The copolymerizations of zinc dimethacrylate (ZMA) and 2-(N-ethylperfluorooctanesulfonamide)ethyl acrylate (RfSA) in various solvents were carried out in relation to the copolymerization of ZMA and RfSA in a synthetic rubber during the peroxide curing process (in situ copolymerization). The ZMA-RfSA copolymerization initiated with 2,2＇-azobisisobutyronitrile at an equimolar mixture of the monomers yielded a copolymer of which the composition was almost the same with that of the comonomer, regardless of the solvent used. It was considered that the sulfonamido group in monomeric RfSA and the copolymer of RfSA specifically improves the miscibility of RfSA with ZMA.