Random and block copolymers of 4-[2-(vinyloxy)ethoxy]azobenzene (AzoVE) and various vinyl ethers (exhibiting LCST-type phase separation) were prepared by living cationic polymerization using 1-(isobutoxy)ethyl acetate/Et1.5 AlCl1.5 in the presence of ethyl acetate at 0 °C. With random copolymers having thermally-responsive and azobenzene units, the phase separation occurs at a higher temperature under UV irradiation compared with that under visible light. This shift made it possible to control the solubility of the polymer by irradiating UV or visible light. Irradiation of a 20 wt % aqueous solution of (AzoVE2-r-EOEOVE200)-b-MOVE400 with visible light caused rapid gelation to give a transparent gel at 42.6 °C. Under subsequent irradiation with UV light, the gel returned to a fluid state with the same viscosity of the initial solution.
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Yoshida et al. (2005) studied this question.
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