GB1604175A - Process for preparing fluorinated polymer containing carbonyl fluoride and/or carboxylic groups - Google Patents

Abstract

Fluorinated ion exchange polymers which have both pendant side chains containing carboxylic groups and pendant side chains which contain sulfonyl groups, when used in the form of membranes to separate the anode and cathode compartments of an electrolysis cell, permit operation at high current efficiency. They are made by oxidation of flourinated polymers which have pendant side chains containing sulfinic groups, or both sufinic and sulfonyl groups. The fluorinated polymers which have pendant side chains containing sulfinic groups, or both sufinic and sulfonyl groups, are in turn made from fluorinated polymers which have pendant side chains containing sulfonyl halide groups by reduction with, for example, hydrazine. Fluorinated ion exchange polymers which have pendant side chains containing -OCF2COOR groups and also pendant side chains which contain sulfonyl groups can also be made by copolymerization of a mixture of monomers, one of which is a vinyl monomer which contains the indicated carboxylic group; and also by treatment of a polymer which contains -OCF2CF2SO3H or salts thereof with a combination of fluorine and oxygen.

Description

PATENT SPECIFICAT 1 ON ( 11) 1604175

Ut ( 21) Application No 41258/80 ( 22) Filed 19 April 1978 t ( 62) Divided out of No 1604173 ( 19 ( 31) Convention Application No 789726 ( 32) Filed 20 April 1977 in ( 33) United States of America (US) ( 44) Complete Specification published 2 Dec 1981 ( ( 51) INT CL 3 CO 8 F 8/06 C 08 J 5/22 C 25 B 13/08//1/46 ( 52) Index at acceptance C 3 J 400 408 AJ AK C 3 L 140 150 180 JC C 3 W 209 212 222 C 3 Y B 262 B 284 B 360 B 362 F 102 G 320 H 400 C 7 B 145 551 552 553 CC ( 54) PROCESS FOR PREPARING FLUORINATED POLYMER CONTAINING CARBONYL FLUORIDE AND/OR CARBOXYLIC GROUPS ( 71) We, E I DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, located at Wilmington, State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly 5

described in and by the following statement:-

This invention concerns a process for the preparation of fluorinated ion exchange polymers, which may be used in the form of films and membranes in chloralkali electrolysis cells.

Fluorinated ion exchange membranes are known in the art The fluorinated 10 ion exchange polymer in such membranes can be derived from a fluorinated precursor polymer which contains pendant side chains in sulfonyl fluoride form.

The sulfonyl fluoride functional groups have been converted to ionic form in various ways, for example, to sulfonate salts by hydrolysis with an alkaline material, to the sulfonic acid by acidification of the salts, and to the sulfonamide by 15 treatment with ammonia Examples of such teachings in the art can be found in U.S 3,282,785, U S 3,784,399, and U S 3,849,243.

Although such polymers and membranes have many desirable properties which make them attractive for use in the harsh chemical environment of a chloralkali cell, such as good long-term chemical stability, their current 20 efficiencies are not as high as is desired, especially when the caustic is produced at high concentration As transport of hydroxyl ion in a chloralkali cell from the catholyte through the membrane to the anolyte increases, current efficiency drops.

Larger amounts of oxygen impurity in the chlorine are thereby produced, and there is a greater buildup of chlorate and hypochlorite contaminants in the brine, which 25 contaminants must be removed and discarded to maintain acceptable cell operation Current efficiencies of at least 90 % are highly desirable.

Accordingly, there is a need for polymers and membranes which will permit cell operation at high current efficiencies, and especially for those which will permit operation at high efficiencies over long periods of time 30 In Application No 15539/78 (Specification No 1,604,173) from which this

Application is divided, we describe and claim a process which comprises contacting a first fluorinated polymer which contains pendant side chains containing -CF-CF 2-SO 2 35 Rfn groups, wherein Rf is F, Cl or C, to C,, perfluoroalkyl, M is H, an alkali metal, an alkaline earth metal, ammonium, substituted ammonium including quaternary ammonium, or hydrazinium including substituted hydrazinium, and N is the valence of M, with an oxidizing agent, and separating therefrom a second fluorinated polymer which contains pendant side chains containing 40 -CF-COO-m Rf groups By "separating" is meant that the second fluorinated polymer is separated from an excess oxidising agent and by-products of consumed oxidising agent.

