Synthesis and characterization of P(AAm-co-AAAB) photoresponsive copolymer and hydrogels

The synthesis and characterization of a novel copolymer Poly(acryl amide-co-acrylamido azobenzene) (P(AAm-co-AAAB)) and its hydrohydrogels consisting of acrylamide (AAm), acrylamido-azobenzene (AAAB) with a photo-responsive azobenzene chromophore, were reported in this article. The copolymerization was carried out with a free-radical polymerization route using 2,2-azobisisobutyronitrile (AIBN) as an initiator, tetrahydrofuran (THF) as a solvent and N,N-methylene bisacrylamide (MBAA) as a crosslinking agent for hydrogel. The structures of P(AAm-co-AAAB) were charactered by Fourier transform infrared spectroscopy (FT-IR) and 1H-NMR spectroscopy, and their photo-responsive behaviors was studied. The spectra of P(AAm-co-AAAB) copolymer solution irradiated with UV light showed one strong intensity peak at about 342 nm, and with the irradiation time increased, the intensity of the absorption decreased. The hydrogels also showed good photoresponses. With the UV irradiation time increased, the volume of the hydrogels decreased gradually. The photoresponsive behaviors was reversible, without the irradiation, the volume of the hydrohydrogels increased to the original state. This photoresponsive behavior was caused by the cis-trans isomerism of azobenzide in the chains of their structures