CA1139780A - Fluorinated ion exchange polymer containing carboxylic groups, and process for making same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
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 compart-ments of an electrolysis cell, permit operation at high current efficiency. They are made by oxidation of fluorinated polymers which have pendant side chains containing sulfinic groups, or both sulfinic and sulfonyl groups. The fluorinated polymers which have pendant side chains containing sulfinic groups, or both sulfinic and sulfonyl groups, are in turn made from fluorinated polymers which have pendant side chains con-taining sulfonyl halide groups by reduction with, for example, hydrazine. Fluorinated ion exchange polymers which have pen-dant 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

BACKGROUND O _ E INVENTION
This invention concerns improvements in and relating to fluorinated ion exchange polymers, and particu-larly to such polymers used in the form of films and membranes used in chloralkali electrolysis cells.
Fluorinated ion exchange membranes are known in the art. The fluorinated 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 treatment with ammonia. Examples of such teachings in the art can be found in U.S. 3,282,875, 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 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 contami-nants 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.
Additionally, it was desired to find a method for modifying the known polymers and membranes which have pendant side chains in sulfonyl fluoride form in such a way to obtain polymers and membranes which will have the high current efficiencies desired.
SUMMARY OF THE INVENTION
It has now been found that fluorinated ion exchange polymers and membranes which contain pendant side chains in ionic carboxylic form and pendant side chains in ionic sulfonyl form have hi.gh current efficiencies.
According to the present invention, there is pro-vided a process which comprises contacting a first fluorinated polymer which contains pendant side chains containing -CF-CF2-SO2-Ml groups, wherein Rf is F, Cl or a Cl to C10 Rf n perfluoroalkyl radical, M is H, and alkali metal, an alkaline earth metal, ammonium, substituted ammonium including qua-ternary ammonium, or hydrazinium including substituted hydrazinium, and n is the valence of M, with an oxidizing agent, and separating therefrom a second fluorinated poly-mer which contains pendant side chains containing -CF-COO-~l groups.
Rf (n) There is also provided according to the present invention a fluorinated polymer which contains pendant side chains containing -CF-CF~-SO2-~
Rf n ,~

: - 3 -, ", .~, :

groups, wherein Rf is F, Cl or a C1 -to C10 perfluoroalkyl radical, M is H, an alkali metal or an alkaline earth metal, ammonium, substituted ammonium including quaternary ammonium, or hydrazinium including substituted hydrazinium, and n is the valence of M. More specifically, the polymer which contains pandant side chains which contain sulfinic groups is t~-CF2~ cx2 cx2 ~ C~2 10 ,CF2 ,CF2 CF-Y CF-z m ~ s CF-Rf ,CF-RE

P t wherein m is 0, 1 or 2, p is 1 to 10, q is 3 to 15, s is 0, 1 or 2, t is 0 to 10, the X's taken together are four fluorines or three fluorines and one chlorine, Y is F or CF3, Z is F or CF3, Rf is F, Cl or a Cl to C10 perfluoroalkyl radical, R is F, Cl or O~l) M is H, alkali metal, alkaline earth metal, ammonium, substituted ammonium including quaternary ammonium, s~D

hydraæinium including substituted hydrazinium, and n is the valence of M. When reduction of sulfonic to sulfinic groups is essentially complete, t in this polymer will be O. More often, both p and t will be at least 1.
There is also provided a Fluorinated polymer which contains pendant side chains, about 10 to about 95% of which side chains contain -0-CF - COO-M(l)groups and about Rf n 5 to about 90% of which side chains contain -CF-CF2-SO3-M~

groups, wherein Rf is F, Cl or a Cl to C10 perfluoroalky:L
radical, M is H, an alkali metal, an alkaline earth meta:L, ammonium, substituted ammonium including quaternary ammonium, or hydrazinium including substituted hydrazinium, and n ïs the valence of M.
More specifically, such a polymer has the repeating units ~ ClF2- CF2 CF2 CF - Y CF - z m O
CF - Rf CF - Rf COOMl~ ~ I 50 M~

wherein m is 0, 1 or 2, p is 1 to 10, q is 3 to 15, r is 1 to 10, s is 0, 1, 2, or 3, the X's taken together are four fluorines or three fluorines and one chlorine, Y is F or CF3, z is F or CF3, Rf is F, Cl or a Cl to C10 perfluoroalkyl radical, M is H, alkali metal, alkaline earkh metal, ammoniumr substituted ammonium including quaternary ammonium, hydrazinium including substituted hydrazinium, and n is the valence of M.
~ ith reference to part o the defini.tion of M, '`ammonium, substituted ammonium including quaternary ammonium, or hydrazinium includin~ suhstituted hydrazinium'`
includes groups defined more speci:Eically as R

R4- N - R6, wherein R is H, lower alkyl such as Cl to C6, or NH2; and R , R
and R are each independently H or lower alkyl such as C
to C6, with the understanding that any two of R4, R5, R6 and R may join to form a hetero ring, such as a piperidine or morpholine ring.
Further within the purview of the present invention is the process for converting chemical compounds containing a -CF-CF2-SO2-M1 group to chemical compounds containing a Rf n -CF-COO-Mlgroup, wherein Rf, M and n are as Rf n defined above, by reaction with an oxidizing agent. There is also provided according to the invention certain novel chemical compounds made with this process, including novel vinyl monomers which contain carboxylic functional groups and which are useful in making the above polymers; also, films and membranes of the polymers; and laminar structures containing the polymers.
There is further provided according to the inven-tion a process for making a fluorinated polymer which has pendant side chains which contain -OCF-COF groups by contact-Rf ing a fluorinated polymer which has pendant side chains which contain -OCFCF2S03H groups or salts thereof with a Rf mixture of fluorine and oxygen. Hydrolysis of the polymer thus obtained produces a fluorinated ion exchange polymer which contains -OCF-COOH groups or salts thereof, or both Rf -OCF-COOH and -OCF-CF2SO3H groups or salts thereof.
Rf Rf The ion exchange membranes of the present inven-tion which contain both ionizable carboxylic and ionizable sulfonyl groups as active ion exchange sites are highly desirable in comparison with prior art ion exchange mem-branes for several distinct reasons. Most importantly, outstanding efficienci.es in a chlor-alkali cell have been obtained in comparison with membranes which contain only sulfonic acid ion exchange groups obtained by hydrolysis of pendant sulfonyl groups. For example, treatment of a mem-brane having pendant sulfonyl groups to modify a surfacelayer to incorporate carboxylic groups according to the present invention results in a dramatic increase in current ~L3g'~

