JP2018065945A - Method for producing polymer electrolyte - Google Patents

Abstract

[PROBLEMS] To use an expensive zero-valent nickel complex in connecting an aromatic hydrophilic segment having a sulfonic acid group and an aromatic hydrophobic segment having no sulfonic acid group by a direct bond of an aromatic ring. And a method for obtaining a high molecular weight polyelectrolyte in a high yield. SOLUTION: A hydrophilic segment precursor containing an aromatic ring containing a sulfonic acid group and having two or more halogen atoms as a main chain, and an aromatic having substantially no sulfonic acid group and having two or more halogen atoms as a main chain. When producing from a hydrophobic segment precursor containing a ring, a complex composed of a zerovalent nickel compound and a ligand is reduced to 0.5% of the sum of halogen atoms contained in the hydrophilic segment precursor and the hydrophobic segment precursor. Use -0.75 molar equivalents, adjust the ratio of zero-valent nickel compound and ligand so that the nickel atom has an electron configuration satisfying the 18-electron rule, and remove oxygen dissolved in the reaction system Process. [Selection figure] None

Description

 The present invention relates to a method for producing a polymer electrolyte membrane suitable for a polymer electrolyte fuel cell.

  In recent years, development of highly efficient and clean energy sources has been demanded from the viewpoint of environmental problems such as global warming. Fuel cells are attracting attention as one candidate for that requirement. A fuel cell directly supplies power by supplying a fuel such as hydrogen gas or methanol and an oxidant such as oxygen to electrodes separated by an electrolyte, while oxidizing the fuel on the one hand and reducing the oxidant on the other. is there. Among the fuel cell materials described above, one of the most important materials is an electrolyte. Various types of electrolyte membranes have been developed so far to separate the electrolyte fuel and oxidant, and in recent years, the electrolyte membrane is composed of a polymer compound containing a proton conductive functional group such as a sulfonic acid group. The development of polymer electrolytes is thriving. In addition to the solid polymer fuel cell, such a polymer electrolyte is used as a raw material for electrochemical elements such as a humidity sensor, a gas sensor, and an electrochromic display element. Among these polymer electrolyte utilization methods, in particular, polymer electrolyte fuel cells are expected as one of the pillars of new energy technology. For example, a polymer electrolyte fuel cell using an electrolyte membrane made of a polymer compound having a proton-conducting functional group has features such as operation at a low temperature and reduction in size and weight. It has already been put to practical use in applications such as cogeneration systems for automobiles, and its application to consumer small portable devices and emergency power supplies is under consideration. As an electrolyte membrane used in a polymer electrolyte fuel cell, there is a polystyrene-based cation exchange membrane developed in the 1950s. However, the fuel cell has poor stability under a fuel cell operating environment and has a sufficient lifetime. Has not yet been manufactured. On the other hand, as an electrolyte membrane having practical stability, a perfluorocarbon sulfonic acid membrane represented by Nafion (registered trademark) has been widely studied. Perfluorocarbon sulfonic acid membranes are said to have high proton conductivity and excellent chemical stability such as acid resistance and oxidation resistance. However, Nafion (registered trademark) has a drawback that it is very expensive because it uses high raw materials and undergoes complicated manufacturing processes. In addition, it has been pointed out that it is deteriorated by hydrogen peroxide generated by the electrode reaction and by-product hydroxy radical. Furthermore, due to its structure, there is a limit to the introduction of sulfonic acid groups that are proton conducting groups.

  Against this background, the development of hydrocarbon electrolyte membranes has come to be expected. The reason for this is that the hydrocarbon-based electrolyte membrane is easy to have a variety of chemical structures, the range of introduction of proton conducting groups such as sulfonic acid groups can be adjusted widely, and it is relatively easy to combine with other materials. This is because there is a characteristic of being.

