One-step polycyclization reaction in supercritical carbon dioxide has been carried out for the first time and a thereby set of polyimides has been synthesized. Diphenyl-2,2-hexafluoropropane-3,3',4,4'-tetracarboxylic acid dianhydride (dianhydride 6F), 4,4'-diaminodiphenyl-2,2-hexafluoropropane (diamine 6F) and 9,9-bis(4-aminophenyl)fluorene were used as monomers. Maximum inherent viscosity of the synthesized polymers is 0.56 dl/g. It is supposed that carbon dioxide act as an acidic catalyst for the reaction in the presence of water admixture. (C) 2002 Elsevier Science B.V. All rights reserved.