Crystallization of isomorphic poly(butylene succinate-co butylene fumarate) biopolyester: Single crystals and ring-banded spherulites

Poly(butylene succinate-co-butylene fumarate) (PBSF) copolymers with butylene fumarate (BF) molar ratio varies from 1% to 40% were synthesized and their single crystals were prepared using a self-seeding method. For PBSFs with low content of BF units, the single crystals are regular hexagonal shape. With the increase of BF molar ratio, the single crystal boundary turns rounded and the aspect ratio decreases. PBSF single crystals with different BF content were prepared at the same temperature, the supercooling degree of the PBSF increases with the increase of BF content, resulting the crystalline density increases and the single crystal size decreases. Selected area electron diffraction (SAED) was used to investigate the crystalline structures of the PBSF single crystals, and the results approve strict isomorphism between butylene succinate (BS) and BF in PBSF, verifying that preparing the single crystal and characterizing the crystalline structure by SAED is a direct method to check for isomorphic polymers. PBSFs can form ring-band spherulites at suitable crystallization temperatures. The band spacing of PBSF increases with the increase of isothermal crystallization temperature. At the same isothermal crystallization temperature, the band spacing PBSF decreases with the increase of BF molar ratios. The crystallization temperature range of forming ring-banded spherulites broadens with the increase of BF molar ratios.