JPS599562B2 - Method for producing graft copolymer for ion exchange membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a graft copolymer for ion exchange membranes.

More specifically, the present invention involves graft copolymerizing a specific side chain monomer onto a main chain polymer consisting of a fluorine-containing polymer using ionizing radiation to produce a graft copolymer for an ion exchange membrane. The present invention relates to an improvement in a method for producing a graft copolymer for ion exchange membranes, which is characterized in that a fluorine-containing polymer is crosslinked in advance. A method has already been proposed for producing a graft copolymer by cografting a side chain monomer mainly consisting of acyloxystyrene and/or hydroxystyrene and a polyene compound onto a main chain polymer consisting of a fluorine-containing polymer using ionizing radiation. It is publicly known. The graft copolymer obtained in this way is a useful polymer substance with various uses,
One of its uses is an ion exchange membrane that utilizes the phenolic hydroxyl groups contained in the membranous copolymer. Of course, a graft copolymer having an acyloxy group can also be used as an ion exchange membrane since it can be quantitatively converted into phenolic hydroxyl groups by hydrolyzing the graft copolymer. In this way, when using a copolymer (membrane) as an ion exchange membrane, the electrical properties of the membrane, such as electrolytic performance, are of course important, but the mechanical strength of the membrane is also important.
There is no question that this is an extremely important issue.

By the way, among the various physical properties required for ion exchange membranes, it is desirable to have low electrical resistance, but increasing the grafting ratio and increasing the concentration of exchange groups increases the membrane's swelling ability with respect to the electrolyte, which lowers its mechanical strength. and ion permselectivity decreases.

In particular, the latter decrease leads to a decrease in current efficiency and a decrease in the purity of the intended product. Therefore, the electrical resistance is low,
In order to obtain a membrane with high mechanical strength and ion permselectivity, it is effective not only to select an optimal grafting ratio but also to introduce a three-dimensional network structure into the membrane. Conventionally, one method has been to add a polyene compound such as divinylbenzene during the grafting reaction to partially introduce a crosslinked network structure into the polymer. However, as a result of various studies, the present inventors found that a similar effect can be obtained by crosslinking the fluorine-containing polymer (membrane) used as the main chain polymer for the graft reaction in advance, and that It is necessary to crosslink the fluorine-containing polymer (membrane), which is the main chain polymer, in advance, and to add a polyene compound during the aforementioned graft reaction to create a partially crosslinked network structure in the graft polymer. The present invention was completed by discovering that a synergistic effect can be obtained by implementing the methods together. Fluorine-containing polymer (film) that becomes the main chain polymer in the present invention
For crosslinking, all known crosslinking methods can be used, such as a method using ionizing radiation, a method in which a radical initiator is added during or after the production of the film-like fluorine-containing polymer, and crosslinking is performed by heating or other methods. Adopted.

Therefore, the present invention is not limited to the method of crosslinking the fluorine-containing polymer that is the main chain polymer. The fluorine-containing polymers used in the present invention include polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride. A hexafluorinated propylene copolymer or the like is used.

As described above, these polymers are pre-crosslinked and then subjected to a graft polymerization reaction. Further, in the present invention, the acyloxystyrene to be subjected to graft copolymerization is represented by the general formula.

[Here, the position of the substituent is ortho, meta, or para, and R is a linear or branched aliphatic, alicyclic, or aromatic hydrocarbon group having 1 to 20 carbon atoms], for example, acetoxystyrene. , propionyloxystyrene, butyryloxystyrene, benzoyloxystyrene, etc., and paraacetoxystyrene is most commonly used. In the present invention, the hydroxystyrene to be subjected to graft copolymerization can be either an orthometa or para isomer, or a mixture thereof.

