JP6885780B2 - Solid polymer electrolyte membrane - Google Patents

Description

The present invention relates to a solid polymer electrolyte membrane.

A solid polymer electrolyte membrane is known as an electrolyte material for a fuel cell.

For example, in Patent Document 1,
The first step of dissolving a metal salt of perfluorosulfonic acid and / or a metal salt of perfluorocarboxylic acid in a polymer dispersion containing a polymer electrolyte precursor that exhibits proton conductivity by alkaline hydrolysis and acid treatment.
The second step of forming a polymer electrolyte precursor film from the dispersion obtained in the first step, and
The third step of alkaline hydrolysis and acid treatment of the polymer electrolyte precursor membrane obtained in the second step to obtain a polymer electrolyte membrane, and
Perfluorosulfonic acid and / or perfluorocarboxylic acid produced by a method including the fourth step of heating and drying the polymer electrolyte membrane obtained in the third step and precipitating a metal oxide in the polymer electrolyte membrane. A solid polymer electrolyte membrane made of an acid-based resin is disclosed.

Japanese Unexamined Patent Publication No. 2010-114020

The presence of water is indispensable for the solid polymer electrolyte membrane obtained by the technique of Patent Document 1 to exhibit proton conductivity. Therefore, in the fuel cell provided with this solid polymer electrolyte membrane, it is necessary to limit the operating temperature to less than the boiling point of water.

The present invention is intended to improve the above circumstances, and an object of the present invention is to provide a solid polymer electrolyte membrane that exhibits high proton conductivity even in an anhydrous environment.

The present invention that achieves the above object is as follows.

（式（２）中、Ｒ^４は水素原子又はメチル基であり、Ｒ^ＩＩは炭素数１〜６のアルキレン基である。）
［１０］前記可塑剤が、プロトン放出性基を有する可塑剤を含む、［１］〜［９］のいずれか一項に記載の固体高分子電解質膜。
［１１］前記プロトン放出性基を有する可塑剤が、芳香族スルホン酸化合物、スルホン酸基含有ポリマー、及びフッ素原子含有スルホニルイミド化合物から選択される化合物を含む、［１０］に記載の固体高分子電解質膜。
［１２］前記可塑剤が、プロトン放出性基を有さない可塑剤を更に含む、［１０］又は［１１］に記載の固体高分子電解質膜。
［１３］前記架橋ポリマー１００質量部に対する前記可塑剤の使用割合が、１０質量部以上１，０００質量部以下である、［１］〜［１２］のいずれか一項に記載の固体高分子電解質膜。
［１４］前記固体高分子電解質膜のガラス転移点が０℃以下である、［１］〜［１３］のいずれか一項に記載の固体高分子電解質膜。
［１５］−４０℃以上２００℃未満の温度範囲において、前記固体高分子電解質膜が膜形状を維持し、且つ前記可塑剤がブリードアウトしない、［１］〜［１４］のいずれか一項に記載の固体高分子電解質膜。
［１６］前記固体高分子電解質膜のプロトン伝導率が、５０℃において１×１０^−４Ｓ／ｃｍ以上である、［１］〜［１５］のいずれか一項に記載の固体高分子電解質膜。
［１７］プロトン伝導膜である、［１］〜［１６］のいずれか一項に記載の固体高分子電解質膜。
［１８］［１］〜［１７］のいずれか一項に記載の固体高分子電解質膜から成る、燃料電池用固体高分子電解質膜。 [1] Contains a crosslinked polymer and a plasticizer
At least one of the crosslinked polymer and plasticizer has a proton-releasing group.
Solid polymer electrolyte membrane.
[2] The solid polymer electrolyte membrane according to [1], wherein the proton-releasing group is selected from a sulfonic acid group, a sulfonylamide group, a sulfonylimide group, and a phosphoric acid group.
[3] The solid polymer electrolyte membrane according to [1] or [2], wherein the crosslinked polymer has a polar group other than the proton-releasing group.
[4] The solid polymer electrolyte membrane according to any one of [1] to [3], wherein the crosslinked polymer is a vinyl-based polymer having a crosslinked structure.
[5] The solid polymer electrolyte membrane according to any one of [1] to [4], wherein the crosslinked polymer has a proton-releasing group.
[6] The item according to any one of [1] to [5], wherein the crosslinked polymer is a vinyl polymer having a proton-releasing group, a polar group other than the proton-releasing group, and a crosslinked structure. Solid polymer electrolyte membrane.
[7] The crosslinked polymer is
The first monomer, which is a vinyl-based monomer having a polar group other than the proton-releasing group,
A second monomer, which is a vinyl-based monomer having a proton-releasing group,
The solid polymer electrolyte membrane according to [6], which is a copolymer with a third monomer which is a crosslinkable vinyl-based monomer.
[8] A vinyl-based monomer in which the first monomer has both a (meth) acrylic acid ester, styrene substituted with a polar group other than the proton-releasing group, and a polar group other than the proton-releasing group and a fluorine atom. The solid polymer electrolyte membrane according to [7], which is one or more selected from the above.
[9] In [7] or [8], the second monomer is one or more selected from allyl sulfonic acid, poly (4-styrene sulfonic acid), and a compound represented by the following formula (2). The solid polymeric electrolyte membrane of the description.

(In the formula (2), R ⁴ is a hydrogen atom or a methyl group, and R ^II is an alkylene group having 1 to 6 carbon atoms.)
[10] The solid polymer electrolyte membrane according to any one of [1] to [9], wherein the plasticizer contains a plasticizer having a proton-releasing group.
[11] The solid polymer according to [10], wherein the plasticizer having a proton-releasing group contains a compound selected from an aromatic sulfonic acid compound, a sulfonic acid group-containing polymer, and a fluorine atom-containing sulfonylimide compound. Electrolyte membrane.
[12] The solid polymer electrolyte membrane according to [10] or [11], wherein the plasticizer further contains a plasticizer having no proton-releasing group.
[13] The solid polymer electrolyte according to any one of [1] to [12], wherein the ratio of the plasticizer used to 100 parts by mass of the crosslinked polymer is 10 parts by mass or more and 1,000 parts by mass or less. film.
[14] The solid polymer electrolyte membrane according to any one of [1] to [13], wherein the glass transition point of the solid polymer electrolyte membrane is 0 ° C. or lower.
[15] In any one of [1] to [14], the solid polymer electrolyte membrane maintains the film shape and the plasticizer does not bleed out in the temperature range of −40 ° C. or higher and lower than 200 ° C. The solid polymer electrolyte membrane of the description.
[16] The solid polymer electrolyte membrane according to any one of [1] to [15], wherein the proton conductivity of the solid polymer electrolyte membrane is 1 × 10 ^{-4 S / cm or more at 50 ° C.} ..
[17] The solid polymer electrolyte membrane according to any one of [1] to [16], which is a proton conductive membrane.
[18] A solid polymer electrolyte membrane for a fuel cell, comprising the solid polymer electrolyte membrane according to any one of [1] to [17].

The solid polymer electrolyte membrane of the present invention has both high proton conductivity and sufficient membrane strength. Therefore, the solid polymer electrolyte membrane of the present invention is particularly suitable for use as a proton conduction membrane in a fuel cell.

FIG. 1 is a schematic diagram of the structure of the solid polymer electrolyte membrane obtained in Example 1. FIG. 2 is a schematic diagram of the structure of the solid polymer electrolyte membrane obtained in Example 2. FIG. 3 is a schematic diagram of the structure of the solid polymer electrolyte membrane obtained in Example 3. FIG. 4 is a DSC curve of the sample obtained in Example 1. FIG. 4A is a DSC curve of the crosslinked PEEA-co-PAMPS, and FIG. 4B is a DSC curve of the solid polymer electrolyte membrane. FIG. 5 is a DSC curve of the solid polymer electrolyte membrane obtained in Comparative Example 3.

The solid polymer electrolyte membrane of the present invention
Contains crosslinked polymers and plasticizers
At least one of the crosslinked polymer and the plasticizer has a proton-releasing group.

The high proton conductivity of the solid polymer electrolyte membrane of the present invention under anhydrous conditions is derived from the presence of proton-releasing groups in the membrane and the fact that the crosslinked polymer exhibits sufficiently high molecular mobility due to the plasticizer. It is thought that. That is, in a preferred embodiment of the present invention, the glass transition point measured for the solid polymer electrolyte membrane is lower than the operating temperature of the solid polymer electrolyte membrane, and the crosslinked polymer is a so-called "rubber" during operation of the solid polymer electrolyte membrane. It is a state that should be called "state" or "pseudo-fluid state", and preferably exhibits high molecular motility together with a liquid plastic agent. Therefore, the protons released from the proton-releasing group of the crosslinked polymer or the plasticizer have a high molecular motion of a mixture of the crosslinked polymer and the plasticizer (hereinafter, also referred to as “proton conduction mixed phase”) that contributes to the conduction of protons. By exhibiting the properties, it can be easily moved even under anhydrous conditions. Therefore, the solid polymer electrolyte membrane of the present invention exhibits high proton conductivity even under anhydrous conditions.

