Synthesis of a block copolymer of poly(3-hydroxybutyrate) and poly(ethylene glycol) and its application to biodegradable polymer blends

Abstract

A block copolymer {P[(R,S)-HB-b-EG]} of atactic poly[(R,S)-3-hydroxybutyrate] {P[(R,S)-HB]} and poly(ethylene glycol) (PEG) was prepared by the ring-opening polymerization of β-butyrolactone in the presence of a macroinitiator (PEG/ZnEt2/H2O) which had been produced by the reaction of α,ω-dihydroxy PEG ( $$\overline M $$ n=3000) with ZnEt2/H2O (1/0.6) catalyst. The block copolymer ( $$\overline M $$ n=10,500, $$\overline M $$ w/ $$\overline M $$ n=1.2) was an A-B-A triblock copolymer comprising atactic P[(R,S)-HB] (A) and PEG (B) segments. The miscibility, physical properties, and biodegradability of binary blends of microbial poly[(R)-3-hydroxybutyrate] {P[(R)-HB]} with the block copolymer P[(R,S)-HB-b-EG] has been studied. The glass-transition temperature (T g) data showed that the P[(R)-HB]/P[(R,S)-HB-b-EG] blend was miscible in the amorphous state. The P[(R)-HB] film became flexible and tough by means of blending with P[(R,S)-HB-b-EG] block copolymer. The enzymatic degradation of blend films was carried out at 37°C and pH 7.4 in a 0.1M phosphate solution of an extracellular PHB depolymerase fromAlcaligenes faecalis. The enzymatic degradation took place solely on the surface of the blend films.