JPH0689075B2 - Process for producing perfluorocarbon polymer having sulfonic acid type functional group - Google Patents

Description

The present invention relates to a method for producing a perfluorocarbon polymer having a sulfonic acid type functional group, more specifically, a high content ratio of a sulfonic acid type monomer by emulsion copolymerization in an aqueous medium, That is, it relates to a novel method capable of producing a sulfonic acid type perfluorocarbon polymer having a high ion exchange capacity.

Conventionally, in emulsion polymerization of a fluorine-containing monomer such as tetrafluoroethylene in an aqueous medium, C ₇ F ₁₅ COONH ₄ , C ₈ F ₁₇ C
A polymerization system using a perfluorocarboxylic acid type emulsifier such as OONH ₄ has been adopted. The same perfluorocarboxylic acid type emulsifier is used in the copolymerization of C ₂ F ₄ etc. with a monomer having a carboxylic acid type functional group such as CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ in an aqueous medium. A perfluorocarbon polymer having a high ion exchange capacity is smoothly and advantageously produced by emulsion copolymerization.

on the other hand, In order to achieve a high ion exchange capacity in the copolymerization of a monomer having a sulfonic acid type functional group such as C ₂ F ₄ and the like, in order to achieve a high ion exchange capacity, a bulk polymerization without using a polymerization medium or a fluorine system such as trichlorotrifluoroethane Solution polymerization using a solvent as a medium has been adopted. With sulfonic acid type monomer
The method of employing emulsion polymerization in an aqueous medium for copolymerization of C ₂ F _{4 and the} like is generally known in the literature. However, according to the study of the present inventors, in the conventional emulsion polymerization in an aqueous medium using a conventional perfluorocarboxylic acid type emulsifier, when performing ultrasonic emulsification treatment (see JP-A-60-250009).
Other than that, only those with extremely low ion exchange capacity can be obtained,
At least 0.5 when used as a cation exchange membrane material
It has been found very difficult to achieve a milliequivalent / gram dry resin.

The present inventor, based on the recognition of the above problems, a sulfonic acid type perfluorocarbon polymer having a high ion exchange capacity by emulsion copolymerization in an aqueous medium that does not require a special treatment such as ultrasonic treatment. As a result of various studies and studies in order to provide a means that can be easily produced, the following interesting findings have been obtained.

That is, in emulsion polymerization in an aqueous medium, C ₈ F ₁₇ CO ₃ NH ₄ is used instead of carboxylic acid type emulsifiers such as C ₇ F ₁₅ CO ₂ NH ₄ and C ₈ F ₁₇ CO ₂ NH ₄ which are conventionally used as emulsifiers. Emulsion copolymerization of sulfonic acid functional group-containing perfluorocarbon monomer and perfluoroolefin using a sulfonic acid type emulsifier such as This is a new finding that a coalesce can be produced. The present invention is the following invention relating to a method for producing a sulfonic acid type functional group-containing perfluorocarbon polymer using this emulsifier.

In the method of emulsion-copolymerizing a perfluorocarbon monomer containing a sulfonic acid type functional group and a perfluoroolefin by the action of a polymerization initiation source in an aqueous medium, a general formula Rf-SO ₃ M Rf: a polyfluoroalkyl group M: H, an alkali metal , or ^{NR 1 R 2 R 3 R 4} (R 1, R 2, R 3, R
^{4. A} method for producing a perfluorocarbon polymer having a sulfonic acid type functional group, characterized in that emulsifiers each represented by H or an alkyl group are independently used.

The sulfonic acid type emulsifier used in the present invention has 3 to 2 carbon atoms.
It is preferable to use one having a polyfluoroalkyl group of 0, preferably 6 to 12, preferably a perfluoroalkyl group, or a mixture thereof because the emulsifying action is large and the chain transfer action is small. Each of R ^{1 to} R ⁴ is preferably a hydrogen atom, and when it is an alkyl group, a lower alkyl group is preferred. Preferred M is NH ₄ , or K or Na, and NH ₄ is particularly preferred. Such a fluorinated emulsifier can be used usually in an aqueous medium at a concentration of 0.001 to 5% by weight, preferably 0.05 to 3% by weight, more preferably 0.1 to 2% by weight. The more the emulsifier is used, the more the polymer having sulfonic acid type functional groups can be obtained. However, if the amount of the emulsifier is excessive, it is not preferable in terms of cleaning and cost of the polymer. Therefore, the upper limit of the amount used is the above level. Appropriate.