On the other hand, although the proton conduction mixed phase in the membrane exhibits sufficiently high molecular motility, the crosslinked structure of the polymer contributes to the maintenance of the membrane shape of the solid polymer electrolyte membrane of the present invention. It is thought that this is because. Due to its own crosslinked structure, the crosslinked polymer maintains its shape even when it exhibits high molecular mobility.

When the solid polymer electrolyte membrane maintains the membrane shape, the solid polymer electrolyte membrane is not loaded in the operating temperature range of the battery (for example, -40 ° C or higher and lower than 200 ° C, typically 0 ° C or higher and 150 ° C or lower). It means that when it is left to stand for 1 hour in a state, it does not substantially deform or contract. Here, when the length change rate in the surface direction and the thickness direction of the solid polymer electrolyte membrane is, for example, 5% or less, 3% or less, or 1% or less, it is determined that the film shape is maintained under that condition. Good.

The fact that the plasticizer does not bleed out means that the plasticizer does not leak to the outside of the membrane when the solid polymer electrolyte membrane is allowed to stand for 1 hour under no load in the operating temperature range of the battery.

The glass transition point Tg in the present specification is a value obtained in accordance with JIS K 7121 based on the DSC curve obtained by measuring at a heating rate of 10 ° C./min.

Hereinafter, the solid polymer electrolyte membrane of the present invention will be described with reference to a preferred embodiment (hereinafter, referred to as “the present embodiment”) as an example.

As used herein, the term "(meth) acrylic acid" is a concept that includes both acrylic acid and methacrylic acid. “(Meta) acrylate”, “(meth) acrylamide” and the like should be understood accordingly. "(Poly) oxyalkylene" means one oxyalkylene unit or a chain of two or more oxyalkylene units.

As used herein, the term "alkylene group" is a concept that includes a methylene group, an alkylmethylene group, and a dialkylmethylene group.

<Crosslinked polymer>
Since the crosslinked polymer in the present embodiment has a crosslinked structure, the film shape can be maintained even at a temperature higher than the glass transition point.

The crosslinked polymer may have good miscibility with a plasticizer described later. Good miscibility between the crosslinked polymer and the plasticizer makes it possible to sufficiently lower the glass transition point Tg of the solid polymer electrolyte membrane, which is a mixture of the two. In this case, since the molecular motility of the proton conduction mixed phase in the membrane can be sufficiently increased, high proton conductivity is exhibited.

The crosslinked polymer may have a polar group in order to improve miscibility with the plasticizer. This polar group may be a polar group other than the proton-releasing group, for example, _{a primary group such as -NH 2} , -OH, -COOH; -O-, -NH-,> C = O, etc. It may be a second-class or third-class group.

Since the crosslinked polymer in the present embodiment is mixed with a plasticizer described later to be in a “pseudo-fluid state” and has high molecular motility, the glass transition point Tg of the polymer alone may be relatively high. However, if the glass transition point is excessively high, there is a concern that the molecular mobility will not be sufficiently improved even after being mixed with the plasticizer. From this viewpoint, the glass transition point of the crosslinked polymer is preferably 400 ° C. or lower, 350 ° C. or lower, 300 ° C. or lower, or 250 ° C. or lower. The crosslinked polymer may have two or more glass transition points. When the crosslinked polymer has two or more glass transition points, the lowest glass transition point is preferably equal to or lower than the operating temperature of the solid polymer electrolyte membrane (for example, in the range of −40 ° C. or higher and 200 ° C. or lower), for example. It may be −40 ° C. or lower, −50 ° C. or lower, or −60 ° C. or lower. The low glass transition point of the crosslinked polymer allows the crosslinked polymer to maintain high molecular mobility with the plasticizer during operation of the resulting polymer electrolyte membrane, thus providing high proton conductivity. Obtainable.

The structure of the main chain of the crosslinked polymer may be arbitrary. For example, a vinyl-based polymer having a crosslinked structure, an ester-based polymer having a crosslinked structure, an amide-based polymer having a crosslinked structure, a silicone-based polymer having a crosslinked structure, or the like may be used. The method for producing each polymer and the method for forming a crosslinked structure are known. Of the above, the crosslinked polymer is preferably a vinyl polymer having a crosslinked structure because the monomer is easily available and molecular modification is easy. Some or all of the hydrogen atoms of the crosslinked polymer may be substituted with fluorine atoms. In particular, a crosslinked polymer in which some or all of the hydrogen atoms in the main chain are replaced with fluorine atoms can be preferably used from the viewpoint of durability.

When the plasticizer described below does not have a proton-releasing group, the crosslinked polymer in this embodiment has a proton-releasing group. When the plasticizer described below has a proton-releasing group, the crosslinked polymer in the present embodiment does not have to have a proton-releasing group, but may have a proton-releasing group.

The crosslinked polymer having a proton-releasing group may be a vinyl-based polymer having a proton-releasing group, a polar group other than the proton-releasing group, and a crosslinked structure. Vinyl-based polymers having a proton-releasing group and a crosslinked structure are, for example,
A copolymer of a first monomer, which is a vinyl-based monomer having a polar group other than a proton-releasing group, a second monomer, which is a vinyl-based monomer having a proton-releasing group, and a third monomer, which is a crosslinkable vinyl-based monomer. Well there;
It may be a copolymer of a second monomer and a third monomer; or
It may be a sulfonic acid-modified product, a sulfonic acid amide-modified product, or a phosphoric acid-modified product of the first monomer and the third monomer, and optionally the copolymer of the second monomer.

The first to third monomers may be used alone or as a mixture of two or more kinds.

The crosslinked polymer having no proton-releasing group may be a vinyl-based polymer having no proton-releasing group and having a polar group other than the proton-releasing group and a crosslinked structure. The vinyl-based polymer which does not have a proton-releasing group and has a polar group other than the proton-releasing group and a crosslinked structure may be, for example, a copolymer of a first monomer and a third monomer.

The crosslinked polymer in the present invention may be one obtained by producing a non-crosslinked vinyl polymer without using a third monomer and then forming a crosslinked structure later with an appropriate crosslinking agent.

[First monomer]
The first monomer is a vinyl-based monomer having a polar group other than the proton-releasing group. The first monomer may be used in the polymerization of the crosslinked polymer for the purpose of imparting high miscibility to the crosslinked polymer with a plasticizer described later. The first polymer is a polar group other than the proton-releasing group capable of forming a non-covalent bond with the plastic agent, for example, _{a primary group such as -NH 2} , -OH, -COOH; -O-, It may be a vinyl-based monomer having a secondary or tertiary group such as −NH−,> C = O.

The first monomer is a monomer selected from, for example, (meth) acrylic acid ester, styrene substituted with a polar group other than the proton-releasing group, a monomer having both a polar group other than the proton-releasing group and a fluorine atom, and the like. It may be.

（式（１）中、Ｒ^１は水素原子又はメチル基であり、Ｒ^Ｉは炭素数１〜６のアルキル基、又は途中が２価の極性基で中断された炭素数２〜１２のアルキル基である。） The (meth) acrylic acid ester as the first monomer may be, for example, a compound having a structure represented by the following formula (1).

(In the formula (1), R ¹ is a hydrogen atom or a methyl group, R ^I is an alkyl group having 2 to 12 carbon atoms which is interrupted by an alkyl group, or in the middle is a divalent polar group of 1 to 6 carbon atoms Is.)

However, the (meth) acrylic acid ester as the first monomer does not contain a compound corresponding to the second monomer or the third monomer described later.

The carbon number of the alkyl group of R ^I can be four or less or 3 or less. Alkyl groups R ^I, specifically, for example, a methyl group, an ethyl group, n- propyl group, may be i- propyl group.

The number of carbon atoms in the alkyl group middle of R ^I is interrupted by divalent polar group may be four or more, or 6 or more, 10 or less, 8 or less, or may be 6 or less. The divalent polar group in the alkyl group interrupted by the divalent polar group in the middle may be, for example, -O-, -S-, -NH-, -COO-, -CONH- or the like. When the divalent polar group contains a carbon atom, the number of carbon atoms of the alkyl group interrupted by the divalent polar group in the middle is counted without including the carbon atom of the polar group.

（上式中、複数のＲ^２はそれぞれ独立に水素原子又は炭素数１〜４のアルキル基であり、複数のＲ^３はそれぞれ独立に水素原子又は炭素数１〜４のアルキル基であり、Ｒ^３がすべて水素原子であることはなく、ｎはそれぞれ１〜４の整数である。） The alkyl group having 2 to 12 carbon atoms interrupted by a divalent polar group in the middle may be, for example, a group represented by each of the following formulas.

(In the above formulas, a plurality of R ² are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a plurality of R ³ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ³ is not all hydrogen atoms, and n is an integer of 1 to 4, respectively.)

The alkyl group having 2 to 12 carbon atoms interrupted by a divalent polar group in the middle may be, for example, a 2- (2-ethoxyethoxy) ethyl group or the like.

The (meth) acrylic acid ester, which is the first monomer, may be, for example, -2- (2-ethoxyethoxy) ethyl acrylate or the like.

