BRANCHED ALIPHATIC POLYCARBONATES: SYNTHESIS AND COATING APPICATIONS

Peter Löwenhielm

Akademisk avhandling

Som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning fredagen den 24e september 2004, kl 10.00 i sal E2, Osquars backe 2, KTH, Stockholm. Avhandlingen försvararas på engelska ABSTRACT

The overall aim of this thesis is to describe the synthesis of branched aliphatic polycarbonates and show the potential application of these polymers in the field of powder coatings. The characterization of the polycarbonates was facilitated by the study of a series of bis-MPA dendrimers, which served as reference of perfectly branched polymers. In addition an ε- caprolactone monomer with a bis-MPA pendant unit was synthesized and polymerized in order to find an alternative synthetic route hyperbranched polyesters.

Cationic ring opening polymerization (CROP) of neopentylene carbonate was utilized to synthesize a number of branched polymers. This monomer was chosen because the thermal properties of poly(neopentylene carbonate) are promising for powder coating applications. CROP enabled the synthesis of branched polymers, which are of great interest because of their reduced melt viscosity and high functionality compared to linear polymers. CROP of neopentylene carbonate, with a series of polyols including a hyper-branched polyester (Boltorn H30), in the presence of fumaric acid resulted in polymers with varied degrees of branching and molecular weights ranging from 2 000-100 000 g mol-1.

Neopentylene carbonate was also used in the synthesis polycarbonate macromonomers possessing a polymerizable methacrylate functional group at one of the chain ends. In thjis case hydroxyethylmethacrylate was used as initiatopr in the reaction catalyzed by methyl sulfonic acid. The MW of this macromonomer was 2500 g mol-1 and it was used to produce polymer brushes by free radical and atom transfer radical polymerization (ATRP).

Αn ε-caprolactone bearing a pendant bis-MPA was synthesized and polymerized by Sn(Oct)2. Copolymerization with ε-caprolactone was performed to introduce linear segm,ents between the branching points. The molecular weights of the homopolymer and the copolymer were 3000 and 8000 g mol-1 respectively as determined by Size exclusion chromatography (SEC) calibrated with polystyrene.

SEC was used to analyze a series of bis-MPA dendrimers, and the results were used to characterize the branched polycarbonates. The Mark-Houwink plots of the dendrimers were produced and used as reference in the characterization of the polycarbonates.

The thermal and rheological characterization of the polycarbonates showed that the polymers were semi-crystalline with Tg between 20-30 °C and Tm between 90-120 °C. Rheology measurements showed that the architecture had a considerable impact on the melt viscosity.

Coating films were produced by UV curing of a series of linear polycarbonates were functionalized with methacrylic groups. The storage stability was tested for one week at 45 °C, no coagulation of the particles was observed at the end of the testing period. The cured films showed good chemical resistance and flexibility. SAMMANFATTNING

Detta arbete beskriver i huvudsak syntes av grenade alifatiska polykarbonater och en studie av dessa för tillämpning inom pulverfärger. Vidare har en serie dendrimer studerats och använts som referens i karakteriseringen av polykarbonaterna. Slutligen har en lakton monomer syntetiserats och ringöppnings polymerisation har använts som en alternativ syntesväg till hyperförgrenade polyestrar.

Katjonisk ringöppningspolymerisation användes för att syntetisera ett antal polymerer av neopentylkarbonat. Denna monomer användes eftersom dess polymers termiska egenskaper är lovande för tillämpningar som pulverfärger. Användandet av ringöppningspolymerisation möjliggjorde syntes av stjärn polymerer vilka är intressanta eftersom de uppvisar en låg viskositet i förhållande till molekylvikt och dessutom har en hög funktionalitet. Polymerisationer av neopentylkarbonat tillsammans med en serie kommersiella polyoler, innefattande en hyperförgrenad polyester (Boltorn H30) skedde i närvaro av fumarsyra och resulterade i polymerer med varierande förgreningsgrad och molekylvikter från 2 000 till 100 000 g mol-1.

Neopentylkarbonat användes också för att syntetisera makromonomerer där den ena kedje ändan bestod av en polymeriserbar akrylatgrupp. Reaktionen utfördes i lösning med hydroxyetylmetakrylat som initatiatior och metylsulfonsyra som katalysator. Makromonomen polymeriserades sedan med fri radikalpolymerisation och kontrollerad radikalpolymerisation för framställning av kampolymerer.

En ε-caprolakton monomer modifierad med bis-metylol propionsyra syntetiserades och polymeriserades genom katalys av Sn(Oct)2. Sampolymerisation utfördes också tillsammans med ε-caprolakton för att introducera linjära segment mellan förgreningspunkterna. Molekyl vikten till 3000 g mol-1 för homopolymeren och 8000 g mol-1 för sampolymeren. Förgrenings graderna beräknades med 1H-NMR till 0,50 och 0,15 för homopolymeren respektive sampolymeren.

Ett antal bis-MPA dendrimerer studerades med kromatografi och viskosimetri. Mark- Houwink plotter konstruerades och användes som referenser i studierna av de grenade polykarbonaterna.

Analys av polykarbonaternas termiska och reologiska egenskaper visade att polymererna var kristallina uppvisande Tg = 20-30°C och Tm = 90-120°C. Reologi mätningarna visade att arkitekturen hade en betydande inverkan på smältviskositeten.

Slutligen tillverkades filmer baserade på linjära polykarbonater med tre olika molekylvikter. Polymerernas kedjeändar hade funktionaliserats med akrylatgrupper för att möjliggöra tvärbindning med UV-härdning. Pulvrets lagrings stabilitet testades genom förvaring vid 45°C i en vecka. Efter testperioden konstaterades att partiklarna ej koagulerat vilket är ett techen på god lagringsstabilitet. De härdade filmerna uppvisade god kemikalie resistens och flexibilitet.

LIST OF PAPERS

The thesis is a summary of the following papers:

I “Poly(neopentylene carbonate) Hyperstars”, P. Löwenhielm, H. Claesson, A. Hult, Macromolecular Chemistry and Physics, 2004, 205, 1489-1496

II “New Approach to Hyperbranched Polyesters: Self-condensing Cyclic Ester Polymerization of Bis(hydroxymethyl)-Substituted ε-Caprolactone” M.Trollsås, P. Löwenhielm, V.Y. Lee, M. Möller, R.D. Miller, and J.L. Hedrick, Macromolecules, 1999, 32, 9062-9066

III “Synthesis and Characterization of 2,2-Bis(methylol)propionic Acid Dendrimers with Different Cores and Terminal Groups” M. Malkoch, H.Claesson, P. Löwenhielm, E. Malmström, A. Hult, Journal of Polymer Science: Part A: Polymer Chemistry, 2004, 42, 1758-1767

IV “Aliphatic Polycarbonate Resins for Radiation Curable Powder Coatings” P. Löwenhielm, D Nyström, M. Johansson, A. Hult, Manuscript

The thesis also contains results part of a manuscript in preparation: “Synthesis and characterization of poly(neopentylene carboanate) brushes”

TTABLE OF CONTENTS

1 PURPOSE OF THE STUDY...... 3

2 INTRODUCTION ...... 4

2.1 Powder Coatings...... 4

2.2 Polymer architecture...... 8 2.2.1 Long chain branching...... 9 2.2.2 Dendritic polymers...... 9

2.3 Ring opening polymerization ...... 10 2.3.1 Polyesters ...... 11 2.3.2 Polycarbonates ...... 11

3 EXPERIMENTAL ...... 15

3.1 Materials ...... 15

3.2 Synthesis...... 15 3.2.1 Synthesis of neopentyl carbonate...... 15 3.2.2 Cationic ring opening polymerization of neopentylcarbonate with fumaric acid...... 15 3.2.3 Synthesis of acrylate terminated poly(neopentyl carbonate) macromonomer...... 16 3.2.4 Synthesis of poly(neopentyl carbonate) brushes...... 16 3.2.5 Synthesis of hyperbranched polyesters by ring opening polymerization...... 17 3.2.6 Characterization of Bis-MPA dendrimers...... 18 3.2.7 Functionalization of polycarbonates for crosslinking ...... 18 3.2.8 Crosslinking of acrylate functional polycarbonates...... 18

3.3 Characterization methods ...... 19 3.3.1 NMR...... 19 3.3.2 SEC...... 19 3.3.3 DSC ...... 19 3.3.4 Rheology ...... 19 3.3.5 Raman spectroscopy...... 19 3.3.6 Curing of films ...... 20 3.3.7 Adhesion...... 20 3.3.8 Pencil hardness...... 20 3.3.9 Erichsen ball test ...... 20 3.3.10 Solvent resistance...... 20 3.3.11 Storage stability...... 20 3.3.12 Gloss...... 20

4 RESULTS AND DISCUSSION...... 21

4.1 Synthesis of neopentyl carbonate star polymers ...... 21 4.1.1 Monomer synthesis ...... 21 4.1.2 Synthesis of branched polycarbonates by cationic polymerization ...... 22

1

4.1.3 Characterization ...... 27

4.2 Synthesis of polycarboante brushes by a Macromonomer approach...... 29 Figure 14. The ATRP initiators...... 30 4.2.2 Polycarbonate brush ...... 30 4.2.3 Star brush...... 30

4.3 Synthesis of hyperbranched polyesters via ring opening polymerization...... 31 4.3.1 Monomer Synthesis...... 32 4.3.2 Polymer synthesis and Characterization ...... 32

4.4 Characterization of bis-MPA dendrimers with different core and periphery ...... 35 4.4.1 Synthesis...... 35 4.4.2 Characterization of dendrimers by size exclusion chromatography ...... 36

4.5 Powder coatings...... 38 4.5.1 Thermal properties ...... 38 4.5.2 Rheological properties...... 40 4.5.3 Functionalization of endgroups (acrylation) for cross-linking...... 42 4.5.4 Powder formulation and storage ...... 43 4.5.6 Film properties ...... 44

5 CONCLUSIONS ...... 46

6 FUTURE WORK...... 48

7 ACKNOWLEDGEMENTS ...... 49

8 REFERENCES ...... 51

2 -----Purpose of the study-----

1 PURPOSE OF THE STUDY

The objective of this thesis work was to synthesize branched polymers and show their application as low temperature curing powder coatings. Key properties of powder coatings are storage stability and flow during the film formation process. The work presented in this thesis aims at the design of polymers that satisfies these conflicting demands.

The chosen approach involved the synthesis of branched semi-crystalline polycarbonates with defined thermal properties. Crystalline polymers were used to achieve storage stability and branched architectures such as stars hyper branched and combs were introduced to tune the melt viscosity of the polymers. A series of bis-MPA dendrimers was used as reference in the characterization of the polycarbonate’s dilute solution properties. In addition, an ε- caprolactone monomer with a pendant bis-methylol propionic acid moiety (bis-MPA) was synthesized and polymerized by ring opening polymerization, as an alternative to polycondensation in the synthesis of hyperbranched polyesters.

