NOVELTY - An ionomer comprises the reaction product of monomer (A) with monomers (B) and (C). The monomer (A) comprises 4-(4-hydroxyphenyl) phthalazinone. The monomer (B) comprises disodium 3,3'-sulfonyl (4,4'-difluoro benzophenone). The monomer (C) comprises 4,4'-difluoro benzophenone.    USE - For use in polymer electrolyte membrane fuel cells.    ADVANTAGE - The inventive ionomer provides fuel cells with improved performance. It has superior temperature oxidation properties than those membrane materials based on other poly(aromatic ether ketone)s of prior art. It has low swelling in water.    DETAILED DESCRIPTION - An ionomer comprises the reaction product of monomer of formula (A) and monomer of formulae (B) and (C). The number of moles of (B) and (C) is equal to that of (A).    R1-R4 = H, alkyl, aromatic or halo;    X1 and X2 = carbonyl or sulfone radical or aromatic compounds connected through a ketone or sulfone linkage;    Y = halo;    M = alkali metal.    INDEPENDENT CLAIMS are included for the following:    (a) A method of preparing a sulfonated poly(phthalazinone ether ketone) comprising copolymerizing 4,4'-di halo(or di nitro)-3,3'-disulfonate salt of benzophenone, di halo (or di nitro) benzophenone, and monomer containing phthalazinone and phenol group, in polar solvents or reaction medium containing mainly polar solvents, in the presence of a catalyst comprising a metallic base (or its salt), to obtain a product; dehydrating the product at high temperature using azeotropic dehydration agents; diluting the product with solvents; coagulating the product using coagulation agents; separating the product; drying the product; and performing the diluting step until drying step for two times;    (b) A method for generating electricity comprising providing anode, cathode, and polymer electrolyte membrane comprising the inventive ionomer; flowing a fuel to the cathode where the fuel is disassociated to release a proton and an electron; transporting the proton across the polymer electrolyte membrane to the anode; and collecting the electron at a collector to generate electricity;    (c) A membrane electrode assembly comprising polymer membrane comprising the inventive ionomer in acid form, between anode and cathode;and    (d) A fuel cell comprising membrane electrode assembly that is sandwiched between a first gas diffusion medium and second gas diffusion medium and is in electronic communication with a current collector.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a membrane formed from a ionomer.