Parahydroxystyrene is most commonly used.
Further, in the present invention, the polyene compounds to be subjected to graft copolymerization include compounds containing two or more polymerizable double bonds in the molecule, such as divinylbenzene, isoprene, butadiene, cyclopentadiene, ethylidene norbornene, and acrylic acid. Alternatively, diol esters of methacrylic acid, divinyl esters of adipic acid, etc. are used.

Among them, divinylbenzene and isoprene are preferably used. Divinylbenzene has three isomers, ortho, meta, and para, and any of these isomers can be used, and a mixture of these is generally used. Furthermore, divinylbenzene that is commonly obtained as a commercial product is often a mixture containing about 45% by weight of ethylvinylbenzene in addition to divinylbenzene.
This mixture may be subjected to the reaction as it is. These acyloxystyrene and/or hydroxystyrene and the polyene compound are dissolved in an organic solvent and subjected to the graft polymerization reaction as a solution. An organic solvent that dissolves the fluorine-containing polymer but does not dissolve the fluorine-containing polymer is used.

For example, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol, ethers such as tetrahydrofuran and dioxane, N,N-dimethylformamide, N,
Aromatic hydrocarbons such as N-dimethylacetamide, benzene and toluene, aliphatic or alicyclic hydrocarbons such as n-heptane and cyclohexane, or mixed solvents thereof are suitable. Among these, those that swell the fluorine-containing polymer are preferably used. The graft copolymerization of the present invention is carried out using ionizing radiation.

Graft copolymerization methods using ionizing radiation include a pre-irradiation method in which the main chain polymer is irradiated with ionizing radiation in advance and then the polymer is brought into contact with a monomer, and a pre-irradiation method in which ionizing radiation is irradiated while the monomer and polymer coexist. Although there is a simultaneous irradiation method, either method may be used in the present invention. Ionizing radiation includes gamma rays, X-rays, electron beams, α
Various types of radiation can be used, such as radiation or mixed radiation. The total radiation dose required for graft copolymerization is usually 105 rats or more. There is no need to particularly limit the temperature during radiation irradiation in the fore-irradiation method, but if the temperature becomes too high, radicals will disappear, which is not preferable, so the temperature during irradiation is preferably room temperature or lower. The graft copolymer (membrane) produced by the method of the present invention is
If necessary, it is washed with an organic solvent such as an alcohol such as methanol, ethanol or propyl alcohol, a ketone such as acetone or methyl ethyl ketone, an aromatic hydrocarbon such as benzene or toluene, or a mixture thereof.

In addition, in order to use a graft copolymer having a side chain containing acyloxystyrene as an ion exchange membrane,
The acyloxy group in the side chain is converted to a hydroxyl group by hydrolysis treatment. This hydrolysis treatment, similar to the commonly practiced hydrolysis of phenol esters, is extremely easy compared to the hydrolysis of esters of primary alcohols, and can be easily carried out under mild conditions. That is, using an acid or a base as a catalyst, a graft copolymer (membrane) is placed in an aqueous solution containing these catalysts or a mixed solution of water and a water-soluble organic solvent, and a hydrolysis reaction of the acyloxy groups in the side chains is carried out. will be carried out. Since the hydrolysis reaction is mainly carried out in a heterogeneous system, a water-soluble organic solvent such as alcohol or ketone is used to increase the affinity between the substrate and the catalyst, and to dissolve the released organic acid when using an acidic catalyst. Preferably, this is carried out in a mixture of water and water. A suitable reaction temperature for hydrolysis is 50 to 100°C. The present invention will be further explained below with reference to Examples.

Example 1 A film 3.609 of tetrafluoroethylene and ethylene copolymer having a thickness of 0.157 x m was exposed to an electron beam of 20 Mrad (acceleration voltage 2 MeV 1 current 1) in air at room temperature.
Pre-crosslinking was carried out by irradiation with mA).

A portion (1.009) was taken and the degree of gelation was determined by a conventional method, and it was found to be 90% or more. The film was left in the air at 45° C. or higher for 360 hours or more, and after confirming that the remaining radicals had completely disappeared, it was used as a raw material. A solution of 50% by weight p-acetoxystyrene and 50% by weight benzene was placed in one leg of an H-type glass ampule.
7rL1 was added and sufficiently degassed by freezing and thawing in vacuo.