As the sulfonic acid type functional group-containing perfluorocarbon monomer used in the present invention, those publicly known or well known can be exemplified in a wide range. Suitable examples include the general formula CF ₂ = CF- (OCF ₂ CFX) l- (O).
_{q- (CF 2) n- (CF} 2 CFX ') mA ( wherein, l is 0 to 3, m
Is 0 to 3, n is 0 to 12, q is 0 or 1, and X is -F
Or a -CF _3, X 'is -F or -CF _3, A is fluoro vinyl compound is exemplified represented by a is) sulfonic acid functional groups. Usually, in terms of availability,
X and X ′ are —CF ₃ , l is 0 or 1, m is 0, and n is 0.
8, q is 0 or 1, and A is preferably —SO ₂ F from the viewpoint of copolymerization reactivity. As a preferable representative example of such a fluorovinyl compound, CF ₂ = CFO (CF ₂ ) _{1 to 8} SO ₂ F, CF ₂ = CF (CF ₂ ) _0-8 SO ₂ F, And so on.

In the present invention, the perfluoroolefin and the sulfonic acid type functional group-containing perfluorocarbon monomer as described above can be emulsion-copolymerized in an aqueous medium, but the sulfonic acid type functional group-containing perfluorocarbon monomer can be used in two or more kinds. But in addition to these monomers,
Other components, for example, a carboxylic acid type functional group-containing perfluorocarbon monomer, CF ₂ = CFORf (Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms), or CF ₂ = CF-CF =
One or two or more of divinyl monomers such as CF ₂ , CF ₂ = CFO (CF ₂ ) _{1 to 4} OCF = CF ₂ may be used in combination. Thus, in the present invention, since a perfluorocarbon polymer in which a sulfonic acid type functional group-containing perfluorocarbon monomer is copolymerized in a high proportion by emulsion copolymerization in an aqueous medium, the sulfonic acid type functional group is usually used. The copolymerization ratio of the group-containing perfluorocarbon monomer is 20
It is desirable to select the use ratio of the above-mentioned various monomers in order to produce a perfluorocarbon polymer having a weight% or more. In particular, it is preferable to select it so as to produce a perfluorocarbon polymer having a copolymerization ratio of the sulfonic acid type functional group-containing perfluorocarbon monomer of about 25 to 60% by weight.

When the sulfonic acid type perfluorocarbon polymer obtained according to the present invention is used as an ion exchange membrane, its ion exchange capacity is selected from a wide range of 0.5 to 2.0 meq / g dry resin, which will be described below. By adopting such conditions, the molecular weight of the produced copolymer can be increased even if the ion exchange capacity is increased, and therefore the mechanical properties and durability of the copolymer are not lowered.
Although the ion exchange capacity varies depending on the type of the copolymer even in the above range, it is preferably 0.7 meq / g dry resin or more, particularly 0.8 meq / g dry resin or more as an ion exchange membrane. It is preferable in terms of mechanical properties and electrochemical performance. Further, the molecular weight of the sulfonic acid type perfluorocarbon polymer obtained in the present invention is important because it is related to the mechanical performance and the film-forming property as an ion exchange membrane, and when expressed by the value of T _Q , 150 ° C or higher, Preferably 170-
The temperature is preferably 340 ° C, particularly about 180 to 280 ° C.

In the present specification, the term "T _Q " is defined as follows. That is, the temperature at which the volumetric flow rate related to the molecular weight of the copolymer is 100 mm ³ / sec is defined as T _Q. Here, the volumetric flow rate is a value obtained by melting the copolymer under pressure of 30 kg / cm ² through an orifice with a diameter of 1 mm and a length of 2 mm at a constant temperature, and showing the amount of the copolymer flowing out in the unit of mm ³ / sec. Is. The "ion exchange capacity" was determined as follows. That is, the H-type cation exchange resin membrane was mixed with 6% in 1N HCl.
The mixture was left at 0 ° C. for 5 hours, completely converted to H-form, and washed sufficiently with water so that HCl did not remain. After that, this H-shaped film 0.
5 g in a solution of 25 ml of 0.1N NaOH and 25 ml of water,
It was allowed to stand at room temperature for 2 days. Then, the membrane is taken out, and the amount of NaOH in the solution is determined by back titration with 0.1N HCl.

In the present invention, the copolymerization reaction of a functional monomer such as a sulfonic acid type monomer with a perfluoroolefin is carried out by using an aqueous medium in an amount of 20/1 by weight ratio of aqueous medium / functional monomer.
It is preferable to carry out the treatment with the following, preferably controlled to 10/1 or less. If the amount of aqueous medium used is too large,
There are disadvantages in terms of work operation such as enlargement of reactor or separation and recovery of copolymer.

