TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The side-chain inducing agent is given by formula: Z'-H. The polymer (P) contains sulfur-containing repeating unit of formula: -Y-((SO2Xa)k'-P'-.Z'=-(Ar1(B1))-(X2Ar2(B2))- to -(Xn-1Arn-1(Bn-1))-(XnArn);Ar1-Arn,B1-Bn-1,n,Y',P'=as defined above;X1-Xn=coupling group chosen from -S-, -CH2-CX"2-, -C(OR")2- and -(C(OR")2)p-;X"=halogen atom excluding fluorine;R"=alkyl;X'=halogen atom, alkali metal or alkaline earth metal;R=H, alkyl or aryl;andk'=1-4.    TECHNOLOGY FOCUS - POLYMERS - Preferred Process: The polyelectrolyte is obtained by converting coupling group precursor into electron withdrawing coupling group and sulfonic acid precursor into sulfonic acid. Preferred Definitions:    P',P"=coupling group chosen from -CO-, -O-, -S-, -SO2- and -C(CF3)2-;    k=1-2;    f=0-2, preferably 0 or 1 and at least one of f is 1;and    Z=group of formula (3), preferably group of formula (4), in which phenyl group and phenylene group are optionally replaced by electron withdrawing group.    EXAMPLE - Victrex PEEK450PF (RTM: polyether ether ketone) (in g) (10) was taken in a reaction container, and 97% sulfuric acid (100) was added and stirred. Ion exchange water was poured, and the obtained polymer was washed with water and dried, to obtain sulfonated polyether ether ketone (10.8) of formula (18). The obtained sulfonated polyether ether ketone (4.27) and thionyl chloride (50 ml) were reacted at 70degreesC for 3 hours. Excess thionyl chloride was distilled, and a chlorosulfonyl polyether ether ketone (4.45) of formula (19), was obtained with a yield of 100%. The obtained chlorosulfonyl polyether ether ketone (4.45) and sulfolane (200 ml), were stirred at 90degreesC. 1,3,5-tris thiophenoxy benzene (20.1) and aluminum chloride (1.6) were added and stirred at 90degreesC for 40 hours. The reaction solution was added to 1 N hydrochloric acid aqueous solution, and the solid was washed by water and ethanol and dried. A polymer (6.02) was obtained with a yield of 95%. The obtained polymer (4) and 34% hydrogen peroxide aqueous solution (40) were stirred at 90degreesC for 6 hours. A polyelectrolyte (3.9) of formula (21) was obtained with a yield of 92%. A polymeric electrolyte film formed using the obtained polymer had high proton conductivity and oxidation resistance.