Material properties of degradable Poly(butylene succinate-co-fumarate) copolymer networks synthesized by polycondensation of pre-homopolyesters

There is a need to develop biodegradable polymers with tunable physical, mechanical, and biochemical properties. The objective of this work was to investigate the effect of chain microstructure and fumarate content on material properties of poly(butylene succinate-co-fumarate) (PBS-BF) copolymers synthesized by a three-step method of separate esterification of succinic acid (SA) and fumaric acid (FA) with butylene glycol (BG) followed by polycondensation of bis(4-hydroxy butyl) succinate (BS) and bis(4-hydroxy butyl) fumarate (BF) pre-homopolyesters. The material properties of the synthesized PBS-BF were compared with those of PBSF copolymers synthesized by a two-step method of esterification of SA and FA with BG followed by polycondensation. The synthesized copolymers were pressed and slowly or rapidly cooled into sheets and crosslinked with UV irradiation. The molecular and microstructure of the copolymers were characterized by 1H NMR, viscometry, and wide-angle x-ray diffraction. For a given fumarate fraction, the degree of randomness of PBS-BF copolymers was less than PBSF but PBS-BF degree of randomness increased with polycondensation reaction time of PBS and PBF pre-homopolyesters. The crosslinked copolymers were characterized with respect to gelation, thermal and mechanical properties, and degradation. Melting (Tm) and crystalline (Tc) temperatures of poly(butylene succinate) (PBS) increased by copolymerization with BF and the increase was proportional to the copolymer fumarate fraction. The rapidly-cooled and crosslinked PBS-BF30 copolymer with 30% fumarate fraction had highest modulus of 393 MPa and lowest elongation at break of 1.3% among all copolymers whereas the rapidly-cooled and uncrosslinked PBSF10 copolymer with 10% fumarate fraction had lowest modulus of 303 MPa and highest elongation at break of 160%. The uncrosslinked PBS polymer had 31% weight loss after 24 weeks whereas the slowly-cooled and crosslinked PBS-BF30 copolymer with 30% fumarate fraction had