Chiral Phases with Controlled Handedness from Block Copolymer Self-Assembly Induced by Chiral Small Molecules

This work aims to study the effect of induced chirality on the self-assembly behavior of block copolymers mediated by noncovalent secondary interactions. By introducing a chiral small molecule, 1,1'-Bi-2-naphthol (BINOL) through association with a diblock copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), it is possible to give the formation of a helical phase (H*) from self-assembly. Owing to the homochiral evolution across different length scales, the handedness of the H* can be controlled by the chiral arrangment of helical PEO chains with exclusive handedness, driven by hydrogen-bonding interactions between the chiral BINOL molecules and the PEO segments. Beyond the H* phase, this concept is extended to a more complex chiral morphology. By associating chiral BINOL with a triblock terpolymer, poly(isoprene)-block-polystyrene-block-poly(ethylene oxide) (PI-b-PS-b-PEO), it is possible to induce the formation of an alternating gyroid (G^A) phase comprising a pair of chiral gyroids with opposite handedness originating from the distinct end blocks (i.e., PI and PEO). Most interestingly, the handedness of the chiral gyroid from PEO associated with BINOL in the G^A can be also controlled by the chirality of introduced BINOL via the homochiral evolution from self-assembly. These results demonstrate a viable strategy for controlling the handedness of complex nanostructures in block copolymer systems through mesochiral self-assembly driven by induced chirality via homochiral evolution.