 In recent years, among the hydrocarbon electrolytes, a block copolymer comprising an aromatic hydrophilic segment having a sulfonic acid group and an aromatic hydrophobic segment having no sulfonic acid group has undergone microphase separation. It has been reported that high proton conductivity required for polymer electrolyte membranes can be obtained due to the formation of a developed proton pathway that exhibits morphology. In particular, polymer electrolytes in which a hydrophilic segment and a hydrophobic segment are connected by a direct bond of an aromatic ring have no hetero bond such as an ether bond or a sulfide bond around the sulfonic acid group. Is characterized by high resistance to peroxides and the like (Patent Document 1). As a method of connecting a hydrophilic segment and a hydrophobic segment by a direct bond of an aromatic ring, a reaction in which a hydrophilic segment precursor having a halogen and a hydrophobic segment precursor having a halogen are coupled using a zero-valent nickel complex. Is preferably used (Patent Documents 1, 2, and 3).

JP2012-229418A JP 2007-177197 A JP 2008-88420 A

  However, in the prior art, the zero-valent nickel complex is generally expensive, and is sensitive to moisture and oxygen, so it is easily decomposed during handling and in the reaction system, and the molecular weight and yield of the polymer electrolyte are It was not high enough.

  In the present invention, when an aromatic hydrophilic segment having a sulfonic acid group and an aromatic hydrophobic segment not having a sulfonic acid group are linked by a direct bond of an aromatic ring, an expensive zero-valent nickel complex Provided is a method for reducing the amount used and obtaining a high molecular weight polymer electrolyte in a high yield.

  The method for producing a polymer electrolyte of the present invention is a method for producing a polymer electrolyte composed of a hydrophilic segment and a hydrophobic segment, and comprises an aromatic ring having a sulfonic acid group and having two or more halogen atoms as a main chain. In the production from the hydrophilic segment precursor containing and the hydrophobic segment precursor containing an aromatic ring having two or more halogen atoms as a main chain substantially not containing a sulfonic acid group, a zero-valent nickel compound and a ligand are used. The complex is used in an amount of 0.5 molar equivalent to 0.75 molar equivalent relative to the sum of halogen atoms contained in the hydrophilic segment precursor and the hydrophobic segment precursor, and the complex is a nickel atom. Includes adjusting the use ratio of the zero-valent nickel compound and the ligand so that the electron configuration satisfies the 18-electron rule, and removing oxygen dissolved in the reaction system And wherein the door.

  According to the present invention, in a method for producing a polymer electrolyte in which a hydrophilic segment having a sulfonic acid group and a hydrophobic segment not having a sulfonic acid group are connected by a direct bond of an aromatic ring, an expensive zero-valent nickel complex is used. Thus, a high molecular weight polymer electrolyte can be obtained in a high yield.

As a result of intensive studies, the inventors of the present invention have adjusted the ratio of nickel atom and ligand in the zero-valent nickel complex to a suitable value and removed dissolved oxygen from the reaction system, thereby obtaining zero-valent nickel. The inventors have found that the intended high molecular weight electrolyte can be obtained in high yield without using an excessive amount of the complex, and the present invention has been completed.
<1. Production method of polymer electrolyte>
The zerovalent nickel complex in the present invention is for coupling an aromatic compound in which a halogen is directly bonded to an aromatic ring.

  A zero-valent nickel complex is a ligand in which a zero-valent nickel metal is coordinated. The stability of the transition metal complex is most stable when the sum of the number of d-electrons of the metal and the number of electrons donated from the ligand is 18 which is the same as the inert gas (so-called 18-electron rule). Rule of thumb). In the case of a zero-valent nickel complex, since nickel has 10 d electrons, it is most stable when 8 electrons (unshared electrons) are supplied from the ligand. If the ligand has one lone pair, when 4 molecules are coordinated, and if the ligand has two lone pairs, when two molecules are coordinated, The 18 electron rule will be satisfied.

  Thus, when a nickel complex that satisfies the most chemically stable 18-electron rule is used, the coupling reaction of the hydrophilic segment precursor and the hydrophobic segment precursor in the present invention proceeds most efficiently, A high molecular weight polymer electrolyte is obtained in high yield.