According to the present invention there is provided a process for making a fluorinated polymer which contain pendant side chains containing S -CF-COF I Rf and/or -CF-COOH groups wherein Rf is F, Cl or C, to Co perfluoroalkyl which comprises contacting a fluorinated polymer which contains pendant side chains containing lo -CF-CF 25 O 2 R 2 1 % Rf groups wherein R 2 is 0 % (jn) M is H, alkali metal or alkaline earth metal, and N is the valence of M, with a mixture of fluorine and oxygen, and, if desired, treating the resulting polymeric 15 product with water or a solution of an alkali metal base to provide a fluorinated ion-exchange polymer which contains pendant side chains containing -CF-COOX R 1 groups wherein X is H or alkali metal.

In another aspect the invention provides a process for making a polymer 20 having the repeating units i CFOT lCX 2 CX 2 l F CF 2o 1 Y CF Z Y m + a 1 Z' f 0 CF Rf -Rf COR Z 2 p;R 2 2 r wherein m is 0, 1 or 2, p is I to 10, q is 3 to 15, r is 1 to 10, S is 0, 1, 2 or 3, each X, which may be the same or different, is H, F, Cl, CF 3 or perfluoroalkoxy subject to the proviso that at least one X is F, Y is F or CF 3, Z is F or CF 3, Rf is F, Cl or C, to 25 Co perfluoroalkyl, R' is F or OH, R 2 is F, Cl or OM 14 M is H, alkali metal, alkaline earth metal, ammonium, substituted ammonium including quaternary ammonium, hydrazinium including substituted hydrazinium, and N is the valence of M, which process comprises the steps of contacting a 30 fluorinated polymer having the repeating units:

1.604 175 1,604,175 4-cx 2 Cx 2 -CF c F 2 LF s t v CF 2z F Rf CF 2 R 2 _r wherein R 2 is OM (t) where M is H, alkali or alkaline earth metal and N is the valence of M, with a mixture of fluorine and oxygen, followed if desired by subjecting the polymeric product therefrom to hydrolysis Preferably the X's taken together are four fluorines or three fluorines and a chlorine.

With reference to part of the definition of M, "ammonium, substituted ammonium including quaternary ammonium, or hydrazinium including substituted t O hydrazinium" includes groups defined more specifically as R 5 R 4-N-R 6, R 7 wherein R 4 is H, lower alkyl such as C, to C 6, or NH 2; and R 5, R 8 and R 7 are each independently H or lower alkyl such as C 1 to C 6, with the understanding that any two of R 4, R 5, R 8 and R 7 may join to form a hetero ring, such as a piperidine or morpholine ring.

The starting material polymers which contain pendant side chains containing -CF-CF 2 SO 2-Rz 1 I Rf groups, wherein Rf and R 2 are as defined hereinabove, are in turn made from nown precursor fluorinated polymers which contain pendant side chains containing -CF-CF 2-SO 2 A I Rf groups wherein Rf is as defined above, and A is F or Cl, preferably F Ordinarily, the functional group in the side chains of the precursor polymer will be present in terminal -O-CF-CF 25 O 2 A groups The -SO 2 A groups of the precursor fluorinated polymers can be converted by hydrolysis to the sulfonic acid or sulfonate groups -SO 2 R 2 The precursor fluorinated polymers employed can be of the type disclosed in U S P.

3,282,875, U S P 3,560,568 and U S P 3,718,627 More specifically, the precursor polymers can be prepared from monomers which are fluorinated or fluorine substituted vinyl compounds The precursor polymers are in general made from at least two monomers, with at least one of the monomers coming from each of the two groups described below 5 The first group is of fluorinated vinyl monomers of the formula CX 2 =CX 2, wherein each X, which may be the same or different, is H, Cl, F, CF 3 or perfluoroalkoxy subject to the proviso that at least one X is F, such as vinyl fluoride, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro(alkyl vinyl ether), tetrafluoroethylene and 10 mixtures thereof In the case of copolymers which will be used in electrolysis of brine, the precursor vinyl monomer desirably will not contain hydrogen, and preferably the X's taken together are four fluorines or three fluorines and one chlorine.