In summary the goals were as follows:

• Synthesize a series of linear and branched semi crystalline polycarbonates (paper I) and study their thermal and rheological properties.

• Synthesize an aliphatic polyester by ring opening polymerisation (paper II).

• Characterize the dilute solution properties of a series of Bis-MPA dendrimers and compare the results with the synthesized polycarbonates (paper III).

• Demonstrate the use of semi-crystalline polycarbonate as a binder in a low temperature powder coating (Paper IV).

3 -----Introduction-----

2 INTRODUCTION

2.1 POWDER COATINGS

Every object in our surrounding has a surface. The way we perceive an object depends on the colour and texture of the surface. Imagine every table or floor being a dull shade of gray instead of a beautiful wooden colour, or every car completely red with rust after one season. The purpose of coatings is twofold: to enhance the appearance of a surface and protect the material beneath. The importance of coatings is evident by the worldwide sales of paint, which exceeded 70 000 000 000 US$ in the year 2002.1

Coatings or paint are generally applied in a liquid form. Traditional coating formulations contain a large portion of solvents, needed for the paint to flow properly while painting. Increasing environmental demands for the reduction of solvent emissions have led to the development of powder coatings, which are completely free from solvents. Powder coatings are very good for the coating of metals and are found in diverse applications ranging from household appliances to automotive coatings.2,3 There are also economic and technological advantages of powder coatings such as: easier handling without solvents, recovery of over sprayed powder and energy savings. In 2000 the market share of powder coatings in Europe was 12 %.4

Powder coatings used on metals are in general based on amorphous resins, which are cured in a thermally activated process. Other components of thermosetting powder coatings include cross-linker, pigment and additives (scheme 1). The most common resins used today are polyesters, acrylics, epoxies and hybrids, which consist of both ester and epoxy components. The molecular weight (Mn) of the resins is usually in the order of a few thousand. Curing is made together with low molecular weight compounds, called cross linkers that react with the resin molecules and create an infinite network.. A powder formulation is prepared by melt mixing the components, which form a solid upon cooling. The solid is subsequently ground to fine powder that can be applied to a substrate by electrostatic deposition.5-7

4 -----Introduction-----

O O

HO R OH + HO R' OH

O O O O

HO R' O R O R' O R OH + Pigment Cross-linker Additives

1. Melt mixing 2. Grinding

Powder coating

Scheme 1. Overview of the components and production of a polyester powder coating.

Solid polyester resins are synthesized by polycondensation of di- or trifunctional acids and alcohols with a functionality of two or higher. Acrylics are synthesized by free radical polymerisation reactions in solution and are therefore more expensive than polyester resins. The relative proportion of components in the reaction dictates the resin properties such as Mn, Tg, functionality (fn), and reactivity. Optimization of these parameters is necessary to satisfy the demands for storage stability, levelling, curing and coating performance.5

A critical property of any powder coating is storage stability. Storage of conventional amorphous resins at 40 °C requires that the glass transition temperature (Tg) of the resin is at least 70 °C in order to prevent agglomeration or caking of the powder particles. A sufficient drop in viscosity, required for levelling during application of the coating, is attained at processing temperatures 50 °C above Tg, which means that the effective curing temperature is usually above 120 °C.3 The use of powder coatings has therefore, until recently, been limited to metal substrates.8

A relatively new technology is “UV-cured powder coatings” that utilizes photo initiators and UV irradiation to initiate cure.4 Photo initiators open the possibility for low temperature curing since they are stable until exposed to UV-light, unlike thermal initiators, which require high activation temperatures because of stability considerations. By lowering the cure temperature to 100 – 120 °C and using infra red (IR) heating it is possible to coat heat sensitive substrates such as plastics or medium density fibre (MDF) board.9 In a UV-curing process the melting of the resin and film formation is achieved prior to the curing step. Curing is complete within a few seconds of UV irradiation and facilitates a more homogeneous cure of the film (figure 1). This is a considerable advantage over thermal cure where the levelling and curing takes place simultaneously, often resulting in structural defects. Rapid curing at decreased temperature also brings about significant energy savings.8

5 -----Introduction-----

Convection oven

160 oC

160 oC

Levelling/Curing: 20-30 min

IR Heater UV-Lamp

120 oC

80 oC

Levelling: 3-5 min Curing: 1-10 seconds

Figure 1. Conventional powder coatings are cured in a thermally activated process (top). In a UV-curing process the levelling and curing steps are separated, allowing faster curing at reduced temperatures and resulting in more homogeneous films.

UV curing proceeds by either a free radical or cationic polymerisation that is initiated by a photo initiator. Photo initiators are compounds that decompose and generate free radicals or acids, when irradiated by UV-light. Resins that cure by the radical mechanism include acrylate-functionalized polyesters, polyurethanes, polyacrylates or epoxy resins while cationic polymerisation can be used with vinyl ethers and epoxy resins. These types of curing mechanisms eliminate the need for cross-linkers like triglycidylisocyanurate (TGIC).2

Functionality, required for crosslinking by free radical polymerization, is bestowed on the polymers by incorporation of unsaturations in the backbone or by functionalization of pendant OH-groups. The synthetic strategy is outlined in scheme 2: backbone unsaturations are readily introduced by adding unsaturated acid such as fumaric acid10 or maleic anhydride in the resin synthesis (A). Pendant functionality is achieved either by esterification with acrylic acid (B) or formation of a urethane through a difunctional isocyanate and a hydoxyfunctional acrylate (C).11,12 The molecular weight of a UV-coating resin is typically between 1000-7000 g mol-1.5

6 -----Introduction-----

O O O O

A HO R OH + HO R' OH + HO OH O O O O

O O HO B OH O

O O O O R OCN NCO HO O C OH O N R NCO O N R N O O O

Scheme 2. Crosslinking by radical polymerization requires the introduction of unsaturations.

The curing at low temperature puts new demands on the resins; good flow at the desired curing temperature must be attained without compromising storage stability. Semi-crystalline resins have been proposed as an alternative to amorphous resins. The reason is that melting is a first order phase transition unlike the glass transition, which is a second order transition. When semi-crystalline polymers are heated above the melting point the viscosity drops several orders of magnitude in a short temperature interval. This behavior is quite different from when an amorphous polymer is heated above Tg. In this case the polymer experiences increased segmental mobility that results in a gradual reduction of viscosity (softening), which takes place over a much longer temperature interval. By employing Tm instead of Tg to transcend from the solid state to the molten state, a rapid decrease in viscosity is attained in a short temperature interval resulting in a lower film forming temperature (figure 2).9,12-14

The formulator can by careful choice of resin(s) optimize the processing properties and the film properties. However the selection of binder resin or combination of resins is merely one of the factors affecting the performance of the cured coating. Other factors, which must be taken into account, include the other parts of the coating formulation including pigment, fillers, additives and photo initiators. Furthermore technological aspects such as UV-lamp type, IR-conveyor speed, and oven design must be considered.

7 -----Introduction-----

Semi-crystalline resin UV-Cured 80-100 °C

Amorphous resin- thermally cured

Viscosity 160-200 °C

Onset of UV-cure

Time

Figure 2. A schematic representation of the viscosity vs time relationship of a conventional amorphous powder coating and a semi-crystalline UV-curing powder coating.

2.2 POLYMER ARCHITECTURE

Polymers are divided into four main architectural classes: linear, cross-linked, branched and dendritic (figure 3).15 Each architectural class is associated with unique properties; for example two polymers composed of the same monomer and with the same molecular weight, but different architecture possess completely different properties e.g. rheologial, thermal and chemical reactivity, etc. By utilizing advanced molecular architecture such as star polymers, graft copolymers and dendrimers, it is possible to control the properties to a greater degree than with conventional linear polymers.15 This presents great opportunities when designing new materials for coatings16, pharmaceuticals17, microelectronics18 or engineering plastics.19

IIIIIIIV

Figure 3. The four classes of polymer architecture comprise, from left to right, I Linear, II Cross-linked, III Branched and IV Dendritic.

8 -----Introduction-----

2.2.1 Long chain branching

The effect of polymer architecture is clearly shown in the case of polyethylene (PE). Although low-density polyethylene (LDPE) has inferior toughness compared to linear low- density polyethylene (LLDPE), the processability is greater.20 Rheological studies of well- defined PE model materials21,22 have shown that shear thinning is increased during extrusion of LDPE. It was shown that this behaviour is caused by the presence of long chain branches (LCB) along the backbone. In this case a long chain branch is defined as a branch that is longer than the entanglement molecular weight.21 Furthermore it was shown that addition of 5% of a PE comb polymer yield extensional thickening of PE.23

A polymer with three or more branches, of similar length that are attached to one common branching point is termed star polymer. Star polymers are the least complex of LCB polymers. If several branching points are present the polymer is called a comb polymer. As is the case with LDPE, star polymers show low melt viscosity. In addition, the intrinsic viscosity of LCB polymers is lower than linear polymers of the same molecular weight and composition. This is the result of the branched polymers adopting conformations that are smaller than the random coil. Another important feature of branched polymers is their increased functionality since each arm provides an additional end group. This functionality can be used for cross-linking or further modification of the polymer.14

The synthesis of well-defined branched polymers is accomplished by the use of synthetic methods that provide good control of the reactions, for example, controlled radical polymerization (CRP) anionic polymerization and living ring opening polymerization. CRP comprises three different techniques: (1) atom transfer polymerizarion (ATRP),24-27 (2) nitroxide mediated polymerization (NMP)28-31, and (3) reversible addition fragmentation polymerization (RAFT)32,33.

2.2.2 Dendritic polymers

Dendritic polymers are the most recently discovered class of polymer architecture (figure 4). This class consists of dendrimers,34-36 hyperbranched37 and dendrigrafts.38,39 Dendrimers are perfectly branched macromolecules where each repeating unit has a branching point. The structure of a dendrimer consists of three domains: core, interior and shell. The interior is separated into layers called generations. The peripheral layer, called the shell contains all the functional groups. The unique characteristics of dendrimers are their monodisperse size distribution and multiple endgroups. Dendrimers are synthesized in stepwise procedures including several protection/deprotection steps, which is costly and time consuming. Hyperbranched polymers are the statistical analogues to dendrimers. Hyperbranched polymers are not perfectly branched like dendrimers but can be synthesized by simple polymerization procedures such as polycondensation. Dendrigraft polymers are branched like dendrimers with linear polymer segments between each branch point. They are easier to synthesize than dendrimers and bring about the properties of the linear polymer segment such as crystallinity.40,41

9 -----Introduction-----

(

) n

) n

( (

)

n ( ( ) ) n n ) n (

) n )n ( ( ) n ( ( )n ( ) n ) ) n ( n ( )n ( )n ( ( n ) ) ( n

) ( n

( )n

Figure 4. The three main subgroups of dendritic architecture: Dendrimers (left), Hyperbranched (center), and dendrigraft (right).

