4-pentenyllithium) was synthesized by Dr. Jonathan Janoski (The Department of Polymer Science, The University of Akron).
2.6.3. Synthesis of α-4-pentenylpolystyrene (PS-V)150
α-4-Pentenylpolystyrene was synthesized by polymerizing styrene (4.91 g, 47 mmol)
using 4-pentenyllithium (4.2 mL, 0.31 mmol) as an initiator in a mixture of benzene (60
mL) and THF (1.1 mL) as solvent. The reaction was carried out in an all glass reactor
similar to the one shown in Figure 2.2. After 6 h the reaction was quenched using
degassed methanol. The solution was then precipitated into methanol and the polymer
(Mn = 2,500, Mw/Mn = 1.02) was obtained after drying under vacuum for 24 h at room
temperature. The polymer (α-4-pentenylpolystyrene) was synthesized by Dr. Jonathan
Janoski (The Department of Polymer Science, The University of Akron).
51 2.6.4. Functionalization of α-4-pentenylpolystyrene using chloromethyldimethylsilane
(PS-Cl)
α-4-Pentenylpolystyrene (0.35 g, 0.012 mmol), chloromethyldimethylsilane (40 mg,
0.036 mmol), Karstedt’s catalyst (2 drops), and toleuene ( 2 mL) were mixed in a 20 mL glass vial. After stirring the mixture at room temperature for 48 h, the solution was precipitated into methanol and dried under vacuum for 24 h to obtain chloromethyldimethylsilane-functionalized polystyrene (0.31 g, 88%).
2.6.5. Functionalization of chloromethyldimethylsilane-functionalized polystyrene with pyrrolidine (PS-N)
Chloromethyldimethylsilane-functionalized polystyrene (0.13 g, 0.05 mmol), pyrrolidine
(0.2 g, 28 mmol), and toluene (5 mL) were added to a round-bottomed flask. After attaching a reflux condenser, argon was bubbled into the flask at room temperature for 30 min. The reaction mixture was then stirred at 80 oC for 48 h. Pyrrolidine-functionalized
polystyrene (0.10 g, 84%) was obtained after precipitating the solution into methanol and
drying under vacuum for 24 h.
2.6.6. Synthesis of (4-vinylphenyl)dimethylsilane79
Distilled THF (50 mL), magnesium turnings (3.42 g, 0.14 mol) and iodine (few pieces)
were mixed in a flask under argon. A reflux condenser was attached to this flask. The reaction was stirred using a Teflon-coated magnetic stir bar. The temperature of reaction
mixture was monitored using a thermometer. 4-Chlorostyrene (16.33 g, 0.11 mol) was slowly added under a positive argon pressure. The temperature of the flask was raised to
65 oC and the reaction was carried out for 90 min. After cooling the reaction mixture to
room temperature, dimethylchlorosilane (11.14 g, 0.11 mol) was added dropwise and the
52 solution was stirred at room temperature for 12 h. The crude reaction mixture was passed
through a column of silica gel using hexane as eluent. After removing hexanes using a
rotary evaporator, the crude product was distilled under high vacuum to obtain a colorless
liquid (14 g, 73% yield).
2.6.7. Synthesis of propargyl 2-bromoisobutyrate (PGBIB)151
Into a dry, 500-mL, round-bottomed flask, propargyl alcohol (4.00 g, 71.3 mmol),
triethylamine (7.18 g, 71.3 mmol) and dichloromethane (30 mL) were added. This
mixture was cooled to 0 oC using an ice water bath. To this solution, α-bromoisobutyryl
bromide (12.50 g, 54.3 mmol) was added dropwise over a period of 1 h. The reaction
mixture was stirred for 24 h at room temperature. The solution was then filtered and
solvent was removed using a rotary evaporator. The final product was dissolved in
hexanes and the excess propargyl alcohol was removed by washing with water in a
separatory funnel. Hexanes from organic layer were removed using a rotary evaporator
and the final product PGBIB was distilled under vacuum (5.72 g, 51% yield).
2.6.8. Atom transfer radical polymerization of methyl methacrylate and (4-
vinylphenyl)dimethylsilane using propargyl 2-bromoisobutyrate as an initiator (B3P65)
Into a dry, round-bottomed flask with an attached Rotaflow® stopcock, methyl
methacrylate (10.5 g, 105 mmol), (4-vinylphenyl)dimethylsilane (2.8 g, 17.4 mmol),
copper bromide (0.1 g, 0.69 mmol), bipyridine (0.1 g, 0.64 mmol), toluene (12 mL), and
PGBIB initiator (1.33 g, 6.5 mmol) were added. The reaction mixture was then frozen using liquid nitrogen and degassed three times. The flask was then placed in an oil bath previously set at 100 oC. After 16 h, the flask was cooled to room temperature and cold
methanol was added to the mixture. The product was dissolved in THF and passed
53 through a neutral alumina column to remove copper.47 Excess solvent was then removed using a rotary evaporator. The residue was dissolved in THF, precipitated into hexane
and dried under vacuum overnight. The product was obtained in 76% yield. The Mn, Mw, and polydispersity index of this polymer (to be called B3P65) were found to be 3,600 g/mol, 4,600 g/mol and 1.29, respectively, by using GPC.
2.6.9. Atom transfer radical polymerization of methyl methacrylate and (4- vinylphenyl)dimethylsilane using ethyl α-bromoisobutyrate (EBIB) as an initiator
(B3P84)
Into a dry, round-bottomed flask with an attached Rotaflow® stopcock, methyl
methacrylate (9.4 g, 93.9 mmol), (4-vinylphenyl)dimethylsilane (2 g, 12.3 mmol), copper bromide (0.45 g, 3.1 mmol), PMDETA (1.09 g, 6.3 mmol), EBIB initiator (0.61 g, 3.1 mmol), and toluene (14 mL) were added. The reaction mixture was then frozen using liquid nitrogen and degassed. This cycle was repeated 3 times. The flask was then kept in an oil bath previously set at 70 oC for 5 h. The flask was cooled to room temperature and
toluene was removed using rotary evaporator. The crude polymer was passed through a
neutral alumina column using THF as an eluent. The polymer solution was then
concentrated using a rotary evaporator and precipitated into hexanes. The Mn, Mw, and polydispersity index of this polymer (to be called B3P84, 7.75 g, 68%) were found to be
4,500 g/mol, 5,800 g/mol and 1.29, respectively, by using GPC.
2.6.10. Functionalization of B3P84 with allyl alcohol (B3P84 allyl alcohol)
The above copolymer B3P84 (0.60 g, 0.0257 mmol of –SiH units) was mixed with 5 mL
of toluene and allyl alcohol (0.09 g, 1.54 mmol). Karstedt’s catalyst (2 drops) was added
after 2 minutes to the above mixture. The reaction was run at room temperature for 6 h.
54 After observing the disappearance of –SiH peak (2116 cm-1) in the IR spectrum, the
product was precipitated into hexanes and dried under vacuum.
2.6.11. Synthesis of tapered block copolymer of isoprene, styrene, and (4-vinylphenyl)-
dimethylsilane
Polymerization was carried out in a round-bottomed flask inside drybox (under argon).
Isoprene (14.98 g, 220 mmol), styrene (4.5 g, 43 mmol) and (4-
vinylphenyl)dimethylsilane (0.22 g, 1.38 mmol) were added to the flask. The volume of
benzene (250 mL) added was ten times the volume of monomers. Reaction was initiated
by addition of sec-butyllithium (0.29 mmol, 0.23 mL of 1.26 M sec-butyllithium in
cyclohexane). Initially light yellow colored solution was observed indicating the start of
isoprene incorporation. After the consumption of isoprene the color of solution changed
to dark orange indicating addition of styrene molecules to the chain. After running the
reaction overnight at room temperature, methanol was added to quench the reaction. The
solution was precipitated into methanol and the polymer was dried under vacuum for 24
hours (17.2 g, 88%). Similarly, a second batch of polymer (15.9 g, 82%) was made
using higher concentration of (4-vinylphenyl)dimethylsilane (2.77 mmol).
2.6.12. Synthesis of N-mesitylimidazole152
2,4,6-Trimethylaniline (1 g, 7.4 mmol) in 5 mL of methanol was reacted with 30%
glyoxal (1.43 g, 7.4 mmol) at room temperature for 20 h. Ammonium chloride (0.8 g,
14.8 mmol) was added after 20 h followed by a 37% solution of formaldehyde (1.2 g,
14.8 mmol).152 After stirring this reaction mixture for 1 h, methanol (20 mL) was added and the reaction mixture was heated for 1 h. Phosphoric acid (2 mL, 85%) was added to
this mixture and the reaction was run for 4 h. Finally methanol from the solution was
55 removed using a rotary evaporator and the crude product was poured onto a mixture of
ice and water. It was neutralized with KOH and extracted with diethyl ether. The excess
ethyl ether was removed from the crude product using a rotary evaporator and the crude
product was passed through silica gel using a mixture of petroleum ether and ethyl
acetate as an eluent. N-mesitylimidazole (1.10 g, 80%) was obtained after removing
petroleum ether and ethyl acetate using a rotary evaporator and drying the product in
vacuum at room temperature for 24 h.
2.6.13. Synthesis of 1H-Imidazolium, 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl) bromide
(imidazolium salt)153
N-Mesitylimidazole (1 g, 5 mmol) and 8-bromo-1-octene (1.02 g, 5 mmol) were heated
in toluene under reflux for 18 h.153 The crude product was filtered using diethyl ether as
solvent and dried under vacuum to obtain the 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl)
bromide (1.60 g, 85%).
2.6.14. Preparation of rutheniumdichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)(tricyclohexylphosphine)
(linear catalyst)153
Imidazolium salt (200 mg, 0.52 mmol) and potassium t-butoxide (58 mg, 0.52 mmol) were mixed in toluene for 90 min under an argon atmosphere. Later Grubbs 1st generation
catalyst (326 mg, 0.40 mmol) was added to the mixture and the reaction was run for 1 h.
Flash chromatography under argon (4/1, v/v, pentane/diethyl ether) produced the linear
catalyst (240 mg, 71% yield).
2.6.15. Synthesis of rutheniumdichloro[1-heptanyl-7-ylidene[3-(2,4,6-trimethylphenyl)-
1H-imidazol-1-yl-2(3H)-ylidene]](tricyclohexylphosphine) (cyclic catalyst)98, 153
56 The linear catalyst (240 mg, 0.286 mmol) was placed in a round-bottomed flask
attached with a Rotaflow® stopcock . Hexane (1000 mL) was distilled into this flask
under vacuum. After closing the Rotaflow® stopcock the reaction mixture was heated at
68 oC for 70 min.98, 153 Flash chromatography of the crude product under an argon flow
was done using a mixture of pentane and ether (3/1, v/v mixture). The yellow colored
cyclic catalyst (60 mg, 28% yield) was obtained after removing the solvents using a
rotary evaporator.
2.6.16. Synthesis of cyclic polybutadiene98
1,5,9-Cyclododecatriene (CDT) (6 g, 0.037 mol) and dichloromethane (5 mL) were mixed along with cyclic catalyst (10 mg).98 The mixture was subjected to three freeze- pump-thaw cycles. Polymerization was carried out at 40 oC for 14 h. The resulting
polymer (4.8 g, 80%) was precipitated in methanol and dried under vacuum.
2.7.17. Synthesis of silyl hydride-functional polystyrene (PS-SiH)
Styrene (18 g, 173 mmol) was polymerized under high vacuum in an all-glass reactor
with ampoules having breakseals similar to the one shown in Figure 2.2. sec-Butyllithium
(1.6 mL in cyclohexane, 2 mmol) was used as an initiator, and the reaction was carried
out in benzene as a solvent (200 mL) at 30 oC for 12 h. After running the reaction
overnight, polymer chains were terminated with excess chlorodimethylsilane (0.6 mL, 5
mmol). The bright red solution turned colorless after addition of chlorodimethylsilane.
2.6.18. Grafting onto cyclic polybutadiene by silyl hydride-functionalized polystyrene
Cyclic polybutadiene (30 mg, Mn = 88,400 g/mol, Mw/ Mn = 2.06, 0.34 mmol of double
bonds) was mixed with toluene (50 mL), and silyl hydride-functionalized polystyrene (2
g, Mn = 8,300 g/mol, 0.24 mmol) under an argon atmosphere. Two drops of Karstedt’s
57 catalyst was added to the mixture. The reaction mixture was heated at 80 oC for 24 h. The
polymer solution was then precipitated into methanol and dried under vacuum. The
resulting polymer was dissolved in 300 mL of toluene and the solution was placed in a
separating funnel. Methanol was added to this solution until it became cloudy. The
cloudy solution was warmed until it became colorless. The warm solution was allowed to
cool down to room temperature overnight. The precipitated polymer (20 mg, 0.9%) was removed from the separating funnel, dissolved in THF, precipitated in methanol, and dried under vacuum at room temperature for 24 h.
2.6.19. Synthesis of 2-chloro-2,4,4-trimethylpentane (TMPCl) 154, 155
The design of reactor for synthesis of TMPCl is shown in Figure 2.3. Hydrochloric acid
gas was generated by reaction of conc. H2SO4 (200 g, 2 mol) with NaCl (228 g, 3.96 mol)
powder. A three-necked flask (A) was equipped with a pressure-equalizing addition
funnel that contained conc. sulfuric acid. The round-bottomed flask (B) that contained
2,4,4-trimethyl-1-pentene (20 g, 178 mmol) was cooled with an ice water bath.
Erlenmeyer flask C was empty and Erlenmeyer flask D had an aqueous sodium
hydroxide solution (10% wt/vol) to neutralize the excess HCl gas. All openings of the
glass reactors were sealed with rubber septa. The two round-bottomed flasks were
connected by a metal canula. Flask B was kept at a lower height compared to flask A to
prevent backflow of HCl gas which is heavier than air. Flasks C and D were kept at
slightly higher elevation compared to flask B. Concentrated H2SO4 was added dropwise
to NaCl powder over a period of 4 h. Bubbling in flask B was observed indicating
generation of HCl gas. After 4 hours, air was bubbled into the flask for 30 min to remove
58 excess HCl gas. 2-Chloro-2,4,4-trimethylpentane (22.7 g, 85%) was obtained after
distilling the crude product under vacuum.
H2SO4 To exhaust in the hood
NaOH
NaCl A B CD TMP
Ice water
Figure 2.3. Design of reactor for synthesis of 2-chloro-2,4,4-trimethylpentane.
2.6.20. Cationic polymerization of isobutylene and reaction with
(4-vinylphenyl)dimethylsilane
A MBraun glovebox (purged with nitrogen) was used for carrying out polymerization.
Experiments were conducted when the moisture and oxygen level dropped below 5 ppm.
All the glassware was dried for 12 h at 130 oC in an oven before transferring into the
glovebox. In a typical experiment, first 200 mL of methylcyclohexane and 130 mL of methyl chloride were added to a three-necked flask kept at -70 oC. Isobutylene (12 g, 214
mmol), 2-chloro-2,4,4-trimethylpentane (2.0 g, 13 mmol), dimethylacetamide (0.6 g, 7 mmol) and 2,6-di-tert-butylpyridine (0.5 g, 3 mmol) were added first to the flask at -70
oC. The reaction was started after addition of precooled titanium tetrachloride dissolved
in a methylcyclohexane (6 mL) and methyl chloride (4 mL) mixture. After running the
59 reaction for 60 min, half of the sample was taken aside and quenched with 10 mL of
precooled (-70 oC) methanol (with 10% NaOH wt/vol). To the rest of the solution, (4-
vinylphenyl)dimethylsilane (5.4 g, 33 mmol) was added which changed the color of the
solution to dark red (that of red kidney beans). After 30 min, 10 mL of precooled
methanol (10% NaOH wt/vol) was added to the solution.
Both the parts (PIBCl, 4.79 g, 98%) and reacted polymer (PIBVPDS, 6.96 g, 98%) were
precipitated into methanol. The dissolution (in dichloromethane) and precipitation (in
methanol) cycle was repeated four times. The precipitated polymers were dried under
vacuum for 72 h.
2.6.21. Synthesis of (tridecafluoro-1H,1H,2H,2H-octyl)dimethylsilane (TDFS)156, 157
A mixture of (tridecafluoro-1H,1H,2H,2H-octyl)dimethylchlorosilane (10 g, 22.6 mmol) and diethyl ether (20 mL) was added dropwise to an ice cold solution of LiAlH4
(Sigma-Aldrich , 0.861 g, 22.6 mmol) and diethyl ether (100 mL). The addition was done in 20 min. The mixture was stirred at room temperature for 16 h. It was then filtered to remove the excess LiAlH4 and mixed with distilled water. The organic layer was
separated and dried using anhydrous MgSO4. The organic layer was filtered using filter
paper and the excess of diethyl ether was removed using a rotary evaporator. The crude
product was then distilled under vacuum to obtain TDFS (5.60 g, 13.8 mmol, 61% yield).
2.6.22. Fluoro Functionalization of styrene butadiene rubber C1205 (C1205Fluoro)
In a 100 mL round-bottomed flask, 1 g of C1205 (Mn = 68,600 g/mol , 1.61 mmol of 1,2
vinyl groups) was dissolved in 10 mL of toluene. To this mixture tridecafluoro-
1H,1H,2H,2H-octyldimethylsilane (0.98 g, 2.41 mmol) was added. After stirring for 2
min, 4 drops of Karstedt’s catalyst was added. The solution immediately turned into a
60 golden yellow color. The mixture was stirred at room temperature for 48 h. It was then precipitated in methanol mixed with 3% BHT (wt/vol). The precipitated polymer was dissolved in THF again and precipitated in methanol with 3% BHT (wt/vol). The final product (1.36 g, 82% yield) was obtained after drying under vacuum.
2.6.23. Synthesis of chloromethyldimethylsilane-functionalized styrene butadiene rubber
Styrene butadiene rubber (C1205, 1.16 g, 1.86 mmol of 1,2-vinyl groups), chloromethyldimethylsilane (0.30 g, 2.80 mmol), Karstedt’s catalyst (2 drops), and toluene (8 mL) were mixed in a 20-mL glass vial. After stirring at room temperature for 2 days, the solution was precipitated into methanol and the polymer (1.54 g, 113%) was obtained after vacuum drying for 24 h at room temperature.
2.6.24. Synthesis of pyrrolidine-functionalized styrene butadiene rubber
Chloromethyldimethylsilane-functionalized styrene butadiene rubber (0.4 g, 2.80 mmol of chloro groups), pyrrolidine (0.40 g, 5.60 mmol), and toluene (8 mL) were mixed in a round-bottomed flask equipped with a reflux condenser. Argon was bubbled through the reaction mixture for 30 minutes. The reaction was heated at 50 oC for 2 days and then the solution was precipitated into methanol. Pyrrolidine-functionalized styrene butadiene rubber (0.31 g, 71%) was obtained after vacuum drying at room temperature for 24 h.
2.6.25. Synthesis of in-chain, silyl hydride-functionalized, deuterated polystyrene
In-chain, silyl hydride-functionalized, deuterated polystyrene was synthesized by polymerizing deuterated styrene (10.0 g, 89 mmol) using sec-butyllithium (8.0 mL, 10 mmol) as an initiator and benzene (100 mL) as solvent. The reaction was carried out in an all glass reactor similar to the one shown in Figure 2.2. After 6 h, the reaction was quenched using dichloromethylsilane (10.35 g, 9 mmol). After 1 day, ethylene oxide
61 (0.23 g, 2 mmol) was added to the remaining solution. After 1 h, the reaction mixture was quenched with degassed methanol. The crude polymer (9.2 g, 92%) was obtained after precipitation into methanol and vacuum drying at room temperature for 24 h. This polymer, in-chain silyl hydride-functionalized, deuterated polystyrene, was synthesized by Dr. Jonathan Janoski (The Department of Polymer Science, The University of Akron).
