GB2053902A - Novel Fluorinated Compounds - Google Patents

Abstract

Novel fluorinated derivatives of formula FSO2(CF2)nY wherein Y is -COY' or -CN [Y' is H, Hal, -NH2, -OM (M is H, a metal ammonium) or -OR<1> (R<1> is C1-10 alkyl or aryl]; and n is 2 to 4 and of formula <IMAGE> wherein n is 2 to 4 and p is 0 to 50 are disclosed. Also a novel fluorinated copolymer is prepared by copolymerization of a fluorinated olefin with a novel sulfur containing fluorinated vinylether of the formula: <IMAGE> wherein k is 0 or 1 and l is an integer of 3 to 5, which is prepared from starting materials which are also novel. Said copolymer is useful for preparation of a fluorinated cation exchange membrane having carboxylic acid groups and/or sulfonic acid groups which can be used advantageously in electrolysis of an aqueous alkali metal halide solution with improved electrolysis performance.

Description

1 GB 2 053 902 A 1

SPECIFICATION Novel Fluorinated Copolymer and Preparation Thereof

This invention relates to a novel fluorinated copolymer useful as a starting material for production of a fluorinated cation exchange membrane or a fluorinated cation exchange resin having sulfornic acid groups and/or carboxylic acid groups and also to a process for preparing the same.

In recent years, there is an increasing trend for development of new chemical processes using fluorinated cation exchange membranes or resins excellent in chemical resistance and heat resistance. As a typical example of such a trend, the ion-exchange membrane process has recently attracted great attention in the chloro-alkali industry wherein caustic soda and chlorine are produced by electrolysis of sodium chloride, because it is more advantageous in various aspects such as prevention of environmental pollution and economical saving of energy than the mercury process and the diaphragm process of prior art and also because it can produce caustic soda having substantially the same quality as that produced by the mercury process.

The greatest factor which controls economy of the ion-exchange membrane process is the characteristic of the cdtion exchange membrane employed. It is necessary for the cation exchange 15 membrane to satisfy the requirements as set forth below.

(1) To have a high current efficiency and a low electric resistance. In order to have a high current efficiency, the membrane is required to have a sufficiently high ion-exchange capacity and low water content, thus giving a high concentration of fixed ions in the membrane. On the other hand, to the effect of lower electric resistance, higher water content is rather more advantageous. Since the water 20 content will vary depending on the types of ion-exchange groups, the ion-exchange capacity and the concentration of external solutions, it is necessary to select the optimum combination of these factors.

(2) To be resistant to chlorine and alkali at higher temperatures for a long time. A cation exchange membrane comprising a fluorinated polymer can be sufficiently resistant generally under the aforesaid atmosphere, but some membranes may be insufficient in chemical stability depending on the ionexchange groups cont0ined therein. Accordingly, it is important to select suitable ion-exchange groups.

(3) To be durable f6r a long time under various stresses working in highly concentrated alkali under the conditions of high temperature and high current density such as a stress of swelling and shrinking, a stress accompanied by vigorous migration of substances to effect peel-off of layers and a stress by vibration of the membrane accompanied with gas generation to cause bending cracks.

Generally speaking, the physical strength of the membrane is different depending on the physical structure of the membrane, the polymeric composition, the ion-exchange capacity and the types of ionexchange groups. Therefore, it is necessary to realize the optimum selection of these factors. (4) To be easy of production steps and low in cost. 35 In the prior art, there have been proposed several fluorinated cation exchange membranes for use 35 in electrolysis of an aqueous alkali metal halide solution. For example, there is known a fluorinated cation exchange membrane having pendant sulfonic acid groups prepared by hydrolysis of a copolymer comprising tetrafluoroethylene and perfluoro-3, 6-dioxa-4-methyl-7-octene sulfonylfluoride. Such a fluorinated cation exchange membrane containing only sulfonic acid groups, however, is liable to permit permeation of hydroxyl ions migrated and diffused from the cathode compartment therethrough due to the high water content afforded by the sulfonic acid groups. For this reason, such a membrane is disadvantageously low in current efficiency. In particular, when electrolysis is conducted, for example, by recovering a highly concentrated caustic soda solution of 20% or higher, the current efficiency is extremely low to a great economical disadvantage as compared with electrolysis by the mercury process or the diaphragm process of prior art.

For improvement of such a drawback of low current efficiency, the ionexchange capacity of sulfonic acid groups may be lowered to, for example, 0.7 milliequivalent or lower per one gram of the H-form dry resin, whereby water content in the membrane can be decreased to make the fixed ion concentration in the membrane higher than the membrane with higher ionexchange capacity. As the result, the current efficiency at the time of electrolysis can slightly be prevented from being lowered. 50 For example, when electrolysis of sodium chloride is performed while recovering caustic soda of 20% concentration, the current efficiency can be improved to about 80%. However, improvement of current efficiency by reduction in ion-exchange capacity of the membrane will cause noticeable increase in electric resistance of the membrane, whereby no economical electrolysis is possible. Moreover, at any higher value of the electric resistance of the membrane, it is very difficult to prepare a commercially 55 applicable sulfonic acid type fluorinated cation exchange membrane improved in current efficiency to about 90%.

In the field of ion-exchange membranes, it is strongly desired to develop a membrane which exhibits high current efficiency and low electric resistance under more severe conditions, has a longer life and can be produced at low cost. The present inventors have made efforts to develop such a membrane and consequently found that the above object can be attained by use of a novel fluorinated vinyl ether compound which is derived from starting materials having specific structure. The present invention has been accomplished based on such a finding.

2 GB 2 053 902 A 2 The first object of the present invention is to provide a fluorinated carboxylic acid or its derivative represented by the formula:

FSO,(CF,)nY wherein Y stands for -COV or -CN[Y' is a halogen, hydrogen, -NH2, -OM(M is hydrogen, a metal or ammonium group), -OR 3 (R 3 is an alkyl having 1 to 10 carbon atoms or an aryi)l; and n stands for 5 an integer of 2 to 4, and a process for producing the same.

In the prior art, as a fluorinated compound having in combination carboxylic acid derivative groups and sulfonic acid groups or groups convertible thereto in the same molecule such as said fluorinated carboxylic acid derivative, there is known only the compound FSO,CF,COF or the compound FSO,CFCFO 1 CF3 as in U.S. Patent 3,301,893. There is no suggestion about a compound comprising a fluorinated alkylene group having 2 to 4 carbon atoms -(- CF27--),,- between the carboxylic acid derivative groups and sulfonic acid groups or the groups convertible thereto such as the compound according to the present 15 invention.

The fluorinated carboxylic acid or its derivative according to the present invention can be prepared by converting the compound obtained by a process comprising the following step (A), (B) or (C) according to the reaction scheme (3), (4), (5) or (6), optionally in combination with various reactions such as acid treatment, hydrolysis treatment or halogenation treatment, into carboxylic acid derivative 20 and sulfonic acid derivative:

(A) A method comprising the step to react tetrafluoroethylene with a carbonic acid ester having 3 to 20 carbon atoms in the presence of a mercaptide represented by the formula R'SM'(R' is an alkyl having 1 to 10 carbon atoms, an aryl or a perfluoroalkyl having 1 to 10 carbon atoms; M' is an metal, ammonium group or a primary to quaternary alkylammonium group):

R 40 (3) RISMI+CI7j=CIF,+ C=O->WSCF2C172 COR 4 25 R 50 U or WSCF2CF2CCF2CF2SW 11 U (wherein R' and R' represent alkyl or aryl, and M' is the same as defined above); (B) A method comprising the step to react tetrafluoroethylene with a compound of the formula:

K2SO2 W is a halogen or an alkoxyl having 1 to 5 carbon atoms) in the presence of an alkali cyanide: 30 (4) (wherein A' is the same as defined above); NaCN+CFi=CF2+A'2S027-NCCF2CF2SO2A' (C) A method comprising the step to react tetrafluoroethylene with a compound of the formula:

Z'S02F or Z'3CSO2F (Z' is a halogen except for F) in the presence of a free radical initiator:

free radical initiator (5) Z'S021=+CF,=CF2 W(WISO2F 35 free radical (6) Z1 3CS021=+CF2=CF2 ' initiator Zt3C(CF2)2SO2F or Z1 PWISOJ In the fluorinated carboxylic acid derivative of the present invention FS02(CF2ny (Y and n are the same as defined above), n may preferably be 2 when considering easiness in preparation and the 40 1 3 GB 2 053 902 A 3 molecular weight of the fluorinated vinyl monomer prepared from said derivative. A compound wherein Y is -COF is also desirable from standpoint of usefulness as starting material for synthesis of a fluorinated vinyl compound. When Y is another carboxylic acid derivative, such a compound may be converted to a compound having the group Y=-COF.

Each of the methods (A), (B) and (C) is hereinafter described in further detail.

1. Method (A) Examples of mercaptide to be used in the method (A) are derivatives of methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, amy] mercaptan, hexyl mercaptan, phenyl mercaptan, benzy] mercaptan, toluy] mercaptan, perfluoromethyl mercaptan, perfluoroethyl mercaptan, perfluoropropyl mercaptan, etc. in the form of sodium salts, potassium salts, cesium salts, ammonium 10 salts, and primary to quaternary alkylammonium salts, preferably an alkyl mercaptan, especially having 1 to 5 carbon atoms, namely methyl-, ethyl-, propyi-, buty]- and amyi- mercaptan in the form of sodium salts or potassium salts.

The carbonic acid ester may be exemplified by dimethyl- diethyl-, dipropyi-, dibutyi-, diphenyi-, or methylethyl-carbonate. Preferably, dimethyl carbonate and diethyl carbonate may be used.

The mercaptide and the carbonic acid ester are usually mixed in an inert medium. But no inert medium is necessarily required when said ester is liquid under the reaction conditions. Typical examples of suitable inert medium are diethyl ether, tetra hydrofu ran, dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, benzene and cyclohexane, having no active hydrogen and being capable of dissolving the carbonic acid ester.

The carbonic acid ester is used in an amount of 0. 1 to 10 equivalents, preferably 0.5 to 5 equivalents, of the mercaptide.

Tetrafluoroethylene is usually employed in gaseous state and may be fed into the reaction system under any desired pressure, irrespective of whether it may be pressurized, normal or reduced.

Tetrafluoroethylene may be added in an amount of 0.1 to 5 equivalents, preferably 0.4 to 3 equivalents 25 of the memaptide.

The reaction is ca'tried out usually at not higher than 1 OOOC, preferably in the range from 80 to OIC, until the pressure of tetrafluoroethylene is substantially constant under the reaction conditions employed. Formation of ketone leads to substantial decrease in the reaction yield based on the mercaptide. For this reason, it is preferred to use a lower temperature in order to suppress formation of 30 the ketone in the reaction scheme (3). The reaction is carried out under substantially anhydrous conditions.

After completion of the reaction, the reaction system is made acidic by adding an acid. In this case, such a mineral acid as hydrochloric acid, sulfuric acid or phosphoric acid is usually used, sulfuric acid being preferred. The amount of a mineral acid should be at least equivalent of the mercaptide 35 initially employed.

In the above reaction procedure, there may also be used in place of the carbonic acid ester a N,N dialkyl formamide having 3 to 7 carbon atoms, whereby a fluorinated aldehyde is obtained.

Alternatively, in some cases, there may also be employed carbonic acid gas in place of the carbonic acid ester.

Isolation of ester, ketone or aldehyde which is the fluorinated carboxylic acid derivative may be performed by conventional technique of separation such as phase separation, distillation or others.