Although dendritic polymers were recently discovered there are already proposed applications of materials based on polymers from this architectural class. An interesting example is as porogens for the production of nanoporous insulating materials. Such improved insulating materials are used to make better microchips needed in the fastest computers.18 The area where dendrimers are expected to have the most significant impact is in bio- and nano technology.42 A good application example is as contrasting agents for magnetic resonance imaging (MRI).43 Attachment of contrasting agents, such as gadolinium complexes,44 to a dendrimer scaffold enhance the resolution, since leakage of agent into the surrounding tissue is hindered. Other areas of applications may be found in drug delivery and anti-HIV drugs.45 Because dendrimers are relatively expensive to produce the applications will be in areas requiring small quantities. Hyperbranched polymers are on the other hand much cheaper to produce and are produced in industrial quantities. The two foremost examples are Boltorn, a polyester46, from Perstorp47 and Hybrane, a polyester amide of DSM.48

Recent research by Hult and others has investigated the use of dendritic and other branched polymers as binders for low temperature curing powder coatings.49,50 In the concept proposed by Hult et al, ε-caprolactone is grafted to a hyperbranched polymer, or a linear polyacrylate by use of living ROP according to a procedure developed by Hedrick et. al. The resulting hyper stars51 and comb polymers14, were cross-linked by a free radical polymerization after functionalization of the end groups by methacrylate moieties. The advantage of these systems is that the melt viscosity is low enough for film formation even if the molecular weight is very high. The thermal properties of the synthesized polymers are however unsuitable for use as powder coatings (Tg = -50°C, Tm = 50°C).

2.3 RING OPENING POLYMERISATION

Ring opening polymerisation of cyclic monomers attracts considerable attention since it allows the synthesis of well-defined polymers and complex molecular architectures with sunsequent tailoring of the material properties. Materials based on polymers obtained by ROP of lactones and carbonates are highly interesting for biomedical applications because of their in vivo degradability.52-54 The polymers of the respective monomers listed in figure 5 are all semi-crystalline except for polytrimethylene carbonate.

10 -----Introduction-----

O O O O

O O OO OO O

O

ε-caprolactone lactide trimethylene- neopentyl- carbonate carbonate

o o o o Tg = -60 C Tg = 60-70 C Tg = -17 C Tg = 30 C T = 50-60 oC T = 160-170 oC T = 100-130 oC m m m

Figure 5. Cyclic monomers and thermal properties of their respective polymers.

2.3.1 Polyesters

Cyclic esters are the most frequently used monomers for ring opening polymerization. Poly ε-caprolactone and polylactide can be polymerized by coordination polymerization yielding well-defined polymer architectures such as block-,55-57 star-58 and dendrigraft polymers40,59. Recently cationic polymerisation of poly ε-caprolactone star polymers (PCL) was reported.60 Polymers of ε- caprolactone are found in for example coating resins61, and biodegradable sutures62.

2.3.2 Polycarbonates

Polycarbonates are more resistant to hydrolysis than lactones or lactides. A reason for this behavior is that polycarbonates do not yield acidic groups upon degradation like polyesters do. Polytrimethylene carbonate can for example be used to prolong the in vivo degradation time.52 Although the carbonate group is more susceptible to hydrolysis than a polyester, the degradation of an aliphatic polycarbonate is slower. This is because free carboxylic groups are formed as the polyester degrades, resulting in an increased rate of degradation. The situation is the opposite in case of the polycarbonate where the end group splits off CO2 while forming a less acidic hydroxyl group (scheme 3). From an industrial point of view, polycarbonates are interesting as diols constituting the soft segments in polyurethanes. Polycarbonate diols bring sbenefits such as increased hydrolytic stability vs polyesters, thermal stability vs polyethers and an increase in outdoor stability.63

11 -----Introduction-----

O O O R R O H O OH O O O O O n n O Hydrolysis Hydrolysis

O O O O R R O O H O H O O O O O O n - y O n - y O

-CO2

O O R H O O O O O n - y

Scheme 3. Hydrolytic degradation of polyesters such as PCL (left) yield terminal carboxyl groups that increase the rate of degradation. Hydrolysis of aliphatic polycarbonates (right) yields terminal hydroxyl carbonates, which rearrange to less acidic hydroxyl groups.

The versatility of ring opening polymerisation and the increased hydrolytic stability of the aliphatic polycarbonate suggests several applications such as coating resins,64 isocyanate free routes to polyurethanes65,66 and medical applications (scheme 4).67

Macro monomers Copolymers O O O O O n H acrylic polymer O O O n H O O

polyester O O O Star polymers n H O H O

O OO epoxy resin O O O n H O O O R' R'' n O

O O O Poly carbonate diols n H O O O H n O O O

HO O O O n O OH

O Urethane cross-link R + Carbonate cross-link H2N + O HO O R'' O O

O N R O O H

R'' OH R'' OH

Scheme 4. Ring opening polymerisation of cyclic carbonates present several routes to new applications.

12 -----Introduction-----

Reports of ring opening polymerization of cyclic carbonates include anionic68,69, cationic70-72, coordination73 and more recently enzymatic ring opening polymerisation74. Cationic polymerisation is highly interesting since metal free organic acids are used to promote the polymerisation. Polymerisation with strong acids is however prone to side reactions that result in a fraction of ether bonds in the polycarbonate71. Endo and co-workers recently synthesized aliphatic polycarbonates by cationic ROP under mild conditions while avoiding decarboxylation.75,76

Copolymerisation of cyclic carbonate with monomers such as lactide, glycolide and ε- caprolactone has been used as a method to tailor the morphology, degradative and thermal properties of new materials.77,78 Incorporation of pendant functional groups in cyclic monomers such as carboxylic acids increases the degradation rate and solubility and provides a means of attaching other functional groups to the backbone.79 Research during the last fifteen years has resulted in the synthesis of a range of aliphatic polycarbonates. A selection of these is found in table 1 that lists their structure and thermal properties.

Cyclic carbonates have high reactivity towards amines, which can be utilized as a way of synthesizing polyurethanes without the use of isocyanates. Such polyurethanes are called hydroxy urethanes and are more stable than isocyanate derived polyurethanes since unstable biuret and allophanate groups do not form in the reaction with cyclic carbonates.66 In a model study Endo et. al. found that the reactivity of six membered rings was higher than that of the five membered, in the presence of primary amines.80

13 -----Introduction-----

Table 1. thermal properties of polycarbonates68

Entry Polymer Tg/°C Tm/°C Ref.

O O * 81 1 * n -17 O

O 82 2 O -51 +56 * O n *

O

83 3 * (CH2)12 +65 O O n *

O O * 69 4 * n +27 +120 O

83,84 5 O O * -28 * n O

83,84 6 O O * -15 * n O

85 O O * 7 * n +60 +117 O O 86 8 O O * -30 * n O O 84 9 O O * -15 * n O O O 10 -7 +48 87 O O * * n O O O N 88 11 H +40 +71 O O * * n O OH 88 O O * 12 * n +27 +117 O

O O 87 13 O O * +9 +86 * n O CN O O * 89 14 * n +69 +133 O F F O F F O 82 15 * O n * -40 +41 F F F F

14 -----Experimental-----

3 EXPERIMENTAL

3.1 MATERIALS

The polyols used in this work: bis-methylolpropionic acid (Bis-MPA), neopentyl glycol (NEO), trimethylolpropane (TMP), ditrimethylolpropane (Di-TMP), ethoxylated pentaerythritol (PP50) and hyperbranched polyester (Boltorn H30) were kindly provided by Perstorp AB. The hydroxyethyl methacrylate (HEMA 99%) and fumaric acid 99%, were obtained from Aldrich and used as received. Methyl sulfonic acid was distilled over phosphorous pentoxide prior to use. Polystyrene standards were purchased from polymer laboratories.

3.2 SYNTHESIS

3.2.1 Synthesis of neopentyl carbonate

(paper1)

Neopentyl glycol was reacted with diethyl carbonate in the presence of stannous(II)-2-ethyl- hexanoate (scheme 5). The reaction proceeds in two steps: first a condensation between the glycol and the carbonate yields an oligomer while releasing ethanol, second a thermal depolymerization. The formed ethanol was removed under reduced pressure and the temperature was increased to 200°C. At this temperature the oligomer depolymerizes yielding the cyclic monomer, which can be recovered by vacuum distillation.

O O Sn(Oct) Sn(Oct) 2 2 OO HO OH + O O prepolymer

NPC

Scheme 5. Synthesis of the carbonate monomer NPC from neopentyl glycol and diethyl carbonate

3.2.2 Cationic ring opening polymerization of neopentylcarbonate with fumaric acid

A series of polyols including a hyperbranched polyester (figure 6) were used for the synthesis of both linear polymers and star polymers with different number of arms and molecular weights

15 -----Experimental-----

OH

O OH O HO OH HO OH O O HO OH OH O O O HO O O O O O OH OH O OH O O OH OH O HO OH HO O O O O O O HO O O O O HO OH O O O O O O O O OH OH O O O O O HO O O O O O OH O O OH OH O O O O O O HO OH OH HO O O O OH PP50 HO OH NEO Di-TMP O O O OH O OH O O OH Boltorn H30 HO OH

Figure 6. Polyols used as initiators for cationic polymerisation

All polymerizations with fumaric acid were performed in bulk at 120 °C. The reaction vessels (round bottom flasks) were dried with a flame prior to addition of the reactants. The polymers were purified from catalyst and residual monomer by precipitation in methanol.

3.2.3 Synthesis of acrylate terminated poly(neopentyl carbonate) macromonomer

(manuscript in preparation)

O O OH OO O +

O O O O O OH O n O O

Scheme 6. Methacrylate terminated polyNPC macromonomer

Hydroxyethyl methacrylate (HEMA) and NPC were dissolved in toluene (HPLC grade). One drop of methyl sulphonic acid was then added to the solution and the reaction was run for a prescribed time (scheme 6). The macromonomer was isolated by precipitation in methanol. NMR and SEC was used to monitor the reactions and characterise the microstructure of all isolated polymers.

3.2.4 Synthesis of poly(neopentyl carbonate) brushes

The polycarbonate macromonomers were polymerized by free radical polymerisation and ATRP (scheme 7).

16 -----Experimental-----

O O O O O O O O O O O OH O OH O O n O O n O O O O O O OH

O O n O ATRP or free radical O O O O polymerisation O OH

O n O

Scheme 7. Synthesis of poly(NPC) brushes through polymerization of a methacrylate terminated macromonomer

PNPC (4 g, 2 mmol) and ethyl acetate (4 ml) were added to a 50 ml round-bottom flask, which was immersed in an oil bath at 65 °C for complete dissolution. The initiator, ethyl-2- bromoisobutyrate, and the ligand, Me6-TREN, were then added to the solution, in accordance with the predetermined monomer and initiator ratio. The solution was cooled to room temperature. The flask was sealed with a rubber septum and evacuated and back-filled with Ar(g) three times. Copper (I) bromide was introduced to the reaction flask under Ar- atmosphere. The reaction flask was again immersed in an oil bath at 65 °C. After complete dissolution, Ar(g) was bubbled for 2-3 minutes through the solution. The polymerisation was allowed to proceed 1-3 days, and the conversion of the macromonomer was monitored with 1H NMR. The polymer was purified by fractionated precipitation using THF as solvent and n- hexane as non-solvent. The same procedure was used for the synthesis of the star brush polymer, except that 1,1,1-tri (2’-bromo-2’-methylpropionyloxymethyl) ethane was used as a trifunctional ATRP-initiator.