2.6.26. Purification of in-chain, silyl hydride-functionalized, deuterated polystyrene
The crude silyl hydride-functionalized dueterated polystyrene (8.9 g) was purified by passing through a column of silica gel using a mixture of cyclohexane and toluene (1/3, v/v) as eluent. The purified product (7.9 g, 90%) was obtained after precipitation into methanol and freeze drying in benzene for 24 h.
2.6.27. Synthesis of in-chain, cyano-functionalized, deuterated polystyrene
Purified silyl hydride-functionalized, deuterated polystyrene (3.38 g, 1.61 mmol), allyl cyanide (0.13 g, 2.01 mmol), Karstedt’s catalyst (2 drops), and benzene (30 mL) were added to a round-bottomed flask equipped with a reflux condenser. The reflux condenser was closed with a rubber septum. Two balloons filled with nitrogen and oxygen were attached to the rubber septum through two separate needles. The reaction mixture was stirred at 80 oC for 14 days. The non-polar silyl hydride-functionalized deuterated polystyrene was removed by column chromatography using silica gel and a mixture of cyclohexane and toluene (1/3, v/v). The desired in-chain, cyano-functionalized, deuterated polystyrene was obtained from the same column by a mixture of ethyl acetate and toluene (1/3, v/v) as eluent. The final product (1.52 g, 45%) was obtained after precipitation into methanol and freeze drying using benzene.
2.7. Electrospinning
62 The set-up for electrospinning is shown in Figure 1.6. Polymer (10% by wt) was
dissolved in a mixture of tetrahydrofuran and N,N-dimethylformamide in 75:25 ratio by
volume. The flow rate of the polymer solution was maintained at 25 mL per hour using a syringe pump. The distance between the tip of the syringe and the collector was kept at
30 cm. A voltage of 30 kV was applied for electrospinning the fibers. Fibers were collected on a glass slide for measuring the contact angle. Electrospinning was done by
Sarfaraj Patel from Dr. George Chase’s group (Department of Chemical Engineering,
The University of Akron).
2.8. Characterization techniques
2.8.1. Column chromatography
Column chromatography was done using silica gel (EM Science, Silica Gel 60) or neutral alumina (Aldrich). Silica gel or neutral alumina were dried in an oven at 130 oC
for 24 h and cooled in a desicator. It was then dispersed in a solvent until all the air
bubbles disappeared. The column was packed with the above dispersion and then dry
sand was added on top (half inch) to maintain uniform flow. When required, the column
was pressurized with argon to increase the flow rate of eluent.
2.8.2. Thin layer chromatography (TLC)
Thin layer chromatography was conducted by spotting solutions onto a silica gel plate
(Selecto Scientific, Silica Gel 60, with F-254 fluoroscent dye). The plates were dipped in
a bottle which had a solvent level lower than the spot on the TLC plates. Spots were
observed using a UV lamp after drying the plates in air.
2.8.3. FT-IR spectroscopy
63 Polymer samples (~10 mg) were dissolved in chloroform (1 mL) or tetrahydrofuran (1
mL). They were then spotted onto a KBr disc and dried under vacuum for five minutes.
An FT-IR spectrometer (DIGILAB, Randolph, MA, USA) was used for recording
spectra. Win-IR software was used for analysis and generation of spectra.
2.8.4. NMR spectroscopy
NMR spectra were recorded using Varian Mercury 300 or Varian 500 NMR
spectrometers. For measuring 1H NMR of small molecules, ~ 20 mg of sample was dissolved in 1.0 mL of deuterated solvent (usually chloroform unless mentioned otherwise). For 1H NMR of polymers, ~ 40 mg of polymer was dissolved in deuterated
solvent (usually chloroform unless mentioned otherwise). For 13C and 29Si NMR, ~ 150 mg of polymer was dissolved in 1.0 mL of deuterated solvent (usually chloroform unless mentioned otherwise). For the 13C NMR spectra, 3600 scans were taken with a relaxation
delay of 10 sec (total time 10 h) on a 500 MHz Varian NMR spectrometer. The 13C NMR spectrum of (4-vinylphenyl)dimethylsilane was predicted using ChemDraw Ultra 7.0 software.
2.8.5. Gel permeation chromatography (GPC)
A Waters 150-C Plus instrument attached with three HR-styragel columns [100 Å, mixed bed (50/500/1000/10000 Å), mixed bed (1000, 10000, 1000000 Å)] and a triple detector system was used for GPC analysis of polymers. A differential refractometer (Waters
410), differential viscometer (Viscotek 100) and laser light scattering detector (Wyatt
Technology, DAWN EOS, λ = 670 nm) were the three detectors used for GPC analysis.
The flow rate of solution was 1.0 mL/ min with THF as a solvent at 35 oC. The sample
concentrations were varied between 25 mg/mL to 1 mg/mL in THF depending on the
64 molecular weights (800,000 g/mol to 2,000 g/mol). The samples were filtered using
Teflon® filter with 0.45 μm pore size before injection. Light scattering technique is an
158 absolute method for determining weight average molecular weight (Mw) of polymers.
Universal calibration principle is used for measuring the number average molecular weight of polymers.158 A detailed discussion on determining the molecular weight of
polymers from GPC can be found in the literature.158
2.8.6. MALDI-TOF mass spectrometry
A Bruker-Ultraflex-III-TOF/TOF (Bruker Dlatonics, Billerica, MA) mass spectrometer
was used for matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)
mass spectrometry analysis. This instrument was equipped with a pulsed Nd:XAG laser
(355 nm, 100 Hz repetition rate), a single stage ion extraction source and a two-stage,
gridless reflector. THF solutions of dithranol (20 mg/mL) (Alfa Aesar, 1,8,9-
anthracenetriol, 97%), or t-2-[3-(4-t-butylphenyl)2-methyl-2-propenylidene]macronitrile
(DCTB) (Fluka, 99%), sodium trifluoroacetate (99%, Fluka) or silver trifluoroacetate
(98%, Aldrich) and polymer (10 mg/mL) were prepared for MALDI-TOF MS analysis.
The above solutions were mixed in a ratio of matrix:cationizing salt:polymer (10:1:2), and 0.5 μL of this solution was deposited onto the MALDI sample target and was allowed to dry. The intensity of the nitrogen laser was attenuated to obtain optimum
signal strength. Positive reflectron modes were used for recording mass spectra and
calibration of the mass scale was done externally by using polystyrene standard molecular weights. The MALDI-TOF mass spectrometry experiments were performed by
Aleer Yol from Dr. Chrys Wesdemiotis group (Department of Chemistry, The University of Akron).
65 2.8.7. Electrospray ionization mass spectrometry (ESI)
Electrospray ionization (ESI) mass spectra were acquired with a SYNAPT HDMSTM
Q/ToF mass spectrometer (Waters, Beverly, MA) equipped with a Z-spray electrospray source. The instrument was operated at a voltage of 3.5 kV, sample cone voltage of 35 V and extraction cone voltage of 3.5 V. The desolvation gas flow was 800 L/h (N2) and the
source temperature was 90 °C. The sample flow rate was set at 10 μL/min. The
concentration of the electrosprayed samples was 0.2 mg/mL in THF/MeOH, 1:1, v:v. The
ESI MS experiments were performed by Aleer Yol from Dr. Chrys Wesdemiotis group
(Department of Chemistry, The University of Akron).
2.8.8. Melt viscosity
Melt viscosity data was obtained using an ARES rheometer (TA Instruments) by using
cone (4 º) and plate geometry in the Newtonian region (shear stress directly proportional
to strain rate). The measurement of melt viscosities of the samples was done by Dr. Sham
Ravindranath (The Department of Polymer Science, The University of Akron).
2.8.9. Contact angle measurements
Contact angle measurements were made using the Drop Shape Analyzer (DSA)
DSA20E by Kruss at room temperature. On an average five different readings were taken
at five different places on each sample kept at horizontal level.
2.8.10. Scanning electron microscopy (SEM)
SEM pictures were taken using a Jeol JSM-5310 scanning electron microscope. A sample of fibrous mat coated on aluminum foil was sputter coated with silver using SPI
Supplies (Model 111) Sputter Coater prior to SEM imaging. SEM pictures were taken by
Sarang Bhawalkar (The Department of Polymer Science, The University of Akron).
66 2.8.11. Atomic force microscopy (AFM)
A 0.01% (weight/volume) solution of the cyclic poly(butadiene-g-styrene) fractionated
polymer (Mn=2,004,000 g/mol, Mw/Mn = 6.19) was prepared in toluene. One drop of this
solution was drop cast on a freshly cleaved mica wafer. The wafer was dried in ambient
for 24 h. AFM analysis was done using a Park Scientific Instruments AutoProbe CP in
tapping mode at a scan rate of 0.7 Hz. AFM images were taken by Rebecca Agapov (The
Department of Polymer Science, The University of Akron).
2.8.12. Differential scanning calorimetry (DSC)
DSC measurements of the polymer samples (~ 10 mg) were taken using TA DSC 2000
instrument under inert (nitrogen) atmosphere. Heating and cooling rates were 10 oC per minute. The glass transition temperatures (Tg) of the samples were determined from heat
flow (W/g) versus temperature (oC) graphs using TA Instruments Universal V4.4A software.
67 CHAPTER III
RESULTS AND DISCUSSION
3.1. Synthesis of star polymers using anionic polymerization
Linear poly(styryl)lithium was reacted with different concentrations of vinyldimethylchlorosilane (VDMCS) in benzene at 30 oC. As reported by Chaumont and
coworkers38, when poly(styryl)lithium anions were reacted with VDMCS in THF at -70
oC, vinylsilane functionalized polystyrenes were obtained as shown in equation 16 .
PS Li + Cl Si PS Si -70 oC, THF (16)
A similar result was expected when poly(styryl)lithium was quenched with varying
quantities of VDMCS (1.28 – 5.21 equivalents) in benzene at 30 oC. A base polystyrene
sample (3 mL solution) was taken prior to the reaction with VDMCS and quenched with
degassed methanol. After reacting poly(styryl)lithium with VDMCS, an aliquot was taken
after 12 hours of reaction and quenched with degassed methanol. Finally, the reaction was
quenched with degassed methanol after 3 days of reaction. All samples were precipitated
into methanol, filtered, and dried in vacuum oven at room temperature for 24 hours.
Figure 3.1 shows the GPC chromatograms of base polystyrene and polystyrene samples
after 12 hours and 3 days of reaction of poly(styryl)lithium with 1.5 equivalents of
68 VDMCS at 30 oC in benzene. Surprisingly, as evident from Figure 3.1, a shift in the
chromatogram peak was observed for polystyrene samples after 12 hours and 3 days of
reaction with VDMCS as compared to the base polystyrene sample. The chromatograms
for polystyrene samples after 12 hours and 3 days of reaction were found to be almost
identical. This shift towards lower elution volume indicated increased molecular weight.
If only vinyl-functionalized polymers were formed, the chromatograms of the base
polystyrene and polystyrene reacted with VDMCS would have been expected to overlap.
The reaction of poly(styryl)lithium with VDMCS in benzene at 30 oC caused an increase
in molecular weight which is contrary to the formation of vinylsilane-functionalized
linear polystyrene as previously reported.38 The star polystyrene was obtained in 82.4%
yield.
PS-VDMCS 30 C-1.5 eq 1.2 PS base at 30 C 1 PS-VDMCS-12hrs 0.8 PS-VDMCS-3days-30C 0.6
RI signal signal RI 0.4
0.2
0 18 20 22 24 26 28 Retention volume
Figure 3.1. GPC chromatograms of base polystyrene (blue curve), and polystyrene reacted with 1.5 equivalents of VDMCS in benzene at 30 oC for 12 hours (pink curve)
and 3 days (yellow curve)
69 All samples of the reaction of poly(styryl)anions with varying concentrations (1.28-5.21
equivalents) of VDMCS at various temperature (30 oC and 50 oC) were analyzed by GPC
and the data is summarized in Table 3.1. Since the data for polystyrene samples reacted
for 12 hours and 3 days was similar, Table 3.1 shows the data for polystyrene samples reacted for 12 hours. The calculated molecular weights of samples were based on the
responses from refractive index, viscometer, and light scattering detectors. The ratio of
molecular weights (f) of the polystyrene obtained after the reaction with VDMCS
compared to the base polystyrene varied between 7.5 to 9.4. The polydispersity indices of
polystyrenes treated with VDMCS were broad (1.27-1.42) as compared to the base
polystyrenes (1.02-1.03). The intrinsic viscosities of the samples were measured using the
viscometer attached to the GPC. The intrinsic viscosity of the polystyrene samples
reacted with VDMCS was compared with intrinsic viscosity of linear polystyrene samples
and their ratios (contraction factor gη) are listed in Table 3.2. This contraction factor was
then compared with the theoretical contraction factor predicted for star polymers based on
Roover’s equation 31, 159, 160 as shown in equation 17,
2 0.58 gη = [(3f-2)/f ] x [0.724- 0.015(f-2)]/0.724 ( 17)
where f is the number of arms on the star polymers.
As seen from Table 3.2, the observed ratio of viscosities (observed contraction factor, gη)
of polystyrenes treated with VDMCS and linear polystyrenes was very close to the
31, 159, 160 theoretically predicted contraction factor (gη) by Roover’s equation indicating the
star nature of the polystyrenes reacted with VDMCS.
Table 3.1. Molecular weight data of base polystyrene (bPS) and polystyrene after reaction
with VDMCS (vPS).
70 Sample Eq of Mn Mw/Mn Mn Mw/Mn f = Mn ID** VDMCS bPS bPS vPS vPS vPS / Mn (g/mol) (g/mol) bPS 1530 1.89 2500 1.02 22,400 1.30 8.9 1550 1.28 1700 1.03 13,600 1.42 8.1 2530 2.80 2200 1.02 21,000 1.35 9.4 2550 3.81 3000 1.02 22,900 1.47 7.5 5030 4.92 2000 1.03 15,600 1.32 7.9 5050 5.21 2100 1.03 17,400 1.21 8.3 ** The last two digits of the sample ID represent the temperature at which polymerization was carried out. e.g. 2530 sample was reacted at 30 oC. VDMCS-
vinyldimethylchlorosilane.
Table 3.2. Intrinsic viscosity data of linear polystyrene (LPS) and polystyrene reacted
with VDMCS (vPS).
Sample f = Mn *[n] LPS [n] vPS gη = [n] vPS/[n] LPS gη a ID vPS / (dL/g) (dL/g) (observed) (calculated by using Mn bPS Roover’s equation) 1530 8.9 0.168 0.077 0.46 0.44 1550 8.1 0.121 0.058 0.48 0.47 2530 9.4 0.161 0.065 0.41 0.42 2550 7.5 0.170 0.083 0.49 0.49 5030 7.9 0.133 0.07 0.53 0.47 5050 8.3 0.142 0.067 0.47 0.46 a The last two digits of sample ID represent the temperature at which polymerization was carried out. e.g. 2530 sample was reacted at 30 oC; k and a values for Mark Houwink
Sakurada equation for linear polystyrene were found to be k = 2.41 x 10-4 dL/g and a =
0.65 in THF at 35 oC; intrinsic viscosity of linear polystyrene (LPS) was calculated using
-4 0.65 Mark Houwink Sakurada equation [η]LPS = 2.41 x 10 x M dL/g where M = molecular
weight of linear polystyrene (LPS).
Formation of star polymer using VDMCS as a linking agent can be explained based on
linking chemistry shown in Scheme 3.1. There are two reactive sites on VDMCS. The
first is the vinyl group and the second is the silicon-chlorine bond. The chloride can be
71 displaced by the poly(styryl)lithium anion by simple nucleophilic substitution (SN2) to yield vinyl 1 as shown in Scheme 3.1. It would be expected that the displacement of chloride will take place first due to the rapid nature of nucleophilic substitution to yield vinylsilane-functionalized polystyrene as observed by Chaumont and coworkers.38
72 Anion 2
n - Li + - Si n Si Cl
n
+ n - Li
Vinyl 1
- n Si Si Si
-
n n Si
Vinyl 1
Si Si Si - Si Si Si
Scheme 3.1. Formation of star polymer using VDMCS as a linking agent.
73 Once vinylsilane-functionalized polystyrene (vinyl 1 in Scheme 3.1) is formed, another
poly(styryl)lithium anion can add to this vinyl 1 group to yield Anion 2 shown in Scheme
3.1. The star polymer grows by addition of anion 2 to vinyl 1 complex as shown in
Scheme 3.1. As the size of the star grows it becomes increasingly difficult for the bulky
(each arm increases the molecular weight by 2,500 g/mol) anion (Anion 2) to add to the
vinyl group (vinyl 1). This explains why addition of more VDMCS (1.28-5.21
equivalents) did not increase the number of arms on star (f =7.5-9.4). This behavior was
surprising compared to the linking reaction of poly(styryl)lithium anions with
divinylbenzene (DVB) wherein the number of arms of star polymer can get as high as 38
with increasing concentration of DVB3 because of the formation of a central core by
3 polymerization of smaller DVB units as shown in Scheme 3.2
P
P Li + DVB Core
P Li
Scheme 3.2. Anionic synthesis of star polymers using divinylbenzene as a linking agent.
1H and 29Si NMR spectra of the samples were taken to further investigate the structures
of the star polymers. As shown in Figure 3.2, no vinyl peaks were found between δ 4 -6 ppm in the 1H NMR spectrum. This indicated star formation as opposed to vinyl
functionalized polystyrene formation shown in equation 18. The absence of vinyl peaks in
74 1H NMR spectrum also suggests the absence of residual vinylsilane groups on the star
polymer.
VDMCS-1.5-50C-3day-H1.espCHLOROFORM-d 7.03
1.0
0.9
0.8
0.7
0.6 1.40 6.54 0.5 Normalized Intensity Normalized 0.4 0.64 1.83 0.3
0.2 0.86 -0.49 7.27 0.1
9 8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm) Figure 3.2. 1H NMR spectrum of star polymer (sample 1550 from Table 3.1).
75 TMS Si reference.esp 1.0 -37.30 0.9 0 0.8
0.7
0.6
0.5
0.4
0.3 TMS Normalized Intensity
0.2
0.1
0
-0.1
32 24 16 8 0 -8 -16 -24 -32 -40 -48 -56 Chemical Shift (ppm)
Figure 3.3. 29Si NMR spectrum of star polystyrene (sample 1530 from Table 3.1).
Silicon NMR (29Si) were also obtained to study the structure of the stars. For star polystyrenes formed under different reaction conditions, only one 29Si NMR signal was obtained at δ -37.30 ppm relative to tetramethylsilane as shown in Figure 3.3 (29Si NMR spectra for the rest of the samples in Table 3.1 are shown in Appendix A). A similar compound (poly(silylene-co-ethylene), with a repeating unit –(C-(CH3CHCH3)2Si-C)-) was analyzed using 29Si NMR spectroscopy and exhibited a resonance peak at δ -37.06 ppm with TMS as external reference.161 This shows that there is just one type of silicon in the star polystyrene (shown in Scheme 3.1, surrounded by alkyl groups). The absence of peaks at δ 19.8 ppm (-SiCl bond) and 9.1 ppm (-SiOCH3 bond) indicates complete substitution of the chlorine atoms on VDMCS.39, 40 No peak that would have
162 corresponded to –Si(CH=CH2) group (-7.0 ppm ) was observed.
76
Figure 3.4. Melt viscosities of linear and star polystyrenes.
