JPS6152843B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an ion-exchangeable fluorinated polymer, and more specifically, to an improvement in the method for producing a fluorinated polymer containing a carboxylic acid type cation exchange group by copolymerization reaction in an aqueous medium. Carboxylic acid type fluororesin cation exchange membranes not only provide high purity alkali hydroxide as a diaphragm in the diaphragm electrolysis method of aqueous alkali chloride solutions, but also enable operation at high current efficiency and high current density. It is known that a high concentration of alkali hydroxide can be supplied to the cathode chamber. For example, even when the concentration of sodium hydroxide produced is 40% or more, the current efficiency can be maintained at 90% or more, which is an excellent performance. Therefore, in the fluorinated polymer containing a carboxylic acid type cation exchange group as described above, a fluorinated polymer having a high ion exchange capacity and a molecular weight as high as possible is produced by a copolymerization reaction in an aqueous medium. case,
The weight ratio of aqueous medium/carboxylic acid type functional monomer is
20/1 or less, and the copolymerization reaction pressure is 7Kg/
It has been proposed that it is effective to increase the temperature to cm ² or more. For example, see Japanese Patent Application Laid-Open No. 53-49090. The present inventor has conducted various studies and studies on the copolymerization reaction of a carboxylic acid type functional monomer and a fluorinated olefin compound such as tetrafluoroethylene in an aqueous medium. It was discovered that the composition of the resulting polymer changes, resulting in a fluorinated polymer with a non-uniform concentration of functional groups. In particular, there is a problem in that the ion exchange capacity of the resulting polymer decreases as the polymer concentration increases. The present inventor has found that by using a perfluoroalkyl group-containing compound having 8 carbon atoms such as C ₈ F ₁₇ COONH ₄ as an emulsifier, the above-mentioned drawbacks can be advantageously overcome, and a high polymer content of 20% by weight or more can be obtained. The surprising fact has been discovered that it is possible to produce a fluorinated polymer having a homogeneous composition without decreasing the ion exchange capacity regardless of the concentration. Thus, the present invention has been completed based on the above findings, and uses a fluorinated ethylenically unsaturated monomer and a polymerizable functional monomer having a carboxylic acid group or a functional group convertible to a carboxylic acid group. emulsion copolymerization in an aqueous medium in the presence of a fluorine-containing surfactant by the action of a polymerization initiation source to produce a copolymer having a functional monomer content of 5 to 30 mol%. A method for producing an ion-exchangeable fluorinated polymer comprising using a perfluoroalkyl group-containing compound having 8 carbon atoms as the fluorinated surfactant. This provides a new manufacturing method. In the present invention, it is important to use a polymerizable monomer containing a carboxylic acid group or a functional group convertible to a carboxylic acid group as the functional monomer. In consideration of the chlorine resistance, oxidation resistance, etc. of the resulting polymer, such carboxylic acid type functional monomer () is usually desirably a fluorovinyl compound, and preferred examples include general fluorovinyl compounds. formula
CF ₂ =CX−(OCF ₂ CFY) _l −(O) _n −(CFY′) _o −A
(Here, l is 0-3, m is 0-1, n is 0-12
X is a fluorine atom or _-CF3 , and Y and Y' are a fluorine atom or a perfluoroalkyl group having 1 to 10 carbon atoms. Also, A is -CN,
−COF, −COOH, −COOR ₁ , −COOM or −
CONR ₂ R ₃ , R ₁ is an alkyl group having 1 to 10 carbon atoms, R ₂ and R ₃ are hydrogen atoms or R ₁ , and M is an alkali metal or a quaternary ammonium group). Vinyl compounds are exemplified. From the viewpoint of performance and availability, X is a fluorine atom, Y is -CF ₃ , Y' is a fluorine atom, l is 0 to 1, and m is 0 to
1, n is 0 to 8, and A is preferably -COOR ₁ from the viewpoint of copolymerization reactivity. Preferred representative examples of such fluorovinyl compounds include _CF2 = _CFO ( _CF2 ) _{1-8 COOCH3} , _CF2 = CFO( _CF2 ) _{1-8 COOC2H5} , _CF2 = CF(CF2 _). ) _{0 to 8} COOCH ₃ , CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ CF ₂ COOCH ₃ , etc. Next, examples of the fluorinated ethylenically unsaturated monomer () include ethylene tetrafluoride, ethylene trifluoride chloride, propylene hexafluoride, ethylene trifluoride, vinylidene fluoride, and vinyl fluoride. , preferably the general formula CF ₂ =CZZ' (where Z and Z' are a fluorine atom, a chlorine atom, a hydrogen atom, or -CF ₃ )