Said fluorinated carboxylic acid derivative of ester, ketone or aldehyde may be converted to various carboxylic acid derivatives according to suitable organic reaction procedures. For example, ester and ketone may be hydrolyzed with an alkali to give a carboxylic acid salt, which carboxylic acid salt may in 45 turn be treated with a mineral acid to give a carboxylic acid. Further, the above carboxylic acid or salt thereof may be reacted with a chlorinating agent such as phosphorus pentachloride, thionyl chloride, etc. to obtain an acid chloride, or alternatively with sulfur tetrafluoride to obtain an acid fluoride. Also, according to the well known reaction to treat an acid chloride with sodium fluoride or potassium fluoride, an acid fluoride can be prepared. An acid fluoride is most useful from standpoint of the starting 50 material for synthesis of a fluorinated vinyl compound according to the reaction scheme (7) as shown below:

(7) (I) FSO (CF) COF + (P' + 1)W - CP 2 2 n 1,, 0 / 2 W 3 PSO 2 (CP 2)n+l O(CFCF 2 0) p CFCOF 1 1 (I1) W 3 U2, 3 , --, Pso 2 (CF 2)n+10 (CFCF 20)p'CF=W 2 1 55 ULL j Uk, 3 wherein n is the same as defined above, and p' is 0 or 1.

4 GB 2 053 902 A 4_ In the above fluorinated carboxylic acid derivative, the sulfide group present on the terminal end opposite to that of carboxylic acid derivative group may also be converted to various derivatives according to suitable organic reaction procedures. For example, it may be converted by treatment with chlorine to sulphenylchlorlde group or sulfonylch lo ride group, or by oxidation treatment to sulfone group. Further, these groups may be subjected to hydrolysis treatment with an alkali to be converted to sulfonic acid group salts, which may be treated with phosphorous pentachloride to be converted to sulfonyl chloride groups. By treatment with sulfur tetrafluoride, such groups may also be converted to sulfonylfluoride groups. Alternatively, according to the well known reactions to treat sulfonylchloride groups with sodium fluoride or potassium fluoride, su lfonylfl uo ride groups can be obtained. Conversion to such various derivative groups does not interfere with the reaction according to the scheme (7), 10 insofar as such groups have no active hydrogen.

111. Method (B) The alkali metal cyanide to be used in the method (B) may include cyanides of lithium, sodium, potassium, cesium, etc. Among then, cyanides of sodium and potassium may preferably be used.

Examples of the compound of the formula A'2SO, are sulfuryl fluoride, sulfuryl chloride, sulfuryl 15 bromide, sulfuryl chlorofluoride, sulfuryl bromofluoride, dimethyl sulfate, diethyl sulfate, dibutyl sulfate, diamyl sulfate, and the like. In some cases, there may also be used sulfur dioxide.

The alkali metal cyanide is used usually as a dispersion in an inert medium. When the compound A12S02 (A' is the same as defined above) is a liquid under the reaction conditions, no such inert medium is necessarily required to be used.

As suitable inert medium, there may be mentioned solvents having no active hydrogen such as diethyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, benzene, cyclohexane, etc. Said inert medium may desirably be capable of dissolving A'2SO2.

The amount of A2SO2 IS used in an amount of 0.1 to 10 equivalents, preferably 0.5 to 5 equivalents of the alkali metal cyanide.

Depending on the A'2SO, employed and the properties thereof, A2SO2 is previously charged in the reaction system to be mixed with the alkali metal cyanide, or fed into the reaction system simultaneously with tetrafluoroethylene, or fed into the reaction system previously mixed with tetrafluoroethylene. 30 Tetrafluoroethylene is used usually under gaseous state and may be fed into the reaction system 30 under any desired pressure, whether it may be pressurized, reduced or normal. Tetrafluoroethylene is added in an amount of 0. 1 to 5 equivalents, preferably 0.4 to 3 equivalents of the alkali metal cyanide. The reaction is carried out at not higher than 25WC, preferably at not higher than 1 001C, until the pressure of tetrafluoroethylene is substantially constant under the reaction conditions employed. 35 The reaction is conducted under substantially anhydrous conditions.

Separation of fluorinated nitrile may be performed according to such procedures as phase separation or distillation. Similarly as described in the method (A), said fluorinated nitrile may be converted to various carboxylic acid derivatives or suifonic acid derivatives, especially sulfonylfluoride group, according to suitable organic reaction procedures, whereby it is most preferred that Y should be 40 -COF.

III Method (C) The compound represented by the formula ZfS02F or Z3CS02F (Z' is the same as defined above) to be used in the method (C) may be exemplified by sulfuryl chlorofluoride, sulfuryl bromofluoride, trichloromethane sulfonylfluoride, tribromomethane sulfonylfluoride, and the like. Among them, sulfuryl 45 chlorofluoride and trichloromethane sulfonylfluoride are preferred.

As the free radical initiator, there may be employed most of those conventionally used in the field of organic chemical reactions. For example, it is possible to use organic peroxides such as benzoyl peroxide, di-t-butyl peroxide, perfluoroacetyl peroxide, di-t-amyl peroxide, etc. and azo-bis type compounds such as azobisisobutyronitrile, azobisisovaleronitrile, azobisnitrile, etc.

In the present invention, instead of permitting the free radical initiator to be present in the reaction, ultra-violet may be irradiated. Alternatively, it is also possible to effect irradiation of ultra violet ray in the presence of a free-radical initiator.

Use of a solvent is not particularly limited, but there may be employed any solvent which is stable chemically to the free radical initiator or ultra-violet ray. Particularly, 1,1,2-trichloro-1,2,2 trifluoroethane and cyclohexane may preferably be ued.

Tetrafluoroethylene is used in at least stoichiometric amount relative to Z'SO,F or Z'3CSO,F.

The amount of the free radical initiator used is in the range from 0.00 1 % to 10% based on Z'S0,17 or Z',CS0217.

The reaction temperature may suitably be determined in view of the halflife period of the free 60 radical initiator or other factors, usually ranging from -1 OOC to 2500C, preferably from OOC to 1 500C.

After completion of the reaction, the intermediates formed according to the reaction scheme (5) or (6) are isolated by phase separation or distillation from the reaction mixture, if desired. Said GB 2 053 902 A intermediates may be subjected to acid treatment using a mineral acid such as conc. sulfuric acid, sulfuric anhydride or fuming nitric acid to be converted to HOOC(CF2)3SO2F or HOOC(CF2)4SO,F.

The above carboxylic acid may be isolated from the reaction mixture by isolation procedure such as extraction, phase separation or distillation. Similarly as described in the method (A), said carboxylic acid may be converted to various carboxylic acid derivatives according to suitable organic chemical reaction procedures. It is particularly preferred that Y should be -COF.

According to another preparation method, it is also possible to carry out reaction betweena disulfide and tetrafluoroethylene in the presence of a free radical initiator to give an intermediate having sulfide groups at both terminal ends of the molecule, which intermediate is then subjected to chlorine treatment to provide a compound having sulfide group at one terminal end and sulfonyl group 10 at the other terminal end. By treatment of said compound with hydroiodic acid, there may also prepared a compound having the sulfide group and the carboxylic acid group. By converting the sulfide group of said compound to sulfonyl-fluoride group, the compound of the present invention is obtained.

Alternatively, a compound having sulpheny1chloride group and sulphenyliodide group may be allowed to react with tetrafluoroethylene in the presence of a free radical initiator, followed by treatment of the resulfant intermediate with an acid such as conc. sulfuric acid, sulfuric anhydride or fuming nitric acid, to provide a compound having both sulfide group and carboxylic acid group. By conversion of the sulfide group to sulfonylfluoride group, the compound of the present invention is obtained. 20 The compound of the present invention, especially an acid fluoride is very useful for synthesis of a 20 fluorinated vinylether compound having terminal groups convertible to sulfonic acid groups as shown in the reaction scheme (7). The above compound is also useful as starting materials for production of various materials such as surfactants, fiber treatment agents, lubricants, agricultural chemicals, etc. The fluorinated carboxylic acid derivative of the present invention can also very advantageously be produced, since there is used no such dangerous reaction as the addition reaction between tetrafluoroethylene and S03 which will occur in production of FS02CF2COF or no such toxic compound as a cyclic sultone intermediate.

The second object of the present invention is to provide a novel fluorinated acid fluoride represented by the formula:

CF3 CF3 1 1 FSO,(CF2n+l-(-U'""-16-U;U- 30 wherein n is an integer of 2 to 4, p is an integer of 0 to 50, and a process for producing said fluorinated acid fluoride compound which comprises reacting a novel compound represented by the formula:

FS02(CF2)nCOF ion.

wherein n is the same as defined above with hexafluoropropylene oxide, in the presence of a fluoride As a fluorinated compound having in combination an acid fluoride group and a functional group convertible to suifonic acid group in the same molecule such as said fluorinated acid fluoride compound, there is known in the prior art only a fluorinated acid fluoride of the following formula:

CF3 CF3 1 1 FS02(CF2) i-27_)q wherein V=2, q'=-50, as disclosed in Japanese published examined patent application No. 40 1664/1967. No such compound of the present invention wherein l' is 3 to 5 is suggested at all in the prior art.

The fluorinated acid fluoride of the present invention can be produced according to the following reaction scheme:

- FSO (CF) COF + (p + 1)W CFCF 2 2 n 3\1 2 0 W W 1 3 1 3 FSO 2 (CF 2)n+l (OCFCF 2) p OCFCOF 45 wherein n and p are the same as defined above.

The reaction between the compound of the formed FSO,(CF2)rCOF (wherein n is the same as defined above) and hexapropylene oxide may preferably be conducted in the presence of a fluoride ion as catalyst. This can easily be done by use of a suitable fluoride, including alkali metal fluorides such as cesium fluoride, potassium fluoride, etc.; silver fluoride; ammonium fluoride; Cl-C4 tetraalkyl 50 ammonium fluoride such as tetramethyl ammonium fluoride, tetraethyl ammonium fluoride and tetrabutyl ammonium fluoride; and so on.

6 GB 2 053 902 A 6 The fluoride catalyst is usually used together with an inert liquid diluent, preferably an organic liquid, which can dissolve at least 0.001 % of the fluoride selected. The fluoride catalyst may be used in an amount of about 0.0 1 to about 2 mole equivalent per one mole of the compound represented by the formula FS02(CF),,,COF wherein n is the same as defined above. Examples of suitable diluents are ' polyethers such as ethyleneglycol dimethylether, dietheyleneglycol dimethylether, tetraethyleneglycol dimethylether, etc. and nitriles such as acetonitrile, proplonitrile, etc. The reaction is slightly exothermic and therefore there should be provided a means for dissipating the reaction heat.

The reaction temperature may be in the range from about -501C to about 2000C, preferably from about -201C to about 1 500C. The pressure is not a critical parameter and may either be lower than or not lower than the atmospheric pressure. The reaction time may usually be from 10 minutes to 10 100 hours. The applicable molar ratio of hexapropylene oxide to FS02(CF2),,COF is from about 1/20 to about 100/1.

When the compound CF3 CF3 1 1 FS02(1-2) n+l tU-;;F2) PU(-"-(;Ul- 15has a low p value, for example, when pis 0 or 1, the relative proportion of FS02(CF2),,1COF is increased, and lower pressure and higher temperature are preferred to be selected. On the other hand, when a product with a high p value is desired to be prepared, it is preferred to increase the relative proportion of hexapropylene oxide and select higher pressure and lower temperature. In the fluorinated acid fluoride of the present invention, CF3 CF3 1 1 FSC)2l;h2)n+l(Ul;t-U[-,)pUUI-'-;UF 20 wherein n and p are the same as defined above, a compound wherein n=2 is preferred from standpoint of easiness in preparation.