efficieney in a chlor-alkali cell. This improvement is considered to be of predominant importance in commercial applicability in redueing the cost of producing a unit of chlorine and caustic. Illustratively, in a chlor-al~ali plant producing, for example, 1000 tons per day of chlorine, the direct savings in electrical power for only a 1~ increase in eEficiency are very significant.
DESCRIPTION OF THE ~REFERRED EM~ODIMENTS
A need has developed in the chlor-alkali industry for improved ion exehange materials whieh ean be used to replaee existing eell compartment separators whieh have been used for deeades without substantial improvement in design.
For use in the environment of a ehlor-alkali cell, the membrane must be fabrieated rom a material which is eapable of withstanding exposure to a hostile environ-ment, such as chlorine and solutions which are highly alkaline. Generally, hydrocarbon ion exchange membranes are totally unsatisfaetory for this kind of use because such membranes cannot withstand this environment.
For commercial use in the chlor-alkali industry, a film must go beyond the ability to be operable for pro-longed time periods in the production of chlorine and caustic. ~ most important criterion is the current effi-ciency for conversion of brine in the electrolytic cell to the desired produets. Improvement in current efficieney can translate into pronouneed savings in the eost of produetion of eaeh unit of ehlorine and euastie. Additionally, from a eommereial standpoint the cost o production of each unit of products will be determinative of the eommereial suit-ability of an ion exehange membrane.

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The ion exchange Polymers of the present inven-tion possess pendant side chains which contain carboxylic groups and pendant side chains which contain sulfonyl groups attached to carbon atoms having at least one fluorine atom ronnected thereto. The ion exchange polymers of the lnven-tion can be made from polymers which contain pendant side chains containing -CF-C~2-SO2--Ml groups wherein Rf is F, Rf (n Cl or a Cl to C10 perfluoroalkyl radical, M is as defined above, and n is the valence of M, by sub~ecting them to an oxidation. A variety of oxidizing agents are found effec-tive for oxidizing pendant side chains containing -CF-CF2SO2-~)groups to side chains containing -CF-COO-M
R~ n Rf ~n groups.
Among suitable oxidizing agents are oxygen, chromic acid, permanganate salts, vanadate salts in acid solution, nitrous acid, and hypochlorite salts. The term "oxygen" is intended to encompass mixtures of ~ases which contain oxygen, such as air. The preferred oxidizing agents are oxygen, chromic acid, permanganate salts and vanadate salts because they are more effective.
Oxygen can be used to oxidize the pendant groups defined above when M is ~1, that is, when the functional group is the free sulfinic acid. T~ith this oxidizing agent, it is preferred to carry out the oxidation in the presence of a metal catalyst. It is also preferred to employ an elevated temperature. At or near room temperature without a catalyst, although oxygen has little or no observable effect even over a period of a few days, significant con-version to carboxyl groups is observed after three to four g ~3~

weeks. At higher temperatures the oxidation is faster;
for example, at 50-60C., without a catalyst, there is a significant amount of oxidation to carboxyl groups by air after only a few days. When oxygen is the oxidant, the polymer, film or membrane to be so treated can simply be exposed to the gas, or it can be contacted with oxygen in a li~uid medium such as water. The use of a catalyst is preferred as it speeds the reaction. Metals which can exist in more than one valence state can be used as catalyst.
(For pxesent purposes, zero is not counted as a valence state.) For example, salts of iron, vanadium, uranium, cobalt, nickel, copper and manganese have been found efec-tive.
Other effective oxidizing agents or the pendant groups, when the functional group is either in the ~ree sulinic acid form or in the form of an alkali metal or alkaline earth metal salt thereof, include permanganate in either acidic or basic media, chromic acid, vanadate salts in acidic media, nitrous acid, and hypochlorite salts in basic media. It should be understood that the polymer can be in either free acid form, or salt thereof, when intro-duced to such oxidizing agents, and that the acid or salt orms may interconvert depending on the pH of the oxidizing medium used. The oxidations are ordinarily carried out at temperatures above room temperature. These oxidations can be carried out in media such as water, or in the presence o inorganic or organic acids such as sulfuric acid, hydrochloric acid, acetic acid, etc.

It has also been observed that pendant -CF-CF2-SO2H
Rf ~L~13~7~D
groups can be converted to -CF-COOH grouPs by placinq them Rf in boiling water or a boiling organic or inorganic acid such as formic acid :Eor a period of at least several hours.
It is believed that air oxidation may be occurring under such conditions. Some oxidizing agents, such as hydrogen peroxide and nitric acid are ineffective for present purposes.
It is a simple matter to distinguish oxidiz:ing agents effec-tive for present purposes from those that are ineffective, merely by determining the presence or absence of character-istic absorption bands in the infrared spectrum of the product corresponding to carboxylic acid groups at about 1785 cm-l or to salts thereof at about 1680 cm-l.
It has also been folmd that a fluorinated compound containing a -CF-CF2-SO2-Ml)group, wherein Rf, M and n are Rf n as defined above can be oxidized to a -CF-COO-Ml~group Rf ~nJ
using oxidizing agents and reaction conditions as described above. The process is generally applicable for compounds V-CF-CF2-SO2-Ml, where V is a straight-chain or branched C
Rf n to C20 perhalogenated radical, optionally containing one or more ether linkages, and the halogen atoms are fluorine and/or chlorine. To cite but a few examples, V can be C F2 ~1' where x is 1 to 20;
CF2 Cl-CFCl-CyF2y , where y is 1 to 18;

and CF2Cl-CFClO~CF2-CF-Otz, where z is 1 to 3, Rf and Rf is as defined above.