Melt viscosity is another important physical property which affects the processing of
polymers.163 The melt viscosities of the star polystyrenes (sample ID 5050 and 1530 in
Table 3.1; Mn = 17,400 and 22,400 g/mol, respectively) were compared with an analogous linear polystyrene (18,400 g/mol) as shown in Figure 3.4. It was found that the melt viscosities of the star polystyrenes were reduced by more than 50% at 160 oC as
compared to analogous linear polystyrene. Even the star polystyrene with higher
molecular weight (22,000 g/mol, sample ID 1530 in Table 3.1) had lower melt viscosity
than the lower molecular weight linear polystyrene (18,000 g/mol). This effect can be
attributed to more compact size of star polymers compared to linear polymers.163 Linear polystyrene is more likely to form entanglements compared to star polystyrene at the same molecular weight.163 Both of these effects contribute to the reduction of melt
viscosity of star polystyrenes relative to the analogous linear polystyrenes.
77 3.2. Synthesis of pyrrolidine-functionalized polystyrene
Amine-functionalized polystyrene was synthesized in two easy steps as shown in
Scheme 3.3. Chloromethyldimethylsilane has been previously used for making dendrimers164, 165 and chloromethyldimethylsilane-functionalized polymers
(polybutadiene)166. However, none of these attempts involved synthesis of functional
polymers from the chloromethyldimethylsilane-functionalized polymers. Vinyl-
functionalized polystyrene (PS-V) was first reacted with chloromethyldimethylsilane via
a hydrosilation reaction using Karstedt’s catalyst to give chloromethyldimethylsilane-
functionalized polystyrene (PS-Cl, 88%). This chloromethyldimethylsilane-
functionalized polystyrene was reacted with pyrrolidine to obtain pyrrolidine-
functionalized polystyrene (PS-N, 84%).
78 H Benzene CH3OH n Li + n 30 oC, 4.2 eq THF
H H 2 da., R.T. Cl Si n n Karstedt's catalyst, Toluene
HSi Cl
H
N Argon, 50 oC, 2 da.
H N Si n
Scheme 3.3. Synthesis of pyrrolidine-functionalized polystyrene.
The GPC chromatograms of the three polymers (PS-V, PS-Cl, and PS-N) are shown in
Figure 3.5. It can be seen that the chromatograms of all the three polymers (PS-V, PS-Cl,
PS-N) were monomodal and overlapped with each other indicating no significant increase in molecular weights. The number average molecular weights of the polymers
PS-V, PS-Cl, and PS-N were found to be 2,500 g/mol (Mw/Mn = 1.02), 2,600 g/mol
(Mw/Mn = 1.02), and 2,700 g/mol (Mw/Mn = 1.03), respectively.
79 GPC curve
1600 1400 1200 1000 PS-V 800 PS-Cl 600 PS-N 400 200
RI detector response RI detector 0 -200 15 20 25 30 35 Elution Vol (mL)
Figure 3.5. GPC chromatograms of vinyl-functionalized (PS-V), chloromethyldimethyl- silane-functionalized (PS-Cl), and pyrrolidine-functionalized (PS-N) polystyrenes.
All three polymers were analyzed by 1H and 13C NMR spectroscopy. The 1H NMR spectrum of the vinyl-functionalized polystyrene (PS-V) is shown in Figure 3.6. Peaks from terminal vinyl groups were observed at δ 4.90 (literature δ 4.9 ppm for the same polymer structure150) and 5.73 ppm (literature δ 5.7 ppm for the same polymer structure150) ), respectively.
80 JON87 POLYMER WITHCHLOROFORM-d VINYL GROUP 2.4 K.ESP
7.27 5.73 H
0.30 4.90 1.49 0.25
0.20
Normalized Intensity Normalized 0.15
0.10 1.93 4.90 0.05 2.27 5.73
0 1.00 1.98 4.57
8 7 6 5 4 3 2 1 Chemical Shift (ppm) Figure 3.6. 1H NMR spectrum of vinyl-functionalized polystyrene (PS-V).
After the reaction of the vinyl-functionalized polystyrene with chloromethyldimethyl- silane, these vinyl peaks disappeared completely as seen in 1H NMR spectrum of chloro-
methyldimethylsilane-functionalized polystyrene (Figure 3.7). New peaks at δ 0.09 and
2.77 ppm appeared which correspond to –Si(CH3)2 (literature value, δ 0.29 ppm for
167 ClCH2Si(CH3)2Si(CH3)2Ph ) and –CH2Cl (literature value δ 2.95 ppm for
167 167 ClCH2Si(CH3)2Si(CH3)2Ph ) groups of PS-Cl.
81 B4P54 NEW.ESP CHLOROFORM-d 2.77
7.27 H Cl 1.0 Si
0.9 n
0.8
0.7 0.09
0.6
0.5 Normalized Intensity Normalized 7.14 0.4 1.50
0.3 0.09 6.64 0.2 2.77
0.1 0.58
0 1.00 1.18 3.44
8 7 6 5 4 3 2 1 0 Chemical Shift (ppm) Figure 3.7. 1H NMR spectrum of chloromethyldimethylsilane-functionalized polystyrene (PS-Cl).
After reacting chloromethyldimethylsilane-functionalized polystyrene with
pyrrolidine, pyrrolidine-functionalized polystyrene (PS-N) was obtained. Figure 3.8
shows the 1H NMR spectrum of pyrrolidine-functionalized polystyrene. It can be
observed that the peak from the –CH2Cl group (δ 2.77 ppm) of PS-Cl disappeared completely. A new peak at δ 2.57 ppm corresponding to –(CH2)N- (from the pyrrolidine
ring, literature value δ 2.39 ppm for the same peak in N-pentylpyrrolidine168) was
bserved.168
82 B4P55 NEWEST BEST PROTON.ESPCHLOROFORM-d 7.27
1.0 H 0.9 N Si 0.8 n 0.7
0.6
0.5
Normalized Intensity Normalized 2.57 0.4
0.3
0.2 0.07 2.57
0.1 0.51
0 2.00 0.97 3.50
8 7 6 5 4 3 2 1 0 Chemical Shift (ppm)
Figure 3.8. 1H NMR spectrum of pyrrolidine-functionalized polystyrene (PS-N).
Figure 3.9 shows the 13C NMR spectrum of vinyl-functionalized polystyrene. Peaks from vinyl group were observed at δ 114.04 (terminal vinyl carbon, literature value δ 117.38 ppm for the same carbon in 5-bromo-1-pentene169) and δ 138.94 ppm (non-terminal vinyl carbon, literature value δ 135.93 ppm for the same carbon in 5-bromo-1-pentene169).
83 138.94
JON 87 2.4K VINYL POLYSTYRENE.ESP CHLOROFORM-d 127.92 1.0 H 0.9 n 0.8
0.7 114.04
0.6
0.5 125.61 Normalized Intensity 0.4 145.29
0.3 40.37 138.94 0.2 33.52 28.83 142.45 43.13 26.73 114.04 0.1
0
170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 Chemical Shift (ppm) Figure 3.9. 13C NMR spectrum of vinyl-functionalized polystyrene.
After the reaction with chloromethyldimethylsilane, these vinyl peaks disappeared
completely as seen in 13C NMR spectrum of chloromethyldimethylsilane-functionalized
polystyrene (Figure 3.10) . New peaks at δ 0.99 and -4.61 ppm were observed which correspond to –CH2Si- and –Si(CH3)2 (literature value δ -4.57 ppm for
167 ClCH2Si(CH3)2Si(CH3)2Ph )groups in this chloromethyldimethylsilane-functionalized
polystyrene.167 Figure 3.11 shows 13C NMR spectrum of pyrrolidine-functionalized polystyrene. As shown in Figure 3.11, the peak from –CH2Cl at δ 0.99 ppm disappeared
completely. Methyl peaks from the –Si(CH3)2 group were shifted from δ -4.61 ppm for
the chloromethyldimethylsilane-functionalized polystyrene to δ -2.99 ppm for the
168 pyrrolidine-functionalized polystyrene. Peaks from the –CH2-N group (from
pyrrolidine) ring were observed at δ 58.11 ppm (literature δ 53.8 ppm for the same
carbon in N-ethylpyrrolidine168).
84 B4P54 JON87 AND CHLOROMETHYLDIMETHYLSILANE.ESP CHLOROFORM-d
-4.61 77.00
127.92 H Cl Si 0.8 n
0.7 -4.61
0.6
0.5 125.61 Normalized Intensity 0.4
0.3 -4.61 145.30 40.37 30.35 0.2 13.53 23.35 142.47 0.1 43.87 0.99
160 140 120 100 80 60 40 20 0 Chemical Shift (ppm)
Figure 3.10. 13C NMR spectrum of chloromethyldimethylsilane-functionalized polystyrene (PS-Cl).
B3P56 amine funct PS.esp 127.91 CHLOROFORM-d 1.0 -2.99
H N 0.9 Si 77.00 n 0.8
0.7
0.6 58.11 125.60 0.5 Normalized Intensity 0.4
0.3 -2.99 145.19 40.36 23.88 0.2 58.11 29.66 43.84 142.47 0.1 15.21
0 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Chemical Shift (ppm)
Figure 3.11. 13C NMR spectrum of pyrrolidine-functionalized polystyrene (PS-Cl).
85
MALDI-TOF and ESI mass spectrometry was carried out to analyze the three polymers
(PS-V, PS-Cl, PS-N). As seen in Figure 3.12, the MALDI-TOF mass spectrum of PS-V
was monomodal with one distribution. Figure 3.13, shows MALDI-TOF spectrum of PS-
V expanded in the region (m/z) 2300-2600. The observed monoisotopic mass peak at
(m/z) 2362.4 corresponds to vinyl-functionalized polystyrene with 21 repeating styrene
units, C5H9(C8H8)21-H Ag+; calculated monoisotopic mass = 69.070425 + 104.0626 x 21
+ 1.007825 + 106.9050 = 2362.3 Da. Similarly, the peak observed at (m/z) 2466.5 corresponds to vinyl-functionalized polystyrene with 22 styrene repeating units
[C5H9(C8H8)22-H Ag+; calculated monoisotopic mass = 69.070425 + 104.0626 x 22 +
1.007825 + 106.9050 = 2466.4 Da].
86 s 4 Inten 2467. 2363.39 2571.519 1.25 2259.339 2675.578 2155.278 2779.639 1.00 2051.215 2883.700 2987.761
0.75 1947.151 3091.823 3195.886
0.50 1843.084 3299.950 1739.018 3404.015
0.25 3508.079 3612.147 1635.946 3716.212 3821.282 1530.871 3924.349 1427.797 4029.416 4133.484 1323.718 0.00 1500 2000 2500 3000 3500 4000
Figure 3.12. MALDI-TOF mass spectrum of vinyl-functionalized polystyrene (PS-V)
H 45
n 2469. Observed 2363.399 2467.459 2362.4 Observed
2466.5 2362.400 2466.451
Calculated Calculated
2362.3 2466.4
21 mer 22 mer
104.1
2375 2400 2425 2450 2475
Figure 3.13. MALDI-TOF mass spectrum of vinyl-functionalized polystyrene (PS-V) expanded in the region m/z = 2300-2600.
87 As seen in Figure 3.14, the MALDI-TOF mass spectrum of PS-Cl was monomodal with
one distribution. Figure 3.15, shows the MALDI-TOF spectrum of PS-Cl expanded in the
region (m/z) 2600-2800. The observed monoisotopic mass peak at (m/z) 2678.6
corresponds to chloromethyldimethyl-functionalized polystyrene with 23 repeating
styrene units, (C3H8SiCl)(C5H10)(C8H8)23-H Ag+; calculated monoisotopic mass =
107.0083 + 70.07825 + 104.0626 x 23 + 1.007825 + 106.9050 = 2678.4 Da. Similarly,
the peak observed at (m/z) 2782.7 corresponds to chloromethyldimethylsilane-
functionalized polystyrene with 24 styrene repeat units, (C3H8SiCl)(C5H10)(C8H8)24–H
Ag+; calculated monoisotopic mass = 107.0083 + 70.07825 + 104.0626 x 24 + 1.007825
+ 106.9050 = 2782.5 Da.
88 3 2 s Inten 2678.6 2782.7
1.0
0.8
0.6
0.4
0.2
0.0 1500 2000 2500 3000 3500 4000 Figure 3.14. MALDI-TOF mass spectrum of chloromethyldimethylsilane-functionalized polystyrene (PS-Cl)
89 Observed H Cl Si 2678.6 n Observed
2782.7
Calculated Calculated
2678.4 2782.5
23 mer 24 mer 2678.639 104.1 2782.727
2680 2700 2720 2740 2760 2780
Figure 3.15. MALDI-TOF mass spectrum of chloromethyldimethylsilane-functionalized polystyrene (PS-Cl) expanded in the region m/z = 2600-2800.
Figure 3.16 shows the ESI mass spectrum of pyrrolidine-functionalized polystyrene
(PS-N). As seen in Figure 3.16, the ESI mass spectrum of PS-N showed two distributions
(one major, one minor). Figure 3.17 shows the ESI spectrum of PS-N expanded in the region (m/z) 1800-2100. The observed monoisotopic mass peak of the major distribution at (m/z) 1879.7 corresponds to protonated pyrrolidine-functionalized polystyrene with 16
+ repeating styrene units, ((CH2)4NH )(C3H8Si)(C5H10)(C8H8)16-H; calculated monoisotpic mass = 71.0734 + 72.0395 + 70.07825 + 104.0626 x 16 + 1.007825 = 1879.2. Similarly, peak observed at 1983.8 corresponds to pyrrolidine-functionalized polystyrene with 17
+ [((CH2)4NH )(C3H8Si)(C5H10)(C8H8)17-H; calculated monoisotpic mass = 71.0734 +
72.0395 + 70.07825 + 104.0626 x 17 + 1.007825 = 1983.3] styrene repeat units. The peaks corresponding to minor distribution [(m/z) 1967.7] could not be attributed to any
90 particular structure. Based on the ratio of intensities of the peaks at (m/z) 1967.7 and
1879.2, the percentage of the unknown product was calculated to be 7.5%.
AMY_071910_10273_#2 56 (1.156) Cm (1:70) 2088.944 2193.104 100 2194.104
2298.290
2401.437 1984.799
2506.655
1880.659 2610.884 %
2715.058 1879.686
1776.539 2716.075
2820.304
1775.547 2923.518 2924.554 1672.425 3027.809 1671.417
0 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 36
Figure 3.16. ESI mass spectrum of pyrrolidine-functionalized polystyrene (PS-N).
91 Observed
AMY_071910_10273_#2 56 (1.156) Cm (1:70) Observed 100 1983.8 1879.7 1984.799 Calculated Calculated 1985.800 1983.3
1879.2 1880.659
1881.665 1983.816 % 17 mer 16 mer 1986.817 1879.686 104.1
1882.687
Unknown peak 1987.801
1883.693 1967.7 1988.802 1864.622 1968.746 1863.605 1866.625 1884.651 1967.734 1970.739
0 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2
Figure 3.17. ESI mass spectrum of pyrrolidine-functionalized polystyrene (PS-N)
expanded in the region m/z = 2600-2800.
Based on the 1H and 13C NMR spectroscopy and MALDI-TOF and ESI mass spectrometry, successful pyrrolidine-functionalization of polystyrene was carried out.
Chloromethyldimethylsilane-functionalized polystyrene was obtained in quantitative yields based on 1H and 13C NMR and MALDI-TOF mass spectra results. The ESI mass
spectrum of pyrrolidine-functionalized polystyrene showed a major distribution
corresponding to the ESI mass spectrum of pyrrolidine-functionalized polystyrene and also showed a minor product (7.5%) which formally arises by methane elimination from the pyrrolidine-functionalized polystyrene could not be identified.
92 3.3. Synthesis of in-chain functionalized polymers using atom transfer radical
polymerization (ATRP) and hydrosilation
3.3.1. Synthesis of propargyl 2-bromoisobutyrate (PGBIB) initiator
Propargyl 2-bromoisobutyrate (51% yield) was synthesized by reacting propargyl alcohol with α-bromoisobutyryl bromide as shown in equation 18.
O Triethylamine, Br O OH CH2Cl2 Br + Br 0 oC 1h, R.T. 16 h O
52%
(18)
The 1H NMR spectrum of the PGBIB initiator was taken as shown in Figure 3.18 to analyze its structure. Strong methyl peaks [(-C(CH3)2Br)] were observed at δ 1.87 ppm.
The peak corresponding to the proton of the acetylene group was observed at δ 2.49 ppm.
The peak corresponding to the –CH2 protons next to the oxygen atom was observed
upfield at δ 4.67 ppm due to deshielding by the more electronegative oxygen atom. The
integrations of proton peaks were consistent with the structure of PGBIB initiator. The
peaks in the 1H NMR spectrum were consistent with those reported in the literature.151
93 1H_PGBIB_012109.esp
c 1.87 CH3
0.8 O c C C Br H H 0.7 2 CH a 3 O 0.6 b
0.5
0.4 Normalized Intensity 4.67 0.3 b
a 2.49 0.2
0.1 CHLOROFORM-d
0 0.13 0.05 0.40
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) 32
Figure 3.18. 1H NMR spectrum of propargyl 2-bromoisobutyrate.
The 13C NMR spectrum further confirmed the structure of initiator as shown in Figure
3.19. The acetylene carbon peaks a and b were observed at δ 75.44 and 76.75 ppm, respectively. The carbonyl peak d was observed upfield at δ 170.74 ppm, as expected due to deshielding by the neighboring electronegative oxygen atom. The presence of the reactive tertiary carbon e was confirmed by the peak at δ 54.72 ppm.151 All of the peaks
observed in the 13C NMR spectrum were consistent with those reported in the
literature.151
94 13C_PGBIB_012109.esp 30.38
0.60 CH3 0.55 b e CHLOROFORM-d 0.50 C O d C
0.45 C C C Br H H2 CH3 53.15 0.40 a c O f f 0.35 c 0.30
Normalized Intensity a
0.25 75.44
0.20
0.15 b 54.72 76.75 0.10 170.48 e 0.05 d 77.00 0
180 160 140 120 100 80 60 40 20 Chemical Shift (ppm) Figure 3.19. 13C NMR spectrum of propargyl 2-bromoisobutyrate
3.3.2. Synthesis of (4-vinylphenyl)dimethylsilane
(4-Vinylphenyl)dimethylsilane was synthesized (section 2.6.2.) as shown in Scheme 3.4.
Mg, Iodine, THF, Ar
650C 90 minutes Cl MgCl
Column Chromatography HClSi using Hexane 73% Yield Vacuum Distillation
MgCl Si H
Scheme 3.4. Synthesis of (4-vinylphenyl)dimethylsilane.
The 1H NMR spectrum of (4-vinylphenyl)dimethylsilane is shown in Figure 3.20. The
assignment of peaks is shown in the inset of Figure 3.20. The peak at δ 4.51 ppm
95 confirms the presence of –SiH group in the molecule.79 A sharp peak at δ 0.41 ppm
corresponds to the methyl protons attached to silicon. Peaks from ortho and meta protons
(relative to the vinyl group) on the phenyl ring were observed upfield at δ 7.57 and 7.47, respectively. Vinyl peaks b, a, and c were observed at δ 6.78, 5.87, and 5.34 ppm, respectively. All of the peaks in the 1H NMR spectrum were consistent with those
reported in the literature.79, 83
b a H H
STYSIH HNMR.ESP 1.0 H f c 0.9 g 0.8 H H H Si H 0.7 H e H H 0.6 d 0.5 e 0.4 Normalized Intensity
0.3 7.06 7.17 5.46 0.2 f g a 4.93 c 4.10
6.37 b d 0.1
0 0.08 0.04 0.04 0.04 0.04 0.24
7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Chemical Shift (ppm) Figure 3.20. 1H NMR spectrum of (4-vinylphenyl)dimethylsilane.
