Recent advances in stereocomplexation of enantiomeric PLA-based copolymers and applications

Poly(lactic acid) or poly(lactide) (PLA) is a biodegradable and biocompatible thermoplastic polymer, being derived from renewable resources such as corn and sugar cane. The building block of PLA, lactic acid is chiral and the polymerization of lactic acids (or lactides) leads to isotatic, syndiotatic and atactic/heterotactic PLA primary structures. The stereoselective interaction between two complementary enantiomeric PLLA and PDLA has led to enhanced physical properties such as mechanical properties, thermal resistance and hydrolytic stability compared with the parent polymers. Progress in controlled and/or living polymerization techniques combined with other new synthetic methodologies has facilitated the preparation of PLA-based copolymers with complex architectures such as diblock, triblock, multiblock, star-shape block, comb-shape block and various PLA-grafted structures. The utilization of stereocomplexation strategy to these newly developed copolymers has opened avenues to access a variety of new materials with unique characteristics, including novel chemical functionalities, bioactivities, and smart (responsive to external stimulus) properties tailored for specific applications. This review presents recent advancements in the synthesis of PLA-based block/graft copolymers having complex architectures, with emphasis on the enhanced material performances induced by PLA stereocomplex formation. The origin of the enhanced thermal mechanical property observed in PLA stereocomplex is first discussed. The strong interaction resulted from stereocomplexation in PLA based copolymers could be exploited not only for fabrication of advanced therapeutic delivery carriers and tissue engineering devices, but also for stabilizing colloidal systems in microparticles, micelles and hydrogels, that further broaden the applications of PLA that could not have been attained with single PLLA or its copolymers. The stereocomplexation could also be used to tailor the interface interactions between fillers and PLA matrix that lead to higher strength and toughness of PLA.