The second group is of the sulfonyl-containing monomers containing the 15 precursor group -CF-CF 2 SO 2 A, I R, wherein Rf and A are as defined above Additional examples can be represented by the general formula CF 1 =CF-Tk,-CF 2 SO 2 F wherein T is a bifunctional perfluorinated radical comprising I to 8 carbon atoms, and k is 0 or 1 The 20 particular chemical content or structure of the radical T is not critical, but it must ave a fluorine atom attached to the carbon atom to which the -CF 2 SO 2 F group is attached Other atoms connected to this carbon can include fluorine, chlorine, or hydrogen although generally hydrogen will be excluded in use of the copolymer for ion exchange in a chlor-alkali cell The T radical of the formula above can be either 25 branched or unbranched, i e, straight-chain, and can have one or more ether linkages It is preferred that the vinyl radical in this group of sulfonyl fluoride containing comonomers be joined to the T group through an ether linkage, i e, that the comonomer be of the formula CF 2 =CF-O T CF 2-SO 2 F Illustrative of such sulfonyl fluoride containing comonomers are 30 CF 2 =CFOCCF 2 CFSO 2 F, CF 2 =-CFCFCF 2 CFOCF 2 CF 25 02 F, I CF 3 CF 2 =CFOCF 2 CFOCF 2 CFOCF 2 CF 25 O 2 F, I I CF 3 CF 3 CF 2 =CFCF 2 CF 2 SO 2 F, and CF 2 =CFOCF 2 CFOCF 2 CF 25 O 2 F I CF 2 35 CF 3 The most preferred sulfonyl fluoride containing comonomer is perfluoro( 3, 6 dioxa 4 methyl 7 octenesulfonyl fluoride), CF 2 =CFOCCF 2 CFOCF 2 CFSO 2 F CF 3 The sulfonyl-containing monomers are disclosed in such references as U S P.

3,282,875, U S P 3,041,317, U S P 3,718,627 and U S P 3,560,568 40 The preferred copolymers utilized as the precursor are perfluorocarbon although others can be utilized as long as the T group has a fluorine atom attached 1,604,175 1,604,175 5 to the carbon atom which is attached to the -CF 2 SO 2 F group The most preferred copolymer is a copolymer of tetrafluoroethylene and perfluoro( 3,6 dioxa 4 methyl 7 octanesulfonyl fluoride) which comprises 20 to 65 percent, preferably, to 50 percent by weight of the latter.

The precursor copolymer used in the present invention is prepared by general 5 polymerization techniques developed for homo and copolymerizations of fluorinated ethylenes, particularly those employed for tetrafluoroethylene which are described in the literature Non-aqueous techniques for preparing the copolymers of the present invention include that of U S P 3,041,317, that is, by the polymerization of a mixture of the major monomer therein, such as 10 tetrafluoroethylene, and a fluorinated ethylene containing a sulfonyl fluoride group in the presence of a free radical initiator, preferably a perfluorocarbon peroxide or azo compound, at a temperature in the range 0-200 C and at pressures in the range 1-200, or more atmospheres The non-aqueous polymerization may, if desired, be carried out in the presence of a fluorinated solvent Suitable fluorinated 15 solvents are inert, liquid, perfluorinated hydrocarbons, such as perfluoromethylcyclohexane, perfluorodimethylcyclobutane, perfluorooctane, perfluorobenzene and the like, and inert, liquid chlorofluorocarbons such as 1,1,2 trichloro 1,2,2 trifluoroethane, and the like.

Aqueous techniques for preparing the precursor copolymer include contacting 20 the monomers with an aqueous medium containing a free-radical initiator to obtain a slurry of polymer particles in non-water-wet or granular form, as disclosed in U S.

Patent 2,393,967, or contacting the monomers with an aqueous medium containing both a free-radical initiator and a telogenically inactive dispersing agent, to obtain an aqueous colloidal dispersion of polymer particles, and coagulating the 25 dispersion, as disclosed, for example, in U S P 2,559,752 and U S P 2,593, 583.

The treatment of the fluorinated polymer which has pendant side chains which contain -CFCF 25 O 2 R 2 Rf with the mixture of fluorine and oxygen results in the formation of 30 -CFCOF I R.

groups The -CFCOF I 1 % groups can then be hydrolyzed to ion exchange groups -CFCOOR 1 35 I R.

wherein RI is Mn) Hydrolysis of -CF-COF I Rf groups to 40 -CF-COOH I groups occur so readily that the product isolated from the fluorine/oxygen reaction will ordinarily be at least partially hydrolyzed to the free carboxylic acid.

Conversion of -CFCF 25 O 2 R 2 I groups to -CFCOF and 5 -CFCOOR 1 I Rf groups can vary from low percentages such as 10 %/ to percentages of more than /%, at least in regard to the surface layer of the article so treated, depending on the amount of treating reagents used, duration of treatment, etc.

