title: Photoreversible gelation of a triblock copolymer in an ionic liquid.
abstract: The reversible micellization and sol-gel transition of block copolymer solutions in an ionic liquid (IL) triggered by a photostimulus is described. The ABA triblock copolymer employed, denoted P(AzoMA-r-NIPAm)-b-PEO-b-P(AzoMA-r-NIPAm)), has a B block composed of an IL-soluble poly(ethylene oxide) (PEO). The A block consists of a random copolymer including thermosensitive N-isopropylacrylamide (NIPAm) units and a methacrylate with an azobenzene chromophore in the side chain (AzoMA). A phototriggered reversible unimer-to-micelle transition of a dilute ABA triblock copolymer (1 wt%) was observed in an IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6), at an intermediate "bistable" temperature (50 °C). The system underwent a reversible sol-gel transition cycle at the bistable temperature (53 °C), with reversible association/fragmentation of the polymer network resulting from the phototriggered self-assembly of the ABA triblock copolymer (20 wt%) in [C4 mim]PF6.
authors.affiliation: Department of Materials Engineering School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan).
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ueki
authors.forename: Yutaro
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Ryoji
authors.initials: R
authors.lastname: Usui
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Kitazawa
authors.forename: Soonyong
authors.initials: S
authors.lastname: So
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Lodge
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Watanabe
keywords: block copolymers; gels; ionic liquids; self-assembly; sol-gel transitions