Application of photoresponsive polymers carrying crown ether and spirobenzopyran side chains to photochemical valve

A vinyl copolymer carrying crown ether and spirobenzopyran side chains, which undergoes significant photoinduced rheology changes, i.e., contraction and extension of its polymer chain, was applied to a material for photocontrol system of solvent permeation rate, so-called, photochemical valve. Macroporous polyethylene membranes coated by the crown ether-spirobenzopyran copolymer can work as a functional membrane controlling solvent permeation rate photochemically. UV-light irradiation on the photoresponsive membrane decreased the permeation rate of hexane, due to the increased polarity of the membrane pore, which was in turn derived from the photoisomerization of its spirobenzopyran moiety to the corresponding ionic merocyanine form. The following visible-light irradiation on the membrane restored the permeation rate by isomerization back to the electrically neutral spiropyran form. To the contrary, the permeation of ethanol through the membrane was enhanced by UV-light irradiation due to the increase in the apparent membrane pore size induced by the polymer chain contraction and vice versa by visible light. Similar photoresponses in the permeation rate of nonpolar and polar solvents were also observed with a sintered glass filter modified chemically by both silane-coupling reagents containing crown ether and spirobenzopyran moieties.