JP5175619B2 - Proton conducting membrane and method for producing the same - Google Patents

Description

  The present invention relates to a proton conductive membrane suitable for use in a fuel cell and having fuel barrier properties, high durability, and high proton conductivity, and a method for producing the same.

  In conventional thermal power generation, the chemical energy of fossil fuels such as oil and natural gas is converted into thermal energy, and the turbine is driven by this thermal energy to convert thermal energy into kinetic energy, which is further converted into electrical energy. Has been converted. On the other hand, since the fuel cell can directly convert chemical energy into electric energy, it has higher power generation efficiency and superior environmental characteristics than thermal power generation. Therefore, fuel cells are in the spotlight as efforts to protect the global environment in recent years have become active. In recent years, it has attracted attention as a power source for small mobile devices and portable devices. For example, it is expected to be mounted on mobile phones and personal computers in place of secondary batteries such as nickel metal hydride batteries and lithium ion batteries. .

In general, fuel cells are classified into several types according to the type of electrolyte. Among them, a polymer electrolyte fuel cell (hereinafter abbreviated as “PEFC”) is in comparison with any other type. It is also considered to become the next generation main power source as a power source for small-sized on-site type, for example, a power source for a vehicle, a mobile device or a portable device.
In PEFC, in addition to the conventional ones that use hydrogen gas as fuel, direct fuel cells that use alcohol or dimethyl ether as fuel and supply them directly without reforming to hydrogen, especially direct output with high output near room temperature. Methanol fuel cells (hereinafter abbreviated as “DMFC”) are attracting attention. Although the DMFC has a lower output than the conventional PEFC, since the fuel is liquid and a reformer is unnecessary, there is an advantage that the energy density is high and the usage time of the on-board equipment per filling is long.

The electrolyte membrane of PEFC such as DMFC is required to have high proton conductivity and fuel cutoff. The fuel permeation through the electrolyte membrane is called fuel crossover and causes a problem that the battery output and the energy efficiency are lowered.
Conventionally, for example, Nafion (DuPont) (registered trademark), which is a sulfonic acid group-containing fluoropolymer, has been used in an electrolyte membrane of a polymer electrolyte fuel cell. However, Nafion has a problem that fuel crossover of methanol or the like is large because sulfonic acid groups in the electrolyte membrane form a cluster structure. Therefore, there has been a demand from the market for practical use of an electrolyte membrane having high proton conductivity equivalent to Nafion and suppressing fuel crossover.

On the other hand, as electrolyte membranes for fuel cells, in addition to fluoropolymers, those made of various kinds of materials such as hydrocarbons and inorganics have been actively developed. Among them, organosilicon compounds have a cross-linked structure consisting of silicon-oxygen bonds with strong binding energy, so they are exposed to high-temperature and high-humidity conditions under strong acidic (proton presence) conditions such as proton conductive membranes. Even if it is, it is comparatively stable and can be suitably used as a crosslinked structure inside the electrolyte membrane (see, for example, Patent Document 1).
Japanese Patent No. 3679104

However, the silicon-carbon bond contained in the film has a slightly lower intermolecular force around the silicon-oxygen bond than the silicon-oxygen bond, and has low impact resistance against environmental changes such as temperature changes. Therefore, for example, when an organosilicon compound is used as an electrolyte membrane for a fuel cell that requires high proton conductivity at high temperature and low temperature, there is a problem that proton conductivity and fuel cutoff may decrease with temperature fluctuation. There was a point.
In order to solve these problems, for example, a crosslinkable compound (A) having a silicon-oxygen bond and an acid group-containing structure (B) covalently bonded to a silane compound and having an acid group are composed of silicon-oxygen. Proton conducting membranes connected by bonds are conceivable. However, in the production process, such a proton conductive membrane, when the reactivity of the polymerization reaction between the raw materials is low, the raw materials are dissolved in a polar solvent such as a solution, in particular, an aqueous methanol solution. There was a problem that there is a possibility that it will decrease.

  This invention is made | formed in view of the said situation, and makes it a subject to provide a proton conductive membrane which has high proton conductivity, and is excellent also in fuel cutoff property and durability.

To solve the above problem,
The invention according to claim 1 includes a crosslinkable compound (A ′) having a silicon-oxygen bond, a group capable of forming a silicon-oxygen-silicon bond and a silane compound (α) having a polymerizable unsaturated double bond, an acid A first step of preparing a polymerizable composition by mixing an acid group-containing compound (β) having a group and a polymerizable unsaturated double bond and a polymerization initiator, and a second step of forming a film of the polymerizable composition And a third step of polymerizing the formed polymerizable composition, wherein the crosslinkable compound (A ′) having a silicon-oxygen bond is represented by the following general formula (A): 1 ′), wherein the acid group-containing compound (β) is a compound having a sulfo group as the acid group, and a plurality of types of polymerization initiators having different 10-hour half-life temperatures are used as the polymerization initiator. In a method for producing a proton conductive membrane, characterized in that That.

(Wherein R ¹ is a divalent hydrocarbon group having 1 to 50 carbon atoms or an oxygen atom; R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group N-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, hydroxyl group or a group represented by the formula “—O—Si—”, at least one of which is a methoxy group, an ethoxy group, or an n-propoxy group. group, Isopuropokishiki group, n- butoxy group, isobutoxy group, sec- butoxy group, a tert- butoxy group or a hydroxyl ^group; when R 1 to R ³ is plural, a plurality of R To R ³ may be the same or different, respectively Re its; m ₂ is an integer of 0 or more).

The invention according to claim 2 uses a plurality of the polymerization initiators having a 10-hour half-life temperature within the range of the polymerization temperature of the silane compound (α) and the acid group-containing compound (β) in the third step. The method for producing a proton conductive membrane according to claim 1, wherein the difference in 10-hour half-life temperature of these polymerization initiators is 16 ° C or more at the maximum.
According to a third aspect of the present invention, in the third step, the reaction is initiated at a temperature below the lowest temperature among the 10-hour half-life temperatures of the polymerization initiator, and the temperature is raised to a temperature above the highest temperature. The method according to claim 1 or 2, wherein the reaction is performed.
The invention according to claim 4 further includes the addition of a crosslinking agent (C) having two or more functional groups in one molecule that can be bonded to the silane compound (α) or the acid group-containing compound (β). The method for producing a proton conductive membrane according to any one of claims 1 to 3, wherein the first step is performed.
In the invention according to claim 5, the R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group or a hydroxyl group. It is a manufacturing method of the proton-conductive film | membrane as described in any one of Claims 1-4 characterized by the above-mentioned.
The invention according to claim 6 is characterized in that the R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a methoxy group or a hydroxyl group. It is a manufacturing method of a conductive film.
The invention according to claim 7 is a proton conductive membrane manufactured by the manufacturing method according to any one of claims 1 to 6.

The invention according to claim 8 is characterized in that the crosslinkable compound (A) having a silicon-oxygen bond and the acid group-containing structure (B) covalently bonded to the silane compound and having an acid group are silicon-oxygen-silicon. A proton conductive membrane connected by a bond, the gel fraction is 96% or more, and the crosslinkable compound (A) having a silicon-oxygen bond is represented by the following general formula (1): The acid group-containing structure (B) has a group capable of forming a silicon-oxygen-silicon bond and a silane compound (α) having a polymerizable unsaturated double bond, and has an acid group and a polymerizable unsaturated double bond. look containing a structure acid group-containing compound and (beta) is covalently bound, the silane compound (alpha) is a compound represented by the following general formula (2), wherein the acid group-containing compound (beta) is , characterized in that it is a compound having a sulfo group as the acid group It is a proton conducting membrane to.

