Crystallization behavior and morphology of double crystalline poly(butylene succinate)-poly(ethylene glycol) multiblock copolymers

The crystallization kinetics, morphology and crystal structure of biodegradable double crystalline poly(butylene succinate)-poly(ethylene glycol) (PBS-PEG) multiblock copolymers (PBSEGs) were studied with different composition and segment chain length by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). The isothermal crystallization kinetics results show that the overall crystallization rate and the equilibrium melting point of PBS increase with the increasing PBS fraction and the segment chain length (LPBS); on the other hand, the higher content or longer PEG segment within PBSEGs possesses larger crystallization rate of PEG chains. The nucleation mechanisms are demonstrated to be instantaneous 3D and 2D aggregates for PBS and PEG segments within PBSEGs, respectively (except for PBSEG2K−50, 2D and 3D aggregates for PBS and PEG segments, respectively). POM observations indicate that the PBS within PBSEG multiblock copolymers presents banded spherulites in the investigated temperature range. After quenched to lower temperature, PBS templates the morphology for PEG crystallization, and PEG crystallization just changes the magnitude of birefringence (lighting the spherulites) but not influences the superstructure. Finally, WAXD measurements determine that the crystal structure is not changed with the compositions.