Approaches to the synthesis of block and graft copolymers with well defined segment lengths

Abstract

The synthesis of amine end-functionalised polymers by controlled free radical techniques has been investigated with a focus on methods that provide primary amino end-functionalised polystyrene. The aim of these investigations was to provide precursors to block and graft polyolefins and polyesters by interchain coupling reactions. The approaches investigated involved developing strategies for the synthesis of phthalimido-functional polymers which can be quantitatively deprotected to yield the desired amino-functional polymers. Initially synthesis by atom transfer radical polymerisation (ATRP) was explored. A number of approaches based on ω-functionalisation (end-group substitution) and α-functionalisation (functional initiator) were examined. A novel ATRP initiator, N-bromomethylphthalimide, provided the most promising results but still had limited applicability because of its low solubility in polymerisation media. The problems encountered with the ATRP approaches prompted an exploration of techniques based on reversible addition fragmentation chain transfer (RAFT) approach. Novel phthalimidomethyl RAFT agents (trithiocabonates, xanthates) were synthesized. The activity and scope of the new RAFT agents was investigated in polymerisations of styrene, n-butyl acrylate, Nisopropylacrylamide, N-vinylpyrrolidone (trithiocarbonate) and vinyl acetate (xanthate). The syntheses of α-phthalimidomethylpolystyrene were successfully scaled up and hydrazinolysis afforded a range of α- aminomethylpolystyrenes of low polydispersity and controlled molecular weight. The syntheses of primary amino-functional polymers using the pthalimidofunctional RAFT agents necessitated the development of a convenient method for conversion of trithiocarbonate groups to inert chain ends. Thermolysis proved a most simple and efficient method of achieving this for both polystyrene and poly(n-butyl acrylate). Thermolysis also provided a means of further characterising the mechanism of the RAFT process.

A simple and efficient method for amino end-group analysis was developed that involved in-situ derivatisation with trichloroacetyl isocyanate followed by 1H NMR analysis. The method was shown to be a suitable method for determining a wide range protic end-groups (NH2, OH, COOH) in synthetic polymers. Finally, metallocene polyolefin based coupling trials largely with controlled amino-functional polystyrene were conducted as an initial investigation into the production of high value added grafted polyolefins (and polyester). The grafting trials were carried out on a small scale with a view to directing future experiments.