(Wherein R ¹ Is a divalent hydrocarbon group having 1 to 50 carbon atoms or an oxygen atom; R ² , R ³ , R ⁴ , R ⁵ , R ⁶ And R ⁷ Are each independently a hydrogen atom, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n -Propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, hydroxyl group or a group represented by the formula "-O-Si-", at least one of which is methoxy A group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group or hydroxyl group; R ¹ ~ R ³ Is a plurality of R ¹ ~ R ³ May be the same or different; m ₁ Is an integer of 1 or more. )

(Wherein R ⁸ Is a divalent hydrocarbon group which may have a substituent, a divalent group in which the hydrocarbon group and an oxycarbonyl group are bonded, or a hetero atom; R ⁹ , R ¹⁰ And R ¹¹ Each independently represents a hydrocarbon group which may have a substituent, a group in which the hydrocarbon group is bonded to a hetero atom, a hydroxyl group, a hydrogen atom, a hetero atom or a halogen atom, at least one of which is silicon-oxygen- A group capable of forming a silicon bond; R ⁰ Is a hydrogen atom or a methyl group; n ₁ Is an integer greater than or equal to 1, n ₂ Is 0 or 1, where n ₂ N is 0, n ₁ Is 1. )

  According to the present invention, a proton conductive membrane having high proton conductivity and excellent fuel cutoff and durability can be obtained.

The present invention will be described in detail below.
In the following description, for example, “reaction between crosslinkable compound (A) and silane compound (α)” means “crosslinkable compound (A) and silane compound in acid group-containing structure (B)” for convenience. The reaction with the site derived from (α) ”is also included.
Similarly, the “polymerization reaction between the silane compound (α) and the acid group-containing compound (β)” refers to the “polymerization reaction between the polymer derived from the silane compound (α) and the acid group-containing compound (β)” for convenience. And “a polymerization reaction between the silane compound (α) and a polymer derived from the acid group-containing compound (β)”.
Similarly, “bonding between the silane compound (α) and the crosslinking agent (C)” includes “bonding between the polymer derived from the silane compound (α) and the crosslinking agent (C)” for convenience. The same applies to “the bond between the acid group-containing compound (β) and the crosslinking agent (C)”.

<Proton conductive membrane>
The proton conductive membrane of the present invention is covalently bonded to a crosslinkable compound (A) having a silicon-oxygen bond (hereinafter sometimes abbreviated as “crosslinkable compound (A)”) and a silane compound. The acid group-containing structure (B) having a group (hereinafter sometimes abbreviated as “acid group-containing structure (B)”) is linked by a silicon-oxygen-silicon bond, and the gel fraction is 96% or more, the crosslinkable compound (A) is represented by the following general formula (1), and the acid group-containing structure (B) can form a silicon-oxygen-silicon bond and polymerizability Silane compound (α) having an unsaturated double bond (hereinafter sometimes abbreviated as “silane compound (α)”), and acid group-containing compound (β) having an acid group and a polymerizable unsaturated double bond (Hereinafter sometimes abbreviated as “acid group-containing compound (β)”). Characterized in that it comprises a structure and formed by.

(Wherein R ¹ is a divalent hydrocarbon group having 1 to 50 carbon atoms or an oxygen atom; R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group N-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, hydroxyl group or a group represented by the formula “—O—Si—”, at least one of which is a methoxy group, an ethoxy group, or an n-propoxy group. group, Isopuropokishiki group, n- butoxy group, isobutoxy group, sec- butoxy group, a tert- butoxy group or a hydroxyl ^group; when R 1 to R ³ is plural, a plurality of R To R ³ may be the same or different, respectively Re its; m ₁ is an integer of 1 or more).

[Crosslinking compound (A)]
The crosslinkable compound (A) serves as a crosslinked basic structure in the proton conductive membrane of the present invention, and is represented by the general formula (1).

In the general formula (1), R ¹ is a divalent hydrocarbon group or an oxygen atom having 1 to 50 carbon atoms.
The divalent hydrocarbon group for R ¹ may be linear, branched or cyclic, and may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

The aliphatic hydrocarbon group may be either a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, but is preferably a saturated aliphatic hydrocarbon group, and is a linear or branched saturated fat. An aromatic hydrocarbon group is more preferable, and a linear saturated aliphatic hydrocarbon group is particularly preferable.
The aliphatic hydrocarbon group preferably has 1 to 20 carbon atoms, and more preferably 1 to 10 carbon atoms.
Particularly preferred examples of the aliphatic hydrocarbon group include methylene group, ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group and decylene group.
The aromatic hydrocarbon group may be monocyclic or polycyclic, but is preferably monocyclic, and particularly preferably a phenylene group.

In addition, the divalent hydrocarbon group of R ¹ may be a divalent group in which an aliphatic hydrocarbon group and an aromatic hydrocarbon group are bonded, and as such, there are two aromatic hydrocarbon groups. Those in which a hydrogen atom is substituted with a divalent aliphatic hydrocarbon group are preferred. Here, as the aliphatic hydrocarbon group and the aromatic hydrocarbon group, a combination in which the total number of carbon atoms is 50 or less may be selected from those described above. Specific examples of preferable ones include those in which hydrogen atoms at the 1-position and 4-position of benzene are substituted with an alkylene group. The alkylene group preferably has 1 to 5 carbon atoms, preferably 1 to 1 carbon atoms. 3 is more preferable, and an ethylene group is particularly preferable.

In general formula (1), R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, or an n-butyl group. , Isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group , A hydroxyl group or a group represented by the formula “—O—Si—”. Here, when any of R ^{2 to} R ⁷ is a group represented by the formula “—O—Si—”, the crosslinkable compound (A) binds to another crosslinkable compound (A). Indicates that
And at least one of R ^{2 to} R ⁷ is a methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group or hydroxyl group. Then, the hydroxyl group or a hydroxyl group (silanol group) generated by hydrolysis of these groups excluding the hydroxyl group in the presence of an acid or base catalyst can undergo a condensation reaction with other molecules having a silanol group. Yes.
In the present invention, R ^{2 to} R ⁷ are preferably each independently a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group or a hydroxyl group, and R ^{2 to} R ⁷ are each independently a methoxy group or a hydroxyl group. It is more preferable that

When R ¹ to R ³ is plural, a plurality of ^R 1 to R ³ may be the same or different, respectively Re it. For example, in the general formula (1), when m ₁ is an integer of 2 or more, the crosslinkable compound (A) includes a divalent hydrocarbon group having 1 to 50 carbon atoms and an oxygen atom as R ^1. As such, the general formula “—Si—R ¹ ′ —Si—O— (wherein R ¹ ′ represents a divalent hydrocarbon group having 1 to 50 carbon atoms). And a compound having a repeating basic skeleton represented by Similarly, a plurality of R ² may be the same or different, and a plurality of R ⁵ may be the same or different.

In general formula (1), m ₁ is an integer of 1 or more.

  As represented by the general formula (1), the crosslinkable compound (A) may be an inorganic compound or an organic-inorganic composite in which an organic compound is combined with an inorganic compound. In particular, in the case of an organic-inorganic composite, the physical properties of the proton conductive membrane can be adjusted by appropriately selecting a combination of an organic compound and an inorganic compound according to the purpose. For example, it is possible to form a proton conductive membrane that has both the heat resistance of an inorganic compound and the flexibility of an organic compound. In addition, by adjusting the degree of cross-linking of the cross-linkable compound (A) and other structures, the fuel blocking property, which is one of the important characteristics of the proton conductive membrane, can be adjusted.

