JP2007115475A - Polymer electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new polymer electrolyte with high oxidation resistance, hardly generating desulfonation even at high temperature, with high proton conductivity, which can be easily manufactured, as one for a solid polymer fuel cell and a binder. <P>SOLUTION: The polymer electrolyte is composed of polymer sulfonic acid having a side chain of such a structure that aromatic rings are jointed by electron-attractive linking groups. The side chain may be a branched side chain or a non-branched side chain, but the branched side chain is preferable. The electron-attracting linking group is selected from -CO-, -CONH-, -C(CF<SB>2</SB>)p-, (p is an integer of 1 to 10), -C(CF<SB>3</SB>)<SB>2</SB>-, -COO-, -SO-, -SO<SB>2</SB>-. The primary chain has a sulfone group, but the side chain does not have a sulfonic group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel polymer electrolyte useful as an electrolyte membrane and a binder for a polymer electrolyte fuel cell and a method for producing the same.

  Up to now, electrolyte materials for polymer electrolyte fuel cells include (1) perfluoroalkylsulfonic acid polymers such as Nafion (manufactured by DuPont) (see, for example, Patent Document 1), and (2) polyether ether. Polymers obtained by sulfonating the main chain of a heat-resistant polymer such as ketone (for example, see Patent Document 2), (3) polymers having a sulfonated side chain (for example, Patent Document 3, Patent Document 4, Patent) Document 5) is known. However, these polymers all have problems as electrolyte materials for polymer electrolyte fuel cells. That is, an operating temperature of 100 ° C. or higher is desired from the viewpoint of improving the output of the fuel cell. However, since the perfluoroalkylsulfonic acid polymer (1) has a low glass transition point of about 120 ° C., the operating temperature is 100. There is a restriction of less than ℃. In addition, the polymers (2) and (3) cannot be used at high temperatures because desulfonation proceeds. Furthermore, the polymers (2) and (3) are not sufficient in oxidation resistance. As a method for improving the oxidation resistance, a method of adding an antioxidant to the polymer electrolyte (for example, see Patent Document 6 and Patent Document 7) has been proposed. However, since this method does not improve the oxidation resistance of the polymer electrolyte itself, it is presumed that when the added antioxidant is consumed, the oxidation resistance of the electrolyte membrane decreases. In addition, the polymer (2) has a problem of becoming water-soluble when the sulfonation rate is increased to improve proton conductivity (see, for example, Non-Patent Document 1). Furthermore, there is a problem that many steps are required to produce the polymer (3). Further, as a polymer electrolyte having a side chain sulfonic acid, a polymer electrolyte having a side chain structure in which aromatic rings are connected by an electron-withdrawing linking group is also used. (For example, see Patent Document 8, Patent Document 9, and Patent Document 10)

US Pat. No. 3,282,875 US Pat. No. 5,795,496 US Pat. No. 5,403,675 JP 2001-329053 A JP 2002-289222 A JP 2003-201352 A JP 2003-201403 A Japanese Patent Laid-Open No. 2004-256797 JP 2005-82757 A WO2005 / 076397 specification Electrochemical and Solid-State Letters, Vol. 6, no. 11, p. A229-A231 (2003)

  The present invention relates to a novel polymer electrolyte and a polymer electrolyte and a binder for a polymer electrolyte fuel cell, which have high oxidation resistance, are resistant to desulfurization even at high temperatures, have high proton conductivity, and can be easily produced. The object is to provide a manufacturing method thereof.

As a result of intensive research in order to solve the above problems, the present inventors have a sulfonic acid group-free side chain having a specific structure that is linked by an electron-withdrawing linking group, and has a sulfonic acid group in the main chain. The present inventors have found that a polymer electrolyte composed of a polymer sulfonic acid can be adapted to the purpose, and have made the present invention based on this finding.
That is, the present invention is as follows.
1. A polymer electrolyte for a fuel cell, comprising at least a repeating unit represented by the following general formula (1A) and a repeating unit represented by the following general formula (1B).

[Y represents a (k + 2) -valent aromatic residue, Y ′ represents a (t + 2) -valent aromatic residue, and P and P ′ represent —CO—, —O—, —S—, —SO—, _{-SO 2 -, - CONH -,} - C (CF 3) 2 -, a single bond, _-CR 2 - (R is a hydrogen atom, an alkyl group or an aryl group) a linking group selected from, a same And k and t are each independently an integer of 1 to 4, and the side chain portion Z in the formula is represented by the following general formula (2).
^{Z = - (X 1 Ar 1} (B 1)) - (X 2 Ar 2 (B 2)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar ⁿ ) (2)
^{B 1 ~B n-1} in the general formula (2) in means a branched chain in the side chain moiety Z, is expressed by the following equation.
B ¹ = - ^{[(X 2 Ar 2 (B 2} )) - (X 3 Ar 3 (B 3)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X ⁿ Ar ⁿ )] _f
B ² = - ^{[(X 3 Ar 3 (B 3} )) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar n) ] _f
・
・
・
B ^n-1 = - ^[X n Ar ^n] _f
In said general formula (2), n is an integer of 1-5 each independently,
f is each independently an integer of 0 to 5;
Ar ¹ to Ar ⁿ is an aromatic residue independently,
X ^{1 to} X ⁿ are each independently —CO—, —CONH—, — (CF ₂ ) _p — (p is an integer of 1 to 10), —C (CF ₃ ) ₂ —, —COO—, —SO—. , —SO ₂ —.
In Z, a —SO ₃ H group is not introduced. ]

2. _2. The fuel cell high element according to item 1, wherein P and P ′ are a linking group selected from —CO—, —O—, —S—, —SO ₂ —, and —C (CF ₃ ) ₂ —. Molecular electrolyte.
3. 3. The polymer electrolyte for fuel cells according to 1 or 2 above, wherein k is an integer of 1 to 2 and f is independently an integer of 0 to 2.
4). 4. The polymer electrolyte for fuel cells as described in 3 above, wherein at least one f is 1 or 2.
5. 4. The polymer electrolyte for a fuel cell as described in 3 above, wherein f is 0 or 1, and at least one f is 1.

