TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The sulfonated copolymer is preferably of formula (3).    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The proton exchange membrane further comprises 10-60 weight% (wt.%), preferably 0.01-60 wt.% of phosphotungstic acid, phosphomolybdic acid or zirconium hydrogen phosphate, preferably phosphotungstic acid, as an inorganic heteropoly acid.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The monomer used for preparing sulfonated polymer comprises 3,3'-disulfonated 4,4'-dichlorodiphenyl sulfone and 4,4'-dichlorodiphenyl sulfone in a molar ratio of 0.001-0.999. The sulfonate groups of the monomers are sulfonic acid groups in the salt form. The co-monomer used for preparing sulfonated polymer is 4,4'-biphenol, hydroquinone, 6F-bisphenol or phenylphosphine oxide bisphenol. The aromatic diamine used for preparing sulfonated polyimide is 2,5-phenylenediamine sulfonic acid,2,5-phenylenediamine sulfonate,4,4'-diamino-biphenyl-2,2'-disulfonic acid or 4,4'-diamino-biphenyl-2,2'-disulfonate. The dianhydride is hexafluorodianhydride or 3,3',4,4'-biphenyl tetracarboxylic dianhydride. The polymerization of an aromatic diamine includes a second diamine. The ratio of the aromatic diamine to the second diamine is 0.001-0.999. Preferred Definitions:    n/n+m = 0.3-0.6.    EXAMPLE - 3,3'-disulfonated-4,4'-dichlorodiphenyl sulfone (SDCDPS) was prepared by reacting 4,4'-dichlorodiphenyl sulfone (DCDPS) and fuming sulfuric acid, and neutralizing using sodium chloride and sodium hydroxide. Biphenol-based sulfonated poly(arylene ether sulfone) was synthesized by direct polycondensation of 4,4'-biphenol, DCDPS and SDCDPS. Copolymerization was carried out in N-methyl-2-pyrrolidone at 190degreesC in the presence of anhydrous potassium carbonate. The copolymer in the salt form was converted to corresponding acid form, by boiling in dilute sulfuric acid solution, washing with deionized water and vacuum drying. Composite membrane was prepared using the acid form sulfonated poly(arylene ether sulfone) (BPSH) and phosphotungstic acid (HPA) by solution-casting method. The polymer and the HPA powder were added to dimethylacetamide and stirred for 12 hours at 80degreesC. The obtained solution was cast on to a clean glass plate and dried. The transparent cast film had a yellowish tint and was of 150 mum thick. The obtained composite membrane had decreased water uptake without sacrificing protonic conductivity. The specific interaction between sulfonic acid and HPA prevented extraction of HPA from the composite in an aqueous environment.