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Guest-Responsive Covalent Frameworks by the Cross-Linking of Liquid-Crystalline Salts: Tuning of Lattice Flexibility by the Design of Polymerizable Units

Authors

  • Dr. Yasuhiro Ishida,

    Corresponding author
    1. RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan), Fax: (+81) 48-467-8214
    2. PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
    • RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan), Fax: (+81) 48-467-8214
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  • Hiroaki Sakata,

    1. Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
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  • Dr. Ammathnadu S. Achalkumar,

    1. RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan), Fax: (+81) 48-467-8214
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  • Kuniyo Yamada,

    1. RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan), Fax: (+81) 48-467-8214
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  • Dr. Yuki Matsuoka,

    1. PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
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  • Nobutaka Iwahashi,

    1. Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
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  • Dr. Sayaka Amano,

    1. Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
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  • Prof. Kazuhiko Saigo

    1. School of Environmental Science and Engineering, Kochi University of Technology, Miyanokuchi, Tosayamada-cho, Kami, Kochi 782-8502 (Japan)
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Abstract

Cross-linked polymers prepared by the in-situ polymerization of liquid-crystalline salts were found to work as solid-state hosts with a flexible framework. As a component of such hosts, four kinds of polymerizable amphiphilic carboxylic acids bearing alkyl chains with acryloyloxy (A), dienyl (D), and/or nonreactive (N) chain ends (monomeric carboxylic acids; MAAA, MANA, MDDD, and MDND) were used. The carboxylic acids were mixed with an equimolar amount of a template unit, (1R,2S)-norephedrine (guest amine; GRS), to form the corresponding salts. Every salt exhibited a rectangular columnar LC phase at room temperature, which was successfully polymerized by 60Co γ-ray-induced polymerization without serious structural disordering to afford the salt of cross-linked carboxylic acid (polymeric carboxylic acid; PAAA, PANA, PDDD, and PDND) with GRS. Owing to the noncovalency of the interactions between the polymer framework P and the template GRS, the cross-linked polymers could reversibly release and capture a meaningful amount of GRS. In response to the desorption and adsorption of GRS, the cross-linked polymers dramatically switched their nanoscale structural order. A systematic comparison of the polymers revealed that the choice of polymerizable groups has a significant influence on the properties of the resultant polymer frameworks as solid-state hosts. Among these polymers, PDDD was found to be an excellent solid-state host, in terms of guest-releasing/capturing ability, guest-recognition ability, durability to repetitive usage, and unique structural switching mode.

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