It is a fluorinated olefin compound represented by
Among these, perfluoroolefin compounds are preferred, and tetrafluoroethylene is particularly preferred. In the present invention, each of the functional monomers () and ethylenically unsaturated monomers () may be used in combinations of two or more, and in addition to these compounds, other monomer compounds may also be used. components, such as olefin compounds () represented by the general formula CH ₂ =CR ₄ R ₅ (where R ₄ and R ₅ represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aromatic nucleus), CF ₂
= Fluorovinyl ether such as CFOR _f (R _f represents a perfluoroalkyl group having 1 to 10 carbon atoms), CF ₂ =CF−CF=CF ₂ , CF ₂ =CFO
( _CF2 ) _1~4 OCF=Divinyl monomer such as _CF2 ,
Furthermore, one or more types of other functional monomers such as sulfonic acid type functional groups can also be used in combination. Preferred representative examples of the olefin compound () include ethylene, propylene, butene-1, isobutylene, styrene, α-methylstyrene, pentene-1, hexene-1, heptene-1, 3-
Methyl-butene-1,4-methyl-pentene-1
Among them, ethylene, propylene, isobutylene and the like are particularly preferred from the viewpoint of production and performance of the resulting copolymer. Furthermore, for example, by using a divinyl monomer in combination, it is possible to crosslink the resulting copolymer and improve the mechanical strength when formed into a membrane. In the ion-exchange group-containing fluorinated polymer of the present invention, the composition ratios of the functional monomer (), the fluorinated olefin compound (), and the olefin compound () and other components are as follows: This is important because it is related to all the performances when used as an ion exchange membrane. First, the amount of the functional monomer () is directly related to the ion exchange capacity, but is preferably 5 to 30 mol% in the copolymer. If the amount of the functional monomer () present is too large, the mechanical strength of the ion exchange membrane will be impaired, and furthermore, the ion exchange performance will be reduced due to an increase in water content. It is not preferred because it does not exhibit ion exchange function. Therefore, the remainder of the compound () in the copolymer of the present invention is occupied by the () and other compounds (),
The amount of the olefin compound in parentheses () is important because it greatly affects the electrical, mechanical properties, chlorine resistance, etc. of the ion exchange membrane. Therefore, when the olefin compound () is used in combination, the molar ratio of the olefin compound ()/fluorinated olefin compound () is preferably 5/95 to 70 to 30,
In particular, it is preferable to set the ratio to 10/90 to 60/40. Further, when fluorovinyl ether, divinyl ether, etc. are used in combination, it is suitable to use the proportion of 30 mol % or less, preferably about 2 to 20 mol %, in the copolymer. In the present invention, the ion exchange capacity is selected from a wide range of 0.5 to 2.2 milliequivalents/gram dry resin, but the characteristic feature is that even if the ion exchange capacity is increased, the molecular weight of the resulting copolymer remains high. Therefore, the mechanical properties and durability of the copolymer do not deteriorate. The ion exchange capacity varies depending on the type of copolymer even within the above range, but is preferably 0.8 meq/g dry resin or more, especially
A ratio of 1.0 milliequivalent/g dry resin or more is preferable in terms of mechanical properties and electrochemical performance as an ion exchange membrane. In addition, the molecular weight of the fluorinated polymer obtained in the present invention is important because it is related to the mechanical performance and film formability as an ion exchange membrane, and T _Q
When expressed as a value of 150℃ or higher, preferably 170~
The temperature is preferably about 340°C, particularly about 180 to 300°C. In this specification, the term " _TQ " is defined as follows. That is, _TQ is defined as the temperature at which the volume flow rate is 100 mm ³ /sec, which is related to the molecular weight of the copolymer. Here, the volumetric flow rate is the copolymer under a pressure of 30 kg/cm ² and a diameter of 1 at a constant temperature.
mm, let the melt flow out from the orifice with a length of 2 mm,
The amount of copolymer flowing out is shown in units of mm ³ /sec. Incidentally, the "ion exchange capacity" was determined as follows. That is, an H-type cation exchange resin membrane was left in 1N HCl at 60°C for 5 hours to completely remove H.
