The crystallization kinetics and morphology of a series of biodegradable poly(butylene succinate-co-ethylene succinate) (P(BS-co-ES)) with ethylene succinate (ES) comonomer composition ranging from 13 to 28 mol% were investigated with various techniques and compared with those of the homopolymer poly(butylene succinate) (PBS) in this work. The crystal structures of P(BS-co-ES) are the same as that of neat PBS, but the crystallinity decreases slightly with increasing the ES composition. The glass transition temperature increases slightly while the nonisothermal melt crystallization peak temperature and melting point decrease for P(BS-co-ES) with increasing the ES composition; moreover, the equilibrium melting point temperature of P(BS-co-ES) is also reduced. The overall isothermal crystallization kinetics of P(BS-co-ES) was studied and compared with that of neat PBS. The crystallization mechanism does not change for either neat PBS and P(BS-co-ES) while the overall crystallization rates of P(BS-co-ES) decrease with increasing ES composition and crystallization temperature. The spherulite growth rates of P(BS-co-ES) also decrease with increasing ES composition and crystallization temperature. Both neat PBS and P(BS-co-ES) exhibit a crystallization regime II to III transition independent of ES composition; moreover, the crystallization regime transition temperature shifts to lower temperatures with increasing the ES composition.

In the present work, we prepared biodegradable poly(ethylene succinate) (PES) and its three novel copolyesters poly(ethylene succinate-co-ethylene adipate) (P(ES-co-EA)) with the ethylene adipate (EA) comonomer composition ranging from 5.1 to 15.3 mol%. Crystal structure, thermal stability, crystallization kinetics, and morphology of P(ES-co-EA) copolyesters with different EA composition were studied in detail with various techniques and compared with those of PES. It is found that P(ES-co-EA) copolyesters have the same crystal structures as neat PES; however, the crystallinity is slightly smaller in the copolyesters than in neat PES. Both neat PES and P(ES-co-EA) copolyesters have high thermal stability; moreover, the presence of EA composition has improved significantly the thermal stability of P(ES-co-EA) compared with neat PES. Increasing the EA composition reduces apparently glass transition temperature, melting point temperature, and equilibrium melting point temperature of P(ES-co-EA). The overall crystallization rates of P(ES-co-EA) decrease with increasing the EA composition and crystallization temperature; however, the crystallization mechanism remains unchanged for both neat PES and P(ES-co-EA). The effects of the EA composition and crystallization temperature on the spherulitic morphology and growth rate of P(ES-co-EA) were also investigated. Both neat PES and its copolyesters show a bell shape for the growth rates in a wide crystallization temperature range regardless of the EA composition. All the samples exhibit a crystallization regime II to III transition; furthermore, increasing the EA composition shifts the crystallization regime transition temperature to the low temperature range.