Multi-Shape Memory Effect of Columnar Side-Chain Liquid Crystalline Polymer

R. Y. Zhao, S. Yang, and E. Q. Chen

Department of Polymer Science and Engineering and Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China

Recently, we are interested in side-chain liquid crystalline (LC) polymers bearing the hemiphasmid side-chain that contains a rod-like mesogen linked with a half-disk end group [1-3]. We found that they could self-organize into the hexagonal and/or rectangular columnar LC phase when the size of flexible tails on the half-disk was properly chosen and the dimension of columnar lattice could approach to 10 nm easily. It is identified that the supramolecular column in the columnar phase shall contain several chains (e.g., ~5 chains) laterally associated together rather than a single chain. This “multi-chain column” provides a new type of physical crosslinking. Namely, within the confined space of the column the backbones and pendant groups of the polymer can get entangled. Using hemiphasmid side-chain LC polynorbornene as the example [4], we demonstrate that such physical crosslinks can be rather robust, giving the polymer with the typical properties of thermal plastic elastomer. Furthermore, taking the physical crosslinks to define the permanent shape and the LC formation to fix the temporary shape, we realized the side-chain polynorbornene with excellent shape memory effect. For the dual shape memory, both the shape fixity (Rf) and shape recovery (Rr) are admirably high (approaching 100%), even when a large strain of 600% was applied. Benefited from a broad LC transition, the polymer can present the high-strain multi-shape memory effect, exampled by its triple- and quadruple-shape memory with high Rf and Rr at each step.

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[4] R. Y. Zhao, T. P. Zhao, X. Q. Jiang, X. Liu, D. Shi, C. Y. Liu, S. Yang, E. Q. Chen, Adv. Mater. DOI 10.1002/adma.201605908 (2017) (link)