CA1162565A - 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

Il 1 6256~
BACKGROUND O~ T~IE INVENTION
_ This invention concerns improvements in and relating to fluorinated ion exchange polymers, and particu-larly to such polymers used in the formof~ilmsandmembranes used in chloralkali electrolysis cells.
Fluorinated ion exchange membranes are known in the art. The fluo~inated ionexchangepolymerin suchm~mbranes can be derived from a fluorinated precursor polymerw~ich contains pendant side chains in sulfonyl fluoridefonm. The sulfonyl fluoride functional groups have been conver~ed to ionic form in various ways, for example, to sulfonate salts by hydrolysis wi~h an alkaline material, tothesulfonicacid by acidification of the salts, and to the sulfonamide by treatment with ammonia. Examplesofsuchteachings intheart can be found in U.S. 3,282,875, U.S. 3,784,399, and U.5. 3,849,243.
Although such polymers and membranes have many desirable properties which make them attractive for use in the harsh chemical environmentofachloralkalicell, ~chas good long-term chemical stability, theircurrentefficiencies are not as high as is desired, especially when the caustic is produced at high concentration. As transportof hydroxyl ion in a chloral~ali cell from the catholyte through the membrane to the anolyte increases, current efficiency drops.
- Larger amounts of oxygen impuxity in the chlorine are - thereby produced, and there is a greater buildupofchlorate and l-ypochlorite contaminants in the brine, which contami-n3nts mus~be rcmovcd and discardcd to maintain acccptable cell o~eration. Current e~ficicncies of at least 90% are hi~llly dcsirablc.

1 1 625~5 Acco~d~n~l~, there ~s ~ need fo~ p~l~ers ~nd ~embranes which ~ill per~i~ ce~l ope~tion at high curxent efficiencies, and especi~lly ~or those whi h will pcrmit opexation at high eficiencies over long periods of time.
Additionally, it was desired ~o find a me~hod for modifying the known polymers and membranes which have pendan~ side chains in sulfonyl fluoride form in such a way to obtain polymers and membranes which will have the high current efficiencies desired.
. S~P.Y OT' ~E I~.~T~O.~.
It has now been found that fluorinated ion exchange polymers and membranes which contain pendant side ch~ins in ionic carboxylic form and pendant side chains in ionic sulfonyl form have high current efficiencies.
According to the present invention, there is pro-vided a process which comprises contacting a ~rstfluorinated polymerwhichcontainspendantsidechainscontaining -CF-CF2-SO2~ groups, wherein Rf is F, Cl or a Cl ~o Clo Rf perfluoroalkyl radical, M is H, an alkalimetal,an ~kaline earth metal, ammonium, substituted ammonium including q~a-ternary ammonium, or hydraziniu~ including substituted hydrazinium, and`n is the valence of M, with an oxidizing agent, and sepaxating therefrom a se~ond fluorinated poly-mer which contains pendant side chains containin~
-CF-COO-~ roups-n R~
There is also provided according to the prescnt invcntion a fluorinatcd polymcr which contains pcndant sidc cl~ains containin~ -~F-C1~2-SO2-~
R~ n.

1 ~ 6~5 groups, ~herein R~ is ~, Cl or a Cl to q~ perfluoroalkyl xadical, M is H, an alka,li metal or an alkaline earth metal, al:unonium, substituted alTrnonium including quatexnary.
ammonium, or hydrazinium including substituted hydrazinium, and n is ~he valence of M. ~ore specifically, the polymer which contains pendant side chains which contain sulfinic groups is lOi tcF cF2~ ~
r CF2 . CF2 .
CF-Y CF-Z
--1--m O

CF-~ CF ~
~F2 . .~F2 2 S2~1 ;P SO~R t wherein m is 0, 1 or 2, p is 1 to 10, ~ is 3.to 15, s is 0, 1 or 2, t is O 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 Clo perfluoroal~yl radical, R2 is F, Cl or 0~

M is H, aJ.~ali mctal, alkaline earth metal, an~onium, substituted ammonium includincJ quaternary ammonium, 1 3 625~
hydrazinium 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 0. More often, both p and t will be at least 1.
r There is also provided a fluorinat~d polymer which contains pendant side chains, about 10 to about 95% of which side chains contain -O-CF - COO-~l groups and about 5 to Rf n) about 90% of which side chains contain -,CF-CF2-S03-~1) groups, wherein Rf is F, Cl or a Cl to C10 perfluoroalkyl radical, 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. ~-More specifically, such a polymer has the repeating units ~ cF2 r ~X2 - CX2 ~ ~F C 2~