The mixture was converted into a mold and thoroughly washed with water to ensure that no HCl remained. Then, 0.5g of this H-type film was heated to 0.1N.
It was left standing at room temperature for 2 days in a solution prepared by adding 25 ml of water to 25 ml of NaOH. The membrane is then 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 between the functional monomer and the fluorinated olefin compound is carried out at a weight ratio of 20/1 of the aqueous medium/functional monomer.
It is preferable to control the ratio to below, preferably 10/1 or less. If the amount of aqueous medium used is too large, the copolymerization reaction rate will decrease significantly,
It takes a long time to obtain a high copolymer yield. Also, too much aqueous medium makes it difficult to achieve high molecular weights when high ion exchange capacities are used. Furthermore, the following difficulties are recognized when using a large amount of an aqueous medium. For example, there are disadvantages in operational aspects such as an increase in the size of the reactor and separation and recovery of the copolymer. Next, in the present invention, it is preferable to employ a copolymerization reaction pressure of 7 kg/cm ² or more. If the copolymerization reaction pressure is too low, the copolymerization reaction rate cannot be maintained at a level that is practically satisfactory, and there are also difficulties in forming a high molecular weight copolymer. Furthermore, if the copolymerization reaction pressure is too low, the ion exchange capacity of the resulting copolymer will become extremely high, and the mechanical strength and ion exchange performance will tend to decrease due to increased water content. In addition, the copolymerization reaction pressure is desirably selected from 50 Kg/cm ² or less, taking into account the reaction apparatus or work operation in industrial implementation. Although it is possible to employ copolymerization reaction pressures higher than this range, it may not proportionately improve the objectives of the present invention. Therefore, in the present invention, the copolymerization reaction pressure is set at 7 to 50
Kg/cm ² , preferably from the range of 9 to 30 Kg/cm ² . In the present invention, it is important to carry out the copolymerization reaction in the presence of a fluorine-based surfactant made of a compound containing a perfluoroalkyl group in which the number of carbon atoms in the perfluoroalkyl group is 8. . When the number of carbon atoms in the perfluoroalkyl group is not 8, such as C ₇ F ₁₅ groups, C ₆ F ₁₃ groups, or C ₁₀ F ₂₁ groups, a fluorine-based surfactant consisting of a perfluoroalkyl group-containing compound can be used. Even in this case, as the polymer concentration increases, the ion exchange capacity of the resulting polymer decreases, making it difficult to obtain a fluorinated polymer with a homogeneous composition. On the other hand, when a compound containing a C ₈ F ₁₇ group in which the perfluoroalkyl group has 8 carbon atoms is used as a fluorosurfactant in the present invention, even if the polymer concentration increases, the formation of The ion exchange capacity of the polymer is not reduced, and a fluorinated polymer having a homogeneous composition can be obtained. In the present invention,
C ₈ F ₁₇ COONH ₄ , C ₈ F ₁₇ OONa, C ₈ F ₁₇ COOK,
_{C8F17COOH , C8F17SO3K , _}

A perfluoroalkyl group-containing compound as shown in the formula is employed as a fluorine-based surfactant, and can be used usually at a concentration of about 0.001 to 5% by weight, preferably about 0.05 to 2.0% by weight in an aqueous medium. In the copolymerization reaction of the present invention, conditions and operations other than the above-mentioned reaction conditions are not particularly limited and may be adopted over a wide range. For example, the optimum copolymerization reaction temperature can be selected depending on the type of polymerization initiation source, reaction molar ratio, etc., but normally, too high or too low a temperature is disadvantageous for industrial implementation. ℃, preferably from about 30 to 80℃. Therefore, in the present invention, as a polymerization initiation source,
It is desirable to select one that exhibits high activity at the above-mentioned suitable reaction temperature. For example, it is possible to use ionizing radiation that is highly active even at room temperature or lower, but it is usually more advantageous to use an azo compound or a peroxy compound for industrial implementation. Polymerization initiation sources suitably employed in the present invention include disuccinic acid peroxide, benzoyl peroxide, which exhibits high activity at about 20 to 90°C under the copolymerization reaction conditions,
Diacyl peroxides such as lauroyl peroxide and dipentafluoropropionyl peroxide, 2,2'-azobis(2-aminodinopropane) hydrochloride, 4,4'-azobis(4-cyanowallerianic acid), azobisiso Azo compounds such as butyronitrile, peroxy esters such as t-butyl peroxy isobutyrate and t-butyl peroxy pivalate, peroxy compounds such as diisopropyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, etc. dicarbonate,
These include hydroperoxides such as diisopropylbenzene hydroperoxide, inorganic peroxides such as potassium persulfate and ammonium persulfate, and their redox systems. In the present invention, the concentration of the polymerization initiator is 0.0001 to 3% by weight, preferably 0.001% by weight based on the total monomers.
