JP2005063778A - Fuel cell electrolyte membrane with excellent oxidation resistance - Google Patents

Abstract

（Ｘは、特定の化学構造からなる。）の構造を有する、ビニルエーテルを骨格とするモノマーもしくはその誘導体の一種または複数種をグラフト重合した後、グラフト鎖にスルホン酸基を導入して得られる、燃料電池用電解質膜。
【選択図】 図１PROBLEM TO BE SOLVED: To improve characteristics such as ion exchange capacity, water retention and oxidation resistance of a conventional polymer ion exchange membrane, particularly an ion exchange membrane grafted with a hydrocarbon monomer such as styrene. In a polymer ion exchange membrane by radiation graft polymerization, a membrane having high conductivity as a solid polymer electrolyte and excellent in swelling suppression ability and oxidation resistance is provided.
A polymer base material is represented by the chemical formula (1).

(X is composed of a specific chemical structure), obtained by graft polymerization of one or more monomers having vinyl ether skeleton or derivatives thereof, and then introducing a sulfonic acid group into the graft chain, Fuel cell electrolyte membrane.
[Selection] Figure 1

Description

  The present invention relates to an electrolyte membrane suitable for a polymer electrolyte fuel cell, and relates to a polymer ion exchange membrane having excellent oxidation resistance.

  Since solid polymer electrolyte fuel cells have high energy density, they are expected to be used as household cogeneration power supplies, portable equipment power supplies, electric vehicle power supplies, and simple auxiliary power supplies. This fuel cell requires a polymer ion exchange membrane having oxidation resistance.

  In the polymer electrolyte fuel cell, the ion exchange membrane functions as an electrolyte for conducting protons, and also functions as a diaphragm for preventing direct mixing of hydrogen or methanol and oxygen as fuel. As such an ion exchange membrane, the ion exchange capacity is high as an electrolyte, and since a large current flows for a long time, the membrane is chemically stable, particularly against hydroxyl radicals which are said to be the main cause of membrane degradation. Excellent resistance (oxidation resistance) and low electrical resistance are required. On the other hand, due to its role as a diaphragm, it is required that the film has strong mechanical strength and excellent dimensional stability, and has low gas permeability for hydrogen gas, methanol, and oxygen gas as fuel.

  Early polymer ion exchange membrane fuel cells used hydrocarbon polymer ion exchange membranes produced by copolymerization of styrene and divinylbenzene. However, this ion exchange membrane has poor durability due to oxidation resistance, so it is not practical. After that, a perfluorosulfonic acid membrane “Nafion (registered trademark of DuPont)” developed by DuPont, etc. It has been used in general.

  However, conventional fluorine-based polymer ion exchange membranes such as “Nafion (registered trademark)” are excellent in chemical durability and stability, but the ion exchange capacity is as small as about 1 meq / g, Insufficient water retention and the ion exchange membrane dries and proton conductivity decreases, or when methanol is used as fuel, the membrane swells with alcohols, and methanol crossover reduces fuel cell characteristics Come. When a large amount of sulfonic acid groups are introduced to increase the ion exchange capacity, the membrane strength is remarkably lowered and easily broken. Therefore, in conventional ion exchange membranes of fluoropolymers, it is necessary to suppress the amount of sulfonic acid groups to such an extent that the membrane strength is maintained, so that the ion exchange capacity can only be about 1 meq / g. In addition, fluorine-based polymer ion exchange membranes such as Nafion (registered trademark) are very expensive due to the complicated synthesis of monomers, which is a major obstacle to the practical application of solid polymer fuel cells in automobiles. It has become. Therefore, efforts have been made to develop a low-cost and high-performance electrolyte membrane that replaces the Nafion (registered trademark) and the like.