2i~ CF - Y CF - Z ¦

CF - Rf ~ 53 wherein . .
m is 0, 1 or 2, p is 1 to 10, ~t q is 3 to 15, 1 ~ ~2565 r is 1 to 10, s is o, 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 OE 3 Rf is F, Cl or a Cl to C10 perfluoroalkyl radical, :
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.
With reference to part of the definition of M, "ammonium, substituted ammonium including quaternary al~monium, or hydrazinium including substituted hydrazinium"
includes groups defined more specifically as RS

R4- N - R6, wherein R4 is H, lower alkyl such as Cl to C6, or NH2; and R5, R6 .
and R7 are each independently H or lower alkyl such as C
i to C6, with the understanding that any two of R4, R5, R6 `~ and R7 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-S02-~1 group to chemical compounds containing a -~
:F n) -fF-COO~ group, wherein Rf, M and n are as Rr n .

1 1 6~565 defined abovc, by reaction with an oxidizing agent. There is alsa provided according to ~he in~ention cextain novel chemical compounds made ~ith this proc~ss, including novel vinyl monomers which contain c~rboxylic functional groups and which are useful in making the above poly~ers; also, films and membranes o~ the poly.mers; and laminar structures con~aining the polymers.
There is further provided according to the inven-tion a process fpr making a fluorinated polymer which has pendant side chains which contain -O~F-COF groups by contac-Rf ting a fluorinated polymer which has pendant side chains which contain -OCFCF2SO3H groups or salts.thereof with a Rf mixture of fluorine and oxygen. H~drolysis o the poly~er thus obtained produces a fluorinated ion exchange polymer which contains -OCF-COOH groups or sal~s thereof, or both . Rf -OCF-COOH and -O~F-C~2SO3~ groups or salts thereof.
Rf Rf The ion exchange membranes of the present in~en-tion which contain both ioni~able carboxylic and ionizable sulfonyl groups as active ion exchange sites are highly desirable in co~parison with prior art ion exchange mem-branes for several distinct reasons. Most importantly, outstanding efficiencies in a chlor-al~ali cell have been obtained in comparison with membranes which contain only sul~onic acid ion exchange groups obtained by hydrolysis of pendant sulfonyl groups. For example, treatmcnt of a mem-brane havin~ pcndant sulfonyl ~roups to modify a surface laycr to incorporatc carboxylic ~roups accordin~ to thc prcscnt invcntion rcsults in a dramatic increase in currcnt 1 ~ ~25~5 ef~icicncy in a chlor-alkali cell. T~lis improvement is considercd to be of predominant importance in commexcial applicability in rcducing the cos~ of pxoducing a unit of chlorine and caustic. Illustratively, in a chlor-alkali plant producing, for example, 1000 tons per day of chlorine, the direct savings in electrical power for only a 1% increase in efficiency are very significant.
DESCRIPTTON OF THE PI~EFERRED EMBODIMENTS
_ .
A need has developed i~ the chlor-alkali industry for improved ion exchange materials which can be used to replace existing cell com~artment separators which have been used for dec,ades without substantial impro~ement in design.
For use in the environment of a chlor-alXali cell, the membrane must be ~abricated from a material which is capable o withstanding exposure to a hostile environ-ment, such as chlorine and solutions which are highly ~
alXaline. Generally, hydrocarbon ion exchange membranes ' are totally unsatisfactory 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~ A most ~nportant criterion is the current effi-ciency for conversion of brine in the electrolytic cell to the desir~d products. Improvement in current efficiency can translate into pronounced savings in the cost of production of each unit o chlorine and caustic. Additionally, rom a conunercial standpoint the cost of production ~f each unit o products will bc determinative of thc conuncrcial suit-abili~y of an ion excllan~e membrane.