Next, in the present invention, it is preferable to adopt a copolymerization reaction pressure of ² kg / cm ² or more. When the copolymerization reaction pressure is too low, it is difficult to maintain the copolymerization reaction rate at a level that is practically satisfactory, and it is difficult to form a high molecular weight copolymer. On the other hand, if the copolymerization reaction pressure is too low, the ion exchange capacity of the produced copolymer will increase, and the mechanical strength and the ion exchange performance will tend to decrease due to an increase in the water content. Incidentally, the copolymerization reaction pressure is preferably selected from 50 kg / cm ² or less in consideration of the reaction apparatus or the work operation in industrial practice. Although it is possible to adopt a copolymerization reaction pressure higher than this range,
It is not possible to proportionally improve the object of the present invention.
Therefore, in the present invention, the copolymerization reaction pressure is 2 to 50 kg.
It is optimum to select from the range of / cm ² , preferably 4 to 30 kg / cm ² .

In the copolymerization reaction of the present invention, other conditions and operations other than the above reaction conditions are not particularly limited and can be adopted over a wide range. For example, the copolymerization reaction temperature may be selected as an optimum value depending on the kind of the weight initiation source, the reaction molar ratio, etc., but usually a too high temperature or a low temperature is disadvantageous for industrial implementation, so that it is 20 to 90. C, preferably about 30-80C.

Therefore, in the present invention, it is desirable to select, as the polymerization initiation source, one that exhibits high activity at the above-mentioned suitable reaction temperature. For example, ionizing radiation having high activity even at room temperature or lower can be adopted, but it is usually more advantageous for industrial practice to use an azo compound or a peroxy compound. The polymerization initiation source preferably adopted in the present invention is, for example, disuccinic acid peroxide, benzoyl peroxide, lauroyl peroxide, dipentafluoropropionyl peroxide, etc. which show high activity at about 20 to 90 ° C. under the copolymerization reaction conditions. Diacyl peroxide, 2,2'-azobis (2-amidinopropane) hydrochloride, 4,4'-azobis (4-cyanovaleric acid), azo compounds such as azobisisobutyronitrile, t-butylperoxy Peroxyesters such as isobutyrate and t-butylperoxypivalate, peroxydicarbonates such as diisopropylperoxydicarbonate and di-2-ethylhexylperoxydicarbonate, hydroperoxides such as diisopropylbenzene hydroperoxide , Potassium persulfate, ammonium persulfate, etc. Inorganic peroxides and their redox systems and the like.

In the present invention, the concentration of the polymerization initiation source is about 0.0001 to 3% by weight, preferably about 0.0001 to 2% by weight, based on all the monomers. By decreasing the concentration of the starting source, it is possible to increase the molecular weight of the produced copolymer, and it is possible to maintain a high ion exchange capacity. If the starting source concentration is too high, the tendency of lowering the molecular weight increases, which is disadvantageous to the formation of a high ion exchange capacity, high molecular weight copolymer.

In addition, a dispersant, a buffering agent, a molecular weight adjusting agent and the like used in ordinary emulsion copolymerization in an aqueous medium may be added. Further, an inert organic solvent such as a fluorinated or fluorinated chlorinated saturated hydrocarbon known as a CFC-based solvent, as long as it does not inhibit the copolymerization reaction in the present invention and has little chain transfer. Can also be added.

Therefore, in the present invention, it is preferable to control the concentration of the produced copolymer to 40% by weight or less, preferably 30% by weight or less. If the concentration is too high, problems such as increased non-uniformity of copolymer composition and dispersion breakage of latex are observed.

The sulfonic acid type perfluorocarbon weight body of the present invention is
The film can be formed by an appropriate means. For example, if necessary, the functional group is hydrolyzed to be converted into a sulfonic acid group, and such a hydrolysis treatment can be performed before or after film formation. Usually, it is desirable to carry out hydrolysis treatment after film formation. Various kinds of film forming means can be adopted, and for example, known or well-known methods such as hot melt molding, latex molding, and cast molding by dissolving in a suitable solution can be appropriately adopted. Furthermore, it is also possible to laminate two or more layers with a film having a different ion exchange capacity or a film having a different functional group such as a carboxylic acid group.
Further, reinforcement with cloth, fibers, non-woven fabric or the like can be added.

