Insights into Stereocomplexation of Poly(lactic acid) Materials: Evolution of Interaction between Enantiomeric Chains and Its Role in Conformational Transformation in Racemic Blends
Meng Zhang, Xiao Fan, Weijie Guo, Haijun Zhou, Zhaolei Li, Yu Ma, Chao Yan, Alain Dufresne
Abstract
Enantiomers alternately packed stereocomplex crystals (SC) compete with homochiral enantiomer-packed homocrystals (HC) during the crystallization of poly(lactic acid) (PLA) racemic blends. However, an intensive understanding of the structural evolution of enantiomeric chains in racemic blends remains challenging because of the narrow time window required for structural evolution. Here, we report the initial conformation evolution and concomitant interaction between the enantiomeric chains in the racemic melt over a wide temperature range using commercial fast-scan chip calorimetry. The results showed that, after cooling the racemic melt at 3,000 K/s, 103 helices always emerged first. The interaction between the enantiomeric chains appeared gradually and triggered the transformation of 103 helices into 31 helices. A comprehensive understanding of the role of the interaction between the enantiomeric chains during the conformation transformation not only provides a physical basis for studying the competition between SC and HC of PLA but also lays a theoretical foundation for the preparation of biodegradable engineering plastics.