On the other hand, the remaining 2.60% of the above-mentioned crosslinked raw material film was exposed to an electron beam of 5 Mrad (acceleration voltage 2 MeV) in nitrogen at room temperature.
After irradiating it with a current of 1 mA, place it in the other leg and create a sufficient vacuum.

After creating a vacuum of 10-2 mmHg or more, the monomer solution was melted and transferred to the film side, and reacted at 60°C for 2 hours.

After the reaction, the ampoule was opened and the film was taken out, thoroughly washed with acetone, and dried under reduced pressure until it reached a constant weight. The grafting rate calculated from the weight difference before and after the reaction was 40%.
This material did not lose weight even after repeated acetone extraction. The film obtained as described above was placed in a 100ml flask equipped with a cooling tube, and the mixing ratio was 1:1 by volume.
50 ml of concentrated hydrochloric acid-methanol solution of No. 4 was added and heated on a water bath for 30 minutes.

When the obtained film was examined by infrared absorption spectrum, the ester groups were completely hydrolyzed and new absorption based on phenolic hydroxyl groups was observed. This membrane was useful as an ion exchange membrane. The ion exchange capacity of this ion exchange membrane was 3 mecv/V, and the electrical resistance in a 40% NaOH aqueous solution was 23 Ω·. Moreover, the tensile strength is 220 kg/Cd, and the tensile strength of the ion exchange membrane manufactured by the same method as above without crosslinking in advance is 150 kg/Cd.
It improved significantly compared to kg/d. Example 2 Graft copolymer obtained by crosslinking and O-rat copolymerization in the same manner as in Example 1 using a membrane of tetrafluoroethylene and hexafluoropropylene copolymer having a thickness of 0.157J1W as the main chain polymer. The combined product was thoroughly washed with acetone to completely remove the by-produced p-hydroxystyrene monopolymer, and then dried under reduced pressure until it reached a constant weight.

The grafting rate calculated from the weight difference before and after the reaction was 45%. Furthermore, this graft copolymer was hydrolyzed in the same manner as in Example 1 to obtain an ion exchange membrane.

The ion exchange capacity of this ion exchange membrane is 3.1 meq/9
The electrical resistance in a 40% NaOH aqueous solution is 20Ω・
It was d. Next, using this ion exchange membrane, electrolysis was carried out in an aqueous NaCl solution under conditions to obtain highly concentrated hydric soda, and as a result, the current efficiency was 80%.

For comparison, the grafting rate of a copolymer obtained by the same treatment as above without crosslinking the main chain polymer was 47%,
And the ion exchange capacity of the ion exchange membrane obtained from it is 3.
The electrical resistance was 3mecV9 and 18Ω·d, and the current efficiency was 68%.

As a result, it was found that crosslinking the main chain polymer in advance is effective in improving current efficiency. Example
3 A copolymer film of tetrafluoroethylene and vinyl ether with a thickness of 0.1511 was heated to 1 in air at room temperature.
Pre-crosslinking was carried out by irradiation with an electron beam of 0 Mrad (acceleration voltage 2 Me, current 1 mA).

A portion (1.00 g) was taken and the degree of gelation was determined by a conventional method, and it was found to be 90% or more. The film was left in the air at 45° C. or higher for 360 hours or more, and after confirming that the remaining radicals had completely disappeared, it was used as a raw material. A solution of 50% by weight p-acetoxystyrene and 50% by weight benzene was placed in one leg of an H-type glass ampule.
ml was added and sufficiently degassed by freezing and thawing in vacuo.

On the other hand, the remaining 2.60% of the above-mentioned crosslinked raw material film was exposed to an electron beam of 10 Mrad (acceleration voltage 2 Me) in nitrogen at room temperature.
After irradiating the tube with a Vs current of 1 mA, place it in the other leg and create a sufficient vacuum.

