Poly(L-lactide)-b-poly(& epsilon;-caprolactone)-b-poly(D,L-lactide) copolymers with enhanced toughness and strength by regulating crystallization and phase separation

Copolymerizing poly(lactide) with other materials to obtain better comprehensive performance is a effective way to expand its application range. In this work, the precursors of hydroxyl terminated (poly(L-lactide) [PLLA], poly(e-caprolactone) [PCL], poly(D,L-lactide) [PDLLA]) were prepared, and PLLA-PCL-PDLLA copolymer were synthesized by chain extension. The effects of the proportion and molecular weight of each component and the amount of chain extender on crystallization, phase structures, mechanical properties and thermal stabilities of PLLA-PCL-PDLLA copolymer were studied in detail. Based on small-angle X-ray scattering results, the competition between crystallization and microphase separation was regulated by the composition and chain length of prepolymers. As the ratio of PLLA/PDLLA was 1:1, crystallization was prevailing and no obvious peak was observed in SAXS pattern. The tensile test results showed that as the ratio of PLLA/PDLLA increased from 1:1 to 1:5, the elongation at break of the copolymer changed from 1.8% to 343%. By using shorter length of PCL and PLLA segments in chain extension, improvement in strength and flexibility were obtained due to moderate degree of crystallization and microphase separation. This work used biodegradable materials to prepare extraordinary toughness copolymers without losing the biocompatibility, which may provide a feasible method for obtaining high toughness and biodegradable PLA-based materials.

Automated summary

Copolymerizing poly(lactide) with other materials is an effective method to improve its comprehensive performance. In this study, precursors of hydroxyl terminated PLLA, PCL, and PDLLA were prepared and copolymerized to synthesize PLLA-PCL-PDLLA copolymer. The effects of component proportion and molecular weight, as well as chain extender, on the copolymer's crystallization, phase structures, mechanical properties, and thermal stabilities were investigated. By adjusting the composition and chain length of prepolymers, the competition between crystallization and microphase separation was regulated. The obtained copolymers showed improved strength and flexibility without losing biocompatibility, providing a feasible method for obtaining high toughness and biodegradable PLA-based materials.