The styrene substituted with a polar group other than the proton-releasing group may be, for example, hydroxystyrene, aminostyrene, vinylbenzoic acid or the like.

Monomers having both polar groups other than proton-releasing groups and fluorine atoms include, for example, 4-hydroxy-4-trifluoromethyl-5-trifluoropentene-1,2-trifluoromethylacrylic acid, and vinyl trifluoroacetate. , (Meta) acrylate pentafluorophenyl, (meth) acrylate-2,2,3,3-tetrafluoropropyl and the like.

[Second monomer]
The second monomer is a vinyl-based monomer having a proton-releasing group. As described above, the proton-releasing group may be selected from a sulfonic acid group, a sulfonylamide group, a sulfonylimide group, and a phosphoric acid group, and is preferably a sulfonic acid group, a sulfonylamide group, or a phosphoric acid group.

（式（２）中、Ｒ^４は水素原子又はメチル基であり、Ｒ^ＩＩは炭素数１〜６のアルキレン基である。） The second monomer having a sulfonic acid group may be, for example, allyl sulfonic acid, poly (4-styrene sulfonic acid), a compound represented by the following formula (2), or the like.

(In the formula (2), R ⁴ is a hydrogen atom or a methyl group, and R ^II is an alkylene group having 1 to 6 carbon atoms.)

^{The R II} in the above formula (2) may be, for example, a methylene group, a 1,2-ethylene group, a 2-methyl-1,2-propylene group or the like.

Specifically, the compound represented by the above formula (2) may be, for example, 2- (meth) acrylamide-2-methylpropanesulfonic acid.

The second monomer having a sulfonylamide group may be, for example, 4-vinyl-N-trifluoromethylsulfonylbenzenesulfonylamide represented by the following formula.

The second monomer having a phosphoric acid group may be, for example, vinylphosphonic acid or the like.

[Third monomer]
The third monomer is a crosslinkable vinyl-based monomer. The third monomer is used to form a crosslinked structure in the crosslinked polymer.

The third monomer may be, for example, a compound having two or more polymerizable double bonds.

（式（３）中、Ｒ^５は水素原子又はメチル基であり、Ｒ^ＩＩＩは炭素数１〜６のアルキレン基である。） The third monomer having two polymerizable double bonds is, for example, divinylbenzene, (poly) oxyalkylene glycol di (meth) acrylate, (poly) oxyalkylene modified bisphenol A di (meth) acrylate, the following formula (3). It may be a compound represented by:

(In formula (3), R ⁵ is a hydrogen atom or a methyl group, and R ^III is an alkylene group having 1 to 6 carbon atoms.)

Specifically, the compound represented by the above formula (3) may be, for example, methylenebisacrylamide, N, N'-ethylenebisacrylamide, or the like.

The third monomer having three or more polymerizable double bonds may be, for example, dipentaerythritol hexa (meth) acrylate or the like.
[Ratio of each monomer used]

The proportion of each monomer used is arbitrary.

The ratio of the number of moles of the second monomer to the total number of moles of the first monomer and the second monomer is, for example, 100 mol% or less, 80 mol% or less, 60 mol% or less, 40% or less, 30 mol% or less, 20. It may be 1 mol% or less, 10 mol% or less, or 5 mol% or less.

If the plasticizer has a proton-releasing group, and if sulfonic acid modification, sulfonic acid amide modification, or phosphoric acid modification is planned after the polymerization of the crosslinked polymer, it is not necessary to use the second monomer, although it is not necessary to use the second monomer. A second monomer may be used.

If the plasticizer has a proton-releasing group, and if sulfonic acid modification, sulfonic acid amide modification, or phosphoric acid modification is planned after the polymerization of the crosslinked polymer, it is relative to the total number of moles of the first monomer and the second monomer. The ratio of the number of moles of the second monomer may be 0 mol%.

On the other hand, when the plasticizer does not have a proton-releasing group and sulfonic acid modification, sulfonic acid amide modification, or phosphoric acid modification is not planned after the polymerization of the crosslinked polymer, the proton conductivity of the obtained film is determined. From the viewpoint of sufficiently high, the ratio of the number of moles of the second monomer to the total number of moles of the first monomer and the second monomer is, for example, 5 mol% or more, 10 mol% or more, 15 mol% or more, 20 mol. % Or more, 25 mol% or more, or 50 mol% or more, and may be 100 mol%.

As for the ratio of the third monomer used, the total number of moles of the first monomer and the second monomer was set to 100 mol% from the viewpoint of sufficiently increasing the crosslink density of the crosslinked polymer so that the film shape could be maintained. As the ratio of the number of moles of the third monomer, for example, it may be 0.5 mol% or more, 1.0 mol% or more, 1.5 mol% or more, or 2.0 mol% or more. On the other hand, from the viewpoint of maintaining the cross-linking density of the cross-linked polymer appropriately to secure the molecular motion of the polymer and sufficiently increasing the proton conductivity of the film obtained by this, the first monomer and the second monomer The ratio of the number of moles of the third monomer when the total number of moles is 100 mol% is, for example, 10 mol% or less, 8.0 mol% or less, 5.0 mol% or less, 3.0 mol% or less, Alternatively, it may be 2.0 mol% or less.

[Polymerization of crosslinked polymer]
The copolymer of the first to third monomers can be obtained by a known polymerization method, for example, a radical polymerization method, a cationic polymerization method, an anion polymerization method, or the like, and a radical polymerization method is preferable.

The radical polymerization may be carried out by contacting a predetermined monomer mixture with a radical polymerization initiator. Radical polymerization may be carried out in the presence of a plasticizer described below.

The radical polymerization initiator may be selected from, for example, an azo compound, hydrogen peroxide, an organic peroxide and the like. The azo compound is selected from, for example, azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) and the like. May be done. The organic peroxide may be selected from, for example, benzoyl peroxide, diisobutyl peroxide and the like.

The ratio of the radical polymerization initiator used is, for example, 0.001 part by mass or more, 0.003 part by mass or more, 0.005 part by mass or more, 0.01 part by mass or more, or more than 100 parts by mass of the total amount of the monomer. It may be 0.05 parts by mass or more, and may be, for example, 1 part by mass or less, 0.5 parts by mass or less, 0.1 parts by mass or less, or 0.05 parts by mass or less.

Radical polymerization may optionally be carried out in a suitable solvent. The solvent may be selected from water and organic solvents. As the solvent for radical polymerization, a mixed solvent of two or more kinds of solvents may be used.

The organic solvent may be a polar organic solvent, for example, an ether such as diethyl ether or tetrahydrofuran; a ketone such as acetone; an amide compound such as N, N-dimethylformamide; a nitrile compound such as acetonitrile. Good. Further, a plasticizer described later may be used as a part or all of the solvent for radical polymerization.

The ratio of the solvent used is arbitrary. However, for example, a range of 10 parts by mass or more and 1,000 parts by mass or less can be exemplified as the ratio of the solvent used with respect to 100 parts by mass of the total amount of the monomers.

Radical polymerization is carried out, for example, at a temperature of 50 ° C. or higher, 60 ° C. or higher, 70 ° C. or higher, or 80 ° C. or higher, for example, 200 ° C. or lower, 150 ° C. or lower, 120 ° C. or lower, or 100 ° C. or lower, for example, 30 minutes or longer. It may be carried out for 1 hour or more, 2 hours or more, 3 hours or more, or 4 hours or more, for example, 20 hours or less, 18 hours or less, 15 hours or less, 12 hours or less, or 10 hours or less.

After the polymerization, in order to remove unreacted monomers, low molecular weight oligomers, radical initiator residues and the like, the obtained polymer may be purified by an appropriate method. The purification method may be, for example, a method such as solvent substitution or reprecipitation.

[RAFT polymerization]
The polymerization of the first to third monomers may be carried out by RAFT polymerization (Reversible Addition-Fragmentation chain Transfer polymerization, reversible addition cleavage chain transfer polymerization).

RAFT polymerization may be carried out by adding an appropriate RAFT agent to the radical polymerization system described above.

The RAFT agent may be a thiocarbonylthio compound, and may be selected from, for example, a bis (thiocarbonyl) disulfide compound, a dithioester compound, a trithiocarbonate compound, a dithiocarbamate compound, a xantate compound and the like.

Bis (thiocarbonyl) disulfide compounds include, for example, tetraethylthiuram disulfide, tetramethylthiuram disulfide, bis (n-octyl mercapto-thiocarbonyl) disulfide, bis (n-dodecyl mercapto-thiocarbonyl) disulfide, bis (benzyl mercapto-thio). Carbonyl) disulfide, bis (n-butyl mercapto-thiocarbonyl) disulfide, bis (t-butyl mercapto-thiocarbonyl) disulfide, bis (n-heptyl mercapto-thiocarbonyl) disulfide, bis (n-hexyl mercapto-thiocarbonyl) Disulfide, bis (n-pentyl mercapto-thiocarbonyl) disulfide, bis (n-nonyl mercapto-thiocarbonyl) disulfide, bis (n-decyl mercapto-thiocarbonyl) disulfide, bis (t-dodecyl mercapto-thiocarbonyl) disulfide, It may be bis (n-tetradecyl mercapto-thiocarbonyl) disulfide, bis (n-hexadecyl mercapto-thiocarbonyl) disulfide, bis (n-octadecyl mercapto-thiocarbonyl) disulfide and the like.

