TECHNOLOGY FOCUS - POLYMERS - Preferred Property: The polyether ketone contains 10-100 mol% of ether repeating unit of formula (1) and 0-90 mol% of ether repeating unit of formula (2).Ar1 = aromatic ring substituted with 1-20C alkyl group, halogen atom and/or halogenated hydrocarbon group, preferably aromatic group of formula (3 or 4);X,Y = proton-acid group chosen from sulfonic acid, carboxylic acid group, phosphoric acid group, sulfonimide, or their metallic salts;x,y = 0-4;andx+y = 1 or more.R1-R12 = H, 1-20C alkyl group or halogen atom, at least one of R1-R12 is 1-20C alkyl group;andA = single bond, -CH2-, -C(CH3)2-, -O-, -SO2- or benzene group of formula (3a).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Group: The proton acid group is sulfonic acid group. Preferred Compound: The radical generating agent is chosen from azo initiator and/or peroxide initiator. The resin composition contains 0.01-5 wt.% of radical generating agent with respect to the total amount of the resin composition. EXAMPLE - 5,5'-carbonyl bis(2-fluoro benzene sodium sulfonate) (in g) (4.22), 2,2-bis(3,5-dimethyl-4-hydroxy phenyl)propane (5.69), 4,4'-difluoro benzophenone (2.18) and potassium carbonate (3.46) were charged in a reactor. Dimethyl sulfoxide (40 ml) and toluene (30 ml) were added to the reactor and the contents were stirred in nitrogen atmosphere. The stirred mixture was heated at 130degreesC for 2 hours and water and toluene were removed. The mixture was reacted at 160degreesC for 14 hours and viscous polymer solution was obtained. The polymer solution was filtered, and dried to obtain sodium sulfonate group-containing cross-linkable polyether ketone powder (10.39) with yield of 92%, glass transition temperature of 230degreesC and reduced viscosity of 0.85 dl/g. Dicumyl peroxide (0.01) and sodium sulfonate group-containing polyether ketone powder (9.99) were dissolved in dimethyl sulfoxide (81.82 ml). The obtained mixed solution was applied on a glass plate and heated at 200degreesC for 4 hours. Sodium sulfonate-containing cross-linkable polyether ketone film was obtained. Proton exchange of the film was performed and proton-conductive film with favorable flexibility, ionic conductivity and strength was obtained.