6). 3. The polymer electrolyte for fuel cells according to item 3 above, wherein Z is the following formula (3):
In the formula, the phenyl group and the phenylene group may be substituted with an electron withdrawing group. ).

7). 3. The polymer electrolyte for a fuel cell according to the item 3, wherein Z is the following formula (4) (wherein the phenyl group and the phenylene group may be substituted with an electron withdrawing group).

8). 8. A method for producing a polymer electrolyte for a fuel cell having a repeating unit represented by the general formula (1) described in item 1 above, wherein a polymer is reacted with a side chain introducing agent. The polymer electrolyte for fuel cells according to item 8 above, wherein a polymer having a repeating unit represented by the following general formula (6A) is reacted with a side chain introducing agent represented by the following general formula (6B): Manufacturing method.

[Y and P are the same as those described in the general formula (1A), and X ′ is selected from a halogen atom, OR (R is a hydrogen atom, an alkyl group, or an aryl group), an alkali metal, and an alkaline earth metal. K ′ is an integer of 1 to 4. Z ′ is represented by the following general formula (5).
^{Z '= - (Ar 1 (} B 1)) - (X 2 Ar 2 (B 2)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar n (5)
In the general formula (5), Ar ^{1 to} Ar ⁿ , B ^{1 to} B ⁿ⁻¹ , n are the same as those described in the general formula (1A), and X ^{1 to} X ⁿ are —S—. , —CH ₂ —, —CX ″ ₂ — (X ″ is a non-fluorine halogen atom), —C (OR ″) ₂ — (R ″ is an alkyl group), —C (OR ″) ₂ —O— (R ″ Is an alkyl group), a linking group precursor selected from — (C (OR ″) ₂ ) _p — (R ″ is an alkyl group), and a linking group described in the general formula (1). ]

10. When the polymer having the repeating unit represented by the general formula (6A) is reacted with the side chain introducing agent represented by the general formula (6B), X ^{1 to} X ⁿ of the side chain introducing agent are electron donations. After the reaction with the polymer, the linking group precursor is converted into an electron-withdrawing linking group, and is represented by the above general formulas (1A) and (1B). The method for producing a polymer electrolyte for a fuel cell according to claim 9, wherein the polymer electrolyte for a fuel cell having a repeating unit is obtained.
11. A polymer for a fuel cell having a repeating unit represented by the above general formulas (1A) and (1B) by using a sulfonic acid precursor instead of a sulfonic acid group and then converting the sulfonic acid precursor into a sulfonic acid. 11. The method for producing a polymer electrolyte for fuel cells according to any one of items 8 to 10, wherein an electrolyte is obtained.

12 8. A polymer electrolyte membrane for fuel cells, wherein the polymer electrolyte according to any one of items 1 to 7 is used.
13. A polymer electrolyte membrane for a fuel cell, characterized by using a polymer electrolyte produced by the method according to any one of items 8 to 11.
14 15. A fuel cell comprising the polymer electrolyte according to any one of 1 to 7 above. 12. A fuel cell using a polymer electrolyte produced by the method according to any one of items 8 to 11.

  The polymer electrolyte of the present invention is a novel polymer electrolyte having high oxidation resistance, hardly causing desulfonation even at high temperatures, high proton conductivity, and excellent mechanical properties. Therefore, it can be suitably used as an electrolyte membrane and a binder for a polymer electrolyte fuel cell.

Hereinafter, the present invention will be specifically described.
The polymer electrolyte of the present invention has a repeating unit represented by the above general formulas (1A) and (1B) (hereinafter sometimes collectively referred to as general formula (1)).

In the above general formula (1), k and t are each independently an integer of usually 1 to 4, preferably 1 or 2.
In the general formula (1), Y represents a (k + 2) -valent aromatic residue, Y ′ represents a (t + 2) -valent aromatic residue, which may be the same or different. Examples include trivalent aromatic residues represented by the general formula (7), tetravalent aromatic residues represented by the following general formula (8), and pentavalent aromatic residues represented by the following general formula (9). . The hydrogen atom of these aromatic residues is an alkyl group, a halogen atom, a halogenated alkyl group, an aryl group, a halogenated aryl group, —CN, —NO ₂ , —COR, —COOR (where R is a hydrogen atom, an alkyl group, a halogen atom, alkyl group, selected from aryl group), -. CONRR '(R ' is the same as R), -. SOR, may be substituted by -SO ₂ R, F, perfluoroalkyl, -CN , —NO ₂ , —COR, —COOR, —CONRR ′, —SOR, —SO ₂ R and the like are preferably substituted.

In the general formulas (7) to (9), the divalent group Q is —CO—, —COO—, —O—, —S—, —SO—, —SO ₂ —, —CCR ¹ ₂ — (R ¹ Is selected from a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group and an aryl group) and a single bond, and preferably selected from —CO—, —O—, —S— and —SO ₂ —.
In the general formula (1), P represents —CO—, —O—, —S—, —SO—, —SO ₂ —, —CONH—, —C (CF ₃ ) ₂ —, —CR ₂ — (R Is a hydrogen atom, an alkyl group, or an aryl group) and a linking group selected from a single bond, preferably from —CO—, —O—, —S—, —SO ₂ —, —C (CF ₃ ) ₂ —. And a linking group selected from —CO—, —O—, —S—, and —SO ₂ —.