  The proton conductive membrane of the present invention is preferably a continuum of particles in which the electrolyte has a particulate structure and the particulate structure is bonded to each other. In such a continuum of particles, the strength and flexibility of the proton conductive membrane can be adjusted as appropriate by adjusting the crosslink density and interparticle bond strength. Furthermore, it is preferable that the particle surface has an acid group and a proton conduction path is formed between the particles. By taking such a structure, the mechanical strength of the electrolyte is improved, and protons are efficiently conducted. Here, the particles are preferably spherical, but may be irregular particles. Here, the irregularly shaped particles refer to particles that are not constituted by a completely curved surface and have a part with a corner in part or in whole. The average particle size of the particles is preferably 3 to 200 nm, more preferably 10 to 100 nm. When the average particle diameter exceeds 200 nm, the surface area of the particles responsible for proton conduction decreases, and high conductivity cannot be obtained, and the gaps between the particles become too large and become brittle. On the other hand, if the average particle diameter is smaller than 3 nm, the layer becomes close to a uniform layer, and efficient proton conduction may not be possible with a smaller number of acid groups. By setting the range of the average particle diameter to the above-described preferable range, it is possible to sufficiently secure the proton conduction path while ensuring sufficient strength. The particle diameter can be determined directly from an electron micrograph such as a field emission scanning electron microscope (FE-SEM), but can also be determined by means such as small angle X-ray scattering. The particle size distribution may be a continuum of particles having a uniform particle size or a continuum of particles having a non-uniform particle size. Here, when the particle size distribution of the particles is uniform, although depending on the particle size, a gap is easily formed geometrically and there is a possibility that high ionic conductivity can be exhibited. On the other hand, if the particle size distribution is wide, dense packing is possible, which contributes to improved fuel shut-off and improved membrane strength. Therefore, it is preferable to select the particle size distribution according to the use situation. The particle size can be controlled by adjusting conditions such as the structure of the raw material used, the molecular weight, the type / concentration of the solvent, and the reaction temperature.

The crosslinkable compound (A) is not particularly limited as long as it satisfies the above-mentioned conditions, but as a preferable one, specifically, one or more selected from the group consisting of the following compounds is used as a monomer, and the monomer is polymerized. Can be exemplified.
Bis such as 1,2-bis (triethoxysilyl) ethane, 1,6-bis (trimethoxysilyl) hexane, 1,9-bis (triethoxysilyl) nonane, 1,8-bis (triethoxysilyl) octane (Alkoxysilyl) alkanes;
Bis (alkylalkoxysilyl) alkanes such as 1,8-bis (diethoxymethylsilyl) octane, 1,8-bis (ethyldimethoxysilyl) octane;
Bis (trialkoxysilylalkyl) benzene such as 1,4-bis (trimethoxysilylethyl) benzene, 1,4-bis (triethoxysilylethyl) benzene;
Alkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane;
Methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltri-n-butoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldiisopropoxysilane, dimethyldi-n-butoxysilane, ethyltrimethoxysilane, Ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-n-butoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltriisopropoxysilane, n-propyltri-n-butoxysilane, Isopropyltrimethoxysilane, isopropyltriethoxysilane, isopropyltriisopropoxysilane, isopropyltri-n-butoxysilane, n-butyltrimethoxysilane, n-buty Triethoxysilane, n- butyl triisopropoxysilane, alkyl alkoxysilanes such as n- butyltri -n- butoxysilane;
Phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltri-n-butoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenylmethyldiisopropoxysilane, phenylmethyldi-n-butoxysilane Arylalkoxysilanes such as;

  Among the above compounds, tetramethoxysilane and tetraethoxysilane are general-purpose products, and are inexpensive and available in large quantities and easily. Therefore, a polymer obtained by polymerizing one or more of these is used as the crosslinkable compound (A). It is preferred to use.

  The crosslinkable compound (A) having a silicon-oxygen bond may be used singly or in combination of two or more. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

[Acid group-containing structure (B)]
The acid group-containing structure (B) includes a structure in which a silane compound (α) and an acid group-containing compound (β) are covalently bonded.

(Silane compound (α))
Silane compound ((alpha)) should just have a group which can form a silicon-oxygen-silicon bond, and a polymerizable unsaturated double bond. Among them, preferred examples include compounds represented by the following general formula (2).

(Wherein R ⁸ is a divalent hydrocarbon group which may have a substituent, and a divalent group in which the hydrocarbon group and an oxycarbonyl group (—O—C (═O) —) are bonded). Or R ⁹ , R ¹⁰ and R ¹¹ are each independently a hydrocarbon group which may have a substituent, a group in which the hydrocarbon group is bonded to a hetero atom, a hydroxyl group, a hydrogen atom or a hetero atom. Or a halogen atom, at least one of which is capable of forming a silicon-oxygen-silicon bond; R ⁰ is a hydrogen atom or a methyl group; n ₁ is an integer of 1 or more, and n ₂ is 0 or 1 if n ₂ is 0, n ₁ is 1.)

In the general formula (2), R ⁸ represents a divalent hydrocarbon group which may have a substituent, a divalent hydrocarbon group bonded to an oxycarbonyl group (—O—C (═O) —). A valent group or a heteroatom.
The divalent hydrocarbon group for R ⁸ may be linear, branched or cyclic, and may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. A divalent group to which a hydrogen group is bonded may be used.
The aliphatic hydrocarbon group may be either a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, but is preferably a saturated aliphatic hydrocarbon group, and is a linear or branched saturated fat. An aromatic hydrocarbon group is more preferable, and a linear saturated aliphatic hydrocarbon group is particularly preferable.
The aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms.
Particularly preferable examples of the aliphatic hydrocarbon group include a methylene group, an ethylene group, a propylene group, a butylene group, and a pentylene group.
The aromatic hydrocarbon group may be monocyclic or polycyclic, but is preferably monocyclic, and particularly preferably a phenylene group.

The divalent group in which the hydrocarbon group of R ⁸ and the oxycarbonyl group (—O—C (═O) —) are bonded is a divalent group having an ester bond, and is a terminal of the hydrocarbon group. Are bonded to the oxygen atom (—O—) of the oxycarbonyl group (—O—C (═O) —).
The hetero atom of R ⁸ is preferably an oxygen atom or a sulfur atom.

Examples of the substituent that R ⁸ may have include an alkyl group, an alkoxy group, a hydroxyl group, and a halogen atom.
The alkyl group or alkoxy group as the substituent preferably has 1 to 3 carbon atoms.
Examples of the halogen atom as a substituent include a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.
The number of substituents is not particularly limited, but is preferably 0 or 1, and more preferably 0.

R ⁹ , R ¹⁰ and R ¹¹ are each independently a hydrocarbon group which may have a substituent, a group in which the hydrocarbon group is bonded to a hetero atom, a hydroxyl group, a hydrogen atom, a hetero atom or a halogen atom.
Examples of the hydrocarbon group of R ^{9 to} R ¹¹ include a monovalent hydrocarbon group in which a hydrogen atom is bonded to the divalent hydrocarbon group of R ⁸ . Of these, an aliphatic hydrocarbon group is preferable, a saturated aliphatic hydrocarbon group is more preferable, and a linear or branched saturated aliphatic hydrocarbon group is particularly preferable.
The aliphatic hydrocarbon group preferably has 1 to 5 carbon atoms, and more preferably 1 to 3 carbon atoms. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, and a neopentyl group. .

Examples of the hetero atom of R ^{9 to} R ¹¹ include an oxygen atom or a sulfur atom, and an oxygen atom is particularly preferable.
The hetero atom in the group in which the hydrocarbon group of R ^{9 to} R ¹¹ is bonded to a hetero atom is the same as described above, and among them, the group in which the hydrocarbon group of R ^{9 to} R ¹¹ is bonded to an oxygen atom is preferable. Particularly preferred is a linear or branched alkoxy group.
As a halogen atom of R < ⁹ > -R < ¹¹ >, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom can be illustrated.