The structure of (4-vinylphenyl)dimethylsilane was further confirmed by 13C NMR
spectral analysis as shown in Figure 3.21. The presence of the Si atom in the molecule
was confirmed by peaks due to methyl groups G attached to silicon at δ -3.78 ppm. Vinyl
peaks C and F were observed at δ 136.83 and 114.25 ppm, respectively. The assignment
96 of the peaks in 13C NMR spectrum was based on the theoretically predicted 13C NMR by the Advanced Chemistry Development, Inc. (ACD/Labs) Software V11.01.
STYSIH C NMR.ESP 136.1 A 114.3 134.24 125.64
1.0 -3.78 E 139.2 0.9 B 126.0 126.0 C B 0.8
132.4 132.4 0.7 C 0.6 136.5 114.25 -3.6 -3.6 0.5 Si
Normalized Intensity D
E 136.83 0.4 D A H 0.3 137.04 138.38 0.2
0.1
140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Chemical Shift (ppm)
Figure 3.21. 13C NMR spectrum of (4-vinylphenyl)dimethylsilane.
3.3.3. Synthesis of the copolymer of methyl methacrylate and (4- vinylphenyl)dimethylsilane using propargyl 2-bromoisobutyrate as an initiator (B3P65)
A model reaction was conducted to study the copolymerization of (4- vinylphenyl)dimethylsilane and methyl methacrylate using propargyl 2-bromoisobutyrate as an initiator as shown in equation 19. 2,2’-Bypyridine and copper bromide (I) were used as ligand and catalyst, respectively. The mechanism of atom transfer radical polymerization reaction can be explained as shown in Scheme 3.5.47, 170 Copper bromide
(I) acts as a catalyst for an atom transfer radical polymerization reaction. Copper bromide
(II) formed after activation of a radical then acts as a deactivator for the growing radical.
This continuous activation and deactivation leads to a better control over molecular
97 weight and molecular weight distribution of the polymer synthesized by atom transfer radical polymerization. A higher deactivation rate compared to propagation rate ensures low polydispersity indices.47 If the deactivation rate is too high compared to the rate of propagation then polymerization will not occur.
Br O + + O 81 % by wt O O 87.5 % by mol
Si 19 % by wt 12.5 % by mol H
Br O CuBr, 2,2’-bypyridine, O m O O n O 95 oC, 14 h, vacuum, O Toluene
Si 76% conversion H
(19)
RBr . +CuBr (L) R + CuBr2 (L) Initiation M Propagation . R-MM CuBr2 (L)
Re-initiation Reversible termination
Polymer-Br + CuBr (L)
98 Scheme 3.5. Atom transfer radical polymerization mechanism.
The GPC curve of the resulting polymer is shown in Figure 3.22. A monomodal
distribution was observed with number average (Mn) and weight average (Mw) molecular
weights of 3,600 and 4,600 g/mol, respectively, based on polystyrene standards. The polydispersity index was found to be 1.29, a value typical of atom transfer radical
polymerization reactions done at higher conversions.47
1.0
0.5 relative scale
0.0
45.0 50.0 55.0 time (min)
Figure 3.22. GPC of polymer B3P65 (RI signal).
1 Figure 3.23 shows the H NMR spectrum of B3P65. The proton peaks from the –CH2O-
group of the initiator are observed at δ 4.63 ppm (reported value δ 4.10 ppm171). The silyl
hydride peak from the 4-phenyldimethylsilane group was observed at δ 4.37 ppm. The
proton signals from the methoxy group of MMA were observed at 3.58 ppm.
After taking the ratio of integration values of the above three peaks, the molar ratios of
MMA:(4-vinylphenyl)dimethylsilane:initiator was found to be 20.64:3.72:1. The molar ratios of MMA:(4-vinylphenyl)dimethylsilane:initiator in the feed was 17.46:3.72:1.
Based on the molar ratio data from the 1H NMR spectrum, the molecular weight of the
polymer B3P65 was calculated to be 2,875 g/mol as follows:
205.05 g/mol (from initiator) + 3.72 x 162.30 g/mol (from (4-
vinylphenyl)dimethylsilane) + 20.64 x 100.12 g/mol (from MMA) = 2,875 g/mol). The
99 number average molecular weight of B3P65 was found to be 3,600 g/mol from GPC; but this value is based on polystyrene standards and is less reliable.
B3P65 NEW NMR ON 500 MHZ 2001.ESP DICHLOROMETHANE-d2 5.32 3.58
0.30
0.25
0.20 0.31
0.15 Normalized Intensity
0.10 2.90
0.05 4.37 4.63 2.51
0
2.00 3.72 61.94 9.55 1.25 28.69
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)
Figure 3.23. 1H NMR spectrum of polymer B3P65.
100
Figure 3.24. FTIR spectrum of polymer B3P65.
The FT-IR spectrum of B3P65 revealed a strong peak from the –SiH group at 2116 cm-1 as shown in Figure 3.24.12 B3P65 was further analyzed using MALDI-TOF mass
spectrometry (see Figure 3.25). Individual groups of polymer B3P65 are labeled in the
inset of Figures 3.26 and 3.27. All of the peaks in the MALDI-TOF mass spectrum were assigned based on elimination of the HBr group from the polymer chain by the laser beam. For example, a peak at 1557.6 Da (Figure 3.26) was assigned to one initiator
molecule (without Br atom), six units of MMA (A), and five units of (4-
vinylphenyl)dimethylsilane (B). The calculated monoisotopic mass = (I + 6 x A + 5 x
B)BrNa+ - HBr = 125.058 + 6 x 100.052 + 5 x 162.086+ 78.9183 + 22.9898-
(1.0078+78.9183) = 1557.8 Da.
101 I S Br O O m O O n O O M
Si
H
500 1000 1500 2000 2500 3000 3500 m/z
Figure 3.25. Complete MALDI-TOF mass spectrum of polymer B3P65. p
I B Br O O m O O n O O A I-A8B4 I-A6B5 Si H I-A5B6
I-A3B7 I-A11B2 I-A13B1
Figure 3.26. Assignment labels of individual MALDI-TOF mass spectral peaks of B3P65 in the region m/z =1550-1630.
102 ] . u . [a .
6000 Intens
5000
4000
1657.635
3000 1695.658 1619.648 I-A10B3
2000 1633.609
1000 1681.690 1671.688
0 1620 1630 1640 1650 1660 1670 1680 1690 1700 m/z
Figure 3.27. Labeling of individual MALDI-TOF mass spectral peaks of B3P65 in the region m/z = 1630-1700.
Similarly, the molecular structures for six other peaks were assigned as shown in Table
3.3. The letters I, A, and B in the Table 3.3 indicate initiator, MMA, and (4-
vinylphenyl)dimethylsilane units, respectively. The numbers next to these letters indicate the number of repeat units of each type.
Table 3.3. Observed and calculated MALDI-TOF peaks for B3P65.
Peak no Observed value Calculated Structure (m/z) value assignmenta (Da) 1 1557.6 1557.8 I-A6B5 2 1571.5 1571.8 I-A11B2 3 1581.6 1581.8 I-A3B7 4 1595.6 1595.8 I-A8B4 5 1609.6 1609.9 I-A13B1 6 1619.6 1619.8 I-A5B6 7 1633.6 1633.9 I-A10B3 a I –PGBIB; A- MMA; B- (4-vinylphenyl)dimethylsilane; numbers next to the letters
indicate the number of each type of repeating units.
103
It can be concluded from these results that the silyl hydride group from (4-
vinylphenyl)dimethylsilane is stable under controlled radical polymerization conditions.
This result was surprising since it is a well known fact that hydrosilation reactions of –
SiH groups can occur in presence of radicals.81 The stability of the silyl hydride group
was confirmed using 1H NMR, FT-IR, and MALDI-TOF mass spectrometric analyses.
3.3.4. Synthesis of copolymer of methyl methacrylate and (4-vinylphenyl)dimethylsilane
using ethyl α-bromoisobutyrate as an initiator (B3P84)
Once the stability of silyl hydride group was established under controlled radical
polymerization conditions as discussed in the previous section (section 3.2.3), a similar
reaction was conducted using ethyl α-bromoisobutyrate (EBIB) as an initiator as shown in equation 18. N,N,N′,N′′,N′′-Pentamethyldiethylenetriamine (PMDETA) and copper bromide (I) were used as ligand and catalyst, respectively. After precipitation and drying, the GPC chromatogram showed a monomodal distribution with Mn = 3,500 g/mol, Mw =
4.200 g/mol, and polydispersity index = 1.20 based on polystyrene standards as shown in
Figure 3.28. The polymer (B3P84) was obtained after 68% conversion (based on the
mass of polymer obtained) and molecular weight based on conversion was 2,800 g/mol
(mass of the polymer obtained divided by the number of moles of initiator).
104 CuBr,PMDETA, Toluene, 70 oC, 5 h Br Br O O + + O O m O On O O O O
Si H Si H
(18)
1.2 1 0.8 0.6
RI Signal 0.4 0.2 0 10 12 14 16 18 20 22 24 26 28 30 32 34
Elution Volume (mL) Figure 3.28. GPC chromatogram (RI signal) of B3P84.
Methyl methacrylate (0.46) and styrene (0.52) have similar reactivity ratios in the case of
170 radical copolymerization. The product of their reactivity ratios (r1r2= 0.239) comes out
to be less than 0.5. When the product of reactivity ratios of two monomers is less than
0.5, an alternating copolymer is obtained.170 Thus, when methyl methacrylate and (4-
vinylphenyl)dimethylsilane are reacted together via radical polymerization, an alternating
copolymer with approximately an alternating distribution of monomers along the polymer
chain will be obtained.
105 1 Figure 3.29 shows H NMR spectrum of B3P84. The proton peaks from the –CH2O-
group of the initiator are observed at 4.07 ppm.172 The silyl hydride peak from (4-
vinylphenyl)dimethylsilane was observed at δ 4.38 ppm. The peak from –Si(CH3)2 groups was observed at δ 0.29 ppm. The ratio of integration values from silyl hydride and methyl protons (from –Si(CH3)2 ) was calculated to be 6.65. Proton signals from the
methoxy group of MMA were observed at δ 3.59 ppm. After taking the ratios of
integration values of the above three peaks, the molar ratios of MMA:(4-
vinylphenyl)dimethylsilane:initiator were calculated to be 19.4:2.7:1. The molar ratios of
MMA:(4-vinylphenyl)dimethylsilane:initiator in the feed were 21.6:2.9:1. Based on the
molar ratio data from the 1H NMR spectrum, the molecular weight of the polymer B3P65
was calculated to be 2,574 g/mol as follows:
194.05 g/mol (from initiator) + 2.7 x 162.30 g/mol (from (4-vinylphenyl)dimethylsilane)
+ 19.4 x 100.12 g/mol (from MMA) = 2574 g/mol. The number average molecular
weight of B3P84 was found to be 3,500 g/mol from GPC; but this value is based on
polystyrene standards and is less reliable.
106 EBIBPMMASTYIH4K.ESP 3.59
1.0
0.9
0.8
0.7
0.6
0.5
0.4 CHLOROFORM-d Normalized Intensity
0.3 0.29 1.81 7.27
0.2 7.38 7.00 2.88
0.1 4.38 4.07
0 6.90 3.32 2.47 71.99 6.69 22.11
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Chemical Shift (ppm) Figure 3.29. 1H NMR spectrum of polymer B3P84.
The FT-IR spectrum of B3P84 revealed a strong peak corresponding to the –SiH group at 2116 cm-1 as shown in Figure 3.30.173 The peak at 1732 cm-1 shown in Figure 3.30 confirmed the presence of carbonyl group from MMA.174 The number average molecular weight of B3P84 was found to be 3,500 g/mol from GPC.
107
Figure 3.30. FTIR spectrum of polymer B3P84.
3.3.5. Synthesis of B3P84 allyl alcohol
The functionalization of B3P84 was carried out to prove the ability of –SiH group in this
polymer to undergo hydrosilation reactions (equation 21). The reaction of –SiH group
with allyl alcohol has been shown to be a fairly quick reaction.175 Allyl alcohol (1.54
mmol) was reacted with B3P84 (0.0257 mmol of –SiH groups) in presence of Karstedt’s
catalyst at room temperature as shown in equation 21. The reaction was found to be
complete in 6 hours based on the disappearance of the peak at 2116 cm-1 in the FT-IR
spectrum corresponding to the –SiH group on B3P84. The GPC chromatograms and 1H
NMR spectrum of B3P84 allyl alcohol polymer are shown in Figures 3.31 and 3.32, respectively. Based on GPC, the molecular weight (Mn) of B3P84 allyl alcohol was found
to be 5,400 g/mol (Mw/Mn = 1.36) based on polystyrene standards. The molecular weight
distribution of B3P84 allyl alcohol was found to be broader compared to B3P84 (Mw/Mn
= 1.20; Figure 3.31). This was attributed possibly to unequal distribution of (4-
108 vinylphenyl)dimethylsilane groups in the polymer chains or to the phase separation
occurring during the functionalization.
Br Karstedt's catalyst, O Br O allyl alcohol, 24 h, O m O toluene, room temp O n O n O m O O O O O
Si H Si OH
(21)
1.2 1 0.8 0.6
RI Signal 0.4 0.2 0 10 12 14 16 18 20 22 24 26 28 30 32 34 Elution Volume (mL)
Figure 3.31. GPC chromatograms (RI signal) of B3P84 (blue curve) and B3P84allyl alcohol (purple curve).
As shown in Figure 3.32, no peak at δ 4.38 (from –SiH) was observed in the 1H NMR
spectrum of the product indicating complete consumption of –SiH groups. The peak from
the –CH2OH groups of the B3P84 allyl alcohol polymer was observed at δ 2.90 ppm
(predicted using ChemDraw Ultra 7.0 software). The ratio of integration values of this
peak (δ 2.90 ppm) and the two methyl groups attached to silicon atom (δ 0.23 ppm) was
1:4.00.
109 B3P86ALLYLALCOHOL6HRS.ESP 3.60
1.0
0.9
0.8
0.7
0.6 CHLOROFORM-d
0.5 7.27
0.4 0.83 Normalized Intensity Normalized 0.23 0.3 1.02 1.81
0.2 0.72 1.55 7.37 7.00 0.1 2.90 4.10
0 0.95 0.25 10.74 1.03 4.00
9 8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm) Figure 3.32. 1H NMR spectrum of B3P84 allyl alcohol.
The –SiH peak at 2116 cm-1 disappeared from FT-IR spectrum of the product as shown
in Figure 3.33. A broad peak at around 3400 cm-1 appeared, indicating the presence of –
OH groups on polymer (compare with Figure 3.30 for B3P84).
110
Figure 3.33. FT-IR spectrum of B3P84 allyl alcohol.
It is clear from the above results that silyl hydride groups on the polymer B3P84 were successfully functionalized with hydroxy groups. Based on FT-IR and 1H NMR
spectroscopy, no evidence of unreacted silyl hydride groups in B3P84 allyl alcohol was obtained indicating quantitative reaction. The main advantage of synthesizing functional polymers via a combination of atom transfer radical polymerization and hydrosilation is that the functionalization can be done by various groups such as hydroxy, amine, cyano, alkoxy, acetate, and fluoro under relatively mild reaction conditions (room temperature, atmospheric pressure, air, and minimum solvent and catalyst).11, 12, 15, 17 Alternative
methods of in-chain functionalization in controlled radical polymerizations include use of
functional monomers for polymerization.176
3.4. Copolymerization of isoprene, styrene, and (4-vinylphenyl)dimethylsilane
Copolymerization of isoprene, styrene, and (4-vinylphenyl)dimethylsilane was done
using anionic polymerization inside the drybox (argon atmosphere). All of the purified
111 monomers were added into the flask with purified benzene. The reaction was initiated by addition of sec-butyllithiium as an initiator. In these kinds of anionic polymerizations three main compositions are observed due to differences in monomer reactivity ratios of dienes (for isoprene, r = 7.7 in benzene at 30 oC) and styrene (r = 0.13 in benzene at 30
oC).3 First, dienes are preferentially incorporated into the polymer due to their high
monomer reactivity ratio.3 The midsection consists of mixture of diene and styrene where
a slow incorporation of styrene takes place until the diene is depleted. The third section
consists of a block of styrene. For example, butadiene and styrene have monomer
reactive ratios of 10 and 0.035 when copolymerized using anionic polymerization in
benzene at 30 oC.3 Thus, a tapered block copolymer will be formed when styrene and
butadiene are copolymerized. The first section (starting section) will be rich in butadiene,
midsection will have a mixture of butadiene and styrene, and the third section will consist
of a styrene block. Isoprene and styrene were found to have monomer reactivity ratios of
7.7 and 0.13, respectively, when benzene was used as a solvent at 30 oC.3 Styrene and (4-
vinylphenyl)dimethylsilane were copolymerized by anionic polymerization using sec- butyllithium initiator in cyclohexane at 30 oC.79 The monomer reactivity ratios for (4-
vinylphenyl)dimethylsilane and styrene were found to be 1.74 and 0.16, respectively. A
higher monomer reactivity ratio for (4-vinylphenyl)dimethylsilane indicates its
preferential addition to the growing polymer chain initially compared to styrene.79 Thus, in the case of copolymerization of isoprene, styrene, and (4-vinylphenyl)dimethylsilane, the expected structure of the polymer is composed of an isoprene block, a segment containing a mixture of (4-vinylphenyl)dimethylsilane, styrene, and isoprene, and a block containing styrene and (4-vinylphenyl)dimethylsilane.
112 In this experiment of copolymerization of isoprene, styrene, and (4- vinylphenyl)dimethylsilane, an initially yellow colored solution was observed indicating the start of isoprene incorporation into the polymer. After a few minutes, the yellow color intensified to give a dark orange colored solution. This was an indication of the start of incorporation of styrene monomers. This is the most noticeable feature of anionic and cationic polymerization where copolymerization can be indicated by observing changes in the color of the solution as compared to all of the other known methods of polymerization. The molar compositions of isoprene:styrene:(4- vinylphenyl)dimethylsilane in the polymers 65LowSi and and 65HighSi were
220:43:1.38 and 220:43:2.77, respectively. The GPC chromatograms of both these polymers are shown in Figures 3.34 and 3.35. As seen from the chromatograms, monomodal and narrow molecular weight distributions were observed for both polymers.
The molecular weights (Mn) as shown in Table 3.4 for 65LowSi and 65HighSi were found to be 77,900 g/mol (Mw/Mn = 1.04) and 72,200 g/mol (Mw/Mn = 1.05), based on dn/dc measured by refractive index and the light scattering detector.
140 120 100 80 60 40 RI Signal 20 0 -20 15 20 25 30 Retention Vol (mL)
Figure 3.34. GPC chromatogram of 65LowSi polymer.
113 140 120 100 80 60
RI signal 40 20 0 -20 15 17 19 21 23 25 27 29 Elution volume
Figure 3.35 GPC chromatogram of 65HighSi polymer.
Table 3.4. Molecular weight data of 65LowSi and 65HighSi polymers.