PNPC (4 g, 2 mmol) and toluene (4 ml) were added to a 50 ml round-bottom flask, which was immersed in an oil bath at 60 °C for complete dissolution. The solution was cooled to room temperature. The proper amount of the initiator, AIBN, and CBr4 was added to the solution, in accordance with the predetermined monomer and initiator ratio. The flask was sealed with a rubber septum and Ar(g) was flushed for 3-5 minutes. The reaction flask was again immersed in an oil bath at 80 °C. After complete dissolution, Ar(g) was bubbled for 2-3 minutes through the solution. The polymerisation was allowed to proceed 3-6 hours, and the conversion of the macromonomer was monitored with 1H NMR. The polymer was purified by fractionated precipitation using THF as solvent and n-hexane as non-solvent.

3.2.5 Synthesis of hyperbranched polyesters by ring opening polymerization.

(paper 2)

A bishydroxymethyl substituted ε-caprolactone monomer was synthesized in four steps starting with cyclohexane diol. One of the hydroxylgroups was selectively substituted by benzylidene protected bis-MPA using dicyclohexyl carbodiimide (DCC) as transesterification reagent. The remaining OH group was oxidized to the ester in two steps. Treatment with pyridinium chlorochromate yielded the ketone in the first step, which was followed by a Bayer-Williger oxidation reaction using meta-chloro peroxybenzoic acid (m-CPBA).

The monomer was polymerized under bulk conditions at 110 °C in the presence of stannous(II)-2-ethyl-hexanoate. Copolymerisations were also performed together with ε- caprolactone in 1-4 and 1-5 ratios.

17 -----Experimental-----

3.2.6 Characterization of Bis-MPA dendrimers

(paper 3)

Three sets of dendrimers were synthesized by a divergent growth approach, utilizing benzylidene-[G#1] anhydride90 and acetonide-[G#1]-anhydride (figure 7).91 Two sets had benzylidene terminal groups with either a trimethylol propane or triphenolic core moiety. The third set had acetonide terminal groups and a triphenolic core. The structure of the dendrimers was confirmed by MALDI-TOF, NMR and SEC. SEC was also used to study the effect of core and terminal groups on the dilute solution properties.

O O O O O O O O O O O O O O

benzylidene-[G#1]-anhydride acetonide-[G#1]-anhydride

Figure 7. Anhydride building blocks for the construction of Bis-MPA dendrimers

3.2.7 Functionalisation of polycarbonates for crosslinking

(paper 4)

A series of linear polycarbonates were functionalised with methacrylate end groups by reaction with methacrylic anhydride (scheme 8). The reaction was performed in the presence of triethyl amine (1.5 equivalents relative OH) with a catalytic amount of dimethylaminopyridine. After complete conversion of the hydroxyl groups the functionalized polymer was recovered by precipitation in methanol. O O O O R H + O O O O O O

Et3N O O O DMAP R O O O O O

Scheme 8. End capping of hydroxyl functional polycarbonate by methacrylic anhydride

3.2.8 Crosslinking of acrylate functional polycarbonates

Six mixtures containing polymer and photo initiator (Irgacure 184) were prepared. Three linear methacrylate polymers were used and the content of photo initiator was 2 or 4 wt %. The mixing was made in acetone and after removal of the solvent the resulting solid was ground to a fine powder (particle size < 100 u). The powder was distributed on metal substrates that were subsequently placed in an oven until the powder had melted. The plates

18 -----Experimental----- were finally placed in a UV-oven from fusion systems and cured at a dose of 61 mJ/cm2 (belt speed 5 m min-1). The samples were passed through the light source 10 times to ensure complete cure.

3.3 CHARACTERIZATION METHODS

3.3.1 NMR

1H-NMR and 13C-NMR experiments were performed at 400 MHz on a Bruker AM400. Deuterated chloroform (CDCl3) was used as solvent and the solvent signal used as internal standard. Quantitative 13C-NMR spectra were acquired by the INVGATE experiment. To shorten the required delay time a magnetic quencher, chromium(III) Acetylacetonate (CrAcAc), was added (10% by sample weight).

3.3.2 SEC

Size exclusion chromatography (SEC) was performed using a TDA Model 301 equipped with one or two GMHHR-M columns with TSK-gel (Tosoh Biosep), a VE 5200 GPC Autosampler, a VE 1121 GPC Solvent pump and a VE 5710 GPC Degasser, all of which were made by Viscotek Corp. THF (1.0 ml min-1) was used as the mobile phase. The SEC apparatus was -1 calibrated with linear polystyrenes (PS), 11 narrow standards (Mp 0.580 to 185 kg mol ). Corrections for flow rate fluctuations were made by using the DRI signal of the injected THF as an internal standard. the right angle laser light scattering (RALLS) was calibrated with -1 -1 linear PS standards (Mw = 250 kg mol , PDI = 2.5, conc 1 mg ml ). The columns and all detectors were thermostated to 35 °C. Viscotek Trisec 2000 version 1.0.2 software was used to process data.

3.3.3 DSC

Differential scanning calorimetry was performed on a Mettler Toledo DSC 820. The sample was first heated from 25 °C to 130°C with a heating rate of 10 or 80°C min-1 and held at 130 °C for one minute. The sample was then cooled to –30°C and held for one minute. The sample was then reheated to 130°C at 10 or 80°C/min. The glass transition temperature was defined as the inflection point of the second heating.

3.3.4 Rheology

Rheological tests were performed on an AR 2000 (TA instruments) equipped with a Peltier plate and a 20 mm plate geometry. The experiments were performed in oscillation mode with a frequency of 0.1 Hz and displacement of 10-5 rad. The semicrystalline samples were first melted on the peltier plate at 130°C and allowed to cool at 40°C for 5 min before starting the measurements. The measurement was conducted with a temperature ramp of 5 C/min up to 130-160°C.

3.3.5 Raman spectroscopy

FT-Raman spectra were recorded using a Spectrum 2000 FT-Raman spectrometer (Perkin Elmer). The relative intensities of the peaks of interest were used to evaluate the degree of unsaturation.

19 -----Experimental-----

3.3.6 Curing of films

All films were polymerized using a Fusion Conveyor, equipped with Fusion electrode less bulbs, standard type BF9. The light intensity and the doses used were measured with a UVICURE® plus from EIT Inc., Sterling, VA, USA

3.3.7 Adhesion

Adhesion was evaluated using crosshatch adhesion according to ISO 2409. In this procedure a right-angle lattice pattern is cut into the coating and penetrating through to the substrate. The method may be carried out as a "pass/fail" test or as a six-step classification test where Gt 0 represents good adhesion and Gt 5 poor adhesion.

3.3.8 Pencil hardness

In this test a pencil is used to scratch the surface. The hardness is given according to the scale (B HB 1H 2H 3H 4H 5H 6H) from soft (B) to hard (6H) (iso 15184).

3.3.9 Erichsen ball test

This method gives relative flexibility of coating films. A steelball was pressed through the substrate, forming a cup in the substrate. The penetration depth of the ball before the coating cracks is measured in mm, ISO 1520.

3.3.10 Solvent resistance

The cured films were rubbed with methyl-ethyl-ketone (MEK). The number of rubs before the film is removed from the substrate gives the relative solvent resistance. A film is characterised as having good solvent resistance if it can withstand more than 200 double rubs.

3.3.11 Storage stability

Powder mixtures containing acrylate functionalized polycarbonate and photo initiator were kept in an oven at 45°C for one week.

3.3.12 Gloss

Gloss measured according to ISO 2813:1994, Gardner 60°. Equipment: Rhopoint Novogloss.

20 -----Results and discussion -----

4 RESULTS AND DISCUSSION

4.1 SYNTHESIS OF NEOPENTYL CARBONATE STAR POLYMERS

Bisphenol-a-polycarbonate, which is one of the main commercial thermoplastics, is produced by polycondensation of the bisphenol-a-diol (BPA) with phosgene in a one-pot reaction and is analogous to the synthesis of polyesters, where diols and diacids are used (scheme 9).92 Condensation polymerisation can however not be used to synthesize well-defined polymers of complex architectures, such as such stars and grafts. Living ROP is a method that allows the synthesis of well-defined polymers, however it involves an extra synthetic step since a cyclic monomer must be synthesized.

O HO OH + n Cl Cl

BPA O

O O

Scheme 9. Syntehesis of polycarbonate from bis-phenol A and phosgene

4.1.1 Monomer synthesis

O O Sn(Oct) Sn(Oct) 2 2 OO HO OH + O O prepolymer

NPC Scheme 10. Synthesis of neopentyl carbonate (NPC)

Neopentylcarbonate consists of two parts: the carbon backbone which is derived from neopentylglycol and a carbonate which can be introduced by condensation of the glycol with a carbonate source such as phosgene, carbonyldiimidazole, chlorophormate or a dialkylcarbonate. The carbonate source used in this work was diethylcarbonate, but diphenyl and dimethyl carbonate can also be used. Diethylcarbonate is very useful for producing

21 -----Results and discussion ----- neopentlycarbonate in the lab since it is easy to handle, as opposed to phosgene, and does not yield any hazardous condensation products (scheme 10).93-97

The preparation of neopentyl carbonate from diethyl carbonate and neopentyl glycol as described by Sarel et al. proceeds in two steps.98 In the first step oligomers or prepolymers are formed which are subsequently subjected to ring closing depolymerization resulting in formation of the cyclic monomer. A drawback of Sarel’s method is that it includes an extraction step before the pyrolysis. In addition, all volatile byproducts and reagents including residual neopentyl glycol were removed under reduced pressure, effectively eliminating the extraction step. With this method the monomer could be conveniently prepared in one pot on 200 g scale. In the present study, Sn(Oct)2 was used as catalyst to ensure formation of prepolymer and increase the rate of ring closing depolymerisation.

4.1.2 Synthesis of branched polycarbonates by cationic polymerisation

NPC was cationically polymerized by fumaric acid in the presence of a series of polyols (Scheme 11). The mild conditions ensured that the polymerisation proceeded according to an activated monomer mechanism. The use of an organic acid as catalyst eliminates metal compounds from the reaction, which is an advantage in for example medical applications.

OH HO

HO OH O O O HO OH O OH O OH NEO OH HO O

O Di-TMP O PP50

OO OO

HO O OH O O O n O O O O O O O n O O O O O O O O HO O O O n O OH n O O O O

O n O O OH Linear poly(NPC) O 4-arm poly(NPC)

HO

Scheme 11. Synthesis of branched polycarbonates

Linear polymers of NPC with neopentylglycol as initiator (scheme 11) were synthesized in bulk with monomer-to-initiator ratios of 10 and 20 to one. The conversions were above 90%. Figure 8 depicts the relationship between Mn and conversion in the polymerization of NPC with neopentylglycol as initiator. A linear correlation can be seen until near quantitative conversion. The polydispersity was narrow even at high conversion (Mw/Mn < 1.2). After complete conversion of the monomer a second feed with the same amount of monomer was

22 -----Results and discussion ----- made. The SEC traces depicted in figure 9 show a shift towards higher Mn with a slight increase of the Mw/Mn. This behaviour is characteristic of a living polymerization.

