To provide a liquid composition capable of forming a membrane excellent in durability against hydrogen peroxide or peroxide radicals and excellent in hydrogen gas barrier property; a polymer electrolyte membrane; a membrane electrode assembly; and a polymer electrolyte fuel cell.

Liquid composition comprising a liquid medium, an acid-type sulfonic acid group-containing fluorocarbon polymer of which the hydrogen gas permeation coefficient under the conditions of a temperature of 80° C. and a relative humidity of 10% is at most 2.5×10.sup.−9 cm.sup.3.Math.cm/(s.Math.cm.sup.2.Math.cmHg), and cerium atoms; a polymer electrolyte membrane 15 comprising the acid-type sulfonic acid group-containing fluorocarbon polymer, and cerium atoms; and a membrane electrode assembly 10 comprising an anode 13 having a catalyst layer, a cathode 14 having a catalyst layer, and the polymer electrolyte membrane 15 disposed between the anode 13 and the cathode 14.

To provide a method for producing a polymer, whereby it is possible to obtain a sulfonic acid group-containing polymer having a high TQ value and a high ion exchange capacity. A method for producing a fluorosulfonyl group-containing fluorinated polymer, which comprises polymerizing a monomer represented by the following formula ml and tetrafluoroethylene, at a temperature of at least 110° C. and at most 250° C.:

##STR00001##

in the above formula, R.sup.F1 and R.sup.F2 are each a C.sub.1-3 perfluoroalkylene group.

To provide an ion exchange membrane for alkali chloride electrolysis which has high membrane strength and low membrane resistance, thereby capable of reducing the electrolysis voltage during alkali chloride electrolysis. In this ion exchange membrane (1) for alkali chloride electrolysis, a reinforcing material 20 formed by weaving reinforcing yarns 22 and sacrificial yarns 24 is disposed in a layer (S) 14, and layer (S) 14 has elution portions 28 formed by elution of at least portions of the sacrificial yarns 24. In a cross section perpendicular to reinforcing yarns of the warp, the average distance (d1) from the center of a reinforcing yarn 22 to the center of the adjacent reinforcing yarn 22, the total area (P) obtained by adding the cross-sectional area of an elution portion 28 and the cross-sectional area of a sacrificial yarn 24 remaining in the elution portion 28, the number (n) of elution portions between adjacent reinforcing yarns 22, and the ion exchange capacity of a layer (Sa) located on the most anode side in the layer (S) 14 during alkali chloride electrolysis, are controlled to be within specific ranges, respectively.

The present invention pertains to a fluoropolymer hybrid organic/inorganic composite, to a film comprising said fluoropolymer hybrid organic/inorganic composite and to uses of said film in various applications, in particular in electrochemical and in photo-electrochemical applications.

To provide a method for producing a fluorinated polymer which enables stable production of a fluorinated polymer having a high molecular weight at a high polymerization rate with good productivity and reduced environmental burdens, a method for producing a fluorinated polymer having functional groups, and a method for producing an electrolyte membrane. A method for producing a fluorinated polymer, which comprises polymerizing a monomer mixture containing tetrafluoroethylene and a fluorinated monomer having a group convertible to a sulfonic acid group or a carboxylic acid group in a polymerization medium, wherein the polymerization medium contains as the main component a C.sub.4-10 cyclic hydrofluorocarbon. Further, a method for producing a fluorinated polymer having functional groups and a method for producing an electrolyte membrane, employing the production method.

To provide a method for producing a fluorinated polymer, in which it is possible to efficiently and easily control the molecular weight to be proper when polymerizing a perfluoromonomer having a dioxolane ring containing a polymerizable double bond in the ring skeleton, and in which the obtainable fluorinated polymer is less susceptible to a decrease in molecular weight even when contacted with a base. A method for producing a fluorinated polymer, comprising polymerizing a raw-material mixture which contains at least one of a monomer composition M11 which comprises a perfluoromonomer represented by the formula m11 and a fluorinated monomer m11H having at least some of fluorine atoms of said perfluoromonomer substituted by hydrogen atoms, and a monomer composition M12 which comprises a perfluoromonomer represented by formula m12 and a fluorinated monomer m12H having at least some of fluorine atoms of said perfluoromonomer substituted by hydrogen atoms, wherein the total amount of the fluorinated monomer mil H and the fluorinated monomer m12H is from 10 to 1,100 ppm to the total amount of the monomer composition M11 and the monomer composition M12.

##STR00001##

An ion permeable membrane includes ion conductor particles and a fiber base material, in which each of the ion conductor particles has a first portion embedded inside the fiber base material, and a second portion exposed on outside surfaces of the fiber base material, and the second portions are continuous between an upper surface and a lower surface in a thickness direction of the ion permeable membrane.

A processing method of a base material sheet includes winding out the base material sheet wound up by a first core and a first porous sheet wound up by a second core, winding up by a third core the base material sheet and the first porous sheet to be overlapped with each other, and processing the base material sheet by a first processing liquid held in the first porous sheet; and winding out the base material sheet and the first porous sheet overlappingly wound up by the third core, winding up the first porous sheet by the second core, and winding up the base material sheet by the first core.

polymeric ion-conducting membrane with an enhanced stability against attacks of free radicals for exteding its service time, which comprises (a) a polymer matrix, and (b) a redox stabilizer, where the redox stabilizer is attached to the polymer matrix by chemical or ligand bonding, or the redox stabilizer is physically mixed with the polymer matrix.

##STR00001##

The copolymer includes divalent units represented by formula [CF.sup.2-CF.sup.2], divalent units represented by formula: (I), and one or more divalent units independently represented by formula: (II) When Z is hydrogen, the copolymer has an alpha transition temperature of up to 100 ?C. The copolymer has an SO.sub.3Z equivalent weight in a range from 300 to 1400, and a variation of the copolymer in which SO.sub.3Z is replaced with SO.sub.2F has a melt flow index of up to 80 grams per ten minutes measured at a temperature of 265 C. and at a support weight of 5 kg. A catalyst ink or polymer electrolyte membrane including the copolymer are also provided.