Precipitation copolymerization of <i>N</i>‐isopropylacrylamide and acrylic acid in supercritical carbon dioxide

Abstract

The copolymerization of N-isopropylacrylamide and acrylic acid in supercritical carbon dioxide was studied in an autoclave at 70 °C and pressures ranging from 150 to 397 bar, with 2,2′-azobisisobutyronitrile as a free-radical initiator. All the polymers were white, dry, fine powders with high yields (>95%). Stimuli-responsive measurements showed that the lower critical solution temperature and pH-dependent swelling of poly(N-isopropylacrylamide-co-acrylic acid) copolymers or crosslinking polymers could be altered by slight modifications of the copolymer compositions.