The poly(3-hydroxbutyrate-co-3-hydroxyvalerate)/poly (e-caprolactone) block copolymers (PHCLs) with three different weight ratios of PCL blocks (38%, named PHCL-38; 53%, named PHCL-53; and 60%, named PHCL-60) were synthesized by using PHBV with two hydroxyl end groups to initiate ring-opening polymerization of e-caprolactone. During DSC cooling process, melt crystallization of PHCL-53 at relatively high cooling rates (9, 12, and 15 C min À1 ) and PHCL-60 at all the selected cooling rates corresponded to PCL blocks so that PHCL-53 and PHCL-60 were used to study the nonisothermal crystallization behaviors of PCL blocks. The kinetics of PCL blocks in PHCL-53 and PHCL-60 under nonisothermal crystallization conditions were analyzed by Mo equation. Mo equation was successful in describing the nonisothermal crystallization kinetics of PCL blocks in PHCLs. Crystallization activation energy were estimated using Kissinger's method. The results of kinetic parameters showed that both blocks crystallized more difficultly than corresponding homopolymers. With the increase of PCL content, the crystallization rate of PCL block increased gradually.

No abstract

Telechelic hydroxylated poly(3-hydroxybutyrateco-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°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 meltprocessing 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 autoaccelerated degradation reaction.

Biodegradable block copolymers containing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly (ε-caprolactone) (PCL) units (PHCLs) with different contents of PCL block were synthesized successfully by using telechelic hydroxylated PHBV (PHBV-diol) with low molecular weight as a macroinitiator to initiate ring-opening bulk polymerization of ε-caprolactone (ε-CL). The chemical structure and molecular weight were characterized by 1 H NMR, FTIR and GPC. The PHBV and PCL blocks in PHCLs were miscible in amorphous state, and formed separate crystalline phases with lower crystallinity than corresponding homopolymers, which was characterized by DSC and WAXD. The results of TGA showed that PHCLs underwent a two-step thermal degradation process. The thermal degradation process of PCL blocks was significantly different from PCL homopolymers. The activation energies of thermal degradation of PCL blocks calculated by Horowitz and Metzger method were much higher than that of each step of thermal degradation of PCL homopolymers.

No abstract