  Zero-valent nickel complexes are usually prepared by adding a ligand to a suitable zero-valent nickel compound. Examples of the zero-valent nickel compound that serves as such a precursor include nickel tetracarbonyl, bis- (1,5-cyclooctadiene) nickel, tetrakistriphenylphosphine nickel, and the like. (1,5-cyclooctadiene) nickel is preferred.

  The ligand is not particularly limited, and examples thereof include phosphine compounds, amine compounds, sulfide compounds, pyridine compounds, and thiophene compounds.

  Examples of the phosphine compound include trimethylphosphine, tributylphosphine, triphenylphosphine, tris (o-toluyl) phosphine, and the like.

  Examples of amine compounds include triethylamine, tributylamine, triphenylamine, tetramethylethylenediamine, pentamethyldiethylenetriamine, and the like.

  Examples of the sulfide compound include dimethyl sulfide, diethyl sulfide, dibutyl sulfide, diphenyl sulfide and the like.

  Examples of pyridine compounds include pyridine, 2-methylpyridine, 2,6-dimethylpyridine, 3-methylpyridine, 2,2'-bipyridyl and the like.

  Examples of thiophene compounds include thiophene, 2-methylthiophene, 2,5-dimethylthiophene, 2,2'-dithiophene.

  Among these, 2,2'-bipyridyl is preferable from the viewpoint of availability and high reactivity when a zero-valent nickel complex is obtained.

  The amount of these ligands used may be an amount satisfying the 18-electron rule with respect to the precursor zero-valent nickel compound as described above. When 2,2'-bipyridyl is used, it is preferably used in the range of 2 to 3 molar equivalents relative to zero-valent nickel. If it is less than 2 molar equivalents, the 18 electron rule is not satisfied, so more nickel complex is required for the coupling reaction, and if it exceeds 3 molar equivalents, the ligand is used unnecessarily in excess. It is uneconomical.

  In the present invention, using a zerovalent nickel complex, a hydrophilic segment precursor containing an aromatic ring containing a sulfonic acid group and having two or more halogen atoms as a main chain, and substantially free of a sulfonic acid group, A polymer segment is obtained as a copolymer by coupling a hydrophobic segment precursor containing an aromatic ring having two or more halogen atoms as a main chain. Since one molecule of the zerovalent nickel complex reacts with two halogen atoms, theoretically, it is sufficient to use 1 mole per 2 moles of halogen atoms in the reaction system. A suitable amount of the zerovalent nickel complex is 0.5 mole equivalent or more and 0.75 mole equivalent or less with respect to the sum of the halogen atom of the hydrophilic segment precursor and the halogen atom of the hydrophobic segment precursor. If it is less than 0.5 molar equivalent, the coupling reaction does not proceed sufficiently, the yield decreases, and the molecular weight of the polymer electrolyte decreases. If it exceeds 0.75 molar equivalent, it will be used unnecessarily in excess, which is uneconomical.

  In the present invention, as described above, by adding a ligand to the zerovalent nickel compound in an amount that satisfies the 18-electron rule, the zerovalent nickel complex is stabilized. This is economically advantageous.

  The present invention further includes a step of removing dissolved oxygen from the reaction system. By adding this step, the stability of the zero-valent nickel complex during the reaction can be further increased, and as a result, a higher molecular weight copolymer can be obtained in a high yield.

  The method for removing dissolved oxygen is not particularly limited, but a method of bubbling nitrogen gas into the reaction system is simple and preferable. Dissolved oxygen can be removed by inserting a suitable tube into the reaction system, sending nitrogen and bubbling. The amount of nitrogen gas bubbling may be adjusted to be 0.1 to 10 times the volume of the reaction mixture per minute. If it is less than 0.1 times, it takes a long time to remove oxygen, and if it exceeds 10 times, bubbling becomes too intense and splashes are generated in the reaction vessel.