For example, an ion exchange membrane synthesized by introducing a styrene monomer into ETFE containing a hydrocarbon structure by a radiation graft reaction and then sulfonating functions as an ion exchange membrane for a fuel cell (see Patent Document 1). However, as a disadvantage, when a large current is passed through the membrane for a long time, the sulfone group introduced into the polystyrene is removed, and the ion exchange capacity of the membrane is greatly reduced. Furthermore, when an ion exchange membrane containing a large amount of this hydrocarbon structure is used for the solid electrolyte membrane, the electrode for the positive electrode where water is generated in the fuel cell reaction, particularly when the catalyst layer of the gas diffusion electrode does not have sufficient water repellency, A problem has been pointed out that the output is reduced due to excessive wetness (see Patent Document 2).
JP-A-9-102322 JP-A-11-111310

  The present invention has the following disadvantages in an ion exchange membrane grafted with a hydrocarbon monomer represented by styrene. In order to overcome the problems of the prior art such as low oxidation resistance, in the polymer ion exchange membrane by radiation graft polymerization, has a high conductivity as a solid polymer electrolyte, Furthermore, the present invention provides a film in which swelling in a wet state is suppressed and oxidation resistance is excellent.

The present invention provides a polymer ion exchange membrane having excellent oxidation resistance and a wide ion exchange capacity, and particularly provides an ion exchange membrane suitable for an electrolyte membrane for fuel cells.
That is, a polymer base material obtained by adding a cross-linked structure to a fluorine polymer or olefin polymer having excellent chemical stability is preferably used as a base matrix.

As a result of radiation graft polymerization of the monomer having the structure or its derivative and introducing a sulfonic acid group into the graft chain of the obtained polymer, each characteristic such as ion exchange capacity and methanol permeation can be controlled in a wide range. The present inventors have invented a polymer ion exchange membrane that can be made and has excellent oxidation resistance.

The polymer ion exchange membrane of the present invention is a fuel cell membrane that can control the ion exchange capacity in a wide range and has excellent water retention and high oxidation resistance.
The ion exchange membrane of the present invention is particularly suitable for a fuel cell membrane. Moreover, it is useful as an inexpensive and durable electrolytic membrane or ion exchange membrane.

  Examples of the polymer substrate that can be used in the present invention include fluoropolymers. Specifically, polytetrafluoroethylene (hereinafter abbreviated as PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter abbreviated as FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter, abbreviated as FEP). PFA), polyvinylidene fluoride (hereinafter abbreviated as PVDF), tetrafluoroethylene-ethylene copolymer (hereinafter abbreviated as ETFE), vinyl fluoride (hereinafter abbreviated as PVF), polychlorotrifluoroethylene (hereinafter referred to as “PFF”). And chlorotrifluoroethylene-ethylene copolymer (hereinafter abbreviated as ECTFE). When the fluoropolymer is crosslinked in advance, the obtained electrolyte membrane is further improved in heat resistance and swelling suppression ability. A method for producing crosslinked PTFE is disclosed, for example, in JP-A-6-116423. A method for producing crosslinked FEP and PFA is disclosed in, for example, JP-A-2001-348439.

Cross-linked PTFE is produced by using PTFE in an inert gas having a temperature range of 300 to 365 ° C. under a reduced pressure of 10 ^{−3 to} 10 Torr or an oxygen partial pressure of 10 ^{−2 to 2} Torr. It can be produced by irradiating with 5 to 500 kGy of radiation. As the inert gas, nitrogen, argon, helium gas or the like can be used.

  Further, as another type of polymer substrate that can be used in the present invention, low density, high density, ultrahigh molecular weight polyethylene and polypropylene, and olefinic polymers represented by polymers having trimethylpentene as a monomer can be mentioned. . Adopting a cross-linked olefin polymer improves the heat resistance of the obtained electrolyte membrane and suppresses swelling, which is preferable for some applications.

  Monomers that can be used in the present invention have the following formula:

(In the formula, X represents the following formula:

Selected independently from the chemical structure of )
And a monomer having a vinyl ether structure and a derivative thereof. Specifically, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octadecyl vinyl ether, dodecyl vinyl ether, hexadecyl vinyl ether, tert-pentyl vinyl ether, cyclohexyl vinyl ether, isopropyl vinyl ether, 2-chloroethyl vinyl ether, 4-hydroxybutyl vinyl ether, isobutyl vinyl ether, Examples thereof include tert-butyl vinyl ether, 2-ethylhexyl vinyl ether, 1,4-butanediol vinyl ether, diethylene glycol vinyl ether, and ethylene glycol butyl vinyl ether. These monomers may be used as a mixture of not only one type but also a plurality of types, or may be used by diluting in a solvent.