,.

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The resulting carboxylic compounds are in some cases known compounds useful, for example, for conversion to vinyl esters from which polymers can be made and fabricated into films, etc. The sulfinic acid having a terminal CF2Cl-CFCl-group can be derived, for example, starting from a known sulfonyl compound which has a terminal vinyl group, by first adding chlorine to saturate the terminal vinyl group, then reducing the sulfonyl to the sulfinic group with bisulfite Or a hydrazine. The intermediate sulfinic acid compound is then oxidized to the carboxylic compound which still has the terminal CF2Cl-CFC1- group, and this in turn can then be decnlorinated, as with zinc, to make an olefinic car-boxylic acid which is useful for making polymers and copoly-mers. The polymers and copolymers can be used, for example, in making f;lms and in ion exchange aPplications.
The ion exchange polymers of the present invention possess pendant side chains which contain carboxylic groups attached to carbon atoms having at least one fluorine atom connected thereto, and pendant side chains which contain sulfonyl groups attached to carbon atoms having at least one fluorine atom connected thereto, as set forth above.
The ion exchange polymers of the present invention which possess pendant side chains which contain carboxylic groups and pendant side chains which contain sulfonyl groups possess general utility as ion exchange resins. When used in a film or membrane to separate the anode and cathode compartments of an electrolysis cell, such as a chloralkali cell, the polymer should have a total ion exchange capac-ity of 0.5 to 1.6 me~/g (milliequivalents/gram), preferably from 0.8 to 1.2 meq/g. Below an ion exchange capacity of ~L3~

0.5 meq/g, the electrical resistivity becomes too high, and above 1.6 meq/g the mechanical properties are poor because of excessive swelling of the polymer. The values of P, q and r in the above formulas of the copolymer should be adjusted or chosen such that the polymer has an equiva-lent weight no greater than about 2000, preferably no greater than about 1500, for use as an ion exchange barrier in an electrolytic cell. The equivalent weight above which the resistance of a film or membrane becomes too high for pratical use in an electrolytic cell varies somewhat with the thickness of the film or membrane. For thinner ilms and membranes, e~uivalent weights up to about 2000 can be tolerated. For most purposes, however, and for films of ordinary thickness, a value no greater than about 1500 is preferred.
The polymers which contain pendant side chains containing -CF-CF2-SO2-Ml)groups, wherein RE, M and n are Rf n as defined hereinabove, are in turn made from known precur-sor fluorinated polymers which contain pendant side chains containing -CF-CF2-SO2A groups wherein Rf is as defined Rf above, and A is F or Cl, preferably F. Ordinarily, the functional group in the side chains of the precursor poly-mer will be present in terminal -O-CF-CF2SO2A groups. When Rf this is the case r the intermediate polymer will contain -O-CF-CF2SO-Ml)(sulEinic) groups, and the polymers prepared Rf n therefrom will contain both -O-CF-COOR1 and -O-CF-CF2SO2R2 Rf Rf ~39'~

groups. The precursor fluorinated polymers employed can be of the type disclosed in U.S.~. 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 made from at least two monomers, with at least one of the monomers cominq from each of the two groups described below.
The first group is fluorinated vinyl compounds such as vinyl fluoride, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro~alkyl vinyl ether), tetrafluoroethylene and mix-tures thereof. In the case of copolymers which will be used in electrolysis of brine, the precursor vinyl monomer desir-alby will not contain hydrogen.
The second group is the sulfonyl-containing mono-mers containing the precursor group -CF-CF2-SO2A, Rf wherein Rf and A are as defined above. Additional examples can be represented by the general formula CF2=CF-Tk-CF2SO2F
wherein T is a biEunctional perfluorinated radical com-prïsing 1 to 8 carbon atoms, and k is 0 or 1. The particu-lar chemical content or structure of the radical T is not critical, but it must have a fluorine atom attached to the carbon atom to which the -CF2SO2F 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 branched or unbranched, i.e., straight-chain, and can have one or ,~

more e-ther linkages. It is preferred that the vinyl radical in this group oE sulfonyl fluoride containing comonomers be joined to the T group through an ether linkage, i.e., that the comonomer be of the formula CF2=CF-O-T-CF2-SO2F.
Illustrative of such sulfonyl fluoride containing comonomers are CF2=CFOCF2CF2SO2F, CF2=CFOCF2CIFOCF2CF2S02F,

