Generalizing the effects of chirality on block copolymer assembly

Hsiao Fang Wang, Kai Chieh Yang, Wen Chun Hsu, Jing Yu Lee, Jung Tzu Hsu, Gregory M. Grason, Edwin L. Thomas, Jing Cherng Tsai, Rong Ming Ho

Research output: Contribution to journalArticle

6 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)4080-4089
Number of pages10
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number10
DOIs
Publication statusPublished - 2019
Externally publishedYes

Keywords

  • Chiral block copolymers
  • Chirality effects
  • Helical phase
  • Homochiral evolution
  • Self-assembly

ASJC Scopus subject areas

  • General

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  • Cite this

    Wang, H. F., Yang, K. C., Hsu, W. C., Lee, J. Y., Hsu, J. T., Grason, G. M., Thomas, E. L., Tsai, J. C., & Ho, R. M. (2019). Generalizing the effects of chirality on block copolymer assembly. Proceedings of the National Academy of Sciences of the United States of America, 116(10), 4080-4089. https://doi.org/10.1073/pnas.1812356116