Self-Assembly and Temperature-Driven Chirality Inversion of Cholesteryl-Based Block Copolymers

Block copolymers (BCPs), comprising a poly(methyl methacrylate) (PMMA) block and a poly(cholesteryloxyhexyl methacrylate) (PChMA) block, were synthesized via reversible addition–fragmentation chain transfer polymerization. The self-assembly of the liquid crystalline BCPs was characterized by differential scanning calorimetry, polarized optical microscopy, and synchrotron-based small/wide-angle X-ray scattering. The results indicate the formation of both tilted and nontilted chiral smectic (SmC* and SmA*) phases. A phase transition from the SmA* to SmC* phase on cooling was observed for BCPs but not for PChMA homopolymers. The layer spacing (5.00 ± 0.18 nm) between those can be controlled to maintain the number of ChMA units while varying the lengths of the PMMA block, thus introducing systematically the SmC* phase. Furthermore, BCPs with the short PMMA block showed inversion of chirality at specific temperatures; however, for PChMA attached with the long PMMA block, no chirality inversion was observed. This mode of chirality switching, investigated by circular dichroism, NMR, and theoretical studies, is associated with the methyl substituents in the backbone affecting the packing of the polymers. The basic rules, described here, have the potential to be implemented for the design of a wide range of functional materials, where helix–helix conversion is of use