Inverse thermally reversible gelation-based hydrogels: synthesis and characterization of N-isopropylacrylamide copolymers containing deoxycholic acid in the side chain

A series of water-soluble, thermosensitive copolymers based on N-isopropylacrylamide (NIPAM) and methacrylate derivatives of deoxycholic acid (MEDCA) were synthesized using free radical copolymerization method by varying feed ratios of monomers. The composition ratios and structure of copolymers were determined by 1H NMR spectroscopy. The glass transition temperature was examined by DSC. The thermoresponsive behaviors of polymeric solutions were investigated by turbidity measurement using UV-Visible spectroscopy. The resultant copolymers exhibit systematic changes in their LCSTs as a function of their chemical composition, as the incorporation of amphiphilic comonomers MEDCA results in a lower and broader LCST of the copolymer solution. An aqueous solution of the copolymer above a critical concentration (2 wt%) experiences four distinct phases such as clear solutions, cloud solutions, gel and shrunken gel upon heating. Finally, the mechanism of the phase transitions was tentatively discussed based on the observations.