On the other hand, a cation exchange membrane prepared from a copolymer of said fluorinated vinyl ether compound and tetrafluoroethylene may desirably have an ion-exchange capacity as large as possible. From this standpoint, said fluorinated vinyl ether compound may preferably have a molecular 25 weight as small as possible. Accordingly, it is preferred that the value of p may be 0 or 1, most preferably 0.

The compound represented by the formula:

CF3 CF3 1 11 FS02(CF2),,+,(OCFCF2)p0CFCOF wherein n and p are the same as defined above is useful as intermediate for preparation of a novel 30 fluorinated vinylether compound having functional groups convertible to sulfonic acid groups. Said compound is also useful as starting material for surfactants, fiber treatment agents, lubricants, agricultural chemicals, etc.

The third object of the present invention is to provide a novel fluorinated vinylether compound represented by the formula:

FSO,(CF2),+,-(-OCFCF27-),,r--OCF=CF, 1 Ut-3 wherein n is an integer of 2 to 4 and p' is an integer of 0 to 5, and a process for preparing the same.

As a fluorinated vinylether compound having functional groups converti61e to sulfonic acid groups such as said fluorinated vinylether compound, there is known in the prior art only the class of 40 compounds:

FSO,(CF2),,--(-OCFCF2-),,-OCF=CF2 1 1 wherein P=2 and m=0 to 2. Nothing is suggested in the prior art about the compounds of the present invention wherein l' is 3 to 5.

The fluorinated vinylether compound of the present invention can be prepared according to the 45 following reaction schemes:

5.

1 1 7 GB 2 053 902 A 7 1 F502 (CF 2) n COF + (P, + 1)cP 3-CF -/ CP 2_ FSO 2 (CF 2)n+l (OCFCF 2)p OWCOF 111 0 1 i C11, 3 CF 3 A 11 PSO 2 (CP 2)n+l (OCFCF 2)p OWCOW PSO 2(CF2)n+l (OCFCF2)p OCF=CF 2 1 1 1 CF 3 CL 3 W 3 wherein, n and p' are the same as defined above, W is F or OM' (M' is an alkali metal).

The fluorinated vinylether compound of the present invention represented by the formula:

FS02(CF2)n+l(OCFCF2)p,0Cl==CF2 5 1 U1-3 wherein n and pl are the same as defined above, can be prepared by pyrolysis of the compound of the formula:

FS02(CF1A0C17CF2)p,CFCOW 1 1 CF3 CF3 wherein n, p' and W are the same as defined above, according to the aforesaid scheme (11). In said reaction, it is preferred to use a compound wherein W=F from standpoint of easiness in the reaction.10 Said reaction can be practiced under substantially anhydrous conditions under either pressurized, normal or reduced pressure. Usually, however, the reaction may conveniently be practiced under normal or reduced pm- sure.

There may also be employed a diluent to a dilution degree of 0 to 100 depending on the mode of reaction, said diluent being selected from inert gases such as nitrogen, helium, carbon dioxide, argon, etc. or inert non-protonic liquids such as polyethers.

When the terminal groups is an acid fluoride group, it is possible and desirable to carry out the reaction in the presence of a metallic salt or a metal oxide. In this case, there may preferably be used a solid base, which can decompose corrosive and toxic COF, generated, such as sodium carbonate, potassium carbonate, sodium phosphate, potassium phosphate, etc.

The reaction temperature may range from 100 to 6001C, preferably from 100to 3501C. If the temperature is too high, side reactions such as decomposition other than vinylization are liable to occur. At too low a temperature, conversion of the starting material is lowered. The reaction time may be from 0. 1 second to 10 hours, preferably from 10 seconds to 3 hours. The reaction temperature and the reaction time should suitably be selected to provide optimum conditions, for example, shorter reaction time at higher reaction temperature or longer reaction time at lower reaction temperature.

In the prior art, it has been deemed commercially difficult to prepare FS02(CF2)20CF=CF2 by a process comprising pyrolyzing

FS02(CF2WX17CF2),,,0CFCOF 1 1 CF3 CF3 (m is an integer of 0 to 2) to form corresponding fluorinated vinylether compound FS02(CF2WOCFCF2) OCF=CF2 1 Ut-3 because cyclization reaction will occur when m is 0. Moreover, depending on the conditions, cyclization may occur also during polymerization to lower polymer properties.

In contrast, according to the present invention, use is made of the fluorinated acid fluoride 35 represented by the formula FS02(CF1A0CFCF 2)pXFCOF 1 1 k;1-3 (;[_3 wherein n and pl are the same as defined above. Thus, due to the difference in size of the ring, pyrolysis can be effected while causing no or negligible cyclization reaction. Therefore, it is possible to produce easily a fluorinated vinylether compound represented by the formula:

8 GB 2 053 902 A 8 FOS,(C172)nJOCI7U 2)p,OCF=CF, i CF3 wherein n and p' are the same as defined above, even when p' may be 0. Said fluorinated vinylether compound is also free from cyclization during polymerization, thereby causing no deterioration of properties of the resultant polymer.

In the fluorinated vinylether compound of the present invention CF3 1 FS02(CF24+1-k-OUCF27-) P,-OCF=CF,, wherein n and p' are the same as defined above, it is preferred from standpoint of easiness in preparation that n is equal to 2.

On the other hand, the cation exchange membrane to be prepared from the copolymer of said fluorinated vinylether compound and tetrafluoroethylene is desired to have an ion-exchange capacity 10 as large as possible. From this standpoint, said fluorinated vinylether compound may preferably be one wherein p' is equal to 0.

The fluorinated vinylether compound of the present invention can be copolymerized with, for example, tetrafluoroethylene to give a fluorinated cation exchange membrane which has very excellent characteristic of sufficiently high ion-exchange capacity while maintaining good mechanical strength.

The fluorinated vinylether compound of the present invention may also be useful as intermediate for synthesis of various fluorinated compounds having functional groups containing sulfur atom at the terminal end of the molecule, for example, surfactants, fiber treating agents, lubricants, etc. It is also possible to prepare a fluorinated elastomer comprising a copolymer of the above fluorinated vinylether compound with a fluorinated olefin using said compound as a constituent or crosslinking monomer of 20 said elastomer.

The fourth object of the present invention is to provide a novel fluorinated copolymer comprising the following recurring units (A) and (13):

(A) -(-CA1A2-CA3A4-)- (A, and A2 are F or H; A3 is F, Cl or H; A4 is F, Cl, CF31 ORF, H or CH,, R. being Cl-C5 perfluoroalkyl) - -(CF,-CM- CF3 (B) 1 1 0-(_CF2CF0MCF2)1SO217 (k=0 or 1; 1 is an integer of 3 to 5) and a process for producing the same. In the above copolymer, the molar ratio of the recurring unit 30 (A)AB) is desired to be in the range from 1 to 16.

When the copolymer is required particularly strongly to have resistance to heat and chemicals, as is required in preparation of a fluorinated cation exchange membrane for use in electrolysis of an aqueous alkali metal halide solution, the recurring unit (a) in the above formula may preferably be:

-(-CF2CIZ-)_ 1 L- (L is F, Cl, CF3, -OR, or H, R. being the same as defined above). It is particularly preferred that L should 35 be F.

In order to produce membranes or resins having high!on-exchange capacity and physical toughness, the notation k may preferably be zero. The ratio (A)/(B) is preferred to be in the range from 1.5 to 14, more preferably from 3 to 11.

From standpoint of easiness in preparation of the monomer, physical properties of the resultant 40 polymer it is also preferred that I should be equal to 3, The above copolymer is substantially a random copolymer having a molecular weight generally in the range from 8,000 to 1,000,000, having a melt index generally in the range from 0.001 g/1 0 min.

to 500 g/1 0 min., as measured by use of an orifice of 2.1 mm in diameter and 8 mm in length, under the load of 2.16 kg at25011C.

The above copolymer may conveniently be identified by measurement of infrared absorption spectrum (IR) or attenuated total reflection (ATR) of a film of the copolymer as shown in Examples.

The composition of the copolymer is estimated by measurement of the ionexchange capacity, 9 GB 2 053 902 A 9 elemental analysis or combination thereof after converting all of the sulfur containing terminal groups to ion-exchange groups such as sulfonic acid groups or carboxylic acid groups.

The structure of the pendant groups contained in the copolymer according to the present invention can also be identified by measurement of IR or ATR of the product formed by converting the sulfur containing terminal groups to ion-exchange groups such as sulfonic acid groups, carboxylic acid 5 groups or suffinic acid groups and then carrying out the reaction for elimination of said ion-exchange groups.

The fluorinated copolymer of the present invention can be prepared by copolymerization of at least one monomer selected from the group consisting of the olefins of the formula:

CA1A2=CA3A4 10 wherein A,, A2, A3 and A4 are the same as defined above, at least one monomer selected preferably from the group consisting of the fluorinated olefins of the formula:

CF2=CIFL wherein L is F, Cl, CF3, -ORF or H, RF being Cl-C, perfluoroalkyl, and at least one monomer selected from the group consisting of sulfur containing fluorinated vinylether compounds of the formula: 15 CF3 1 CF2=CFO(CF2C-Uk---l'i502F wherein k and I are the same as defined above.

In this case, there may also be copolymerized a minor amount of other vinyl compounds mixed with the above monor,,,,ers. It is also possible to effect crosslinking by copolymerization of a divinyl compound such as perfluorobutadiene orperfluorodivinyletherora fluorinated vinyl compound having 20 terminal groups capable of effecting crosslinking reaction such as CF21, etc.

1 The fluorinated olefin to be used in the present invention may preferably one containing no hydrogen atom from standpoint of heat resistance and chemical resistance of the resultant copolymer.

Above all, tetrafluoroethylene is most preferred.

Among the sulfur containing fluorinated vinylether compounds, those wherein k=O are preferred 25 for providing membranes with greater ion-exchange capacity and excellent physical toughness. Of course, there may also be used a minor amount of the compound wherein W. The class of compound wherein 1=3 are also preferred from standpoint of easiness in preparation as well as the physical properties of the resultant polymer. A compound with 1=6 or more can difficultly be produced and can provide no membrane having sufficiently high ion-exchange capacity, thus being inferior to those with 30 1=3 to 5.

Typical example of the sulfur containing fluorinated vinylether compounds preferably used in the present invention are as follows:

CF3 1 CF2=CFO(CF2Ut-UJkl;1-2(jt-2CF2SO2F wherein k is 0 or 1, preferably 0.

As compared with the sulfur containing vinylether compound of the following formula:

CF3 1 CF2=CFO(CF2'I-UI,'2k1-2SO2F (m=O to 2) conventionally used in the prior art for preparation of fluorinated cation exchange membranes or fluorinated cation exchange resins having sulfonic acid groups and/or carboxylic acid groups, the sulfur containing fluorinated vinylether compound of the present invention is substantially 40 free from or remarkably decreased in such cyclization reaction as previously described in the vinylization step, even when k=O, due to the difference in the number of members constituting the ring.

Thus, a compound With k=O can also easily be produced. Also during polymerization, there is no deterioration of the polymer properties due to cyclization reaction. Accordingly, vinylether compound with k=O can principally be used in polymerization to provide a fluorinated copolymer containing 45 substantially no or a minor amount of pendant CF3 1 -CIF2t;l-U- GB 2 053 902 A 10 As the result, the content of fluorinated olefin can be increased at the same level of ion-exchange capacity of membranes or resins, whereby there can be obtained membranes or resins having higher ion-exchange capacity and also having good physical toughness.

The ratio of the olefin and the sulfur containing fluorinated vinylether compound copolymerized can be controlled by suitable selection of the ratio of monomers charged and polymerization conditions.

