TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation: No general preparation is given. Preferred Compound: The benzene-containing compound is of formula (2 or 3).A,B',D,X,R1-R20,l,m,t,q,n=same as defined above;P'=structure of formula (4, 5 or 6);p'=0.01-1;andPh=sulfonic acid-containing structure of formula (7).    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: A polyarylene copolymer has a sulfonic acid group, and contains polyarylene-type polymer containing benzene-containing structural unit of formula (8) and sulfonic acid group-containing structural unit of formula (9).Y'=-CO-, -SO2-, -SO-, -CONH-, -COO-, -(CF2)i- or -C(CF3)2-;Z=direct bond, -(CH2)i-, -C(CH3)2-, -O- or S-;Ar=-SO3H, -O(CH2)rSO3H or -O(CF2)rSO3H;r=1-12;j,k=0-10;andh=1-4.A solid polymer electrolyte and a proton conductive film contain polyarylene copolymer. Preferred Definitions:    Ph=naphthalene, anthracene, tetracene or pentacene.    EXAMPLE - 2,7-Dihydroxy naphthalene (in g) (67.8), 1,3-bis(1-methyl-1-(4-hydroxylphenyl)ethyl)benzene (220.1), 4,4'-difluroro benzophenone (205.4), 4-chloro-4'-fluorobenzophenone (52.5) and potassium carbonate (175.6) were mixed and vacuum-dried under reduced pressure. Then, dimethyl acetamide (1250 ml) and toluene (500 ml) were added and heat-refluxed at 130 degrees C under nitrogen atmosphere. After 3 hours, toluene was removed, and the reaction mixture was stirred at 165 degrees C for 7 hours. Then, 4-chloro-4'-fluorobenzophenone (30.4) was added and stirred for 3 hours. The resulting mixture was filtered. The obtained filtrate was poured into methanol/hydrochloric acid aqueous solution. The deposited substance was filtered, washed and vacuum-dried. The resulting dried product was dissolved in tetrahydrofuran (1.1 kg) and poured into methanol (4.2L). The deposited substance was filtered and vacuum-dried to obtained benzene-containing compound (389) with yield of 86%. The obtained benzene-containing compound had number average molecular weight of 6000 and weight average molecular weight of 9800. A sulfonated polymer having weight average molecular weight of 190000, was formed using the obtained benzene-containing compound. 21 weight% N-methylpyrrolidone/methanol solution of the obtained sulfonated polymer was applied on a glass substrate, and dried to obtain protective film with film thickness of 30 mu m. The obtained film had methanol permeability of 64 g/m2/hour and membrane resistance of 0.23 ohm.cm2.