3 years ago

Physicochemical Characterization of a Photoinduced Sol–Gel Transition of an Azobenzene-Containing ABA Triblock Copolymer/Ionic Liquid System

Physicochemical Characterization of a Photoinduced Sol–Gel Transition of an Azobenzene-Containing ABA Triblock Copolymer/Ionic Liquid System
Ryoji Usui, Hisashi Kokubo, Ryota Tamate, Masayoshi Watanabe, Yuzo Kitazawa, Xiaofeng Ma
We have previously reported that an ABA triblock copolymer with poly(ethylene oxide) as the B block and a thermo-/photoresponsive random copolymer of 4-phenylazophenyl methacrylate (AzoMA) and N-isopropylacrylamide (NIPAm) (P(AzoMA-r-NIPAm)) as the A block exhibited a reversible photoinduced sol–gel transition in a hydrophobic ionic liquid. Such reversible sol–gel transitions can be used to realize photohealable ion gels. This study contributes to a deeper physicochemical understanding of the photoinduced sol–gel transitions observed in the ion gel, showing that the glassy state of P(AzoMA-r-NIPAm) block domains is responsible for the long relaxation times. Importantly, the controlled photoisomerization of azobenzene moieties allows the glass transition temperature of P(AzoMA-r-NIPAm) block domains to be varied by choosing irradiation conditions. The photoinduced sol–gel transition can be understood as an elastic solid–viscoelastic liquid or a viscoelastic solid–viscoelastic liquid transition, depending on the dissimilarity in the magnitude of relaxation times under visible and UV light.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b01538

DOI: 10.1021/acs.macromol.7b01538

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