TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Solvent: The organic solvent which is not interacted with the polymer segment (A), is organic solvent which does not contain nitrogen which is single bond or double bond as a coupling scheme of substituent on a nitrogen atom, and organic solvent having -O-, -OH-, -CO-, -SO2-, -SO3-, -CN, -NO2- and/or CO2.    TECHNOLOGY FOCUS - POLYMERS - Preferred Property: The width of lamella structure of the polymer segment (B) which forms micro phase separation structure is 5-200 nm.Preferred Polymer: The film contains block copolymer in which polymer segments (A and B) are covalently bonded. The block copolymer has a structure of principal chain structure in which the aromatic ring is covalently bonded with suitable bonding group, and structure of polymer segment (A) containing sulfonic acid group in a side chain. EXAMPLE - Polyarylene oligomer of formula (I) having number average molecular weight (Mn) of 4000, glass transition temperature of 157degreesC and thermal decomposition temperature of 500degreesC was prepared. Polyarylene copolymer having Mn of 57000, and weight average molecular weight (Mw) of 165000, was prepared using the obtained oligomer, 2,5-dichloro-4'-(4-phenoxy) phenoxy benzophenone, bis(triphenyl phosphine) nickel dichloride, sodium iodide, triphenyl phosphine, zinc dust and N-methyl-2-pyrrolidone. Polyarylene copolymer containing sulfonic acid group with Mn of 56000 and Mw of 171000, was prepared using obtained copolymer and 98% sulfuric acid. Gamma-butyrolactone (in g) (18.3) and tetrahydro furan (12.3) were added to the obtained polymer (5) and stirred for 24 hours, and uniform polymer solution with viscosity of 5000 cp was obtained. The obtained solution was casted on a polyethylene terephthalate film, dried at 80degreesC for 30 minutes, 160degreesC for 60 minutes, and uniform and transparent film of 100 microns film thickness was obtained. The film had micro phase separation structure in which the segment (A) having sulfonic acid group formed a continuous phase and sulfonic acid group-free segment (B) formed discontinuous lamella structure, in film morphology. The width of lamella structure of the polymer segment (B) was 30-34 nm. The film had methanol flux of 80 g/m2.hour, area change rate of 115%, and conductivity of 0.141 S/cm at 60degreesC and 80% relative humidity and 0.067 S/cm at 25degreesC and 80% relative humidity.