Tailoring of block copolymers based on the stoichiometric control of the end-functionality of telechelic oligomers and the utilization of large-scalefractionation by phase fluctuation chromatography: A synthetic strategy for the preparation of end-functionalized poly(L-lactide)-block-poly(oxyethylene)

An AB diblock copolymer of poly(L-lactide) (PLLA) and poly(oxyethylene) (PE G) with a cinnamate terminal in the PEG block was prepared by the copolymer ization of L-lactide and partially end-modified PEG followed by fractionati on. The first step was the terminal modification of PEG with cinnamoyl chlo ride (CC), in which the degree of cinnamoylation of the hydroxyl terminals of PEG was roughly controlled by the feed ratio of both reactants, The resu ltant PEG cinnamate was subjected to copolymerization with L-lactide to pro duce a mixture of unreacted PEG dicinnamate (C-PEG-C), the diblock copolyme r (PLLA-PEG-C), and the triblock copolymer (PLLA-PEG-PLLA) corresponding to the three components of the PEG cinnamate. This mixture was separated by p hase fluctuation chromatography (PFC) to obtain PLLA-PEG-C in sufficient pu rity. This process, involving the stoichiometric control of the terminal re action of telechelic oligomers and the utilization of PFC for fractionation , can be an efficient method for synthesizing end-functionalized diblock co polymers from readily available telechelic oligomers. (C) 2000 John Wiley & Sons, Inc.