The side chain portion Z in the general formula (1) is represented by the following general formula (2).
^{Z = - (X 1 Ar 1} (B 1)) - (X 2 Ar 2 (B 2)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar ⁿ ) (2)
^{B 1 ~B n-1} in the general formula (2) in means a branched chain in the side chain moiety Z, is expressed by the following equation.
B ¹ = - ^{[(X 2 Ar 2 (B 2} )) - (X 3 Ar 3 (B 3)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X ⁿ Ar ⁿ )] _f
B ² = - ^{[(X 3 Ar 3 (B 3} )) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar n) ] _f
・
・
・
B ^n-1 = - ^[X n Ar ^n] _f

In the general formula (2), each n independently represents an integer selected from 2 to 5, preferably selected from 2 to 4, and more preferably selected from 2 to 3. f represents an integer independently selected from 0 to 5, preferably from 0 to 2, and at least one f is 1 or 2, more preferably from 0 to 1, and at least One f is 1.
In the general formula (2), when f is 1 or more, the side chain represented by the general formula (2) has a branched structure in the aromatic residues Ar ^{1 to} Ar ^n-1 . Each branched chain may have a different chain length and branched structure. That is, the side chain represented by the general formula (2) of the present invention can have a structure represented by the following general formula (10), for example.

Ar ^{1 to} Ar ^n-1 in the general formula (2) represent an (f + 2) -valent aromatic residue, for example, a divalent aromatic residue represented by the following general formula (11), the general formula (7) And a trivalent aromatic residue represented by the general formula (8), a pentavalent aromatic residue represented by the general formula (9), and the like. The hydrogen atom of these aromatic residues is an alkyl group, a halogen atom, a halogenated alkyl group, an aryl group, a halogenated aryl group, —CN, —NO ₂ , —COR, —COOR (where R is a hydrogen atom, an alkyl group, a halogen atom, alkyl group, selected from aryl group), -. CONRR '(R ' is the same as _{R), -. SO 3 R} , -SOR, may be substituted by -SO ₂ R, F, par An electron withdrawing group such as fluoroalkyl, —CN, —NO ₂ , —COR, —COOR, —CONRR ′, —SO ₃ R, —SOR, —SO ₂ R, etc. is preferably substituted. Ar ^{1 to} Ar ^n-1 may be the same as or different from each other.

In addition, Ar ⁿ in the general formula (1) represents an aryl group at the end of the side chain, and examples thereof include an aryl group represented by the following general formula (12), and the hydrogen atom of the aryl group is an alkyl group, a halogen atom, a halogen atom. Alkyl group, aryl group, halogenated aryl group, —CN, —NO ₂ , —COR, —COOR (R is selected from a hydrogen atom, an alkyl group, a halogenated alkyl group, and an aryl group), —CONRR ′ ( R ′ is the same as R.), —SO ₃ R, —SOR, —SO ₂ R may be substituted, and Ar ⁿ may be the same or different from each other.

The ^X 1 to X ⁿ in the general formula (1) represents a divalent electron withdrawing group, for example, -CO -, - CONH -, - (CF 2) p - ( wherein, p is from 1 to 10 is an _{integer), - C (CF 3)} 2 -, - COO -, - SO -, - SO 2 - is like, preferably _{-CO -, - C (CF 3} ) 2 -, - SO-, -SO ₂ - and more preferably -CO -, - SO -, - SO 2 - and the like are used. X ^{1 to} X ⁿ may be the same as or different from each other. In the general formula (1) of the present invention, specific examples of the side chain represented by Z include a group of the following formula (13).

In the present invention, a side chain selected from an unbranched side chain and a branched side chain is usually used, and a branched side chain is preferably used.
In the general formula (2), when f is 1 or more, the side chain represented by the general formula (2) has a branched structure in the aromatic residues Ar ^{1 to} Ar ^n-1 . Each branched chain may have a different chain length and branched structure. That is, the side chain represented by the general formula (2) of the present invention can have, for example, the structure represented by the general formula (10).

The polymer electrolyte of the present invention has at least the repeating units (1A) and (1B) represented by the general formula (1), and the repeating unit (1A) is generally used with respect to 100 mol% of the total repeating units. 0.1 to 50 mol% and 60 to 1 mol% of the repeating unit (1B), preferably 1 to 40 mol% of the repeating unit (1A) and 40 to 3 mol% of the repeating unit (1B), More preferably, it contains 2 to 30 mol% of the repeating unit (1A) and 30 to 5 mol% of the repeating unit (1B). However, the total content of the repeating unit (1A) and the repeating unit (1B) is usually 1.1 to 100 mol%, preferably 4 to 80 mol%, more preferably 100 mol% of the total repeating units. 7 to 60 mol%.
The polymer electrolyte of the present invention has a weight average molecular weight of 1,000 to 1,000,000, preferably 10,000 to 1,000,000, more preferably 20,000 to 800,000, particularly preferably 30,000 to 400,000.

The polymer electrolyte of the present invention has high proton conductivity compared to conventional polymer electrolytes. The reason is estimated as follows. The polymer electrolyte of the present invention is structurally larger than conventional polymer electrolytes [(A) polymer electrolytes having sulfonic acid only in the main chain or (B) side chain sulfonic acid type polymer electrolyte]. There is a difference. That is, a sulfonic acid group does not exist in the side chain of the polymer electrolyte of the present invention, and sulfonic acid exists only in the main chain. Due to the presence of the side chain, a space composed of relatively rigid voids composed of the main chain sulfonic acid and the side chain is formed, and water accumulates in this space, resulting in an increase in water retention in the vicinity of the sulfonic acid. It is considered that proton conductivity is increased. In particular, in the present invention, when the side chain is branched, the proton conductivity is high because the shape of the side chain becomes bulky in the case of the branched side chain, so that it is considered that particularly high water retention is obtained. . On the other hand, in the case of a conventional polymer electrolyte, (a) a polymer electrolyte having a sulfonic acid only in the main chain does not have a side chain and thus has low water retention, and therefore has a low proton conductivity, and (b) a side chain. The sulfonic acid type polyelectrolyte also holds water in the space between the side chains, and the amount is thought to affect the proton conductivity, but the size of the space constantly fluctuates due to the molecular movement of the side chains, so the water retention is It is estimated that the polymer of the present invention is higher.
The polymer electrolyte of the present invention has a side chain structure in which aromatic rings are connected by an electron withdrawing group, and has high oxidation resistance.
Further, the polymer electrolyte of the present invention does not need to introduce a sulfonic acid or a sulfonic acid precursor into the side chain precursor in advance. Therefore, it can be produced by a simpler method as compared with conventional polymer electrolytes.