The ion exchange membrane from the sulfonic acid type perfluorocarbon polymer of the present invention has various excellent performances,
It can be widely adopted in various fields, purposes, applications, and the like. For example, it is preferably used as a diffusion dialysis, electrolytic reduction, a diaphragm of a fuel cell, and the like, particularly in a field requiring touch resistance.
In particular, when it is used as a cation-selective membrane for alkaline electrolysis, it can exhibit high performance in a laminated membrane with a carboxylic acid type membrane. For example, with the cation exchange resin film as described above, the anode and the cathode are partitioned to form an anode chamber and a cathode chamber, an alkaline chloride aqueous solution is supplied to the anode chamber for electrolysis, and the cathode chamber is hydroxylated. Even in the case of a so-called two-chamber type tank for obtaining alkali, by using an aqueous sodium chloride solution having a concentration of ² N or more as a raw material and electrolyzing at a current density of 5 to 50 A / dm ² , sodium hydroxide having a high concentration of 30% or more can be obtained. Can be manufactured stably for a long period of time with high current efficiency and low cell voltage.

Next, examples of the present invention will be described in more detail, but it goes without saying that the present invention is not limited by the description.

EXAMPLES Example 1 Ion exchange water _{100g, C 8 F 17 SO 3} NH 4 0.20g, Na 2 HPO 4 · 12H 2 O
0.50g, NaH ₂ PO ₄・ 2H ₂ O 0.29g, (NH ₄ ) ₂ S ₂ O ₈ 35mg, and CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F 20g .
After charging into a stainless steel autoclave in No. 2 and thoroughly degassing with liquid nitrogen, bring the temperature to 57 ° C and add tetrafluoroethylene.
The charge polymerization was started up to 6 kg / cm ² . During the reaction, tetrafluoroethylene was introduced from outside the system to keep the pressure constant. After 5 hours, unreacted tetrafluoroethylene was purged to terminate the polymerization, and the obtained latex was coagulated.
After washing and drying, 17.4 g of a copolymer was obtained. The ion exchange capacity of the copolymer was 1.20 meq / g dry resin. A tough film was obtained by press-forming the copolymer at 250 ° C., and a sulfonic acid type ion exchange membrane was obtained by hydrolysis with a 25% aqueous solution of HaOH.

Then, instead of C ₈ F ₁₇ SO ₃ NH ₄ as an emulsifier, C ₈ F ₁₇ -CO ₂ NH ₄
Polymerization and post-treatment were carried out in the same manner except that 0.20 g was used, and the ion exchange capacity of the obtained copolymer was 0.1 meq / g dry resin or less.

Example 2 Polymerization and post-treatment were carried out in the same manner as in Example 1 except that the pressure of tetrafluoroethylene was changed to 9 kg / cm ² , and the ion exchange capacity of the obtained copolymer was 0.85 meq / g dry resin. Met.

Example 3 Polymerization was carried out in the same manner as in Example 1 except that 0.20 g of C ₈ F ₁₇ SO ₃ K was used as an emulsifier and the pressure of tetrafluoroethylene was set to 5 kg / cm ² . The ion-exchange capacity of the obtained copolymer was 0.82.
It was meq / g dry resin.

Example 4 Polymerization and post-treatment were carried out in the same manner as in Example 1 except that 1.00 g of C ₈ F ₁₇ SO ₃ NH ₄ was used as an emulsifier and the pressure of tetrafluoroethylene was set to 9 kg / cm ² , which was obtained. The ion exchange capacity of the copolymer was 1.05 meq / g dry resin.

EFFECTS OF THE INVENTION The present invention provides a perfluorocopolymer having a large amount of sulfonic acid groups, which cannot be obtained unless special treatment such as ultrasonic treatment is performed in conventional emulsion copolymerization using a carboxylic acid type emulsifier. By using a sulfonic acid type emulsifier, a means for easily synthesizing without special treatment is provided.

The sulfonic acid type functional group of the emulsifier may be either a salt type or an acid type, but particularly when an ammonium salt type is used, it is easy to increase the copolymerization ratio of the monomer having a sulfonic acid type functional group. .

Claims (4)

[Claims] 1. A method of emulsion-copolymerizing a perfluorocarbon monomer having a sulfonic acid type functional group and a perfluoroolefin by the action of a polymerization initiation source in an aqueous medium, wherein Rf-SO ₃ M Rf is a polyfluoroalkyl group M. : H, alkali metal, or NR ¹ R ² R ³ R ⁴ (R ¹ , R ² , R ³ ,, R
^{4. A} method for producing a perfluorocarbon polymer having a sulfonic acid type functional group, characterized in that emulsifiers each represented by H or an alkyl group are independently used. 2. The method according to claim 1, wherein Rf in the general formula is a perfluoroalkyl group. 3. The method according to claim 2, wherein Rf in the general formula is a perfluoroalkyl group having 6 to 12 carbon atoms. 4. A sulfonic acid type functional group-containing perfluorocarbon monomer is CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F, and the perfluoroolefin to be copolymerized therewith is tetrafluoroethylene. And the former copolymerization ratio is
The method according to claim 1, which is 20% by weight or more.