2 CFocF2TFocF27FocF2cF2so2 CF2=cFcF2cF2so2F~ and CF~2=cFocF2cFocF2cF2so2F
lF2 T

CF3.
The most preferred sulfonyl fluoride containing comonomer is perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride), CF2=cFocF2lFocF2cF2so2F-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.
3l718,627 and U.S.P. 3, 560,568.
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 to the carbon atom which is attached to the -CF2SO2F group. The most preferred copolymer is a copolymer oF tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) which comprises 20 to 65 percent, preferably, 25 to 50 percent by weight of the latter.
The precursor copolymer used in the present invention is prepared by general polymeriza-tion techniques developed for homo- and copolymerizations of fluorinated ethylenes, partic-ularly those employed for tetrafluoroethylene which are described in the literature. Nonaqueous techniques for preparing the copolymers of the present invention include that of U.S.P. 3,041,317, that isr by the polymerization of a mixture o the major monomer therein, such as tetrafluoro-ethylene, and a fluorinated ethylene containin~ a sulfonyl fluoride group in the presence of a free radical initiator, preferably a perfluorocarbon peroxide or aæo compound, at a temperature in the range 0-200C. and at pressures in the range 1-200, or more atmospheres. The nonaqueous polymeriza-tion may, if desired~ be carried out in the presence of a fluorinated solvent. Suitable fluorinated solvents are inert, li.quid, perfluorinated hydrocarbons, such as per-fluoromethylcyclohexane, perfluorodimethylcyclobutane, perfluorooctane, perfluorobenzene and the like, and inert, liquid chlorofluorocarbons such as 1,1,2-trichloro-1,2,2-trifluoroethane, and the like.
Aqueous techni~ues for preparing the copolymer of this invention include contacting the monomers with an aqueous medium containing a free-radical initiator to obtain a slurry of polymer particles in non-water-wet or granular : - 16 -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 coagula~in~ the dispersion, as disclosed, for example, in U.S.P. 2,559,752 and U.S.P. 2,593,583.
The novel intermediate polymers which contain pendant side chains containing -CF-CF2-SO2-~h groups are R n made from the known precursor fluorinated polymers which contain pendant side chains containing -CF-CF2-SO2~ groups Rf R8 by reduction with a compound having the ~ormu]a H2NN~ g wherein R8 is H or Cl to C8 alkyl radical, and R is H or a Cl to C8 alkyl radical, preferably H. The preEerred reduc-ing agent is hydrazine in view of its ready availability.
Another effective compound is methylhydrazine. Accordingly, the preferred reducing agents are those which have the formula H2NNHR .
A variety of reaction conditions can be used for the reduction. For example hydrazine has been ound effec-tive when used anhydrous, as the known hydrazine hydrate, as a 50% by weight solution in water, or in solution in other solvents such as dimethylsulfoxide. The reduction with a hydrazine can advanta~eously be carried out in the presence of an acid acceptor. The acid acceptor can be a tertiary amine such N-methylmorpholine, N,N,Nl,Nl-tetra-methylethylenediamine, pyridine or triethylamine, or a metal hydroxide such as KOH or NaOh. Use of a hydroxide or tertiary amine is preferred because the sulfinic acid " 1139~

product and by-product hydrogen fluoride can form salts with the hydraæine reagent, and the hydroxide or tertiary amine forms a salt with the sulfinic acid and frees the hydrazine to be available for reducing other sulfonyl halide groups.
Reduction with a hydrazine is ordinarily done at temperatures from about room temperature to about 40C., although higher temperatures can also be used. The reaction rate increases as the amount of water in the reaction medium is decreased. Also the reaction rate increases in dimethyl-sulfoxide as a medium, and in the presence of a hydroxide or tertiary amine.
The sulfinic groups in the reduced polymer will be in the form of sulfinic acid groups, or an alkali metal or al~aline earth metal salt thereof. Similarly, any sulf-onyl halide groups that have been hydrolyzed will be in the form of sulfonic acid groups, or an alkali or alkaline earth metal salt thereof. In both cases, the form will depend on the nature of the last medium with which the polymer was treated, and will ordinarily be the salt of the strongest base in medium ~or the last medium) to which it is (or was) exposed. Interconversion between acid and salt forms can be accomplished by treatment with solutions of acids or bases, as desired. Treatment times must, of course, be increased as the thickness of the layer to be treated is increased. Following reduction by a hydrazine, it is best to wash the polymer to free it of excess hydrazine before proceeding to the oxidation step. At the same time, an acid or alkaline wash can be carried out, if desired, to put the polymer in free acid or salt form if a specific , . .

form is desired for the particular oxidi2ing agent to be used.
Although the precursor fluorinated polymer can be in the form of powder or granules when subjected to the reduction and oxidation reactions described hereinabove, more oten it will be in the form of a Eilm or membrane when subjected to these reactions.
The polymers of the invention which posses pen-dant side chains which contain carboxylic ~roups and pendant side chains which contain sulfonyl groups can also be made by copolymerizing a mixture o the appropriate monomers.
The carboxyl-containing monomer is one or more compounds from a third group represented by the formula CF2=cFtocF2cF~ocF-c(~ol~
Y Rf wherein R is F, Cl, or a Cl to C10 per1uoroalkyl radical, R is lower alkyl or M
(n~
M is H, alkali metal, alkaline earth metal, ammonium or quaternary ammonium, n is the valence of M, Y is F or CF3, and m is 0, 1 or 2.
The most preferred monomers are those wherein Rl is lower alkyl, generally Cl to C5, or M where M is H, because of ease of polymerization. Those monomers wherein m is 1 are also preferred because their preparation and isolation in good yield is more easily accomplished than when n is 0 or 2.

O~J~ , The novel compounds 2 2, 2 3 and the corresponding free carboxylic acid are especially useful monomers.
Monomers of this third group can be prepared, for example, from compounds having the formula CF2=cF~oc~'2cF~ocFcF2so2F
Y Rf wherein Rf, m and Y are as defined above, by (1) saturating the terminal vinyl group wi~h chlorine to protect it in subsequent steps by converting it to a CF2Cl-CFCl- group;
(2) oxidation with nitrogen dioxide to convert the -OCFCF2SO2F group to an -OCFCOF group; (3) esterification Rf Rf with an alcohol such as methanol to form an -OCFCOOCH3 Rf group; and (~) dechlorination with zinc dust to regenerate the terminal CF2=CF- group. It is also possible to replace 2~ steps (2) and t3) of this sequence by the steps (a) reduc-tion of the -OCFCF2SO2F group to a sulfinic acid Rf -OCFCF2SO2H or alkali metal or al~aline earth metal salt Rf thereof by treatment with a sulfite salt or hydrazine; (b) oxidation of the sulfinic acid or salt thereof with oxygen or chromic acid, whereby -OCFCOOH groups or metal salts thereof are formed as is more fully described hereinabove, and (c) esterification to -OCFCOOC~3 by known methods.
Rf The carboxyl-containing monomer of the third group is copolymerized with fluorinated vinyl compounds - 2~ -:,~

Erom each oE -the irst and second groups oE comonomers defined here:inabove, and under non-aqueous polymerization techniques also defined hereinabove.
Yet another me-thod for Preparing copolymers oE
the invention which possess pendant side chains which contain carboxylic groups and pendant side chains which contain sulfonyl groups is by treating a 1uorinated polymer which has pendant side chains which conta:in -CFCF2SO2R groups wherein R2 is OMl~ M is H or alkali R n metal or alkaline earth metal, and n is the valence of M, with a mixture of fluorine and oxygen, whereby -CFCOF groups are ormed. The -CFCOF groups can then be Rf Rf hydrolyzed to ion exchange groups -CFCOORl wherein Rl is R

Mlj Hydrolysis of -CF-COF groups to -CF-COOH groups n Rf Rf occurs so readily that the product isolated rom the fluorine/oxygen reaction will ordinarily be at least partially hydrolyzed to the free carboxylic acid.

