Computational Investigation of the Structural Properties of Poly(lactic acid) and Its Stereoisomers: Shape, Size, and Flexibility.

In an effort to support the common cause of making the polymer industry more sustainable, studies involving computational methods have been enriched with polymers of natural origin. Owing to their complex structure often resembling proteins more than synthetic polymers, simulation studies of biobased polymers are very challenging. In this work, we present an atomistic study of poly-(lactic acid) and its stereoisomers of multiple molecular weights in the melt. We show that while the L- and D-stereoisomers exhibit similar global structural properties, copolymer chains consist of more compact and more spherical domains than their homopolymer analogues. We investigate the local folding in these structures by examining intramolecular hydrogen bonding, packing length, and the geometrical parameters characterizing the n-π* interaction. This work provides a detailed description of the inner structure of this biodegradable polymer over various molecular weights and reveals its structural similarities with synthetic and biopolymer materials.