TECHNOLOGY FOCUS - POLYMERS - Preparation: No preparation method is given. Preferred Component: The perfluorochloro ionomers are made by copolymerization of perfluorochloro monomer(s) and functional monomer(s) fluorinated with ionic group or convertible to ionic group moiety. The perfluorochloro monomer includes chlorotrifluoroethylene and dichlorodifluoroethylene. The functional monomers include compounds of formula: CF2=CF-(O-CF2-CF(CF2X))n-O-CF(Rf)-(CF(Rf))a-(CF2)b-Y'. The perfluorochloro ionomers has pendant side chain of formula: -(O-CF2-CF(CF2X))n-O-CF(Rf)-(CF(Rf))a-(CF2)b-Z. The partial fluorochloro ionomers are made by copolymerization of fluorochloro monomer(s) and functional monomers, or made by terpolymerization of fluorochloro monomers, functional monomer, and another monomer comprising alkenes including ethylene, propylene, butylene, and/or vinyl acetate. The functional monomer of partial fluorochloro ionomers include (meth)acrylic acid, tert-butyl acrylate, maleic anhydride, maleic acid, itaconic acid, itaconic anhydride, (methyl)styrene, 2-acrylamido-2-methyl-1-propanesulfonic acid, vinyl sulfonic acid, vinyl phosphonic acid, allyl chloride, allyl bromide, vinyl imidazole, vinylpyridine, and/or (3-acrylamidopropyl)trimethylammonium chloride.X=F and/or Cl;Rf=X, perfluoroalkyl, or chloroperfluoroalkyl;Y'=functional group convertible to ionic group including -SO2W', and COOR;W'=X;R=1-12C alkyl;Z=-SO3H or its salt, -SO2NR-, -SO2N(R1)SO2R2;R1,R2=(perfluoro)alkyl, -COOH or its salt, -PO(OH)2, -SO2N(-R-)2NR, sulfonamide imidazole, and sulfonamide quat. amine; anda,b,n=0-2.Preferred Properties: The ionomers are in a physical form of membrane or film having 5-200 mu m thickness. Preferred Material: The membrane of film is a composite membrane where the perfluorochloro ionomer is partially or fully impregnated on porous substrates, or a multi-layered membrane comprising different types of perfluorochloro ionomers. The porous substrates include microporous membranes of nylon, poly(vinylidene fluoride) or PTFE. The multi-layered membrane includes a layer of perfluorochloro ionomer with sulfonic acid group and another layer of ionomers with carboxylic acid group, and/or a layer of the ionomers with anionic charge group and a layer of the ionomers with cationic charge group. EXAMPLE - No suitable example given.