Particular thermal properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) oligomers

Telechelic hydroxylated poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBV-diols) were synthesized by transesterification with ethylene glycol, which could be used as the macromonomers for synthesis of block copolymers. PHBV-diols owned particular thermal properties. PHBV-diols had much lower the melting temperatures (T(m)s) and better thermal stability than original PHBV. With the decrease of molecular weight, T(m)s of PHBV-diols decreased gradually and maximum degradation temperatures (T(max)s) increased gradually. T-max-T-m of PHBV-diol could increase by 57.9 degrees C in comparison with original PHBV. It was meaningful that PHBV block in the block copolymers based on PHBV-diol owned the good thermal stability and low melting temperature of its precursor PHBV-diol, which widened greatly the melt-processing window of PHBV. In addition, thermal degradation kinetics was studied by Ozawa method, the integration method and Kissinger method. The results showed that the thermal degradation of original PHBV and PHBV-diols proceeded by at least two steps including a random degradation process and subsequent thermal degradation process due to the auto-accelerated degradation reaction.