  Nitrogen bubbling is preferably performed before adding the zero-valent nickel compound in order to avoid contact between the zero-valent nickel complex and dissolved oxygen as much as possible. That is, it is preferable to perform bubbling in a state where components other than the zerovalent nickel compound including the reaction solvent are charged, and then add the zerovalent nickel compound.

  In this case, the bubbling time is not particularly limited, but is preferably 1 minute to 1 hour, and more preferably 5 minutes to 30 minutes. If it is shorter than 1 minute, removal of dissolved oxygen is insufficient, and if it is longer than 1 hour, the total time required for the reaction becomes long, and productivity is lowered. Nitrogen bubbling may be stopped immediately before the addition of the zero-valent nickel compound, or may be continued after the addition until the reaction is completed.

  In the present invention, a hydrophilic segment precursor containing an aromatic ring containing a sulfonic acid group and having two or more halogen atoms as a main chain, and two halogen atoms as a main chain substantially not containing a sulfonic acid group The hydrophobic segment precursor containing the aromatic ring having the above is coupled using the zero-valent nickel complex to obtain a polymer electrolyte.

  Such a hydrophilic segment precursor is not particularly limited, and various types can be used. From the availability of raw materials and ease of synthesis, any of the following general formula group 1 (Chemical formula 1) is used. Those having the structure represented are preferred.

（式中、ｍは１〜４の整数、ｋ、ｌは０〜４の整数を表し、ｋ＋ｌは１以上の整数である。ｐは０〜１０の整数、ｑは０〜１０の整数、ｒは１〜４の整数を表す。Ｈａｌはハロゲンを、Ｘは、−ＣＯ−、−ＳＯ₂−、−Ｃ（ＣＦ₃）₂−からなる群より選ばれた少なくとも１種の構造を表す。Ｙは、−ＣＯ−、−ＳＯ₂−、−ＳＯ−、−ＣＯＮＨ−、−ＣＯＯ−、−（ＣＦ₂）_t−（ｔは１〜１０の整数）、−Ｃ（ＣＦ₃）₂−からなる群より選ばれた少なくとも１種の構造を表し、Ｚは直接結合又は、−（ＣＨ₂）_o−（ｏは１〜１０の整数）、−Ｃ（ＣＨ₃）₂−、−Ｏ−、−Ｓ−からなる群より選ばれた少なくとも１種の構造を表す。Ａｒ¹は、−ＳＯ₃Ｈ又はＯ（ＣＨ₂）_sＳＯ₃Ｈ（ｓは１〜１２の整数）で表される置換基を有する芳香族基を表す。）

(In the formula, m represents an integer of 1 to 4, k and l represent an integer of 0 to 4, k + 1 represents an integer of 1 or more, p represents an integer of 0 to 10, q represents an integer of 0 to 10, r Represents an integer of 1 to 4. Hal represents halogen, and X represents at least one structure selected from the group consisting of —CO—, —SO ₂ —, and —C (CF ₃ ) ₂ —. Consists of —CO—, —SO ₂ —, —SO—, —CONH—, —COO—, — (CF ₂ ) _t — (t is an integer of 1 to 10), —C (CF ₃ ) ₂ —. Represents at least one structure selected from the group, Z is a direct bond, or — (CH ₂ ) _o — (where o is an integer of 1 to 10), —C (CH ₃ ) ₂ —, —O—, — Represents at least one structure selected from the group consisting of S—, Ar ¹ is a substituent represented by —SO ₃ H or O (CH ₂ ) _s SO ₃ H (s is an integer of 1 to 12); Have It represents an aromatic group.)

  Here, the precursor of a hydrophilic segment refers to a compound having a halogen directly bonded to an aromatic ring, which becomes a hydrophilic segment by a copolymerization reaction with a precursor of a hydrophobic segment described later. A polymer electrolyte having a hydrophilic segment and a hydrophobic segment is formed by copolymerizing the hydrophilic segment precursor and the hydrophobic segment precursor by a coupling reaction using a zerovalent nickel complex.