6000 1,2 1,18 5000 1,16 1,14 4000 1,12 3000 1,1 PDI 1,08 Mn (SEC) 2000 1,06 1,04 1000 Mn PDI 1,02 0 1 0 20 40 60 80 100 Conversion (%)

Figure 8. Mn obtained from SEC and PDI as a function of conversion for the polymerization of 40 equiv NPC with neopentyl glycol at 130°C in the presence of fumaric acid

23 -----Results and discussion -----

Table 2 Polymerizations of NPC with polyols in the presence of fumaric acid

M a Time Conv. Yield M a M a M a ID Initiator DP n n n w PDI αd aim theo. (h) (%) (%) 1H-NMR SEC SEC 1 Neo 10 2 700 20 95 85 2 500 2 600 2 700 1.04 0.69 2 Neo 20 5 300 40 95 85 4 700 4 800 5 000 1.04 0.70 3 Di-TMP 10 5 400 9 70 55 3 400 3 100 4 300 1.40 0.39 4 PP50 10 5 600 9 87 75 3 900 4 700 6 000 1.30 0.46 5 PP50 20 10 700 40 95 90 7 600 8 200 9 800 1.20 0.46 6 Boltorn H30 5 23 000 4 73 b 22 000 4 500 33 000 7.30 0.14 7 Boltorn H30 10 42 000 6 80 65 30 000 8 500 52 000 6.00 0.12 8 Boltorn H30c 10 42 000 - - - - 25 000 99 000 4.00 0.28 9 Boltorn H30 20 81 000 16 60 55 - 14 000 75 000 5.40 0.11 10 Boltorn H30c 20 81 000 - - - - 38 000 104 000 2.70 0,16 11 Boltorn H30 30 120 000 24 92 75 47 000 4 000 20 000 5.00 0.12 a g mol-1. b No precipitation. c Data in this row is from a fractional precipitation of the sample above it.d determined by SEC-vicometry.

24 -----Results and discussion -----

Mn = 7600 Mn = 5100 PDI = 1.2 PDI = 1.1

15.5 17.5 19.4

Elution Volume (mL)

Figure 9. SEC traces of the poly(NPC) polymers obtained by the polymerisation of 40 equiv of NPC with neopentyl glycol in the presence of fumaric acid. A second monomer addition shifts the trace to the higher molecular weight region.

Figure 10 displays the relationship between Mn and molecular weight for polymerization with an initiator containing four OH-groups. The Mw/Mn was slightly higher than for the linear polymer and increased up to 2 above 90% conversion, indicating an increase in intermolecular side reactions.

6000 2 1,9 5000 1,8

4000 1,7 1,6 3000 1,5 PDI 1,4 Mn(SEC) 2000 Mn 1,3 1000 PDI 1,2 1,1 0 1 0 20406080100 Conversion (%)

Figure 10. Mn obtained from SEC and PDI as a function of conversion for the polymerization of NPC, with a four-arm initiator (di-TMP) and a DPaim of 10, by fumaric acid at 130°C.

The polymerizations from multifunctional initiators gave Mn values lower than the theoretical values. The deviation of Mn from the theoretical value was more pronounced at higher M/I ratios, and may be attributed to the formation of linear polymer. The reasons for this could be spontaneous thermal polymerization or initiation from impurities. An experiment was

25 -----Results and discussion ----- therefore performed to determine the extent of thermal polymerization or decomposition of monomer; NPC was heated at 130°C for 24 hours resulting in 6% conversion according to 1H- NMR. OH

O OH O HO OH HO OH O O HO OH OH O O O HO O O O O O OH O OH O O OH OH O O O O O O HO O O O O O O O O O OH O O O O O HO O O O O O O OH O O O O O O HO OH OH O O OH HO OH O O O OH O OH O O OH Boltorn H30 HO OH

O

OO

OH

O O OH n OH HO O

O O O O O O O n OH HO O O O O O O O O O O HO n OH O O O O O O O O O O O O n O OH O O O O O O O n n O O O n O HO O O O O O O O O O O O O O O n O O O O OH O O O O O O O HO OH O O O O O n O OH O O O O O O n O O O O O O O O O O O OH O O O O O O O O n O O O O O O O O O O O O O O n O O O O OH O O O n OH O O O O O HO O O O O O O O O n O OH O n O O O O O O O O O O O O O O OH HO O n O n O O O O HO O

O O O O O n O OH O Multi-arm poly(NPC) OH OH

Scheme 12 Synthesis of 30 arm star polymers based on Boltorn H30 and NPC

Polymerizations with Boltorn H30 as a hyperbranched initiator (scheme 12) were performed with M/I ratios of 5, 10, 20 and 30 with respect to initiating hydroxyl groups. Conversion was kept below 90% to avoid gelation. The SEC analysis showed the presence of a linear polymer fraction that increased with the M/I ratio (samples 9 and 11 in figure 11). Precipitation in methanol from a solution of dichloromethane effectively removed residual monomer and

26 -----Results and discussion ----- catalyst, except in case of sample 6 (Boltorn, M/I=5, table 2, p. 23) where the polymer did not precipitate. However, fractionation was needed for the removal of the linear polymer byproduct. A fractionated Boltorn H30 npc star (sample 10) was then used as initiator for polymerization of additional npc with fumaric acid (figure 11). The sec trace (10b) of a sample taken from the reaction mixture shows a shift of the hyper star to the higher molecular weight region. The trace also shows that the peak representing the linear polymer fraction does not increase. One explanation may be that all impurities initially present in the Boltorn H30 initiated polymerization of linear polymer in the first grafting. Another possibility is that the end groups of the chains are more accessible as initiators compared to the end groups of the Boltorn H30, which favors the formation of star polymers.

Hyperstar Linear 11 9 10 10b

12.6 14.8 17.1 19.3 Elution Volume (ml)

Figure 11 SEC traces of PNPC polymerized from H30 before (9,11) and after fractionation (10). A second addition of monomer to the fractionated sample (10) shifts the molecular weight without increasing the linear peak (10b).

Cationic polymerization of cyclic carbonates is known to result in a degree of decarboxylation yielding undesirable ether bonds.71 1H-NMR however showed no evidence of formation of ether bonds in any of the polymerizations. The NMR characterization are discussed in the next section.

4.1.3 Characterisation

Characterization by NMR

1H-NMR was employed to monitor conversion and estimate the degree of polymerization DPNMR (figure 12). Conversion was estimated by comparing the peak integral at 1.12 ppm with the peak at 0.99 ppm. The peak at 1.12 ppm (b) corresponds to the protons of the methyl groups in the monomer and the peak at 0.99 ppm (b´) represents the methyl groups of the polymer backbone. The DPNMR was calculated by comparing the integrals of the repeating unit peak at 0.99 ppm (b´) and the peak at 0.93 ppm (d), corresponding to the methyl groups in the terminal repeat unit. The DPNMR is thus equal to I0.99/I0.93+1. This calculation can also be performed on the integral at 3.34 ppm (c) that corresponds to the CH2 in the α position to * the terminal hydroxyl group. In this case DPNMR is equal to I0.99/3 I3.34+1. If di-TMP is present as initiating polyol, the protons located next to the ether bond in di-TMP yield a resonance peak in the vicinity of 3.3 ppm, which makes it impossible to calculate DP using the peak integral at 3.34 ppm. However, the peaks arising from the ether bond in di-TMP indicate where peaks would likely emerge if ether bonds were formed during the polymerizations. A

27 -----Results and discussion ----- peak at 3.3 ppm indicates the presence of ether bonds during the polymerization. The integral of this resonance peak did not increase during the polymerization from di-TMP and it was not present in any of the polymerizations.

(b´) O (a´) O c R H O O O n O O d (b´) a´

O

OO (a) (b) (a) b HBP (d) HBP (c)

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 (ppm)

Figure 12. 1H-NMR spectra of a Boltorn-PNPC reaction mixture containing monomer.

50 48 46 (ppm)

160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 (ppm) Figure 13. Quantitative 13C-NMR spectra of a Boltorn-PNPC (sample 7). The enlarged area shows the quaternary carbons.

The degree of substitution of the hydroxyl groups in the hyperbranched polyester core was investigated by quantitative 13C-NMR. Hult et al. have shown that the 13C-NMR resonance corresponding to the quaternary carbon of the bis-MPA repeat unit is dependent on the degree of substitution.99 The resonance shifts for the fully substituted, mono substituted and terminal

28 -----Results and discussion ----- repeat units are found at 46, 48 and 50 ppm respectively. A distinct peak was detected at 46 ppm accompanied by a much smaller peak at 48 ppm, suggesting that the majority of the hydroxyl groups of the Boltorn were substituted (figure 13).

Characterization by SEC Analysis of branched polymers by conventional calibration using a single concentration detector and linear standards is often misleading since branched polymers have a different hydrodynamic relationship to the molecular weight than their linear counterparts. By the addition of a viscosity detector to the instrument setup and employing universal calibration (UC) it is possible to determine the molecular weight of polymers with branched architecture.100-102 In both cases however, the employed standards are linear. In the case of sample 11 (table 2, p. 23) the presence of large fraction of linear polymer with the unpurified Boltorn-NPC polymer affects the MW determination and yields a very low molecular weight value. Polymers with long chain branches such as star or comb polymers have reduced hydrodynamic radius compared to linear polymers of the same MW. By comparing the intrinsic viscosities of a linear reference polymer and a branched polymer it is possible to observe an increase in branching. The relationship between molecular weight and the intrinsic viscosity for a given polymer is described by the Mark-Houwink equation.

η = KM α

In this study the degree branching of the synthesized polymers was investigated by comparing the Mark-Houwink exponent α of the respective polymers.103,104, 105 A trend of decreasing values of α with increased branching is seen when comparing the linear polymers to the branched 4-arm stars and hyper stars (table 2, p. 23). This effect is the result of the polymers becoming denser when the branching increases.

4.2 SYNTHESIS OF POLYCARBOANTE BRUSHES BY A MACROMONOMER APPROACH

Like star polymers comb polymers have unique rheological properties. Brush polymers based on poly(neopentylene carbonate) macromonomers were synthesized in order to investigate their potential as powder coating resins. Two methods synthetic methods were investigated: Free radical polymerization (FRP) and atom transfer radical polymerization (ATRP). ATRP was included in the study since it allows better control of the reaction than FRP

4.2.1 Macromonomer

Methacrylate functional macromonomers with acrylate end functionality were synthesized by cationic ring opening polymerisation of NPC with HEMA in the presence of methyl sulfonic acid. The synthesis was performed in toluene solution as reported by Nakano.64 The polymers were isolated by precipitation in methanol. NMR analysis showed a 1:1 ratio between OH and acrylate end groups. The Mw was 2500 and the PDI below 1.2. This molecular weight was chosen to allow crystallization and maintain a reasonably high cross-link density after curing.

