NOVELTY - Sulfonated polyphenylene polymer having repeat units (I), which is derived by controllably sulfonating a polyphenylene polymer with a sulfonating agent, is new.    USE - (I) is useful for producing nanocomposites, polymer electrolyte membranes, electrodes, membrane electrode assemblies, and electrode casting solution for use in fuel cells (e.g. hydrogen fuel cells and direct methanol fuel cells), high-performance capacitors, dialysis equipment and ultrafiltration. (I) is useful as battery separators, electrolytes for electrosynthesis cells, electrolytes for electrolysis cells, electrolytes for gas generating electrochemical systems, as ionic membranes in electrochemical sensors, as electrolytes in electrochemical scrubbers and other purification systems and as electrolytes in primary and secondary batteries.    ADVANTAGE - (I) has proton conductivity at 25degreesC of 10-125 mS/cm (claimed). (I) provides more efficient fuel cell. (I) provides improved polymer electrolyte membrane with: improved proton conductance, at 90-130degreesC; higher temperature of glass transition; and high-performance. (I) has reduced segmental mobility of polymer chains. (I) provides improved and high-performance sulfonated polyphenylene nanocomposites. (I) has: improved water retention properties, decreased low-carbon fuel permeability, and increased ion exchange capacity.    DETAILED DESCRIPTION - Sulfonated polyphenylene polymer having repeat units of formula (I), which is derived by controllably sulfonating a polyphenylene polymer with a sulfonating agent, is new.    R1-R3 = H or optionally inertly-substituted aromatic moiety;    n = lesser than or equal to 2; and    Ar1, Ar2 = optionally inertly-substituted aromatic moiety.    Where: a pendant side chain of a sulfonyl group attaches to a carbon atom; 1-6 sulfonyl groups are attached per repeat unit; and any combination of R1-R3, Ar1, Ar2 comprises a sub-combination of R1 is different than R2, R1 is different than R3, R2 is different than R3, Ar1 is different than Ar2, and R1 equal to R2 equal to R3 equal to Ar1 equal to Ar2.    DESCRIPTION OF DRAWING(S) - The figure shows the membrane electrode assembly.    Membrane (101)    Anode (103)    Cathode (105)    External circuit. (107)