-- U --1 ~ ~25~5 The ion ~xchan~e ~oly~ers of the pxesent inv~n-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 fluoxine atom connected thereto. The ion exchange polymers of the inven-tion can be made from polymers which contain pendant side chains containing -Ç~-CF2-SO2-Ml~ grOUpS wherein Rf is F, Rf ~n) Cl or a Cl to C10 perfluoroalkyl radical, M ~s as defined above, and n is ~he valence of M, by subjecting them to an oxidation. A variety of oxidizing agents are found effec-tive for oxidizing pendant side chains containing -CF-CF2S~2-Ml~ groups to side chains containing -~F-COO-M
Rf ~n . R ~n groups.
A~ong 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 gases 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 H, that is, when the functional group is the free sulfinic acid. With 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 ~leva~ed temperature. At or near room temperature without a catalyst, alt~lo~l~h o~y~cn has littlc or no observable cffect cven ovor a pcriod o~ a few days, si~ni~icant con-vcrsion to car~o~yl ~roups i5 obscrvcd ~fter three to four ~ ~ ~2~

weeks. ~t high~r 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 treat~d can simply be exposed to the gas, or it can be contacted with oxygen in a liquid medium such as water. The use of a catalyst is preferred as it speeds the reaction. .Metals which can exis~ in more than one valence state can be used ascat~yst.
~For present purposes, zero is not counted as a valence sta~e.) For example, salts of iron, vanadium, uranium, cobalt, nickel, copper and manganese have been found effec-.
tive.
Other effecti.ve oxidizing-agents for the pendant groups, when the functional group is either in the free sulfinic acid form or in the form of an alkali metal or alkaline earth metal salt thereo~, include permanganate in either acidic or basic media, chromic acid, vanadate salts in acidic media, nitrous aci~, and hypochlorite salts in basic media. It should be understood that the polymer can be in either fr~e acid form, or salt thereo~, when intro-duced to such oxidizing agents, and that the acid or salt forms 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 of inorganic or organic acids sucl- as sul~uric acid, hydrochloric acid, acetic acid, etc.
It has ~lso becn observcd ~la~pendant-CF-CF2-S021-1 R~

~ 3 625~
groups can be converted to -CF-COOH groups by placing them f in boiling water or a boiling organic or inorganic acid such as formic acid for 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 ine~fective for present purposes.
It is a simple matter to distinguish oxidizing agents effec-tive for present ~urposes from those that are ineffective, merely by determining the presence or absence of character-istic absorption bands in the infrared spectrum of the product correspo~ding to carboxylic acid groups at about 1785 cm-l or to salts thereof at about 1680 cm-l.
It has also been found 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 (n) 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 Cx F2X+l, where x is 1 to 20;
CF2 Cl-CFCl-CyF2y , where y is 1 to 18;

and CF2Cl-CFClOtCF2-CF-Otz, where z is 1 to 3, R~
and Rf is as defined above.

,~ ,.

t J 6~S6S
The resulting carboxylic compounds ~rc in some caseskno~n compounds useful, for example, for convcrsion to vinyl esters from which polymcrs can be made and fabricated into films, etc. The sulfinic acid ha~ing a terminal CF2Cl-CFCl-group can be derived, for example, starting rom a known~fonylc~mpoundwhichh3sa terminal vinyl group, ~y ~irst 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-CFCl- group, and this in turn can then be dechlorinated, as with zinc, to make an olef~nic car-~oxylic acid ~hich is useful for making pol~mers and copoly-mers. The polymers and copolymers can be used, for example, in makin~ films and in ion exchange applications.
The ion exchange polymers o~ the presentinvention possess pendant side chains which contain carboxylic g~oups 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.
~ he ion exGhange polymers of the presentinvention ~hich 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 men~rane to separate the anode and cathode compaxtments of an el~ctrolysis cell, such as a chloral~ali cell, thc polymer should have a total ion exchangc capac-ity o 0.5 to 1.6 mcq/g (milliequivalents/~ram), pre~erably ~rom 0.8 to 1.2 mcq/g. Belo~ an ion exchangc capacity of ~ 12 ~

