The advantages of aqueous emulsion method are demonstrated for producing copolymers as a material for Nafion®- and Aquivion®-type proton exchange membranes. The features of copolymerization of tetrafluoroethylene (TFE) with sulfonyl fluoride monomers in microdroplets of monomer in emulsion are discussed. For the first time, the copolymerization constants were found for TFE reaction with perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride (FS-141) or perfluoro-3-oxapentenesulfonyl fluoride (FS-81) monomers in the aqueous emulsion medium. The producing of long- and short-side chain copolymers realizes by different mechanisms, depending on the way of copolymer accumulation in the system – either by persisting in monomer microdroplets or by segregation in latex particles. Aqueous emulsion copolymerization allows regulate the copolymer composition, keeping it constant till high degrees of monomer conversion, thus obtaining the membrane copolymer precursors with improved properties.