A Synthetic Hydrogel with Thermoreversible Gelation. I. Preparation and Rheological Properties

Block copolymers composed of poly(N-isopropylacrylamide-co-n-butyl methacrylate) [poly(NIPAAm-co-BMA)] and poly(ethylene glycol) (PEG) were prepared. Aqueous solutions of the block copolymers were characterized by dynamic viscoelastic measurement as a function of temperature. The fluid solutions turned into hydrogels upon heating while keeping their transparency and without syneresis. The hydrogels turned back into solutions upon cooling. The thermoreversible sol-gel transition was observed with no hysteresis. The sol-gel transition temperatures were closely correlated to the lower critical solution temperature of the poly(NIPAAm-co-BMA) in the block copolymers. Gelation is believed to be caused by thermoreversible crosslinkages between intermolecular poly(NIPAAm-co-BMA) blocks due to hydrophobic interaction.