I 1 6~5~5 O.5 meqJg, the ~lectrical xesistiYity becomes too high, and abo~e 1.6 meq/g th2 mcchanical properties are poor because of excessive s~elling o~ ~he pol~mer. The values of p, q and r in the above formulas o~ the copolymer should be adjusted ox chosen such that the polymer has an equi~a-lent weight no greater than ~bout 2000, pre~erably no greater than about 1500~ for use as an ion exchange barrier in an electrolytic cell. The equivalent weight above which the resis~ance of a film or membrane becomes too high for practical use in an electrolytic cell varies somewhat with the thickness of t~e film or membrane. For thinner films and membranes, equivalent weights up to about 2000 can be tolerated. For most purposes, however, and for films of ordinary thickness, a value no greater t~an a~out 1500 is preferred.
The polymers which contain pendant side chains containing -CF-C~ -SO2 -(l)groups, wherein Rf, M and n are ~ n as defined hereinabove, are in turn made from known precur-

2~ 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, p~eferably F. Ordinarily, the functional group in the side chains of the precursor poly-mer will be present in terminal -O-CF-CF2SO2A groups. When R~
this is the c~se, the int~rmediate polymer will contain F-cF2so2-~ sulfinic3 groups, and the polymers prepared R~ n ther~rom ~ill contain both -O-CF-COORl and -O-CF-CF2SO2R2 ~f Rf ~ 13 -1 ~ 62S65 grOUpS. The pr~cursor fluorinated polymers employcd ca~
be o~ the ~pe disclosed in V.S.P. 3,282,875, U.S~P.3,560,568 and U.S~P, 3,718,627~ More specifically, the precursor pol~mers can be prepared from monomers which axe fluorinated or fluorine substitu~ed vinyl compounds~ The precuxsor polymers are made from at least t~o monomers, with at least one of the monomers coming from each of the two groups described below.
The first group is fluorinated vinyl compounds such as vinyl fluoxide, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, per~luoro(alkyl vinyl ether), tetrafluoroethylene and mix-tures thereof. In the case of copolymers which will be used in electolysis of brine, the precursor vinyl monomer desir-alby will not contain hydrogen.
The second group is the sulfonyl-containing monomers containing the precursor group -CF-CF2-SO2A, Rf wherein Rf and A are as defined above. ~dditional examples can be represented by the general formulaC~2=C~-Tk-CF2SO2F
wherein T is a bi~unctional perfluorinatedradical com-prising 1 to 8 carbon atoms, and k is 0 or 1. The particu-lar ch~mical content or structure of the radical T is not critical, but it must have a fluorine atom a~tached to the carbon atom to which the -CF2SO2F ~roup is attached. Other atoms connec~ed to this carbon can include fluorine,chlorine, or hydrogen although generally hydrogen will be excluded in usc of the copolymer for ion exchange in a chlor-al~licell.
The T radical of the ~ormula above can be eitl-cx branclled or unbranchcd, i.e., straight-chain, and can have onc or 1 3 6256~
more cthcrlinkages.. It is pxce~ed ~latthe~Lnyl radical in this group o~ sul~onyl fluoride containing comonomexs be joined to th~ T group through an ether linkage, i.e., that the comonomer be of the formula CF2=CF-O-T-CF2-S02F.
Illustrative of such sulfonyl ~luoride containing comonomers are CF2=cFocF2cF2~o2~
CF2 =GI;~oCF2nFoCF2C3?2so2F~
. CF3 CF2 ~,FOC~21FOC~2IFocF2cF2so2r, CF2=cFcF2cF~so2F~ and CF2=cFocF2lFOc~zCF2SO2F

~2 p bF3. ' Thc mo~t preferred sul~onyl fluorid~ containin~ comonon~er is perfluoro(3,6-dioxa~ methyl-7-octen~sul~onyl rluoride), CF2=cFocF2cFocF2~F2so2F .

ne ~ on~l-con~inin~ mollo~crs arc cli5c105~1 in 3~lch refcrences 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.
The prc~crred copolymers utilized as the precursor are pcrfluorocarbon although others can be utilizcd as long ~o as the T ~rouL~ has a ~luorine atom attach~d to thc car~on - 15 ~