Mn Mw Mw/Mn
65LowSi 77,900 g/mol 80,800 g/mol 1.04
65HighSi 72,200 g/mol 76,000 g/mol 1.05
Both the polymers were studied using 1H NMR spectroscopy and the spectra are shown
in Figures 3.36 and 3.37. In both polymers a sharp peak at δ 4.43 ppm corresponding to
the –SiH group was observed. The Si(CH3)2 protons from the incorporation of (4-
vinylphenyl)dimethylsilane were observed at δ 0.35 ppm. These observed peaks are consistent with those reported in the literature.79 The ratio of integration values of these
two peaks was found to be 1:4.41 and 1:5.85 for 65LowSi and 65HighSi, respectively.
These ratios were very close to ~1:6 (a lower than expected ratio of integration values was observed due to very low concentration of –SiH groups, 1.38-2.77 mmol per 263 mmol of isoprene and styrene). Thus, for every silyl hydride proton there were approximately six methyl protons attached to the silicon atom consistent with incorporation of (4-vinylphenyl)dimethylsilane units into the polymer. Both polymers
114 showed strong peaks at δ 6.59 and 6.61 ppm, respectively, which correspond to ortho protons (phenyl ring) of block polystyrene.177 Both of the polymers also showed a broad peak at δ 7.16 ppm, which corresponds to ortho (non-block polystyrene), meta (block and non-block polystyrene), and para (block and non-block polystyrene) protons of phenyl rings of styrene units in the polymer.177 Thus, it can be concluded that both polymers
(65LowSi and 65HighSi) had non-block and block polystyrene in them confirming their tapered nature.
TAPERED 65-1CHLOROFORM-d STY SIH AND ISOPRENE 70KESP.ESP 1.70
TAPERED 65-1 STY SIH AND ISOPRENE 70KESP.ESP 1.70
1.0 7.27 5.15 2.07 1.70 1.62 0.9
0.8
0.7
0.6 1.62
0.5 1.62
Normalized Intensity Normalized 0.4
0.3
0.15 0.2
0.1
0 46.49 33.00
1.75 1.70 1.65 1.60 1.55 1.50 Chemical Shift (ppm)
0.10 46.49 33.00 Normalized Intensity Normalized 7.16
0.05 4.78 4.70 0.34 6.59 4.43 5.30 5.49
0 37.15 7.21 1.36 33.00 6.01
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)
Figure 3.36. 1H NMR spectrum of 65LowSi polymer.
115 TAPERED 65-2 STY SIH AND ISOPRENE 70K.ESP
1.70 2.07 1.70 1.63
TAPERED 65-2 STY SIH AND ISOPRENE 70K.ESP 1.70
1.0
0.9
0.8
0.7 0.25 0.6 1.63 0.5 1.63 5.15
Normalized Intensity 0.4
0.3
CHLOROFORM-d 0.2 0.20 0.1 0 44.55 32.66
1.70 1.65 1.60 Chemical Shift (ppm) 7.27 44.55 32.66 0.15 Normalized Intensity
0.10 7.16 0.35 4.78 0.05 4.71 6.61 4.43
0 37.03 8.74 2.07 36.32 12.35
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)
Figure 3.37. 1H NMR spectrum of 65HighSi polymer.
1H NMR spectra of both the polymers were analyzed to determine the microstructure of
the polyisoprene block. The assignment of various protons of four different
microstructures of polyisoprene is shown in equation 22. 178
1.70-1.71 1.63 4.85-5.5 CH3 H2 H CH3 H2 H C 2 H3C C C C CH C C C H2C H H C 2 H2 4.85-5.5 H2C H C CH3 2 4.78 1.62-1.63 4.71 1,2-vinyl 1,4-trans 1,4-cis 3,4-vinyl (22)
For the polymer 65LowSi, the ratio of integration values at δ 4.70-4.71, 4.78, and 4.8-5.5 ppm yielded 8% 1,2-, 8% 3,4-, and 78% 1,4-microstructure of isoprene units. The ratio of
116 integration values at δ 1.62-1.63 and 1.70 ppm yielded a 59% 1,4-cis and 41% 1,4-trans composition of the 84% 1,4- microstructure of polyisoprene. Similarly, the percentages of
1,2-, 3,4-, and 1,4-microstructure in the polymer 65HighSi were found to be 9.5%, 9.5%, and 81% (58% 1,4-cis and 42% 1,4-trans), respectively.
These polymers were subjected to 29Si NMR spectroscopic analysis to determine the
presence and type of silicon atoms in the polymer chain as shown in Figures 3.38 and
3.39. The peaks were assigned based on the reference 29Si NMR peak (δ 0 ppm) of
tetramethylsilane. One sharp peak was observed at δ -17.7 ppm in both the cases. The
peak for 65HighSi was sharper due to higher percentage of (4-
vinylphenyl)dimethylsilane. The 29Si NMR of (4-vinylphenyl)dimethylsilane was also
taken as shown in Figure 3.40. Only one peak was observed at δ 17.2 ppm, which was
assigned to the silicon atom in (4-vinylphenyl)dimethylsilane. Peaks observed in both the
polymers were consistent with the peak observed at δ 17.2 ppm for (4-
vinylphenyl)dimethylsilane. No other peaks were observed in 29Si NMR spectra of both
the polymers. This further confirmed the presence of (4-vinylphenyl)dimethylsilane units
in these polymers.
117 SINMR652LOWSI.ESP 1.0
0.9
0.8
0.7
0.6
0.5
Normalized Intensity 0.4
0.3 -17.77
0.2
0.1
140 120 100 80 60 40 20 0 -20 Chemical Shift (ppm) Figure 3.38. 29Si NMR spectrum of 65LowSi polymer.
SINMR652HIGHSI.ESP -17.75
1.0
0.9
0.8
0.7
0.6
0.5 Normalized Intensity 0.4
0.3
0.2
0.1
140 120 100 80 60 40 20 0 -20 -40 Chemical Shift (ppm) Figure 3.39. 29Si NMR spectrum of 65HighSi polymer.
118 -17.24
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
60 40 20 0 -20 -40 -60 Chemical Shift (ppm)
Figure 3.40. 29Si NMR spectrum of (4-vinylphenyl)dimethylsilane.
FT-IR analysis of both the polymers was done as shown in Figures 3.41 and 3.42. Sharp peaks at 2118 cm-1(65LowSi) and 2117 cm-1 (65HighSi) were observed in both the spectra corresponding to the –SiH groups.
119
Figure 3.41. FT-IR spectrum of 65LowSi polymer.
Figure 3.42. FT-IR spectrum of 65HighSi polymer.
120 It is clear from the above results that (4-vinylphenyl)dimethylsilane underwent successful copolymerization with styrene and isoprene. The presence of the silyl hydride groups was confirmed by 1H and 29Si NMR and FT-IR spectra. The GPC chromatograms did not show any increased molecular weight indicating no side reactions. These polymers can be used to make in-chain functional polymers which will affect the bulk properties of the polymers.
3.5. Synthesis of cyclic polybutadiene using ring opening metathesis polymerization.
Cyclic polybutadiene was synthesized by ring opening metathesis of 1,5,9- cyclododecatriene.98 The catalyst used for this polymerization was synthesized as described in the following sections.
3.5.1. Synthesis of N-mesitylimidazole
N-Mesitylimidazole (white powder, 80%) was synthesized by reaction of 2,4,6- trimethylaniline and glyoxal in presence of ammonium chloride and formaldehyde as shown in equation 23.152
CH3 1. MeOH,16 h CH3 2. NH Cl,CH O (37% aq.),1 h, 4 2 HC CH HC CH 3. H3PO4 (85% aq.), 16 h H3C NH2 + H3C N N O O C 30% aq. H CH3 CH3
2,4,6-trimethylaniline glyoxal (23)
The 1H NMR spectrum of N-mesitylimidazole is shown in Figure 3.43. The assignment of peaks is shown in the inset of Figure 3.43. As evident from the figure, the –CH peak, f, from the five membered imidazole ring was observed at δ 7.4 ppm. Vinyl peaks d and e from the double bond were observed at δ 7.2 and 6.9 ppm, respectively. Integration
121 values of these peaks were consistent with structure of N-mesitylimidazole. All the peaks
were consistent with those reported in the literature.152 The ratios of integration peaks
a:b:c:d:e:f (3.65:6.82:2:0.89:1:0.98) was very close to the expected ratios (3:6:2:1:1:1).
Nmesitylimidazole64scans.esp 1.99
0.65 0.60 b b CH 0.55 c 3 d e 2.33 0.50 CH CH H C N N 0.45 a 3 C H a 0.40
CH3 0.35 CHLOROFORM-d c f c 0.30 b 6.96 Normalized Intensity Normalized 0.25 e 0.20 f d 6.88
0.15 7.23 7.42 0.10 7.27 0.05
0 0.98 0.89 1.00 3.65 6.82
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Chemical Shift (ppm)
Figure 3.43. 1H NMR spectrum of N-mesitylimidazole.
3.5.2. Synthesis of 1H-imidazolium, 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl) bromide
(imidazolium salt).
The imidazolium salt [(1H-imidazolium, 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl)
bromide, 85%)] was synthesized by reaction of N-mesitylimidazole and 8-bromo-1-
octene in toluene shown in equation 24.
122 CH3
HC CH Toluene, 16 hr
Br H3C N N C H
CH3
CH3
HC CH Br H3C N N C H
CH3
(24)
The 1H NMR spectrum of the product is shown in Figure 3.44 and the assignment of
peaks is shown in the inset. The structure of the product was confirmed when a sharp
peak was observed at δ 1.37 ppm confirming the presence of aliphatic protons from 8-
bromo-1-octene in the molecule. New vinyl peaks m,n, and o of the octene chain were
observed at δ 5.72, 5.00, and 4.73 ppm, respectively, compared to the spectrum of the
starting material, N-mesitylimidazole (see Figure 3.43).
COMPOUND7CIMIDAZOLIUMSALT.ESP 2.07
1.0 CH3 d e HC CH 0.9 h j l n,o H3C N N Br b 0.8 C a H g i 0.7 f k m c CH3 CHLOROFORM-d 0.6 b 2.33
0.5 7.27 1.37
0.4 a h~l Normalized Intensity 6.99
0.3 n,o g
0.2 c m 4.73
f e 5.00
10.46 d 5.72
0.1 7.78
0 0.74 0.87 2.00 0.91 3.93 3.3410.23 5.79
10 9 8 7 6 5 4 3 2 1 Chemical Shift (ppm)
Figure 3.44. 1H NMR spectrum of imidazolium salt (1H-Imidazolium, 1-(7-octen-1-yl)-3-
(2,4,6-trimethylphenyl) bromide) (CDCl3).
123 3.5.3. Synthesis of ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)(tricyclohexylphosphine)
(linear catalyst).153
Imidazolium salt (1H-imidazolium, 1-(7-octen-1-yl)-3-(2,4,6-trimethylphenyl) bromide) was treated with benzylidene-bis(tricyclohexylphosphine)dichlororuthenium (Grubb’s first generation catalyst) and potassium t-butoxide in toluene as shown in equation 25.
CH3
HC CH
H3C N N Br C H
CH3 CH3
t-BuOK/ Toluene, rt, 1.5 h HC CH
H3C N N PCy3 Cl Cl Ru C Ph H C Ph CH3 Ru Cl H PCy3 Cl PCy3 (25)
The final product ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)(tricyclohexylphosphine)
(linear catalyst, 71%) was obtained as red powder after filtration and column
chromatography through a silica gel column using a pentane and ether (4:1, v:v) mixture.
The 1H NMR spectrum of the linear catalyst is shown in Figure 3.45. In addition to peaks
from imidazolium salts as assigned in Figure 3.44, one very distinct new peak was
observed at δ 19.26 ppm (reported value δ 19.24 ppm153). This peak corresponds to the
153 =CHC6H5 group next to the ruthenium atom. Such a high downfield shift is observed
due to presence of strong electron withdrawing groups attached to ruthenium. The linear
catalyst was further analyzed by 31P NMR spectroscopy (based on external phosphoric
124 acid standard at δ 0 ppm) and the spectrum is shown in Figure 3.46. The presence of just one peak at δ 34.3 ppm (reported value δ 34.1 ppm153) in the 31P NMR spectrum of the catalyst confirmed the presence of tricyclohexylphosphine ligand on the linear catalyst.
All the peaks in 1H and 31P NMR were consistent with those reported in the literature.153
12CH1.ESP 1.27 1.65
1.0 CH3
HC CH 1.93 0.9
H3C N N 0.89
0.8 Cl CH Ru C Ph 3 H 0.7 Cl PCy3
0.6
0.5 0.87 Normalized Intensity 0.4 7.27 2.37 0.3 7.13 0.08 19.26 0.84 4.72 0.2 6.81 4.74 7.41 4.69 7.43 4.98 5.06
0.1 6.31
0 22 20 18 16 14 12 10 8 6 4 2 0 -2 -4 -6 Chemical Shift (ppm)
Figure 3.45. 1H NMR spectrum of linear catalyst.
125 12CP31.ESP 34.31
1.0
CH3 0.9 HC CH
0.8 H3C N N
0.7 Cl CH Ru C Ph 0.6 3 H Cl PCy3 0.5 Normalized Intensity Normalized 0.4
0.3
0.2
0.1
40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 -35 Chemical Shift (ppm)
31 Figure 3.46. P NMR spectrum of linear catalyst (H3PO4).
3.5.4. Synthesis of ruthenium dichloro[1-heptanyl-7-ylidene[3-(2,4,6-trimethylphenyl)-
1H-imidazol-1-yl-2(3H)-ylidene]](tricyclohexylphosphine) (cyclic catalyst).
The cyclic catalyst (ruthenium dichloro[1-heptanyl-7-ylidene[3-(2,4,6-trimethylphenyl)-
1H-imidazol-1-yl-2(3H)-ylidene]](tricyclohexylphosphine)), was synthesized by heating the linear catalyst in hexane under high vacuum at 68 oC as shown in Scheme 3.6.
126 CH3
HC CH
H3C N N
Cl CH Ru C Ph 3 H Cl PCy 3 n-Hexane reflux 1h CH3
HC CH
H3C N N
Cl
CH3 Ru Cl 3 PCy3
Scheme 3.6. Cyclization of ruthenium dichloro[1,3-dihydro-1-(7-octenyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene](phenylmethylene)(tricyclohexylphosphine)
It was then purified by passing through a silica gel column using a mixture of pentane
and ether (4/1, v/v). The peak corresponding to the =CH- group next to the ruthenium
atom was shifted from δ 19.26 ppm in the linear catalyst to δ 19.72 ppm (reported value δ
20.22 ppm153) in the cyclic catalyst as shown in the 1H NMR spectrum (Figure 3.47). The cyclic catalyst was analyzed by 31P NMR spectroscopy (based on phosphoric acid as an
external standard at δ 0 ppm) and the spectrum is shown in Figure 3.48. A sharp peak
(based on phosphoric acid as an external standard at δ 0 ppm) at δ 28.9 ppm (reported
value δ 26.3 ppm179) corresponding to tricyclohexylphosphine ligand of the cyclic
catalyst was observed. All the peaks in the 1H and 31P NMR spectra were consistent with
those reported in the literature.153
127 CYCLICPUREH1.ESP 7.27 2.32 1.27 0.89 1.73 N N 0.09
Cl 0.87 0.08 Ru 0.07 Cl 3 PCy3 0.06
0.05 Normalized Intensity
0.04 6.99 0.84
0.03 3.74
0.02 6.84 19.72 0.01
0 22 20 18 16 14 12 10 8 6 4 2 0 -2 -4 Chemical Shift (ppm)
1 Figure 3.47. H NMR spectrum of the cyclic catalyst (CDCl3).
128 CYCLICCATAPUREP31.ESP 28.94
1.0
0.9
0.8 N N
0.7 Cl
0.6 Ru Cl 0.5 3 PCy3 Normalized Intensity 0.4
0.3
0.2
0.1
40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 -35 Chemical Shift (ppm)
31 Figure 3.48. P NMR spectrum of the cyclic catalyst (CDCl3).
3.5.5. Synthesis of cyclic polybutadiene by ring opening metathesis polymerization
(ROMP).
Cyclic polybutadiene was synthesized by ring opening metathesis polymerization
(ROMP) of 1,5,9-cyclododecatriene using the cyclic catalyst in dichloromethane as shown in equation 26.
129 (n+2)
N N
Cl
Ru CH2Cl2, Vacuum, Cl o n 3 40 C, 14 h PCy3
(26)
In 2002, Bielawski and coworkers97 first reported the synthesis of cyclic polymers from cyclooctene using cyclic catalyst via ROMP. In 2003, cyclic polybutadiene was made from 1,5,9-cyclododecatriene using the same cyclic catalyst via ROMP.98 GPC chromatography was used to prove the cyclic nature of polybutadiene (CyPBD). It was reported that cyclic polybutadienes exhibited longer elution volumes compared to their linear analogues (LPBD). In other words, for the same molecular weight, CyPBD had a more compact size than LPBD. The intrinsic viscosities of the cyclic polybutadiene were also shown to be lower for the analogous LPBDs.
In this research, grafting of cyclic polybutadiene was achieved via hydrosilation reaction as shown in equation 27 in order to prove the cyclic nature of the polybutadiene.
130
m m
m
Si m Si Si m Si Si
Karstedt's catalyst, m o m
80 C, 24 h Si Si m
Si Si m H Si m Si Si
m m n m Si Si m
m Si Si m Si Si
m m Si Si
m Si m
m
(27)
A similar GPC (coupled with RI, viscometer, and light scattering detectors) analysis was done for the linear and cyclic polybutadienes prepared in this research. The GPC chromatograms (RI detector response) of CyPBD and LPBD are shown in Figure 3.49. A plot of molecular weight (log scale) versus elution time can also be seen in the same figure (Figure 3.49). Based on the GPC data, Mn, Mw, and Mw/Mn for CyPBD were found
to be 88,400 g/mol, 182,600 g/mol, and 2.06, respectively. For LPBD, Mn, Mw, and
Mw/Mn were found to be 52,000 g/mol, 69,000 g/mol, and 1.46, respectively. Molecular
weights determined were absolute based on light scattering data. As seen from Figure
3.49 (log molecular weight versus elution time), for the same elution time the cyclic
polymer has a higher molecular weight compared to the linear polymer indicating its
compact nature. A plot of intrinsic viscosity (log scale) as a function of molecular weight
(log scale) for CyPBD and LPBD is shown in Figure 3.50. It can be seen that, for the
same molecular weight CyPBD exhibits a lower intrinsic viscosity than LPBD. This
131 indicates that cyclic chains have a smaller hydrodynamic volume compared to linear
chains (LPBD).
1.0x106
1.0x105 molar mass (g/mol) mass molar
35.0 40.0 45.0 time (min) Figure 3.49. Log molecular weight and RI signal versus elution time for cyclic (blue curve) (Mn = 88,400 g/mol ,Mw/Mn = 2.06) and linear (red curve) polybutadiene (Mn =
52,000 g/mol ,Mw/Mn = 1.46).
Figure 3.50. Intrinsic viscosity versus molecular weight for cyclic (blue curve) (Mn =
88,400 g/mol ,Mw/Mn = 2.06) and linear (red curve) polybutadiene (Mn = 52,000 g/mol
,Mw/Mn = 1.46).
