Biosynthesis and thermal characterization of polyhydroxyalkanoates bearing phenyl and phenylalkyl side groups

Polyhydroxyalkanoate (PHA) synthase 1 (PhaCl(PS)) from Pseudomonas sp. 61-3 is a broad-substrate-specific enzyme. In this study, by employing Ralstonia eutropha PHB-4 recombinant expressing PhaCl(PS), a novel type of 3-hydroxybutyrate (3HB)-based PHA copolymer, poly(3HB-co-3-hydroxy-3-phenylpropionate) [P(3HB-co-3H3PhP)], bearing phenyl side groups, was synthesized. The 3H3PhP fraction was increased up to 8.9 mol% by feeding 3H3PhP precursors. As the phenyl side group was introduced into P(3HB), the melting temperature and the enthalpy of fusion decreased, while the glass transition temperature (T-g) increased, demonstrating a distinct thermal behavior as a result of the phenyl side group. Furthermore, PHAs bearing phenylalkyl side groups were synthesized from omega-phenyl-alkanoates by Pseudomonas putida KT2440, and their thermal properties were characterized. Based on the measured and predicted T-g values, the effect of the alkyl chain length in the aromatic side group on T-g was investigated. This study demonstrates the role that aromatic side groups play in the thermal properties of PHAs. (C) 2014 Elsevier Ltd. All rights reserved.