The dithioester compound may be, for example, 2-phenyl-2-propylbenzothioate, 4-cyano-4- (phenylthiocarbonylthio) pentanoic acid, 2-cyano-2-propylbenzodithioate or the like.

Trithiocarbonate compounds include, for example, S- (2-cyano-2-propyl) -S-dodecyl trithiocarbonate, 4-cyano-4-[(dodecylsulfanyl-thiocarbonyl) sulfanyl] pentanoic acid, cyanomethyldodecyl. Trithio-carbonate, 2- (dodecylthiocarbonothiolthio) -2-methylpropionic acid, S-1-dodecyl-S'-(α, α'-dimethyl-α "-acetic acid) trithiocarbonate, etc. You may.

The dithiocarbamate compound may be, for example, cyanomethylmethyl (phenyl) carbamodithioate, cyanomethyldiphenylcarbamo-dithioate or the like.

The xanthate compound may be, for example, a xanthate ester or the like.

The ratio of the RAFT agent used is, for example, 0.005 mol% or more, 0.01 mol% or more, or 0.05 mol% or more as the ratio of the number of moles of the RAFT agent when the total amount of the monomers is 100 mol%. It may be, for example, 0.5 mol% or less, 0.3 mol% or less, 0.2 mol% or less, or 0.1 mol% or less.

[Crossing with a cross-linking agent]
The crosslinked polymer in the present embodiment may be one obtained by producing a non-crosslinked vinyl polymer without using the third monomer and then forming a crosslinked structure later with an appropriate crosslinking agent. The cross-linking agent in this case may be, for example, sulfur, hydrogen peroxide, an organic peroxide or the like.

[Modification of copolymer]
Proton-releasing groups can be introduced into the copolymers of the first and third monomers by subjecting them to sulfonic acid modification, sulfonic acid amide modification, or phosphoric acid modification. The copolymers of the first to third monomers and the copolymers of the second and third monomers already have a proton-releasing group, but this copolymer is also sulfonic acid-modified and sulfonic acid. Amide modification or phosphoric acid modification may be performed.

(Sulfonic acid denaturation)
The sulfonic acid modification of the copolymer is optionally catalyzed by, for example, the copolymer and at least one sulfonate selected from chlorosulfonic acid, anhydrous sulfuric acid, sulfuric acid, fuming sulfuric acid, polyalkylbenzene sulfonic acid and the like. And may be reacted in an organic solvent or in the absence of a solvent, for example, at 5 to 200 ° C.

(Sulfonic acid amide denaturation)
The sulfonic acid amide modification of the copolymer may be carried out, for example, by converting the sulfonic acid-modified product of the copolymer into a sulfonyl halide compound and then reacting it with a primary or secondary amine compound.

(Phosphate denaturation)
Phosphoric acid modification of the copolymer is optionally catalyzed with, for example, the copolymer and _{at least one phosphorus compound selected from H 3} PO ₃ , H ₃ PO _2, etc., and esters or salts thereof. And may be reacted in an organic solvent or in the absence of a solvent, for example, at 5 to 200 ° C.

A desired modified crosslinked polymer can be obtained by distilling off an organic solvent from the reaction solution after performing a sulfonic acid modification, a sulfonic acid amide modification, or a phosphoric acid modification reaction as described above.

<Plasticizer>
The plasticizer in the present embodiment is a component having a function of imparting flexibility to the crosslinked polymer, lowering the glass transition point Tg of the solid polymer electrolyte membrane, and enhancing the molecular motility of the crosslinked polymer in the solid polymer electrolyte membrane. is there. The plasticizer may be a high molecular weight substance or a low molecular weight substance. However, since it is assumed that the electrolyte membrane of the present embodiment is applied to battery applications, the plasticizer is used in the operating temperature range of the battery (for example, −40 ° C. or higher and lower than 200 ° C., typically 0 ° C. It is preferably non-volatile at (150 ° C. or lower). The fact that the plasticizer is non-volatile in the operating temperature range of the battery means that the boiling point of the plasticizer is, for example, 200 ° C. or higher, 210 ° C. or higher, 220 ° C. or higher, 230 ° C. or higher, 240 ° C. or higher, or 250 ° C. or higher. It means that it is high enough. Further, it is desired that the plasticizer does not decompose in the operating temperature range of the battery.

The plasticizer is desired to be in a liquid state in the operating temperature range of the battery in order to exert a function of enhancing the molecular mobility of the crosslinked polymer in the solid polymer electrolyte membrane. When the plasticizer is liquid in the operating temperature range of the battery in the operating temperature range of the battery, the melting point of the plasticizer is, for example, 0 ° C. or lower, -2 ° C. or lower, -4 ° C. or lower, or -6 ° C. or lower. Say something.

The plasticizer may have polar groups to interact with the crosslinked polymer in the solid polymer electrolyte membrane. A plastic agent having a polar group has the effect of suppressing bleed-out from the solid polymer electrolyte membrane by interacting with the polar group of the crosslinked polymer (for example, forming a non-covalent bond) in the solid polymer electrolyte membrane. Is considered to have. The polar group of the plasticizer may be a polar group other than the proton-releasing group, for example, a hydroxyl group, a thiol group, an ether group, a thioether group, an ester group, a thioester group, an amino group, an amide group, an imide group and the like. You may.

When the crosslinked polymer described above does not have a proton-releasing group, the plasticizer in this embodiment includes a plasticizer having a proton-releasing group. When the crosslinked polymer described above has a proton-releasing group, the plasticizer in the present embodiment does not have to have a proton-releasing group, but may have a proton-releasing group.

The proton-releasing group contained in the plasticizer may be selected from a sulfonic acid group, a sulfonylamide group, a sulfonylimide group, and a phosphoric acid group, and is preferably a sulfonic acid group or a sulfonylimide group.

The plasticizer having a sulfonic acid group is, for example, an aromatic sulfonic acid compound such as p-toluenesulfonic acid, 1,2-ethanedisulfonic acid, 1,3,6-naphthalentrisulfonic acid; vinyl alcohol-vinyl acetate co-weight. It may be a sulfonic acid modified product of coalescence, a sulfonic acid group-containing polymer such as poly (styrene sulfonic acid), or the like. From the viewpoint of maintaining high molecular mobility of the proton conduction mixed phase composed of a mixture of the crosslinked polymer and the plasticizer, the weight average molecular weight when the plasticizer is a polymer compound is 200,000 or less, 150,000 or less, 12 It is better that it is 10,000 or less, 100,000 or less, or 80,000 or less.

The plasticizer having a sulfonylimide group may be, for example, a fluorine atom-containing sulfonylimide compound or the like, and specifically, for example, bis (trifluoromethanesulfonyl) imide or the like.

The plasticizer having no proton-releasing group is preferably a plasticizer that is in a liquid state at the operating temperature of the battery, and may be, for example, polyalkylene glycol, polyvinyl ether, polyol ester, or the like. Of these, as the plasticizer having no proton-releasing group, polyalkylene glycol is preferable, and specifically, for example, tetraethylene glycol or the like may be used.

The plasticizer may be used alone or in combination of two or more. When the plasticizer is a mixture of two or more, the entire plasticizer as a mixture is liquid in the operating temperature range of the battery, and each of the plasticizers in the mixture is non-volatile in the operating temperature range of the battery). , And it is preferable not to decompose.

When the plasticizer is a mixture of two or more, it is preferable that each of the plasticizers in the mixture has a polar group for interacting with the crosslinked polymer. In order to suppress the bleed-out of the plasticizer from the solid polymer electrolyte membrane, the proportion of the plasticizer having a polar group among the plasticizers constituting the mixture is, for example, 30% by mass or more with respect to the total mass of the mixture. , 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more.

A compound having a proton-releasing group is often in a solid state, and when it is used alone, the function of enhancing the molecular motility of the crosslinked polymer may not be sufficiently exhibited. In addition, there is a concern that the molecular mobility of the plasticizer itself will be insufficient. In such a case, a mixture of a compound having a proton-releasing group and a compound having no proton-releasing group may be used as a plasticizer. The mixing ratio of the compound having a proton-releasing group and the compound having no proton-releasing group is arbitrary. The ratio of both is, for example, 10% by mass or more, 20% by mass or more, and 30 as the mass ratio of the compound having a proton-releasing group to the total of the compound having a proton-releasing group and the compound having no proton-releasing group. It may be 90% by mass or more, or 40% by mass or more, and may be, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less.