29 -----Results and discussion -----

Br O O O O

O O Br O O

Br Br (1) (2)

Figure 14. The ATRP initiators

4.2.2 Polycarbonate brush

Free radical polymerisation and ATRP were employed in the synthesis of molecular brushes. The polydispersity of the polymers obtained by ATRP was lower than the polymers obtained by free radical polymerization (table 3). The polydispersities of the polymers 1 and 2 were slightly higher than expected from the ATRP polymerizations. In addition the molecular weights were above the aimed value. This indicates unsatisfactory control of the polymerization, which may be attributed to the structure of the initiator.106,107 The initiator, Ethyl 2-bromoisobutyrate used in this study (figure 14) forms a relative stable tertiary radical in the initiating step, while the propagating polymer radical is secondary and less stable. This may lead to non-uniform initiation, and a high concentration of radicals at the beginning of the polymerisation, causing termination by recombination. An alternative initiator is Ethyl 2- bromopropionate, which yields a secondary radical of similar reactivity as the propagating poly(macro monomer) radical.

Table 3. Synthesis of polycarbonate brushes Conversion MW SEC ID Method Initiator DP, aim MW, aim (%) (g/mol) PDI α 1 ATRP mono (1) 50 100000 97 145100 1,35 0.07 2 ATRP mono (1) 100 200000 62 181100 1,36 0.21 3 Free radical AIBN 50 100000 148200 1,84 0.24 4 Free radical AIBN 100 200000 81 193600 2,71 0.23 5 ATRP tris (2) 50 300000 low ~15 227900 1,43 0.30

4.2.3 Star brush

1,1,1-tri (2’-bromo-2’-methylpropionyloxymethyl) propane was employed as a trifunctional ATRP initiator (figure 14) for the synthesis of a three arm, star brush. The polymerizations formed gels at conversions above 20%. One of the polymerisations (sample 5, table 3) was therefore stopped at a conversion of 15 % and analyzed by SEC (figure 15). The molecular weight was much higher than the expected, which is likely the result of poor initiation control due to the structure of initiator or the reaction conditions, which were not optimized. Careful examination of the chromatogram reveals a shoulder in the peak corresponding to the brush

30 -----Results and discussion ----- indicating recombination termination reactions. There was a great difference in molecular weight when comparing the results obtained by universal calibration and conventional calibration. Since conventional calibration underestimates the molecular weight of branched polymers, it is likely that this polymer (sample 5, table 3) shows a reduction in hydrodynamic volume as a consequence of the branching. The SEC results however do not answer the question whether the polymers are stars or not. NMR could only determine if complete substitution was achieved at the core. Matjyaschewski et al., have used AFM to visualize star brushes and determine their size distribution. It was evident that some of the stars were connected with other stars and that there was a distribution of the arm lengths.108

macromonomer

molecular brush

6.1 12.9 19.6 Rv (ml)

Figure 15. SEC trace of a solution containing macromonomer and a star shaped molecular brush.

4.3 SYNTHESIS OF HYPERBRANCHED POLYESTERS VIA RING OPENING POLYMERISATION

In this study self-condensing cyclic ester polymerization of a bis(hydroxymethyl)-substituted ε-caprolactone monomer was investigated as a means for the synthesis of hyberbranched polyesters. Ring opening polymerisation of cyclic monomers is an alternative to polycondensation reactions, which yield low control of the molecular structure and high molecular weight distributions. Copolymerization of cyclic monomers that yield branching with ordinary monomers like lactones and carbonates offers an alternative route to dendritic polymers with semi crystalline linear segments between the branching points.

The hydroxy methyl substitution was introduced for two reasons. First because ε- caprolactones with secondary OH-groups in the backbone are subject to intramolecular rearrangements, which was observed upon the hydrogenolysis of 5-benzyloxy-ε-caprolactone, where hydroxyethyl functionalized δ-butyrolactone was formed instead of the expected 5- hydroxycaprolactone (scheme 13). The other reason is that the methylol groups of bis-MPA are effective initiators for ROP of lactones and lactides in the presence of Sn(Oct)2.

31 -----Results and discussion -----

O O O

O H2 O O

Pd/C O HO HO

(1) (2) (3)

Scheme 13. The 7 membered lactone rearranges upon deprotection of the hydroxyl group.

4.3.1 Monomer Synthesis

Bis(hydroxymethyl)-substituted-ε-caprolactone was synthesized in four steps (scheme14), starting with 1,4-cyclohexanediol. Reaction with 2,2-bis(phenyldioxymethyl)propionyl chloride gave the monosubstituted ester (4). The remaining alcohol was then oxidized to the ketone (5) and subsequently to the ester (6). In the final step, the benzylidene-protecting group was effectively removed by hydrogenolysis, yielding the monomer (7).

OH OH O O O

DCC PCC m-CPBA O H2 O

Pd/C

OH O O O O O O O O

O O O O O O OH OH

(7)

(4) (5) (6)

Scheme 14. Synthesis of a lactone monomer with a pendant bis-MPA unit.

4.3.2 Polymer synthesis and Characterization

The polymerizations were performed in bulk at 110°C since side reactions in these types of 109,110 reactions are considerably reduced below 120 °C. The ratio of monomer to Sn(Oct)2 was kept as high as possible, between 200-400, in order to avoid transesterification reactions.

32 -----Results and discussion -----

O O O O O OH O OH O O O O O OH OH O

OH OH

O O

O O O OH OH O O O

OH O O O OH O HO O O OH O OH O OH O HO O O O OH + O O + OH OH O O O O OH O O O O OH OH O OH O HO HO

O O HO O OH O HO OH O O O OH O O OH O HO O O O OH O HO O O OH O O O O OH O O O O O O O O O O O OH OH O O O OH HO HO O O

OH OH

Scheme 15. Ring opening multibranching polymerisation of Bis-MPA functionalized lactone

Initiation of lactones from the hydroxyl groups of bis-MPA with Sn(Oct)2 is a living process58,59 and it was therefore interesting to investigate the polymerization behavior. Scheme 15 illustrates the early stages of the polymerisation and a few likely reaction products from the ROP of the bis-MPA lactone monomer. The molecular weight increase was similar to that observed for a classical condensation polymerization. The reaction proceeded with a slow increase in molecular weight and in the early stages only dimers up to tetramers were observed by SEC. Higher molecular weight oligomers and polymers were not detected until after 36-48 hours. This behavior could indicate that the rings react first, in the early stages of the reaction, and form oligomers that start to polymerize by transesterification after all the rings have been consumed. Another explanation could be that steric crowding slows down the reaction when the molecular weight increases (scheme 15). The molecular weight of the homopolymer (table 4) was about 3000 g mol-1, related to a linear polystyrene standard, and the polydispersity was quite high (2.8).

Table 4 results of the ROP of bis-MPA ε-caprolactone. -1 ID Monomer Mw (g mol ) PDI DB 1 bis-MPA-ε-caprolactone (7) 3000 2.8 0.50 2 (7) + -ε-caprolactone 1:4 8000 2.8 0.15

33 -----Results and discussion -----

1.3 1.2 1.1 1.0 0.9 0.8 0.7 1.25 1.20 1.15 1.10 1.05 1.00 ppm (D O) ppm (CDCl ) 2 3

Figure 16 1H-NMR spectra of hyperbranched polymers obtained by ROP of bis-MPA lactone (polymer 1, left) and a copolymerization with ε-caprolactone (polymer 2 right).

The degree of branching (DB) was determined by 1H-NMR. This was accomplished by comparing the relative intensities of the peaks corresponding to the methyl group in the bis- MPA units, which adopt different shifts depending on the degree of substitution. Figure 16 depicts two NMR spectra corresponding to a hyperbranched bis-MPA-ε-caprolactone and a copolymer consisting of bis-MPA-ε-caprolactone (7) and ε-caprolactone. Assignments of the NMR signals were made by using of model compounds synthesized in a previous study by Trollsås et al. (scheme 16).111 The relative peak intensities of polymer 1, dendritic (D = 1.0), linear (L = 3.9), and terminal (T = 3.0) corresponded to a DB of 0.5 according to Frechets definition (table 4).112 D + T DB = D + T + L

34 -----Results and discussion -----

Structure ppm(-CH3)

O (T) OH O O O OH OH O (T) RO 0.99-1.04 O + HO O OH O DCC DPTS

O OH (L) O O OR' O RO 1.14-1.15 O O (L) O O OH O

HO

O O (D) OR' O (D) RO 1.19-1.21 O O O OR' HO O O

O

O

O O O O O

HO O

(D) O

HO

Scheme 16. Model compounds and the 1H-NMR shifts of the branching units in hyerbranched poly(ε-caprolactone)

In addition to the homopolymerisation, a copolymerisation was made with ε−caprolactone (polymer 2, table 4 ). The molecular weight was increased considerably (Mw = 8000) but still with a high distribution (PDI = 2.8). The increased number of linear segments in this polymer reduced the degree of branching to 0.15.

4.4 CHARACTERISATION OF BIS-MPA DENDRIMERS WITH DIFFERENT CORE AND PERIPHERY

4.4.1 Synthesis

A series of Bis-MPA polyester dendrimers was synthesized (figure 17) in order to gain molecules that resemble a compact or globular structure in solution. The goal was to use size exclusion chromatography (SEC) analysis of these molecules to obtain reference data needed for the characterization of the branched polycarbonates. In addition, the characterisation of these dendrimers gave insight into the effects of core and peripheral structure on the overall size of bis-MPA dendrimers in solution. Synthesis of the dendrimers was accomplished by divergent growth, utilizing the recently developed anhydride chemistry90,91, which facilitated the synthesis of the dendrimers.

35 -----Results and discussion -----

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O OOO O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O OO O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O OO O O O OO O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O OO O O O O O O O O O O O O O O OO O O O O

Acetonide-[G#4]-Ar Bz-[G#4]-TMP Bz-[G#4]-Ar

Figure 17. The fourth generation dendrimers in the respective sets, with different terminal groups and core moieties. From left to right acteonide-trisphenolic, benzylidene- trimethylolpropane, benzylidene-trisphenolic

4.4.2 Characterization of dendrimers by size exclusion chromatography

-1,2

-1,25

-1,3 α = 0.52 -1,35 ] η -1,4

Log[ α = 0.08 -1,45 Bz-G#-Ar α = 0.10 Ac-G#-AR -1,5 Bz-G#-TMP

-1,55 α = 0.07 polystyrene

-1,6 2,5 2,7 2,9 3,1 3,3 3,5 3,7 3,9 4,1

Log(MW)

Figure 18. Mark-Houwink plots of Bis-MPA dendrimers with different cores moieties and terminal groups

The dendrimers were characterized by SEC, equipped with three detectors connected in series. This setup included a refractive index detector, a viscosimeter, and a light scattering detector. Use of the viscometer allowed the construction of Mark-Houwink plots for each of the dendrimer sets (figure 18).

