Аннотация:Cyclization reactions accompanying the nucleophilic displacement polymerization of bisphenol A and difluorobenzophenone (DFB) were studied. Size distribution and amounts of cyclic species were determined depending on the concentration and isomerism in DFB. Experimental cyclization constants were found to be consistent with the values calculated using Jacobson and Stock-mayer's theory for a freely rotating chain of virtual bonds in the case of 4,4'-DFB. For 2,4'-DFB, hindered rotation around some virtual bonds should be taken into account.