TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Monomers: The phosphoric acid group containing unsaturated monomer is monomer of general formula (1), phosphoric acid group containing diester group unsaturated monomer of general formula (2), pyrophosphoric acid group containing unsaturated monomer of general formula (3) and/or phosphoric acid group containing triester group unsaturated monomer of general formula (4).R1,R3,R6,R8,R11,R12,R15,R17=hydrogen or alkyl, preferably methyl;R2,R4,R5,R9,R10,R13,R14,R16=H or optionally substituted alkyl, preferably methyl or chloromethyl;andn,k,p,r,s,x-z=1-6.The vinyl aromatic conjugated diene group liquid oligomer is a copolymer with styrene, isoprene and/or 1,3-butadiene. The phosphoric acid group containing unsaturated monomer and another unsaturated monomer copolymerizable with oligomer (b) are copolymerized. The other unsaturated copolymerizable monomer is unsaturated monomer (c) which has acid group and/or amino group, and ethylenically unsaturated bond(s), and/or unsaturated monomer (d) which has ethylenically unsaturated double bond(s), and does not contain acidic or amino group. Monomer (d) contains functional group chosen from sulfonic acid group, carboxylic acid group, alcoholic hydroxyl group and/or amino group. The monomer (d) is (meth)acrylonitrile, (meth)acrylic ester, optionally substituted styrene, halo-vinyl, fatty acid vinyl esters and/or fluorine group containing unsaturated monomer which has one or more fluorine group.    TECHNOLOGY FOCUS - POLYMERS - Preferred Film: The mixture ratio (mass ratio) of phosphoric acid group containing unsaturated monomer (a) and vinyl aromatic-conjugated diene group liquid oligomer (b) is 99/1-40/60. EXAMPLE - Phosphoric acid group containing unsaturated monomer containing solution containing (in wt.%) Phosmer M (RTM: methacryloyl oxyethyl phosphate) (8.9) and acrylonitrile of molecular weight 210 (2.0), was prepared. Kuraprene LIR-310 (RTM: styrene-isoprene liquid oligomer) solution having solid content concentration of 9.9 wt.% was prepared. The oligomer solution (50.0) was dropped into a polymerization reactor and heated at 80degreesC. Phosphoric acid group containing unsaturated monomer containing solution (39.9) was dropped and heated at 80-85degreesC for 3.5 hours, and copolymer containing solution was obtained. The solution was cooled, flow-spreaded and heated at reduced pressure for 5 minutes at 130degreesC, and solid polymer electrolyte film was produced. The film had thickness of 171 microns. The film was immersed in methanol for 24 hours, vacuum dried, and then immersed in large excess of methanol, at room temperature for 24 hours, and methanol extractability was measured to be 5.5 mass%. The film showed excellent proton conductivity when used in open-system impedance cell, and electric conductivity of 10-4-10-2 cm-1 at 90% relative humidity and 30-80degreesC.