The copolymer of the present invention may be prepared according to well known polymerization methods used for homopolymerization or copolymerization of a fluorinated ethylene. The methods for preparation of the copolymer of the present invention may include both a method in which polymerization is conducted in a non-aqueous system and a method in which polymerization is 10 conducted in an aqueous system. The polymerization temperature may generally range from 0 to 2000C, preferably from 20 to 1 00"C. The pressure may be from 0 to 200 kg/cm', preferably from 1 to 50 kg/cm'. The non-aqueous polymerization may frequently be carried out in a fluorinated solvent. Suitable non-aqueous solvents may include inert 1,1,2-trichloro- 1,2,2-trifluoroethane or perfluoro- hydrocarbons e.g. perfiuoromethylcyclohexane, perfluorodimethylcyclobutane, perfluorooctane, 15 perfluorobenzene, etc.

As an aqueous polymerization method for preparation of the copolymer, there may be mentioned an emulsion polymerization method wherein monomers are brought into contact with an aqueous medium containing a free radical initiator and an emulsifier to provide a slurry of polymer particles or a suspension polymerization method wherein monomers are brought into contact with an aqueous medium containing both free radical initiator and dispersion stabilizer inert to telomerization to provide a dispersion of polymer particles, followed by precipitation of the dispersion. As the free radical initiator to be used in the present invention, there are redox catalysts such as ammonium persulfate sodium hydrogen sulfite, etc.; organic peroxides such as t-butyl peroxide, benzoyl peroxide, etc.; azo-bis type compounds such as azobisisobutyronitrile, and fluorine radical initiators such as N,F,, etc.

After polymerization, the polymer may be molded into membranes or granules, if desired. There may be used conventional technique for molding the polymer into a thin film or pellets by melting the polymer.

The copolymer of the present invention is useful as starting materials for preparation of a fluorinated cation exchange membrane having sulfonic acid groups and/or carboxylic acid groups. In 30 this case, the above membrane may, sometimes preferably, be laminated with a membrane made from a copolymer having a greater copolymer ratio of the sulfur containing fluorinated vinylether compound.

As the membrane to be laminated, there may be used a membrane prepared from the copolymer of the monomers selected from the group of the above sulfur containing fluorinated vinylether compounds and the groups of fluorinated olefins. Alternatively, there may also be employed a membrane prepared 35 from the following sulfur containing fluorinated vinylether compound:

25, CF3 1 CF,CFOCF2CFOCF2CF2SO2F The membrane to be used for lamination may preferably have a thickness of 1/2 to 19/20 times the thickness of the entire laminated product in order to make smaller the electric resistance thereof.

The above membrane can be reinforced in strength by backing with a mechanical reinforcing material such as a net. As such backing materials, there may most suitably be used a net made of polytetrafluoroethylene fibers. A porous polytetrafluoroethylene sheet is also useful.

It is also possible to increase the strength of the membrane by incorporating polytetrafluoroethylene fibers during molding into a membrane. When a membrane with laminated structure is employed, the reinforcing material may preferably be embedded on the side of the membrane with greater copolymerization ratio of sulfur containing fluorinated vinylether compound.

Reinforcing materials may be embedded in the membrane by laminating, press contact embedding or vacuum fusion embedding. For example, when a net is to be embedded, a membrane is placed on a net and the surface of the membrane opposite to that contacted with the net is heated to a temperature no higher by 200C than the melting point of the membrane and the surface of the membrane contacted 50 with the net maintained at a temperature higher by at least 601C than the melting point of the membrane, while providing pressure difference between both sides of the membrane. The pressure on the side contacted with the net is made lower than the opposite side.

Other than the above method, it is also possible to embed the - net in the membrane after converting the exchange groups on the side opposite to that contacted with the net to carboxylic acid 55 esters.

The thickness of the membrane is generally 2500 micron or less, preferably 1000 micron or less, more preferably 500 micron or less. The lower limit is restricted by the mechanical strength required, but usually 10 micron or more.

The copolymer of the present invention may be formed into particles during polymerization or 60 molding according to conventional procedures for preparation of ion- exchange resins, and then i A 11 GB 2 053 902 A 11 subjected to the reaction used for converting a membrane into a fluorinated cation exchange membrane to provide fluorinated ion-exchange resin particles.

These ion-exchange resins can be processed into any desired shape such as granules, membranes, fibers, strands, etc. By utilization of heat resistance and chemical resistance superior to hydrocarbon type resins, they are useful generally in separation processes making avail of adsorption such as adsorptive separation of metallic ions or separation of organic high molecular substances. They are also useful as acid catalyst for organic reactions.

The copolymer according to the present invention can also be used in the form of fibers or strands as ion-conductive reinforcing material for a fluorinated cation exchange membrane.

Said copolymer may also be blended with other fluorocarbon type or hydrocarbon type copolymers 10 to provide various blends useful for various purposes. It may also be provided as it is or as a mixture with suitable solvent for use as lubricants, surfactants, etc. It is also useful as the starting material for a fluorinated elastomer.

The fluorinated copolymer of the present invention can provide a novel fluorinated cation _ 15 exchange membrane or resin, comprising the following recurring units (C) and (D), by converting all of 15 the sulfur containing t6rminal groups to sulfonic acid groups:

(C) -(-CF2-CF-)- 1 L (L is F, Cl, CF3, ORF or H, RF being Cl-C, perfluoroalkyl) (D) -(-CF,-CF-)-CF3 1 1 0-(CF2CF0)XFA-SO3M (k is 0 or 1, 1 is ac integer of 3 to 5, and M is H, a metal or ammonium). In the above cation exchange membrane, the relative proportion of the recurring units (C)/(D) may preferably be in the range from 1.5 to 14 more preferably from 3 to 11.

This membrane is useful as diaphragm for use in electrolysis of an aqueous alkali halide metal solution, electrolysis of water or fuel cells. For the reason as already mentioned, this membrane is superior to the fluorinated cation exchange membrane containing sulfonic groups conventionally used 25 in commercial application.

The membrane of the fluorinated copolymer of the present invention can also be formed into a novel fluorinated cation exchange membrane having carboxylic acid groups and sulfonic acid groups, comprising essentially the above recurring units (C), (D) and the following recurring unit (E):

(E) -(-CF:--CF-)-CF, 1.1 0-(CF2Cr-Ul k7- L'-21 M-C02M 30 In said membrane, the ratio of the numbers of the recurring units (C), (D) and (E) may preferably be (C)/[(D)+(E)1=1.5 to 14, more preferably 3.5 to 6. When said membrane is to be used in electrolysis of an aqueous alkali metal halide solution, it is preferred that the carboxylic acid groups may be distributed in the membrane locally near one surface portion of the membrane. More specifically, the carboxylic acid group density, which is defined as the percentage of the number of carboxylic acid 35 groups based on the total number of all ion-exchange groups present in a layer substantially parallel to the surfaces of the membrane may desirably satisfy the following requirements:

(a) The carboxylic acid group density on one surface should be at least 20%; and (b) The carboxylic acid group density should gradually be decreased from said one surface toward innerside of the membrane at the maximum gradient of 209/6/micron.

One specific feature of the above membrane resides in having excellent electrolysis performance of high current efficiency and low electrolysis voltage. Another specific feature of the membrane resides in stability under more severe conditions than those usually employed, whereby said excellent electrolysis performance can be maintained for a long time. The membrane can also economically be produced with ease and at low cost.

The excellent electrolysis performance of the membrane according to the present invention may be ascribed to the specific structure of the membrane, having a carboxylic acid group density on one surface of 20% to 100%, preferably 40% or more, more preferably 60% or more, said carboxylic acid group density gradually decreasing from said one surface toward innerside of the membrane, i.e. in the direction of thickness of the membrane. To give a quantitative expression of such a gradual decrease of 50 carboxylic acid group density from one surface of the membrane toward the depth of the membrane in terms of the maximum gradient, which is defined as the greatest decrease of carboxylic acid group density per unit thickness in the membrane, the maximum gradient should preferably be 20 to 0. 1 % per one micron of the membrane thickness, more preferably 10% to 1 %. As a preferable structure, said 12 GB 2 053 902 A 12 carboxylic acid group density may reach substantially zero % at a depth of not more than 1/2 of the entire thickness of the membrane from one surface. In other words, the carboxylic acid groups should preferably be present in the membrane locally in one half side of the membrane, being more enricheq.

with gradual increase as nearer to the surface on one side, while the other half side of the membrane contains other exchange groups, namely sulfonic acid groups. More preferably, the depth at which the carboxylic acid group density reaches zero % may be less than 1/2 of the entire thickness of the membrane, i.e. 1/4 or less, most preferably 1/6 or less, to the lower limit of about 1 y.

When the above membrane is used for electrolysis of an aqueous alkali metal halide solution, it is preferred to use the membrane with the surface having higher carboxylic acid group density facing toward the cathode. With such an arrangement, said surface is shrinked when contacted with a highly 10 concentrated alkali due to the presence of carboxylic acid groups to increase the concentration of fixed ions. As the result, permeation, migration and diffusion of hydroxyl ions into the membrane can effectively be inhibited, whereby high current efficiency can be exhibited.

The carboxylic acid group density on said one surface of the membrane may be variable depending on various factors such as the value of the ratio (C)/[(D)+(E)I, the current density, the 15 temperature and the alkali concentration employed in electrolysis and can optimally be determined by controlling the conditions in preparation. Generally speaking, as the value of (C)/[(D)+(E)l is greater, the carboxylic acid group density may be lower.

On the other hand, according to a preferred embodiment of the above membrane, carboxylic acid groups are present primarily in a thin layer on the side of one surface of the membrane, only sulfonic 20 acid groups being present in most of the residual portion. For this reason, the electric resistance in - migration of alkali metal ions from the anode chamber to the cathode chamber is extremely low as compared with, for example, a membrane containing only carboxylic acid groups.

One reason why the membrane of the present invention can be used more stably than the membrane of prior art even under more severe conditions than those conventionally used maybe 25 ascribed to the specific structure of the polymer substantially consisting of the recurring units (C), (D) and (E) as described above. For obtaining a membrane having high ionexchange capacity as well as good physical toughness, it is preferred that the suffix k should be equal to zero, but there may also partially mixed a polymer wherein k is 1. It is also preferred from easiness in preparation of the monomer, the physical properties of the resultant polymer and greater variable range of the polymer 30 properties that the suffix I should be equal to 3. A membrane with a I value of 6 or more is inferior to those with I values of 3 to 5 from standpoint of difficulty in commercial production of the monomer and insufficient ion-exchange capacity obtained. A membrane wherein L is fluorine atom is particularly preferred from aspects of heat resistance and chemical resistance.

The specific feature of the polymer structure as mentioned above is based on the specific feature 35 of the structure of the sulfur containing fluorinated vinylether of the following formula used for preparation of the membrane of the invention:

CF3 1 CFi=CFO(CF2;-U)W--;1-2)ISO,F wherein k and I are the same as defined above.

The above monomer is different in number of members of the ring in cyclized product by- 40 produced in the vinylization step, as compared with the sulfur containing fluorinated vinylether of the formula:

CF3 1 CF2CFO-(CF2kl-U In'U_ 2t";2SO2F wherein n' is 0 to 2, which is used as starting material for a sulfonic acid type membrane of prior art or a sulfonic acid type membrane having formed by chemical treatment carbqxylic acid groups in the surface stratum thereof, and therefore it is possible to form substantially no or decrease to a great extent the cyclization reaction in the vinylization step as mentioned above. Thus, a monomer with k=O can easily be prepared and there is also no deterioration of polymer properties due to cyclization during polymerization.