At least one of R ^{9 to} R ¹¹ is a group capable of forming a silicon-oxygen-silicon bond, and preferred examples include an alkoxy group and a hydroxyl group. The alkoxysilyl group forms a silicon-oxygen-silicon bond between molecules by condensation with a silanol group or the like after the hydrolysis reaction.

R ⁰ is a hydrogen atom or a methyl group.
n ₁ is an integer of 1 or more, preferably 1 to 5, more preferably 1 to 3, and particularly preferably 1.
n ₂ is 0 or 1, provided that when n ₂ is 0, n ₁ is 1.

Specific examples of preferred silane compounds (α) include 3- (trimethoxysilyl) propyl acrylate, 3- (methyldimethoxysilyl) propyl acrylate, 3- (triethoxysilyl) propyl acrylate, and 3- (methyldiethoxysilyl). Propyl acrylate, trimethoxyvinylsilane, triethoxyvinylsilane, 3- (trimethoxysilyl) propyl methacrylate, 3- (methyldimethoxysilyl) propyl methacrylate, 3- (triethoxysilyl) propyl methacrylate, 3- (methyldiethoxy Examples include silyl) propyl methacrylate, p-styryltrimethoxysilane, p-styryltriethoxysilane and the like.
Among these, as the silane compound (α), 3- (trimethoxysilyl) propyl methacrylate and trimethoxyvinylsilane are particularly preferable.

  A silane compound ((alpha)) may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

(Acid group-containing compound (β))
The acid group-containing compound (β) may be any compound having an acid group and a polymerizable unsaturated double bond.
The acid group is preferably an acid group-containing compound (β) having a pKa of 5 or less as defined by an acid dissociation constant in water, such as a sulfo group (—SO ₃ H), a carboxy group, and a phosphate group. And a sulfo group is particularly preferable.
Preferred examples of the acid group-containing compound (β) include (meth) acrylates having a straight chain structure having three or more heteroatoms capable of protonation and two or more methylene groups linked. it can. Here, examples of the heteroatom that can be protonated include an oxygen atom, a sulfur atom, and a nitrogen atom, and may be an atom in an atomic group constituting the acid group, such as a sulfo group.

  Preferred examples of the acid group-containing compound (β) include compounds represented by the following general formulas (3) to (5).

(In the formula, R ¹² is an alkylene group, an arylene group or a carbonyloxyalkylene group having 10 or less carbon atoms which may have a substituent; and R ¹³ has 10 or less carbon atoms which may have a substituent. An alkyl group, an aryl group, a carbonyloxyalkyl group or an aminocarbonyl group; X is an acid group.)

In the formula, R ¹² is an alkylene group having 10 or less carbon atoms, an arylene group, or an oxycarbonylalkylene group which may have a substituent.
The alkylene group for R ¹² may be linear or branched and preferably has 2 to 8 carbon atoms, more preferably 2 to 5 carbon atoms.
The arylene group for R ¹² is preferably a phenylene group.
The alkylene group in the carbonyloxyalkylene group represented by R ¹² preferably has 2 to 6 carbon atoms, more preferably 2 to 4 carbon atoms, and is preferably linear. The carbon atom constituting the carbonyl group of the carbonyloxyalkylene group is bonded to the carbon atom constituting the carbon = carbon double bond in the above formula.

The alkylene group, arylene group, or carbonyloxyalkylene group represented by R ¹² may have a substituent. Here, having a substituent means that a part of the hydrogen atoms bonded to the carbon atom of the alkylene group, arylene group or carbonyloxyalkylene group is substituted with a substituent.
Here, preferred examples of the substituent include an alkyl group, an alkoxy group, a halogen atom, an amino group, a sulfo group, and a carboxy group. It is preferable that the alkyl group and alkoxy group as a substituent have 1 to 3 carbon atoms. The halogen atom as a substituent can be exemplified by a fluorine atom, a chlorine atom, a bromine atom or an iodine atom. Among these, as a substituent, an alkoxy group, a carboxy group, an amino group, or a sulfo group is preferable, and an amino group or a sulfo group is more preferable.

In the formula, R ¹³ is an alkyl group having 10 or less carbon atoms, an aryl group, a carbonyloxyalkyl group or an aminocarbonyl group which may have a substituent.
Examples of the alkylene group for R ¹³ include those in which a hydrogen atom is bonded to the alkylene group for R ¹² .
Examples of the aryl group of R ¹³ include those in which a hydrogen atom is bonded to the arylene group of R ¹² .
Examples of the carbonyloxyalkyl group for R ¹³ include those in which a hydrogen atom is bonded to the carbonyloxyalkylene group for R ¹² .

The alkyl group, aryl group, carbonyloxyalkyl group or aminocarbonyl group of R ¹³ may have a substituent. Here, having a substituent means that a part of hydrogen atoms bonded to carbon atoms of the alkyl group, aryl group or carbonyloxyalkyl group is substituted with a substituent, or a nitrogen atom of an aminocarbonyl group. It shows that part or all of the hydrogen atoms bonded to is substituted with a substituent.
Examples of the substituent in the alkyl group, aryl group or carbonyloxyalkyl group include the same substituents as those in R ¹² .
Preferred examples of the substituent in the aminocarbonyl group include an alkyl group having 1 to 3 carbon atoms.

  In formula, X is an acid group and is the same as the acid group in said acid group containing compound ((beta)).

Specific examples of preferred acid group-containing compound (β) include 2-acrylamido-2-methylpropanesulfonic acid, 2- (methacryloyloxy) ethylsulfonic acid, 3-sulfopropyl methacrylate, p-stilsulfonic acid, 4, Examples thereof include 4′-diaminostilbenzene-2,2′-disulfonic acid, bis (3-sulfopropyl) itaconate, and the like.
Among these, 2-acrylamido-2-methylpropanesulfonic acid is particularly preferable as the acid group-containing compound (β).

  An acid group containing compound ((beta)) may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

[Crosslinking agent (C)]
The proton conductive membrane of the present invention may be prepared by further blending a crosslinking agent (C) in addition to the crosslinking compound (A) and the acid group-containing structure (B) as necessary. Thus, since the proton conductive membrane has a structure cross-linked with the cross-linking agent (C), the flexibility is further improved and a strong cross-linked structure is obtained, so that the impact resistance and the polar solvent resistance are further improved. Further improvement.

The cross-linking agent (C) has two or more functional groups in one molecule that can be bonded to the silane compound (α) or the acid group-containing compound (β) that is a raw material of the acid group-containing structure (B). Is preferred. Preferable examples of the crosslinking agent (C) include N, N′-methylenebis (acrylamide), neopentyl glycol diacrylate, 1,4-bis (acryloyloxy) butane, 1,3-bis (methacryloyloxy) — 2-propanol, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1- (acryloyloxy) -3- (methacryloyloxy) -2-propanol, divinylbenzene, 3- (methacryloylamino) propyltrimethylammonium chloride, vinyl methacrylate And hydrocarbon-based crosslinking agents such as
Among these, as the crosslinking agent (C), N, N′-methylenebis (acrylamide), divinylbenzene, trimethylolpropane triacrylate, and neopentyl glycol diacrylate are particularly preferable.
Moreover, when using a crosslinking agent (C), you may use together fluorine-type monomers, such as 2,2,2-trifluoroethyl acrylate and 2,2,2-trifluoroethyl methacrylate.

