Process for preparing an ion exchange membrane

A process for preparing an ion exchange membrane comprising the steps of:

• (1) providing a membrane of at least one fluorinated resin having pendant ion exchange precursor groups,
• said fluorinated resin being at least one copolymer obtained by reacting at least one fluorovinyl compound represented by the formula:
• CF.sub.2 .dbd.CF--O--(CF.sub.2 CFL).sub.m --O--(CF.sub.2).sub.n --W
• wherein L represents a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms, m is an integer of 0 to 3, n is an integer of 1 to 3, and W represents a functional group selected from the group consisting of:
• --SO.sub.2 X and --CY
• wherein X represents a halogen atom or --OR in which R represents an alkyl group having 1 to 4 carbon atoms, and Y represents a nitrogen atom or --OX in which X is as defined above, with at least one fluorinated olefin represented by the formula:
• CF.sub.2 .dbd.CFZ
• wherein Z represents a hydrogen atom, a chlorine atom, a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms, said w forming said pendant ion exchange precursor groups, and
• (2) contacting without preswelling said membrane with an aqueous solution consisting essentially of at least one basic organic compound for a period of from about 0.5 to about 100 hours to hydrolyze said precursor groups of the formula --SO.sub.2 X and/or said precursor groups of the formula --CY to sulfonate groups and/or carboxylate groups, respectively,
• said basic organic compound being at least one basic nitrogen compound selected from the group consisting of triethanolamine, diethanolamine, triethylamine, diethylamine, morpholine, isopropylmethylamine, ethylmethyl-n-propylamine, ethyleneimine, dimethy,laminoethanol, n-octylamine, benzylmethylamine, N,N'-dimethylbenzylamine, dodecylamine, tertiary octylamine, tri-n-octylamin diethylenetriamine, isopropanolamine, diisopropanolamine, triisopropanolamine, pyrrolidine, piperidine and piperazine.