3.5.6. Synthesis and characterization of cyclic polybutadiene grafted with silyl hydride- functionalized polystyrene
Even though all of the above GPC analysis indicated the compact nature of CyPBD, it did not, however, confirm necessarily the cyclic nature of CyPBD. A new attempt, hence, was made to prove the cyclic nature of CyPBD. For this purpose, grafting of CYPBD was
132 desired as discussed in section 1.4.2. Grafting onto the cyclic polybutadiene was done
with PS-SiH as shown in equation 27. The linear polymer used for grafting (PS-SiH, Mn
1 = 8,300 g/mol, Mw / Mn = 1.01) was analyzed by GPC, and H NMR and FT-IR
spectroscopy. As shown in the GPC chromatogram of PS-SiH (Figure 3.51), a
monomodal distribution was obtained with a narrow polydispersity index ( Mw/ Mn =
1.01). The 1H NMR (Figure 3.52) showed a distinct peak at δ 3.68 ppm corresponding to
–SiH group79 of PS-SiH. FT-IR spectrum (Figure 3.53) showed presence of –SiH group
in PS-SiH (2111 cm-1).12
800
700
600
500
400
RI Signal RI 300
200
100
0 15 20 25 30 Elution Volume (mL)
Figure 3.51. GPC chromatogram of PS-SiH.
133 B2P35NEWER.ESP 6.99 6.49 1.76 1.34
0.15
0.10 Normalized Intensity Normalized 7.27
0.05 0.61 -0.20 3.68
0 1.00 6.53
7 6 5 4 3 2 1 0 Chemical Shift (ppm)
Figure 3.52. 1H NMR spectrum of PS-SiH.
Figure 3.53. FT-IR spectrum of PS-SiH
134 The grafted polymer was obtained after fractionating the reaction mixture using toluene
and methanol as described in section 2.6.13. The grafting efficiency of the PS-SiH chains
was found to be 0.98% based on the mass of the grafted product obtained (mass of
grafted product / sum of mass of cyclic polybutadiene and PS-SiH = 0.02 x 100/ 2.03 =
0.98%). The molecular weight data for these polymers is summarized in Table 3.5.
Figure 3.54 shows the GPC curves of the starting polymers and the products of the
grafting reaction. It can be seen that the high molecular weight grafted polymer elutes
much earlier compared to CyPBD and PS-SiH. Its broad PDI suggests varied degrees of
grafting on CyPBD because of bulky nature of PS-SiH. The difference between the
molecular weight (Mn) of CyPBD and grafted ring was found to be 1,915,600 g/mol. The
ratio of this difference in molecular weight (1,915,600 g/mol) and the molecular weight
(Mn) of PS-SiH (8,300 g/mol) yielded an estimate of the number of grafted PS-SiH chains as 230 per molecule of CyPBD. This is consistent with a significant amount of grafting of PS-SiH by hydrosilation.
Table 3.5. Molecular weight data of cyclic polybutadiene and grafted cyclic polybutadiene.
Sr.No Sample ID Mn (g/mol) Mw (g/mol) Mw/Mn
1 PSSiH 8,300 8,400 1.01
2 CyPBD 88,400 182,000 2.06
3 Grafted Ring 2,004,000 12,400,000 6.19
135 SEC curves
RALS of CyPBD RALS of PSSiH RALS of Grafted Ring Light Scattering Intensity Scattering Light
10 15 20 25 30 Elution Volume (mL)
Figure 3.54. GPC chromatograms (light scattering detector response) of cyclic polybutadiene (CyPBD, blue curve), linear silyl hydride-functionalized polystyrene
(PSSiH, purple curve), and grafted ring (red curve).
The grafted polymer (5 x 10-4 M) was dissolved in toluene. The polymer solution was
cast by putting a drop of the above solution on a clean mica wafer. The mica wafer was then dried at room temperature for 24 hours. AFM analysis of this mica wafer was done in tapping mode and the obtained images are shown in Figure 3.55. Rings were observed on the sample prepared with 5 x 10-4 M solution. Samples prepared with two lower concentrations of solution were also imaged but no rings were observed. Several spots on the 5 x 10-4 M solution samples were imaged. However, rings were not observed in every
spot. This indicated that the rings did not uniformly cover the sample surface when
prepared via drop casting.
The inner diameter of the cyclic rings (shown in Figure 3.55) was found to be 14 nm (± 4
nm), whereas the outer diameter was found to be 76 nm (± 13 nm). The height of the ring
136 was found to be 7 Å (± 3 Å). The variations in height indicated either that the rings were
not lying flat on the mica substrate or that a large difference in grafting density was
present. SPMLab Analysis was used to calculate the average inner and out diameter
diameters of the ring as well as the standard deviations from line cuts through the AFM
image. Representative line cuts are presented in Appendix D. The diameters were
measured from the middle of the rising slope to the middle of the declining slope instead
of from bottom edge to bottom edge. This was done to account for tip convolution180 of
an 8-10 nm diameter tip. As seen from Figure 3.55 and Table 3.5 (Mw/Mn for grafted ring
= 6.19) the distribution of the chain sizes observed in the image was not representative of
the distribution before grafting since only 1% of the cyclic polymer was grafted. There
could be a possibility of fractionation while preparing the polymer solutions for AFM imaging.
Bigger rings with the same average amount of grafting would appear thicker (taller height), wider (larger outer diameter) or both. No chain scission was observed in the
AFM images. No half circles or arcs were observed either. There was also no evidence of linear polymer observed during imaging. The images shown in Figure 3.55 were consistent with grafting of cyclic polybutadiene as shown in equation 27. The rings in the images are expected to each be a single molecule since each of the starting polybutadiene molecules is cyclic in nature. The rings imaged were very stable. There was no observable difference between the images after scanning in x- and y-direction and no rings were translated due to the tip motions. Tip wearing was observed when the same spot was scanned multiple times causing a slight reduction in the observed inner diameter of the rings. The presented images were recorded before any tip wearing was observed.
137 The noise in the images was low and the rings were observed above the noise level. Piezo
bending was taken into account when the images were leveled. “Ghost” rings (Figure
3.55) were found to have lower heights in the z-direction than the other observed rings.
The lower height may be due to lower polystyrene grafting density compared to the other
rings.
Figure 3.55. AFM image of cyclic polybutadiene grafted with PS-SiH.
Based on the number average molecular weight of 88,000 g/mol for cyclic polybutadiene, the average degree of polymerization is calculated to be 1629. As shown in equation 28, each repeat unit has 2 single bonds with a length of 1.54 Å181 each and 1 double bond with a length of 1.34 Å.181 Considering the bond angle between the two
single bonds (120o)182, the average length of a monomer unit can be calculated to be 0.44
nm (1.54 x cosine 60 + 1.54 x cosine 60 + 1.54 + 1.34) = 4.4 Å = 0.44 nm.
0.13 nm
0.15 nm
(28)
138 Thus, the length of the polymer chain (circumference in case of cyclic polymer) can be
estimated to be 716 nm. Using this length as a circumference of the polymer chain, the
diameter of cyclic ring is calculated to be 228 nm. This expected value was based on the
following assumptions: 1) all parts of the ring would lay flat on the mica surface, 2) the
rings would not overlay on top of each other or be twisted, and 3) the rings would be
stretched. The assumption of the ring backbone laying flat on the substrate was highly
ideal. The radius of gyration of the grafted polystyrene side chains was calculated to be 5
nm. The thickness of the ring due to these grafted polystyrene rings was calculated to be
10 nm assuming that there would be some grafted chains on the inside and some grafted
chains on the outside of the ring. Thus, the calculated difference between outer and inner
diameter would be ~20 nm (taking into account the chain thickness from both the sides of
the ring). There would be a slightly higher probability that the grafted chains would tend
to lie outside of the ring because of increased volume available outside the ring relative to
the inside of the ring. A larger than calculated difference between inner and outer
diameter was observed in the images. This can be partially attributed to the tip
convolution180. It may also be due to an incorrect assumption that each grafted side chain
will be in the form of a Gaussian coil. If the grafted chains are stretched the ring
backbone will be thicker than if the grafted chains are all in a Gaussian coil.
Based on the above results, successful hydrosilation was carried out on cyclic polybutadiene. This new technique was used to graft the cyclic 1,4-butadiene units with silyl hydride-functionalized polystyrene. Increased molecular weight indicated successful grafting of polystyrene on cyclic polybutadiene. This result was also supported by AFM imaging.
139 3.6. Carbocationic polymerization
Isobutylene was polymerized via cationic polymerization using 2-chloro-2,4,4-
trimethylpentane (TMPCl) as an initiator and then reacted with (4-
vinylphenyl)dimethylsilane. A diblock copolymer as shown in Scheme 3.7 was expected
to form.
TiCl4 Cl
TiCl5
TMPCl IB
Hexanes/ MeCl, 60/40 (v/v), Si -70 oC H Si VPDS H
Scheme 3.7. Expected structure of diblock copolymer synthesized from isobutylene and
(4-vinylphenyl)dimethylsilane.
3.6.1. Synthesis of 2-chloro-2,4,4-trimethylpentane (TMPCl).
2-Chloro-2,4,4-trimethylpentane (TMPCl) was synthesized by passing HCl gas through
2,4,4,-trimethyl-1-pentene (TMP) as shown in equation 29 .
o HCl, 0 C Cl
(29)
The 1H NMR spectrum of TMPCl is shown in Figure 3.56. Peaks were assigned to the
molecule as shown in the inset of Figure 3.56. Since no vinyl peaks were observed
between δ 4-6 ppm, it was concluded that the product was obtained in quantitative yield.
The observed peaks were in good agreement with those reported in the literature.122, 183-185
140 TMPCL DISTILLED JAN 19 2010.ESP 1.07
1.0 c 0.9
0.8 1.68
0.7 Cl
0.6 b a
0.5 a c
0.4 Normalized Intensity Normalized
0.3
CHLOROFORM-d 1.89
0.2 b 7.27 0.1
0 2.00 5.74 8.72
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)
Figure 3.56. 1H NMR spectrum of 2-chloro-2,4,4-trimethylpentane.
3.6.2. Reaction of polyisobutyl cations with (4-vinylphenyl)dimethylsilane
After polymerizing isobutylene, a base sample of polyisobutylene (PIBCl) was taken and the remaining solution was treated with a precooled solution of (4- vinylphenyl)dimethylsilane. The treated polymer (PIBVPDS) was quenched with precooled solution of methanol. Both the polymers PIBCl and PIBVPDS were dried under vacuum for 3 days and analyzed by GPC (coupled with refractive index, viscometer, and light scattering detectors).
700 600 500 400
300 200
RI detector response detector RI 100
0 10 15 20 25 30 35 a) Retention Vol (mL)
141 790 780 770 760 RALS 750 740 730 10 15 20 25 30 35 b) Retention Vol (mL)
Figure 3.57. GPC chromatograms a) RI detector b) light scattering detector response for
PIBCl (blue curve) and PIBVPDS (purple curve) as a function of elution volume.
The GPC chromatograms (RI detector response and light scattering detector response) of PIBCl and PIBVPDS as a function of elution volume are shown in Figure 3.57. As indicated in the RI detector response (Figure 3.57 a) both PIBCl and PIBVPDS elute at the same elution volume indicating that they have the same molecular weight. Light scattering data (Figure 3.57 b) showed the same trend. This showed that there was no significant difference between the molecular weights of PIBCl and PIBVPDS. The molecular weight data (Mn, Mw and PDI ) of PIBCl and PIBVPDS are summarized in
Table 3.6. As seen from the table there is no significant difference between the molecular weights of PIBCl and PIBVPDS. Polydispersity indices (PDI) of both the polymers were also similar.
Table 3.6. Molecular weight data of PIBCl and PIBVPDS.
Polymer Mn Mw Mw/ Mn
(g/mol) (g/mol) PIBCl 1,600 2,000 1.25
PIBVPDS 1,700 2,200 1.27
142
The 1H NMR spectrum of PIBCl is shown in Figure 3.58. The peaks are assigned to
PIB-Cl chains based on the reported literature122, 183-185 as shown in the inset of Figure
3.58. The resonances of the terminal –CH3 and –CH2 groups were observed at δ 1.70 and
1.98 ppm, respectively.122, 183-185
B4P33 proton on 500 MHz newest 64 scans 5 s relax delay.esp 1.12
0.55
0.50 1.70
0.45 Cl 0.40 1.43 1.43 1.43 0.35 1.12 1.12 0.30 1.98
0.25
Normalized Intensity CHLOROFORM-d 0.20
0.15 7.27
0.10 1.70
0.05 1.98
0 2.005.80 312.50
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)
Figure 3.58. 1H NMR spectrum of PIBCl.
The proton NMR spectrum of PIBVPDS is shown in Figure 3.59. It can be seen that the
peaks from the terminal –CH3 (δ 1.70 ppm) and –CH2 (δ 1.98 ppm) groups from PIBCl
are no longer present in PIBVPDS. A small peak at δ 1.70 ppm is observed which
corresponds to the terminal –CH group.122
Both polymers were also analyzed by 13C NMR spectroscopy. Figure 3.60 shows the
13C NMR spectrum of PIBCl. The assignment of the peaks based on the reported
143 literature183-185 is shown in structure A. The most notable peak was observed at δ 71.71
ppm which corresponds to the terminal tertiary carbon bonded to a chlorine group (-C-
Cl).183-185 When PIBVPDS was analyzed by 13C NMR spectroscopy (Figure 3.61), the
peak at δ 71.71 ppm was no longer present. The structure assignments of 13C NMR peaks
of PIBVPDS are shown in the structure B based on the reported literature.122, 183-185 A new peak at δ 24.23 ppm was observed which was assigned to terminal –CH group.122
122 The peak at δ 55.23 ppm corresponds to the –CH2 group next to terminal –CH group.
B4P33 PART 2 ON 500 MHZ NMR 64 SCANS.ESP
CHLOROFORM-d 1.43 1.13 1.11
0.065 7.27 0.060
H 0.055 1.43 1.43 n
0.050 1.12 1.12 0.92 1.70
0.045 1.43 1.13 1.11
0.040 0.92 0.035
0.030 Normalized Intensity Normalized 1.70 0.025
0.020 1.70
0.015 1
0.010 1.70
0.005
9 8 7 6 5 4 3 2 1 0 Chemical Shift (ppm) Figure 3.59. 1H NMR spectrum of PIBVPDS.
144 B4P33 PIBCL C13 SPECTRA.ESP CHLOROFORM-d 77.00 38.19
0.30 31.23
0.25 59.58
0.20 Normalized Intensity 0.15
0.10 37.82 32.61
0.05 58.26 58.89 71.71 35.19 36.02
104 96 88 80 72 64 56 48 40 32 24 Chemical Shift (ppm)
Figure 3.60. 13C NMR spectrum of PIBCl
32.61 38.19 32.61 36.02 71.71
Cl 32.61 58.26 n 32.61 31.23 59.58 58.89 (A)
145 cdcl3_01 38.21
1.0
0.9 31.31
0.8
0.7
0.6
0.5 59.59 Normalized Intensity 0.4 CHLOROFORM-d 0.3
0.2 77.00 32.52 58.27 25.88 58.90 29.61 36.09
0.1 24.23 55.23 56.64
96 88 80 72 64 56 48 40 32 24 16 Chemical Shift (ppm)
Figure 3.61. 13C NMR spectrum of PIBVPDS.
The assignment of peaks based on the reported literature122, 183-185 is as follows: 32.52 31.31 36.09 38.21 32.52 24.23
H 32.52 32.52 59.59 31.31 36.09 58.27 55.23 (B)
It is proposed that the formation of PIBVPDS involves hydride transfer from the silane
and the mechanism of hydride transfer is shown in Scheme 3.7.121, 186, 187 The type of reaction was shown to be first order with respect to both carbenium ion and silane concentration.121, 186, 187 The rate determining step is the hydride transfer from (4-
vinylphenyl)dimethylsilane to PIBC. It is followed by rapid reaction with the counterion
- (Ti2Cl9 ) to yield (4-vinylphenyl)dimethylchlorosilane. Thus, contrary to expected
146 diblock structure (Scheme 3.7) a saturated chain of polyisobutylene was obtained with a
terminal hydrogen group. Based on 1H and 13C NMR spectroscopy and GPC results, it was concluded that the hydride transfer from (4-vinylphenyl)dimethylsilane was preferred over addition to vinyl group.
Initiation
2 TiCl4 Cl Ti2Cl9
TMPCl
Propagation
n
IB Ti2Cl9 Ti2Cl9
Hydride Transfer VPDS
Si H H + Ti2Cl9 Si
Rate determining step Ti2Cl9
A Rapid
2 TiCl4 +
Si Cl Scheme 3.8. Mechanism of reaction between (4-vinylphenyl)dimethylsilane and
polyisobutyl carbenium ion.
147 3.7. Synthesis of superhydrophobic surfaces by electrospinning.
An attempt was made to synthesize superhydrophobic surfaces from fluorinated styrene butadiene rubber. First, styrene butadiene rubber was functionalized with tridecafluoro-
1H,1H,2H,2H-octyldimethylsilane to obtain fluorinated polymer. Superhydrophobic surfaces were made using this polymer via electrospinning.
3.7.1. Synthesis of tridecafluoro-1H,1H,2H,2H-octyldimethylsilane (TDFS).
Tridecafluoro-1H,1H,2H,2H-octyldimethylsilane (TDFS) was synthesized by reduction of (1 H, 1 H, 2H, 2H-tridecafluorooctyl) dimethylchlorosilane using LiAlH4 as shown in
equation 30.156, 157
1 eq. LiAlH4 F2 Si C F2 Si C Cl C CF3 F2 Diethyl ether H C CF3 F 4 0 oC 2 4
(30)
The 1H NMR spectrum of TDFS is shown in Figure 3.62. The assignment of the peaks of
TDFS as shown in the inset of Figure 3.62 was based on the reported literature.156, 157 A
peak at δ 3.94 ppm was assigned to the –SiH group of TDFS. Integration values of the proton peaks were consistent with the expected structure of TDFS. An FT-IR spectrum was obtained to analyze the structure of TDFS as shown in Figure 3.63. A strong signal at
2126 cm-1 confirmed the presence of the –SiH group.
148 1H Tridecafluoro-1H,1H,2H,2H-octyldimethylsilane.esp 0.15
0.9 F d 2 F2 F2 b C C C 0.8 H F3C C C F Si 0.7 2 F2 c a 0.6
0.5 c
0.4 Normalized Intensity
0.3 b d a CHLOROFORM-d 0.2 0.86 2.10 3.94
0.1 7.27
0 1.00 2.08 2.01 5.54
10 9 8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 3.62. 1H NMR spectrum of TDFS.
Figure 3.63. FT-IR spectrum of TDFS.
149
3.7.2. Fluoro functionalization of styrene butadiene rubber C1205 (C1205Fluoro)
Fluoro groups impart low surface energy to the polymers.134 Various functional and graft
copolymers have been synthesized by reacting the 1,2-vinyl groups (-CH=CH2) of
polybutadiene with a variety of silanes via hydrosilation reactions.166, 188-193 Thus,
analysis of microstructure of the tapered styrene butadiene block copolymer (C1205) was
necessary in order to evaluate the percentage of 1,2-vinyl groups of polybutadiene in the
molecule. Figure 3.64 shows the 1H NMR spectrum of C1205. Peaks from the terminal
178, 194 1,2-vinyl protons (=CH2) of butadiene units are observed at δ 5.00 ppm. Peaks at δ
5.39 ppm and 5.43 ppm represent vinyl proton signals from 1,4-cis and 1,4-trans (-
CH=CH-), respectively.178, 194 Peaks from non terminal 1,2-vinyl butadiene units (-CH=) are observed at δ 5.58 ppm. After taking ratio of the integration values at δ 4.97 ppm
(twice the number of protons from the 1,2-vinyl groups), and δ 5.39-5.58 ppm, the percentage of 1,2-vinyl groups on polybutadiene units was calculated to be 6.98%.
Presence of blocky polystyrene on the C1205 polymer was confirmed by a peak at 6.58 ppm.177
150 C1205N.ESP 2.05
0.7
0.6
0.5
CHLOROFORM-d 0.4 5.43 5.39
0.3 7.27 Normalized Intensity Normalized
0.2 1.45
0.1 7.12 4.97 6.58 5.58
0 10.61 1.00
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)
Figure 3.64. 1H NMR spectrum of C1205.
