Temperature-sensitive materials were prepared by free radical precipitation copolymerization of N-isopropylacrylamide (NIPA) with acrylic acid (AA) or 1-vinyl-2-pyrrolidone (VP) in supercritical carbon dioxide (scCO(2)). Dry, fine, powdered, nano-sized polymer product was produced at 70 degrees C and pressures ranged from 150 to 400 bar. The resulting high yield (> 96%) of temperature-sensitive microgels was obtained in the absence of stabilizer. The effects of comonomer, reaction pressure and reaction time on the yield and morphology of the copolymers have been investigated. It was found that solubility of NIPA in scCO(2) was remarkably enhanced in the presence of comonomers. The morphology of polymers could be controlled conveniently by changing reaction parameters. In addition, the reaction could be completed in short time in the presence of divinyl monomer.