TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The benzene ring-containing repeating unit is of formula (IIa). Preferred Process: The polymer is doped with metal-containing compound of formula: M2I (3). The concentration of metal-containing compound is 0.1-10 wt.%, preferably 4-5 wt.%.M2=M.Preferred Method: The polymer is obtained by performing polycondensation reaction of isophthalic acid compound, sulfur-containing compound of formula (f) and hydrochloric in presence of methanesulfonic acid or polyphosphoric acid. The molar ration of isophthalic acid compound and sulfur-containing compound is 1/10-1/100, preferably 1/15-1/50.    TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): An isophthalic acid compound and sulfuric acid are reacted to obtain a sulfur-containing compound of formula (a). The obtained sulfur-containing compound is subjected to polycondensation reaction with chlorine-containing compound of formula (b) in presence of methanesulfonic acid or polyphosphoric acid to obtain polymer of formula (c). The polymer is sulfonated using metal-containing compound of formula: MH (d) and sulfur-containing compound of formula (e) to obtain polymer. Preferred Composition: The sulfite-containing compounds are same. Preferred Compounds: The nitrogen-containing repeating unit is of formula (Ia). The polymer further contains a benzene ring-containing repeating unit of formula (II). The benzene ring-containing repeating unit sulfite-containing compounds of formula: R4-SO3M (2) as pendants, which is linked to two or four nitrogen atoms.R4=R1;R2=R3;y=integer;andx/y=1/10-1/100. Preferred Definitions:    R1,R4=1-20C hydrocarbon, preferably 1-6C hydrocarbon, more preferably -(CH2)n-, most preferably -(CH2)3-, where R1 comprises a flexible side chain with different conformation states for improved flexibility and solubility;    n=integer;    M=Li+ as cation;    x=100 or more;and    x/y=1/15-1/50.    EXAMPLE - Poly((1,7-dipropylsulfo-sodium-benzo(1,2-d:4,5-d')diimidazole-2,6-diyl)-2-(2-sulfo)-m-phenylene) polymer, water and aprotic solvents such as dimethylsulfoxide and dimethylacetamide were reacted to obtain a polymer. The obtained polymer was treated with concentrated hydrochloric acid to obtain poly((1,7-dipropylsulfobenzo(1,2-d:4,5-d')diimidazole-2,6-diyl)-2-(2-sulf-o)-m-phenylene), dissolved in methanesulfonic acid or polyphosphoric acid and reacted to obtain polymer.