1 ~ 6~
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 2~ 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 polymerization 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 is, by the polymerization of a mixture of the major monomer therein, such as tetrafluoro-ethylene, and a fluorinated ethylene containing a sulfonyl fluoride group in the presence of a free radical initiatGr, preferably a perfluorocarbon peroxide or azo 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, liquid, 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 techniques for preParing the co~olymer 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 ~ 1 625~5 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 dis~ersion, 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-Ml groups are Rf n made from the known precursor fluorinated polymers which contain pendant side chains containing -CF-CF2-SO2X groups Rf R8 by reduction with a compound having the formula H2NN~ g wherein R8 is H or Cl to C8 alkyl radical, and R9 is H or a Cl to C8 alkyl radical, preferably H. The preferred 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 found 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 advantageously 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 NaO~. Use of a hydroxide or tertiary amine is preferred because the sulfinic acid ~ ~ ~25~5 product and by-product hydrogen fluoride can form salts with the hydrazine 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 ~roups, or an alkali metal or alkaline 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 wlth 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. Followin~ reduction by a hydrazlne, 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 ~ 1 ~2~
form is desired for the particular oxidi~ing 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 often it will be in the form of a film or membrane when subjected to these reactions.
The polymers of the invention which possess pen-dant side chains which contain carboxylic groups and pendant side chains which contain sulfonyl groups can also be made by copolymerizing a mixture of the appropriate monomers.
The carboxyl-containing monomer is one or more compounds from a third group represented by the formula CF2=cF~ocF2cFtmocF-cooR
Y Rf wherein Rf is F, Cl, or a Cl to C10 perfluoroalkyl radical, Rl is lower alkyl or M(l~, 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 m is o or 6 ~

The novel compounds CF2=cFocF2cFocF2coo(~H3 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=cFtocF2cFtocFcF2so2F
~ Rf wherein Rf, m and Y are as define~ above, by (1) saturating the terminal vinyl group with 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 (4) dechlorinatlon with zinc dust to regenerate the terminal CF2-CF- group. It is also possible to replace steps (2) and (3) of this sequence by the steps (a) reduc-tion of the -OCFCF2SO2F group to a sulfinic acid Rf -OCFCF2SO2H or alkali metal or alkaline earth metal salt ,j .

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 Rf thereof are formed as is more ~ully described hereinabove, and (c) esterification to -OCFCOOCH3 by known methods.
Rf The carboxyl-containing monomer of the third group is copolymerized with fluorinated vinyl compounds , .

1 ~ 62565 from each of the firs~ and second groups of comonomersdefined hereinabove, and under non-aqueous polymerization techniques also defined hereinabove.
Yet another method for preDaring copolymers of the invention which possess pendant side chains which contain carboxylic groups and pendant side chains which contain sulfonyl grouPs is by treating a fluorinated polymer which has pendant side chains which contain -CFCF2SO2R groups wherein R2 is ~1' M is H or alkali Rf n metal or alkaline earth metal, and n is the valence of M, with a mixture of fluorine and oxygen, whereby -CFCOF groups are formed. The -CFCOF groups can then be Rf Rf hydrolyzed to ion exchange groups -CFCOORl wherein Rl is Rf Ml Hydrolysis of -CF-COF groups to -CF-COOH groups (n Rf Rf occurs so readily that the product isolated from the ~luorine/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%t at least in regard to the surface layer of the article so treated, depending on the amount of treating reagents used, duration of treatmentl 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 5~

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 ~cx2 cx~ ~ CF2 t ¦ ,CF2 ~ CF - Z
s ¦ CF - Rf ¦ SO2 wherein Rf, p, q, r, s, X, and Z are as defined hereinabove, and R2 is OM where M and n are as defined hereinabove.
(n) 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 group~
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 o~ the initial polymer, copolymer of the invention c~taining both 1 ~ 62~5 carboxylic and sulfonyl groups meeting 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 ~luorine 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 hydroly~ed 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 sulfonic 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 ha~e only -O-CFCF2SO3H groups (or salts thereof), and the surface Rf 5~5 layer or layers will have both -O-CFOOH and -O-CFCF2S03H
Rf Rf groups (or salts thereof).
The polymers of the present invention can be in the form of films and membranes.
When the polymers of the ~nvention are in the form of a film, desirable thicknesses of the order of 0.002 to .02 inch are oridinarily used. Excessive film thicknesses will aid in obtaining higher strength, but with the result-ing deficiency of increased electrical resistance.
The term "membrane" refers to non-porous struc-tures for separating compartments cf 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 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 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 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 compet'~ng reactions which produce different products.
For example, when iOO~ hydrazine is used as the reagent in the reduction reaction, conversion to sulfinic functional group, and eventualiy to carboxylic functional group can be ~ ~ ~25~5 quite high., of the order of 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 of others to sulfonic acid salt form; because the sulfonic salt form is not affected during the oxidation step, the ultimate result is a combination of carboxylic and sulfonyl groups in rela-tive amount which varies with the xelative 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 amounts of the original sulfonic groups, while - other oxidizing agents such as hypoch.lorite 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 si.de 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 combinati.on 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)mQ, wherein Q is H, NH4, cation of an alkali ....

