To provide a production method whereby an ion exchange membrane for alkali chloride electrolysis can be obtained which has high current efficiency, little variation in current efficiency and high alkaline resistance. This is a method for producing an ion exchange membrane 1 having a layer (C) 12 containing a fluorinated polymer (A) having carboxylic acid type functional groups, by immersing an ion exchange membrane precursor film having a precursor layer (C) containing a fluorinated polymer (A) having groups convertible to carboxylic acid type functional groups, in an aqueous alkaline solution comprising an alkali metal hydroxide, a water-soluble organic solvent and water, and converting the groups convertible to carboxylic acid type functional groups to carboxylic acid functional groups, wherein the concentration of the water-soluble organic solvent is from 1 to 60 mass % in the aqueous alkaline solution (100 mass %); the temperature of the aqueous alkaline solution is at least 40 C. and less than 80 C.; and the proportion of structural units having carboxylic acid type functional groups in the fluorinated polymer (A) is from 13.0 to 14.50 mol % in all structural units (100 mol %) in the fluorinated polymer (A).

The copolymer includes divalent units represented by formula [CF.sub.2CF.sub.2], divalent units represented by formula: and one or more divalent units independently represented by formula: The copolymer has an SO.sub.2X equivalent weight in a range from 300 to 2000. A polymer electrolyte membrane that includes the copolymer and a membrane electrode assembly that includes such a polymer electrolyte membrane are also provided.

A non-humidified proton-conductive membrane according to the present invention includes a polymer and a proton-conductive substance. The polymer includes a glassy or crystalline first site having a glass-transition temperature or melting temperature higher than the service temperature of the proton-conductive membrane and a second site capable of forming a noncovalent bond. The proton-conductive substance includes a proton-releasing/binding site capable of noncovalently binding to the second site of the polymer and a proton coordination site capable of coordinating to protons, the proton-releasing/binding site and the proton coordination site being included in different molecules that interact with each other or being included in the same molecule. A proton-conductive mixed phase that includes the second site to which the proton-releasing/binding site of the proton-conductive substance is bound and the proton-conductive substance is lower than the service temperature of the proton-conductive membrane. The amount of the proton-releasing/binding site is excessively large compared with the amount of the second site of the polymer.

A multi-catalytic material that includes a polyelectrolyte membrane and methods of preparing the same are provided herein.

A polymer electrolyte membrane according to the present invention has a cluster diameter of 2.96 to 4.00 nm and a converted puncture strength of 300 gf/50 m or more. The polymer electrolyte membrane according to the present invention has a low electric resistance and an excellent mechanical strength.

The fluoropolymer dispersion includes a copolymer having divalent units represented by formula [CF.sub.2CF.sub.2], divalent units represented by formula: [Formula should be inserted here], and one or more divalent units independently represented by formula: [Formula should be inserted here] dispersed in at least one of water or organic solvent. Methods of making the fluoropolymer dispersion and methods of using the fluoropolymer to make a at least one of a catalyst ink or polymer electrolyte membrane are also provided.

##STR00001##

A method for producing a fluorosulfonyl group-containing compound to obtain a compound represented by the following formula 5 from a compound represented by the following formula 1 as a starting material and a method for producing a fluorosulfonyl group-containing monomer in which the fluorosulfonyl group-containing compound is used:

##STR00001##

wherein R.sup.1 and R.sup.2 are a C.sub.1-3 alkylene group, and R.sup.F1 and R.sup.F2 are a C.sub.1-3 perfluoroalkylene group.

A fluorosulfonyl group-containing polymer having units represented by the following formula u1, a sulfonic acid group-containing polymer having fluorosulfonyl groups in the fluorosulfonyl group-containing polymer converted into sulfonic acid groups, its production method and its applications:

##STR00001##

wherein R.sup.F1 and R.sup.F2 are a C.sub.1-3 perfluoroalkylene group.

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.

Improved additives can be used to prepare polymer electrolyte for membrane electrode assemblies in polymer electrolyte fuel cells. Use of these improved additives can not only improve durability and performance, but can also provide a marked performance improvement during initial conditioning of the fuel cells. The additives are chemical complexes comprising certain metal and organic ligand components.