Thermoresponsive chitosan/N-isopropylacrylamide copolymer through atom transfer radical polymerization

Regioseletive copolymerization of N-isopropylacrylamide (NIPAM) onto chitosan was achieved by atom transfer radical polymerization (ATRP) by using a regioselective 3,6-di-O-bromoisobutyryl-2-N-phthaloyl chitosan as a macroinitiator. The degree of polymerization (DP) of polyNIPAM onto the chitosan derivative changed by varying the ratio between NIPAM monomer, macroinitiator, ligand, and transition metal. ATRP successfully proceeded and a DP of polyNIPAM up to 110.5 was obtained. The thermal decomposition temperature of the 3,6-di-O-bromoisobutyryl-2-N-phthaloyl chitosan was significantly improved by increasing the DP of the NIPAM component. The polyNIPAM-g-chitosan derivative showed a thermoresponsive property. Although it formed a stable suspension in water at room temperature, it caused a hydrophilic-to-hydrophobic transition at around 32°C, resulting in precipitate formation.