Reversal of handedness of ionic liquid-based chiral block copolymers via self-assembly in solution and bulk phase

Abstract

Polymerized ionic liquid (PIL)-based ionic chiral block copolymers (BCPs*) were synthesized by functionalization of a poly(4-vinyl pyridine) segment in poly(styrene)-block-poly(4-vinyl pyridine) (PS-b-P4VP) block copolymer. Because of the ease of the ion exchange reaction with the quaternized PIL block, chirality was induced with L-/D-histidine, which acted as chiral auxiliaries, via ion-exchange reaction. Interestingly, the self-assembled helical nanofibrils of BCPs* divulged the reversal of handedness with respect to intrinsic chirality at the molecular level. Remarkably, a similar reversal of handedness was also observed at the quaternary phase. This peculiar behavior of reversal of handedness was correlated to the molecular packing of helical chains according to a cholesteric hard-core model of liquid crystals possessing a large helical pitch to helix diameter (P/d) ratio, where P and d denote the helical pitch and helix diameter, respectively.