<Ratio of cross-linked polymer and plasticizer used>
The ratio of the crosslinked polymer to the plasticizer is, for example, the ratio of the plasticizer used to 100 parts by mass of the crosslinked polymer from the viewpoint of enhancing the molecular motility of the proton conduction mixed phase and obtaining sufficiently high proton conductivity. It may be 10 parts by mass or more, 50 parts by mass or more, 100 parts by mass or more, 150 parts by mass or more, 200 parts by mass or more, 250 parts by mass or more, 300 parts by mass or more, 350 parts by mass or more, or 400 parts by mass or more. .. On the other hand, from the viewpoint of maintaining the film strength and ensuring the stability as a film, the ratio of the plasticizer used to 100 parts by mass of the crosslinked polymer is, for example, 1,000 parts by mass or less, 900 parts by mass or less, and 800 parts by mass. Hereinafter, it may be 700 parts by mass or less, 600 parts by mass or less, or 500 parts by mass or less.

When the plasticizer is a mixture of a plurality of types, the usage ratio of the above-mentioned plasticizer is the total usage ratio of the plurality of types of plasticizer.

In order to achieve both high proton conductivity and sufficient membrane strength, the ratio of the liquid component (that is, the plastic agent having no proton-releasing group) to the total mass of the solid polymer electrolyte membrane of the present embodiment is set. Generally, it may be adjusted in the range of 50% by mass or more and 80% by mass or less.

<Solid polymer electrolyte membrane>
The solid polymer electrolyte membrane of the present embodiment exhibits high molecular mobility as a whole by containing the crosslinked polymer and the plasticizer. The high molecular motility of the solid polymer electrolyte membrane can be evaluated by the low glass transition point Tg.

Since the solid polymer electrolyte membrane of the present embodiment has a low glass transition point Tg as a membrane, the proton conduction mixed phase in the solid polymer electrolyte membrane can maintain high molecular motility even at a low temperature. , High proton conductivity can be obtained. The glass transition point Tg of the solid polymer electrolyte membrane is preferably not more than the lower limit of the operating temperature of the solid polymer electrolyte membrane, for example, 0 ° C. or less, -20 ° C. or less, -40 ° C. or less, -60 ° C. or less. , Or may be −65 ° C. or lower.

The solid polymer electrolyte membrane of the present embodiment has a sufficiently low glass transition point Tg, so that it conducts protons in the operating temperature range of the battery (for example, −40 ° C. or higher and lower than 200 ° C., particularly 0 ° C. or higher and 150 ° C. or lower). Although the mixed phase exhibits high molecular mobility and the plasticizer is in a liquid state, the plasticizer does not bleed out and the film shape can be maintained.

The present inventors speculate that this phenomenon is due to the formation of a non-covalent bond between the crosslinked polymer and the plasticizer. That is, it is considered that the bleed-out of the plasticizer is suppressed because the plasticizer is liquid but is bonded to the crosslinked polymer which can maintain the film shape by having a crosslinked structure by a non-covalent bond. Be done.

The non-covalent bond between the crosslinked polymer and the plasticizer may be, for example, a hydrogen bond, an ion-ion interaction, a dipole-ion interaction, or the like.

The non-covalent bond as described above can be realized by appropriately adjusting the concentration of polar groups in the crosslinked polymer and the plasticizer.

The solid polymer electrolyte membrane of this embodiment exhibits high proton conductivity. Specifically, the proton conductivity of the solid polymer electrolyte membrane of the present embodiment is, for example, 1 × 10 ^-4 S / cm or more, 2 × 10 ^-4 S / cm or more, 3 × 10 ^{− at 50 ° C. 4} S / cm or more, 4 × 10 ^-4 S / cm or more, 5 × 10 ^-4 S / cm or more, 10 × 10 ^-4 S / cm or more, or 12 × 10 ^-4 S / cm or more. Yes, at 80 ° C, for example, 2 × 10 ^-4 S / cm or more, 3 × 10 ^-4 S / cm or more, 4 × 10 ^-4 S / cm or more, 5 × 10 ^-4 S / cm or more, 8 × It can be 10 ^-4 S / cm or more, 10 × 10 ^-4 S / cm or more, 12 × 10 ^-4 S / cm or more, or 15 × 10 ^-4 S / cm or more, and at 95 ° C., for example. 3 × 10 ^-4 S / cm or more, 4 × 10 ^-4 S / cm or more, 5 × 10 ^-4 S / cm or more, 10 × 10 ^-4 S / cm or more, 12 × 10 ^-4 S / cm or more, It can be 15 × 10 ^-4 S / cm or more, or 18 × 10 ^-4 S / cm or more.

The solid polymer electrolyte membrane of the present embodiment exhibits high proton conductivity even when the membrane does not contain water. Therefore, the water content of the solid polymer electrolyte membrane may be, for example, 1% or less, 0.1% or less, 0.01%, or 0.001% or less as the mass ratio to the total mass of the membrane.

<Manufacturing of solid polymer electrolyte membrane>
In the solid polymer electrolyte membrane of the present embodiment, the crosslinked polymer and the plasticizer are in a mixed state.

The solid polymer electrolyte membrane of the present embodiment may be produced, for example, by mixing a crosslinked polymer and a plasticizer. Mixing of the crosslinked polymer with the plasticizer may be carried out in a suitable solvent with high volatility. The solvent used here may be selected from those exemplified above as the polymerization solvent of the crosslinked polymer. The solid polymer electrolyte membrane of the present embodiment is obtained by removing the solvent after mixing the crosslinked polymer and the plasticizer.

The solid polymer electrolyte membrane of the present embodiment may be produced by polymerizing the crosslinked polymer in the presence of a plasticizer and then removing the polymerization solvent. In this case, it is preferable to go through a step of removing unreacted monomer, low molecular weight oligomer, radical initiator residue and the like by an appropriate method such as solvent substitution and reprecipitation.

In order to form the solid polymer electrolyte membrane into a film shape, for example, a casting method, a pressing method, or the like may be used as appropriate.

<Use of solid polymer electrolyte membrane>
The solid polymer electrolyte membrane of the present embodiment is suitable as a solid polymer electrolyte membrane of a battery. Since the solid polymer electrolyte membrane of the present embodiment has high proton conductivity even under anhydrous conditions, it can be particularly preferably used as an anhydrous proton conductive membrane of a fuel cell.

Hereinafter, the present invention will be described in detail in the form of examples. The following examples do not limit the use of the present invention in any way.

<Example 1>
In this example, a solid polymer electrolyte membrane containing a crosslinked polymer having a proton-releasing group and a plasticizer was prepared, and its proton conductivity was examined.

(1) Synthesis of crosslinked polymer A column packed with basic alumina was purified by passing unpurified -2- (2-ethoxyethoxy) ethyl acrylate.

As the first monomer, the above-mentioned purified -2- (2-ethoxyethoxy) ethyl (EEA) 685 mg (3.64 mmol), and as the second monomer, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) 322 mg ( 1.55 mmol), 15.9 mg (0.103 mmol) of N, N'-methylenebisacrylamide (MBAA) as the third monomer, S-1-dodecyl-S'-(α, α'-dimethyl-α) as the RAFT agent. "-Acetic acid) Trithiocarbonate 1 mg (0.003 mmol), azobisisobutyronitrile (AIBN) 0.1 mg (0.0006 mmol) as a radical polymerization initiator, and distilled water 249 mg (13.8 mmol) and N as a solvent. , N-dimethylformamide (DMF) 2.84 mg (3.89 mmol) was mixed in a sample bottle to obtain a raw material solution. The first monomer: second monomer: third monomer: RAFT agent in this raw material solution. The molar ratio of was approximately 1,400: 600: 40: 1.

After bubbling the raw material solution with nitrogen gas for 15 minutes, the temperature was raised to 80 ° C. under normal pressure by an oil bath, and polymerization was carried out under stirring at 500 rpm for 7 hours. After 7 hours, the sample bottle was removed from the oil bath and polymerization was stopped. At this time, it was confirmed that the solution in the sample bottle did not flow and was gelled.

The sample in the sample was transferred to a Teflon (registered trademark) beaker, 20 mL of methanol was added, and the mixture was immersed for 1 hour. After 1 hour, methanol was removed, the same amount of fresh methanol was added, and immersion was performed again for 1 hour. This methanol immersion operation was repeated 3 times to remove unreacted monomers, low molecular weight oligomers, solvents and the like for purification. Then, after allowing to stand on a hot plate at 50 ° C. for 12 hours, the crosslinked polyacrylic acid-2- (2-ethoxyethoxy) was dried in a vacuum dryer at room temperature for 12 hours to completely remove methanol. Ethyl-co-poly (2-acrylamide-2-methylpropanesulfonic acid) (crosslinked PEEA-co-PCMPS) was obtained.

The structure of the obtained crosslinked PEEA-co-PAMPS is shown in the following chemical formula.

The resulting crosslinked PEEA-co-PAMPS, conforming to JIS K 7121, at a heating rate 10 ° C. / min conditions, the glass transition point _{The T g} was measured in the temperature range of -90 ° C. to 30 ° C., - It was 50 ° C. The DSC curve obtained at this time is shown in FIG. 4 (a).

