Generalizing the effects of chirality on block copolymer assembly

Abstract

We explore the generality of the influence of segment chirality on the self-assembled structure of achiral–chiral diblock copolymers. Poly(cyclohexylglycolide) (PCG)-based chiral block copolymers (BCPs*), poly(benzyl methacrylate)-b-poly(d-cyclohexylglycolide) (PBnMA-PDCG) and PBnMA-b-poly(l-cyclohexyl glycolide) (PBnMA-PLCG), were synthesized for purposes of systematic comparison with polylactide (PLA)-based BCPs*, previously shown to exhibit chirality transfer from monomeric unit to the multichain domain morphology. Opposite-handed PCG helical chains in the enantiomeric BCPs* were identified by the vibrational circular dichroism (VCD) studies revealing transfer from chiral monomers to chiral intrachain conformation. We report further VCD evidence of chiral interchain interactions, consistent with some amounts of handed skew configurations of PCG segments in a melt state packing. Finally, we show by electron tomography [3D transmission electron microscope tomography (3D TEM)] that chirality at the monomeric and intrachain level ultimately manifests in the symmetry of microphase-separated, multichain morphologies: a helical phase (H*) of hexagonally, ordered, helically shaped tubular domains whose handedness agrees with the respective monomeric chirality. Critically, unlike previous PLA-based BCP*s, the lack of a competing crystalline state of the chiral PCGs allowed determination that H* is an equilibrium phase of chiral PBnMA-PCG. We compared different measures of chirality at the monomer scale for PLA and PCG, and argued, on the basis of comparison with mean-field theory results for chiral diblock copolymer melts, that the enhanced thermodynamic stability of the mesochiral H* morphology may be attributed to the relatively stronger chiral intersegment forces, ultimately tracing from the effects of a bulkier chiral side group on its main chain.

Supramolecular Chirality Transfer toward Chiral Aggregation: Asymmetric Hierarchical Self‐Assembly

“…Furthermore, they studied the homochirality evolution from monomeric, to conformational, and to meso‐domain chirality across multiple size scales during self‐assembly processes. [ 41 ] By eliminating the crystallization of the chiral block, they observed the formation of an equilibrium helical phase. In PBnMA‐ b ‐PLCG and PBnMA‐ b ‐PDCG, the bulkier chiral side group of the PCG might generate a more persistent helical bias, which could assist in strengthening the chiral anisotropy of intersegment forces, thereby leading to chiral meso‐domains.…”

Networks with controlled chirality via self-assembly of chiral triblock terpolymers

“…Note that, by using a chiral monomer, a novel helical phase (H*) could be obtained in AB diblock copolymer composed of chiral block (designated as chiral block copolymer, BCP*) ( 22 – 24 ). Chirality transfers from molecular (monomeric) to conformational (chain) and, ultimately, to hierarchical (multichain domain) chirality in self-assembled BCPs* could be achieved to give the H* with controlled chirality, demonstrating the generic behaviors of homochiral evolution at different length scales from self-assembly ( 25 – 27 ).…”

Reversible Micrometer‐Scale Spiral Self‐Assembly in Liquid Crystalline Block Copolymer Film with Controllable Chiral Response

“…For the chiral BCP self‐assembly under annealing, helix is the most popular structure [7b, 14] . More recently, Ho et al.…”