Poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) Four-arm Star Functional Copolymers by Quasiliving ATRP: Equivalent Synthetic Routes by Protected and Nonprotected HEMA Comonomers

Abstract

Comprehensive investigations were carried out on the synthesis of well-defined poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) P(MMA-co-HEMA) copolymers, i.e., PMMA with predetermined average number of pendant hydroxyl functionalities, by using HEMA and trimethylsilyl-protected HEMA (TMS-EMA) under quasiliving ATRP conditions by a tetrafunctional initiator and CuCl/2,2′-bipyridyl (bpy) catalyst system in methanol at 10°C. It was found that these two synthetic routes, that is the direct and protected approaches, are equivalent in terms of yields, hydroxyl functionality and molecular weight distribution (MWD). Bulk copolymerization of MMA and HEMA by ATRP led to broad multimodal MWD in contrast to copolymers with narrow MWD in the presence of methanol. A two-step purification method applying silica-alumina chromatography followed by treatment with an acidic ion-exchange resin, used also as the deprotecting agent, was found to provide copolymers free of catalyst contamination. At higher monomer conversions, GPC analyses indicate the occurrence of chain-chain coupling by recombination of the macroradicals resulting in lower than theoretical apparent initiating efficiencies. According to the results on the effect of reaction time on monomer conversion, relatively short reaction times, less than 2 h, are sufficient to obtain high yields and PMMA with desired functionalities and MW under the applied quasiliving ATRP conditions. The resulting four-arm star hydroxyl-functional P(MMA-co-HEMA) copolymers offer a variety of new possibilities for the preparation of a variety of novel PMMA-based macromolecular architectures.