Photoresponsive properties of poly(N-isopropylacrylamide) hydrogel partly modified with spirobenzopyran.

A photoresponsive hydrogel was prepared by radical copolymerization of N-isopropylacrylamide, a vinyl monomer having a spirobenzopyran residue and cross-linker. By the observation of photoresponsive shrinking and the conductance change, it was confirmed that the hydrogel in an acidic condition exhibited drastic and rapid volume shrinkage and proton dissociation when it was irradiated with blue light. Further, to examine its application to the mass transfer control, we prepared a photo- and thermoresponsive gate membrane by introducing this photoresponsive hydrogel to the surface of a porous membrane. As the first demonstration of the photocontrol of membrane permeation for liquid, it was observed that its permeability for 1 mM HCl aqueous solution increased by 2 times in response to the blue light irradiation, and this photoresponse of the permeability was confirmed to be repeatable.