  By using a copolymer consisting of a hydrophilic segment and a hydrophobic segment as described above, the morphology of the polymer electrolyte membrane becomes a microphase separation structure, and the hydrophilic segment forms a continuous proton conduction path. Proton conductivity, particularly proton conductivity under low humidification is improved.

  Since the hydrophilic segment has a sulfonic acid group, the proton conductivity of the polymer electrolyte is expressed, and the main chain of the hydrophilic segment is mainly composed of an aromatic ring, so that the polymer electrolyte has heat resistance and chemical durability. It will be excellent.

  Examples of the sulfonic acid group in the present invention include a sulfonic acid group, a sulfonate group, a sulfonic acid ester group, and the like. That is, the sulfonic acid group may be a salt such as sodium or potassium, or may be protected with an ester group such as neopentyl ester, methyl ester or propyl ester. In particular, during the synthesis of the polymer electrolyte, it is often preferable to have a protective group such as a salt or an ester group, but when the polymer electrolyte is used as, for example, an electrolyte membrane of a fuel cell, It is often used by being converted into a sulfonic acid group by immersing in an aqueous solution of an inorganic acid. Therefore, in the present invention, the sulfonic acid group includes a group having a protective group such as a salt or an ester as long as it is a group that easily becomes a sulfonic acid group.

  The amount of the sulfonic acid group is preferably 1 to 6 and more preferably 1 to 4 per precursor unit forming the hydrophilic segment. When the amount of the sulfonic acid group is larger than 6, the water solubility of the hydrophilic segment increases, and the handling during synthesis tends to be difficult. If it is less than one, sufficient proton conductivity tends to be difficult to develop.

  As the hydrophilic segment precursor exemplified above, a commercially available product can be used as it is, or it can be obtained by sulfonating a corresponding aromatic compound with a sulfonating agent. Examples of the sulfonating agent include chlorosulfonic acid, sulfuric anhydride, fuming sulfuric acid, sulfuric acid, acetyl sulfuric acid and the like. Chlorosulfonic acid and fuming sulfuric acid are preferable because they have appropriate reactivity.

  In the sulfonation reaction, a solvent may or may not be used. In the case of using a solvent, the solvent is not particularly limited as long as it is inert to the sulfonated agent, and examples thereof include hydrocarbon solvents and halogenated hydrocarbon solvents. Examples of the hydrocarbon solvent include saturated aliphatic hydrocarbons, and linear or branched hydrocarbons having 5 to 15 carbon atoms are particularly preferable. From the viewpoint of solubility, pentane, hexane, heptane, octane and decane are preferable. More preferred. Examples of halogenated hydrocarbons include halogenated saturated aliphatic hydrocarbons and halogenated aromatic hydrocarbons. Examples of the halogenated saturated aliphatic hydrocarbon include monochloromethane, dichloromethane, trichloromethane, tetrachloromethane, monochloroethane, dichloroethane, trichloroethane, tetrachloroethane, and the like. Dichloromethane is preferable because of easy handling. Examples of the halogenated aromatic hydrocarbon include chlorobenzene, dichlorobenzene, trichlorobenzene, and the like, and chlorobenzene is preferable because of easy handling.

  The reaction temperature of the sulfonation process may be set as appropriate according to the reaction, specifically, it may be set to −80 ° C. to 200 ° C. which is the optimum use range of the sulfonation agent, more preferably −50 ° C. to 150 ° C, more preferably -20 ° C to 130 ° C. If the temperature is lower than −80 ° C., the reaction is slow, and the intended sulfonation tends not to proceed to 100%, and if the temperature is higher than 200 ° C., side reaction tends to occur.

  The reaction time of the sulfonation step can be appropriately selected depending on the structure of the aromatic compound to be sulfonated, but it is usually sufficient if it is within the range of about 1 minute to 50 hours. When it is shorter than 1 minute, uniform sulfonation tends not to proceed, and when it is longer than 50 hours, side reaction tends to occur.