After determining the percentage of 1,2-vinyl groups, fluoro functionalization of C1205 was done using TDFS (1.5 equivalents compared to moles of 1,2-vinyl groups on polybutadiene) as shown in structure C. The final product (C1205Fluoro) was
precipitated in methanol and dried under vacuum. The 1H NMR spectrum of
C1205Fluoro is shown in Figure 3.65. Peaks from the terminal 1,2-vinyl protons at δ 5.00
ppm disappeared completely consistent with successful grafting of TDFS onto the
polymer chain. New peaks at δ 0.74 and 0.48 ppm were observed that correspond to the –
156, 157 CH2 and –CH2Si groups of TDFS grafted onto the polymer chain. A sharp peak at δ
0.02 ppm is observed which corresponds to methyl protons attached to the Si atom of
TDFS.156, 157 The 19F NMR spectrum of C1205Fluoro revealed fluorine peaks
corresponding to the grafted TDFS units as shown in Figure 3.66. Assignment of peaks to
the six types of individual fluorine atoms based on the reported literature156, 157 is shown
151 in structure D. C1205Fluoro was also subjected to FT-IR analysis as shown in Figure
3.67. No –SiH peak was observed near 2100 cm-1 consistent with complete grafting of
TDFS on C1205.
Mn = 68,600 g/mol, 6.98% 1,2-vinyl groups
F F F F F F Karstedt's catalyst, Si Tolune, 48 h, R.T. H F F F 1.5 eq. F F F
Si
F F
F F
F F
F F
F F
F F
F (C)
152 B4P57 AFTER 2 DAYS.ESPCHLOROFORM-d 7.27 2.05
1.0
0.9 0.03
0.8
0.7
0.6 5.42
0.5 Normalized Intensity Normalized 0.4
0.3 1.41 0.73 0.2 0.48 2.69 6.00 6.59 0.1
0 2.00 2.10 5.31
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 3.65. 1H NMR spectrum of C1205Fluoro.
153 B4P57FLUNMR128NEWERSCANS.ESP -85.60
1.0
0.9
0.8
0.7 -130.96 0.6 -128.04 -126.78 0.5 -120.89 Normalized Intensity 0.4
0.3
0.2
0.1
-72 -80 -88 -96 -104 -112 -120 -128 -136 -144 -152 Chemical Shift (ppm)
Figure 3.66. 19F NMR spectrum of C1205Fluoro.
Si
-120.89 F F
F F -126.28
-127.70 F F
F F -128.04
-130.96 F F
F F
F -85.60
(D)
154
Figure 3.67. FT-IR spectrum of C1205Fluoro
GPC chromatograms of C1205 and C1205Fluoro are shown in Figure 3.68. The
molecular weight (Mn) of C1205 was 68,600 g/mol with a polydispersity index of 1.02.
The GPC chromatogram of C1205Fluoro was shifted towards lower elution volume
indicating an increase in molecular weight as expected. The molecular weight (Mn) and polydispersity index (Mw/Mn) of C1205Fluoro were found to be 138,000 g/mol and 1.26,
respectively. This broadened molecular weight distribution (as compared to C1205,
Mw/Mn = 1.02) was an indication of vinyl group coupling previously described in the
literature195 during hydrosilation reactions in presence of transition metal catalysts. DSC
analyses of C1205 and C1205Fluoro were done and the results are shown in Figure 3.69.
Based on the DSC results, the Tg of polybutadiene block from C1205 was found to be -91
o 196 o C (reported Tg -95 C). After grafting C1205 with TDFS, the Tg of polybutadiene
o block increased to -69 C. The increased Tg was an indication of the highly polar nature
155 of side chains. Highly polar side chains tend to restrict the motion of polybutadiene
molecules due to hydrogen bonding that occurs between highly polar fluoro groups and
hydrogen atoms on the backbone.
Figure 3.68. GPC chromatograms of C1205 and C1205Fluoro.
Figure 3.69. DSC curves of C1205 and C1205Fluoro.
3.7.3. Electrospinning and characterization of electrospun fibers
Both C1205 and C1205Fluoro polymers were electrospun from a mixture of DMF:THF
(25:75, vol:vol; 10% polymer by wt) as solvent. Figures 3.70 and 3.71 show the SEM images of C1205 electrospun fibers. The SEM image of C1205 electrospun fibers showed
156 a beaded structure connected by long fibers as seen in Figure 3.70. The average bead
diameter of C1205 electrospun fibers was 14.8 μm with a standard deviation of 4.5 μm.
The average bead diameter was determined after taking 50 measurements from SEM
images of the C1205 electrospun fiber. Beaded structure in electrospun fibers is attributed
to increased surface tension forces compared to electrostatic forces. 197 Electrostatic
forces pull the fiber in the forward direction whereas forces due to surface tension oppose
this forward movement. These opposing forces cause beading when forces due to surface
tension overcome the forward electrostatic force.
No beading was observed when the C1205Fluoro polymer was electrospun under the
same conditions (Voltage 30 KV, d = 25 cm, and flow rate = 25 mL per hour) as shown
in Figure 3.71. This change can be attributed to the presence of low energy fluoro groups on C1205Fluoro. These groups will reduce the surface tension of the C1205Fluoro solution. Thus, forces due to surface tension do not overcome electrostatic forces. Thus, smooth fibers were observed (Figure 3.71). The average diameter of C1205Fluoro fibers was found to be 800 nm with a standard deviation of 490 nm.
157
Figure 3.70. SEM image of electrospun C1205 fiber.
Figure 3.71. SEM image of C1205Fluoro electrospun fiber.
158
The water contact angles of the electrospun fiber mats of both C1205 and C1205Fluoro polymers were measured. The contact angle for C1205 fiber mat (Figure 3.73) was found to be 151.2o with a standard deviation of 2.4o. The contact angle for C1205 spun coat film
(Figure 3.72) on the other hand was found to be 90.5o with a standard deviation of 1.8o.
The increased contact angle can be attributed to higher surface area of C1205 electrospun
fibers.134, 135
Figure 3.72. Contact angle picture of spun coated film of C1205.
159
Figure 3.73. Contact angle picture of electrospun mat of C1205.
The contact angle for the C1205Fluoro fiber mat was found to be 162.8o with a standard
deviation of 3.8o (Figure 3.75). The contact angle for C1205Fluoro spun coat film (Figure
3.74) was found to be 84.3o with a standard deviation of 6.2o. The increased contact angle
can be attributed to combined effect of higher surface area of C1205Fluoro electrospun
fibers and the low surface energy of fluoro groups on C1205Fluoro polymer.134, 135
160
Figure 3.74. Contact angle picture of spun coated film of C1205Fluoro.
Figure 3.75. Contact angle picture of electrospun mat of C1205Fluoro.
161 3.8. Synthesis of pyrrolidine-functionalized styrene butadiene rubber
Pyrrolidine-functionalized styrene butadiene rubber was synthesized (Scheme 3.9)
similar to the synthesis of pyrrolidine-functionalized polystyrene described in a previous
section (section 3.2). Chloromethyldimethylsilane-functionalized styrene butadiene
rubber (C1205-chloro) was obtained (113%) after hydrosilation reaction of styrene
butadiene rubber (C1205, Mn = 68,600 g/mol, Mw/Mn = 1.02, 1.86 mmol 1,2-vinyl
groups) with chloromethyldimethylsilane (2.8 mmol). A higher than expected yield
suggested that the hydrosilation reaction may also be occurring at 1,4-butadiene units of
C1205.
Figure 3.76 shows 1H NMR spectrum of chloromethyldimethylsilane-functionalized
styrene butadiene rubber (C1205-chloro) It can be seen that, after the reaction with
chloromethyldimethylsilane, peaks due to the terminal 1,2-vinyl group (4.98 ppm) of butadiene units of C1205 disappeared completely. Two new peaks at δ 0.08 and 2.79 ppm
167 corresponding to –Si-CH2Cl and –Si(CH3)2 groups were observed. Pyrrolidine- functionalized styrene butadiene rubber (C1205-N, 71%) was obtained after reacting chloromethyldimethylsilane-functionalized styrene butadiene rubber (C1205-chloro, 2.80 mmol chloro groups) with pyrrolidine (5.60 mmol). Figure 3.77 shows the 1H NMR spectrum of pyrrolidine-functionalized styrene butadiene rubber (C1205-N). It can be seen that the peak at δ 2.79 ppm (from –SiCH2Cl group, Figure 3.76) disappeared
completely. A new peak at δ 2.52 ppm corresponding to –N-CH2- (from pyrrolidine ring)
168 was observed. The ratio of integration values of the peaks from the –N-CH2- group
(from pyrrolidine ring) and –Si(CH3)2 was found to be 1.31 (1.50 based on
stoichiometry).
162 Hydrosilation HSi Cl Karstedt's catalyst
Si
H o 50 C, 2 eq. Cl 2 da, Toluene N
Si
N
Scheme 3.9. In-chain, amino functionalization of styrene butadiene rubber.
163 B4P51 C1205 AND CHLOROMETHYLDIMETHYLSILANE AFTER PPT AND VACUUM DRYING.ESP 1.0
0.9 0.08
0.8 Si CHLOROFORM-d 0.7 0.08
Cl 2.79
0.6 7.27 2.79
0.5
0.4 Normalized Intensity 1.29 1.99 0.3
0.2 5.40 1.63 5.28 5.17
0.1 0.57
0 2.00 0.95 5.02
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 3.76. 1H NMR of chloro-functionalized styrene butadiene rubber.
B4P52PROTONNMR.ESP 0.07
1.0
0.9
Si 0.8
0.7 N
0.6 1.78 2.52 2.06 0.5
CHLOROFORM-d 2.52 0.4 Normalized Intensity Normalized 1.26 0.3 7.27
0.2 5.19 5.37
0.1 7.10 0.50 6.59
0 4.87 0.65 6.41
8 7 6 5 4 3 2 1 0 Chemical Shift (ppm)
Figure 3.77. 1H NMR of pyrrolidine-functionalized styrene butadiene rubber.
164 Figure 3.78 shows GPC chromatograms of C1205 and C1205-Cl. It can be seen that
after functionalizing C1205 (Mn = 68,600 g/mol, Mw/Mn =1.02) with
chloromethyldimethylsilane, the molecular weight (Mn) of C1205-Cl increased to
118,000 g/mol (Mw /Mn =1.27). The expected molecular weight of C1205-Cl was 91,000
g/mol (based on the mass of the C1205-Cl obtained). A higher than expected molecular
weight and broad molecular weight distribution was an indication of vinyl group coupling
previously described in the literature195 during hydrosilation reactions in presence of
transition metal catalysts.
GPC
1.2
1
0.8
0.6 C1205
0.4 C1205-chloro RI Response 0.2
0 0 5 10 15 20 25 30 -0.2 Elution Vol (mL)
Figure 3.78. GPC chromatograms of styrene butadiene rubber (C1205) and chloromethyldimethylsilane-functionalized styrene butadiene rubber (C1205-Cl).
Based on the above results, it is clear that styrene butadiene rubber (C1205) was functionalized with chloromethyldimethylsilane in a quantitative manner. Peaks from –
CH2Cl and –Si(CH3)2 groups were observed at δ 2.79 and 0.08 ppm, respectively
confirming successful grafting of chloromethyldimethylsilane onto 1,2-vinyl groups of
the butadiene units of C1205. The ratio of integration values from the above two peaks
165 was found to be 2.51 (3.0 based on stoichiometry). The 1H NMR spectrum of pyrrolidine- functionalized styrene butadiene rubber indicated quantitative functionalization. A peak observed at δ 2.52 ppm corresponded to –N-CH2- (from pyrrolidine ring). A peak from the –Si(CH3)2 groups were observed at δ 0.07 ppm confirming the structure of
pyrrolidine-functionalized C1205. The ratio of integration values from the above two
peaks was found to be 1.31 (1.50 based on stoichiometry). The molecular weight of
pyrrolidine-functionalized styrene butadiene rubber could not be determined because of
interference of amine groups with the GPC column.
3.9. Synthesis of in-chain, cyano-functionalized, deuterated polystyrene
In-chain functionalized deuterated polystyrene was synthesized as shown in Scheme
3.10. Deuterated poly(styryl)lithium (1 eq) was quenched with dichloromethylsilane (0.9
eq). The remainig poly(styryl)lithium was reacted with 2 equivalents of ethylene oxide.
The final mixture was quenched with methanol. In this way, a mixture of hydroxy- and
silyl hydride-functionalized deuterated polystyrenes was obtained. The polar hydroxy-
functionalized deuterated polystyrene was removed from the non-polar silyl hydride-
functionalized deuterated polystyrene by passing the crude product through silica gel
using a mixture of cyclohexane and toluene (1/3, v/v). All the polymers were obtained by
precipitating into methanol and freeze drying in benzene at room temperature for 24
hours.
166 D D o Benzene, 30 C D D D D Li Li D D n-1 D D D D D
D D D D D D D D D D D
0.45 eq. 90% H
D D Cl Si Cl H D D D D D D D Si Li D D D n-1 n D D O n D D D 2 eq D D D D D D D D D D D D D D D D D D D D OH D
n-1 D D D D
D D D D D D 10%
Scheme 3.10. Synthesis of in-chain, silyl hydride-functionalized, deuterated polystyrene.
Figure 3.79 shows the GPC chromatograms of crude (Mn = 2,100 g/mol, Mw/Mn =
1.06) and purified (Mn = 2,100 g/mol, Mw/Mn = 1.01) silyl-hydride functionalized
deuterated polystyrene. It can be seen that after removing the hydroxy-functionalized
deuterated polystyrene, the silyl hydride-functionalized deuterated polystyrene exhibited
a narrower polydispersity index (Mw/Mn = 1.01).
167 1.20
1.00
0.80
0.60 B4P64 crude 0.40 B4P64 pure
0.20 RI detector response RI detector 0.00 20.00 25.00 30.00 35.00 -0.20 Elution volumel (mL)
Figure 3.79. GPC chromatograms of crude (B4P64 crude) and purified silyl hydride-
functionalized (B4P64 pure) deuterated polystyrene.
The crude and purified silyl hydride-functionalized polystyrenes (B4P64 pure) were
analyzed by 1H NMR spectroscopy. Figure 3.80 shows the 1H NMR spectrum of crude
silyl hydride-functionalized polystyrene (B4P64 crude). The peak observed at δ 3.33
12 ppm corresponds to –CH2-OH of hydroxy-functionalized deuterated polystyrene. The
peak observed at δ 3.58 ppm corresponds to –SiH group of silyl-hydride functionalized
deuterated polystyrene.12
168 B4P64crudenew.esp 7.27
0.55
0.50
0.45
0.40
0.35 0.73
0.30
0.25 Normalized Intensity Normalized
0.20
0.15 0.95 1.09 0.10 -0.43 3.33 -0.25 0.05 3.58
0 3.00 4.20
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 3.80. 1H NMR spectrum of crude, in-chain, silyl hydride-functionalized, deuterated polystyrene.
Figure 3.81 shows 1H NMR spectrum of purified, silyl hydride-functionalized,
deuterated polystyrene. It can be seen that a peak from –CH2-OH group of hydroxy- functionalized deuterated polystyrene at δ 3.33 ppm disappeared. The peak at δ 3.59 ppm corresponds to –SiH group of purified silyl hydride-functionalized deuterated polystyrene.12
169 B A
B4P64HIGHCONCPROTON.ESP H 0.83 B D D B 0.76 D Si D D 0.7 D n n 0.6 C D D D D 0.5 B B D 0.4 CHLOROFORM-d D 1.04 D D D
Normalized Intensity 0.3 D 1.17 C 0.2 1.32
A -0.33 -0.17 0.1 3.59
0 1.31 11.99 3.69
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 3.81. 1H NMR spectrum of purified silyl hydride-functionalized deuterated
polystyrene.
Both the crude and purified silyl hydride-functionalized deuterated polystyrenes were
analyzed by FT-IR spectroscopy. Figure 3.82 shows FT-IR spectrum of crude silyl
hydride-functionalized deuterated polystyrene. A broad peak at 3458 cm-1 corresponds to hydroxy group of hydroxy-functionalized deuterated polystyrene.174 After purification
using a silica gel column, this broad peak disappeared as seen in FT-IR spectrum of
purified silyl hydride-functionalized deuterated polystyrene (Figure 3.83). The peak
corresponding to –SiH group (2110 cm-1)12 could not be observed since it overlapped
with the –C-D stretching band from deuterated polystyrene (2100-2200 cm-1).198 The absence of peaks between 2900-3200 cm-1 from –C-H stretching confirmed the
deuterated nature of polymer.198
170 Figure 3.82 FT-IR spectrum of crude, silyl hydride-functionalized, deuterated polystyrene.
171
Figure 3.83. FT-IR spectrum of purified silyl hydride-functionalized deuterated polystyrene.
The purified silyl hydride-functionalized deuterated polystyrene was functionalized with allyl cyanide (1.25 eq) using Karstedt’s catalyst as shown in Scheme 3.11. The progress of the reaction was monitored by thin layer chromatography (TLC). After functionalizing the silyl hydride-functionalized polystyrene for 2 weeks, the crude product was purified by using a silica gel column with a mixture of cyclohexane and toluene (1/3, v/v) as eluent. This eluent removed the non-functionalized product (silyl hydride-functionalized, deuterated polystyrene) from the column. The cyano-functionalized, deuterated polystyrene was then removed from the column using a mixture of ethyl acetate and
172 toluene (1/3, v/v) as eluent. The polymer was precipitated into methanol and freeze dried
using benzene for 24 hours at room temperature.
H D D D Si D D D n n D D Allyl cyanide D D Karstedt's catalyst
D D 14 da, 80 oC D D D D
CN
D D D Si D D D n n D D D D
D D D D D 45% D
Scheme 3.11. Synthesis of in-chain cyano-functionalized deuterated polystyrene.
Figure 3.84 shows GPC chromatograms of silyl hydride- (Mn = 2,100 g/mol, Mw/Mn =
1.01) and cyano- (Mn = 2,200 g/mol, Mw/Mn = 1.02) functionalized, deuterated
polystyrenes. As seen from the chromatograms, no appreciable change in molecular
weights was observed.
173 1.20
1.00
0.80
0.60 B4P65 CN 0.40 B4P64 pure
0.20 RI detetor response RI detetor 0.00 15.00 17.00 19.00 21.00 23.00 25.00 27.00 29.00 31.00 -0.20 Elution volume (mL)
Figure 3.84. GPC chromatograms of pure in-chain, silyl hydride- (B4P64 pure) and
cyano-(B4P65 CN) functionalized deuterated polystyrene.
Figure 3.85 shows 1H NMR spectrum of the cyano-functionalized, dueterated
polystyrene. It can be seen that the peak at δ 3.76 ppm (-SiH group) disappeared completely. Two new peaks at δ 0.20 and 0.39 ppm were observed which correspond to
12 the –SiCH2- group of cyano-functionalized polystyrene.
174 B4P65PSINCHAINCNHIGHCONC.ESP 0.81
0.8 CHLOROFORM-d
CN 0.7 A 7.27
D D D Si 0.6 D D D 1.37 n n 0.5 D D D D
0.4 D D 1.02 D D D Normalized Intensity
0.3 D 1.15
0.2 A -0.18 1.95 0.39 0.20 0.1 2.15
0 2.88 10.32 2.00 3.40
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 3.85. 1H NMR spectrum of in-chain, cyano-functionalized, deuterated polystyrene.