  In the present invention, graft polymerization can be carried out by further combining one or a plurality of hydrocarbon vinyl monomers and / or fluorocarbon vinyl monomers with the above monomers.

  Examples of hydrocarbon-based vinyl monomers that can be used in the present invention include ethylene, isobutylene, isobutene, butadiene, and acetylene derivatives, benzene skeleton, ester skeleton, functional group (halogen group, epoxy group, hydroxyl group, sulfonic acid group). Any kind of hydrocarbon vinyl monomer may be used as long as it does not contain any other.

  Examples of the fluorocarbon vinyl monomer that can be used in the present invention include heptafluoropropyl trifluorovinyl ether, ethyl trifluorovinyl ether, hexafluoropropene, perfluoro (propyl vinyl ether), pentafluoroethyl trifluorovinyl ether, perfluoro (4 -Methyl-3,6-dioxanon-1-ene), trifluoromethyl trifluorovinyl ether, hexafluoro-1,3-butadiene, etc., and benzene skeleton, ester skeleton, functional group (halogen group, epoxy group, hydroxyl group, Any fluorocarbon vinyl monomer that does not contain a sulfonic acid group or the like may be used.

These monomers may be used after being diluted with a solvent.
It is also possible to add 10% or less by weight of a crosslinking agent such as divinylbenzene to the monomer to crosslink the graft chain.

Further, after the graft polymerization, it is possible to crosslink the graft chain by reacting with a cross-linking agent such as a polyfunctional monomer or triallyl isocyanurate.
As the crosslinking agent that can be used for crosslinking the graft chain in the present invention, 1,2-bis (p-vinylphenyl), divinylsulfone, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, Divinylbenzene, cyclohexanedimethanol divinyl ether, phenylacetylene, diphenylacetylene, 2,3-diphenylacetylene, 1,4-diphenyl-1,3-butadiene, diallyl ether, 2,4,6-triallyloxy-1,3 , 5-triazine, triallyl-1,2,4-benzenetricarboxylate, triallyl-1,3,5-triazine-2,4,6-trione and the like.

  The graph-polymerization of the above-mentioned monomer onto the polymer substrate is performed by causing the substrate to react with the monomer after irradiation with radiation, grafting by a so-called pre-irradiation method, or simultaneously irradiating the substrate and the monomer with radiation and grafting. Graft polymerization can be performed by any of the so-called simultaneous irradiation methods, but the pre-irradiation method in which the amount of homopolymer produced is small is preferable.

  There are two types of pre-irradiation methods: a polymer radical method in which a polymer substrate is irradiated in an inert gas, and a peroxide method in which a substrate is irradiated in the presence of oxygen, both of which can be used. is there.

  As an example of the pre-irradiation method, after inserting the polymer substrate into a glass container or the like, the container is vacuum degassed and replaced with an inert gas atmosphere. Thereafter, the container containing the base material is irradiated with an electron beam or γ-ray at 1 to 500 kGy at a temperature of −10 ° C. to 80 ° C., preferably near room temperature, and then bubbling or freezing deaeration with an inert gas not containing oxygen. The container containing the irradiated base material is filled with a monomer solution obtained by removing oxygen in a monomer mixture or solvent. When the polymer substrate is a cross-linked fluoropolymer film, the graft polymerization temperature is usually 30 ° C. to 150 ° C., preferably 40 ° C. to 80 ° C., to introduce the polymer graft chain.

  The graft ratio of the polymer increases as the pre-irradiation dose increases. The graft ratio of the obtained graft polymer is 6 to 150 wt%, more preferably 10 to 100 wt%, based on the weight of the polymer substrate.