The molar ratio of fluorine to oxygen can vary widely, e g from 1:5 to 1:1000, 10 preferably 1:50 to 1:200 Diluent gases such as nitrogen, helium or argon can be used Total gas pressure in the system can also vary widely, e g from 0 1 to 1000 atmospheres Ordinarily the pressure will be about 75 atmospheres Temperatures from -100 C to 250 C can be used, preferably from 20 to 70 C Treatment can conveniently be carried out in a corrosion resistant metal pressure vessel 15 A specific example of the type of polymer which can be treated with a fluorine/oxygen mixture is one having the repeating units -cx 2 CX q CF CF 220 q I CH 2 CF Z S F Rf CF 2 502 R 2 r+p wherein Rf, p, q, r, s, X, and Z are as defined hereinabove, and R 2 is (M 1 20 where M and N are as defined hereinabove Following treatment with fluorine/oxygen and hydrolysis, the resulting ion exchange polymer will have r of the sulphonyl-containing groups remaining, and p of them converted to -OCF 2 COF and/or -OCF 2 COOH groups It should be understood that while treatment with the mixture of fluorine and oxygen will effectively destroy and 25 remove all of the sulfonate groups on at least the surface of the initial polymer, not all of the pendant side chains from which the sulfonate groups are removed will be converted to pendant side chains which contain carboxylic groups; it is believed that some are converted to pendant side chains which terminate in a-CF 3 group.

It will be further understood, however, that by proper choice of the initial polymer, 30 copolymers containing both carboxylic and sulfonyl groups meeting the composition defined hereinabove can be prepared.

The initial polymer which contains r+p sulfonyl-containing side chains can in turn be made by copolymerizing fluorinated vinyl monomers of the first and second groups of monomers described above Such fluorinated polymers are described in 35 U.S P 3,282,875, U S P 3,560,568, and U S P 3,718,627.

Although the sulfonyl-containing fluorinated polymer to be treated with a mixture of fluorine and oxygen can be in the form of powder or granules when ubjected to such treatment, more often it will be in the form of a film or membrane 'n it is so treated 40 n l:in i 1,604,175 A convenient method for controlling the extent of the reaction brought about by treatment with fluorine and oxygen is to begin with a film or membrane of a polymer which has pendant side chains which contain -O-CFCF 25 O 2 F groups, and to bring about a partial hydrolysis to 5 -O-CFCF 25 03 H D (or metal salts thereof) such that the film or membrane is hydrolyzed on either one or both surfaces thereof to a controlled depth Upon subsequent treatment with the mixture of fluorine and oxygen, the layer in sulfonyl fluoride form remains unaffected, and the layer in sulfonic acid form reacts such that 10 -O-CFCOF I are produced as described above Upon subjecting the film or membrane to a full hydrolytic treatment, the interior layer will have only -0 CFCF 25 O 3 H Rf IS groups (or salts thereof), and the surface layer or layers will have both 15 -O-CFCOOH and groups (or salts thereof).

The polymers produced by the process of the present invention can be in the 20 form of films and membranes.

When the polymers are in the form of a film desirable thicknesses of the order of 0 002 to 0 02 inch are ordinarily used Excessive film thicknesses will aid in obtaining higher strength, but with the resulting deficiency of increased electrical resistance 25 The term "membrane" refers to non-porous structures for separating compartments of an electrolysis cell and which may have layers of different materials, formed, for example, by surface modification of films or by lamination, and to structures having as one layer a support, such as a fabric imbedded therein.

It is possible according to the present invention to make films and membranes 30 wherein the pendant side chains are essentially wholly (i e, 90 % or more) or wholly (i.e, up to about 99 %) in the carboxylic form throughout the structure, and also wherein the pendant side chains throughout the structure are in carboxylic and sulfonyl form, for example 10 to 90 %/ of each.

Control of the relative amounts of carboxylic and sulfonyl functional groups 35 can be exercized to some extent during the reaction with fluorine and oxygen.

So that the final film or membrane will have as low an electrical resistivity as possible, it is desirable that essentially all of the sulfonyl halide groups in the precursor polymer be converted to active cation exchange groups, i e to either carboxylic or sulfonyl groups of a type which will ionize or form metal salts In this 40 respect, it is highly undesirable that a film or membrane to be used for ion exchange purposes in an electrolytic cell to have a neutral layer, or that a film or membrane to be used in a chloralkali cell have either a neutral layer or an anion 1.604 175 exchange layer The film and membrane of the present invention do not have neutral or anion exchange layers In this context, fiber or fabric reinforcing is not considered as a neutral layer, inasmuch as such reinforcing has openings, i e, its effective area is not coextensive with the area of the film or membrane.