It is about 2% by weight. By lowering the initiator concentration, it is possible to increase the molecular weight of the resulting copolymer and maintain a high ion exchange capacity. If the initiator concentration is too high, the tendency to decrease the molecular weight increases, which is disadvantageous to the production of high ion exchange capacity, high molecular weight copolymers. Other surfactants, dispersants, buffers, molecular weight regulators, etc. used in ordinary aqueous medium polymerization can also be added. In addition, as long as it does not inhibit the copolymerization reaction between the fluorinated olefin compound and the specific functional monomer and has low chain transfer, for example, fluorinated or fluorinated chlorinated solvents known as fluorocarbon solvents can be used. Inert organic solvents such as saturated hydrocarbons 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 stirring load, difficulty in removing heat, and insufficient diffusion of the fluorinated olefin monomer will occur. The fluorinated polymer of the present invention can be formed into a film by any appropriate means. For example, if necessary, functional groups are converted to carboxylic acid groups by hydrolysis, but such hydrolysis treatment can be performed either before or after film formation. It is usually preferable to perform hydrolysis treatment after film formation. Various methods can be used for forming the film, and known methods such as hot melt molding, latex molding, and cast molding after dissolving it in an appropriate solution can be used as appropriate. Since the ion exchange membrane made from the fluorinated polymer of the present invention has various excellent performances, it can be widely adopted in various fields, purposes, and uses. For example, it is suitably used in fields where corrosion resistance is particularly required, such as in diffusion dialysis, electrolytic reduction, and as diaphragms in fuel cells. In particular, when used as a cation-selective diaphragm for alkaline electrolysis, it can exhibit high performance that cannot be obtained with conventional ion exchange membranes. For example, an anode and a cathode are separated using a cation exchange resin membrane made of the fluorinated polymer of the present invention to form an anode chamber and a cathode chamber, and an aqueous alkali chloride solution is supplied to the anode chamber for electrolysis. Even in the case of a so-called two-chamber type tank in which alkali hydroxide is obtained from the cathode chamber, 40% or more can be obtained by electrolyzing at a current density of 5 to 20 A/dm ² using a sodium chloride aqueous solution with a concentration of 2N or higher as a raw material. 90% high concentration of sodium hydroxide
With this high current efficiency, stable production can be achieved over a long period of time. Furthermore, electrolysis is possible at low cell voltages of 4.5 volts or less. 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 such explanations. Example 1 1000g of water was placed in an autoclave equipped with 2 baffle plates and equipped with an electromagnetic induction stirrer.
C ₈ F ₁₇ 2 g of COONH ₄ , 5 g of Na ₂ HPO ₄・12H ₂ O
g, 3 g of NaH ₂ PO ₄ 2H ₂ O, 0.26 g of (NH ₄ ) ₂ S ₂ O ₈
g, then CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃
I prepared 200g. After thoroughly degassing with liquid nitrogen, 55
The temperature was raised to .degree. C., and ethylene tetrafluoride was introduced up to 10.7 Kg/ ^cm.sup.2 to start the reaction. During the reaction, tetrafluoroethylene was introduced into the system and the pressure was maintained at 10.7 Kg/cm ² . During the reaction, a portion of the latex was extracted from the autoclave at intervals shown in Table 1 below, and the polymer concentration of the latex and the composition of the obtained polymer were measured. The composition of CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ in the polymer is obtained by hydrolyzing the polymer by a conventional method.
