Multi-sensitive copolymer hydrogels of N-isopropylacrylamide with several polymerizable azobenzene-containing monomers

Three kinds of photosensitive and two kinds of photo/pH-sensitive polymerizable azobenzene-containing monomers were designed and synthesized. Three thermo/light dual-responsive and two thermo/light/pH triple-responsive copolymer hydrogels were prepared via copolymerization of those new azobenzene-containing monomers, N-isopropylacrylamide, and a crosslinker. The properties of those hydrogels were researched carefully by UV–Vis absorption spectrometry, differential scanning calorimetry, and gravimetry. It was found that the molecular structure, i.e., the methylene chain length, quaternary ammonium group and carboxyl group of azobenzene-containing monomers, had an important influence on the UV light response rate, phase transition and swelling ability of the copolymer hydrogel. Three hydrogels with good overall performances were screened, i.e., GelNDEP, GelNAEP0.01 and GelNAP0.01, which should be used as carriers in later studies. Analysing the influence of the molecular structure will help to fine-tune such a copolymer gel to a desired state, which is very important from an applications point of view.