Accordingly, since it is possible to use a monomer with k=O as principal starting material for 50.

preparation of a membrane, the resultant polymer carf have a structure containing substantially no or a very small proportion of pendant groups:

CF3 1 -C[_21;l-U- Consequently, with the same level of the ion-exchange capacity, the content of fluorinated olefin can z 13 GB 2 053 902 A 13 be increased. In other words, there can be produced a physically tough membrane with enhanced ionexchange capacity. Moreover, while its mechanism has not yet been clarified, such a membrane can maintain stable performance, being prevented from peel-off or crack of the carboxylic acid layer, even when used under more severe conditions than those conventionally used.

Another reason why the membrane of the present invention is stable under severe conditions may be ascribed to the relative ratio of the recurring units (C), (D) and (E), i.e. the ratio of (C)/[(D)+(E)l which is generally in the range from 1.5 to 14, preferably from 3 to 11, more preferably from 3.5 to 6. When said ratio is less than 1.5, the membrane is liable to be swelled during usage and therefore cannot maintain stable performance for a long term. On the other hand, if it is greater than 14, the membrane is liable to be shrinked to make the electric resistance of the membrane impractically high. 10 The ion-exchange capacity of the above membrane may be represented by the following formula as being dependent on the structure of the recurring units, the ratio of recurring units and the carboxylic acid group density:

Ion-exchange capacity=l 000/[r(81 +M,)+d(l 42+166k+50m)+0 -d) (1 78+166k+ 501)l (meq/g-dry H-form resin) wherein r--(C)/[(D)+(E)I, ML is the molecular weight of the atomic group L and d is the carboxylic acid group density.

In the prior art, the ion-exchange capacity of an ion-exchange membrane has been indicated in specific numerical values, as disclosed by Japanese published unexamined patent applications No.

120492/1975, No. 130495/1976, No. 36589/1977 and No. 24176/1977, and U.S. Patent 4,065,366. According to the study by the present inventors, however, swelling and shrinking behaviours of a membrane with a given species of ion-exchange groups is not controlled by the ion exchange capacity per se of the membrane but by the most important factors including the fluorinated olefin constituting the copolymer, the copolymer ratio of the fluorinated vinylether having ion-exchange groups and the presence or absence of CF3 1 -CF2Ut"U_ In order to obtain a membrane having sufficiently low electric resistance and good physical toughness with small swelling or shrinking when used in electrolysis, it is required to use a fluorinated vinylether having no CF3 1 -CF.CF0- 1 groups as principal component and control the above copolymerization ratio within a certain range. The ion-exchange capacity as represented by the above formula is based on such considerations.

It is not clear why the above copolymerization ratio has such a decisive influence on the swelling and shrinking behaviours of a membrane. For convenience of explanation, reference is made to a membrane containing the most preferred fluorinated olefin, i.e. tetrafluoroethylene. From analysis of X- 35 ray diffraction of the membrane, tetrafluoroethylene seems to be partially crystallized. Since the degree of crystallization is greatly dependent on the above copolymerization ratio, it may be estimated that the crystallized region will function as quasi-crosslinks which control swelling and shrinking behaviours of the membrane.

In the above membrane, it is possible to provide a structure containing substantially no ora small 40 amount of pendant groups:

CF3 1 -CF2'-U- When a membrane with the same ion-exchange capacity is to be prepared, the copolymerization ratio of tetrafluoroethylene can be increased in the above membrane, as compared with a membrane 45 prepared by use of CF3 1 Ur-2=ljhUkh2CFOCF2CF2SO2F as a sulfur containing fluorinated vinylether, thereby providing a membrane having both high ion exchange capacity and good physical toughness.

As described above, the membrane prepared from the fluorinated copolymer of the present invention is specific in having a carboxylic acid group density which is gradually decreased from the 50 surface to the innerside, preferably at a gradient within a specific range. This is still another reason why 14 GB 2 053 902 A 14 the above membrane is by far stable than the membrane of prior art under more severe conditions than those conventionally used.

The membrane having a laminated structure comprising a membrane containing carboxylic acld groups and a membrane containing sulfonic acid groups, as disclosed by Japanese published unexamined patent applications No. 36589/1977 and No. 132089/1978, in complete in bonding as 5 previously mentioned and liable to cause peel-off or water bubbles in a short period at the laminated portion. On the other hand, according to the experience of the present inventors,

even when the carboxylic acid density can be controlled to a certain extent in a membrane having carboxylic acid groups formed by chemical treatment, as disclosed by Japanese published unexamined patent applications No. 24176/1977, No. 104583/1978, No. 116287/1978 and No. 6687/1979, the resultant membrane is liable to cause peel-off or crack of carboxylic acid layer, as compared with thg membrane of the present invention, presumably due to the problem in polymeric structure as previously mentioned.

In contrast, as illustrated in Examples, the above membrane can maintain stable performance for 15 by far longer time than the membranes of prior art without causing abnormal phenomena such as peeloff or crack of the carboxylic acid layer even under the conditions of a high current density of 110 A/dml and a high temperature of 950C or higher. The above membrane may also have laminated on one surface of the membrane with lower carboxylic acid group density a fluorinated cation exchange membrane consisting substantially of the 20 unit (C) as previously mentioned and the following recurring unit (F):

(F) -(-CF27-CF-)-CF3 1 1 0-(CF2WO),,i--(CF2)-SO3F wherein p11=0 or 1, q an integer of 3 to 5, M has the same meaning as defined above, the ratio of recurring units being in the following range:

(C)/(F)<(C)/(D) or (C)/[(D)+(E)l 25 Such a structure is also preferred from standpoint of lowering the electric resistance of a membrane. In this case, in order to obtain a membrane having lower electric resistance with physical toughness, it is preferred that p" may be equal to zero and q equal to 1. It is also preferred that the thickness of the fluorinated cation exchange membrane comprising the recurring unit (F) may have a thickness 1/2 to 19/20 as thick as the entire membrane.

The membrane of the fluorinated copolymer of the present invention may also be formed into a fluorinated cation exchange membrane, comprising essentially the recurring units (C) and (E), having a ratio of the numbers of said recurring units of (C)/(E)=1.5 to 14, preferably 3 to 1 T, having substantially only carboxylic acid groups.

The above membrane having carboxylic acid groups and sulfonic acid groups can be prepared 35 from the membrane of the fluorinated copolymer of the present invention according to the following procedures. Fluorinated cation exchange membranes having only suffonic acid groups or carboxylic acid groups may also be prepared by utilizing a part of the reactions in said procedures.

As the first step for preparing the membrane having sulfonic acid groups and carboxylic acid groups from the membrane of the fluorinated copolymer of the present invention, a membrane 40 prepared by the method as mentioned above comprising essentially the recurring units (C) and (B) as shown below:

(C) (L is the same as defined above) -(-CF2CI:-)_ 1 L (B) ' -(-CF27-CF-)-C173 1 1 U-(U'-2Ul-U1k7--U1"211-S02X 45 (k and I are the same as defined above) is subjected as it is, or after hydrolysis of a part or all of the membrane with an alkali, to conversion of the terminal groups to sulfonylhalide groups, preferably sulfonylchloride groups -CF,SO,CI.

The sulfonic acid groups obtained by hydrolysis may easily be converted to sulfonylchloride groups by reaction with vapors of phosphorus pentachloride or a solution of phosphorus pentachloride 50 dissolved in phosphorus oxychloride, an organic halide compound, etc. according to the method and the conditions as described in Japanese published unexamined patent applications No. 134888/1977 1 GB 2 053 902 A 15 and No. 4289/1979. A mixture of phosphorus trichloride with chlorine may also be used.

Further, as the second step, a part or all of the sulfonylhalicle groups, preferably sulfonylchloride groups or sulfonylfluorlde groups, at the terminal end of the recurring unit (G):

(G) -(-CF27-CF-)-CF3 i - 1 U-M 21hU-I-kCF2)!--S02X (wherein k and I are the same as defined above, X is a halogen, preferably F or CO are converted to 5 carboxylic acid groups. From standpoint of easiness in reaction and handling, sulfonylchloride groups may preferably be used.

Such a conversion can be accomplished by treatment of a membrane comprising the recurring units (C) and (G) with a reducing agent and according to the reaction method and reaction conditions as generally described in Japanese published unexamined patent applications No. 24176/1977, No. 10 24177/1977 and No. 132094/1978, thereby converting -CF,- directly bonded to sulfur atom directly or via sulfuric acid groups into carboxylic acid groups.

The reducing agents to be used in the present invention may preferably be selected from acids having reducing ability such as hydrolodic acid, hydrobromic acid, hypophosphorous acid, hydrogen sulfide water, arsenous acid, phosphorous acid, sulfurous acid, nitrous acid, formic acid, oxalic acid, 15 etc., their metal salts, ammonium salts, and hydrazines, from standpoint of reactivity and easiness in handling. Among them, an inorganic acid having reducing ability is most preferred. These reducing agents may be used alone or, if necessary, as a mixture.

The structure of the membrane comprising carboxylic acid groups enriched on only one surface of the membrane, which is the excellent specific feature of the above membrane may be realized easily by 20 applying the first step reaction or preferably the second step reaction on one surface of the membrane. In case of a membrane having a laminated structure, these reactions may be applied on the surface opposite to that on which lamination is effected.

The gradient of the carboxylic acid group density may be controlled to a desired shape of the density curve by adequately controlling various factors in the reactions in the first or the second step 25 such as temperature, time, pressure, solvent composition, etc. to thereby balance the reaction rate and the diffusion velocity of a reagent into the membrane. For easiness in control, it is preferred to effect such controlling in the second step.

As a preferable method for controlling the carboxylic acid group density, there may be mentioned a method wherein the above treatment with a reducing agent is effected in the presence of at least one 30 organic compound selected from Cl-C,, alcohols, carboxylic, acid, sulfonic acids, nitriles or ethers, using especially a solution of said organic Compounds dissolved in an aqueous reducing agent solution.

In particular, carboxylic acids may preferably be used as such organic compounds. These organic compounds may be added in an amount, which is variable depending on the membrane employed, the reducing agent and organic compound employed as well as the reaction conditions and may suitably 35 be selected within the range of 100 pprn or more.

Examples of alcohols to be used in the present invention may include methanol, ethanol, propanol, ethylene glycol, diethylene glycol, 1,4-butane diol, 1,8-octane diol, glycerine, and the like.

As typical examples of carboxylic acids and sulfonic acids, there may be mentioned formic acid, acetic acid, propionic acid, butyric acid, iso-butyric acid, n-valeric acid, caproic acid, n-heptanoic acid, 40 caprylic acid, lauric acid, fluoroacetic acid, chloroacetic acid, bromoacetic acid, clichloroacetic acid, malonic acid, glutaric acid, trifluoroacetic acid, perfluoropropionic acid, perfluorobutyric acid, perfluorovaleric acid, perfluorocaproic acid, perfluoro-n-heptanoic acid, perfluorocaprylic acid, perfluoroglutaric acid, trifluoromethane sulfonic acid, perfluoroheptane sulfonic acid, methane sulfonic acid, ethane sulfonic acid, propane sulfonic acid, butane sulfonic acid, pentane sulfonic acid, hexane 45 sulfonic acid, heptane sulfonic acid, and so on. Preferably, acetic acid, propionic acid, caprylic acid, trifluoroacetic acid, perfluorocaprylic acid or perfluorobutyric acid may be used.

Typical examples of nitriles are acetonitrile, propionitrile, adiponitrile, and the like. Ethers may be exemplified by diethylether, tetrahydrofuran, dioxane, ethylene glycol climethylether, diethylene glycol dimethyl ether, etc. Among these organic compounds, some compounds may undergo chemical changes depending on the reducing agent employed and therefore such a combination is desired to be avoided.