Conversion of ~CFCF2SO2R groups to -CFCOF and -CFCOOR
Rf Rf Rf groups can vary from low percentages such as 10% to per-centages of more than 50%, at least in regard to the surface layer o:E the article so treated, depending on the amount of treating reagents used, duration of treatment, etc.
In this method, the molar ratio of fluorine to oxygen can vary widely, e.g., from 1:5 to 1:1000, 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 -100C. to 250C. can be used, from 20 to 70C. Treatment can conveniently be carried out in a corrosion resistant metal pressure vessel.
A specific example of the type of polymer which can be treated with a fluorine/oxygen mixture is one having the repeating units ~C~2 - CX2 ~ - CF2--1--CF - Z
s CF - Rf C~' r~p wherein Rf, p, q, r, s, X, and Z are as defined hereinabove, and R2 is OMl 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 sulfonyl-containing groups remaining, and p of them converted to-OCF2COF and/or -OCF2COOH groups. It should be understood that while treatment with a mixture of fluorine and oxygen will effectively destroy and 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 con-verted to pendant side chains which terminate in a -CF3 group.

It should be further understood, however, that by proper choice of the initial polymer, copolymer of the invention containing bcth carboxylic and sul~onyl groups meetinq the composition defined hereinabove can be prepared.
The initial polymer which contains r+p sulfonyl-containing side chains is in turn made by copolymerizing fluorinated vinyl monomers of the first and second groups of monomers described above. Such fluorinated polymers are described in 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 sub-jected to such treatment, more often it will be in the form of a film or membrane when it is so treated.
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-CFCF2SO2F
Rf groups, and to bring about a partial hydrolysis to -O-CFCF2SO3H (or metal salts thereof) such that the film Rf or membrane is hydrolyzed on either one or both surfaces thereof to a controlled depth. Upon subsequent treatment with a mixture of fluorine and oxyqen, the layer in sulfonyl fluoride form remains unaffected, and the layer in sulEonic acid form reacts such that -O-CFCOF groups are produced as R~
described above. Upon subjecting the film or membrane to a full hydrolytic treatment, the interior layer will have only -O-CFCF2SO3H groups (or salts thereof), and the surface Rf x .

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layer or layers will have both -O-CFOOH and -O-CFCF2S03H
Rf Rf groups tor salts thereof).
The polymers of the present invention can be in the form of films and membranes.
When the polymers of the invention are in the form of a film, desirable thicknesses of the order of ~.002 to 0.2 inch are oridinarily used~ Excessive film thicknesses will aid in obtaining higher strength, but wlth the result-ing deficiency of increased electrical resistance.
The term "membrane" refers to non-porous struc-tures 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 lamina-tion, and to structures ha~ing as one layer a support, such as a fabric imbedded therein, It is possible according to the present invention to make films and membranes wherein the pendant side chains are essent~ally wholly (i.e., 90% or more) or wholly (i.e., up to about 99%~ in the carboxylic form throu~hout 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 in this respect is exercised during the reduction of the precursor polymer which contains sulfonyl halide groups to the intermediate polymer which contains sulfinic groups, by using or not using competl~ng reactions which produce different products~
For example, when 100% hydrazine is used as the reagent in the reduction reactiQn, con~ersion to sulfinic functional group, and eventually to carboxylic functional group can be 3a 1~3i~3~
quite high, of -the order oE 90-95%, and it is believed that in the ultimate surface layers conversion to sulfinic or carboxyl groups can be as high at 98 or 99%. Use of a combination of hydrazine and a hydroxide in a solvent like water or dimethylsulfoxide will result in reduction of some groups to sulfinic form and hydrolysis o-f others to sulfonic acid salt form; because the sulfonic salt form is not affected during the oxidation step, the ul-timate result is a combination of carboxylic and sulfonyl groups in rela-tive amount which varies with the relative amounts of hydra-zine, water and hydroxide used. Control of the relative amounts of carboxylic and sulfonyl functional groups can also be exercized to some extent during the oxidation step. Some oxidizing agents such as chromic and vanadate salts will produce relatively larger amounts of carboxylic and small amoun-ts of the original sulfonic groups, while other oxidizing agents such as hypochlorite will produce relatively smaller amounts of carboxylic and larger amounts of the original sulfonic groups.
In similar fashion, it is possible to make pro-ducts where various other functional groups are present in pendant side chains, in combination with carboxylic groups in other pendant side chains. For example, the precursor polymer which contains sulfonyl halide groups can be treated with hydrazine in combination with ammonia or a primary amine, whereby not only will some sulfonyl groups be reduced to sulfinic form, but others will be converted to sulfonamide or N-substituted sulfonamide groups. The technique whereby groups of the precursor polymer can be converted to the form -(SO2NH)mO, wherein Q is H, NH4, cation of an alkali - ~ ~3~

