Abstract: A cation exchange membrane having having durability, which is adapted for use in electrolysis or an alkali metal chloride, which comprises a quadrilateral base membrane and, disposed on at least one marginal area of one surface of the base membrane, a diffusion coating having a capability for an alkali metal hydroxide to diffuse therethrough at a diffusion velocity greater than that at which the alkali metal hydroxide diffuses through a fluorocarbon polymer layer constituting the base membrane when the base membrane is composed of one fluorocarbon polymer layer or through one outermost layer of the base membrane which layer has thereon the diffusion coating and has a water sorption smaller than that of the opposite outermost layer of the base membrane, when the base membrane is composed of a plurality of fluorocarbon polymer layers.

Abstract: A fluorinated polymer having pendant cation exchange groups selected from sulfonic acid, carboxylic acid or sulfonamide groups, or their salts, is modified with a sulfonium compound and/or a phosphonium compound for substitution of the counter-ions of the cation exchange groups with sulfonium ions and/or phosphonium ions. The polymers treated in this manner are improved in their melt-flow characteristic to make fusion bonding between these polymers possible. The process is particularly suitable for repairing damaged cation exchange membranes for use in chlor-alkali electrolytic cells to advantageously elongate the life of the membranes.

Abstract: In performing melt processing of a fluorinated polymer which contains such pendant functional groups as sulfonic acid, carboxylic acid, sulfonamide and salts thereof, an aqueous medium is allowed to be present in the polymer to improve its melt-flow characteristic. Excellent heat sealing can be effected without degradation of the polymer. This method is particularly suitable for repairing the damaged ion-exchange membranes of fluorinated polymers used in the electrolysis of sodium chloride to enable elongation of their life to a great economical advantage.

Abstract: Addition polymerizable polymeric compounds produced by esterification reaction or addition reaction of a copolymer having pendent carboxyl groups and about 0.03 to 1.0 equivalent, based upon the carboxyl groups of said copolymer, of an ethylenically unsaturated compound having one oxirane ring, said copolymer being obtained by copolymerizing (1) about 10 to 95 percent by weight of at least one member selected from the group consisting of styrene and the methyl-substituted styrene derivatives (2) about 5 to 70 percent by weight of at least one ethylenically unsaturated mono- or di-carboxylic acid, its anhydride or its monoalkyl of 1 to 4 carbon atoms ester, (3) up to about 30 percent weight of at least one member selected from the group consisting of acrylonitrile and methacrylonitrile, (4) up to about 85 percent by weight of at least one compound of the formula ##EQU1## wherein R.sup.1 represents a hydrogen atom or methyl group; and R.sup.