  A crosslinking agent (C) may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

The proton conductive membrane exhibits high proton conductivity by forming a proton conduction path in which acid groups are present at a high concentration and acid is continuously present.
By including the acid group-containing structure (B), the proton conductive membrane of the present invention can maintain a state where acid groups are present in a high concentration in the membrane, and can increase the proton concentration in the membrane. Thus, stable fuel cell operation for a long time can be achieved.
FIG. 1 schematically illustrates the structure of the proton conductive membrane of the present invention. As shown here, in the proton conductive membrane of the present invention, the acid group-containing compound (β) reacts with the crosslinkable compound (A) to be a crosslinked basic structure (skeleton) and the silane compound (α). And an acid group-containing structure (B) bonded via a covalent bond.
In addition, the structure of the proton conductive membrane shown here is only an example, and for example, a polymer of silane compounds (α) or a polymer of acid group-containing compounds (β) may be included, The crosslinking agent (C) may form a crosslinked structure with the silane compound (α) or the acid group-containing compound (β), or the crosslinking agent (C) may form a crosslinked structure.

FIG. 2A schematically shows the structures of a crosslinkable compound (A), a silane compound (α), an acid group-containing compound (β), and a crosslinker (C), which are raw materials for the proton conductive membrane of the present invention. It is a figure illustrated.
The crosslinkable compound (A) shown here is represented by the general formula (1), the silane compound (α) is represented by the general formula (2), and an acid group-containing compound. (Β) is represented by the general formula (5).
R ¹⁴ in the crosslinking agent (C) is an alkylene group; a group in which a carbon atom of the alkylene group is substituted with a divalent group such as an amide group or a carbonyloxy group; an arylene group.
FIG. 2B is a diagram schematically illustrating the structure of the proton conductive membrane formed by the reaction of the raw material shown in FIG.
However, it goes without saying that the structure of each raw material and proton conductive membrane shown here is only an example.

In general, since the silicon-oxygen crosslinked structure has a rigid structure, if there are many highly polar parts, the proton conductivity and the fuel cutoff performance may be deteriorated due to temperature fluctuations. In the present invention, as shown in FIG. 1, the acid group (X) in the acid group-containing compound (β) is bonded to the crosslinkable compound (A) via the silane compound (α), thereby preventing fuel blocking. Various film properties such as strength can be further improved. In particular, the acid group (X) is bonded to the silicon atom constituting the siloxane bond in the crosslinkable compound (A) via at least four or more carbon-carbon single bonds, whereby the acid group (X) and As compared with the case where the distance from the silicon atom is short, it is possible to effectively suppress the destruction of the film and the deterioration of characteristics due to the rapid penetration of the polar solvent.
Furthermore, by configuring the acid group-containing structure (B) so as to include many organic sites, flexibility is imparted to the proton conductive membrane, and impact resistance is improved.

  In the present invention, desired flexibility and high polar solvent resistance can be imparted to the proton conductive membrane by appropriately selecting the combination of the silane compound (α) and the acid group-containing compound (β).

<Method for producing proton conductive membrane>
The method for producing a proton conductive membrane of the present invention comprises a crosslinkable compound (A ′) having a silicon-oxygen bond (hereinafter sometimes abbreviated as “crosslinkable compound (A ′)”), a silane compound (α). , A first step of preparing a polymerizable composition by mixing the acid group-containing compound (β) and a polymerization initiator, a second step of forming a film of the polymerizable composition, and a formed polymerizable composition A plurality of types of polymerization initiators having different 10-hour half-life temperatures as the polymerization initiator, wherein the crosslinkable compound (A ′) is represented by the following general formula (1 ′): It is characterized by using an agent.

(Wherein R ¹ is a divalent hydrocarbon group having 1 to 50 carbon atoms or an oxygen atom; R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group N-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, hydroxyl group or a group represented by the formula “—O—Si—”, at least one of which is a methoxy group, an ethoxy group, or an n-propoxy group. group, Isopuropokishiki group, n- butoxy group, isobutoxy group, sec- butoxy group, a tert- butoxy group or a hydroxyl ^group; when R 1 to R ³ is plural, a plurality of R To R ³ may be the same or different, respectively Re its; m ₂ is an integer of 0 or more).

(Crosslinkable compound (A ′))
The crosslinkable compound (A ′) is represented by the general formula (1 ′).
In general formula (1 ′), R ^{1 to} R ⁷ are the same as R ^{1 to} R ⁷ in general formula (1).
m ₂ is an integer of 0 or more.
That is, the crosslinkable compound (A ′) represents the crosslinkable compound (A) when m ₂ is an integer of 1 or more, and when m ₂ is 0, the crosslinkable compound (A ′) ) Represents a monomer as a raw material.
In the production method of the present invention, the crosslinkable compound (A) is used in the first step, and as described later, this may be combined with the acid group-containing structure (B) in the third step. As described later, the crosslinkable compound (A ′) is used in one step, and this is polymerized in the third step to form a crosslinkable compound (A), which is combined with the acid group-containing structure (B). good.

A crosslinking compound (A ') may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose. For example, as the crosslinkable compound (A ′), a compound in which m ₂ is 0 and a compound in which m ₂ is 1 or more may be used in combination.
Hereinafter, each step will be described in detail.

[First step]
(Polymerization initiator)
Among the polymerization initiators used in the first step, the polymerizable unsaturated double bond of the silane compound (α) and the acid group-containing compound (β) can form a covalent bond by a polymerization reaction. A plurality of types having different 10-hour half-life temperatures are used. Specifically, those that generate radicals by heating or light irradiation (thermal polymerization initiators, photopolymerization initiators) are preferable, and may be appropriately selected from known ones. As such, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] hydrochloride (44 ° C.), 2,2′-azobis [2- (2-imidazolin-2-yl) ) Propane] sulfate (47 ° C.), 2,2′-azobis (2-methylpropionamidine) hydrochloride (56 ° C.), 2,2′-azobis {2-methyl-N- [1,1-bis ( Hydroxymethyl) -2-hydroxyethyl] propionamide} (60 ° C.), 2,2′-azobisisobutyronitrile, 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine Hydrate (57 ° C.), 2,2′-azobis [2- (2-imidazolin-2-yl) propane] (61 ° C.), 2,2′-azobis (1-imino-1-pyrrolidino-2) -Methylpropane) dihydrochloride (67 ° C.), 2 , 2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide} (80 ° C.), 2,2′-azobis [2-methyl-N- ( Azo initiators such as 2-hydroxyethyl) propionamide] (87 ° C.);
Benzophenone, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- [ 4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) ) -Benzyl] phenyl} -2-methyl-propan-1-one, 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1 -(4-morpholinophenyl) -butanone-1,2- (dimethylamino) -2-[(4-methylphenyl) methyl] -1- [4- (4-morpholini) ) Phenyl] -1-butanone, 2,4,6-trimethylbenzoyl - diphenyl - photopolymerization initiators such as phosphine oxide;
Organic peroxides such as dibenzoyl peroxide (74 ° C.), t-butyl hydroperoxide (167 ° C.), di-t-butyl peroxide (116 ° C.);
2 or more types selected from the group consisting of
In addition, about some of the said polymerization initiators, the 10-hour half-life temperature is illustrated in () immediately after the compound name.