q ~ 6256~
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 partïculaxly sodium or potassium. The technique whereby sulfonyl groups of the precursor polymer can be converted to N-monosubstituted sulfonamide groups and salts thereof are as set forth in ~.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 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 exchange layer. The film and membrane of the present inven-tion 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 cell, polymers which contain ~0-95~ pendant side chains containing carboxylic groups and S-60~ pendant side chains containing sulfonyl groups provide excellent current efficiency. An equally important criterion in a chlor-alkali cell, however, is the amount of power .

~ J ~5~5 required for each unit of chlorine and caustic. It is considered that the polymers of the type disclosed herein permit a proper combination of operating conditions to realize an excellent and unexpected reduction in power~
Since the power requirement (which may be expressed in watt-hours) 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 cell voltages. Additionally, a polymer with an inherent high current efficiency allows a proper combina-tion of parameters as in fa~rication into the film and/or operation of the electrolytic cell to realize the potential theoretical reduction in power. Illustratively, the poly-mer can be fabricated at a lower equivalent weight which may result in some loss of current efficiency which is more than compensated by a reduction in voltage. Polymers 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 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 chains in carboxylic form and pendant side chains in sulfonyl form, and an interior layer , S,'!.~

1 1 62S~S
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, 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 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 fa~e either the anode or cathode in an electrolysis cell, and in the case of a chloralkali cell it will ordinarily face the cathode.
~nder~most circumstances, layered structures will be such that the layer of carboxylic polymer will be about 1/4 to 5 mils thick, the base laver 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 contemplated.

. ~ ~

6 ~
Illustratively, permeation selection of cations is direetly encompassed. One method of determination of cation exehange properties is a measurement of permselectivity with separa-tion of the same eations 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.
The polymers which contain sulfinic groups are useful as intermediates to polymers, films and membranes which contain carboxylic groups.
A 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 ~etherlands patent application 72.17598, published June 29, 1973. In a similar fashion as these teaehings, a eonventional chloralkali cell is employed with the critical distinetion of the type of polymeric film used to separate the anode and cathode portions of the cell. While the description of said German and Duteh publications is direeted to use in a ehloralkali cell, it is within the seope of the present diselosure to produce alkali or alkaline earth metal hydroxides and halogen sueh as chlorine from a solution of the alkali or alkali earth metal salt. While efficieneies in eurrent and power eonsumption differ, the operating eonditions of the eell are similar to those disclosed for sodium chloride.
An outstanding advantage has been found in terms of eurrent efficiency in a chlor-alkali cell with ~he fluorinated polymers of the type disclosed herein with ~16'2~65 pendant groups which contaln carboxylic groups and pendant groups which contain sulfonyl groups.
To further illustrate the innovative aspects 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 oxy~en. 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 sulfuric 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 70~C
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 1 ~ 62565 fluoride) 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 entixe thickness of the film. 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 rinsed with water and then heated for 16 hours to 130~C. in an atmosphere of oxygen.
IR analysis at this point indicated the formation of -CF2CO2H functional groupsl the presence of -CF2SO3H groups, and the complete absence of -SO2F of the starting material as well as -SO2R grou~s of the sul~inate 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 perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having arl equivalent weight 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, 2 gm ammonium vanadate, 1 gm vanadyl sulfate 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 minutes to g0C in a solution containing 13% potassium hydroxide ana 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.
Example 4 A 4-mil film of a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4 methyl 7-octenesulfonyl fluoride) having an equivalent weight of ].100 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 indicated 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 1 1 ~2565 solution of sodium hydroxide. Aqueous sodium chloride was electrolyzed at a current density of 2.0 asi to produce 33%
sodium hydroxide at a current efficiency of 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 weight 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.
~ he 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 film was again washed with water. Staining of a cross-section with Sevron~ Brilliant ~ed 4G indicated a depth of reaction of 0.5 mils.
The unreacted SO2F groups were hydrolyzed by heating for 30 minutes to 90~C. 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% NaO~ 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 11 1 ~256~
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 completed by 2 hours immersion in a solu-tion of 2% CrO3 and 3~ H2SO4 in 75~ acetic acid (balance water) at 50C.
10 r 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 of 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 hydro~ide was being produced at a concentration of about 32.5~ at a current efficiency of 89~ 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 "Teflon"
fabric imbedded therein, and having one surface layer of about 1 mil depth which had been hydrolyæed 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 ~-methy~morpholine in 35 ml dimethyl-sulfoxi-de 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 staining with Sevron~ Brilliant Red 4G at this point indicated that reaction with hydrazine had occurred to a depth of 0.6 mils.
The sample was then washed with 5~ sulfuric acid and exposed to air for 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 of 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 of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) having an equivalent weight of 1100 was folded and sealed to a bag, except for a small opening to permit the intro-duction of reagents. A mixture of 250 ml dimethylsulfoxide, 100 ml N-methylmorpholine and 90 ml hydrazine hydrate was poured into the bag and permitted to react for 7 minutes at room temperature. The bag was then emptied, rinsed with water and exposed or 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 solution of 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 l hour with a solution containing 1 ~ 62~

