Synthesis of SBC, SC and BC block copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(epsilon-caprolactone) (C) block

The sequential anionic polymerization of polystyrene-block-polybutadiene-block-poly- (epsilon-caprolactone) (SBC) triblock copolymers as well as polystyrene-block-poly(epsilon-caprolactone) (SC) and polybutadiene-block-poly(epsilon-caprolactone) (BC) dib lock copolymers was achieved in benzene. To initiate the polymerization of the highly reactive epsilon-caprolactone, the nucleophilicity of the carbanion has to be reduced. For this purpose 1,1-diphenylethylene (DPE) was used. To avoid inter- and intramolecular transesterification reactions of the growing caprolactone block, the reaction time of this monomer in the block copolymers was strictly controlled. The reaction between polybutadienyl anions and DPE is too slow, and an incomplete reaction results in side reactions when epsilon-caprolactone is added. An alternative method was developed, which consisted in the addition of a small quantity of styrene, after the polymerization of butadiene, to diminish the total reaction time and reduce the probability of chain transfer.