After creating a vacuum of 10-211 Hg or more, the monomer solution was melted and transferred to the film side, and reacted at 60°C for 5 hours.

After the reaction, the ampoule was opened and the film was taken out, thoroughly washed with acetone, and dried under reduced pressure until it reached a constant weight. The grafting rate calculated from the weight difference before and after the reaction was 45%.
This material did not lose weight even after repeated acetone extraction. The film obtained as described above was placed in a 1007R1 flask equipped with a cooling tube, and the mixing ratio was 1 by volume.
: Add 50ml of concentrated hydrochloric acid-methanol solution of 4,
Heat on a water bath for 30 minutes.

When the obtained film was examined by infrared absorption spectrum, the ester groups were completely hydrolyzed and new absorption based on phenolic hydroxyl groups was observed. This membrane was useful as an ion exchange membrane. The ion exchange capacity of this ion exchange membrane is 2.9 mecv/f! The electrical resistance in a 40% NaOH aqueous solution was 23Ω·d. Example 4 Thickness 0.15m7! L polytetrafluoroethylene film 3.609 was exposed to a dose rate of 5 x 105ra under vacuum at room temperature.
Pre-crosslinking was carried out by irradiation at d/Hr for 5 hours.

A portion (1.009) was taken and the degree of gelation was determined by a conventional method, and it was found to be 90% or more. The film was left in the air at 45° C. or higher for 360 hours or more, and after confirming that the remaining radicals had completely disappeared, it was used as a raw material. A solution of 50% by weight p-acetoxystyrene and 50% by weight benzene was placed in one leg of an H-type glass ampule.
ml and thoroughly degassed using the freeze-thaw method in a vacuum.

On the other hand, the remaining crosslinked raw material film mentioned above is 2.60f!
was irradiated with cobalt-60 gamma line at a dose rate of 5 x 105 rad/Hr for 5 hours in nitrogen at room temperature, and then placed in the other leg and sufficiently evacuated.

After creating a vacuum of 10-211 Hg or more, the monomer solution was melted and transferred to the film side, and reacted at 60°C for 2 hours.

After the reaction, the ampoule was opened and the film was taken out, thoroughly washed with acetone, and dried under reduced pressure until it reached a constant weight. The grafting rate calculated from the weight difference before and after the reaction was 38%.
This product did not lose weight even after repeated ascent extraction. The film obtained as above was placed in a 100ml flask equipped with a cooling tube, and the mixing ratio was 1S by volume.
Concentrated hydrochloric acid monomethanol solution 501n1 which is 4! was added and heated on a hot water bath for 30 minutes.

When the obtained film was examined by infrared absorption spectrum, the ester groups were completely hydrolyzed and new absorption based on phenolic hydroxyl groups was observed. This membrane is useful as an ion exchange membrane. The ion exchange capacity and electrical resistance of this ion exchange membrane are 2.8me9/9 and 25Ω・
It was hot in ml. In order to compare this, we compared this with a film obtained by the same grafting reaction using the same type of film that had not been cross-linked in advance as a raw material, and found that the film obtained from the cross-linked raw material had better heat resistance and strength. found that the electrical properties were significantly superior to membranes obtained from uncrosslinked raw materials.

Claims (1)

[Claims] 1. A fluorine-containing polymer containing acyloxystyrene and/or
Alternatively, in a method for producing a graft copolymer for an ion exchange membrane by cograft polymerizing a monomer mixture containing hydroxystyrene as a main component using ionizing radiation, the fluorine-containing polymer is crosslinked in advance by a known method. A method for producing a graft copolymer for an ion-exchange membrane, characterized by: 2. The method according to claim 1, characterized in that the monomer mixture is a monomer mixture whose main components are acyloxystyrene and/or hydroxystyrene and a polyene compound.