Thermal stability and degradation of biological terpolyesters over a broad temperature range

Because of high susceptibility to thermal degradation during conventional melt processing of poly(3-hydroxybutyrate) (P3HB) homopolymer, incorporation of a second or third monomer unit in the polyester backbones is expected to reduce the melting temperature and crystallinity, resulting in a controlled thermal degradation with improved stability. In this work, random poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) (P3HB3HV4HV) terpolyesters biologically synthesized by Cupriavidus necator were investigated for the thermal stability and degradation over a broad temperature range (100-300 degrees C) in comparison with P3HB homopolyester. The work revealed that below the complete melting point (around 150 degrees C), the terpolyester exhibited a high thermal stability and became an amorphous semisolid suitable for conventional thermal processing. Size exclusion chromatography plus nuclear magnetic resonance analysis was used to examine the thermal degradation products and the vulnerability of different monomer units at high temperatures (240-290 degrees C). We found that 3HV unit in P3HB3HV4HV copolymers was more vulnerable to thermal degradation than 3HB unit under air. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41715.