After converting COOCH ₃ to -COOH, the carboxylic acid was titrated with an alkali, and the functional group capacity was expressed as milliequivalents of the carboxylic acid per unit weight of the polymer.

[Table] The functional group capacity of the polymer does not change depending on the polymer concentration, and a polymer with a constant composition can be obtained. Comparative example 1 2 1000g of water in an autoclave,
C ₇ F ₁₅ 5 g of COONH ₄ , 5 g of Na ₂ HPO ₄・12H ₂ O
g, 3 g of NaH ₂ PO ₄ 2H ₂ O, 0.15 g of (NH ₄ ) ₂ S ₂ O ₈
g, then CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃
I prepared 200g. 57℃ after sufficient degassing with liquid nitrogen
The temperature was raised to 1, and tetrafluoroethylene was introduced up to 12.0 Kg/cm ² to start the reaction. During the reaction, tetrafluoroethylene was introduced into the system and the pressure was maintained at 12 Kg/cm ² . Example 1
In the same manner as above, a portion of the latex was extracted from the autoclave at intervals shown in Table 2 below during the reaction, and the polymer concentration and composition were determined.

[Table] Functional group capacity decreases with increasing polymer concentration. It can be seen that the obtained composition is a cumulative polymer composition, and the functional group capacity of the polymer instantaneously generated in each polymer concentration range is lower than this, resulting in a non-uniform polymer composition. Comparative Example 2 C ₆ F ₁₃ COONH ₄ and
A similar experiment was conducted using C ₁₀ F ₂₁ COONH ₄ , but as in Comparative Example 1, it was observed that the functional group capacity decreased as the polymer concentration increased.

Claims (1)

[Claims] 1. A fluorinated ethylenically unsaturated monomer and a polymerizable functional monomer having a carboxylic acid group or a functional group convertible to a carboxylic acid group are combined by the action of a polymerization initiation source. An ion-exchangeable fluorinated polymer comprising emulsion copolymerization in an aqueous medium in the presence of a fluorosurfactant to produce a copolymer containing 5 to 30 mol% of the functional monomer. A method for producing an ion-exchangeable fluorinated polymer, characterized in that a perfluoroalkyl group-containing compound in which the perfluoroalkyl group has 8 carbon atoms is used as the fluorine-based surfactant. 2 As a functional monomer, the general formula CF ₂ =CX−
(OCF ₂ CFY) _l −(O) _n −(CFY′) _o −A (in the formula, l is an integer from 0 to 3, m is an integer from 0 to 1, n is an integer from 0 to 12, and X is an integer from 0 to 12. is an elementary atom or _-CF3 , Y,
Y' is a fluorine atom or a perfluoroalkyl group having 1 to 10 carbon atoms, and A is -CN, -COF, -
COOH, _-COOR1 , -COOM or _-CONR2R3 , _R1 is an alkyl group having 1 to 10 carbon atoms, _R2 , _R3 are _a hydrogen atom or _R1 , M is an alkali metal or a quaternary Claim 1 using a fluorovinyl compound represented by
Manufacturing method described in section. 3. A fluorinated olefin represented by the general formula CF ₂ =CZZ′ (where Z and Z′ are a fluorine atom, a chlorine atom, a hydrogen atom, or CF ₃ ) as a fluorinated ethylenically unsaturated monomer. The manufacturing method according to claim 1, which uses the compound. 4 General formula as a functional monomer (However, l in the formula is 0-1, m is 0-1, n is 0
8, A is -COOR ₁ and R ₁ is a lower alkyl group. 5. The manufacturing method according to claim 3, wherein tetrafluoroethylene is used as the fluorinated ethylenically unsaturated monomer. 6. The production method according to claim 1, which is carried out at a copolymerization reaction temperature of 20 to 90°C. 7 Reduce the copolymer concentration in the produced copolymer slurry to 40
2. The method according to claim 1, wherein the copolymerization reaction is carried out by controlling the amount to be less than or equal to % by weight. 8. The production according to claim 1, wherein a fluorine-based surfactant comprising a perfluoroalkyl group-containing compound whose perfluoroalkyl group has 8 carbon atoms is used at a concentration of 0.001 to 5% by weight in an aqueous medium. Law.