Stimuli-Sensitive Xanthan Derivatives/N-Isopropylacrylamide Hydrogels: Influence of Cross-Linking Agent on Interpenetrating Polymer Network Properties

This article first describes the preparation and characterization of a novel class of unsaturated polysaccharide derivatives/beta-cyclodextrin acrylate/N-isopropylacrylamide stimuli-responsive hydrogels synthesized by free radical polymerization. Xanthan gum was partially functionalized by esterification with maleic anhydride under various conditions. By copolymerization of these maleate polysaccharides with a known temperature sensitive precursor (N-isopropylacrylamide) water-swollen hydrogels with interpenetrating polymer networks (IPN) were obtained. The hydrogels were characterized for their temperature and pH-responsive behavior by equilibrium swelling experiments and differential scanning calorimetry. The investigation of these materials also includes solid-state (CP)-C-13/MAS NMR, elemental analysis of the nitrogen content and thermogravimetric measurements. Morphology was visualized by scanning electron microscopy. Depending upon composition, the hydrogels showed different response rates to the external changes of temperature as well as pH. By changing the feed composition ratio of precursors and cross-linking agent (beta-cyclodextrin acrylate or N,N'-methylenebisacrylamide, respectively) the phase transition temperature (lower critical solution temperature) could also be adjusted near the body temperature for the potential applications in biomedical and biotechnology fields. The role of the cross-linking agent on these properties is more particularly discussed.