The method for producing the polymer electrolyte of the present invention is not particularly limited. For example, the following method 1, method 2, and the like can be used.
<Method 1> A method of polymerizing a monomer having at least a side chain:
(I) It can also be obtained by polymerizing at least the monomer corresponding to the repeating unit (1A) and the monomer corresponding to the repeating unit (1B),
(Ii) First, an oligomer is synthesized from a monomer corresponding to the repeating unit (1A), a monomer corresponding to the repeating unit (1B), and a monomer corresponding to another repeating unit, and then reacting the oligomers with each other or the oligomer and the monomers. Can also be manufactured,
(Iii) A monomer corresponding to a structure in which the repeating unit (1A) and the repeating unit (1B) are linked to one or more other repeating units is synthesized in advance, and homopolymerization of the monomer, or this and other repeating structures It can also be produced by polymerization with monomers corresponding to.

<Method 2> Method of introducing a side chain by reacting a polymer with a side chain introducing agent:
(I) Repeating —Y—P— (Y is a divalent aromatic residue, P is as described above) and general formula (1B) corresponding to the structure in which Z is not substituted in general formula (1A) It may be produced by reacting a side chain introducing agent to a polymer having a unit and introducing Z,
(Ii) -Y (U) -P- (Y is a trivalent aromatic residue, U is a reactive group, P is as described above) and a general formula (1B) in which a reactive substituent is introduced in advance. The polymer having as a repeating unit may be produced by reacting a side chain introducing agent that reacts with the reactive group U and introducing Z,
(Iii) -Y (U ')-P- [U' is a reactive group convertible to sulfonic acid, Y and as described above] and a side chain introducing agent are reacted, and then unreacted U 'is converted to sulfone It can also be produced by introducing Z by conversion to an acid,
(Iv) After allowing Z to be introduced by reacting a side chain introducing agent with a polymer having -Y-P- (Y and P are as described above) as a repeating unit, only the main chain is sulfonated. Can also be manufactured.
A preferred specific example of Method 2 is shown below. That is, a polymer having a repeating unit represented by the following general formula (6A) and a side chain introducing agent represented by the following general formula (6B) are reacted, and if necessary, hydrolyzed to give the above general formula ( The polymer electrolyte represented by 1) can be produced. In this case, X ¹ in the general formula (2) is —SO ₂ —.

上記一般式（６Ａ）において、ＹおよびＰは一般式（１）に記載のものと同様であり、Ｘ’はハロゲン原子、ＯＲ（Ｒは水素原子、アルキル基、またはアリール基）から選ばれる。

In the general formula (6A), Y and P are the same as those described in the general formula (1), and X ′ is selected from a halogen atom and OR (R is a hydrogen atom, an alkyl group, or an aryl group).

上記一般式（６Ｂ）のＺ’は、下記一般式（５）で表される。
Ｚ’＝−（Ａｒ^１（Ｂ^１））−（Ｘ^２Ａｒ^２（Ｂ^２））−・・・−（Ｘ^ｎ−１Ａｒ^ｎ−１（Ｂ^ｎ−１））−（Ｘ^ｎＡｒ^ｎ） （５）

Z ′ in the general formula (6B) is represented by the following general formula (5).
^{Z '= - (Ar 1 (} B 1)) - (X 2 Ar 2 (B 2)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar n (5)

In the general formula (5), Ar, B, and n are the same as those described in the general formula (2), and X except for X ¹ is a linking group and a linking group precursor described in the general formula (2). Chosen from the body. )
A linking group precursor refers to a group that can be converted to a linking group. As a method for converting the linking group precursor into a linking group, a known method can be used. Table 1 shows an example.

  The linking group precursor may be converted to the linking group at any point, but the following method is preferably used. That is, when the polymer having the repeating unit represented by the general formula (6A) and the side chain introducing agent represented by the general formula (6B) are reacted, X of the side chain introducing agent is an electron donating agent. A fuel cell for a fuel cell having a repeating unit represented by the general formula (1) by reacting with a polymer and then converting the linking group precursor into an electron-withdrawing linking group. This is a method for obtaining a molecular electrolyte.

Examples of the polymer having a repeating unit represented by the general formula (6A) used in the present invention are shown below.
A divalent aromatic residue selected from the residues represented by the general formula (11), and —CO—, —O—, —S—, —SO—, —SO ₂ —, —CONH—, —C ( CF ₃ ) _2- , a polymer composed of a combination of linking groups P selected from single bonds, usually having -SO ₂ X 'introduced therein, preferably a divalent aromatic selected from phenylene, naphthylene, and biphenylene residues and -CO -, - O -, - S -, - SO 2 - which was introduced -SO ₂ X 'in the polymer combinations of the linking group P is selected from is used, more preferably polyether ketone , polyether sulfone, polythioether ketone, polythioether sulfone, polyether ether sulfone, which was introduced -SO 2 X _'polyether ether ketone is used, or more preferably, the following general (14) and Z in the polymer of the formula (15) include the -SO ₂ X 'is used.

Note that the introduction of the -SO 2 X _'may be any known method for introducing. X ′ in SO ₂ X ′ of the general formula (6A) is usually selected from a halogen atom and OR (R is a hydrogen atom, an alkyl group, or an aryl group), and preferably selected from a halogen atom and a hydroxyl group.
Examples of the side chain introducing agent Z′-H represented by the general formula (6B) are shown in the following general formula (16) and formula (17).

上記一般式（１６）中、ジフェニルスルフィドが、また上記一般式（１７）中、トリスチオフェノキシベンゼンが特に好ましく用いられる。

In the general formula (16), diphenyl sulfide is particularly preferably used, and in the general formula (17), tristhiophenoxybenzene is particularly preferably used.

