TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compounds: The organo silicon compound has polysiloxane structure. An organic group bonds with silicon atom to form side chain and terminal. The silicon atom and organic group form silicon-carbon bond. The organo silicon compound is chosen from compounds of formulae (1-4).R1-R4=organic group having ethylenically unsaturated bond, (un)substituted alkyl or aryl;R5,R6=(un)substituted alkyl or aryl;m,n=1 or more;R7=H or alkyl;R8=(un)substituted alkylene;p=0-2;R1'-R3'=(meth)acrylate group, methyl or phenyl group, preferably (meth)acrylate group;andR7'=H or methyl.The phosphoric acid-containing unsaturated monomer is chosen from phosphoric acid-containing unsaturated monomer of formula (5), phosphoric acid-containing diester type unsaturated monomer of formula (6), pyrophosphoric acid-containing unsaturated monomer of formula (7) and phosphoric acid-containing triester unsaturated monomer of formula (8).R13,R15,R17,R19,R21,R23,R25,R27=H or alkyl, preferably methyl;R14,R16,R18,R20,R22,R24,R26,R28= (un)substituted alkylene, preferably -(CH2)2-, -CH2CH2(CH3)-, -CH2CH2(CH2Cl)- or -(CH2)4-;andx,y,z=1-6.Alternately, the organo silicon compound and another unsaturated compound are copolymerized. The unsaturated compound is other than phosphoric acid group-containing monomer, and is chosen from compound (a) which does not have acidic group and has ethylenically unsaturated bonds, and/or unsaturated compound (b) having acidic group and ethylenically unsaturated bonds. The compound (a) is (meth)acrylonitrile, (meth)acrylamide, (meth)acrylic acid ester, conjugated diene type liquid oligomer or its derivative(s), vinylated aromatic conjugated diene type oligomer or its derivative(s), (un)substituted styrene, halogenated vinyl, fatty acid substituted vinyl ester or fluorine group-containing unsaturated monomer. The compound (b) has acidic group chosen from sulfonic acid group, carboxylic acid group, phosphonic acid group and boric acid group. The other unsaturated compound is hardener containing 2 or more ethylenically unsaturated bonds in the molecule, preferably tetrafunctional urethane (meth)acrylate of formula (9), trifunctional urethane (meth)acrylate of formula (10) or bifunctional urethane (meth)acrylate of formula (11).R29-R32,R29'-R31',R29",R31"=H or methyl;andR33,R33',R33"=alkylene group.The solvent is 1-6C aliphatic alcohol, dimethyl formamide, N,N-dimethyl acetamide, tetrahydrofuran or dimethyl sulfoxide.    TECHNOLOGY FOCUS - POLYMERS - Preferred Property: The polymer electrolyte film has proton electroconductivity of more than 1x10-3 S/cm at relative humidity of 95% or less and temperature between room temperature and 60degreesC. EXAMPLE - Phosmer PE (RTM: phosphoric acid group-containing unsaturated monomer) (in mol%) (20), phosphoxy ethyl methacrylate (80) and X-22-164 AS (RTM: organosilicon compound) were copolymerized and the obtained copolymer solution was flow-spread on polyethylene terephthalate sheet. The copolymer solution was dried under reduced pressure to obtain solid polymer electrolyte film. The obtained film had excellent methanol extractability, and high proton conductivity in low humidity.