“10-hour half-life temperature” refers to a temperature at which about half of the initial amount of the polymerization initiator remains unreacted after 10 hours when the polymerization initiator is present alone. Then, as will be described later, when a solvent is used in the first step, when the polymerization initiator is present alone in the solvent, the amount of the polymerization initiator of about ½ of the initial amount is 10 The temperature that remains unreacted after a time.
In the present invention, the polymerization reaction of unsaturated double bonds in the third step can be promoted at any stage by using a plurality of types of polymerization initiators having different 10-hour half-life temperatures. For example, when a polymerization initiator having a low 10-hour half-life temperature is used alone, or when a plurality of types of polymerization initiators having a low and similar 10-hour half-life temperature are similar or close together, Although the reaction is promoted at the stage, the reaction becomes difficult to proceed as the polymerization time becomes longer. On the other hand, when a polymerization initiator having a high 10-hour half-life temperature is used alone, or when a plurality of types of polymerization initiators having a high and similar 10-hour half-life temperature are used, the reaction time is remarkably increased. It becomes long or the reaction cannot be performed sufficiently. In this way, when a polymerization initiator is used alone or when a plurality of types of polymerization initiators having similar or close 10-hour half-life temperatures are used in combination, the reactivity of the polymerization reaction between unsaturated double bonds decreases. However, a proton conductive membrane having a sufficiently high degree of crosslinking cannot be obtained.
In contrast, in the present invention, since a plurality of types of polymerization initiators having different 10-hour half-life temperatures are used, the reaction can be accelerated from the initial stage to the end of the polymerization reaction, and the silane compound (α) and the acid group-containing compound A structure formed by covalently bonding (β) can be obtained efficiently. Then, the acid group-containing structure (B) containing such a structure and the crosslinkable compound (A) are linked by a silicon-oxygen-silicon bond, and a proton conductive membrane having a sufficiently high degree of crosslinking is obtained. As a result, the residual amount of the silane compound (α) and the acid group-containing compound (β) can be reduced, and the amount of soluble components in the polar solvent can be reduced, so that the polar solvent resistance of the resulting proton conductive membrane is improved. .

  A plurality of types of polymerization initiators having different 10-hour half-life temperatures may be used, but many types are more advantageous as long as the effects of the present invention are not hindered. However, considering the balance between operability and effect, 2 to 4 types are preferable.

  In the present invention, it is preferable to use a polymerization initiator having a 10-hour half-life temperature within the range of the polymerization temperature of the silane compound (α) and the acid group-containing compound (β) in the third step. In this case, it is preferable to use a plurality, preferably 2 to 4, of such polymerization initiators so that the difference in 10-hour half-life temperature of these polymerization initiators is 16 ° C. or more at the maximum. Here, the “difference in 10-hour half-life temperature” refers to a difference in 10-hour half-life temperature for any two of a plurality of types of polymerization initiators.

  The total amount of polymerization initiator used is usually 0.01 to 25% by mass relative to the total amount of raw materials excluding the solvent. However, the greater the total amount used, the higher the dispersibility in the reaction solution, and the higher the polymerizability. The reactivity of the unsaturated double bond is improved, and the amount remaining unreacted is reduced. As a result, the polar solvent resistance of the resulting proton conductive membrane is improved. Therefore, also in the present invention, it is preferable to increase the total amount of the polymerization initiator as long as the solubility during mixing of the raw materials is not hindered.

The first step may be performed by adding a crosslinking agent (C).
Furthermore, it can also carry out by adding arbitrary components, such as compatibilizers, such as sodium dodecyl sulfate, in the range which does not impair the effect of this invention.

In preparing the polymerizable composition in the first step, it is preferable to use a solvent. Although the kind of solvent is not specifically limited, What can mix each raw material uniformly is preferable. Specific examples include water; alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, and tert-butanol; ether solvents such as tetrahydrofuran and 1,4-dioxane.
Although the usage-amount of a solvent is not specifically limited, Usually, it is preferable to set a usage-amount so that solid content concentration may be about 10-90 mass%.
In the third step, for example, when the hydrolysis reaction of an alkoxysilyl group or the like is simultaneously performed, the amount of water used may be selected in consideration of the amount necessary for the hydrolysis reaction. For example, water is usually added in an equimolar amount with respect to the hydrolyzable silyl group, but an amount exceeding the equimolar amount may be added to accelerate the hydrolysis reaction, and the hydrolysis reaction is performed slowly. An amount less than an equimolar amount may be added.

The ratio (molar ratio) of the amounts used of the crosslinkable compound (A ′), the silane compound (α), the acid group-containing compound (β) and the crosslinking agent (C) may be appropriately selected according to the purpose. That is, it is preferable to adjust in consideration of the physical properties of a desired proton conductive membrane, and it is not generally defined.
For example, if the crosslinkable compound (A ′) is a compound having m ₂ of 0, the ratio (molar ratio) of the crosslinkable compound (A ′) / silane compound (α) is 1 to 7 is preferable, and 2 to 5 is more preferable.
The ratio (molar ratio) of the crosslinkable compound (A ′) / acid group-containing compound (β) is preferably 0.05 to 0.6, and more preferably 0.1 to 0.4.
The ratio (molar ratio) of [silane compound (α) and acid group-containing compound (β)] / crosslinking agent (C) is preferably from 3 to 10, and more preferably from 6 to 9.

The method for mixing the raw materials is not particularly limited as long as sufficient mixing is possible, and may be appropriately selected from known methods such as stirring and vibration. Moreover, you may perform pressurization, defoaming, deaeration, etc. at the time of mixing as needed.
The temperature and time at the time of mixing are preferably adjusted appropriately according to the purpose in consideration of the type of raw materials and solvents used, etc., but the temperature is usually preferably 0 to 5 ° C., and the time is 3 to 3. It is preferably 10 minutes. The mixing time is preferably shorter as long as a uniform liquid can be obtained. If the mixing time becomes too long, the manufacturing time becomes longer and the cost increases.

[Second step]
The method for forming the polymerizable composition is not particularly limited as long as it is a method capable of obtaining a uniform film, and may be appropriately selected from known methods such as casting, coating, and casting.
What is necessary is just to select the film thickness at the time of film-forming suitably according to the film thickness calculated | required by the proton-conductive film | membrane after manufacture. In the proton conductive membrane for a fuel cell, a preferable film thickness is appropriately determined from the required proton conductivity, fuel barrier properties, and mechanical strength of the membrane, and is preferably 20 to 300 μm. From this point of view, in the present invention, it is usually preferable that the film thickness when forming the polymerizable composition is 10 μm to 1 mm.

In the second step, a film may be formed by adding a support or reinforcing material such as fiber, mat, fibril or the like to the polymerizable composition, or the polymerizable composition is added to the support or reinforcing material. You may form into a film using what was impregnated.
The material of the support and the reinforcing material may be selected in consideration of heat resistance and acid resistance. Preferred examples include glass, silicone resin, fluororesin, cyclic polyolefin, and ultrahigh molecular weight polyolefin.
The method for impregnating the polymerizable composition is not particularly limited, and may be appropriately selected from known methods such as a dipping method, a potting method, a roll press method, and a vacuum press method. Moreover, you may perform a heating, pressurization, etc. at the time of impregnation.

  In the present invention, in order to increase the strength of the proton conductive membrane, it is preferable to impregnate the polymerizable composition with a polymer material membrane made of fluororesin, polyethylene or polyimide. As the fluororesin, polytetrafluoroethylene is preferable. The membrane made of a polymer material is preferably a porous membrane having a thickness of 20 to 100 μm, a pore diameter of 0.05 to 1 μm, and a porosity of 60% or more, and has been subjected to a hydrophilic treatment. Is preferred.