The type of reaction when the side chain introduction agent is reacted with the polymer is not particularly limited. As a preferable method for reacting the polymer represented by the general formula (6A) with the side chain introducing agent represented by the general formula (6B), (i) Friedel Crafts using Lewis acid as a catalyst. Well-known reactions such as type sulfonylation reactions and (ii) condensation reactions using a condensing agent such as diphosphorus pentoxide (dehydration) can be mentioned.
The usual reaction conditions when using the Friedel-Crafts type sulfonylation reaction are described below. In the presence of an acid catalyst such as AlCl ₃ , FeCl ₃ , sulfuric acid, acidic zeolite, etc., a solvent such as halogenated hydrocarbon, nitrobenzene, sulfolane is used, and the reaction temperature is not particularly limited, but is usually −60 to 200 ° C., preferably -30 to 150 ° C. Moreover, reaction time is 0.5 to 1,000 hours normally, Preferably it is 1 to 200 hours.

The production method of the polymer represented by the general formula (6A) in the preferred production method of the present invention is not particularly limited, but is usually a high polymer containing —Y—P— (Y and P are as described above) as a repeating unit. The molecule is introduced with a sulfonic acid group by (i) sulfonation (in the present invention, sulfonation refers to a reaction of substituting the hydrogen atom of the group —H with SO ₃ H) to produce —Y (SO ₃ H) -P— (Y and P are as described above), and (ii) then, if necessary, can be prepared by converting sulfonic acid groups to —SO ₂ X ′ groups.

A known method can be used as a reaction method for sulfonation of the polymer. Usually, the polymer having no sulfonic acid group is treated with a sulfonated agent (anhydrous sulfuric acid, fuming) in the absence of a solvent or in the presence of a solvent. Sulfuric acid, chlorosulfonic acid, sulfuric acid, sodium hydrogen sulfite). Examples of the solvent include hydrocarbon solvents such as n-hexane, ether solvents such as tetrahydrofuran and dioxane, aprotic polar solvents such as dimethylacetamide, dimethylformamide, and dimethylsulfoxide, tetrachloroethane, dichloroethane, chloroform, And halogenated hydrocarbons such as methylene chloride. The reaction temperature is not particularly limited, but is usually −50 to 200 ° C., preferably −10 to 100 ° C. Moreover, reaction time is 0.5 to 1,000 hours normally, Preferably it is 1 to 200 hours.
As a method for converting a sulfonic acid group to a —SO ₂ X ′ group, a known method can be used. For example, when X ′ = Cl, it can be converted by reacting with phosphorus pentachloride, phosphorus trichloride, thionyl chloride or the like in the absence of a solvent or in the presence of a solvent. Although reaction temperature does not have a restriction | limiting in particular, Usually, -50-200 degreeC, Preferably it is 0-100 degreeC. Moreover, reaction time is 0.5 to 500 hours normally, Preferably it is 1 to 100 hours.

The aromatic residue contained in the main chain of the polymer electrolyte of the present invention preferably has at least one electron withdrawing group bonded thereto. The electron withdrawing group in this case is, for example, —CO—, —CONH—, — (CF ₂ ) _p — (wherein p is an integer of 1 to 10), —C (CF ₃ ) ₂ —, — Divalent groups such as COO—, —SO—, —SO—, —SO ₂ —; F, perfluoroalkyl, —CN, —NO ₂ , —COR, —COO R (R is selected from hydrogen, an alkyl group, a halogenated alkyl group, an aryl group, and a halogenated aryl group), —CONRR ′ (R ′ is the same group as the above R), —SO ₃ R, — And monovalent groups such as SOR and —SO ₂ R.

A structural example of the polymer electrolyte of the present invention is shown below. [In formula, Z shows the side chain represented by the said General formula (1), Although a sulfonic acid group is not described, it can be substituted by arbitrary aromatic rings. ]

Examples of particularly preferable structures as the polymer electrolyte of the present invention include polyether ether ketone (hereinafter abbreviated as PEEK) and / or polyether sulfone, and are represented by the following general formula (3) and / or the following general formula (4). And a polymer electrolyte having a side chain.

An outline of a typical production method of the polymer electrolyte of the present invention will be described below by taking the above particularly preferred structure as an example.
(I) PEEK is sulfonated with concentrated sulfuric acid to produce sulfonated PEEK;
(Ii) converting sulfonated PEEK to chlorosulfonyl PEEK with thionyl chloride;
(Iii) Reacting chlorosulfonyl PEEK and tristhiophenoxybenzene by Friedel-Crafts reaction to introduce a side chain into the PEEK main chain,
(Iv) Convert the side chain sulfide group to sulfone with hydrogen peroxide.

  The amount of sulfonic acid groups in the sulfonic acid group-containing polymer of the polymer electrolyte of the present invention is 0.2 to 5 milligram equivalent / g, preferably 0.3 to 4 milligram equivalent / g, more preferably 0.4 to 3 milligram equivalent / g. When the amount of sulfonic acid group is low, proton conductivity does not increase. On the other hand, when the amount of sulfonic acid group is high, hydrophilicity is improved, and depending on the structure, it becomes a water-soluble polymer. The amount of the sulfonic acid group can be adjusted by the reaction conditions (temperature, time) and the charged amount (composition).

The molecular weight of the polymer electrolyte of the present invention thus obtained before sulfonation or sulfonic acid precursor is 1,000 to 1,000,000, preferably 10,000 to 1,000,000 in terms of polystyrene-converted weight average molecular weight. More preferably, it is 20,000 to 800,000, particularly preferably 30,000 to 400,000. If it is less than 1000, the molded film is liable to break, and there is also a problem in strength properties. On the other hand, when it exceeds 1,000,000, there are problems such as insufficient solubility, high solution viscosity, and poor processability.
Next, the polymer electrolyte of the present invention comprises the sulfonic acid group-containing polymer. In addition to the sulfonic acid group-containing polymer, an inorganic acid such as sulfuric acid and phosphoric acid, an organic acid containing a carboxylic acid, an appropriate amount You may use water together.

