Polymers derived from N-isopropylacrylamide and azobenzene-containing acrylamides:: Photoresponsive affinity to water

N-Isopropylacryamide was copolymerized by free-radical polymerization with N-[2-(4-phenylazophenoxy)ethyllacrylamide derivatives that were substituted at their 4'-position with ethoxy, methoxyethoxy, or isopropyl units, or with N-{2-[4(pyridin-2-ylazo)phenoxyl ethyl) acrylamide. The polymers were soluble in cold water and possessed lower critical solution temperatures (LCSTs). The value of the LCST rose a few degrees after UV irradiation and dropped after irradiation with visible light, reversibly, in processes that corresponded to the isomerization of the azobenzene units. The polymers became increasingly hydrophobic after increasing their azobenzene content. The difference of hydrophobicity correlates with the absorption band height at about 400 nm. The structure of the substituent on the azobenzene unit affected both the transition temperature and the hydrophobicity. A change in photoinduced wettability for water was observed to occur on a prepared film at a temperature different from the LCST determined in water. (C) 2004 Wiley Periodicals, Inc.