JP3280727B2 - Method for producing perfluorocarbon polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a perfluorocarbon polymer having a sulfonic acid type functional group.

[0002]

2. Description of the Related Art Conventionally, in emulsion polymerization of a fluorine-containing monomer such as tetrafluoroethylene using water as a medium,
A polymerization system using a perfluorocarboxylic acid type emulsifier such as C ₇ F ₁₅ CO ₂ NH ₄ and C ₈ F ₁₇ CO ₂ NH ₄ is employed. _{Then, CF 2 = CFO (CF 2} ) 3 CO 2 CH also in the copolymerization of perfluorocarbon monomers having _3-mentioned carboxylic acid functional group and CF ₂ = like CF ₂ and, similar perfluorocarboxylic acid type emulsifier Used
High ion exchange capacity perfluorocarbon polymers are advantageously produced by emulsion copolymerization.

On the other hand, CF ₂ = CFOCF ₂ CF (CF ₃ )
In the copolymerization of such perfluorocarbon monomer CF ₂ = CF ₂ with such sulfonic acid functional group of OCF ₂ CF ₂ SO ₂ F, in order to achieve a high ion exchange capacity, bulk polymerization without using a polymerization medium Alternatively, solution polymerization using a fluorinated solvent such as trichlorotrifluoroethane as a medium is employed.

[0004] Sulfonic acid type monomer and tetrafluoroe
How to adopt in aqueous medium the emulsion polymerization in the copolymerization, such as styrene, it is also generally known in the literature. However, according to the study of the present inventor, in the conventional emulsion polymerization using a perfluorocarboxylic acid type emulsifier, only an extremely low ion exchange capacity can be obtained, and at least when used as a raw material of an ion exchange membrane, etc. It has proven very difficult to achieve 0.5 meq / gram dry resin.

As a solution, ultrasonic waves (Japanese Unexamined Patent Publication No.
No. -250009) and a homogenizer (JP-A-62-2).
No. 88617), a method in which sulfonic acid type monomers are emulsified in advance and then copolymerized, or a method using a special emulsifier (JP-A-62-288614, JP-A-62-2886).
No. 15, JP-A-62-288616). However, in the method of emulsifying in advance, the production process becomes complicated, and in the method of using a special emulsifier, these emulsifiers are more expensive than ordinary perfluorocarboxylic acid type emulsifiers, the amount used is large, and the production cost is high. There were problems such as rising.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problem.
It was made to be decided, special pre-processing and special
Provided is a method for easily producing a perfluorocarbon polymer having a large ion exchange capacity at a high yield without using an emulsifier .

[0007]

Means for Solving the Problems The present invention is intended to solve the above problem, in an aqueous medium, emulsion sulfonic acid functional group-containing perfluorocarbon monomers and perfluoro I Fi down by the action of the polymerization initiating source in method in which copolymerization, sulfonic acid functional group in -SO ₂ F
There are, using the fluorinated emulsifier, and certain water-soluble organic solvent in the production method of perfluoro car <br/> Bonn polymer which comprises adding to the aqueous medium.

In the method of the present invention, as the fluorinated emulsifier, those conventionally used in emulsion polymerization of tetrafluoroethylene and other fluorinated monomers can be widely used. For example, C ₇ F ₁₅ CO ₂ NH ₄ , C ₈ F ₁₇ CO
Perfluorocarboxylic acid type emulsifier such as ₂ NH ₄ , C ₈ F
₁₇ perfluorosulfonic acid type emulsifiers such as ₁₇ SO ₃ NH ₄ ,
A perfluoroethercarboxylic acid type emulsifier such as C ₂ F ₅ [CF ₂ OCF (CF ₃ )] ₃ CO ₂ NH ₄ can be used. They can also be used potassium salt type or sodium salt-type, readily available, highly expensive and emulsifying effect NH ₄
The use of a mold is preferred.

The amount of the fluorinated emulsifier can be used in an aqueous medium at a concentration of about 0.01 to 5% by weight, preferably about 0.05 to 2.0% by weight.

The water-soluble organic solvent used in the present invention is preferably a water-soluble organic solvent having oxygen in the molecular formula, for example, lower alcohols such as ethanol, propanol and butanol, ketones such as acetone and methyl ethyl ketone, tetrahydrofuran, and the like. Ethers such as dioxane are used. Among them propanol since the greater sulfonic acid functional group-containing perfluorocarbon polymer having a molecular weight can be obtained, t-butanol, acetone and the like
preferable. Particularly, use of t- butanol is preferred.

