Poly(lactic acid) stereocomplexes based molecular architectures: Synthesis and crystallization

This review presents the state of the art of complex macromolecular architectures based on polylactide stereocomplexes (PLA-sc) from the viewpoint of synthesis and crystallization. First, we discuss the nomenclature, synthesis, epimerization, and lactide (LA) properties as a bio-derived cyclic dimeric monomer comprising two chiral carbons. Among several polymerization methods, catalytic ring-opening polymerization (ROP) is the most common and versatile technique to access stereoregular (isotactic) PLA, which is the prerequisite to preparing PLA-sc. Combined with other living and controlled/living polymerization techniques, ROP of LA has yielded various PLA-sc-based macromolecular architectures, including copolymers, stars, graft, cyclic, brush, and hybrid materials. New approaches to synthesizing monodisperse discrete oligoLA are also discussed. We show that a small change in the architectures, microstructures, molecular weight, or other chemical and physical modifications affects the behavior of PLA-sc. Moreover, the crystallization of PLA-sc, after more than 30 years of study, still presents many challenges. The crystalline morphology is also a subject of debate. Recent findings suggest a new crystalline unit cell for PLA-sc. Adding a third component or changing chain architecture can significantly modify the properties of the formed PLA-sc. The complex relationship between flexibility, nucleation, diffusion, and the interactions needed for the joint crystallization of the enantiomers constitutes a very large source of variables. As a result, PLA-based stereocomplex materials can be tailored by manipulating one or several of these variables. ; VL and NH thankfully acknowledge the support of King Abdullah University of Science and Technology (KAUST). This work has been supported by KAUST funding. AJM gratefully acknowledges funding from the Basque Government through Grant IT1309-19. This publication is part of the R+D+i project PID2020-113045GB-C21 funded by MCIN/AEI/10.13039/501100011033/.