36 -----Results and discussion -----

The slope of the curves obtained by plotting log MW vs log [η] corresponds to the α exponents in the Mark-Houwink equation.

η = KM α

The slopes of the dendrimer curves ranged from 0.07-0.1, which are very low values compared to linear polymers that usually show slopes above 0.5. This acquired data was compared to the Mark-Houwink exponents of the branched polycarbonates (table 2) and used as reference to perfectly branched polymers.

The retention volume of the Bz-[G#4]-TMP was greater than observed for Bz-[G#4]-Ar and Acetonide-[G#4]-Ar, which both eluted at the same volume (figure 19). This observation suggests that the hydrodynamic volume of these dendrimers depends on the structure of the core moiety rather than the terminal groups.

100

78

55

32 Relative Response

9

-13 8.0 8.4 8.8 9.3 9.7 10.1 Retention Volume (mL)

Figure 19. SEC traces of the 4th generation dendrimers: Acetonide-[G#4]-Ar, Bz-[G#4]-Ar and Bz-[G#4]-TMP.

To determine the magnitude of this effect, the viscosimetric radius (Rv) of each dendrimer was calculated by Einsteins equivalent sphere model:

1  3  3 R =  []η M  v 10πN   A  that is based on the Stokes-Einstein relationship for the viscosity of suspended spheres. The values of Rv (table 5) were calculated using the molecular weights, obtained by MALDI-TOF and the intrinsic viscosity, obtained by the online viscometer. The Rv of the dendrimers with TMP core moieties were in general slightly lower than the corresponding dendrimers with

37 -----Results and discussion -----

Table 5. Molecular weights and viscosity data of the bis-MPA dendrimers -1 a -1 b -1 Dendrimer Mcalcv (g mol ) M (g mol ) [η] (dl g ) RV (Å) Bz-[G#1]-Ar 919 917 0.037 8.10 Bz-[G#2]-Ar 1880 1877 0.038 10.5 Bz-[G#3]-Ar 3802 3708 0.041 13.4

Bz-[G#4]-Ar 7646 7636 0.035 16.3

Bz-[G#1]-TMP 747 747 0.029 7.00 Bz-[G#2]-TMP 1708 1706 0.031 9.42 Bz-[G#3]-TMP 3630 3623 0.032 12.3 Bz-[G#4]-TMP 7474 7452 0.034 15.9 Bz-[G#5]-TMP 15162 15099 0.034 20.1

Acetonide-[G#1]-Ar 774 - 0.033 7.40 Acetonide-[G#2]-Ar 1592 1588 0.037 9.78 Acetonide-[G#3]-Ar 3226 3221 0.039 12.6 Acetonide-[G#4]-Ar 6493 6486 0.041 16.2 a determined by MALDI-TOF, b measured by SEC aromatic core moieties, as indicated by the chromatograms (figure 19). The difference in size was a marginal 0.3 angstroms

4.5 POWDER COATINGS

The polycarbonate resins were evaluated for use as powder coatings. The thermal and rheological properties of a series of linear and branched polycarbonates were evaluated by DSC and rheology measurements. A set of linear polymers, with varied chain length, was end functionalized with methacrylate groups and crosslinked by UV-initiated radical polymerisation after deposition on metal substrates. After crosslinking, the films were evaluated with conventional coating testing methods. In addition, the storage stability of the acrylate powder resins was investigated.

4.5.1 Thermal properties

The thermal and rheological properties are critical to the performance of a powder coating. A high Tg results in good storage stability and mechanical properties but hinders flow. In this study semi-crystalline polymers are used to maintain storage stability and provide a rapid drop in viscosity, at the desired processing temperature, which allows low temperature curing. However the use of semi-crystalline polymers introduces a conflict between the properties; long chains yield a higher degree of crystallinity but reduce the cross-link density resulting in poor mechanical properties. DSC measurements performed on the polycarbonate resins, displayed in table 3, show a Tg around 30°C and melting points between 85-120°C. These

38 -----Results and discussion ----- melting temperatures are in the vicinity of processing temperatures that allow use of a powder coating on a substrate such as medium density fibreboard (MDF).

As seen in table 6, melting endotherms were observed in the second heating for the linear and 4-arm star polymers with an arm length of 8-10 repeating units or more. In addition, Boltorn- PNPC (sample 11 table 2 p. 23) showed two peaks in the second heating but this sample contained a large fraction of linear crystalline oligomers (figure 20 #11). The Boltorn-PNPC samples 8 and 10 did not show melting peaks in the second heating although a Tm of 90°C was observed in the first heating. A new experiment was therefore made where the temperature was kept at 50°C for one hour prior to the second heating of these samples. However, no indication of crystallization was found. A recent study has shown that dendritic cores of star polymers reduce the level of crystallinity in poly ε-caprolactone star polymers.113 Some thermograms obtained at a heating rate of 10°C/min show two peaks in the first heating and one peak in the second heating. After increasing the heating rate to 80°C/min the distance between the first heating peaks decreased and in some cases only one broad peak was observed. These findings are consistent with previous reports and indicate changes in crystallite size or unit cell structure.70,98,114 The linear and 4-arm star polymers showed glass transition temperatures between 20-30°C and melting temperatures between 90-115°C. The length of the polymer chains affected the melting point, which was increased with chain length.60 In the cases of short chains with low melting points there was a relatively narrow interval between the Tg and Tm, which is beneficial for solid coating applications.

Table 6 DSC data for PNPC linear and star polymers found in table 2 p. 23 M SEC Heating rate T T T ID Initiator w DP PDI g m cryst (g/mol) arm (°C/min) (°C) (°C) (°C) 1 Neo 2 700 20 1.04 80 25 116 101 1 Neo 2 700 20 1.04 10 - 111 101 2 Neo 5 000 36 1.04 80 30 119 107 2 Neo 5 000 36 1.04 10 - 114 107 3 di-tmp 4 300 8 1.40 80 20 105 85 3 di-tmp 4 300 8 1.40 10 - 102 85 5 pp50 9 800 16 1.20 80 25 95,105b 55 5 pp50 9 800 16 1.20 10 - 87,105b 55 8 Boltorn 99 000 24 4.00 80 10 105a - 8 Boltorn 99 000 24 4.00 10 - 65-75-85a,b - 10 Boltorn 104 000 26 2.70 80 15 112a - 10 Boltorn 104 000 26 2.70 10 - 96a - a On 1st heating, b More than one melting peak present

39 -----Results and discussion -----

Linear PNPC #1 Di-TMP-PNPC #3 PP50-PNPC #5 Boltorn-PNPC #11 o d En

-50 0 50 100 150 Temperature (°C)

Figure 20 . DSC thermogram of selected polycarbonates. The ID # refer to the polymers listed in table 2 on page 23.

Table 7 DSC data for PNPC brushes described in table 3 M SEC Heating T T 1st T 2nd T ID w PDI g m Integral m Integral cryst (initiator) (g/mol) -rate (°C) (°C) (J/g) (°C) (J/g) (°C)

1(ATRP) 145100 1.35 80°C/min 21 116 52 - - -

1(ATRP) 145100 1.35 10°C/min - 97 44 87* 0,27 -

2(ATRP) 181100 1.36 80°C/min ° 107 49 99 15 59

2(ATRP) 181100 1.36 10°C/min - 93 46 94 18 59

3(AIBN) 148200 1.84 80°C/min 14 105 52 - - -

3(AIBN) 148200 1.84 10°C/min - 90 50 81* 4,6 -

4(AIBN) 193600 2.71 80°C/min 22 111 48 98 14 70

4(AIBN) 193600 2.71 10°C/min - 98 49 91 17 53

5(ATRP) 227900 1.43 80°C/min 22 115 51 - - -

5(ATRP) 227900 1.43 10°C/min - 100 48 93 12 64

The DSC measurements of the brushes (table 7) showed similar properties as the stars. Melting points were observed both in the first and second heating, however the integral was reduced considerably in the second heating. It appears that the crystallisation is hindered or slowed down due to the branched structure.

4.5.2 Rheological properties

The polycarbonate resins were analysed by a rheometer to determine the flow characteristics at the intended processing temperatures. In a typical measurement the resin was melted on a peltier plate before the geometry was put into contact with the sample and cooled until it

40 -----Results and discussion ----- solidified. The sample was then heated up to 130°C and the melting transition observed (figures 21 and 22). The graphs show melting in the temperature range 85-120 C. The measurements show a very high complex viscosity until the onset of melting when the viscosity starts to drop rapidly, five orders of magnitude in an interval of a few degrees. This illustrates the sought properties for use as powder coatings: stability up to a defined temperature followed by a rapid drop in viscosity that facilitates levelling. The melting point varied with chain length and architecture in the same way as observed in the DSC analysis; the melting point decreased with reduced chain length and introduction of branching.

It is also clear that the architecture has a significant effect on the melt viscosity. The viscosity decreased with the introduction of branching. For example, the H30 star polymers were of considerable higher molecular weight than the linear polymers but had only slightly higher melt viscosity. However the H30 hyper star with an arm length below ten failed to crystallize. The use of these resins as coating binders requires optimization of the chain length to yield enough crystallisation while keeping the arms short enough for sufficient cross-link density.

The synthesized comb polymers showed melt viscosities that were slightly above the desired level for powder coatings (figure22), although brushes with a lower molecular weight would likely fit in the right viscosity region.

1,00E+08 H30 PNPC (long) #10 1,00E+07 H30 PNPC (short) #8 linear PNPC Mw 5 000 1,00E+06 linear PNPC Mw 2 700 PP50 PNPC Mw 9 800

1,00E+05 ) s 1,00E+04 (Pa ) * (n

1,00E+03 g o l 1,00E+02

1,00E+01

1,00E+00

1,00E-01 70 80 90 100 110 120 130 140 Temperature

Figure 21 . Complex viscosity vs. temperature for linear and branched polycarbonates (table 2 p. 23). Melting transitions are seen for all the samples except the “H30 PNPC (short) #8”, which has arm length less than 10 units.

41 -----Results and discussion -----

1,00E+07 #1 Mw 145000, PDI 1.4

1,00E+06 #2 Mw 180000, PDI 1.4 #3 Mw 150000, PDI 1.8 #4 Mw 195000, PDI 2.7 1,00E+05 #5 Star Mw 230000 ) s

a 1,00E+04 *) (P

(n 1,00E+03 g lo

1,00E+02

1,00E+01

1,00E+00 70 80 90 100 110 120 130 140 Temperature

Figure 22 . Complex viscosity vs. temperature for polycarbonate brushes (table 5 p. 31).

