Synthesis, crystallization kinetics and morphology of novel poly(ethylene succinate-co-ethylene adipate) copolymers

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.