  The addition amount of the sulfonated agent in the sulfonation process is preferably 1 equivalent to 50 equivalents when the total amount of the sulfonated aromatic compound is 1 equivalent. When the amount is less than 1 equivalent, the sulfonated site tends to be non-uniform, while when it exceeds 50 equivalents, the sulfonated aromatic compound main chain tends to be cleaved.

  The concentration of the aromatic compound in the sulfonating step is not particularly limited as long as the reaction proceeds uniformly when brought into contact with the sulfonating agent, but the aromatic compound does not cause side reactions such as low molecular weight, and the solvent. From the viewpoint of cost advantage due to the suppression of the amount, it is preferably 1 to 30% by weight based on the weight of the whole compound used in the sulfonation reaction.

  The ion exchange capacity of only the hydrophilic segment (hereinafter, the ion exchange capacity may be referred to as IEC) can be set to high IEC as a polymer electrolyte membrane, and can exhibit high proton conductivity under low humidification. 4.0 meq. / G or more is preferable. The IEC of the hydrophilic segment is obtained by calculating by NMR analysis or by dividing the IEC of the polymer electrolyte (which can be easily obtained by a conventionally known method such as titration) by the weight ratio of the hydrophilic segment. However, in the present invention, the latter method is used. That is, the IEC of the hydrophilic segment is obtained by dividing the IEC of the polymer electrolyte obtained in the same manner as the IEC measurement method of the polymer electrolyte membrane described in the examples by the weight ratio of the hydrophilic segment. meq. / G means milliequivalent / g. An example of the specific structure of the hydrophilic segment precursor thus obtained is represented by the following chemical formula (Formula 2).

（上記式中、Ｈａｌはハロゲンを表す）

(In the above formula, Hal represents halogen)

  In addition, examples of the halogen atom include fluorine, chlorine, bromine and iodine, but chlorine, bromine and iodine are preferable from the viewpoint of ease of coupling reaction using a zerovalent nickel complex, and further, availability of raw materials. To chlorine is preferred.

  The hydrophobic segment of the polymer electrolyte used in the present invention has substantially no sulfonic acid group. Thereby, the phase separation from the hydrophilic segment is clarified, the proton conductivity of the polymer electrolyte under low humidification is improved, and the strength of the polymer electrolyte is improved. The hydrophobic segment preferably has no sulfonic acid group introduced therein, but may be relatively hydrophobic with respect to the hydrophilic segment, and the number of sulfonic acid groups per repeating unit may be that of the hydrophilic segment. It may be 1/10 or less. That is, “substantially has no sulfonic acid group” means that the hydrophobic segment has no sulfonic acid group or the number of sulfonic acid groups per repeating unit in the hydrophobic segment is It means 1/10 or less of the number of sulfonic acid groups per repeating unit.

  The hydrophobic segment is preferably a polyimide-based, polybenzimidazole-based, polyether-based, polyphenylene-based, etc. structure having a main chain mainly composed of an aromatic ring from the point of heat resistance, A polyphenylene type is more preferable from the viewpoint of ease of synthesis. Here, “the main chain is mainly composed of an aromatic ring” means that the molecular weight of the portion other than the main chain linking group (ether group, sulfone group, ketone group, sulfide group, etc.) in the hydrophobic segment is 100%. , Which means that 70% or more of them are composed of aromatic rings. As the precursor of such a hydrophobic segment, those having the structure described in the following general formula group (2) are preferable from the viewpoint of availability of raw materials and ease of synthesis.

  Here, the precursor of the hydrophobic segment is represented by the following general formula group (2) (formula 3) having a halogen directly bonded to an aromatic ring, which becomes a hydrophobic segment by a copolymerization reaction with the hydrophilic segment precursor. Refers to the compound.

（式中、Ａｒは、２価の芳香族基、Ｈａｌはハロゲンを表す。ｎは1〜５０の整数。ａ,ｂ,ｃは０〜５０の整数。但し、２≦ａ＋ｂ＋ｃ≦５０を満足する。）

(In the formula, Ar represents a divalent aromatic group, Hal represents halogen. N represents an integer of 1 to 50. a, b, and c represent integers of 0 to 50. However, 2 ≦ a + b + c ≦ 50 is satisfied. .)