The gradient of the carboxylic acid group density in the membrane may be determined, as illustrated in Examples, by staining the cross-section of a membrane with a suitable dye and observing the result of staining, or alternatively by scraping the membrane substantially in parallel to the surface 55 thereof (usually in thickness of about 1 to 5 micron per each scraping), subjecting the scraped face to attenuated total reflection (hereinafter referred to as ATR) and calculating from the changes in intensity of the absorption peak based on the carboxylic acid groups.

In the membrane of the present invention or other fluorinated cation exchange membranes, the pendant structure having bonded ion-exchange groups can be identified by measurement of ATR or IR 60 absorption spectrum after the reaction for elimination of ion-exchange groups. The composition of the 16 GB 2 053 902 A 16 copolymer is estimated by combination of ion-exchange capacity measurement and elemental analysis.

Other than the method as described above wherein a reducing agent is used, there may also be used the same method as described in Japanese published unexamined patent application No.

125986/1978, wherein sulfonyl halide groups are once converted to -CF21, followed by conversion to carboxylic acid groups. Alternatively, the membrane comprising the recurring units (B) may be irradiated with ultra-violet rays or electron beam to be directly converted to carboxylic acid groups. It is also possible to obtain a membrane containing carboxylic acid groups with more -CF27- than that obtained by use of a reducing agent according to the method as described in Japanese published unexamined patent applications No. 104583/1978 and No. 116287/1978. Said method comprises 10 reacting a membrane having sulfonyl halide groups or a membrane having sulfinic acid groups or -CF21 obtained as intermediate in the method as described above with a compound having carbonyl groups or unsaturated bonding under the conditions to eliminate SO, or iodine atom ionically or radically. According to these methods, however, it is very difficult to control the gradient of the carboxylic acid density; many steps are required for the reaction; the cost is high; expensive reagents are necessary; side reactions can difficultly be suppressed; pendant groups cannot be in the form of perfluoro groups; or the membrane may be damaged physically during the treatment. In any of these respects, any of said alternative methods is inferior to the method wherein a reducing agent is used. For this reason, in preparation of a membrane to be used under more severe conditions than those conventionally used, it is more preferable to use the method employing a reducing agent than those alternative methods as mentioned above.

The third step for preparation of the membrane of the present invention is to convert all of the residual sulfur containing terminal groups to sulfonic acid groups. This can easily be done according to the reaction as mentioned in the second step reaction or by application of the reactions such as oxidation, hydrolysis, etc. as described in Japanese published unexamined patent applications No. 24176/1977 and No. 24177/1977.

As apparently seen from the preparation methods as described above, the above membrane having carboxylic acid groups and sulfonic acid groups can be derived from common starting materials according to simple reactions to have carboxylic acid groups and sulfonic acid groups. Thus, the membrane can be manufactured easily at advantageously low cost.

The cation exchange membrane prepared from the copolymer according to the present invention may favorably be employed in electrolysis of an aqueous alkali metal halide solution. That is, the membrane is useful not only in electrolysis of an alkali metal halide under conventional electrolysis conditions, i.e. a current density of 10 to 70 A/dml, a temperature of 20 to 1 00C alkali metal halide concentration of 1 to 5 N and an alkali concentration of 1 to 15 N, but also useful under severe conditions, i.e. a current density of 70 to 200 AMml and a temperature of 100 to 1 501C, with stable performance for a long time.

The copolymer of the present invention can also be formed into granular fluorinated ion-exchange resins by forming the polymer into particles at the time of polymerization or molding according to conventional technique for preparation of ion-exchange resins and then applying the reactions as described above used in converting the membrane of the fluorinated copolymer to the fluorinated cation exchange membrane, said resins comprising the following recurring units (A) and (D) and/or (E):

(A) -(-CA,A--CA,A47--) (wherein A, A2, A3 and A, are the same as defined above) (D) -(-CF27-CF-)- CF3 1. 1 U-(-CF2CFO)k7-(CF2)C-S03M 45 wherein k, 1 and M are the same as defined above) (E) -(-CFi--CF-)- CF, k7-(CF2) rn-CO2M (wherein k, m and M are the same as defined above) The present invention is illustrated in further detail by referring to the following Examples, by 50 which the present invention is not limited.

Reference Example 1 (A) In a stainless steel autoclave of 3-liter capacity, there are charged 250 g of sodium ethyl mercaptide, 530 g of dimethyl carbonate and 750 9 of tetrahydrofuran, and then the reaction system is brought into a reduced pressure of 50 to 60 mm Hg. While maintaining the temperature at 1 50C under vigorous agitation of the reaction system, tetrafluoroethylene is gradually blown into the system under 55 17 GB 2 053 902 A 17 reduced pressure. With the progress of the reaction, the rate of tetrafluoroethylene consumed is lowered until, finally at the tetrafluoroethylene pressure of 1 kg/cM2, there is no more consumption of tetrafluoroethylene. After the reaction, the reaction mixture is neutralized with 300 g of 98% sulfuric acid. The sodium sulfate formed is filtered off and the filtrate is previously evaporated by an evaporator to remove tetrahydrofuran, followed by distillation of the residue, to obtain 520 g of the fraction of distillate at 84'C/30 mm Hg. Said fraction is found to have the structure of C21-1.SCF2CF2CO0CH, from elemental analysis, IR and NIVIR spectra.

M characteristic absorption (liquid: (-CF 2960,2930,2870CM-I(C2Hg---),1780cm -COI--),1300-1100cm 2_) Elemental analysis: CAF402S Calculated: C, 323; H, 3.6; F, 34.5; S, 14.5 Found: C, 32.2; H, 3.9; F, 33.9; S, 14.3 (B) The compound CASCF2CF2CO0C1-13 prepared in (A) as described above (330 g) is added dropwise at room temperature over one hour, while under vigorous agitation, into a reactor wherein chlorine gas (500 mVminute) is previously passed through trifluoroacetic acid (100 mi). After said dropwise addition, the reaction mixture is left to stand for 10 hours, followed by distillation of the product and collection of the fraction of distillate at 70-751C/60 mm Hg to give 310 g of said fraction of distillate.

Said fraction is identified by IR spectrum, NIVIR spectrum and elemental analysis, to have the 20 formula CISCF2CF2CO2CH3.

Elemental analysis values:

Found: C, 21.4; H, 1.2; F, 33.1; S,13.9 Calculated (for C41-1,F4SO2Cl): C, 21.2; H, 1.3; F, 33.5; S, 14.1 (C) While passing chlorine gas at the rate of 500 mVminute into a cold water (200 mi) previously saturated with chlorine, under vigorous agitation, the sulphenylchloride prepared in (B) (226.5 g) is 25 added gradually thereto. After the addition is completed, the reaction is continued for additional 5 hours. Then, the lower layer is taken out to obtain 232 g of the fraction of distillate at 80-82 'C under mm Hg.

Said fraction is identified by IR spectrum, elemental analysis, and NIVIR spectrum to have the structure of C1S02CF2CF2CO2CH,, IR absorption spectrum:

0 il 1415 cm-1(-S-CI), 1785 em-'(-COOCH,), 2960 cm-1(-CH) 11 U Elemental analysis:

Found: C, 183; H, 1.0; F, 29.1; S, 12.6 Calculated (for C41-1,F4SO4CO: C, 18.6; H, 1.2, F, 2 9.4; S, 12.4 35 (D) The perfl uo ro-3-ch lorosu Ifo nyl methyl propionate (258.5 g) obtained in (C) is neutralized with 8N-NaOH, followed by removal of water and methanol.

After the residue is dried, phosphorus pentachloride (312 g) and phosphorus oxychloride (150 g) are added thereto and the reaction is carried out under reflux on a heating bath at 1 301C for 10 hours.

After the reaction, distillation of the product gives 220 g of the fraction of distillate at 701C under 100 40 mm Hg.

This substance is identified by IR absorption spectrum, elemental analysis and NIVIR spectrum to be C1S02CF2C172CC)C1 (perfluoro-3-chlorosuifonylpropionyI chloride).

IR absorption spectrum:

1790 cm-'(-COCI), 1415 cm-1(-S02C1) Elemental analysis:

Found: Q13.4; 17,28.5; S,12.1; C127.3 Calculated (for C3F4SOP2): Q13.7; F, 28.9; S,12.2; C1,27.0 Example 1 50 A vessel containing sulforane (224 mi) and sodium fluoride (336 g) is heated on a heating bath 50 at 801C and there is added dropwise the perfluoro-3-chiorosuifonylpropionyl chloride (263 g) prepared in (D) of the Reference Example 1. The reaction is carried out for one hour. After the reaction, the product is subjected to distillation to give 218 g of the fraction of distillate boiling at 50 to 551C. Said fraction is identified by M and NIVIR spectra and elemental analysis to be FSO,CF2CF2COF (perfluoro-3-fluorosuifonyi-propionyl fluoride).

18 GB 2 053 902 A 18 IR absorption spectrum: 1890 cm-1(-COF), 1470 CM -S02F) Elemental analysis:

Found: C,15.5; FA9.5; S,13.8 Calculated (for C3F.,So): C, 153; F, 50.0; S, 13.9 Example 2

The perfluoro-3-fluorosuifonyi-propiony[fluoride (230 g) prepared in Example 1 is charged together with diethyleneglycol dimethylether (72 ml) and potassium fluoride (5.4 g) into an autoclave. While stirring the mixture at room temperature, hexafluoropropylene oxide (182.6 g) is then pressurized into the autoclave over 30 minutes and the reaction mixture is left to stand under stirring 10 for additional 30 minutes.

After the reaction, the reaction mixture taken out is found to be separated into two layers. The lower layer is subjected to distillation to give 225 g of a fraction boiling at 451C under 60 mm Hg.

Said fraction is identified by IR and NMR spectra, elemental analysis and molecular weight titration to have a structure of FS02(C1710CFCOF 1 CF3 (perfluoro-6-fluorosulfony]-3-oxa-2-methyi-hexanoylfluoride). IR absorption spectrum: 1880 cm-1(-COF), 1465 cm-1(-SOJ) 20 Elemental analysis:

Found:

Calculated (for Cj12SC)C Molecular weight titration:

C, 18.0; F, 57.8; S, 8.0 C, 18.2; F, 5 7.6;S, 8.1 Titrated: 397, Calculated: 396 Example 3

While an electric tubular furnace previously filled with sodium carbonate (932 g) is maintained at 21 OIC, nitrogen is passed therethrough at the flow rate of 100 to 150 mVminute. From the inlet of said tubular furnace, there is added dropwise 480 g of the perf[uoro-6- fluorosuifonyi-3-oxa-2methylhexanoyl fluoride prepared in Example 2 at the rate of 20 cc/hour, and the effluent is stored in a reservoir cooled with cold water. Then, the effluent is subjected to distillation to give 200 g of a 30 fraction boiling at 6411C under 200 mm Hg.

Said fraction is identified by IR and NMR spectra and elemental analysis to have a structure of FS02(dFI0C17=CF2 (perfluoro-4-oxa-5-hexenesuffonyl fluoride).

IR absorption spectrum:

1840 ern-I(CF2=CF0-), 1460 cm-'(-SO,F) Elemental analysis:

Found:

Calculated (for C51710S03):

Comparative Example 1 The procedure of Example 3 is repeated except that FS0,(CF,),OCKOF 1 CF3 is used and passed through the sodium carbonate bed in place of FS02(CF1OUCOF 1 Ll-3 Z C, 18.2; F, 573; S, 9,5 C, 18.2; F, 57.6; 0, 14.5;S,93 whereby no objective C172=CI7O(CF1SO2F is obtained but only the cyclized product P3 1 cr - 0CP CP 1 1 can be obtained.