In order to form the polymer electrolyte of the present invention into a film, for example, a casting method in which the sulfonic acid group-containing polymer of the present invention is dissolved in a solvent and then formed into a film by coating, a melt molding method, or the like can be mentioned. Here, examples of the solvent in the casting method include aprotic polar solvents such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, and dimethylsulfoxide, and alcohol solvents such as methanol.
The structure of the polymer electrolyte of the present invention can be confirmed by, for example, an infrared absorption spectrum or a nuclear magnetic resonance spectrum ( ¹ H-NMR, ¹³ C-NMR). The composition ratio can also be measured by elemental analysis, and the sulfonic acid content can be measured by neutralization titration.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. In addition, various measurement items in the examples were obtained as follows.
[Weight Average Molecular Weight] The number average molecular weight and weight average molecular weight of the precursor polymer before sulfonation were determined by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.
[Ion exchange capacity] The obtained polymer is sufficiently washed with water until it becomes neutral, dried, weighed in a predetermined amount, dissolved in a THF / water mixed solvent, phenolphthalein as an indicator, and NaOH. The ion exchange capacity (sulphonation equivalent) was determined from the neutralization point.
[Measurement of proton conductivity] A film sample having a thickness of 40 to 60 µm placed under 100% relative humidity was sandwiched between platinum electrodes, and complex impedance measurement was performed to calculate proton conductivity.

[Fenton test] A Fenton reagent was prepared so that the hydrogen peroxide concentration was 3% by weight and the ferric sulfate heptahydrate concentration was 20 ppm. 200 g of Fenton reagent was collected in a 250 cc polyethylene container, charged with a polymer electrolyte membrane cut to 3 cm × 4 cm and a film thickness of 40-60 μm, sealed, and then immersed in a constant temperature water bath at 50 ° C. for 6 hours. A test was conducted. After the Fenton test, the film was taken out, washed with ion-exchanged water, kept at 25 ° C. and 50% RH for 24 hours to adjust the humidity, and weighed. The weight retention rate in the Fenton test was calculated by the following mathematical formula.
Weight retention in Fenton test (%) = (film weight after Fenton test / film weight before Fenton test) × 100
Moreover, the ion exchange capacity retention rate was calculated | required by following Formula from the ion exchange capacity before and behind a Fenton test. Indicating that the higher the ion exchange capacity retention rate is low de-SO ₃ properties.
Ion exchange capacity retention rate (%) in Fenton test = (ion exchange capacity before Fenton test / ion exchange capacity after Fenton test) × 100

[Example 1]
(1) Synthesis of polymer electrolyte (1-1) Synthesis of sulfonated polyetheretherketone [formula (18) below]
Victrex PEEK450PF (10.0 g) was taken into a three-necked flask, and 100 g of 97% sulfuric acid was slowly poured and stirred with a mechanical stirrer equipped with a Teflon (registered trademark) blade, and stirred at room temperature for 96 h. . The stirred reaction solution was poured into ion exchange water to precipitate a polymer. The polymer was washed with water. The washed polymer was heated and dried under vacuum to obtain 10.8 g (88% yield) of sulfonated polyetheretherketone. ^{From 1} H-NMR, the sulfonation rate of this polymer was 83%.

(1-2) Synthesis of chlorosulfonyl polyetheretherketone [the following formula (19)] 4.27 g (10 mmol) of the sulfonated polyetheretherketone obtained in the above (1) was added to a thermometer, a dropping funnel, and a three-way cock. The flask was placed in a three-necked flask and purged with nitrogen. 50 ml of thionyl chloride was added dropwise with a dropping funnel and stirred at 70 ° C. for 3 hours. After stirring, excess thionyl chloride was distilled off under reduced pressure to obtain 4.45 g (yield 100%) of a reddish brown polymer. From the IR spectrum, it was confirmed that the sulfonic acid group was converted to a chlorosulfonyl group.

(1-3) Introduction reaction of 1,3,5-tristhiophenoxybenzene into chlorosulfonyl polyetheretherketone 4.45 g (10 mmol) of chlorosulfonylpolyetheretherketone obtained in (1-2) above was heated to a temperature. The total was placed in a three-necked flask equipped with a three-way cock with a dropping funnel, and the atmosphere was replaced with nitrogen. 200 ml of dehydrated and purified sulfolane (tetrahydrothiophene-1,1-dioxide) was poured and stirred at 90 ° C. to dissolve the polymer. To this solution, 20.1 g (50 mmol) of 1,3,5-tristhiophenoxybenzene was added and dissolved, and then 1.60 g (12 mmol) of aluminum chloride was added little by little. After all the aluminum chloride was added, the mixture was stirred at 90 ° C. for 40 hours. The stirred reaction mixture was poured into 1N aqueous hydrochloric acid solution to precipitate the product. This product is washed with water, then once with ethanol, then washed with a 2 wt% acetylacetone / toluene mixed solution at room temperature, and then repeatedly washed with the same mixed solution at 80 ° C. until the color of the solution disappears. It was. The product was vacuum-dried to obtain 6.02 g (yield 95%) of the desired polymer [the following formula (20)].

(1-4) Oxidation of Side Chain Sulfide 4.0 g of the polymer obtained in (1-3) above [formula (20)] was put into a 2 liter glass reaction vessel and acetic acid was added in 0.2 liter and 34%. A hydrogen peroxide aqueous solution (40 g) was added, the temperature was gradually raised while stirring, and the reaction was continued at 90 ° C. for 6 hours. After the reaction, the mixture was allowed to cool, and the polymer was separated by filtration, washed with water, and then vacuum dried to obtain 3.9 g (92%) of a desired polymer electrolyte [following formula (21)]. Structural analysis confirmed that the sulfide group was converted to a sulfone group. Since the ion exchange capacity calculated by neutralization titration of this polymer was 0.69 milligram equivalent / g, the introduction ratio of 1,3,5-tristhiophenoxybenzene per sulfonic acid was 53%.

