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

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 -butyrolactone in the presence of a macroinitiator (PEG/ZnEt₂/H₂O) which had been produced by the reaction of ,-dihydroxy PEG ( _n=3000) with ZnEt₂/H₂O (1/0.6) catalyst. The block copolymer ( _n=10,500, _w/ _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.