metal and/or cation of an alkaline earth metal and m is the valence of Q, are set forth in U.S.P. 3,784,399. Preferred definitions of Q include NH4 and~or cation of an alkali metal particularly sodium or potassium. The technique whereby sulfonyl groups of the precursor polymer can be converted to N-monosubstituted sulfonamide groups and sal-ts thereof are as cet forth in U.S. Patent 4,085,071, which issued 1978 April 18.
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 respect, it is highly undesirable that a film or membrane to be used for ion exchange purposes in an eleetrolytic 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 exchange layer. The film and membrane of the present inven-tion do not have neutral or anion exchange layers. In thiscontext, 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 cell, polymers whieh contain 40-95% pendant side chains containing carboxylic groups and 5-60% pendant side chains containing sulfonyl groups provïde excellent current efficiency. An equally important criterion in a chlor-alkali cell, however, is the amount of power required for each unit of ehlorine and caustic. It is eonsidered that the polymers of -the type disclosed herein permit a proper eombination of operating eonditions to realize an exeellen-t and unexpected reduction in power.
Since the power requirement (whieh may be expressed in watt-hours) is a funetion of both eell voltage and current efficieney, low cell voltages are desirable and necessary.
However, a polymer without a high current efficiency eannot operate effeetively from a commereial standpoint even with extremely low cell voltages. Additionally, a polymer with an inherent high current efficiency allows a proper combina-tion of parameters as in fabrication into the film and/or operation of the eleetrolytie eell to realize the potential theoretieal reduetion in power. Illustratively r the poly-mer can be fabricated at a lower equivalent weight which may result in some loss of eurrent efficiency which is more than compensated by a reduction in voltage. Polymers of the present invention whieh have 50-95% pendant side ehains eontaining earboxylie groups and 5-50% pendant side ehains eontaining sulfonyl groups have low power eonsumption.
It is also possible aecording to the present invention to make films and membranes whieh are structured to have one surfaee wherein the poIymer has pendant side ehains whieh are in earboxylie form, and pendant side ehains whi.eh are in sulfonyl form, and the other surfaee wherein the pendant side chains of the polymer are wholly in the sulfonyl form. It is further possible to make films and membranes struetured to have both surfaees wherein the polymer has pendant side chains in carboxylie form and 30 pendant side chains in sulfonyl form, and an interior layer ~3~3'~
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 80% of the thickness. When both surfaces are modified, the depth of each modified layer will be less than half the thickness of the structure, anfl will normally be from 0.01 to 40%
of the thickness. The thicXness 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 bag-like configuration which is sealed shut, and to treat only the outside or inside of the bag. ~hen 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 o a chloralkali cell it will ordinarily face the cathode.
Under~most circumstances, layered structures will be such that the layer of carboxylic polymer will be about 1/~ to 5 mils thïck, 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 indica-ted thicknesses are effective film thicknesses, i.e., thicknesses which exclude reinforcing fibers and other members which do not contain ion exchange groups.
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 contem~lated.

.

~3~

Illustratively, permeation selection of cations is directly encompassed. One method o-f determination of cation exchange properties is a measurement oE permselectivity with separa-tion of the same cations in solutions but at different concentrations. This involves cation transport, and a permselectivity measurement oE no voltage would indicate the polymer does not function for ion exchange.
The polymers which contain sulfinic groups are useful as intermediates to polymers, films and membranes which contain carboxylic groups.
~ specific use for the polymers of the present invention which contain both carboxylic and sulfonyl groups is in a chloralkali cell, such as disclosed in German patent application 2,251,660, published April 26, 1973, and Netherlands patent applica-tion 72.17598, published June 29, 1973. In a similar -Eashion as these teachings, a conventional chloralkali cell is employed with the critical distinction of the type of po~ymeric film used to separate the anode and cathode portions of the cell. ~hile the description of said German and Dutch publications is directed to 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 or alkali 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.
An outstanding advantage has been found in terms of current efficiency in a chlor-alkali 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 aspec-ts of the present invention, the following examples are provided.
Example 1 A 4-mil film of a copolymer of tetrafluoroethy-lene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having an equivalent weight of 1100 was immersed for 16 hours at room temperature in 85~ hydrazine hydrate, washed with water and immersed for 30 minutes at room temperature in a 5% solution of potassium hydroxide. The film was washed with water and immersed at room tempera-ture in a mixture of 25 ml formic acid and 5 ml 37%
hydrocloric acid in an atmosphere of oxygen~ Increasing conversion to the carboxylic acid form was observed by IR anlaysis after 5 and 60 hours at room temperature and after an additional 2 hours at 70-80C. in this medium.
The degree of conversion to the carboxylic acid form was further increased by heating the -film (after a water wash) for 2 hours at 50C in a mixture of 75% acetic acid, 3~ concentrated suluric acid, 2% chromium trioxide and 20% water. The film was washed with water, and con-ditioned for cell testing by heating for 2 hours to 70C
in a 10% solution of sodium hydroxide. Aqueous sodium chloride was electrolyzed at a current density of 2.0 asi (amps/in ) to give 35% NaOH at a current efficiency of 91%
at a cell voltage of 4.9 volts.
Example 2 A 4-mil film of a copolymer of tetrafluoroethy-lene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl .~

~"

1uoride) having an equivalent weight of 1100 was immersed for 48 hours at room temperature in 85% hydrazine hydrate.
IR analysis at this point indicates essentially complete conversion to the sulfinic salt form through the entire thickness of the Eilm. The film was then heated for 20 minutes to 90C. in a solution of potassium hydroxide (13%) in aqueous dimethyl sulfoxide (30%), rinsed with water and immersed for 20 minutes at room temperature in a mixture of 20 ml aqueous hydrochloric acid and 100 ml glacial acetic acid. The film was again rlnsed with water and then heated for 16 hours to 130C. in an atmosphere of oxygen.
IR analysis at this point indicated the formation o -CF2CO2H functional groups, the presence of -CF2SO3F~ groups, and the complete absence of -SO2F of the starting material as well as -SO2R groups of the sulfinate intermediate~
The film was conditioned for cell testing by heating for 2 hours in a 10% solution of sodium hydroxide.
Aqueous sodium chloride was electrolyzed at a current density of 2.0 asi to give 32% NaOH at a current efficiency of 91~ at a cell voltage of 4.7 volts.
Example 3 A 4-mil film of a copolymer of tetrafluoroethylene and perEluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having an equivalent weiqht of 1100 was immersed for 20 hours at room temperature in a mixture of 300 ml dimethyl-sulfoxide, 100 ml N-methylmorpholine and 80 ml 85% hydrazine hydrate. The film was then washed with dilute potassium hydroxide solution and water and immersed for 10 minutes at room temperature in a mixture of 200 ml acetic acid, 10 ml.
concentrated sulfuric acid, ~ gm ammonium vanadate, 1 gm vanadyl sul:Eate and 300 ml water. After that the film was washed with water and exposed -to air at room tempera-ture for 6 days.
The film was then converted to the potassium salt form by heating for 30 minu~es to 90C in a solution containing 13% potassium hydroxide and 30% dimethylsulfoxide and washing with water.
Anaylsis by X-ray fluorescence at this point showed a potassium content of 0.965 gram atoms per kg and 0.075 gm atoms of sulfur per kg. This indicates a content of 0.89 meq/gm of carboxylate groups and 0.075 meq/gm of sulfonate groups.
Aqueous sodium chloride was electrolyzed at a current density of 2.0 asi in a cell with this film as the membrane to produce 35% NaOH as a current efficiency of 92~ at a cell voltage of 4.9 volts.
~.
:
A 4-mil film of a copolymer of tetra~luoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride~
having an equivalent weight of 1100 was immersed for 30 hours at room temperature in 85% hydrazine hydrate (54%
hydrazine on an anhydrous basis). The film was then washed with water and a dilute solution of potassium hydroxide.
Infrared analysis indlcated that this treatment caused substantially complete reduction of sulfonyl groups to sulfinic groups through the entire thickness of the film.
The film was then heated for 17 hours to 70C.
in a solution containing 5% chromium trioxide and 50%
acctic acid in water, rinsed with water, and conditioned for cell testing by heating for 2 hours to 70C in a 10%