(2) Evaluation as a polymer electrolyte membrane 10 g of the polymer electrolyte and NMP are placed in a flask so that the solid content of the polymer electrolyte is 10 wt%, and the polymer varnish is dissolved by heating at 80 ° C. with stirring. Got. Using a bar coater (for 200 μm), after coating on a PET thin film affixed on a glass substrate, the coating film was peeled off from the PET thin film by preliminarily drying at 80 ° C. for 0.5 hours with a dryer. The peeled coating film was dried at 100 ° C. for 3 hours in a vacuum dryer. Furthermore, the film from which NMP was removed was obtained by immersing in ion-exchanged water of 1,000 times the coating weight at room temperature for 2 days.
Next, various physical properties were measured after humidity control by allowing the film to stand in an environment of 25 ° C. and 50% RH for 24 hours. The results are shown in Table 2. The obtained polymer electrolyte film showed high resistance to the Fenton test and high proton conductivity. This result shows that the polymer electrolyte of the present invention has high oxidation resistance, high proton conductivity, and low de-SO ₃ property necessary as an electrolyte material for fuel cells.

[Example 2]
(1) Synthesis of polymer electrolyte The polymer electrolyte was prepared in the same manner as in (1-3) and (1-4) of Example 1 except that the reaction temperature was 90 ° C. and the stirring time was 80 h. Was synthesized. The ion exchange capacity was 0.44 milligram equivalent / g, and the 1,3,5-tristhiophenoxybenzene introduction rate per sulfonic acid group was 75%.
(2) Evaluation as a polymer electrolyte membrane Using the same method as in Example 1 except that the polymer electrolyte obtained above was used, a conditioned polymer electrolyte film was obtained, and various physical properties were measured. The results are shown in Table 2. The obtained polymer electrolyte film exhibited high resistance to the Fenton test, and exhibited high proton conductivity and low de-SO ₃ property.

[Example 3]
(1) Synthesis of polymer electrolyte Example 1 except that the amount of 1,3,5-tristhiophenoxybenzene added was 4.0 g (10 mmol), the reaction temperature was 80 ° C., and the stirring time was 20 h. A polymer electrolyte was synthesized by the same method as in (1-3) and (1-4). The ion exchange capacity was 1.9 mg equivalent / g, and the 1,3,5-tristhiophenoxybenzene introduction rate per sulfonic acid group was 10%.
(2) Evaluation as a polymer electrolyte membrane Using the same method as in Example 1 except that the polymer electrolyte obtained above was used, a conditioned polymer electrolyte film was obtained, and various physical properties were measured. The results are shown in Table 2. The obtained polymer electrolyte film exhibited high resistance to the Fenton test, and exhibited high proton conductivity and low de-SO ₃ property.

[Example 4]
(1) Synthesis of polymer electrolyte A sulfonated polyetheretherketone was synthesized in the same manner as in (1-1) of Example 1 except that it was stirred at room temperature for 24 hours. The sulfonation rate was 37%. Using this sulfonated polyetheretherketone, chlorosulfonyl polyetheretherketone was synthesized in the same manner as in Example 1-2 (1-2). (1-3) and (1-4) of Example 1 except that the amount of 1,3,5-tristhiophenoxybenzene added, the reaction temperature, and the stirring time were the same as in Example 3. The polymer electrolyte was synthesized by the same method as in (1). The ion exchange capacity was 0.47 milligram equivalent / g, and the 1,3,5-tristhiophenoxybenzene introduction rate per sulfonic acid group was 49%.
(2) Evaluation as a polymer electrolyte membrane Using the same method as in Example 1 except that the polymer electrolyte obtained above was used, a conditioned polymer electrolyte film was obtained, and various physical properties were measured. The results are shown in Table 2. The obtained polymer electrolyte film exhibited high resistance to the Fenton test, and exhibited high proton conductivity and low de-SO ₃ property.

[Comparative Example 1]
(1) Synthesis of polymer electrolyte The polymer electrolyte was prepared by the same method as in (1-3) and (1-4) of Example 1 except that the reaction temperature was 105 ° C. and the stirring time was 100 h. Was synthesized. The ion exchange capacity was 0.03 milligram equivalent / g, and the 1,3,5-tristhiophenoxybenzene introduction rate per sulfonic acid group was 89%.
(2) Evaluation as a polymer electrolyte membrane Using the same method as in Example 1 except that the polymer electrolyte obtained above was used, a conditioned polymer electrolyte film was obtained, and various physical properties were measured. The results are shown in Table 2. This result shows that proton conductivity is low when the number of sulfonic acid groups is as small as 0.6 mol% even when repeating structural units are present.

[Comparative Example 2]
The sulfonated polyetheretherketone [Formula (18)] synthesized as an intermediate in Example 1 was evaluated as a polymer electrolyte membrane. The results are shown in Table 2. When this result is compared with Example 3, it turns out that the polymer electrolyte of this invention shows high proton conductivity and high oxidation stability by having a repeating structure (1A).

[Example 5]
(1) Synthesis of polyelectrolyte (1-1) Introduction reaction of diphenyl sulfide into chlorosulfonyl polyetheretherketone Using 4.4 g (40 mmol) of diphenyl sulfide instead of 1,3,5-tristhiophenoxybenzene The target product [formula (22)] was obtained in a yield of 86% by using the same method as in (1-3) of Example 1. The structure was confirmed by NMR and IR spectra.

(1-2) Oxidation of Side Chain Sulfide The target product [Formula (23) was used in the same manner as in (1-4) of Example 1 except that the polymer [Formula (22)] obtained above was used. Was obtained in a yield of 99%. The structure was confirmed by NMR and IR spectra. The ion exchange capacity was 1.2 milligram equivalent / g, and the introduction rate of diphenyl sulfide per sulfonic acid group was 38%.