In the case of films and membranes to be used as separators in a chloralkali 5 cell, polymers which contain 40-95 % pendant side chains containing carboxylic groups and 5-0/% pendant side chains containing sulfonyl groups provide excellent current efficiency An equally important criterion in a chloralkali cell, however, is the amount of power required for each unit of chlorine and caustic It is considered that the polymers of the type disclosed herein permit a proper 10 combination of operating conditions to realize an excellent and unexpected reduction in power Since the power requirement (which may be expressed in watthours) is a function of both cell voltage and current efficiency, low cell voltages are desirable and necessary However, a polymer without a high current efficiency cannot operate effectively from a commercial standpoint even with extremely low 15 cell voltages Additionally, a polymer with an inherent high current efficiency allows a proper combination of parameters as in fabrication into the film and/or operation of the electrolytic cell to realize the potential theoretical reduction in power Illustratively, the polymer can be fabricated at a lower equivalent weight which may result in some loss of current efficiency which is more than 20 compensated by a reduction in voltage Polymers produced by the process of the present invention which have 50-95 %/ pendant side chains containing carboxylic groups and 5-50 % pendant side chains containing sulfonyl groups have low power consumption.

It is also possible according to the present invention to make films and 25 membranes which are structured to have one surface wherein the polymer has pendant side chains which are in carboxylic form, and pendant side chains which are in sulfonyl form, and the other surface wherein the pendant side chains of the polymer are wholly in the sulfonyl form It is further possible to make films and membranes structured to have both surfaces wherein the polymer has pendant side 30 chains in carboxylic form and pendant side chains in sulfonyl form, and an interior layer wherein the pendant side chains of the polymer are wholly in the sulfonyl form.

When only one surface of the precursor structure is modified to contain carboxylic groups, the depth of the modified layer will normally be from 0 01 % to 35 % of the thickness When both surfaces are modified, the depth of each modified layer will be less than half the thickness of the structure, and will normally be from 0.01 to 40 % of the thickness The thickness of a layer modified to contain carboxylic groups will ordinarily be at least 200 angstroms in thickness A convenient way to treat only one surface of a film or membrane is to fabricate a 40 bag-like configuration which is sealed shut, and to treat only the outside or inside of the bag When only one surface is modified to contain carboxylic groups, that surface can face either the anode or cathode in an electrolysis cell, and in the case of a chloralkali cell it will ordinarily face the cathode.

Under most circumstances, layered structures will be such that the layer of 45 carboxylic polymer will be about 1/4 to 5 mils thick, the base layer of sulfonyl polymer will be about 1 to 15 mils thick, and the total thickness of the structure will be about 2 to 20 mils thick The indicated thicknesses are effective film thicknesses, i.e, thicknesses which exclude reinforcing fibers and other members which do not contain ion exchange groups 50 Polymers according to the present invention which contain both carboxylic and sulfonyl groups have utility to function for ion exchange Accordingly, general utility of the polymer for ion exchange is directly contemplated Illustratively, permeation selection of cations is directly encompassed One method of determination of cation exchange properties is a measurement of permselectivity 55 with separation of the same cations in solutions but at different concentrations.

This involves cation transport, and a permselectivity measurement of no voltage would indicate the polymer does not function for ion exchange.

A specific use for the polymers of the present invention which contain both carboxylic and sulfonyl groups is in a chloroalkali cell, such as disclosed in German 60 Patent Application 2,251,660, published April 26, 1973, and Netherlands Patent Application 72 17598, published June 29, 1973 In a similar fashion as these teachings, a conventional chloralkali cell is employed with the critical distinction of the type of polymeric film used to separate the anode and cathode portions of the cell While the description of said German and Dutch publications is directed to 65

1,604,175 R use in a chloralkali cell, it is within the scope of the present disclosure to produce alkali or alkaline earth metal hydroxides and halogen such as chlorine from a solution of the alkali in alkaline earth metal salt While efficiencies in current and power consumption differ, the operating conditions of the cell are similar to those disclosed for sodium chloride 5 An outstanding advantage has been found in terms of current efficiency in a chloralkali cell with the fluorinated polymers of the type disclosed herein with pendant groups which contain carboxylic groups and pendant groups which contain sulfonyl groups.

To further illustrate the innovative aspects of the present invention, the 10 following Examples are provided.