The silyl hydride- and cyano-functionalized deuterated polystyrenes were analyzed by
13C NMR spectroscopy. Figure 3.86 shows the 13C NMR spectrum of the silyl hydride- functionalized, deuterated polystyrene. The peak from the –SiCH3 groups was observed
at δ -9.35 ppm.12 Figure 3.87 shows the 13C NMR spectrum of cyano-functionalized,
deuterated polystyrene. A new peak δ 119.34 ppm (reported value δ 119.34 ppm12) was
observed which corresponds to –CN group of cyano-functionalized, deuterated
polystyrene.
175 B4P64 HIGH CONC C13 NMR.ESP CHLOROFORM-d H D D D Si D 127.48 77.00 D D n n 0.55 D D 0.50 D D 0.45 D D 0.40 D D D 0.35 D 0.30 Normalized Intensity Normalized 125.06 0.25 39.66
0.20 31.34 11.04 0.15 145.54 29.74
0.10 18.62 142.47 -9.35 0.05
0
140 120 100 80 60 40 20 0 Chemical Shift (ppm)
Figure 3.86. 13C NMR spectrum of in-chain, silyl hydride-functionalized, deuterated polystyrene.
176 B4P65 high conc 13C NMR.esp CHLOROFORM-d A
CN 77.00
D D D Si D D D 0.45 127.48 n n D D 0.40 D D
0.35 D D D D D
0.30 D
0.25 Normalized Intensity
0.20
0.15 125.06 39.64 31.32 145.09 0.10 11.04 119.34 29.66 18.61 141.88
0.05 -8.77
0 140 120 100 80 60 40 20 0 Chemical Shift (ppm)
Figure 3.87. 13C NMR spectrum of in-chain cyano-functionalized deuterated polystyrene.
Figure 3.88. FTIR spectrum of in-chain, cyano-functionalized, deuterated polystyrene.
177 The FTIR spectrum of in-chain, cyano-functionalized, deuterated polystyrene was
obtained as shown in Figure 3.88. The peak from the cyano group12 at 2247 cm-1 was not observed since it overlapped with –C-D stretching band from deuterated polystyrene
(2100-2200 cm-1).198
MALDI-TOF mass spectrometry was used to analyze the silyl hydride- and cyano-
functionalized deuterated polystyrenes. Figure 3.89 shows MALDI-TOF mass spectrum
of silyl hydride-functionalized deuterated polystyrene. Figure 3.90 shows MALDI-TOF
mass spectrum of silyl hydride-functionalized, deuterated polystyrene expanded in the
region m/z 2100-2400. A monoisotopic peak observed at m/z = 2193.2 corresponds to
silyl-hydride-functionalized deuterated polystyrene with 17 deuterated styrene and 1
styrene unit (with two deuterium atoms instead of hydrogen atoms),
(C4H9)(C8D8)9SiH(CH3)(C8D8)8(C8H6D2)(C4H9).Na+; calculated monoisotopic mass =
57.07042 + 112.1128 x 9 + 44.0082 + 112.1128 x 8 + 106.07515 + 57.070425 + 22.9898
= 2193.1 Da. The deuterated styrene purchased had a purity of 98% (Aldrich). The remaining quantity of monomer is usually the non-deuterated or partially deuterated
styrene.199 This explains the presence of styrene units with hydrogen in the MALDI-TOF mass spectrum of the deuterated polystyrene.
178 H D D D Si D D D n n D D D D
D D D D D D
Figure 3.89. MALDI-TOF mass spectrum of in-chain, silyl hydride-functionalized, deuterated polystyrene.
Observed Observed 2193.2 2305.3
17 dSt + 1 Sty + 2D 18 dSt + 1 Sty + 2D H D D D Si D D D n n Calculated Calculated D D D 2305.2 2193.1 D D D D D D 112.1 D
Figure 3.90. MALDI-TOF mass spectrum of in-chain, silyl hydride-functionalized, deuterated polystyrene expanded in the region m/z 2100-2400.
179 Figure 3.91 shows MALDI-TOF mass spectrum of cyano-functionalized deuterated
polystyrene. Figure 3.92 shows MALDI-TOF mass spectrum of cyano-functionalized
deuterated polystyrene expanded in the region m/z 2100-2400. A monoisotopic peak
observed at m/z = 2260.3 corresponds to cyano-functionalized deuterated polystyrene
with 17 deuterated styrene and 1 styrene unit (with six hydrogen atoms instead of
deuterium atoms), (C4H9)(C8D8)9Si(CH2CH2CH2CN)(C8H6D2)(CH3)(C8D8)8(C4H9).Na+; calculated monoisotopic mass = 57.07042 + 112.1128 x 9 + 44.0082 + 67.0421 +
112.1128 x 8 + 106.07515 + 57.070425 + 22.9898 =2260.2 Da.
CN
D D D Si D D D n n D D D D
D D D D D
Figure 3.91. MALDI-TOF mass spectrum of in-chain, cyano-functionalized, deuterated
polystyrene.
180 CN
D D D Si D D D n n D D D D
D D D D D Observed Observed 2260.3 112.1 2372.4
Calculated Calculated 2260.2 2370.3
17 dSt + 1 Sty + 2D 18 dSt + 1 Sty + 2D
Figure 3.92. MALDI-TOF mass spectrum of cyano-functionalized deuterated polystyrene expanded in the region m/z 2200-2400.
Based on the above results, it is clear that the in-chain, cyano-functionalized, deuterated polystyrene (45%) was successfully obtained by hydrosilation of in-chain, silyl hydride- functionalized, deuterated polystyrene using Karstedt’s catalyst. The presence of cyano group on the polymer chain was proven by 1H and 13C NMR spectroscopy, and MALDI-
TOF mass spectrometry.
181 CHAPTER IV
CONCLUSIONS
Linear poly(styryl)lithium synthesized by anionic polymerization was quenched with
varying concentrations of vinyldimethylchlorosilane (VDMCS) at different temperatures
and times. Surprisingly, instead of vinyl-functionalized polystyrene, formation of branched polystyrene was observed. This star formation was a result of simultaneous nucleophilic substitution of the chloride ion and addition to the vinyl group of VDMCS
by the living poly(styryl) anion. Star polystyrene so formed was analyzed by GPC
coupled with viscometric and light scattering detectors. The degree of branching varied
from 7.5 to 9.4. It was found that the concentration of VDMCS had little effect on the
degree of branching, which is unlike the behavior of divinylbenzene (DVB). In case of
star polymers prepared by linking with DVB, the degree of branching increases with
increases in the concentration of DVB. The intrinsic viscosities and melt viscosities of
star polystyrenes were found to be lower than those of the corresponding linear
polystyrenes of the same molecular weight. Cold flow problems associated with linear
polymers can be solved by branching3; hence, these star polymers can be very useful in
the tire industry.
Amine-functionalized polystyrene was successfully synthesized from vinyl-
functionalized polystyrene. The molecular weights of vinyl-, chloro-, and pyrrolidine-
functionalized polystyrenes were found to be 2,500 g/mol (Mw/Mn = 1.02), 2,600 g/mol
182 (Mw/Mn = 1.02), and 2,700 g/mol (Mw/Mn = 1.03), respectively. Vinyl- and chloro- functionalized polystyrene were obtained in quantitative yields based on 1H and 13C NMR and MALDI-TOF mass spectra results. ESI mass spectrum of pyrrolidine-functionalized polystyrene showed a major distribution of the expected (pyrrolidine-functionalized polystyrene) product. ESI mass spectrum of pyrrolidine-functionalized polystyrene also showed a minor product (7.5%) which could not be identified.
Copolymerization of methyl methacrylate and (4-vinylphenyl)dimethylsilane was successfully done using ethyl α-bromoisobutyrate as an initiator under atom transfer radical polymerization conditions. The stability of SiH group during controlled radical polymerization was proven using NMR, IR, and MALDI-TOF analyses, contrary to literature reports of silyl hydride groups undergoing hydrosilation reactions under radical polymerization conditions. The final polymer was functionalized with allyl alcohol. FT-
IR data confirmed complete reaction silyl hydride group with allyl alcohol. This method represents a versatile way of functionalizing various polymers quantitatively via a combination of atom transfer radical polymerization and hydrosilation. One polymer can be used to prepare a wide variety of functional polymers with different properties.
Tapered block copolymers of isoprene, (4-vinylphenyl)dimethylsilane, and styrene were synthesized via alkyllithium-initiated anionic polymerization in benzene with varying concentrations of (4-vinylphenyl)dimethylsilane (0.5% and 1.04% by mol) . Polymers with narrow molecular weight distributions (Mw / Mn = 1.04 and 1.05) were obtained for two tapered block copolymers (Mn = 77,900 g/mol and 72,200 g/mol). The silyl hydride group was found to be stable under anionic polymerization conditions. The presence of
SiH group was proved by 1H and 29Si NMR, and IR spectroscopy. Because of the
183 difference in reactivity ratios of isoprene, styrene, and (4-vinylphenyl)dimethylsilane
formation of a tapered block copolymer was expected. 1H NMR analysis of the
copolymers revealed peaks from block and non-block polystyrene confirming their
tapered nature.
Cyclic polybutadiene (CyPBD, Mn = 88,400 g/mol, Mw/Mn = 2.06) was successfully
decorated by grafting with silyl hydride functional polystyrene (Mn = 8,300 g/mol,
Mw/Mn = 1.01) via hydrosilation. Increased molecular weight (Mn = 2,004,000 g/mol,
Mw/Mn = 6.19) was confirmed by a shift in the SEC chromatogram of the grafted
CyPBD. AFM images provided direct evidence for the cyclic nature of the grafted rings.
Polyisobutylene was synthesized via cationic polymerization and was reacted with (4- vinylphenyl)dimethylsilane before quenching the reaction with methanol. The cations
preferred hydride transfer from (4-vinylphenyl)dimethylsilane over competing
electrophilic addition to the π bond. This was confirmed with the help of GPC , 1H NMR
and 13C NMR spectroscopic studies. No evidence for any vinyl group addition was observed which indicated that hydride transfer is a very rapid process compared to electrophilic addition. This research also confirmed that –SiH functionalized compounds such as (4-vinylphenyl)dimethylsilane cannot be used as comonomers for synthesizing functional polymers via cationic polymerization.
Tapered styrene butadiene rubber (SBR) was successfully grafted with tridecafluoro-
1H,1H,2H,2H-octyldimethylsilane in a quantitative manner. The presence of grafted tridecafluoro-1H,1H,2H,2H-octyldimethylsilane was detected by 1H and 19F NMR spectroscopy. Tapered styrene butadiene rubber and fluorinated tapered styrene butadiene rubber were electrospun into fiber mats and tested for water contact angles. SBR
184 electrospun fibers were found to have a beaded structure because of higher surface
tension forces as compared to electrostatic forces. The contact angle for SBR electrospin
fibers was found to be 151.2o ± 2.4o. The fluorinated SBR yielded smooth nanofibers
with a contact angle of 162.8o ± 3.8o. The high contact angle for SBR electrospun fiber
was attributed to its beaded structure (high surface roughness).134, 135 The high contact
angle for fluorinated SBR fibers was attributed to the low surface energy of grafted fluorinated groups.134, 135 This method of preparing electrospun fibers from fluorinated
elastomers can be very useful in constructing soft superhydrophobic surfaces.
In-chain functionalization of styrene butadiene rubber using chloromethydimethylsilane was successfully done via hydrosilation reaction using Karstedt’s catalyst. 1H NMR spectroscopy confirmed quantitative grafting of styrene butadiene rubber with chloromethyldimethylsilane. Pyrrolidine-functionalized styrene butadiene rubber was obtained after reacting pyrrolidine with chloromethyldimethylsilane-functionalized
1 styrene butadiene rubber (Mn = 128,000 g/mol, Mw/Mn = 1.28, 113%). H NMR spectroscopy of pyrrolidine-functionalized styrene butadiene rubber (71%) confirmed successful grafting of pyrrolidine molecules on styrene butadiene rubber.
In-chain silyl hydride-functionalized deuterated polystyrene (Mn = 2,100 g/mol, Mw/Mn
= 1.01) was synthesized successfully by a combination of living anionic polymerization and hydrosilation. The silyl hydride-functionalized deuterated polystyrene was functionalized with allyl cyanide. 1H and 13C NMR spectroscopy, and MALDI-TOF mass spectrometry confirmed efficient functionalization of silyl hydride-functionalized deuterated polystyrene with allyl cyanide. Lower yield of cyano-functionalization (45%)
185 was attributed to steric hindrance around –SiH group. The cyano-functionalized deuterated polystyrene has been proven to be useful in dielectric spectroscopy.22, 23
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200 APPENDICES
APPNEDIX A
VDMCS-1.5-50C-3DAY-SI.ESP -37.30 1.0
0.9 0.8 0.7
0.6
0.5
Normalized Intensity 0.4 0.3 0.2
0.1
32 24 16 8 0 -8 -16 -24 -32 -40 -48 -56 Chemical Shift (ppm)
Figure 4.1. 29Si NMR spectrum of star polystyrene (sample 1550 from Table 3.1).
VDMCS-2.5-50C-3DAY-SI.ESP -37.30
1.0
0.9
0.8 0.7
0.6
0.5
Normalized Intensity 0.4 0.3
0.2
0.1
32 24 16 8 0 -8 -16 -24 -32 -40 -48 -56 Chemical Shift (ppm)
201
Figure 4.2. 29Si NMR spectrum of star polystyrene (sample 2550 from Table 3.1).
VDMCS-2.5-30C-3DAY-SI.ESP
-37.30 1.0 0.9
0.8
0.7 0.6
0.5
Normalized Intensity 0.4
0.3
0.2
0.1
32 24 16 8 0 -8 -16 -24 -32 -40 -48 -56 Chemical Shift (ppm)
Figure 4.3. 29Si NMR spectrum of star polystyrene (sample 2530 from Table 3.1).
VDMCS-5EQ-30C-3DAY-SI.ESP
-37.30 1.0 0.9
0.8
0.7 0.6
0.5
Intensity Normalized 0.4
0.3 0.2
0.1
32 24 16 8 0 -8 -16 -24 -32 -40 -48 -56 Chemical Shift (ppm) 202
Figure 4.4. 29Si NMR spectrum of star polystyrene (sample 5030 from Table 3.1).
VDMCS-5EQ-50C-3DAY-SI.ESP -37.30
1.0
0.9 0.8
0.7
0.6 0.5 Normalized Intensity 0.4
0.3 0.2
0.1
32 24 16 8 0 -8 -16 -24 -32 -40 -48 -56 Chemical Shift (ppm)
Figure 4.5. 29Si NMR spectrum of star polystyrene (sample 5050 from Table 3.1).
203 VDMCS-1.5-30C-3DAY-H1NEW.ESP 7.04
1.0
0.9
0.8
0.7
0.6 1.40
0.5 6.53 Normalized Intensity Normalized 0.4 0.65
0.3 1.82
0.2 7.27 -0.44 0.1
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 4.6. 1H NMR of star polystyrene (sample 1530 from Table 3.1).
VDMCS-2.5-30C-3DAY-H1.ESP 7.02
1.0
0.9
0.8
0.7 1.37
0.6 6.53
0.5 Normalized Intensity Normalized 0.4 1.81
0.3 0.65
0.2 -0.52 7.27 0.1
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 4.7. 1H NMR of star polystyrene (sample 2530 from Table 3.1).
204 VDMCS-2.5-50C-3DAY-H1.ESP 7.02
1.0
0.9
0.8 1.37
0.7
0.6 6.53
0.5
Normalized Intensity Normalized 0.4 1.81
0.3 0.65 0.2 7.27 0.1 -0.44
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 4.8. 1H NMR of star polystyrene (sample 2550 from Table 3.1).
VDMCS-5EQ-30C-3DAY-H1.ESP 7.02
1.0
0.9
0.8
0.7 1.39 0.6 6.53
0.5
Normalized Intensity Normalized 0.4 0.65 1.82 0.3
0.2 7.27 -0.45 0.1
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 4.9. 1H NMR of star polystyrene (sample 5030 from Table 3.1).
205 VDMCS-5EQ-50C-3DAY-H1.ESP 7.04
1.0
0.9
0.8
0.7
0.6 1.40 6.53 0.5
Normalized Intensity Normalized 0.4 0.65 0.3 1.82
0.2 7.27 -0.44 0.1
8 7 6 5 4 3 2 1 0 -1 Chemical Shift (ppm)
Figure 4.10. 1H NMR of star polystyrene (sample 5050 from Table 3.1).
APPENDIX B
Synthesis of linear polybutadiene
Linear polybutadiene (0.61 g, 70%) was synthesized by ring-opening metathesis
polymerization of 1,5-cyclooctadiene (1.0 mL, 10.4 mmol, Aldrich, 99%, stirred over Na
before distilling) using Grubb’s 2nd generation catalyst [6.8 mg dissolved in 1 mL of dry
toluene, 8.1 mmol, Materia Inc., (1,3-Bis(2,4,6-trimethylphenyl)-2-
imidazolidinylidene)dichloro-(phenylmethylene)(tricyclohexylphosphine)ruthenium] in
toluene (6.5 mL, EMD, Aldrich, stirred over calcium hydride before distilling). The
polymerization reaction was carried out in a round-bottomed flask under dry nitrogen for
1 h. The reaction was terminated by ethyl vinyl ether (1 mL, 10.44 mmol, Aldrich, 98%)
after 1 h. The polymer solution was precipitated into methanol and dried under vacuum
206 for 24 h. The polymer was made by Alexander Agapov, Gladys R. Montenegro-Galindo, and Sarang Bhawalkar under the guidance of Prof. Scott Collins and Marcia Weidknecht
(Department of Polymer Science, The University of Akron).
LPBD2.ESP 2.04
1.0
0.9
0.8
0.7
0.6
0.5
0.4 5.42 Normalized Intensity
0.3
0.2 2.08 5.38 0.1 7.27
0
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)
Figure 4.11. 1H NMR spectrum of linear polybutadiene.
APPENDIX C
Predicted 13C NMR of (4-vinylphenyl)dimethylsilane
Using Chemdraw Ultra 7.0 Software the predicted 13C NMR of (4- vinylphenyl)dimethylsilane is shown in the Figure 4.12.
207 135.8 112.3
125.8 125.8 136.2
132.2 135.7 135.7
-4.7Si -4.7
H
Figure 4.12 Predicted 13C NMR spectrum of (4-vinylphenyl)dimethylsilane.
4.3. Microstructure determination of 65LowSi and 65HighSi
65LowSi 65HighSi
1,2-vinyl = 3.60 x 100/ (37.15+7.21) = 4.37 x 100/ (37.03+8.74)
= 8% = 9.5%
3,4-vnyl = 3.60 x 100/ (37.15+7.21) = 4.37 x 100/ (37.03+8.74)
= 8% = 9.5% 1,4- = 37.15 x 100/ (37.15+7.21) = 37.03 x 100/ (37.03+8.74)
= 84% = 81 %
1,4-cis = 46.49 x 100/ (46.49 + 33) = 44.55 x 100/ (44.55 + 32.66)
= 59% = 58 %
1,4-trans = 33 x 100/ (46.49 + 33) = 32.66 x 100/ (44.55 + 32.66)
= 41% = 42 %
4.4. 1,2-Vinyl content of C1205
Percentage of 1,2-vinyl = (1.00/2) x 100 /((10.61-0.50) x 0.5 + 0.50)
208 = 9.00 %
Since C1205 had 77.6% polybutadiene, the percentage of 1,2-vinyl = 9.00 x 0.776 = 6.98 %
APPENDIX D
209 210 211
212