(2) Preparation of solid polymer electrolyte membrane 48.9 mg of the crosslinked PEEA-co-MeOH obtained above was cut into strips (thickness 0.096 cm) of 1.14 cm × 0.21 cm, and Teflon (registered) having a capacity of 10 mL. In a beaker made of (trademark), 9 mL of methanol and 115 mg of tetraethylene glycol (TEG, melting point: about -6 ° C) as a plasticizer were added, and the mixture was allowed to stand on a hot plate at 50 ° C for 2 days to crosslink PEEA-co-. A membrane sample was obtained by introducing TEG into PAMPS and completely removing methanol. Since a small amount of TEG remained on the surface of this membrane sample, it was wiped off to obtain a solid polymer electrolyte membrane sample having a thickness of 0.16 cm.

Since the mass of the solid polymer electrolyte membrane sample after wiping the TEG was 141.4 mg, it was found that the TEG content in this membrane sample was 65% by mass.

A schematic diagram of the structure of the obtained solid polymer electrolyte membrane sample is shown in FIG. In FIG. 1, the crosslinked PEEA-co-PAMPS is a crosslinked polymer, TEG is a plasticizer, and the sulfonic acid groups in the crosslinked PEEA-co-PAMPS are proton-releasing groups. It is considered that the sulfonic acid group and the amide group in the crosslinked PEEA-co-PAMPS form a non-covalent bond with the hydroxyl group and the ether group of TEG, respectively. Some of the sulfonic acid groups in the crosslinked PEEA-co-PAMPS are freed with protons to become sulfonate ions.

The obtained solid polymer electrolyte membrane sample, conforming to JIS K 7121, at a heating rate 10 ° C. / min conditions, the glass transition point _{The T g} was measured in the temperature range of -90 ° C. to 30 ° C., - It was 79 ° C., which was clearly lower than the operating temperature of the solid polymer electrolyte membrane. The DSC curve obtained at this time is shown in FIG. 4 (b). _{The DSC curve of FIG. 4 (b) shows the T g} (-50 ° C., FIG. 4 (a)) of the crosslinked PEEA-co-PAMPS contained in the solid polymer electrolyte membrane sample, and the melting point of TEG (about -6 ° C.). ) Was not observed, and a single Tg as a solid polymer electrolyte membrane was observed.

According to the Tg obtained above, this solid polymer electrolyte membrane should be in a quasi-fluid state at the measurement temperature (50 ° C, 80 ° C, and 95 ° C) of the AC impedance measurement in the next section, but the polymer is crosslinked. Because it was made, it did not flow and maintained the film shape.

When the solid polymer electrolyte membrane sample obtained above was allowed to stand for 1 hour under no load while changing the temperature, no leaks were observed in the range of -40 ° C to 200 ° C, and the operating temperature range of the battery was observed. It was confirmed that the plasticizer did not bleed out.

(3) AC Impedance Measurement Using a platinum net with a thickness of 0.1 mm as an electrode, the AC impedance of the obtained solid polymer electrolyte membrane sample was measured.

A solid polymer electrolyte membrane sample (thickness 0.16 cm) was sandwiched between a pair of electrodes arranged so as to face each other with a distance between the electrodes of 0.70 cm. The solid polymer electrolyte membrane sample sandwiched between the electrodes was placed in a natural convection constant temperature constant temperature dryer and dried under the conditions of a temperature of 50 ° C. and a relative humidity of 5 RH% for 1 hour. A professional thermo-hygrometer testo635-2 (manufactured by Testo) was used to measure the relative humidity.

After drying vessel temperature is waited to stabilize, with the FRA (frequency response analyzer) with options potentiometer / galvanostat VERSASTAT 4-400 (Prinston Applied Ltd. Research), voltage 80 mV, at 1Hz units from ¹⁰ 6 Hz frequency The AC impedance was measured under non-humidified conditions. When the absolute value of the resistance value is almost read a resistance value in a constant and becomes the frequency domain, was 4.2 × 10 ⁴ Ω. Further, when the proton conductivity of this solid polymer electrolyte membrane sample was determined by the following mathematical formula (1), ^{it was 2.3 × 10 -4} S / cm.
Proton conductivity = distance between electrodes / (membrane thickness x membrane width x resistance value) (1)

Then, the measurement conditions Temperature 80 ° C., was subjected to the AC impedance measured as relative humidity 1.5RH%, the resistance value in the frequency domain where the absolute value is substantially constant resistance value is 3.0 × 10 ⁴ Ω, The proton conductivity was 3.2 × 10 ^-4 S / cm. Moreover, the measurement conditions Temperature 95 ° C., was subjected to the AC impedance measured as relative humidity 0.9RH%, the resistance value in the frequency domain where the absolute value is substantially constant resistance value was 2.0 × 10 ⁴ Ω, The proton conductivity was 4.8 × 10 ^-4 S / cm.

As described above, the proton conductivity increased as the temperature increased. It is considered that this is because the molecular motility of the quasi-fluid state proton conduction mixed phase increases as the temperature rises, and as a result, the proton conductivity improves.

In the solid polymer electrolyte membrane sample in this example, no eluate was observed during the measurement of the AC impedance, and the membrane shape was maintained without flowing.

<Comparative example 1>
In this comparative example, an attempt was made to prepare a membrane containing a non-crosslinked polymer having a proton-releasing group and a plasticizer.

(1) Synthesis of non-crosslinked polymer 10.2 g (54.0 mmol) of -2- (2-ethoxyethoxy) ethyl (PEEA) acrylate purified as the first monomer by the same method as in Example 1, as the second monomer. 4-34 g (21.1 mmol) of 2-acrylamide-2-methylpropanesulfonic acid (PAMPS), S-1-dodecyl-S'-(α, α'-dimethyl-α "-acetic acid) trithiocarbonate as a RAFT agent 17.2 mg (0.047 mmol), 1.5 mg (0.009 mmol) of azobisisobutyronitrile (AIBN) as a radical polymerization initiator, and 5.66 g (77.) N, N-dimethylformamide (DMF) as a solvent. 5 mmol) was mixed in a round bottom flask with a cock to obtain a raw material solution. The molar ratio of the first monomer: second monomer: RAFT agent in this raw material solution is approximately 1,150: 450: 1. ..

After bubbling the raw material solution with nitrogen gas for 30 minutes, the temperature was raised to 80 ° C. under normal pressure in an oil bath, and polymerization was carried out under stirring at 500 rpm for 45 minutes. After 45 minutes, the round bottom flask was immersed in liquid nitrogen to terminate the polymerization.

A mixed solvent of tetrahydrofuran (THF): methanol = 1: 1 (volume ratio) was added to the solution after the polymerization to prepare a polymer solution having a concentration of 8% by mass. This polymer solution was added dropwise to a large excess of hexane to precipitate the polymer. The polymer separated by decantation was thoroughly dried in a vacuum dryer.

The dried polymer was redissolved in a mixed solvent of THF: methanol = 1: 1 (volume ratio), and the obtained solution was added dropwise to methanol to precipitate the polymer. Uncrosslinked PEEA-co-PAMPS was obtained by removing the monomer, low molecular weight oligomer and the like.

The uncrosslinked PEEA-co-PAMPS as a sample, was subjected to ¹ H-NMR analysis using dimethylsulfoxide _{d 6} as the solvent, the copolymerization ratio of PAMPS in uncrosslinked PEEA-co-PAMPS is 35 mol% It turned out.

The structure of the obtained non-crosslinked PEEA-co-PAMPS is shown in the following chemical formula.

(2) Preparation of Solid Polymer Electrolyte Membrane 106.3 mg of the non-crosslinked PEEA-co-PAMPS obtained above and 242.5 mg of TEG were mixed in 1.0 g of methanol to prepare a solution. The obtained solution was transferred to a container made of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) and allowed to stand on a hot plate at 50 ° C. for 2 days to completely remove methanol, thereby causing TEG. A liquid mixture having a content of 69% by mass was obtained.

Since the obtained sample was a fluid (liquid state), the glass transition point Tg was not measured. In addition, the film was in a liquid state even at the measurement temperatures (50 ° C., 80 ° C., and 95 ° C.) of the AC impedance measurement, and because it was not crosslinked, it flowed and the film shape could not be maintained. Therefore, the AC impedance of the sample obtained in this comparative example could not be measured as a film.

<Comparative example 2>
In this comparative example, obtained in Example 1 crosslinked PEEA-co-PAMPS: without introducing TEG into film _(T g -50 ℃), was AC impedance measurement. As the electrode, a platinum net having a thickness of 0.1 mm was used.

A crosslinked PEEA-co-PAMPS film (width 0.30 cm, thickness 0.16 cm) was sandwiched between a pair of electrodes arranged so as to face each other with a distance between the electrodes of 0.70 cm. The membrane sample sandwiched between the electrodes was placed in a natural convection constant temperature constant temperature dryer and stabilized at a temperature of 95 ° C. and a relative humidity of 1.0 RH%. Thereafter, the voltage 80 mV, and varied 1Hz units from ¹⁰ 6 Hz frequency, was AC impedance measurement in non-humidified conditions. However, the measured value could not be obtained because the resistance value was extremely large. Therefore, it was found that the proton conductivity of the membrane sample in this comparative example was extremely low.

It is considered that the membrane sample of this comparative example did not contain a plasticizer, so that the molecular motility of the proton conduction mixed phase was low, and therefore the proton movement did not easily occur and the proton was hardly conducted. Be done.