4.5.3 Functionalization of endgroups (acrylation) for cross-linking.

The hydroxyl endgroups of three linear polycarbonates were readily functionalized with methacrylate endgroups to enable cross-linking. Methacrylic anhydride was used in a base catalyzed reaction that resulted in complete functionalization of all endgroups, as confirmed by 1H-NMR (figure 23). Complete substitution was verified by the disappearance of the peak at 0.93 ppm, corresponding to the methyl groups of the terminal repeating unit. After the reactions all obtained polymers were characterized by SEC to investigate if any premature polymerisation had occurred and no increase in polydispersity was noted.

42 -----Results and discussion -----

O O O O R H + O O O O O O

Et3N O O O DMAP R O O O O O

Before acrylation

After acrylation

Figure 23. Acrylation of polycarbonate with methacrylic anhydride is verified by NMR.

4.5.4 Powder formulation and storage

Formulations composed of acrylate functional polycarbonate (DP 10, 20 and 40) and photoinitiator (2 or 4 wt%) were prepared by mixing the components in acetone. This procedure ensured complete mixing of the components. A solid was obtained, after evaporation of the solvent that was ground and sieved to afford powder particles with sizes below 100 µ. Three powder-coating formulations (10 2, 20 2 and 40 2 in table 5) were tested for storage stability at 45°C for one week. At the end of the test period the powder flowed as in the same way as before the test.

4.5.5 UV-curing of polycarbonate films

Films were prepared by deposition and curing of powders on metal substrates. Application with the fluidized bed technique available showed that the particles adhered to the metal substrate, however, due to the limited amount of polymer available it was difficult to cover the entire substrate by this method. Samples were therefore prepared by a simple procedure in

43 -----Results and discussion ----- which the powder was strewn onto the substrate. A limitation with this procedure is that it is difficult to control the film thickness. Levelling was accomplished in an oven at 140°C where the substrate reached a temperature of 120°C after 3 minutes. Smooth films were obtained after UV irradiation in the fusion UV-curing apparatus.

before cure after cure

1720 1700 1680 1660 1640 1620 1600 1580 1560 1540 wave number

Figure 24. Raman spectra of uncured polycarbonate and cured films. The peak at 1640 cm-1 corresponds to the unsaturations of the acrylate.

4.5.6 Film properties

Table 8 contains the properties of films obtained by curing three linear, methacrylate functionalized poly(neopentylcarbonate)s with different chain lengths. The amount of photo initiator was 2 or 4 wt-% yielding a total of six films.

Table 8. Properties crosslinked polycarbonate films. Thickness Erichsen test Pencil Cross ID* MEK-rubs Gloss (µm) (mm) hardness hatch

10 2 98 200 10.6 1 H 1 75-80

10 4 111 200 13.8 1 H 1 75-80

20 2 63 100 13.1 2 H 1 75-80

20 4 205 170 13.2 2 H 2 75-80

40 2 168 150 6.2 3 H 4 Opaque** 40 4 52 80 6.9 4 H 5 Opaque** * The ID is given as segment length, wt % photo initiator, ** post cure crystallization in films.

The MEK rub test (table 8) showed that curing was successful with a tolerance of up to 200 double rubs. The films were also analysed with RAMAN spectroscopy and the

44 -----Results and discussion ----- results compared with uncured resin to determine the degree of residual unsaturation. The peak at 1640 cm-1, corresponding to the carbon-carbon double bond in the acrylate, was not present in the cured films (figure 24). IR analysis was also performed but no signal was detected for the double bonds in the uncured polymers.

The films were in general clear although the films of polycarbonates with more than 30-40 repeating units between cross-links became slightly opaque. This is likely caused by crystallisation of the long chain segments. The Erichsen ball test showed that the flexibility and adhesion was good except for the long polycarbonates, probably due to crystallisation. The crosshatch test gave the same result. The films were soft (1-2 H pen hardness)(table 8).

45 -----Conclusions -----

5 CONCLUSIONS

Linear and star shaped poly (neopentyl carbonate) were synthesized by ring opening polymerisation in the presence of fumaric acid. The polymerisations appeared to proceed by an activated monomer mechanism that reduced the risk of side reactions and formation of ether bonds. Star polymers with up to 30 arms were synthesized by ring opening polymerisation of neopentylcarbonate from a commercial hyperbranched polymer, Boltorn™.

Comb polymers, consisting of a polyacrylate backbone and neopentylcarbonate grafts, were synthesized, both by free radical polymerisation and ATRP. These compounds are interesting as rheological additives or binders in powder coatings. As binders in powder coatings the low viscosity of comb polymers enables use of binders with higher molecular weight than usual.

Hyperbranched polyesters were synthesized by ring opening polymerisation of an e- caprolactone monomer bearing a pendant Bis-methylopropionic acid moiety. The polymerisation was initiated by Sn(Oct)2 and resulted in a polymer with a molecular weight of 2-3000, PDI of 2.8 and a DB of 0.5. A Copolymerisation with ε-caprolactone resulted in a molecular weight of 8000, polydispersity of 2.8 and a DB of 0.15.

Bis–MPA dendrimers with different cores and end groups were used as model compounds representing spherical polymers in solution. The Mark-Houwink a exponents of the dendrimers was calculated and compared with the values obtained for the series of polycarbonates. The α values of the Boltorn H30 star polymers were close to the values of the ddendrimers, indicating that the H30 stars assume denser conformation than the random coil in solution. The chromatograms of the dendrimer series suggested that the core moiety had an effect on the hydrodynamic volume of the dendrimers, whereas the terminal groups did not. This observation was supported by calculation of the viscosity radius derived by Einstein’s equivalent sphere model.

The thermal and rheological properties of the polycarbonates are suitable for use as powder coatings. DSC showed a Tg transition between 20-30 °C and melting from 90-120 °C. The rheological measurements showed a rapid decrease of viscosity at the melting point, to a level suitable for levelling of a powder coating. The branched polymers showed reduced melt viscosity compared to the linear, which can be used to tune the viscosity of a coating formulation.

Linear poly neopentyl carbonates were end capped with acrylate groups to enable crosslinking by a free radical mechanism. Six powder coating formulations containing binder and photo initiator were applied on metal substrates and cured by UV irradiation. The obtained coatings showed good solvent resistance, good flexibility and low pencil hardness (1-2H). Post cure crystallisation was observed in the films with chain lengths of more than 20 units between the

46 -----Conclusions ----- cross-links. The amount of photoinitiator (2 or 4%) had no visible effect on the coating properties.

47 -----Futurework -----

6 FUTURE WORK

The results show that there is potential for semicrystalline polycarbonates to be used as UV- curable powder coatings. However further testing is necessary to further investigate the rheological and mechanical properties of these polymers. The properties of model coating systems can be tuned by blending resins with different architecture and molecular weight. In a later stage pigment and fillers could be added to yield a formulation that resembles a commercial powder coating. Mechanical testing of a series of formulations could be performed with dynamic mechanical thermal analysis (DMTA) and scratch testing with a nano scratch-testing (NST) device that allows analysis of small coating samples.coatings wold also need to be tested for weathering stability and compared with commercial systems. Such measurements could be performed in an accelerated weathering test. The polymers synthesized in the thesis work can also be used as model compounds for comparison with polymers obtained in condensation reactions of carbonates and diols.To accommodate the increased quantities of polycarbonate required for these tests, a scale up of the synthesis is necessary.

Hyperbranched polymers could be synthesized by copolymerization of a cyclic carbonate such as neopentyl carbonate and a cyclic AB2 monomer that yields branching upon polymerization. Potential cyclic AB2 monomers that could be investigated are cyclic carbonates with pendant hydroxyl groups. Such monomers could be synthesized in fewer synthetic steps than the cyclic ester presented in this thesis.

Processing methods other than melt mixing such as suspension techniques could be investigated to prepare powder resins.

The carbonate brushes need more evalution and optimization of the reaction condition. It would be interesting to investigate if AFM could be used to characterise the stars. However, the rheology measurements show that the polymers obtained by the free radical technique possess the sought rheological properties.

48 -----Acknowledgements -----

7 ACKNOWLEDGEMENTS

I would like to express my sincere thanks to the following people:

My supervisor Anders Hult for accepting me as his student, for his patience over the last five- six years and for all the fun and rewarding times with the group.

Stefan Lundmark for introducing me to the industrial side of science and for all his advice and inspiration.

Eva Malmström and Mats Johansson for all their help and discussions, Eva in particular for her valuable comments during the thesis writing.

Prof. Ann Christine Albertsson is thanked for her leadership as head of the department. The other professors Ulf Gedde, Sigbritt Karlsson and Bengt Stenberg are acknowledged for their work towards a creative atmosphere at the department

The administrative staff for a nice job especially always being very helpful: Inger, Viktoria, Maggan, Emma, Maria, Barbara and Ove

Perstorp AB is greatly thanked for the financial support

Members of ytgruppen for creating a crazy and scientific atmosphere and for never failing to amaze me – Thierry Glauser, Claire Pitois, Helene Magnusson, Phillippe Busson, Linda Sundberg,Tommy Haraldsson, Jonas Örtegren, Michael "Mys Mys, Habib" Malkoch thanks for the fashion tips and showing me the art of eating a falafel at Orontes. Hasse "Big Mamma" Claesson, for being the true resource in training and for his honesty. Andreas "Kruppe" Krupicka for Havanna Club and late night cappuccinos. Johan Samuelsson for his help with the layout of this thesis. Robert “Rauken” Westberg for his peculiar dance moves and for being such an excellent host at Husby parties (w/ a little help from Ana). Emma Östmark for taking care of the sec after I am gone. My pet(e)rified roomies Josefina Lindquist and Hanna Lönnberg. Hanna for her work with the polycarbonates. Daniel “JPIL” Nyström, Linda Fogelström, Andreas “METRO” Nyström, Per "starkis" Antoni for help with Microsoft stuff, Magnus Jonsson, Kattis, Robert ”Mini Bob” Westlund. Anna Carlmark for helping me with the dishes and for a nice time in the lab, Cecilia Stenberg for finding use for the CL and Daniel “the trucker” Ståhlberg for his coatings expertise.

The people from “the other side of the river” Björn Olander and Natalia Andranova for all the coffee and philosophy in 469, Janis “the golf pro” Ritums, Gunnar Karlsson for the time at söder, Rickard “Sleepy” Olsson. Karl F Brunius, Kamyar Fateh Allawi and Guillaume Gallet for the foie grois and the chess matches. And all you who I did not mention here.

49 -----Acknowledgements -----

David Sandquist for the work on the HBP carbonate.

Björn Atthoff at Uppsala University is thanked for letting us use the rheometer and helping with the measurements.

Andreas Woldegiorgis is thanked for the MALDI analysis.

Mikael Trollsås and Jim Hedrick for an excellent introduction to the field of polymer science during my diploma work at IBM. Mikael is also thanked for suggesting that I should begin with the phd.

Henrik Ihre for your advice and help

To my friends in the real world I don’t expect you to read this far but thank you all for the good times and your support.

To my family Charlotte, Stefan and Mikael. Thanks for your love and support during these years, and for putting up with this “nutty professor”

Finally to Elin for being such a loving person and for bringing out my good sides. Thank you for all your help with the thesis and for brightening my day.

50 -----References -----

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