TECHNOLOGY FOCUS - POLYMERS - Preferred Resin: The cross-linkable aromatic resin containing proton-acid group is aromatic polyether cross-linkable using light, heat or electron beam. The polyether has 1-10C alkenyl group or methylene group directly coupled to 1-10C alkyl group bonded to the aromatic ring. The cross-linkable aromatic resin contains 10-100 mol% of ether repeating unit of formula (1) and 0-90 mol% of ether repeating unit of formula (2).R1-R10 = H, 1-10C alkyl or alkenyl group;A1-A3 = -CH2-, -C(CH3)2-, -C(CF3)2-, -O-, -SO2- or -CO-;i-l = 0 or 1X1-X10 = H or proton-acid group of formula: -CnH2n-SO3Y;n = 0-10;andY = H, sodium or potassium.The hydrogen atom of the aromatic ring is optionally substituted by 1-10C alkyl or alkenyl group, proton acid group, chlorine, fluorine or trifluoro methane. The aromatic resin having basic group is polyether pyridine. EXAMPLE - 5,5'-carbonyl bis(2-fluoro benzene sodium sulfonate) (in g) (33.78), 2,2-bis(3,5-dimethyl-4-hydroxy phenyl)propane (22.59) and potassium carbonate (13.82) were charged in a reactor. Dimethyl sulfoxide (200 ml) and toluene (160 ml) were added to the reactor and the contents were stirred in nitrogen atmosphere. The stirred mixture was heated at 135degreesC for 16 hours and water and toluene were removed. The mixture was reacted at 160degreesC for 12 hours and viscous polymer solution was obtained. The polymer solution was filtered, and dried to obtain sodium sulfonate group-containing polyether ketone powder (45.33) with yield of 85% and reduced viscosity of 0.84 dl/g. Polyether pyridine (0.425) and sodium sulfonate group-containing polyether ketone powder (3.733) were dissolved in N-methyl pyrrolidone (16). The obtained mixed solution was passed on a glass plate and heated in inert atmosphere. N-methyl pyrrolidone was removed and the formed film was cross-linked. Proton exchange of the film was performed and proton-conductive film with favorable flexibility, ionic conductivity and methanol proof property.