<Comparative example 3>
In this comparative example, a membrane containing a crosslinked polymer having no proton-releasing group and a plasticizer having no proton-releasing group was prepared, and the proton conductivity thereof was examined.

(1) Synthesis of crosslinked polymer 1.01 g (5.37 mmol) of -2- (2-ethoxyethoxy) ethyl (EEA) acrylate purified as the first monomer by the same method as in Example 1, and N as the third monomer. , N'-methylenebisacrylamide (MBAA) 16.4 mg (0.106 mmol), S-1-dodecyl-S'-(α, α'-dimethyl-α "-acetic acid) as RAFT agent 1 mg (0) .003 mmol), 0.1 mg (0.0006 mmol) of azobisisobutyronitrile (AIBN) as the radical polymerization initiator, and 258 mg (3.53 mmol) of N, N-dimethylformamide (DMF) as the solvent in the sample bottle. To obtain a raw material solution, the molar ratio of the first monomer: third monomer: RAFT agent in this raw material solution is approximately 2,000: 40: 1.

After bubbling the raw material solution with nitrogen gas for 20 minutes, the temperature was raised to 80 ° C. under normal pressure by an oil bath, and polymerization was carried out under stirring at 500 rpm for 7 hours. After 7 hours, the sample bottle was removed from the oil bath and polymerization was stopped. At this time, it was confirmed that the solution in the sample bottle did not flow and was gelled.

The sample in the sample was transferred to a Teflon (registered trademark) container, a large excess amount of methanol was added, and the sample was immersed for 1 hour. After 1 hour, methanol was removed, a large excess of fresh methanol was added, and immersion was performed again for 1 hour. This methanol immersion operation was repeated 3 times to remove unreacted monomers, low molecular weight oligomers, solvents and the like for purification. The crosslinked polyacrylic acid-2- (2-ethoxyethoxy) was then allowed to stand on a hot plate at 50 ° C. for 12 hours and then dried in a vacuum dryer at room temperature for 12 hours to completely remove methanol. Ethyl (crosslinked PEEA) was obtained.

The structure of the obtained crosslinked PEEA is shown in the following chemical formula.

(2) Preparation of Membrane Samples 75.0 mg of crosslinked MeOH obtained above was cut into strips (thickness 0.073 cm) of 0.82 cm × 0.44 cm and placed in a Teflon (registered trademark) beaker with a capacity of 10 mL. 9 mL of methanol and 175.8 mg of TEG as a plasticizer were added, and the mixture was allowed to stand on a hot plate at 50 ° C. for 2 days to introduce TEG into the crosslinked PEEA, and the methanol was completely removed to obtain a membrane sample. Since a small amount of TEG remained on the surface of this film sample, a film sample having a thickness of 0.085 cm was obtained by wiping it off.

Since the mass of the membrane sample after wiping the TEG was 104.7 mg, it was found that the TEG content in this membrane sample was 28% by mass.

The obtained polymer electrolyte membrane sample where, conforming to JIS K 7121, at a heating rate 10 ° C. / min conditions, the glass transition point was measured _{T g} at a temperature range of -90 ° C. to 30 ° C., Three Tg were found at −83 ° C., −57 ° C., and -12 ° C. From this, it was suggested that the solid polymer electrolyte membrane sample in this comparative example was insufficiently mixed with each component and did not form a uniform proton conduction mixed phase. The DSC curve obtained at this time is shown in FIG.

(3) AC impedance measurement Using a platinum net with a thickness of 0.1 mm as an electrode, the AC impedance of the obtained film guide sample was measured.

The obtained membrane sample (width 0.48 cm, thickness 0.085 cm) was sandwiched between a pair of electrodes arranged so as to face each other with a distance between the electrodes of 0.70 cm. The membrane sample sandwiched between the electrodes was placed in a natural convection constant temperature and constant temperature dryer, and dried under the conditions of a temperature of 50 ° C. and a relative humidity of 5 RH% for 1 hour.

The dryer temperature was raised to 80 ° C., after which the internal temperature is waited to stabilize, voltage 80 mV, and varied 1Hz units from ¹⁰ 6 Hz frequency, with no humidity under a relative humidity of 2.0RH% AC impedance measurement was performed. However, the measured value could not be obtained because the resistance value was extremely large. Therefore, it was found that the proton conductivity of the membrane sample in this comparative example was extremely low.

Although the crosslinked polymer in the membrane sample of this comparative example was in a quasi-fluid state, it is considered that neither the crosslinked polymer nor the plasticizer contained a proton-releasing group, so that the crosslinked polymer showed almost no proton conductivity.

In the membrane sample in this comparative example, elution was observed after the measurement of AC impedance. This eluate is considered TEG. In the membrane sample in this comparative example, it is probable that TEG was eluted from the membrane sample because almost no effective non-covalent bond was formed between the ether group of the crosslinked PEEA and the hydroxyl group of TEG.

<Example 2>
In this example, a solid polymer electrolyte membrane containing a crosslinked polymer having no proton-releasing group and a plasticizer having a proton-releasing group was prepared, and its proton conductivity was examined.

(1) Synthesis of crosslinked polymer A column packed with basic alumina was purified by passing unpurified -4-hydroxybutyl acrylate.

As the first monomer, 1.5 g (10.4 mmol) of the purified 4-hydroxybutyl acrylate (HBA) described above, and as the third monomer, 32.1 mg (0.208 mmol) of N, N'-methylenebisacrylamide (MBAA). ), S-1-dodecyl-S'-(α, α'-dimethyl-α "-acetic acid) trithiocarbonate 2.3 mg (0.0063 mmol) as RAFT agent, azobisisobutyronitrile as radical polymerization initiator 0.1 mg (0.0006 mmol) of (AIBN) and 758 mg (10.4 mmol) of N, N-dimethylformamide (DMF) as a solvent were mixed in a sample bottle to obtain a raw material solution. The molar ratio of the first monomer: third monomer: RAFT agent is approximately 2,000: 40: 1.

After bubbling the raw material solution with nitrogen gas for 20 minutes, the temperature was raised to 80 ° C. under normal pressure by an oil bath, and polymerization was carried out under stirring at 500 rpm for 7 hours. After 7 hours, the sample bottle was removed from the oil bath and polymerization was stopped. At this time, it was confirmed that the solution in the sample bottle did not flow and was gelled.

The sample in the sample was transferred to a Teflon (registered trademark) container, 20 mL of methanol was added, and the mixture was immersed for 1 hour. After 1 hour, methanol was removed, the same amount of fresh methanol was added, and immersion was performed again for 1 hour. This methanol immersion operation was repeated 3 times to remove unreacted monomers, low molecular weight oligomers, solvents and the like for purification. Then, after allowing to stand on a hot plate at 50 ° C. for 12 hours, the mixture was dried in a vacuum dryer at room temperature for 12 hours to completely remove methanol to completely remove the methanol, thereby performing cross-linked polyacrylic acid-4-hydroxybutyl (cross-linked PHBA). Got

The structure of the obtained crosslinked PHBA is shown in the following chemical formula.

(2) Preparation of Solid Polymer Electrolyte Membrane 19.1 mg of crosslinked methanol obtained above is cut into strips (thickness 0.10 cm) of 0.8 cm × 0.1 cm, and a beaker made of Teflon (registered trademark) having a capacity of 10 mL. And 9 mL of methanol and 42.5 mg of plasticizer were added. As the plasticizer, a mixture of TEG premixed at a mass ratio of 58:42 and bis (trifluoromethanesulfonyl) imide (HTFSI) represented by the following formula was used.

The beaker after adding methanol and a plasticizer was allowed to stand on a hot plate at 50 ° C. for 2 days to introduce TEG and HTFSI into the crosslinked PHBA, and the methanol was completely removed to obtain a membrane sample. .. Since a small amount of plasticizer remained on the surface of this membrane sample, it was wiped off to obtain a solid polymer electrolyte membrane sample having a thickness of 0.14 cm.

Since the mass of the solid polymer electrolyte membrane sample after wiping the TEG was 52.0 mg, the ratio of the crosslinked PHBA, HTFSI, and TEG in this membrane sample should be 37:37:26 as a mass ratio. I understood.

A schematic diagram of the structure of the obtained solid polymer electrolyte membrane sample is shown in FIG. In FIG. 2, the cross-linked PHBA is a cross-linked polymer, TEG and HTFSI are plasticizers, and the sulfonylimide group in HTFSI is a proton-releasing group. It is considered that the sulfonylimide group of HTFSI and the hydroxyl group and ether group of TEG each form a non-covalent bond with the hydroxyl group in the crosslinked PHBA. Some of the sulfonylimide groups in HTFSI are liberated into sulfonylimide ions.

The Tg of the crosslinked PHBA site is about −40 ° C. The melting point of TEG is about −6 ° C., and the mixture of TEG and HTFSI is liquid at room temperature.

The obtained solid polymer electrolyte membrane sample in the present embodiment, conforms to JIS K 7121, at a heating rate 10 ° C. / min condition, the glass transition temperature _{T g} in a temperature range of -90 ° C. to 30 ° C. As a result of measurement, a single Tg as a solid polymer electrolyte membrane was found at −67 ° C.

