TECHNOLOGY FOCUS - POLYMERS - Preferred Compounds: Sulfonated polyimides have preferably equivalent molecular wt. (defined by wt. of polymer in grams per sulfonic acid equivalent) equal 400-2500, and molecular wt. 10000-100000. Full Definitions: In (Ix), (Iy) and (I), 1) C1 and C2, same or different, may represent each a benzene cycle optionally substituted with one or two 1-10C alkyl or alkoxy groups or halogen atoms; or number of benzene cycles optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms, and linked to each other with one simple bond or divalent group A; or C1 and C2 can also each represent condensed polycyclic group, optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms; or C1 and C2 can also represent heterocycle or condensed heterocycle, of aromatic type, optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms (more specifically, C1 can be benzene cycle while C2 can be in form of two benzene cycles linked with oxygen bridge; or C1 may consist of two benzene cycles linked with perfluoroalkylene group(s) and C2 consists of two benzene cycle linked together with divalent perfluoroalkyl or perfluoroalkylene group(s); or C1 is benzene cycle while C2 is naphthalene cycle; or both are naphthalene cycles); 2) Ar1 and Ar2, same or different, can also represent each e.g. divalent benzene cycle with meta- or para- attachment position, optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms, or number of benzene cycles optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms and linked together with one simple bond or divalent group A; or Ar1 and Ar2 can each represent condensed polycycle optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms; or Ar1 and Ar2 may also represent heterocycle or condensed heterocycle of aromatic character, optionally substituted with one or more 1-10C alkyl or alkoxy groups, or halogen atoms (more specifically, Ar1 can be diphenylmethane, or benzenic, or diphenyl ether group while Ar2 is biphenyl-disulfonic group). In (I), C3 can be benzene or naphthalene cycle optionally substituted with one or more of 1-10C alkyl or alkoxy groups, or halogen atoms. Divalent group A is selected from a) 1-10C linear or branched alkyl group optionally substituted with one or more F, Cl, Br or I and/or one or more hydroxyl groups, b) heteroatom O or S, and c) groups of formulae (III)-(XII)    R3, R4 = 1-10C alkyl group such as methyl, ethyl, isopropyl etc.    .