Bio-based thermoplastic poly(butylene succinate-co-propylene succinate) copolyesters: effect of glycerol on thermal and mechanical properties

Poly(butylene succinate-co-propylene succinate) (PBSPS) was polymerized using succinic acid, 1,4-butanediol, 1,3-propanediol, and glycerol (GC). The PBSPS copolyester with a BS/PS ratio of 7/3 has a low melting point (T-m, 80 degrees C) and crystallization temperature (T-c, 20 degrees C) in addition to excellent thermal stability with a thermal degradation temperature (T-d) above 300 degrees C. Isodimorphism was observed for 30-50 mol% PS, lowering T-m and T-c. The featured crystalline lattices (021) and (110) of PBS at 2 theta = 21.5 degrees and 22.5 degrees gradually disappeared with PS content greater than 50 mol% and transformed into a PPS crystalline lattice at 2 theta = 22.3 degrees. Young's modulus decreased with increasing PS content due to crystallinity loss. Wide-angle X-ray diffraction demonstrated that the chain movement regularity was affected by the GC content, reducing the crystallinity. The PBSPS copolyesters were elastic with 0.001 mol% GC but became rigid with GC content greater than 0.01 mol%. The chain conformation was flexible for 0.001-0.01 mol% GC and exhibited an irregular steric architecture for 0.02-0.03 mol% GC due to more GC acting as nodes. Thus, the thermal and mechanical properties of the synthesized bio-based PBSPS copolyesters can be controlled by adjusting the GC content; therefore, such copolyesters are suitable for medical support, coating, and phase-change material applications.