[Third step]
In the third step, the formed polymerizable composition is polymerized. Here, “polymerize” refers to forming a covalent bond between polymerizable unsaturated double bonds in the polymerizable composition, and forming a silicon-oxygen-silicon bond by a condensation reaction.
Since both the silane compound (α) and the acid group-containing compound (β) have a polymerizable unsaturated double bond, they are polymerized in the third step to produce an acid group-containing structure (B).
In addition, as described above, the crosslinkable compound (A) is at least a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, or Since the hydroxyl group is bonded to the silicon atom, the condensation reaction is similarly performed in the presence of an acid or base catalyst with a silane compound (α) having a group capable of forming a silicon-oxygen-silicon bond such as an alkoxysilyl group or a hydroxyl group. To form a silicon-oxygen-silicon bond. Usually, an alkoxysilyl group is hydrolyzed to become a silanol group, and the silanol groups are condensed to form a silicon-oxygen-silicon bond.
In addition, when the crosslinkable compound (A ′) is used in the first step instead of the crosslinkable compound (A), the crosslinkable compound (A ′) is also at least a methoxy group, an ethoxy group, an n-propoxy group. Group, isopropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group or hydroxyl group is bonded to a silicon atom, so that the crosslinkable compound (A A polymer having ') as a monomer is produced to form a crosslinkable compound (A), and then bonded to the silane compound (α) in the same manner as described above.
Furthermore, when the crosslinking agent (C) is used in the first step, for example, a bond is also formed between the silane compound (α) or the acid group-containing compound (β) and the crosslinking agent (C).
In the third step, the reaction proceeds as described above, and a proton conductive membrane including a continuum of particles having a silicon-oxygen crosslinked structure is formed. Such a proton conductive membrane stably exhibits proton conductivity even at high temperatures, has excellent fuel blocking properties, and has little shape change.

Formation of a silicon-oxygen-silicon bond by hydrolysis and condensation reaction of an alkoxysilyl group or the like is well known as a sol-gel reaction.
In the sol-gel reaction, an acid or base catalyst is usually used to control the reaction rate. In the present invention, either an acid or a base can be used as a catalyst.
In general, when an acid is used, it is known that the reaction proceeds evenly in individual molecules due to competition between hydrolysis and condensation, resulting in a linear crosslinked structure with few branches. . On the other hand, it is known that when a base is used, hydrolysis occurs at once, and when hydrolysis occurs in one molecule, the reaction proceeds intensively in that molecule, resulting in a highly branched dendritic structure. ing.
In the present invention, any method can be applied in consideration of desired film properties. For example, in order to highlight the characteristics of the formation of particles and their continuum, it is preferable to use a base, and in this case, it is preferable to salt the acid group-containing compound (β). On the other hand, when an acid is used, an acid group in the acid group-containing compound (β) may be used as the acid, or an acid may be added separately.
The addition amount of the acid or base can be arbitrarily set, and may be appropriately determined in consideration of the reaction rate, compatibility of raw materials, and the like.
The step of adding the acid or base may be any of the first to third steps. For example, adding in the first step is the simplest in terms of operation, but in this case, it is necessary to consider the pot life and set time in the second step.

  The hydrolysis reaction may be performed under water vapor so that water can be replenished into the reaction solution as needed. Moreover, in order to prevent rapid drying of a film | membrane, you may carry out under solvent vapor | steam.

The temperature during the condensation reaction may be room temperature, but it is preferable to heat in order to shorten the reaction time and to make the reaction more efficient. Heating may be performed by a known method, and examples thereof include heating with an oven, pressure heating with an autoclave, far infrared heating, electromagnetic induction heating, and microwave heating. Usually, the temperature during heating is preferably 15 to 300 ° C, more preferably 100 to 250 ° C. However, as described later, the reaction temperature may be set in consideration of a polymerization reaction between polymerizable unsaturated double bonds.
The condensation reaction may be performed by gradually changing the reaction conditions, for example, by performing the condensation reaction at a room temperature for a certain period of time and then gradually raising the temperature by heating.
The condensation reaction may be performed under reduced pressure or in an inert gas atmosphere such as nitrogen gas or argon gas.

The conditions for the polymerization reaction of the polymerizable composition may be appropriately adjusted depending on the type of the polymerizable composition, such as the type and amount used of the raw material, but in consideration of the polymerization reaction between the polymerizable unsaturated double bonds, the reaction temperature Is preferably 40 to 150 ° C., and the reaction time is preferably 1 to 24 hours.
Under such conditions, a structure formed by covalently bonding the silane compound (α) and the acid group-containing compound (β) is efficiently generated, and the acid group-containing structure (B) including such a structure is efficient. Is obtained.
Under such reaction conditions, a condensation reaction between the crosslinkable compound (A) and the silane compound (α) and a polymerization reaction of the crosslinkable compound (A ′) to the crosslinkable compound (A) are also performed in parallel. Progress better.

  When performing the hydrolysis and the condensation reaction in parallel, a preferable method is a method in which the heating temperature is gradually increased from about room temperature to a high temperature, and then the heating is continued for a predetermined time at the high temperature. For example, the reaction temperature may be raised from 60 to 80 ° C. over a range of 25 to 35 ° C. over 4 to 8 hours, and then reacted at 100 to 250 ° C. for 2 to 6 hours.

  In the third step, it is preferable to start the reaction at a temperature not higher than the lowest temperature among the 10-hour half-life temperatures of the polymerization initiator. The reaction is preferably performed by raising the temperature to a temperature equal to or higher than the highest temperature among the 10-hour half-life temperatures of the polymerization initiator. And in this invention, it is preferable to satisfy | fill all these conditions.

In the third step, the reaction rate of each polymerizable unsaturated double bond in the silane compound (α) and the acid group-containing compound (β) is preferably 30% or more, and preferably 50% or more. More preferred. Here, “reaction rate of polymerizable unsaturated double bonds” means the total number of polymerizable unsaturated double bonds in the silane compound (α) and the acid group-containing compound (β) before the reaction (i), When the total number of unreacted polymerizable unsaturated double bonds in the proton conductive membrane is (ii), the value is calculated by the following formula.
Reaction rate of polymerizable unsaturated double bond (%) = {(i) − (ii)} / (i) × 100
The reaction rate of the polymerizable unsaturated double bond can be adjusted by appropriately selecting the combination of the silane compound (α) and the acid group-containing compound (β) and the conditions for the polymerization reaction.

By applying the reaction conditions as described above, in the production method of the present invention, the condensation reaction between the crosslinkable compound (A) and the silane compound (α), and the silane compound (α) and the acid group-containing compound (β ), The proton conductive membrane having a silicon-oxygen-silicon bond and a sufficiently high degree of crosslinking can be obtained.
The degree of crosslinking of the proton conductive membrane can be evaluated by the gel fraction measured by the following method. Usually, the raw material remaining without undergoing the polymerization reaction is highly soluble in the polar solvent, but the proton conductive membrane is not dissolved in the polar solvent but becomes a gel. According to the production method of the present invention, the gel fraction of the proton conductive membrane can be 96% or more. The gel fraction can be adjusted by adjusting the conditions of the polymerization reaction, but in particular, it can be adjusted by selecting an appropriate combination of polymerization initiators.
(Measurement of gel fraction)
The mass (mass I) of a proton conductive membrane slice having a size of 4 cm × 4 cm is measured. The section is then added to 100 ml of pure and left at 80 ° C. for 4 hours. Next, the dry mass (mass II) of the residue (gel) that did not dissolve in water is measured, and the gel fraction (%) is calculated according to the following formula.
Gel fraction (%) = (mass II) / (mass I) × 100