EXAMPLE 1

A piece of 7-mil film of a copolymer of tetrafluoroethylene and perfluoro( 3,6 dioxa 4 methyl 7 octenesulfonyl fluoride) having an equivalent weight of 1200, and containing one surface layer of approximately 1-mil depth which had 15 been converted to the corresponding sodium salt of the sulfonic acid, was heated with 15 psi (absolute) of 25 % fluorine in nitrogen and 400 psi (absolute) of compressed air at 500 C for 2 hours The excess gases were removed, air added, and the film removed The infrared spectrum of the whole film thickness showed the presence of sulfonyl fluoride groups and absorption at 5 6 microns due to 20 carboxylic acid The infrared spectrum of the starting film was almost identical, but lacked the 5 6 micron absorption.

EXAMPLE 2

A piece of 7-mil film of a copolymer of tetrafluoroethylene and perfluoro( 3,6 dioxa 4 methyl 7 octenesulfonyl fluoride) having an equivalent weight of 25 1100, and containing one surface layer of approximately I mil depth which had been converted to the corresponding sodium salt of the sulfonic acid, was heated with 15 psi (gauge) of 25 % fluorine in nitrogen and 1000 psi (gauge) of oxygen at 300 C for 4 hours The film was removed and treated at 900 C with a mixture of dimethylsulfoxide, water and potassium hydroxide for 1 hour After washing, the 30 film was mounted in a chloralkali cell, and aqueous sodium chloride electrolyzed at a current density of 2 0 asi to give 33 0-38 6 % Na OH at current efficiencies of 75.8-81 7 % at a cell voltage of 39-4 2 volts.

Claims (7)

WHAT WE CLAIM IS:-

1 A process for making a fluorinated polymer which contains pendant side 35 chains containing -CF-COF and/or -CF-COOH Rf groups wherein R, is F, Cl or C 1 to C,0 perfluoroalkyl which comprises contacting a 40 fluorinated polymer which contains pendant side chains containing -CF-CF 25 O 2 R 2 Rf groups wherein R 2 is M is H, alkali metal or alkaline earth metal, and N is the valence of M, with a 45 mixture of fluorine and oxygen, and, if desired, treating the resulting polymeric product with water or a solution of an alkali metal base to provide a fluorinated ion-exchange polymer which contains pendant side chains containing 1,604, 175 1,604,175 10 -CF-COOX l groups wherein X is H or alkali metal.

2 A process according to Claim 1 for making a polymer having the repeating units Cx -C Fi-C:F CF 2 CX 2 C 21 q,g C 7 -Y 2 F 2 CF Z f 05 CF Rf F R f J p OR 2 2 r wherein m is 0, 1 or 2, p is I to 10, q is

3 to 15, r is I to 10, S is 0, 1, 2 or 3, each X, which may be the same or different, is H, F Cl, CF 3, or perfluoroalkoxy subject to the proviso that at least one X is F, Y is F or CF 3, Z is F or CF 3, Rf is F Cl or C 1 to C,o perfluoroalkyl, R' is F or OH, R 2 is F, Cl or n 10 M is H, alkali metal, alkaline earth metal, ammonium, substituted ammonium including quaternary ammonium, hydrazinium including substituted hydrazinium, and N is the valence of M, which process comprises the steps of contacting a fluorinated polymer having the repeating units:

C 2 4 CF CF 2F 2 F r+p ',s 15 F -Rf W 2 R 2 _r+ p wherein R 2 is OM) (t) where M is H, alkali or alkaline earth metal and N is the valence of M, with a mixture of fluorine and oxygen, followed if desired by subjecting the polymeric product tllefrom to hydrolysis 20 3 A process according to Claim 2, wherein the X's taken together are four fluorines or three fluorines and a chlorine.

4 A process according to Claim 1 substantially as described in Example I or 2.

11 1,604,175 11 A fluorinated polymer when produced by a process as claimed in any one of the preceding claims.

6 A film or membrane of a fluorinated ion exchange polymer as claimed in Claim 5.

7 An electrolytic cell comprising a housing with separate anode and cathode 5 sections, said cell being separated by a film or membrane as claimed in Claim 6.

J A KEMP & CO, Chartered Patent Agents, 14, South Square, Gray's Inn, London, WC 1 R 5 EU.

Printed for Her Majesty's Stationery Office, by the Courier Press, Leamington Spa, 1981 Published by The Patent Office, 25 Southampton Buildings, London WC 2 A l AY, from which copies may be obtained.