Double-twisted helical lamellar crystals in a synthetic main-chain chiral polyester similar to biological polymers

摘要

Phase structures and transformation mechanisms of chiral biological and synthetic polymers are fundamentally important topics in understanding their macroscopic responses in different environments. Synthetic polymers having chiral centers along the main-chain backbones are difficult to polymerize and thus, up to today only very few examples have been reported. In this study, we describe a novel observation in crystalline morphology, double-twisted helical lamellar crystals, evolved from the melt in one synthetic chiral polyester. These crystals have been found to be similar to Bombyx mori silk fibroin crystals of the #beta#-modification grown from solution. In a less ordered form, this geometry has also been found in a chromosome of dinoflaggellate (in Prorocentrum micans). Crystal structures of this polyester in both flat and helical lamellar crystals are identical regardless of the twisted helical geometry. The polymer chain folding direction in both flat and helical lamellar crystals is along the same direction (along the long axis of the lamellar crystals). The geometrically frustrated helical crystals may result from a competition between chain molecular close packing (parallelism) and chiral configuration.