PROCESS FOR PRODUCING FLUORINATED CATION EXCHANGE MEMBRANE

摘要

PURPOSE:To obtain high-performance membrane which is stable under severe electrolysis conditions, by a method wherein a membrane is produced from a copolymer of a fluorinated olefin and a specified sulfur-contg. fluorinated vinyl ether, and chemically treated so as to give a specified distribution of sulfonic gp. and carboxyl gp. CONSTITUTION:There is provided a membrane having repeating units of formulae A (wherein L is F, Cl, CF3, -ORf, H; Rf is 1-5C perfluoroalkyl), B (wherein k is 0, 1; l is 3-5, M is H, methal, ammonium ion) and C (wherein m=l-1) in a ratio of A/(B+C) of 1.5-14 in which the density of carboxy gp. on one side is higher than that on another side, the density becomes lower and lower toward the interior layer, and the density of carboxyl gp. becomes zero at a position where the thickness of the membrane is about a half of the whole thickness of the membrane from the surface thereof. Such membrane is prepd. as follows: A membrane is prepd. from a copolymer of CF2=CF2 and a sulfur-contg. fluorinated ether of formula I. One side of the membrane is treated with Cl2, etc. to convert the side to -CF2SO2Cl, etc. which is then converted to -COOH by using an appropriate reducing agent. Appropriate reactants are used according the structure of cpd. to produce cation exchange membrane in which the density of -COOH on one side is higher than that on another side. In this way, there is obtd. an ion-exchange membrane which has good durability and exhibits good current efficienty and exhibits good current efficiency in electrolysis of a highly conc. aq. soln. of NaCl, etc.