  After introducing the graft chain into the polymer substrate, a sulfone group is then introduced. The conditions for sulfonation are disclosed in JP-A-2001-348439. For example, 1,2-dichloroethane is used as a solvent, and a graft film base material is added to a 0.2 to 0.5 molar chlorsulfonic acid solution. The reaction is performed by immersing at room temperature to 70 ° C. for 2 to 48 hours. After reacting for a predetermined time, the membrane is thoroughly washed with water. As the sulfonating agent necessary for the sulfonation reaction, concentrated sulfuric acid, sulfur trioxide, sodium thiosulfate, or the like can be used, but any type can be used as long as it is a sulfonating agent capable of introducing a sulfonic acid group.

  In the electrolyte membrane for fuel cells according to the present invention, the ion exchange capacity of the electrolyte membrane can be controlled over a wide range according to the graft ratio and the amount of sulfonic acid groups to be introduced. Here, the ion exchange capacity is the amount of ion exchange groups (meq / g) per gram weight of the dry ion exchange membrane. When the graft ratio is 6% or less, the ion exchange capacity is insufficient. On the other hand, when the graft ratio is 150% or more, the membrane swells when it contains water and the strength of the membrane decreases. Will become bigger. Therefore, the ion exchange capacity of the fuel cell electrolyte membrane according to the present invention is 0.3 meq / g to 6 meq / g, more preferably 0.5 meq / g to 2.0 meq / g.

In general, when the polymer ion exchange membrane has an electric conductivity at 25 ° C. of 0.05Ω ⁻¹ cm ⁻¹ or less, the output as a fuel cell often decreases significantly. it is 0.05? ^-1 cm ^-1 or more, it is often designed above 0.1 [Omega ^-1 cm ^-1 in the higher performance of the ion exchange membrane. In the electrolyte membrane for a fuel cell according to the present invention, the electric conductivity of the ion exchange membrane at 25 ° C. was higher than that of the Nafion (registered trademark) membrane.

  In order to increase the electric conductivity of the ion exchange membrane, it is also conceivable to reduce the thickness of the ion exchange membrane. However, at present, an ion exchange membrane that is too thin is easily damaged, and an ion exchange membrane having a thickness of 30 μm to 200 μm is usually used. In the fuel cell electrolyte membrane of the present invention, a film thickness of 5 μm to 200 μm, preferably 20 μm to 100 μm is useful.

  In the fuel cell membrane, the conventional Nafion (registered trademark) membrane is a perfluorosulfonic acid membrane and has no intermolecular cross-linking structure, so that it is greatly swollen by methanol which is considered as one of the fuel candidates. It is regarded as a serious problem that power generation efficiency is lowered by diffusion through the cell membrane from the anode (fuel electrode) to the cathode (air electrode). However, in the electrolyte membrane for fuel cells according to the present invention, although the substrate matrix is present despite the high ion exchange capacity, the membrane is less swelled by alcohols such as methanol. For this reason, it is useful as an electrolyte membrane of a direct methanol fuel cell using methanol directly as a fuel without using a reformer.

  In the fuel cell membrane, the oxidation resistance of the membrane is a very important characteristic related to the durability (life) of the membrane. In the oxidation of the membrane, OH radicals or the like generated during battery operation attack the ion-exchange membrane and degrade the membrane. The polymer ion exchange membrane obtained by graft-polymerizing styrene on a fluorine-containing polymer substrate and then sulfonating the polystyrene graft chain has extremely low oxidation resistance. For example, a polystyrene graft-crosslinked PTFE ion exchange membrane sulfonated with a polystyrene chain with a graft rate of 100% deteriorates in an aqueous 3% hydrogen peroxide solution at 80 ° C., and the ion exchange capacity is almost half in about 60 minutes. It becomes. This is because the sulfone group introduced into the benzene ring is dropped by the attack of the OH radical. On the other hand, the electrolyte membrane for fuel cells according to the present invention has very high oxidation resistance because there is no benzene ring in the graft chain, and the ion exchange capacity even when placed in a 3% hydrogen peroxide aqueous solution at 80 ° C. for several months or more. Hardly changes.

  As described above, the electrolyte membrane for a fuel cell of the present invention has excellent oxidation resistance and methanol permeation-preventing property, and has an ion exchange capacity of 0.3 to 6.0 meq / g, which is an important characteristic as a membrane. It can be controlled in a wide range.

Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to these.
In addition, each measured value was calculated | required by the following measurements.
(1) Graft ratio When the polymer base material is the main chain portion and the portion where the monomer is graft polymerized is the graft chain portion, the weight ratio of the graft chain portion to the main chain portion is the graft ratio of the following formula: X _ds (wt% ).

X _ds = 100 (W ₂ −W ₁ ) / W ₁ (1)
W ₁ : Weight of polymer base material before graft polymerization (g)
W ₂ : Weight of the polymer-containing substrate (dry state) after graft polymerization (g)
(2) Ion exchange capacity The ion exchange capacity of the membrane, I _ex (meq / g), is expressed by the following equation.

I _ex = n (acid group) _obs / W _d (2)
n (acid group) _obs : acid group concentration of the ion exchange membrane (mM / g)
W _d : dry weight of ion exchange membrane (g)
In order to measure n (acid group) _obs , the membrane is immersed in a 1M (1 molar concentration) sulfuric acid solution at 50 ° C. for 4 hours so as to obtain a more accurate measurement. Was immersed in an aqueous NaCl solution at 50 ° C. for 4 hours to form —SO ₃ Na type, and the substituted protons (H ⁺ ) were neutralized and titrated with 0.2 M NaOH to determine the acid group concentration.
(3) Moisture content After removing the ion exchange membrane stored in water at room temperature from water and wiping it lightly (after about 1 minute), the weight of the membrane is defined as W _s (g). When the weight W _d (g) of the film after vacuum drying for 16 hours is defined as the dry weight, the water content is obtained from W _s and W _{d according} to the following equation.

Moisture content = 100 (W _s −W _d ) / W _d (3)
(4) Electrical conductivity The electrical conductivity of the ion exchange membrane is measured by the AC method (New Experimental Chemistry Course 19, Polymer Chemistry <II>, p. 992, Maruzen). The film resistance (R _m ) was measured and evaluated using an Packard LCR meter, E-4925A. A 1M sulfuric acid aqueous solution was filled in the cell, the resistance between platinum electrodes (distance 5 mm) depending on the presence or absence of the film was measured, and the electric conductivity (specific conductivity) of the film was calculated using the following equation.

κ = 1 / R _m · d / S (Ω ⁻¹ cm ⁻¹ ) (4)
κ: electrical conductivity of the membrane (Ω ^-1 cm ^-1 )
d: thickness of ion exchange membrane (cm)
S: Current-carrying area of the ion exchange membrane (cm ² )
For comparison of electrical conductivity measurements, Mark W. Verbrugge, Robert F .; Measurements were made using a cell, potentiostat and function generator similar to Hill et al. (J. Electrochem. Soc. (1990) 137, 3770-3777). There was a good correlation between the measured values of the AC and DC methods. The values in Table 1 below are measured values by the AC method.
(5) Oxidation resistance (weight residual rate%)
The weight of the film after vacuum drying at 60 ° C. for 16 hours is defined as W _3, and the weight after drying of the film treated with a 3% hydrogen peroxide solution at 80 ° C. for 3 weeks is defined as W ₄ .

Oxidation resistance = 100 (W ₄ / W ₃ )
(Example 1)

The following irradiation was performed to obtain a crosslinked PTFE film. Thickness 50 [mu] m, PTFE film 10cm square (manufactured by Nitto Denko, No. Nanba900) a SUS autoclave irradiation vessel (inner diameter 4 cm, height 30 cm) with a heater placed in, after degassing vessel 10 ^-2 Torr Filled with 1 atmosphere of argon gas. Subsequently, the temperature of the PTFE film was set to 340 ° C. by heating with an electric heater, and ⁶⁰ Co-γ rays were irradiated at a dose rate of 3 kGy / h and a dose of 120 kGy. After irradiation, the container was cooled and the PTFE film was taken out.

  This crosslinked PTFE film was cut into 4 cm square, put into a glass separable container with a cock (inner diameter: 3 cm, height: 15 cm), and after deaeration, filled with argon gas at 1 atm. In this state, the crosslinked PTFE film was again irradiated with γ rays (dose rate 10 kGy / h) up to 60 kGy at room temperature. Next, 40 g of butyl vinyl ether degassed in advance was put in a glass container containing the irradiated crosslinked PTFE film, and the film was immersed therein. The vessel was sealed and the inside of the vessel was replaced with nitrogen, and then reacted at 60 ° C. for 48 hours. After the reaction, it was washed with toluene and then with acetone and dried. The graft rate was 31%.

