Block copolymerization of styrene using azo-containing poly(γ-benzyl l-glutamate) initiator and interaction of the block copolymers with blood

Abstract

Poly(γ-benzyl l-glutamates) containing an azo group (Azo-PBLG) were synthesized. They were shown to take an α-helical conformation in solid phase and in dimethylformamide solution, when the degree of polymerization was higher than ten. The rate constants of decomposition and initiation of styrene polymerization by Azo-PBLG were found to be affected by the degree of polymerization of Azo-PBLG. The rate of polymerization of styrene with Azo-PBLG in dimethylformamide solution at 120°C was proportional to [styrene] 2.83 and [Azo-PBLG] 0.45, which suggests the occurrence of chain-transfer reaction to solvent. With increasing degree of polymerization of Azo-PBLG, the overall rate constant increased, which suggests the participation of styrene-Azo-PBLG interaction in the polymerization. The block copolymerization yielded poly(γ-benzyl l-glutamate)-polystyrene-poly(γ-benzyl l-glutamate) (A-B-A-type) block copolymers, whereas the block copolymerization in the presence of n-hexylmercaptane gave A-B-type block copolymers. In vitro blood-clotting test of the block copolymers showed that the block copolymer containing ca. 15 mol% of γ-benzyl l-glutamate unit was most antithrombogenic and the adsorption of plasma proteins to this block polymer caused a low degree of denaturation.