Self-oscillation of polymer and photo-regulation by introducing photochromic site to induce LCST changes

We have developed polymers and gels with autonomous self-oscillating function by utilizing the Belousov–Zhabotinsky (BZ) reaction. The self-oscillating polymer is composed of poly(N-isopropylacrylamide), in which ruthenium tris(2,2′-bipyridine) is copolymerized as a catalyst for the BZ reaction. Under the coexistence of the reactants, the polymer undergoes spontaneous cyclic soluble–insoluble changes or swelling–deswelling changes (in the case of gel) without any on–off switching of external stimuli. In this study, spirobenzopyran was introduced into the self-oscillating polymer as the photochromic site. Under acidic condition necessary for the BZ reaction, photochromism of the spirobenzopyran occurs and the lower critical solution temperature of the polymer solution shifts to lower temperature with isomerization by photo-irradiation. As a result, on–off switching of the soluble–insoluble self-oscillation for the polymer solution is possible by photo-irradiation.