In order to sulfonate the crosslinked PTFE film obtained by this graft polymerization, it was reacted by immersing in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane at 60 ° C. for 20 hours and washed with water. Table 1 shows the ion exchange capacity, water content, and electrical conductivity of the obtained membrane.
(Example 2)

  Place a 50μm thick, 8cm square ETFE film cross-linked by electron beam irradiation at 220kGy in a nitrogen atmosphere at room temperature in a glass separable container with a cock (inner diameter 3cm, height 12cm). did. In this state, γ rays (dose rate 10 kGy / h) were irradiated again at room temperature up to 60 kGy. Into a glass container containing the irradiated crosslinked ETFE film, 40 g of previously deaerated dodecyl vinyl ether was placed, and the film was immersed. The vessel was sealed and the inside of the vessel was replaced with nitrogen, and then reacted at 70 ° C. for 24 hours. After the reaction, it was washed with toluene and then with acetone and dried. The graft rate was 28%.

The ETFE membrane obtained by the graft polymerization was immersed in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane for 18 hours at 60 ° C. and reacted with water. Table 1 shows the ion exchange capacity, water content, and electrical conductivity of the obtained membrane.
(Example 3)

  A PVDF film having a thickness of 50 μm and a 10 cm square was placed in a SUS pressure-resistant autoclave with a cock (inner diameter: 4 cm, height: 40 cm), and after deaeration, replaced with argon gas. In this state, γ rays (dose rate 10 kGy / h) were irradiated at 60 ° C. up to 60 kGy. After irradiation, the container was vacuum degassed, and 20 g of isobutyl vinyl ether and 20 g of benzene that had been degassed in advance were added and stirred well before the film was immersed. The vessel was sealed and the inside of the vessel was replaced with nitrogen, and then reacted at 60 ° C. for 6 hours. After the reaction, it was washed with toluene and then with acetone and dried. The graft rate was 35%.

The PVDF film obtained by this graft polymerization was immersed in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane for 24 hours at 60 ° C. and reacted with water. Table 1 shows the ion exchange capacity, water content, and electrical conductivity of the obtained membrane.
Example 4

  In Example 3, the film was made of high-density polyethylene having a thickness of 50 μm, and 20 g of a mixture of butyl vinyl ether and ethylene glycol butyl vinyl ether (composition 50: 50 wt%) was used instead of isobutyl vinyl ether. The graft rate was 39%.

The film obtained by the graft polymerization was reacted by immersing in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane at 60 ° C. for 5 hours, and then washed with water. Table 1 shows the ion exchange capacity, water content, and electrical conductivity of the obtained membrane.
(Example 5)

  A 4 cm square PTFE film cross-linked under the conditions of Example 1 was placed in a SUS autoclave container, and after degassing, it was filled with 1 atm of argon gas. In this state, the cross-linked PTFE film was again irradiated with γ rays (dose rate 10 kGy / h) up to 60 kGy at room temperature. Next, 40 g of butyl vinyl ether, 10 g of isobutene, and 100 g of toluene, which had been previously sharpened, were placed in a container containing the irradiated crosslinked PTFE film, and reacted for 24 hours at 60 ° C. without oxygen. After the reaction, it was washed with toluene and then with acetone and dried. The graft rate was 45%.