-S02 1 19 GB 2 053 902 A 19 Example 4 Example 2 is repeated except that the amount of hexafluoropropylene oxide is changed to 315 g. The reaction product is subjected to distillation to give 91 g of FS02(CF1OUCOF 1 U-3 and 281 g of FSO,(CF2),OCFCF2OCFCOF 1 1 CF3 CF3 These structures are identified by IR and NMR spectra, and elemental analysis.

Example 5 The compound FSO,(CF2),OCFCF2OCFCOF 10 CF3 CF3 (290 g) prepared in Example 4 is introduced into a tubular furnace filled with sodium carbonate and the reaction is effected at 2601C. As the result, there is obtained 153 g of FS02(CF2)30CFCF2OCF=CF2 1 Ut-3 (perfluoro4,7-dioxa-5-methy]-8-nonene sulfonylfluoride).

Said product is found to have a boiling point of 82'C/60 mm Hg and its structure is identified by 15 IR and NMR spectra and elemental analysis.

Example 6 An emulsion is formed by charging 10 g of CF2=CFO(CF)3SO,F, 95 cc of purified water containing 1 ppm of copper sulfate, 0.28 g of ammonium persulfate and 0.90 g of ammonium 20 perfluorooctanoate in a stainless steel autoclave of 300 cc capacity. Then, 5 cc of an aqueous 0. 12% 20 sodium hydrogen sulfite solution is added to the mixture, and polymerization is conducted under the pressure of tetrafluoroethylene of 5 kg/cM2, While maintaining the temperature at 400C. During the polymerization, the pressure of tetrafluoroethylene is controlled so as to keep constant the rate of polymerization. 25 The resultant polymer is found to contain 3.56 wt.% of sulfur by elemental analysis. A part of this 25 polymer is hydrolyzed and subjected to measurement of its!on- exchange capacity. As the result, the polymer is found to have an ion- exchange capacity of 1.08 meq/g-dry resin. Thus, the ratio of the recurring units of tetrafluoroethylene and the above vinyl monomer, i.e.

-(-CF2CF--)-/-(-CF,CF-) 1 O(CU3SO2F is found to be 6.0.

The above copolymer is found to have a melt index of 0.2 g/1 0 min., as measured under the conditions of the temperature of 2750C and the load of 2.16 kg by means of an orifice of 2.1 mm in diameter and 8 mm in length.

The above sulfonylfluoride type copolymer is formed into membrane with thickness of 250 y, followed by hydrolysis with an alkali to form a sulfonic acid type membrane. Said membrane is dried 35 and then subjected to treatment with a 1:1 mixture (weight ratio) of phosphorus pentachloride and phosphorus oxychloride at 1200C. The treated membrane is subjected to measurement of ATR, whereby the absorption by sulfonyl groups at 1470 cm-1 observed before treatment is found to be vanished and instead thereof there appears absorption of sulfonylchlorlde groups at 1420 cm-1.

One surface of said membrane having sulfonylchloride groups is treated with a mixture comprising 57% hydrolodic acid and glacial acetic acid at a volume ratio of 30:1 at 720C for 16 hours and then hydrolyzed with an alkali. Further, the membrane is treated with an aqueous 5% sodium hypochlorite solution at 901C for 16 hours. When the cross-section of the membrane is stained with an aqueous Malachite Green solution, the membrane is stained in blue to the depth of 12 P from the surface on one side, the residual portion being stained in yellow. By measurement of ATR of the surface 45 GB 2 053 902 A 20 stained in blue, there is observed an absorption at 1690 cm-1 due to carboxylic acid salt. The gradient of carboxylic acid group density in the layer stained in blue is measured according to the following method.

According to the method similar to that described above, there is prepared a membrane having the same exchange capacity wherein all the ion-exchange groups are converted to carboxylic acid groups. ATR of this membrane is measured and absorbance of carboxylle acid salt at 1690 cm-1 is calculated according to the base line method, said absorbance being determined as 100. The surface layer on the side having carboxylic acid salt groups of the aforesaid membrane is scraped evenly and the scraped surface is subjected to measurement of ATR. Absorbance of carboxylic acid salt is calculated and the percentage A% based on the absorbance of the film of the above membrane containing only carboxylic acid groups. On the other hand, the thicknesses before and after scraping are measured to determine the difference B p therebetween. Thus, the density of carboxylic acid groups in the thickness of B A from the surface layer is determined as Avo.

The density of carboxylic acid groups in the membrane of this Example as found in the scraped section from the surface layer is 100% and the maximum density gradient of carboxylic acid salt 15 groups 4.2Y./iu.

The electrolysis performance of said membrane is measured according to the following method, with the surface having carboxylic acid salt groups facing toward the cathode side.

There is used an electrolytic cell comprising the anode compartment and the cathode compartment separated by said membrane with a current passage area of 0. 06 dM2 (2 cmx3 cm) and 20 said membrane is assembled in the cell so that the surface having carboxylic acid groups may face toward the cathode side. As the anode, a dimensionally stable metal electrode is used and as the cathode an iron plate. Into the anode compartment is flown a saturated aqueous sodium chloride solution and pH of the anolyte is maintained at 3 by addition of hydrochloric acid. While 10 N aqueous caustic soda solution is circulated to the cathode compartment, water is added thereto in order to maintain the concentration at a constant value.

While maintaining the temperatures in both the anode compartment and the cathode compartment at 95 'C, current is passed at the current density of 110 AMM2. The current efficiency is calculated by dividing the amount of caustic soda formed in the cathode compartment by the theoretical amount calculated from the quantity of current passed.

results:

The current efficiency and the cell voltage are measured with lapse of time to obtain the following Current passage time (hrs.): Current efficiency M: Voltage M:

24 720 95 95 4.9 4.9 After passage of current, the membrane is observed to find no physical damage such as water bubbles, cracks or peel-off.

Comparative Example 2 In a stainless steel autoclave of 300 cc capacity, there are charged 10 g of CF3 1 CF,=CFOCF2;U;,-;-2b02F, 0.1 g of ammonium persulfate and water. The mixture is emulsified using ammonium perfluorooctanoate as emulsifier and polymerized at 501C under the pressure of tetrafluoroethylene of 3 kg/cM2, while adding sodium hydrogen sulfite as co-catalyst. The ion-exchange capacity of the resultant copolymer is measured after hydrolysis of a part thereof to be 1.3 meq/g-dry resin. The ratio 45 of the recurring units of this polymer, i.e.

-(-CF2CFi--)-/-(-CF2CF-)- 1 U';'-2U[-UkU'-2),SO,H 1 Ut-3 is found to be 3.3.

After washing the above polymer with water, the polymer is formed into a film with thickness of 250 It, which is in turn hydrolyzed with an alkali. The resultant membrane is too low in mechanical 50 strength to perform evaluation thereof.

*Example 7

The sulfonylfluoride type polymer prepared in Example 6 is extrusion molded into a strand, which is in turn pelletized by a pelletizer to prepare granular resin with diameter of 1 mm.

i 4 21 GB 2 053 902 A 21 Said granular resin is treated with a solution of 3 N caustic soda in 50% methanol at 601C for 20 hours to provide a sulfonic acid type fluorinated cation exchange resin. Said granular resin has an ionexchange capacity, which is found to be 1. 08 meq/g-dry resin, as measured by acid-base exchange.

Example 8

The resin prepared in Example 7 is dried and then treated. with a 1:1 mixture (weight ratio) of 5 phosphorus pentachloride and phosphorus oxychloride. After said resin is washed with carbon tetrachloride and dried, it.is immersed in a 1:1 mixture (volurne ratio) of 57% hydrolodic acid and acetic acid to be treated at 83 IC for 100 hours therein, followed further by alkali treatment to give a carboxylic acid typefluorinated cation exchange resin. By staining with Malachite Green, the cross- section of this resin is found to be stained allover the surface. There is no sulfur detected by elemental 10 analysis. Said resin is found to have an!on-exchange capacity of 1. 19 meq/g-dry resin, as measured by acid-base exchange.

Example 9 The resin obtained in Example 8 after washing with carbon tetrachloride and drying is treated with 57% hydroiodic acid at 721C for 20 hours. Then, the resin is subjected to hydrolysis treatment with 15 3N caustic soda/50% methanol solution, followed further by treatment at 901C for 16 hours with a 5% aqueous sodium hypochlorite solution to give a fluorinated cation exchange resin having both sulfonic acid groups and carboxylic acid groups. Said resin is found to have an ion-exchange capacity of 1.13 meq/g-dry resin. The cross-section of the resin is found to be stained by staining with Malachite Green such that the central portion is stained in yellow, while the circumferential portion therearound in blue. 20 Example 10 An emulsion is formed by charging 10 g of CF,=CFOCF,CFO(CF2,SO,F 1 U1-3 cc of water containing 1 ppm of copper sulfate, 0. 18 g of ammonium persulfate, 2.0 g of sodium hydrogen phosphate and 1.9 g of ammonium perfluorooctanoate. Then, 5 cc of an aqueous 0. 16% 25 sodium hydrogen sulfite is added to the mixture, and copolymerization is carried out under the pressure of 4 kg/cm2 of tetrafluoroethylene, while maintaining the temperature at 401C and controlling the pressure of tetrafluoroethylene to keep the polymerization rate constant.

The resultant polymer is found to contain 2.47% by weight of sulfur by elemental analysis. A part of the polymer is subjected to hydrolysis for measurement of ion-exchange capacity, which is found to 30 be 0.72 meq/g-dry resin. The ratio of recurring units tetrafluoroethylene and the vinyl monomer of the polymer, i.e.

-(-CF2CF-)-/-(-CF2CF-1 UUI-2ut-uUF2)3SO2F is found to be 8.9.

The above sulfonylfluoride type polymer is press molded into a membrane with thickness of 250 35 It and subsequently treated similarly as described in Example 6 to prepare a cation exchange membrane having carboxylic acid groups in surface layer on one side of the membrane. Electrolysis performance is measured similarly as in Example 6 with the surface having carboxIlc acid groups facing toward the cathode side at caustic soda concentration of 6.5 N and a current density of 100 A/dmI, whereby current efficiency is found to be 96%.

Example 11

The polymer prepared in Example 6 is molded into a film with thickness of 200 y. A fabric made of polytetrafluoroethylene fibers is embedded in this film according to the following method. The device used in this embedding procedure comprises two aluminum plates (2 cm), each being provided on the upper surface by mechanical working with a series of grooves so as to create pressure difference across the upper surface of the plate. The pressure difference is applied through the hole bored through the side surface of the plate, which hole being connected to the grooves on the upper surface of the plate. On this plate is placed a 60-mesh wire-screen so that the pressure difference may be applied on every point on the upper surface. A sheet of asbestos paper is placed on the upper surface of the wire-screen, and on said sheet is superposed a "leno- woven" fabric with thickness of 50 about 0.15 mm made of polytetrafluoroethylene fibers comprising, each 25 per inch, 400 denier multi filaments as weft and 200 denier multi-filamentsx2 as warp. On said fabric is further placed the above film. The size of the film is made slightly larger than other comr)onents and the marginals of the sheets GB 2 053 902 A 22 of the fluorinated polymer are fastened onto the aluminum plates with a tape, thus forming an air-tight package.

The embedding device is placed between the electricallly heated hot plates, whereby the hot plate contacted with the aluminum plate is maintained at 3001C and the hot plate contacted with the film at 1851C for 5 minutes. Then, through the hole on the side surface of the aluminum plate, evacuation is effected to provide 100 mm Hg pressure difference. Under such conditions, the whole composite is left to stand for 3 minutes. The temperature of the hot plates is then cooled to room temperature and the pressure difference is removed. By observation of the cross-section of the film, the fabric is completely embedded within the film.

