The present invention provides composite particles which are capable of forming an ion exchange membrane with fewer defects and an ion exchange membrane. The composite particles according to the present invention comprise pellets comprising a fluorinated polymer having groups convertible to ion exchange groups, and a powder held on the pellet surface which comprises a polymer, wherein the powder has an average particle diameter of at least 1 μm and at most 1,000 μm, and the ratio of the average particle diameter of the pellets to the average particle diameter of the powder is 2 to 4,500.

An ion exchange membrane includes a layer S including a fluorine-containing polymer having a sulfonic acid group, a layer C including a fluorine-containing polymer having a carboxylic acid group, and a plurality of strengthening materials arranged inside the layer S and functioning as at least one of reinforcement yarn and sacrifice yarn. A and B satisfy following formulas:
B≤240 μm  (1)
2.0≤B/A≤5.0  (2) wherein, when the ion exchange membrane is viewed from the top surface, A represents an average cross-sectional thickness of the membrane measured in pure water for a region, in which the strengthening materials do not exist, and B represents an average cross-sectional thickness of the membrane measured in pure water for a region, in which strands of the reinforcement yarn overlap with each other, and in a region, in which the reinforcement yarn overlaps with the sacrifice yarn.

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 a method for producing pellets from which an ion exchange membrane excellent in stability of the electrolysis voltage can be formed, pellets, and an ion exchange membrane.

The method for producing pellets of the present invention is a method for producing pellets, which comprises extruding a melt containing a fluorinated polymer having groups convertible to ion exchange groups from a die of a melt-extruder to obtain a strand containing the fluorinated polymer, and cutting the strand to obtain pellets containing the fluorinated polymer, wherein the temperature of the die when the melt containing the fluorinated polymer is extruded from the die is less than 200° C., and when the groups convertible to ion exchange groups of the fluorinated polymer are converted to ion exchange groups, the ion exchange capacity of the resulting fluorinated polymer is at least 1.1 milliequivalent/g dry resin.

An ion exchange membrane has multiple layers of ionic polymers which each contain substantially different chemical compositions. i.e. varying side chain lengths, varying backbone chemistries or varying ionic functionality. Utilizing completely different chemistries has utility in many applications such as fuel cells where for example, one layer can help reduce fuel crossover through the membrane. Or one layer can impart substantial hydrophobicity to the electrode formulation. Or one layer can selectively diffuse a reactant while excluding others. Also, one chemistry may allow for impartation of significant mechanical properties or chemical resistance to another more ionically conductive ionomer. The ion exchange membrane may include at least two layers with substantially different chemical properties.

A method for manufacturing a reinforced composite polymer electrolyte comprises: manufacturing a porous thin film, impregnating the porous thin film with an electrolyte, and irradiating the impregnated porous thin film with ultraviolet rays.

The manufactured reinforced composite polymer electrolyte may maintain the electrochemical performance thereof while stably maintaining a structure thereof against mechanical deformation such as folding, bending and rolling, and can be used for a flexible lithium secondary battery.

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.

An ion exchange membrane material is composed of a crosslinked polymer network including a first poly(styrene-b-ethylene-r-butylene-b-styrene) triblock copolymer (SEBS), and second SEBS, and a linker crosslinking the first SEBS and the second SEBS. At least one phenyl group from the first SEBS and the second SEBS is functionalized with an alkyl group, and the carbon at the benzylic position of these alkyl groups is saturated with at least two additional alkyl groups. The linker is a diamine bound to the alkyl functional groups. The ion exchange membrane material is made via a substantially simultaneous quaternization and crosslinking reaction between the diamine linker and SEBS functionalized with alkyl halide groups. Increasing concentration of crosslinker in produces membranes with reduced water uptake, leading to an expectation of enhanced stability under hydrated conditions and greater durability. Advantageously, this reduction in water uptake came with little change to ion exchange capacity.

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.

An electrolyte membrane is prepared from a liquid composition comprising at least one member selected from the group consisting of trivalent cerium, tetravalent cerium, bivalent manganese and trivalent manganese; and a polymer with a cation-exchange group. The liquid composition is preferably one containing water, a carbonate of cerium or manganese, and a polymer with a cation-exchange group, and a cast film thereof is used as an electrolyte membrane to prepare a membrane-electrode assembly. The present invention successfully provides a membrane-electrode assembly for polymer electrolyte fuel cells being capable of generating the electric power in high energy efficiency, having high power generation performance regardless of the dew point of the feed gas, and being capable of stably generating the electric power over a long period of time.