solution of sodium hydroxide. ~queous sodium chloride was electrolyzed at a current density of 2.0 asi to produce 33 sodium hydroxide at a current efficiency o 90% and a cell voltage of 4.1 volts.
Example 5 A 7-mil film of a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having an equivalent wei~ht of 1100 was placed as a liner in a dish and anhydrous hydrazine (95%) was poured into the liner so as to contact only the upper surface of the film.
After 2 minutes at room temperature, the hydrazine was removed and the film was washed with water.
The film was then immersed in 50 ml glacial acetic acid, and 25 ml of a 20% solution of sodium nitrite was added in portions during a period of 1 hour. The Eilm was again washed with water. Staining of a cross-section with Sevron~ Brilliant Red 4G indicated a depth of reaction of 0.5 mils.
The unreacted SO2F groups were hydrolyzed by heating for 30 minutes to 90C. in a solution of potassium hydroxide (13%) in aqueous dimethylsulfoxide (30%~. The film was installed in a chloralkali cell with the hydrazine treated and oxidized side toward the catholyte.
Aqueous sodium chloride was electrolyzed at a current density of 2.0 asi to give 25~ NaOH at a current efficiency of 81% at a cell voltage of 4.3 volts.
Example 6 A 4-mil film of a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) 30 having an equivalent weight of 1100 was immersed for 16 ~L13~
hours at room temperature in 85% hydrazine hydrate. The film was rinsed with water, then with a hot 2~ solution of sodium hydroxide, and again with water. The film was then heated for 1 hour to 50-60C in a solution of 1%
potassium bisulfate :in 80% acetic acid (balance water), wiped off and exposed to room temperature air for 3 days.
The oxidation was com~leted by 2 hours immersion in a solu-tion of 2~ CrO3 and 3% H2SO4 in 75~ acetic acid (balance water) at 50C.
' The film was washed with water, then heated to 70C. for 1 hour in a 10~ solution of NaOH, and evaluated in a chloralkali cell. Aqueous sodium chloride was elec-trolyzed at a current density o 2.0 asi (2.0 amps/in2) to give 30% sodium hydroxide at a current efficiency of 91%
at a cell voltage of 4.5 volts. After 130 days of opera-tion sodium hydroxide was being produced at a concentration of about 32~5~ at a current efficiency of ~9% and a cell voltage of 4.3 volts.
Example 7 A 7-mil film of a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having an equivalent weight of 1100, having a T-24 "Teflonl' fabric imbedded therein, and having one surface layer of about 1 mil depth which had been hydrolyzed to the corres-ponding potassium salt of the sulfonic acid, was exposed on the sulfonyl fluoride side to a solution of 18 ml hydrazine hydrate and 45 ml N-methylmorpholine in 35 ml dimethyl-sulfoxide for 15 minutes at room temperature. The sheet was washed with water, dilute potassium hydroxide and again with water. Cutting the sheet through its thickness and staininy with Sevron~ Brilliant Red 4G at this point indica-ted that reaction with hydraz ne had occurred to a depth o 0.6 mils.
The sample was then washed with 5% sulfuric acid and exposed to air :Eor 20 hours at room temperature, followed by chromic acid oxidation like that described in Example 6. The sheet was evaluated in a chloralkali cell at a current density of 2.0 asi, and sodium hydroxide was produced at a concentration o:f 37% at a current efficiency of 88% and a cell voltage of 4.6 volts after 20 days of operation.
Example 8 A 7-mil film of a copolymer o tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having an e~uivalent weight of 1100 was folded and sealed to a bag, except for a small opening to permit the intro-duction o- reagents. A mixture o~ 250 ml dimethylsu].oxide, 100 ml N-methylmorpholine and 90 ml hydrazine hydrate was poured into the bag and permitted to react or 7 minutes at ; room temperature. The bag was then emptied, rinsed with water and exposed for l hour on the inside with a solution containing 10% KOH and 10% dimethylsulfoxide, rinsed again with water, and then with dilute acetic acid. The bag was then opened, the film was cut through its thickness, and staining with Sevron~ Brilliant Red 4G indicated a depth of reaction of 0.6 mils. The film was then treated for 30 minutes with a solut.ion o.~ 5 gm VOSO4, 5 gm NH4VO3 and 5 ml concentrated H2SO4 in 3 liters of water, washed with water and hung up for drying.
After 3 days of air exposure at room temperature, the film was treated for 1 hour with a solution containing ' ~