When the thus prepared membrane is treated similarly as described in Example 6, there is 10 obtained a membrane having similar current efficiency according to the same evaluation test of electrolysis performance as described therein.

Claims (45)

Claims

1. A fluorinated carboxyic acid or its derivative represented by the formula:

is FS0,(C17jY 15 wherein Y is -COV or -CN[YI is a halogen, hydrogen, -NH,, -OM(M is hydrogen, a metal or ammonium) or -OR' (R' is Cl-Cl. alkyl or an aryi)l; and n is an integer of 2 to 4.

2. A fluorinated carboxylic acid or its derivative according to claim 1, wherein n is 2.

3. A fluorinated carboxylc acid or its derivative according to claim 1 or claim 2, wherein Y is -COF formula:

4. A process for producing a fluorinated carboxylic acid or its derivative represented by the FS02(CF1Y wherein, Y is -COV or -CN[Y1 is a halogen, hydrogen, -NH2, -OM(M is hydrogen, a metal or ammonium) or-OR'(Rl is Cl-Clo alkyl or an aryffl, which comprises reacting tetrafluoroethylene 25 with a carbonic acid ester having 3 to 20 carbon atoms in the presence of a mercaptide represented by the formula:

R'SIVII wherein R' is Cl-Cl. alkyl, an aryl or C,-C,, perfluorpalkyl; and M' is an alkali metal, ammonium or 30 primary- to tertiary-alkylammonium to form a compound of the formula:

R'SC172CF2COR1 5 U wherein R' and R' are the same as define above, and then converting the group R'S in said compound to the group -S02F.

5. A process according to claim 4, wherein the reaction product is subjected to hydrolysis to form 35 a fluorinated carboxylic acid or its salt.

6. A process according to claim 5, wherein the fluorinated carboxylic acid or its salt is further treated with sulfur tetrafluoride to obtain an acid fluoride.

7. A process according to claim 5, wherein the fluorinated carboxylic acid or its salt is converted to an acid chloride by use of a chlorinating agent and then reacting the acid chloride with an alkali 40 metal fluoride to obtain an acid fluoride.

8. A process according to any of claims 4 to 7, wherein the carbonic acid ester is a di-alkyl carbonic acid ester, said alkyl having 3 to 11 carbon atoms.

9. A process according to any of claims 4 to 8, wherein the terminal grc; ups are converted by treatment with chlorine to sulfonylchoride groups, followed by the reaction with an alkali metal 45 fluoride, to form sulfonyi fluoride groups.

10. A process for producing a fluorinated carboxylic acid or its derivative represented by the formula:

FSO,(CF,),Y - i wherein Y is -COV or -CN[Y1 is a halogen, hydrogen, -NH 21 -OM(M is hydrogen, a metal or ammonium) or-ORI(Rl is C,-C,,, alkyl, oran ary01, which comprises reacting tetrafluoroethylene 50 with a compound of the formula:

A2S02 1 23 GB 2 053 902 A 23 wherein A is a halogen or Cl-C, alkoxyl, in the presence of an alkali metal cyanide, and then converting the terminal groups containing sulfur of the reaction product to sulfonyl-fluoride groups.

11. A process according to claim 10, wherein the reaction product is hydrolyzed to produce a fluorinated carboxylic acid or its salt.

12. A process according to claim 11, wherein the fluorinated carboxylic acid or its salt is further 5 treated with sulfur tetrafluorlde to obtain an acid fluoride thereof.

13. A process according to claim 11, wherein the fluorinated carboxylic acid or its salt is converted to an acid chloride thereof by use of a chlorinating agent and then the acid chloride is reacted with an alkali metal fluoride to obtain an acid fluoride thereof.

14. A process for producing a fluorinated carboxylic acid or its derivative of the formula: 10 FS0,(CF,V wherein Y is -COY' or -CN[YI is a halogen, hydrogen, -NH21 _OM(M is hydrogen, a metal or ammonium) or -ORI(RI is C1-C10 alkyl or an aryl)]; and n is an integer of 2 to 4, which comprises reacting tetrafluoroetHylene with a compound of the formula ZS02F or ZCS02F wherein Z is a halogen except fluorine in the presence of a free radical initiator.

15. A process according to claim 14, wherein the reaction product is treated with a mineral acid to produce a fluorinated carboxylic acid or its salt.

16. A process according to claim 15, wherein the fluorinated carboxylic acid or its salt is further treated with a sulfur tetrafluoride to obtain an acid fluoride thereof.

17. A process according to claim 15, wherein the fluorinated carboxylic acid or its salt is converted to an acid fluoride thereof by use of a chlorinating agent and then reacted with an alkali metal fluoride to obtain an acid fluoride.

18. A novel fluorinated acid fluoride represented by the formula:

CF3 CF3 1 1 FS02(CF2)n+l-UU'-U1-2--U.,r,ur wherein n isan integerof 2 to4andp isan integerof Oto 50.

19. A fluorinated acid fluoride according to claim 18 wherein n is 2.

20. A fluorinated acid fluoride according to claim 18 or claim 19, wherein p is 0 or 1.

2 1. A process for producing a novel fluorinated acid fluoride as defined in claim 18, which comprises reacting a compound represented by the formula:

FS02(WICOF 30 wherein n is an integer of 2 to 4, with hexafluoropropylene oxide in the presence of a fluoride ion.

22. A process according to claim 2 1, wherein n is 2.

23. A process according to claim 21 or claim 22, wherein p is 0 or 1.

24. A novel fluorinated vinylether compound represented by the formula:

FS02(CF2)n+l(OCFCF),DCF=CF2 35 1 U1-3 wherein n is an integer of 2 to 4 and p' is an integer of 0 to 1.

25. A compound according to claim 24, wherein n is 2.

26. A compound according to claim 24 or claim 25, wherein p' is 0.

27. A process for producing a novel fluorinated compound as defined in claim 24, which comprises subjecting a compound represented by the formula:

FSO 2(CF2),,+1(OCFCF2)P,OCFCOW 1 1 CF3 CF3 wherein n and pI have the same meanings as defined in claim 24 and W is F or OMWI is an alkali metal), to pyrolysis, optionally in the presence of a metal salt or a metal oxide.

28. A process according to claim 27, wherein n is 2. 45

29. A process according to claim 27 or claim 28, wherein p' is 0.

30. A process according to any of claims 27 to 29, wherein W is F.

3 1. A novel fluorinated copolymer, comprising essentially the following recurring units (A) and (B):

24 GB 2 053 902 A 24 (A) -(-CA,Ai--CA3A4--)- wherein each of A, and A2 is F or H; A3 is F, Cl or H; A4S F, Cl, CF31 - ORF or CH,, RF being Cl-C5 perfluoroalkyl, (B) -(-CFi--CF-)- CF3 O(CF2CFO)k(CF2)1So2F wherein k is 0 or 1, 1 is an integer of 3 to 5, the molar ratio of unit s (A)/(B) being from 1 to 16.

32. A copolymer according to claim 3 1, wherein the recurring unit (A) has the following formula:

-(-CI72-CF-) 1 L wherein L is F ' Cl, CF3, -RF(RF is the same as defined in claim 31) or hydrogen.

33. A copolymer according to claim 31 or claim 32, wherein k is 0.

34. A copolymer according to any of claims 31 to 33, wherein I is 3.

35. A copolymer according to any of claims 31 to 34, wherein the ratio (A)/(B) is 1.5 to 14.

36. A copolymer according to any of claims 31 to 35, wherein the copolymer is shaped in the form of a membrane.

37. A process for producing a novel fluorinated copolymer as defined in claim 31, which 15 comprises copolymerizing an olefin represented by the formula:

CA,A,=CA^ wherein A,, A,, A, and A4 have the same meanings as defined in claim 31 with a sulfur containing fluorinated vinylether represented by the formula:

CF3 I C F2=C FO (CY-; U I kI; 1-21 ISO 2F is wherein k and I have the same meanings as defined in claim 22, in a solvent in the presence of a free 20 radical initiator.

38. A process according to claim 37, wherein the free radical initiator is selected from the group consisting of redox catalysts, organic peroxides, azo-bis type compounds and fluorine radical initiators.

39. A process according to claim 37, wherein the solvent is water or a fluorinated organic solvent.

40. A process according to claim 37, wherein the polymerization is carried out at a temperature of 20 to 1 001C and under a pressure of 1 to 50 kg/cml.

41. A process for producing a fluorinated cation exchange membrane having both carboxylic acid groups and sulfonic acid groups, which comprises subjecting one surface layer of a membrane of a fluorinated copolymer comprising essentially the following recurring, units (C) and (B):

(C) -(-CF2-CF-)- 1 L wherein L is F, Cl, CF3, -ORF or H, RF being C,-C, perfluoroalkyl, (B) -(-CF2-CF-)1 U-S 1-1-2t r-0) k-(CU f-S02F wherein k is 0 or 1, and I is an integer of 3 to 5, to treatment with an aqueous solution of at least one reducing agents selected from the group consisting of inorganic acids having reducing ability, salts 35 thereof and hydrazines in the presence of at least one organic compound having 1 to 12 carbon atoms selected from the group consisting of alcohols, carboxylic acids, sulfonic acids, nitriles and ethers.

42. A process according to claim 41, wherein there is used a mixed solution containing the organic compound dissolved in the aqueous reducing agent solution ' -

43. A process according to claim 41, wherein the reducing agent is a hydrazine.

44. A process for producing a fluorinated cation exchange membrane according to claim 41 which is reinforced with a reinforcing material, wherein there is used a membraneof a fluorinated 1 1 1 il GB 2 053 902 A 25 copolymer comprising a reinforcing material embedded therein by providing a pressure difference between both sides of the membrane, while maintaining the temperature of the surface of the membrane opposite to that contacted with a reinforcing material at no higher by 201C than the melting point of the membrane and the temperature of the surface of the membrane contacted with the reinforcing material at higher by at least 600C than the melting point of the membrane.

45. A process for producing a fluorinated cation exchange membrane having sulfonic acid groups, which comprises hydrolyzing the pendant terminal groups of a membrane of a fluorinated copolymer comprising essentially the following recurring units (C) and (B):

(C) -(-CF2-CF-)- 1 L wherein L is F, Cl, CF3, ORF or H, RF being Cl-C,, perfluoroalkyl, (B) -(-CF2-CF-)-CF3 1 1 U-M-2U l-U) C-S02F wherein k is 0 or 1, and 1 is an integer of 3 to 5.

New Claims or Amendments to Claims filed on 21 November 1980 Superseded Claims 41.

New or Amended Claims:- 41. A process fc producing a fluorinated cation exchange membrane having both carboxylic acid groups and sulfonic acid groups, which comprises subjecting one surface layer of a membrane of a fluorinated copolymer comprising essentially the following recurring units (C) and (B):

(C) -(-CF2-CF-)- 1 L wherein L is F, Cl, CF., -OR, or H, R, being Cl-C5 perfluoroalkyl, -(CF2-CF-)-CF, 1 i.

O-CF,CF0),C-(UJ,-SO2F wherein k is 0 or 1, and I is an integer of 3 to 5, to treatment with an aqueous solution of at least one reducing agents selected from the group consisting of inorganic acids having reducing ability, salts thereof and hydrazines in the presence of at least one organic compound having 1 to 12 carbon atoms 25 selected from the group consisting of alcohols carboxylic acids, sulfonic acids, nitriles and ethers.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies maybe obtained.