In order to sulfonate the crosslinked PTFE film obtained by this graft polymerization, it was immersed in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane for 20 hours at 60 ° C. and then washed with water. Table 1 shows the ion exchange capacity, water content, and electrical conductivity of the membrane obtained in this example.
(Example 6)

In Example 5, 10 g of perfluoro (propyl vinyl ether) was added instead of isobutene and graft polymerization was performed. The graft rate was 25%.
In order to sulfonate the crosslinked PTFE film obtained by this graft polymerization, it was immersed in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane for 20 hours at 60 ° C. and then washed with water. Table 1 shows the ion exchange capacity, water content, and electrical conductivity of the membrane obtained in this example.
(Example 7)

In Example 1, 0.1 g of phenylacetylene as a crosslinking agent was further added to 40 g of butyl vinyl ether, and graft polymerization was performed. The graft rate was 38%.
In order to sulfonate the crosslinked PTFE film obtained by this graft polymerization, it was immersed in 0.3 molar chlorosulfonic acid diluted with 1,2-dichloroethane for 20 hours at 60 ° C. and then washed with water. The ion exchange capacity, water content, and electrical conductivity of the membrane obtained in this example were measured and are shown in Table 1.
(Comparative Examples 1 and 2)

As Comparative Examples 1 and 2, the results of ion exchange capacity, water content, and electrical conductivity measured for Nafion 115 and Nafion Il7 (manufactured by DuPont) are shown in Table 1.
(Comparative Example 3)

The crosslinked FTFE film (thickness 50 μm) obtained in Example 1 was put into a glass separable container (inner diameter 3 cm, height 15 cm) with a cock, and after deaeration, it was replaced with argon gas. In this state, the cross-linked PTFE film was again irradiated with γ rays (dose rate 10 kGy / h) up to 60 kGy at room temperature. Styrene monomer, from which oxygen was removed by bubbling with argon gas, was introduced into a glass container containing a crosslinked PTFE film until the film was immersed. The vessel was stirred and reacted at 60 ° C. for 5 hours. Thereafter, the graft copolymer membrane was washed with toluene and then with acetone and dried. The graft rate was 39%. This graft polymerized membrane was immersed in 0.3 molar chlorosulfonic acid (1,2-dichloroethane solvent) and subjected to sulfonation reaction at 60 ° C. for 24 hours. Thereafter, this membrane was washed with water to obtain sulfonic acid groups.
Measurement of swelling degree of alcohol The membrane of Example 1 and Nafion 117 were immersed in a 3M sulfuric acid solution, and the sulfonic acid group was changed to the H type. Subsequently, it was immersed in room temperature water and the dimension was measured in the wet state. Next, the membrane was immersed in each alcohol solution of methanol and isopropanol (IPA), held at 60 ° C. for 3 hours, and allowed to cool overnight at room temperature, and then the dimensional change of the membrane was measured. The results are shown in FIG. The membrane obtained in Example 1 was found to be extremely effective as a membrane material for a direct methanol fuel cell with almost no swelling of the membrane due to methanol or the like compared to the Nafion membrane.

  FIG. 1 and Table 1 demonstrate the effectiveness of the present invention.

FIG. 1 is a diagram showing the swelling property of a film by a mixed solvent of alcohol and water.

Claims (7)

In the polymer substrate, the following formula:

(In the formula, X represents the following formula:

Selected independently from the chemical structure of )
A fuel cell electrolyte membrane obtained by graft polymerization of a monomer having a vinyl ether skeleton or a derivative thereof having one of the following structures and introducing a sulfonic acid group into the graft chain. In the chemical formula (1), X is _{-C n H 2n + 1 (n} = 1-18), an electrolyte membrane for a fuel cell according to claim 1, wherein.   Combining one or more of the monomers represented by the chemical formula (1) or a derivative thereof with another hydrocarbon vinyl monomer (Compound A) and / or a fluorocarbon vinyl monomer (Compound B) and combining them with a polymer group The electrolyte membrane for a fuel cell according to claim 1 or 2, which is graft-polymerized to the material.   The electrolyte membrane for a fuel cell according to any one of claims 1 to 3, wherein the graft polymerized sulfonic acid group-retaining polymer chain has a crosslinked structure.   The electrolyte membrane for a fuel cell according to any one of claims 1 to 4, wherein the polymer substrate comprises an olefin polymer or a fluorine polymer.   The electrolyte membrane for fuel cells according to any one of claims 1 to 5, wherein the polymer substrate has a crosslinked structure.   The fuel according to any one of claims 1 to 6, wherein the obtained graft polymer has a graft ratio of 6 to 200% and an ion exchange capacity of 0.3 to 6.0 meq / g. Battery electrolyte membrane.

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