The addition amount of the water-soluble organic solvent is as follows:
Against the aqueous medium body, it used 2 to 25 wt%. If the amount is less than this, the effect is poor, and if it is too large, the resulting emulsified particles may be destroyed. More preferably, 5 to 20% by weight is used.

The sulfonic acid type functional group-containing perfluorocarbon monomer to be polymerized in the present invention can be exemplified in a wide range. Preferred is a compound of the general formula CF ₂ ＣＦCF— (OCF ₂ CFX) _p — (O) _q —
(CF ₂ ) _r- (CF ₂ CFZ) _s -A (where p is 0
To 3, q is 0 or 1, r is 0 to 12, s is 0 to 12, X is -F or -CF _3, Z is -F or -CF
Is _3, A is represented by -SO ₂ a F). Usually in view of availability, X and Z are _-CF 3, p is 0 or 1, r is 0 to 8, s is Ru 0 der. The A is -SO ₂ F are preferred from such copolymerization reactivity.

Preferred representative examples of such a fluorovinyl compound include CF ₂ ＣＦCFO (CF ₂ ) _t SO ₂ F and CF ₂ ＣＦCFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _t SO
_{2 F, CF 2 = CF (} CF 2) u SO 2 F, CF 2 = CF [OCF 2 CF (CF 3)] x SO 2 F ( wherein, t is 1 to 8, u is 0 to 8, x Is 1) to 5) .

In the present invention, the perfluoroolefin
Is preferably tetrafluoroethylene. In the present invention, and such as described above perfluoroolefin and scan Le <br/> acid functional group-containing perfluorocarbon monomer is made to emulsion copolymerization in an aqueous medium, a sulfonic acid functional group-containing perfluorocarbon monomer In addition to these monomers, not only these monomers can be used, but also other components such as a carboxylic acid type functional group-containing perfluorocarbon monomer, CF ₂ ＣＦCFOR _f (R _f has 1 to 10 carbon atoms)
Perfluoroalkyl group) or CF ₂ ＝
_{CF-CF = CF 2, CF} 2 = CFO (CF 2) y OCF =
One or two or more kinds of divinyl monomers such as CF ₂ (y is 1 to 4) may be used in combination.

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 is intended, the sulfonic acid type functional group is usually used. The copolymerization ratio of the contained perfluorocarbon monomer is 2
In order to produce a perfluorocarbon polymer of 0% by weight or more, it is desirable to select the use ratio of the above various monomers. In particular, the copolymerization ratio of the sulfonic acid type functional group-containing perfluorocarbon monomer is 25 to 60% by weight.
It is preferred that it be selected in order to produce a certain degree of perfluorocarbon polymer.

When the sulfonic acid type perfluorocarbon polymer obtained by 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. But
By adopting the conditions described below, even if the ion exchange capacity is increased, the molecular weight of the produced copolymer can be increased, and thus the mechanical properties and durability of the copolymer can be increased. The ion exchange capacity varies depending on the type of the copolymer even in the above range, but is preferably 0.6 meq / g dry resin or more, especially 0.7 meq / g dry resin or more. It is preferable in terms of mechanical properties and electrochemical performance as an exchange membrane. 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 , it is 150 ° C. or more. Preferably, the temperature is set to about 170 to 340 ° C, particularly about 180 to 280 ° C.

In the present invention, the term "T _Q " is defined as follows. That, T _Q is the temperature der the volume flow rate related to the molecular weight of the copolymer exhibits a 100 mm ³ / sec
You. Volume flow rate, the copolymer 30kg / cm ² pressure,
Diameter 1mm at a constant temperature, allowed molten outflow from the orifice of length 2 mm, in which the copolymer amount flowing shown in units of mm ³ / sec.

The "ion exchange capacity" was determined as follows. That is, the H-type cation exchange resin membrane is
Was left at 60 ° C. for 5 hours in HCI to completely convert to Form H, and washed thoroughly with water so that HCl did not remain. Thereafter, 0.5 g of the H-type membrane was added to 0.1 N NaOH 2
The mixture was allowed to stand at room temperature for 2 days in a solution obtained by adding 25 ml of water to 5 ml. The membrane is then removed and the NaOH in solution
Is determined by back titration with 0.1N HCl.

In the present invention, the copolymerization reaction between a functional monomer such as a sulfonic acid type monomer and a perfluoroolefin is carried out by using an aqueous medium in an amount of 20/1 by weight of the aqueous medium / functional monomer. It is preferable to carry out the process under the following control, preferably at 10/1 or below. If the amount of the aqueous medium used is too large, there are disadvantages in terms of work operation such as enlargement of the reactor or separation and recovery of the copolymer. Here, the aqueous medium represents a mixture of water and a water-soluble solvent.

