Poly(L‐lactide)‐b‐poly(ε‐caprolactone)‐b‐poly(D,L‐lactide) copolymers with enhanced toughness and strength by regulating crystallization and phase separation

Abstract

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(ε‐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.

Crystallinity-Independent Toughness in Renewable Poly(l-lactide) Triblock Plastics

“…A similar trade-off between crystallization rate and enhanced ductility was reported for chain-extended PLLA-b-poly(isobutylene)-b-PLLA triblocks with 0.061 < f PLLA < 0.74 59 and poly(εcaprolactone)-b-PLLA-b-poly(D,L-lactide) multiblocks with f PLA = 0.8. 60 Beyond linear architectures, graft-block copolymers (0.5 < f PLLA < 0.7) with crystallizable PLLA outer graft blocks have demonstrated substantial toughness enhancement, though at the expense of Young's modulus and with maximum crystallinities of 11%. 61,62 We desired to synthesize a PLLA block polymer with well-entangled rubbery blocks that microphase separate from an entangled PLLA matrix that can crystallize on meaningful processing time scales, producing a tough and highly crystalline plastic with a single, simple thermal history.…”