s~ a~
5% acetic acid, 2% K2SO4 and 2% KHSO4 in water.
The Eilm was then washed with water and ~7acuum laminated to a T-25 Teflon~ fabric, followed by total hydrolysis for 20 minutes in a solution of KOH in aqueous dimethylsulfoxide.
The resulting membrane was evaluated in a chlor-alkali cell with the hydrazine treated and oxidized surace facing the catholyte. Sodium hydroxide was produced at a concentration o 31% by weigh~ at a current efficiency of 87% and a cell voltage of 5.8 volts at a current density of 2 asi.
Example 9 Preparation of CF2=CFOCF2CF(CF3) OCF2COOCH3, Methyl perfluoro-4-methyl-3,6-dioxa-7-octenoate A 2-liter 3-necked flask was fitted with a stir-rer, gas inlet tube and dry ice cooled condenser. The apparatus was blanke~ed with nitrogen, 3276.1 g of per-fluoro[2 ~(2-fluorosulfonylethoxy)-propyl vinyl ether~ added and chlorine bubbled into the flask while irradiating with a sunlamp until no more chlorine was absorbed. Distillation yielded 2533.8 g (66.7%) o perfluoro[2-(2-fluorosulfonyl-ethoxy)-propyl-1,2-dichloroethyl ether], bp 165C.
To a ~uartz tube (l-inch outside diameter and 1 foot long) heated to 550C. were added nitrogen dioxide at a rate of approximately 0.2 g/min and 37.6 g perfluoro ~2-(2-fluorosulfonylethoxy)-propyl-1,2-dichloroethyl ether] at a rate of 0.33 ml/min. The product was trapped in a dry ice cooled trap, allowed to come to room temperature, treated with 20 ml methanol, and washed with 250 ml water to give 19.3 g of product. The combincd distillation of a number ~ t~3 of similar runs yielded methyl perfluoro-7,8-dichloro-4-methyl-3,6-dioxaoctanoate, bp 167C., whose structure was confirmed by infrared and NMR spectroscopy.
A mixture of 10 g crude methyl perEluoro-7,8-dichloro-4-methyl-3,6-dioxaoctanoate, 5 g zinc dust, 50 ml anhydrous diethylene glycol dimethyl ether and Q.l g iodine was heated 140C., and then distilled. The distillate was washed with water and the product chromatographed to yield appreciable amounts of CF2=CFOCF2CF(CF3)OCF2COOCH3.
The structure of the final product was proven by IR spec-troscopy and by conversion with bromine to CF2BrCFBrOCF2CF(CF3)OCF2COOCH. The structure of the vinyl ether was further confirmed by its boiling point, 75C. at 50 mm of Hg, and its NrqR spectrum.

Example 10 A piece of 7-mil film o a copolymer of tetra-fluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesul-fonyl fluoride) having an equivalent weight of 120Q, and containing one surface layer of approximately l-mil depth which had 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 50C. 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 sul:~onyl fluoride groups and absorption at 5.6 microns due to carboxylic acid. The infrared spectrum of the starting film was almost identical, but lacked the 5.6 micron absorption.

Example 11 A piece of 7-mil film o-f a copolymer of tetra-fluoroethylene and perfluoro(3l6-dioxa-4-methyl-7-octenesul-Eonyl fluoride) having an equivalent weight of 1100, and containing one surface layer of approximately 1 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 30C. for 4 hours. The film was removed and treated at 90C. with a mixture of dimethylsulfoxide, water and potassium hydroxide for 1 hour. After washing, the 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% NaOH at current efficienc~es of 75.8-81.7% at a cell voltage of 3.9-4.2 volts.
Example 12 Conversion of CClE2CClF2OCF2CF(CF3)OcF~cF2sO2F to CclF2cclFocF2cF(CF3)ocF2coocH3 A mixture of 150 ml water, 50 ml 1~2-dimethoxy-20 ethane, 76 g sodium sulfite and 103.4 g CClF2CclFOcF2cF(cF3)OCF2CF2so2F was heated in a nitrogen atmosphere for 16 hours at 85-87C. The mixture was cooled to 50C., 600 ml of isopropanol added, heated to 70C. and filtered. The solids were washed twice with hot isopropanol, and all the filtrates were combined and evaporated to dryness.
; The resulting solid was dissolved in 600 ml water, and the solution was cooled and acidified with 50 ml concentrated sulfuric acid while keeping the temperature ~39'~
below 10C. Two grams of ferrous ammonium sulfate was added and air was bubbled through the solution at room temperature for 48 hours. The reaction mixture which contained two liquid layers and a solid was extracted three times with ether, and the ether extracts were com-bined and distilled to give 53.8g of a colorless liquid, b.p. 92-110C at 11 mm Hg.
The 53.8g of liquid was added to 70 mil anhydrous methanol and 1 ml concentration sulfuric acid and refluxed for 22 hours; the mixture was added to 300 ml water, and a lower layer separated. The lower layer was washed with water and dried with calcium chloride to give 35.6g (40.2 yield based on starting CClF2CClFOCF2CF(CF3)OCF2CF2SO2F) of CClF2CClFOCF2CF(CF3)OCF2COOCH3 whose infrared spectrum and gas chromatographic retention time were identical to authentic material.
Although the invention has been described by way of specific embodiments, it is not intended to be limited thereto. As will be apparent to those skilled in the art, numerous embodiments can be made without departing from the spirit of the invention or the scope of the following claims.
The application is a division of copending Canadian Application Serial No. 301 530, filed 1978 April 18.

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process which comprises contacting a first fluorinated compound containing a group, wherein Rf is F, Cl or a Cl to C10 perfluoroalkyl radical, M is H, an alkali metal or an alkaline earth metal, and n is the valence of M, with an oxidizing agent, and separating therefrom a second fluorinated compound containing a group.

2. The process of Claim 1 wherein the first fluorinated compound contains a group wherein M is H and n is 1, and the oxidizing agent is oxygen.

3. The process of Claim 2 wherein contacting with oxygen is carried out in the presence of a catalytic amount of a metal which can exist in more than one valence state.

4. The process of Claim 1 wherein the oxidizing agent is a permanganate salt, chromic acid, nitrous acid or a hvpochlorite salt.