Synthesis and characterisation of poly(methylphenylsilane) block copolymers

Samples of α,ω-dichloropoly(methylphenylsilane) (diCIPMPS) were synthesised via the Wurtz-reductive coupling polymerisation. Subsequent bromination of PMPS afforded monomodal polymers with halogenated chain ends, namely α,ω-dihalopoly- (methylphenylsilane) (diXPMPS). Condensation reactions of diXPMPS with alcohols were investigated in order to determine the reactivity of the halide end groups. Condensation reactions involving polymeric alcohols such as poly(ethylene oxide) and poly(ethylene glycol) methyl ether with diXPMPS to form amphiphilic block copolymers were attempted, but proved ultimately unsuccessful.

An alternative route whereby a PMPS macroinitiator was used to form ABA block copolymers via a transformation mechanism is described. ABA block copolymers of methyl methacrylate and methylphenylsilane (PMMA-PMPS-PMMA) were synthesised using a methodology based on atom transfer radical polymerisation (ATRP). The reaction of samples of diXPMPS with 2-hydroxyethyl-2-methyl-2- bromopropanoate gave suitable macroinitiators for the ATRP of methacrylic monomers. Amphiphilic ABA block copolymers were synthesised via the polymerisation of either 2-hydroxyethyl methacrylate (HEMA) or methoxy-capped oligo(ethylene glycol) methacrylate (OEGMA). In addition, an alternative PMPS macroinitiator was synthesised to form block copolymers of styrene and methylphenylsilane via TEMPO-mediated free radical polymerisation. In this case, diXPMPS was endcapped with 2,2,6,6,-tetramethyl-l-(l-phenyl-2-hydroxyethyloxy)- piperidine to form a suitable macroinitiator.

All block copolymers were characterised using 'H NMR and l3C NMR spectroscopy and size exclusion chromatography. Preliminary evidence of phase separation in samples of PMMA-PMPS-PMMA was observed via differential scanning calorimetry. The amphiphilic block copolymers were also investigated to determine their suitability for applications in three areas of research - drug delivery systems, cell growth, and bioelectronics.