Next, in the present invention, 2 kg / cm ²
It is preferable to employ the above copolymerization reaction pressure. If the copolymerization reaction pressure is too low, it is difficult to maintain the copolymerization reaction rate at a practically satisfactory height, 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 water content. Incidentally, the copolymerization reaction pressure is desirably selected from 50 kg / cm ² or less in consideration of the reaction apparatus or operation in industrial practice. Although it is possible to employ a copolymerization reaction pressure higher than this range, the object of the present invention cannot be proportionately improved. Therefore, in the present invention, it is optimal to select the copolymerization reaction pressure from the range of ² to 50 kg / 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 can be employed over a wide range without any particular limitation. For example, the optimum value of the copolymerization reaction temperature can be selected depending on the type of the weight initiation source, the reaction molar ratio, and the like. However, usually too high or low temperature is disadvantageous for industrial practice, ° C, preferably from about 20 to 80 ° C.

In the present invention, it is desirable to select a polymerization initiating source having a high activity at the above-mentioned suitable reaction temperature. For example, ionizing radiation having high activity can be employed even at room temperature or lower, but it is usually advantageous to employ an azo compound or a peroxy compound for industrial implementation.

The polymerization initiation source preferably employed in the present invention includes:
The copolymerization reaction disuccinic acid peroxide showing a high activity at about 10 to 90 ° C. under conditions, benzoyl peroxide, lauroyl peroxide, bis (pentafluoropropionyl) diacyl peroxides such as peroxide, 2,2' Azobis (2-amidinopropane)
Hydrochloride, 4,4'-azobis (4-cyano bar Leilian acid), azo compounds such as azobisisobutyronitrile, t
Peroxyesters such as -butylperoxyisobutyrate and t-butylperoxypivalate; and peroxydicarbonates such as diisopropylperoxydicarbonate and bis ( 2-ethylhexyl ) peroxydicarbonate . , Hydroperoxides such as diisopropylbenzene hydroperoxide, inorganic peroxides such as potassium persulfate and ammonium persulfate, and redox series thereof.

In the present invention, the concentration of the polymerization initiator is
It is about 0.0001 to 3% by weight, preferably about 0.0001 to 2% by weight, based on all monomers. By lowering the concentration of the polymerization initiator , it is possible to increase the molecular weight of the produced copolymer and to maintain a high ion exchange capacity. If the concentration of the polymerization initiator is too high,
The tendency to decrease the molecular weight increases, which is disadvantageous for a device having a high ion exchange capacity and a high molecular weight copolymer. In addition, a dispersing agent, a buffering agent, a molecular weight modifier and the like used in an ordinary emulsion copolymerization using water as a medium can be added.

In the present invention, the produced copolymer concentration is 4
It is suitable to control at 0% by weight or less, preferably at 30% by weight or less. If the concentration is too high, difficulties such as an increase in the non-uniformity of the copolymer composition and dispersion destruction of the latex are recognized. When an ion-exchange membrane is produced from the sulfonic acid type perfluorocarbon weight body of the present invention, the membrane can be formed by an appropriate means. For example, if necessary, a functional group is converted into a sulfonic acid group by hydrolysis. Such a hydrolysis treatment can be performed before or after film formation. Usually, it is desirable to carry out hydrolysis treatment after film formation. The film means may be adopted various ones, for example, heat melting molding, latex molding, may be employed known or well-known methods such as cast molding of dissolved in an appropriate solution as appropriate. Additionally, film is had with different ion exchange capacity can be laminated film and the two or more layers having different functional groups of a carboxylic acid group. Reinforcement with cloth, fiber, nonwoven fabric, etc. can also be added.

The ion-exchange membrane made of the sulfonic acid-type perfluorocarbon polymer of the present invention has various excellent performances, and therefore can be widely used in various fields, objects and applications. For example, it is suitably used as diffusion dialysis, ozone generating electrolysis, electrolytic reduction, a diaphragm of a fuel cell, a polymer catalyst, and the like, particularly in the field where contact resistance is required. Among them, when used as a cation exchange membrane for alkaline electrolysis, it can exhibit high performance in a laminated film with a carboxylic acid type membrane.