(2) Evaluation as a polymer electrolyte membrane Using the same method as in Example 1 except that the polymer electrolyte obtained above was used, a conditioned polymer electrolyte film was obtained, and various physical properties were measured. The results are shown in Table 2. The obtained polymer electrolyte film exhibited high resistance to the Fenton test, and exhibited high proton conductivity and low de-SO ₃ property.

[Comparative Example 3]
A sulfone oxide of polymer B represented by the following formula (24) was obtained by the method described in Reference Example 2 of JP-A-2003-201403, and this was evaluated as a polymer electrolyte membrane. The results are shown in Table 2.

（但し、ｊ／ｋ＝６．９であり、ｎは５．５である。）

(However, j / k = 6.9 and n is 5.5.)

  The present invention is useful as an electrolyte and a binder for a polymer electrolyte fuel cell.

Claims (15)

A polymer electrolyte for fuel cells, comprising at least a repeating unit represented by the following general formula (1A) and a repeating unit represented by the following general formula (1B).

[Y represents a (k + 2) -valent aromatic residue, Y ′ represents a (t + 2) -valent aromatic residue, and P and P ′ represent —CO—, —O—, —S—, —SO—, _{-SO 2 -, - CONH -,} - C (CF 3) 2 -, a single bond, _-CR 2 - (R is a hydrogen atom, an alkyl group or an aryl group) a linking group selected from, a same And k and t are each independently an integer of 1 to 4, and the side chain portion Z in the formula is represented by the following general formula (2).
^{Z = - (X 1 Ar 1} (B 1)) - (X 2 Ar 2 (B 2)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar ⁿ ) (2)
^{B 1 ~B n-1} in the general formula (2) in means a branched chain in the side chain moiety Z, is expressed by the following equation.
B ¹ = - ^{[(X 2 Ar 2 (B 2} )) - (X 3 Ar 3 (B 3)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X ⁿ Ar ⁿ )] _f

B ² = - ^{[(X 3 Ar 3 (B 3} )) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar n) ] _f
・
・
・
B ^n-1 = - ^[X n Ar ^n] _f
In the general formula (2), each n is independently an integer of 1 to 5,
f is each independently an integer of 0 to 5;
Ar ¹ to Ar ⁿ is an aromatic residue independently,
X ^{1 to} X ⁿ are each independently —CO—, —CONH—, — (CF ₂ ) _p — (p is an integer of 1 to 10), —C (CF ₃ ) ₂ —, —COO—, —SO—. , —SO ₂ —.
In Z, a —SO ₃ H group is not introduced. ] _2. The fuel cell according to claim 1, wherein P and P ′ are a linking group selected from —CO—, —O—, —S—, —SO ₂ —, —C (CF ₃ ) ₂ —. Polymer electrolyte.   3. The polymer electrolyte for fuel cells according to claim 1, wherein k is an integer of 1 to 2, and f is an integer of 0 to 2 each independently.   4. The polymer electrolyte for fuel cells according to claim 3, wherein at least one f is 1 or 2.   4. The polymer electrolyte for a fuel cell according to claim 3, wherein f is 0 or 1, and at least one f is 1. The polymer electrolyte for a fuel cell according to claim 3, wherein Z is the following formula (3) (wherein the phenyl group and the phenylene group may be substituted with an electron withdrawing group).

The polymer electrolyte for a fuel cell according to claim 3, wherein Z is the following formula (4) (wherein the phenyl group and the phenylene group may be substituted with an electron withdrawing group).

  2. The method for producing a polymer electrolyte for a fuel cell according to claim 1, wherein a side chain introducing agent is reacted with the polymer. The high fuel cell fuel cell according to claim 8, wherein a polymer having a repeating unit represented by the following general formula (6A) is reacted with a side chain introducing agent represented by the following general formula (6B). A method for producing a molecular electrolyte.

[Y and P are the same as those described in the general formula (1A), and X ′ is selected from a halogen atom, OR (R is a hydrogen atom, an alkyl group, or an aryl group), an alkali metal, and an alkaline earth metal. K ′ is an integer of 1 to 4.
Z ′ is represented by the following general formula (5).
^{Z '= - (Ar 1 (} B 1)) - (X 2 Ar 2 (B 2)) - ··· - (X n-1 Ar n-1 (B n-1)) - (X n Ar n (5)
In the general formula (5), Ar ^{1 to} Ar ⁿ , B ^{1 to} B ⁿ⁻¹ , n are the same as those described in the general formula (1), and X ^{1 to} X ⁿ are —S—. , —CH ₂ —, —CX ″ ₂ — (X ″ is a non-fluorine halogen atom), —C (OR ″) ₂ — (R ″ is an alkyl group), —C (OR ″) ₂ —O— (R ″ Is an alkyl group), a linking group precursor selected from — (C (OR ″) ₂ ) _p — (R ″ is an alkyl group), and a linking group described in the general formula (1). ] When the polymer having the repeating unit represented by the general formula (6A) is reacted with the side chain introducing agent represented by the general formula (6B), X ^{1 to} X ⁿ of the side chain introducing agent are electron donations. After the reaction with the polymer, the linking group precursor is converted into an electron-withdrawing linking group, and is represented by the above general formulas (1A) and (1B). The method for producing a polymer electrolyte for a fuel cell according to claim 9, wherein the polymer electrolyte for a fuel cell having a repeating unit is obtained.   A polymer for a fuel cell having a repeating unit represented by the above general formulas (1A) and (1B) by using a sulfonic acid precursor instead of a sulfonic acid group and then converting the sulfonic acid precursor into a sulfonic acid. The method for producing a polymer electrolyte for a fuel cell according to any one of claims 8 to 10, wherein an electrolyte is obtained.   A polymer electrolyte membrane for a fuel cell, comprising the polymer electrolyte according to claim 1.   A polymer electrolyte membrane for a fuel cell, comprising the polymer electrolyte produced by the method according to claim 8.   A fuel cell using the polymer electrolyte according to claim 1. A fuel cell using the polymer electrolyte produced by the method according to claim 8.