Synthesis of cross-linked poly (N-isopropylacrylamide) microparticles in supercritical carbon dioxide

Herein, we report a new method that has been developed to prepare thermoresponsive polymers. The white, dry, fine powders were obtained directly from cross-linking polymerization of N-isopropylacrylamide in supercritical carbon dioxide (scCO₂) with N,N-methylenebisacrylamide as a cross-linker. The effects of the reaction pressure and time as well as the initial concentrations of the initiator, cross-linker, and monomer on the yield and morphology of the resulting polymer were investigated systematically. The polymer yield was increased with the concentrations of the cross-linker, monomer, and reaction time. Under the condition of using higher cross-linker concentrations, the cross-linked poly (N-isopropylacrylamide) microparticles with diameters of 50 nm were generated in scCO₂ in high-yield and short reaction times. These results suggest that the synthetic method using scCO₂ can be used to prepare biomedical materials such as the controlled drug-release system.