Synthesis of water-soluble polymethacrylates by living anionic polymerization of trialkylsilyl-protected oligo(ethylene glycol) methacrylates

2-[2-[(tert-Butyldimethylsilyl)oxyl ethoxy]ethyl methacrylate (2) and 2-[2-[2-1(tert-butyldimethylsilyl)oxyl ethoxyl ethoxyl ethyl methacrylate (3) were polymerized anionically in THF at -78 degreesC for 2-24 h. The anionic initiator systems included 1,1-diphenyl-3-methylpentyllithium/lithium chloride and diphenylmethylpotassium/diethylzinc. The polymerization of novel tert-butyldimethylsilyl-protected oligo-(ethylene glycol) methacrylates, 2 and 3, proceeded quantitatively in each case.. The resulting polymers possessed the predicted molecular weights based on the molar ratios of monomers to initiators, and narrow molecular weight distributions (M-w/M-n < 1.1). The stability of the propagating carbanion of poly(2) and poly(3) was ascertained by the quantitative efficiencies of the sequential block copolymerizations using tert-butyl methacrylate (tBMA). Well-defined block copolymers, poly(2)-block-poly(tBMA) and poly(3)block -poly(tBMA), were obtained. The trialkylsilyl protecting groups of poly(2) and poly(3) were quantitatively hydrolyzed using 2 N HCl in aqueous THF at 0 degreesC for 2 h to give tailored poly [di(ethylene glycol) methacrylate] and poly [tri(ethylene glycol) methacrylate], respectively. Both polymethacrylates obtained after deprotection were readily soluble in water due to the high polarity of the hydrophilic oligo(ethylene glycol) pendant units with terminal OH functionality.