TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Antioxidant: The antioxidant containing tri-valent phosphorus is selected from formulae (I- VI).R1, R2, R4, R5, R6-R10 and R13-R17 = H, 1-20C alkyl or 1-20C alkoxy;R3 = H or 1-8C alkyl;X = sulfur, -CHRa-, 2-8C alkylene or a direct bonding;Ra = H or 1-8C alkyl;A = 2-8C alkylene, carbonyl or (asterisk)-CORb-, where (asterisk) shows oxygen side bonding;Rb = 1-8C alkylene;one of Y and Z = hydroxyl or 1-20C alkoxy, and the other is H or 1-20C alkyl;R11, R12 = 1-20C alkyl;B = direct bonding, sulfur, -CHRc or 2-8C alkylene;Rc = 1-8C alkyl; andE = 1-20C alkoxy group or halogen.The antioxidant containing sulfur is sulfide compound selected from(R18SCH2CH2C(O)OCH2)4C (VII)(R22OC(O)CH2CH2)2S (VIII)R18 and R22 = 1-30C alkyl, 7-30C aralkyl or 6-30C aryl; andR19-R21 = H, 1-30C alkyl, 7-30C aralkyl or 6-30C aryl.    TECHNOLOGY FOCUS - POLYMERS - Preferred Support: The supporter is a porous support membrane comprising an aliphatic polymer or a fluorine-containing polymer. SPECIFIC COMPOUNDS - Specific Antioxidants: Several antioxidants containing trivalent phosphorus are disclosed, e.g. 2,4,8,10-tetramethyl-6- (3-(3-methyl-4-hydroxy-5-tert-butylphenyl) propoxy)dibenzo (d,f) (1,3,2) dioxaphosphepin. Several antioxidants containing sulfur are disclosed, e.g. pentaerythrityltetrakis(3- methylthiopropionate).    EXAMPLE - Anhydrous cuprous chloride and 2- methylbenzimidazole were stirred in toluene at room temperature for 15 minutes. 2-Phenylphenol, 4,4'-dihydroxybiphenyl and toluene were added and stirred at 50 degreesC for 10 hours and poured in methanol containing hydrochloric acid to precipitate a polymer. The polymer was filtered and dried to obtain a poly(phenylphenylene ether). A polyether sulfone with hydroxy group(s) at the terminal(s) SUMIKAEXEL PES5003P (RTM), potassium carbonate, N,N-dimethylacetamide and toluene were added and stirred with heating. Dehydration was performed under azeotropic distillation of toluene and water. Toluene was removed by distillation and 4,4'-difluorobenzophenone was added and stirred by heating at 160degreesC for 10 hours. The reaction solution was added to hydrogen chloride-acetic methanol and the precipitate obtained was filtered and dried to obtain a block copolymer. The block copolymer was sulfonated by stirring and dissolving in 98 % sulfuric acid at room temperature. The product was added to ice water and the precipitate was filtrated, rinsed and dried to obtain a sulfonated block copolymer.    A solution was prepared by mixing copolymer (in g) (1.425), 2,4,8,10-tetra- tert-butyl-6-(3-(3-methyl-4-hydroxy-5-tert- butylphenyl)propoxy)dibenzo (d,f)(1,3,2) dioxaphosphepin as an antioxidant containing trivalent phosphorus (0.075) and dimethyl acrylate (9.075). The mixture was applied on a glass plate. The solvent was dried under normal pressure to obtain polymer electrolyte membrane having homogeneous appearance. The membrane had excellent radical resistance.