From miscible to partially miscible biodegradable double crystalline poly(ethylene succinate)-b-poly(butylene succinate) multiblock copolymers

A series of biodegradable double crystalline poly(ethylene succinate)-b-poly(butylene succinate) (PES-b-PBS) multiblock copolymers with various PES and PBS block lengths were successfully synthesized by chain-extension reaction of dihydroxylated poly(ethylene succinate) (HO-PES-OH) and poly(butylene succinate) (HO-PBS-OH) using 1,6-hexamethylene diisocyanate (HDI) as a chain-extender. The compositions and structures were characterized by proton nuclear magnetic resonance spectroscopy (1H NMR). The miscibility of amorphous phase and crystallization behaviors of the two blocks were investigated by standard differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC), polarized light optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). When the block length of PBS and PES were less than 4710 g mol−1, the amorphous phases of the two blocks were miscible. As the block length increased to more than 5430 g mol−1, the amorphous phases of the two blocks changed to be partially miscible, and the miscibility decreased with further increasing the block lengths. The crystallizability of both PBS and PES blocks increased with an increase in size of their blocks. POM observation showed that the copolymers displayed banded spherulitic morphologies, and the crystallization of PES happened in confined space after crystallization of PBS blocks. WAXD analysis suggested that the crystals of the copolymers were composed of crystals of both PES and PBS blocks.