For example, the anode and the cathode are partitioned by the above-mentioned cation exchange resin membrane to form an anode chamber and a cathode chamber, and an aqueous solution of alkali chloride is supplied to the anode chamber to perform electrolysis. In the case of a so-called two-chamber tank in which alkali hydroxide is obtained from water, an aqueous solution of sodium chloride having a concentration of 2 mol / liter or more is used as a raw material and electrolysis is performed at a current density of 5 to 50 A / dm ² , so that the concentration is 30% or more. Concentration of sodium hydroxide can be stably produced over a long period of time with high current efficiency and low cell voltage. Next, examples of the present invention will be described more specifically, but it goes without saying that the present invention is not limited by such descriptions.

[0028]

[Example 1] [Example 1] 90 g of ion-exchanged water, 10 g of t- butanol, C ₈ F
_{17 CO 2 NH 4 0.35g, Na} 2 HPO 4 · 12H 2 O
0.5 g, NaH ₂ PO ₄ .2H ₂ O 0.30 g, (N
H ₄ ) ₂ S ₂ O ₈ 100 mg and CF ₂ ＣＦCFOCF ₂ C
30 g of F (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F with an internal volume of 0.
After charging into a 2-liter stainless steel autoclave and sufficiently degassing with liquid nitrogen, the temperature was adjusted to 60 ° C., and tetrafluoroethylene was charged until the pressure reached 10 kg / cm ² to initiate polymerization.

During the reaction, tetrafluoroethylene was introduced from outside the system to keep the pressure constant. After 3.6 hours, unreacted tetrafluoroethylene was purged to terminate the polymerization, and the obtained latex was agglomerated, washed and dried.
9.6 g of the copolymer was obtained. The ion exchange capacity of the copolymer was 0.71 meq / g dry resin. Tough film is obtained when pressing film forming the copolymer at 250 ° C., hydrolysis when a sulfonic acid type ion-exchange membrane was obtained in 25% N NaOH aqueous solution.

Comparative Example Next, polymerization was carried out in the same manner using 100 g of ion-exchanged water except that t- butanol was not added, and post-treatment was carried out. The ion exchange capacity of the obtained copolymer was 0%. .19 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 85 g of ion-exchanged water and 15 g of t- butanol were used, and the ion exchange capacity of the obtained copolymer was 1 0.22 meq / g dry resin.

[0032] Instead of C ₈ F ₁₇ CO ₂ NH ₄ [Example 3] Emulsifier C ₈ F ₁₇ SO
₃ but using NH ₄ is polymerized in the same manner as in Example 1, was subjected to post-treatment, ion-exchange capacity of the resulting copolymer was 0.99 meq / g dry resin.

Example 4 Polymerization was performed in the same manner as in Example 1 except that 92 g of ion-exchanged water and 8 g of t- butanol were used and the pressure of tetrafluoroethylene was changed to 8 kg / cm ² , and post-treatment was performed. ,
The ion exchange capacity of the obtained copolymer was 0.97 meq / g dry resin.

[0034]

According to the present invention, a perfluorocarbon polymer having a large sulfonic acid type functional group content can be easily produced at a high yield without using a special pretreatment such as ultrasonic waves or using a special emulsifier.

Continuation of the front page (56) References JP-A-49-29389 (JP, A) JP-A-49-62584 (JP, A) JP-A-56-50947 (JP, A) JP-A-59-206006 (JP, A) JP-A-2-182710 (JP, A) JP-A-3-243608 (JP, A) JP-A-61-223007 (JP, A) JP-A-4-106111 (JP, A) 62-285907 (JP, A) JP-A-59-196308 (JP, A) JP-A-62-288614 (JP, A) JP-A 55-160008 (JP, A) JP-A 60-250009 (JP, A) A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08F 214/18-214/28 C08F 14/18-14/28 C08F 2/24-2/30

Claims (3)

(57) [Claims] 1. A method for emulsion-copolymerizing a sulfonic acid type functional group-containing perfluorocarbon monomer and a perfluoroolefin in an aqueous medium by the action of a polymerization initiation source, wherein the sulfonic acid type functional group is -SO ₂ F, A method for producing a perfluorocarbon polymer, comprising using a fluorinated emulsifier and adding a water-soluble organic solvent to an aqueous medium. 2. A process according to claim 1, wherein the water-soluble organic solvent is t- butanol. 3. The method of claim 2, wherein the sulfonic acid type functional group-containing perfluorocarbon monomer is CF ₂ CFOCF ₂ CF (CF ₃ ) OC.
F Ri ₂ CF ₂ SO ₂ F der, perfluoro olefin to which is copolymerizable are tetrafluoroethylene, resulting et al
The ion exchange capacity of the copolymer
The method of claim 1 or 2 wherein the amount is dry resin / gram .