Synthesis of Tactic Poly(Alkyl Methacrylate) Homo and Copolymers

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Anionic polymerization of alkyl methacrylates, especially methyl methacrylate (MMA), has been studied extensively over the last two decades.1–5 The vast majority of these investigations have dealt with the kinetic and mechanistic aspects of anionic methacrylate polymerization. Relatively few investigations, however, have been concerned with the synthesis of novel homo- and copolymers.6 Two major reasons synthetic studies of these sytems have lagged behind the voluminous work done on the hydrocarbon monomers, e.g. styrene, butadiene and isoprene, are problems with methacrylate monomer purity and the inherent side reactions found in most anionic polymerizations involving polar monomers. The problem of side reactions to the methacrylate carbonyl has been well documented in the literature.7 Methods have been developed in the past to avoid these deleterious side reactions, namely bulky initiators, low temperatures, and polar solvents. We have been able to synthesize narrow distribution poly(alkyl methacrylates) by utilizing the well established route of THF at −78°C with the bulky initiator diphenyl hexyl lithium (DPHL). A much less appreciated aspect of the anionic synthesis of methacrylate polymers, however, has been the problem of monomer purification. Suitable methods are available for the scrupulous purification of hydrocarbon monomers. For example, the organometallic reagent dibutyl magnesium (DBM) has been well documented as a highly sensitive reagent which reacts with the last traces of water, air, or other terminating impurities present in styrenic and diene monomers.8