S% acetic acid, 2% ~2S04 and 2~ KHS04 in water.
The film was then washed with water and vacuum -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 surface --facing the catholyte. Sodium hydroxide was produced at a -concentration of 31~ by weight 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-~,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 blanketed with nitrogen, 3276.1 g of per-fluoro~2-(2-fluorosulfonylethoxy)-propyl vinyl ether] added and chloxine bubbled into the flask while irradiating with a sunlamp until no more chlorine was absorbed. Distillation ¦~
20 yielded 2533.8 g ~66.7%) of perfluoro[2-(2-fluorosulfonyl-ethoxy)-propyl-1,2-dichloxoethyl ether], bp 165C.
To a quartz tube (l-inch outside diameter a~d 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 combined distillation of a number '.

I t 1 ~ 62S~5 of similar runs yielded methyl perfluoro-7,8-dichloro-4-methyl-3,6-dioxaoctanoate, bp 167C., whose structure was confirmed by infrared and N~R spectroscopy.
A mixture of lO g crude methyl perfluoro-7,8-dichloro-4-methyl-3,6-dioxaoctanoate, 5 g zinc dust, 50 ml anhydrous diethylene glycol dimethyl ether and 0.1 g iodine was heated 140~C., and then distille~. 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 NMR spectrum.
Exam~le 10 -A piece of 7-mil film of a copolymer of tetra-fluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesul-fonyl fluoride) havin~ an equivalent weight of 1200, and containing one surface layer of approximately l-mil depth which had heen converted to the corresponding sodium salt of the sulfonic acid, was heated with 15 psi (absolute] f 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 sulfonyl 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.

~ 37 -~,-~ J 62565 Example 11 A piece o~ 7-mil fllm of a copolymer of tetra-fluoroethylene and ~erfluoro(3,6-dioxa-4-methyl-7-octenesul-fonyl fluoride) having an equivalent weight of 1100, a~d 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 dimethylsulEoxide, water and potassium hydroxide for 1 hour. After washing, the film was mounted in a chloralkali cell, and a~ueous sodium chloride electrolyzed at a current density of 2.0 asi to give 33.0-38.6% NaOH at current efficiencies of 75.8-81.7~ at a cell voltage of 3.9-4.2 volts.
Exam~le 12 Conversion of CClF2CClF2OCF2CF(CF3)OCF2CF2SO2F 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 filterea. 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 '':

1 ~ $2~
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 Hq.
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)OCF2C~2SO2F) 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 (5)

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

1. A compound of the formula CF2 = wherein m is 0, 1 or 2 and R1 is lower alkyl or M?
where M is H, alkali metal or alkaline earth metal, and n is the valence of M.

2. The compound of Claim 1 wherein m is 1.

3. The compound of Claim 2 wherein R1 is CH3.

4. The compound of Claim 1 wherein m is 0.

5. The compound of Claim 4 wherein R1 is CH3.