Helical assemblies from chiral block copolymers

Abstract

Helical assemblies from chiral block copolymers (BCPs*) have been intensively studied due to their unique hierarchical architectures arising from the interplay of various secondary interactions. Helical architectures from BCP* self-assembly in solution have been found in peptide-based and lactide-based BCPs*. Inspired by the concept of chiral information transfer from the molecular level to macroscopic features, polystyrene-block-poly(L-lactide) (PS-PLLA) BCPs* composed of an achiral PS block and a chiral PLLA block has been designed for fabrication of helical assemblies. In contrast to a variety of helical assemblies resulting from solution, a helical phase (H*) having hexagonally packed helical PLLA microdomains in a PS matrix can be obtained in bulk by introducing chirality starting from the molecular level for BCP self-assembly. Phase behavior was examined and phase transitions from the H* phase to both cylinder and gyroid phases were found after long-time annealing, suggesting that the H* phase is a long-lived metastable phase. The morphologies of the H* phase can be manipulated into stretched helices (eventually leading to straight cylinders) by applying the stimulation (i.e., crystallization) so as to result in spring-like behavior. Also, by taking advantage of the degradable character of polylactides, a nanoporous PS polymer can be obtained after PLLA hydrolysis to be used as a template for fabrication of helical nanohybrids.