Copolymerization of acrylic acid and 1H,1H,11H-perfluoroundecyl acrylate in supercritical carbon dioxide was successfully carried out. The products were obtained in the form of dry white powder with diameter about 0.2 mum. Viscosities of 2% aqueous solution of the copolymers were much higher than that of poly(acrylic acid) and it showed a strong dependence on pH, which is due to the intermolecular association.