The Tg obtained above is clearly lower than the operating temperature of the solid polymer electrolyte membrane. According to this Tg, the solid polymer electrolyte membrane of this example should be in a quasi-fluid state at the measurement temperature (50 ° C, 80 ° C, and 95 ° C) of the AC impedance measurement in the next section, but is crosslinked. Therefore, it did not flow and maintained the film shape.

When the solid polymer electrolyte membrane sample obtained above was allowed to stand for 1 hour under no load while changing the temperature, no leaks were observed in the range of -40 ° C to 200 ° C, and the operating temperature range of the battery was observed. It was confirmed that the plasticizer did not bleed out.

(3) AC Impedance Measurement The AC impedance of the obtained solid polymer electrolyte membrane sample (width 0.17 cm, thickness 0.14 cm) was measured by substantially the same procedure as in Example 1.

The measurement temperature is set to 3 levels of 50 ° C (relative humidity 10.5 RH%), 80 ° C (relative humidity 2.9 RH%), and 95 ° C (relative humidity 1.4 RH%), and the absolute value of the resistance value is The resistance value in a frequency region that is almost constant and the proton conductivity were determined by the above equation (1). The results are shown in Table 1.

As shown in Table 1, the proton conductivity increased as the temperature increased. It is considered that this is because the molecular motility of the quasi-fluid state proton conduction mixed phase increases as the temperature rises, and as a result, the proton conductivity improves.

In the solid polymer electrolyte membrane sample in this example, no eluate was observed during the measurement of the AC impedance, and the membrane shape was maintained without flowing.

<Example 3>
In this example, a solid polymer electrolyte membrane containing a crosslinked polymer having a proton-releasing group and a plasticizer having a proton-releasing group was prepared, and its proton conductivity was examined.

(1) Synthesis of crosslinked polymer As the second monomer, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) 605 mg (2.92 mmol), and as the third monomer, N, N'-methylenebisacrylamide (MBAA) 11.2 mg ( 0.0726 mmol), 3.0 mg (0.018 mmol) of azobisisobutyronitrile (AIBN) as a radical polymerization initiator, and poly (4-styrene sulfonic acid) (PSS, manufactured by Sigma-Aldrich) as a plasticizer. , 1.68 g of an 18 mass% aqueous solution having a weight average molecular weight of 75,000) and 2.21 g of TEG were mixed in a sample bottle to obtain a raw material solution.

After bubbling the raw material solution with nitrogen gas for 10 minutes, the temperature was raised to 70 ° C. under normal pressure by an oil bath, and polymerization was carried out under stirring at 500 rpm for 1 hour. After 7 hours, the sample bottle was removed from the oil bath and polymerization was stopped. At this time, it was confirmed that the solution in the sample bottle did not flow and was gelled. The obtained gel is taken out from the sample bottle and dried in a vacuum dryer at 40 ° C. for 2 days to remove water, thereby removing a solid polymer electrolyte membrane (crosslinked poly (2-acrylamide-2-methylpropanesulfonic acid). ) (Cross-linked acrylamide), PSS, and TEG mixture (mass ratio 2: 1: 7)).

The structure of the crosslinked PAMPS is shown in the chemical formula below.

A schematic diagram of the structure of the obtained solid polymer electrolyte membrane is shown in FIG. In FIG. 3, the cross-linked PAMPS is a cross-linked polymer, PSS and TEG are plasticizers, and each of the sulfonic acid group in the cross-linked PAMPS and the sulfonic acid group in the PSS is a proton-releasing group. It is considered that the sulfonic acid group of PSS and the hydroxyl group and ether group of TEG form a non-covalent bond with the sulfonic acid group and the amide group in the crosslinked PAMPS. It is considered that protons are liberated from some of the sulfonic acid groups in the solid polymer electrolyte membrane to form sulfonate ions.

The obtained solid polymer electrolyte membrane, conforming to JIS K 7121, at a heating rate 10 ° C. / min conditions, the glass transition point _{The T g} was measured in the temperature range of -90 ° C. to 30 ° C., -75 It was ° C. This Tg is clearly lower than the operating temperature of the solid polymer electrolyte membrane. According to this Tg, this solid polymer electrolyte membrane should be in a pseudo-fluid state at the measurement temperatures of AC impedance measurement (50 ° C, 80 ° C, and 95 ° C), but it flows because the polymer is crosslinked. The film shape was maintained without doing so.

When the solid polymer electrolyte membrane sample obtained above was allowed to stand for 1 hour under no load while changing the temperature, no leaks were observed in the range of -40 ° C to 200 ° C, and the operating temperature range of the battery was observed. It was confirmed that the plasticizer did not bleed out.

(3) AC Impedance Measurement Using the obtained solid polymer electrolyte membrane cut into strips with a width of 0.47 cm and a thickness of 0.051 cm as a sample, AC impedance measurement was performed by substantially the same procedure as in Example 1. went.

The measurement temperature is set to 3 levels of 50 ° C (relative humidity 5.9 RH%), 80 ° C (relative humidity 1.3 RH%), and 95 ° C (relative humidity 0.8 RH%), and the absolute value of the resistance value is The resistance value in a frequency region that is almost constant and the proton conductivity were determined by the above equation (1). The results are shown in Table 1.

As shown in Table 1, the proton conductivity increased as the temperature increased. It is considered that this is because the molecular motility of the quasi-fluid state proton conduction mixed phase increases as the temperature rises, and as a result, the proton conductivity improves.

In the solid polymer electrolyte membrane sample in this example, no eluate was observed during the measurement of the AC impedance, and the membrane shape was maintained without flowing.

The abbreviations for monomers and plasticizers in Table 1 have the following meanings, respectively.
[First monomer]
EEA: -2- (2-ethoxyethoxy) ethyl acrylate HBA: -4-hydroxybutyl acrylate [second monomer]
AMPS: 2-acrylamide-2-methylpropansulfonic acid [third monomer]
MBAA: N, N'-methylenebisacrylamide [Plasticizer]
HITFSI: Bis (trifluoromethanesulfonyl) imide PSS: Poly (4-styrene sulfonic acid), manufactured by Sigma-Aldrich, weight average molecular weight 75,000, supplied as 18% by mass aqueous solution TEG: tetraethylene glycol

Claims (13)

Contains crosslinked polymers and plasticizers
The crosslinked polymer
The first monomer, which is a vinyl-based monomer having a polar group other than the proton-releasing group,
A second monomer, which is a vinyl-based monomer having a proton-releasing group,
With a third monomer, which is a crosslinkable vinyl-based monomer
Is a copolymer of
Solid polymer electrolyte membrane. The solid polymer electrolyte membrane according to claim 1, wherein the plasticizer contains a plasticizer having a proton-releasing group. The solid polymer electrolyte membrane according to claim 1 or 2, wherein the plasticizer further contains a plasticizer having no proton-releasing group. The solid polymer electrolyte membrane according to any one of claims 1 to 3, wherein the proton-releasing group is selected from a sulfonic acid group, a sulfonylamide group, a sulfonylimide group, and a phosphoric acid group. The first monomer is selected from (meth) acrylic acid ester, styrene substituted with a polar group other than the proton-releasing group, and a vinyl-based monomer having both a polar group other than the proton-releasing group and a fluorine atom. The solid polymer electrolyte membrane according to any one of claims 1 to 4, which is one or more. The second monomer is one or more selected from allyl sulfonic acid, poly (4-styrene sulfonic acid), and a compound represented by the following formula (2), according to any one of claims 1 to 5. The solid polymeric electrolyte membrane of the description.

(In the formula (2), R ⁴ is a hydrogen atom or a methyl group, and R ^II is an alkylene group having 1 to 6 carbon atoms.) The invention according to any one of claims 2 to 6 , wherein the plasticizer having a proton-releasing group includes a compound selected from an aromatic sulfonic acid compound, a sulfonic acid group-containing polymer, and a fluorine atom-containing sulfonylimide compound. Solid polymer electrolyte membrane. The solid polymer electrolyte membrane according to any one of claims 1 to 7 , wherein the ratio of the plasticizer used to 100 parts by mass of the crosslinked polymer is 10 parts by mass or more and 1,000 parts by mass or less. The solid polymer electrolyte membrane according to any one of claims 1 to 8 , wherein the glass transition temperature of the solid polymer electrolyte membrane is 0 ° C. or lower. The solid polymer according to any one of claims 1 to 9 , wherein the solid polymer electrolyte membrane maintains the film shape and the plasticizer does not bleed out in a temperature range of −40 ° C. or higher and lower than 200 ° C. Electrolyte membrane. The solid polymer electrolyte membrane according to any one of claims 1 to 10 , wherein the proton conductivity of the solid polymer electrolyte membrane is 1 × 10 ^-4 S / cm or more at 50 ° C. The solid polymer electrolyte membrane according to any one of claims 1 to 11 , which is a proton conductive membrane. A solid polymer electrolyte membrane for a fuel cell, comprising the solid polymer electrolyte membrane according to any one of claims 1 to 12.

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