Dual Responsive Poly(N-isopropylacrylamide) Hydrogels Having Spironaphthoxazines as Pendant Groups

Stimuli responsive hydrogels (PNIPA-Am-MSp) with a thermoresponsive backbone and photochromic pendant groups were synthesized via free radical polymerization using N-isopropylacrylamide, modified spironaphthoxazines with a polymerizable double bond (MSp) as photochromic monomer, the crosslinker N,N'-methylenebis(acrylamide) and the initiator 2,2'-azobis(isobutyronitrile) in dimethylsulfoxide. The polymers are dual responsive, in that poly(N-isopropylacrylamide) (PNIPAAm) responds to temperature changes whereas the pendant spironaphthoxazines respond to light. Irradiation enhanced the water absorption of the polymers while increases in temperature decreased it. The irradiated PNIPAAm-MSp showed best water absorption at 0 degrees C (Q = 3.25) while water desorbed at higher temperatures (35 degrees C; Q = 0.30); where Q is the amount of water absorbed by a gram of dry polymer. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3318-3325, 2009