Exploring the frontiers of macromonomer chemistry

Abstract

Since the discovery of catalytic chain transfer polymerisation (CCTP) in the 1970s, the reactive low molecular weight macromonomers characteristic of this technique have proven to be chemically versatile and easily industrially-scalable. However, despite detailed investigations into the mechanism and properties of these CCTP-derived macromonomers, little attention has been paid to the combination of CCTP with other polymerisation techniques in either industry or academia. Indeed, although CCTP has been effectively used in combination with radical techniques such as reversible addition fragmentation chain transfer (RAFT) polymerisation and atom transfer radical polymerisation (ATRP) and CCTP-derived macromonomers been used as comonomers in a second-stage conventional free radical polymerisation (FRP), non-radical techniques have not been explored. The use of multiple polymerisation mechanisms in a single polymer eliminates the restrictions of monomer-technique compatibility, and increases the possible monomer combinations, thus polymer properties obtainable. In this thesis, a toolbox of radical and non-radical polymerisation techniques as well as post-polymerisation modifications in combination with CCTP have been explored and developed. Macromonomers synthesised via CCTP contain a reactive double bond, which can undergo a Michael addition with lithium ester enolates, resulting in the formation of a macroinitiator capable of polymerising methacrylic monomers anionically. The resultant block copolymers contain a predominantly atactic block (derived from the radical CCTP) and an isotacticoid or syndiotactoid block (derived from the anionic polymerisation). The nature of the second block depends heavily on the conditions of the polymerisation. Functional macromonomers based on styrene and maleic anhydride (pSMA) and styrene, maleic anhydride and a-methyl styrene (pASMA) have been synthesised using CCTP. Chain transfer constants for these polymerisations have been determined and detailed 2D NMR analysis was used to reveal that the end group of pSMA is maleic anhydride-based with a vinylic moiety, and for pASMA the end group is predominantly a-methyl styrene, also with a vinylic moiety. Further post-polymerisation functionalisation of pSMA via Diels-Alder and thiol-ene reactions has also been explored. Thiol chemistry has been exploited to synthesise block copolymers. Thiol-ene reactions have also been used to modify methacrylic macromonomers for use in polyurethane chemistry to generate triblock copolymers. Synthesis of block copolymers of poly(ethylene-b-methyl methacrylates) have been attempted using two routes. The coupling of methyl methacrylate-based macromonomers to thiol-terminated polyt(ethylene) proved futile under the reaction conditions restrictions set by the properties of poly(ethylene). The same block copolymers could, however, be realised using the thiol-terminated poly(ethylene) as a macro-chain transfer agent in a radical polymerisation of not only methyl methacrylate but also butyl acrylate and styrene. The vinylic functionality of dimers of methyl methacrylate (MMA) can be epoxidised using m-chloroperoxybenzoic acid. Model studies of the epoxidised dimer of MMA (e-MMA2) showed that homopolymerisation of the epoxide results in back-biting of the epoxide, even under cationic ring opening polymerisation conditions. Polymerisation of THF in the presence of e-MMA2 (using BF3.OEt2 as the initiator) gave surprising results. e-MMA2 does not copolymerise with THF, but rather catalyses the reaction. Then once the THF maximum conversion has been reached, e-MMA2 end-caps the polymer. e-MMA2 has also been used in coupling reactions to amines and (macro)alcohols. CCTP-derived co-macromonomers of cyclohexyl methacrylate and MMA have also been synthesised. These co-macromonomers have then been copolymerised radically with 2-dimethylaminoethyl acrylate (DMAEA) to form graft copolymers with a range of different grafting densities and graft lengths. The properties of these polymers were investigated with respect to the suitability of these polymers for use as anti-static and anti-fogging additive for polycarbonate substrate. As coatings for polycarbonate, the graft copolymers showed promising results, for both anti-static and anti-fogging applications. A toolbox of different chemistries has been developed for use in combination with CCTP, significantly contributing to both the fields of CCTP and complex architectures. The potential of these chemistries is large owing to the versatility and range of different techniques used, providing many options in terms of monomer choice and polymeric architecture. Although at present there are no direct applications for the majority of the chemistries developed as part of this thesis, the scope and the variability of the techniques and monomeric starting materials are redolent with possibilities. As such, the use of graft copolymers as surface modifiers for polycarbonate is just the beginning to a host of different applications.