The membrane obtained by polymerization may be washed with water as necessary to remove unreacted substances, acids or bases, or may be ion exchanged using sulfuric acid or the like.
The water used for washing is preferably water containing no metal ions, such as distilled water or ion exchange water. The washing with water may be performed efficiently by performing heating, pressurization, vibration, etc. in parallel. Furthermore, in order to promote the penetration of water into the membrane, it may be washed with water using a mixed solvent of water and an organic solvent such as methanol, ethanol, n-propanol, isopropanol, acetone, and tetrahydrofuran.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.
[Example 1]
Tetramethoxysilane 0.7 g, 3- (trimethoxysilyl) propyl methacrylate 0.15 g, trimethoxy (vinyl) silane 0.05 g, 2-acrylamido-2-methylpropanesulfonic acid 3.0 g, N, N′-methylenebis ( Acrylamide (0.3 g) was mixed with water (3 g), and 2,2′-azobis [2- (2-imidazolin-2-yl) propane] hydrochloride (10 hour half-life temperature: 44 ° C.) as an initiator. 05 g, 2,2′-azobis (2-methylpropionamidine) hydrochloride (10 hour half-life temperature 56 ° C.) 0.05 g, 2,2′-azobis {2-methyl-N- [1,1-bis ( Hydroxymethyl) -2-hydroxyethyl] propionamide} (10-hour half-life temperature 60 ° C.) 0.02 g was sufficiently stirred for about 5 minutes with ice-cooling to obtain a polymerizable composition I got a thing.
Next, the obtained polymerizable composition was impregnated into a polyethylene porous film to form a film having a thickness of 40 to 60 μm.
Next, the filmed polymerizable composition was heated from 30 to 70 ° C. over 6 hours and polymerized by heating at 100 ° C. for 4 hours to obtain a proton conductive membrane.

[Comparative Example 1]
In the same manner as in Example 1, except that only 0.15 g of 2,2′-azobis [2- (2-imidazolin-2-yl) propane] hydrochloride was used as an initiator, a proton conductive membrane was prepared. Obtained.

(MCO (methanol permeability) evaluation)
Two circular cells having a circular window with a diameter of 2 cm are used, and a proton conductive membrane is sandwiched between the window portions through rubber packing. One cell contains 30% by mass methanol aqueous solution and the other cell contains Pure water was added and stirred with a stirrer at 25 ° C. for 3 hours. Thereafter, the amount of methanol permeated to the pure water side was measured by gas chromatography, and the ratio of the permeation amount to the permeation amount (MCO ratio) when Nafion 117 (manufactured by DuPont) (registered trademark) was used was calculated. The results are shown in Table 1.

(Gel fraction)
The proton conductive membrane was cut into 4 cm square, weighed, put into 100 mL of pure water, and left at 80 ° C. for 4 hours. Thereafter, water was discarded, insoluble matter was dried and weighed, and the gel fraction (%) was calculated. The results are shown in Table 1.

As shown in Table 1, the proton conductive membrane of Example 1 had a sufficiently high gel fraction, excellent polar solvent resistance, and excellent MCO performance. On the other hand, the proton conductive membrane of Example 1 of Comparative Example 1 was inferior in both polar solvent resistance and MCO performance.

  The present invention is applicable to fuel cells, particularly fuel cells for small mobile devices and portable devices.

It is a figure which illustrates typically the structure of the proton conductive membrane of this invention. (A) schematically illustrates the structures of a crosslinkable compound (A), a silane compound (α), an acid group-containing compound (β), and a crosslinker (C), which are raw materials for the proton conductive membrane of the present invention. It is a figure, (b) is a figure which illustrates typically the structure of the proton conductive film | membrane which these raw materials react.

Claims (8)

Crosslinkable compound (A ′) having silicon-oxygen bond, group capable of forming silicon-oxygen-silicon bond and silane compound (α) having polymerizable unsaturated double bond, acid group and polymerizable unsaturated double A first step of preparing a polymerizable composition by mixing an acid group-containing compound (β) having a bond and a polymerization initiator, a second step of forming a film of the polymerizable composition, and the formed polymerizable property A method for producing a proton conducting membrane comprising a third step of polymerizing the composition,
The crosslinkable compound (A ′) having a silicon-oxygen bond is represented by the following general formula (1 ′):
The acid group-containing compound (β) is a compound having a sulfo group as the acid group,
A method for producing a proton conductive membrane, wherein a plurality of types of polymerization initiators having different 10-hour half-life temperatures are used as the polymerization initiator.

(Wherein R ¹ is a divalent hydrocarbon group having 1 to 50 carbon atoms or an oxygen atom; R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group N-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, hydroxyl group or a group represented by the formula “—O—Si—”, at least one of which is a methoxy group, an ethoxy group, or an n-propoxy group. group, Isopuropokishiki group, n- butoxy group, isobutoxy group, sec- butoxy group, a tert- butoxy group or a hydroxyl ^group; when R 1 to R ³ is plural, a plurality of R To R ³ may be the same or different, respectively Re its; m ₂ is an integer of 0 or more).   A plurality of the polymerization initiators having a 10-hour half-life temperature within the range of the polymerization temperature of the silane compound (α) and the acid group-containing compound (β) in the third step are used. The method for producing a proton-conductive membrane according to claim 1, wherein the difference in time half-life temperature is at most 16 ° C or more.   In the third step, the reaction is started at a temperature below the lowest temperature among the 10-hour half-life temperatures of the polymerization initiator, and the reaction is performed by raising the temperature to a temperature above the highest temperature. The method for producing a proton conductive membrane according to claim 1 or 2.   Further, the first step is performed by adding a crosslinking agent (C) having two or more functional groups capable of binding to the silane compound (α) or the acid group-containing compound (β) in one molecule. The method for producing a proton conductive membrane according to any one of claims 1 to 3. The R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group or a hydroxyl group. The manufacturing method of the proton-conductive film | membrane as described in any one of -4. 6. The method for producing a proton conductive membrane according to claim 5, wherein R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a methoxy group or a hydroxyl group.   A proton conductive membrane manufactured by the manufacturing method according to claim 1. Proton conduction in which a crosslinkable compound (A) having a silicon-oxygen bond and an acid group-containing structure (B) covalently bonded to a silane compound and having an acid group are linked by a silicon-oxygen-silicon bond A sex membrane,
The gel fraction is 96% or more,
The crosslinkable compound (A) having a silicon-oxygen bond is represented by the following general formula (1):
The acid group-containing structure (B) comprises a group capable of forming a silicon-oxygen-silicon bond and a silane compound (α) having a polymerizable unsaturated double bond, an acid group and a polymerizable unsaturated double bond. acid group-containing compound having (beta) and is covalently bonded structure only including,
The silane compound (α) is a compound represented by the following general formula (2),
The proton conductive membrane, wherein the acid group-containing compound (β) is a compound having a sulfo group as the acid group .

(Wherein R ¹ is a divalent hydrocarbon group having 1 to 50 carbon atoms or an oxygen atom; R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, Methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, phenyl group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group N-butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, hydroxyl group or a group represented by the formula “—O—Si—”, at least one of which is a methoxy group, an ethoxy group, or an n-propoxy group. group, Isopuropokishiki group, n- butoxy group, isobutoxy group, sec- butoxy group, a tert- butoxy group or a hydroxyl ^group; when R 1 to R ³ is plural, a plurality of R To R ³ may be the same or different, respectively Re its; m ₁ is an integer of 1 or more).

(In the formula, R ⁸ is a divalent hydrocarbon group which may have a substituent, a divalent group in which the hydrocarbon group and an oxycarbonyl group are bonded, or a hetero atom; R ⁹ , R ¹⁰ And R ¹¹ are each independently a hydrocarbon group which may have a substituent, a group in which the hydrocarbon group is bonded to a hetero atom, a hydroxyl group, a hydrogen atom, a hetero atom or a halogen atom, at least one of which is silicon A group capable of forming an oxygen-silicon bond; R ⁰ is a hydrogen atom or a methyl group; n ₁ is an integer of 1 or more, n ₂ is 0 or 1, provided that n ₂ is 0 In this case, n ₁ is 1.)

Images