Synthesis and modification of thermoresponsive poly(oligo(ethylene glycol) methacrylate) via catalytic chain transfer polymerization and thiol-ene Michael addition

Various poly(oligo(ethylene glycol) methyl ether methacrylate)s (POEGMEMAs) have been prepared by Catalytic Chain Transfer Polymerization (CCTP) using a range of OEGMEMA monomers (molecular weight from 180 to 1100 g mol(-1)). The chain transfer constants of bis(boron difluorodimethylglyoximate) cobalt(II) (CoBF) were determined and are reported for each monomer. The copolymerization of POEGMEMA (M-n = 475 g mol(-1)) with diethylene glycol methyl ether methacrylate (DEGMEMA) yielded thermoresponsive polymers. The lower critical solution temperatures (LCSTs) of the polymer chains can be tuned by the copolymer composition over the range 30 degrees C to 95 degrees C. In addition, the presence of the vinylic end-group, characteristic of CCT polymerization, provided further scope for post-synthetic modification via thiol-ene click chemistry, through nucleophilic Michael addition with various functional thiol compounds such as 2-mercaptoethanol, 3-mercaptopropionic acid, benzyl mercaptan and 1-dodecanethiol. The thiol-ene reaction was rigorously tested, optimized and characterized in this study in terms of solvents and most importantly the choice of the catalyst: dimethyl phenyl phosphine, tertiary amine or hexylamine. The optimum conditions reported allow near-quantitative functionalization of these macromonomers without significant side reactions. The effect of the end-group on the LCST has also been investigated, as well as thermal stability temperature of the copolymers.