Fabrication of poly (N-isopropylacrylamide-co-itaconic acid) hydrogels in DMSO/water mixtures and their characterization

In this article, pH and temperature double responsive poly (N-isopropylacrylamide-co-IA) hydrogels were prepared by copolymerization in mixed solvents of water and dimethylsulphoxide (DMSO) above zero. The freshly fabricated P(NIPAAm-co-IA) hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) techniques to investigate their chemical compositions, structures, and morphologies. The results showed that all of these gels have similar chemical compositions and structures but differ in surface morphologies. The hydrogels prepared with highest DMSO/water ratios have porous surfaces, while the other gels exhibit smooth and dense surfaces. Temperature and pH sensitivities of the resultant hydrogels were examined through swelling ratios and deswelling/reswelling kinetics experiments, as well. The results indicated that only hydrogels prepared in the highest DMSO/water ratio media exhibited improved properties such as higher swelling ratios, faster deswelling and reswelling kinetics compared with traditional P(NIPAAm-co-IA) hydrogels, as the other hydrogels possessed lower swelling ratios and slower deswelling and reswelling dynamics. We have proposed that there maybe an energy barrier existed for conformation transitions in the process of removal of DMSO by water. Only the gels which could overcome the energy barrier exhibited expanded network structures and improved properties while, the other gels maintained their contracted network structures and poor properties.