  In addition, when the repeating unit of the said General formula group (2) (Formula 3) is repeated in multiple times, several Ar may be mutually the same or different. Preferred examples of the divalent aromatic group for Ar include a group represented by the following formula (3) (Chemical formula 4).

  Moreover, the divalent aromatic group of Ar may have a substituent. Examples of the substituent include an alkyl group having 1 to 6 carbon atoms (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, etc.), and an alkoxy group having 1 to 6 carbon atoms (methoxy group, ethoxy group). Group, propoxy group, butoxy group, pentyloxy group, hexyloxy group, etc.), phenyl group, cyano group and the like. One or more substituents may be included.

  Examples of the monomer constituting the hydrophobic segment include monomers that can constitute the structure of the above general formula group (2) (Chemical Formula 3), and specifically, represented by the following formula (Chemical Formula 5). A monomer etc. are mentioned preferably.

  Moreover, what has a thiol group instead of the hydroxyl group of the compound which has said phenolic hydroxyl group can be used suitably as a monomer. In order to synthesize the precursor of the hydrophobic segment using the above monomer, a known method may be used. For example, a method of polycondensing a monomer having a nucleophilic substituent such as a hydroxyl group or a thiol group with another monomer having halogen as a leaving group can be mentioned.

  Since the hydrophobic segment precursor needs to be halogenated at the terminal, it is necessary to use an excess of a monomer having halogen. The molecular weight of the hydrophobic segment precursor can be adjusted by adjusting the charging ratio of the monomer having halogen and the monomer having a nucleophilic substituent such as a hydroxyl group.

In order to accelerate the reaction, a basic compound is usually used. As the basic compound, an alkali metal salt, an alkaline earth metal salt, or the like is suitably used. For example, LiOH, NaOH, KOH, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , LiHCO ₃ , NaHCO ₃ , KHCO _{3 and the} like. The polycondensation reaction can be performed in a molten state without using a solvent, but is preferably performed in a suitable solvent. As the solvent, those that dissolve both the reactant (monomer) and the polymer to be produced are preferable. Specific examples include aromatic hydrocarbon solvents, halogen solvents, ether solvents, ketone solvents, amide solvents. , Sulfone-based solvents, sulfoxide-based solvents, and the like. Among them, N, N-dimethylformamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone are mentioned in terms of solubility. An amide solvent such as halobenzene, a halogen solvent such as dichlorobenzene and trichlorobenzene, and a sulfoxide solvent such as dimethyl sulfoxide are preferable. These may be used alone or in combination of two or more. The reaction temperature of the polycondensation may be appropriately set according to the polymerization reaction, and is 20 ° C to 250 ° C, more preferably 40 to 200 ° C. Even within this temperature range, if the temperature is low, the reaction rate is slow, and if it is too high, the main chain may be cleaved. In order to promote the reaction, it is preferable to discharge by-product water out of the system. In that case, a method of adding a small amount of toluene or the like as a cosolvent and performing azeotropic dehydration is used.

  The molecular weight of the hydrophobic segment precursor varies depending on its chemical structure and ease of synthesis, but the number average molecular weight is preferably 700 to 30,000 g / mol, more preferably 2000 to 10,000 g / mol. If it is less than 700 g / mol, the strength of the polymer electrolyte membrane tends to be insufficient, and if it is more than 30,000 g / mol, synthesis tends to be difficult due to problems such as solubility.

  A polymer electrolyte can be produced by reacting a hydrophilic segment precursor and a hydrophobic segment precursor in the presence of a zero-valent nickel complex. The reaction is preferably carried out in a suitable solvent. As the solvent, those that dissolve the reactant and the polymer electrolyte to be produced are preferable. Specific examples include aromatic hydrocarbon solvents, halogen solvents, ether solvents, ketone solvents, amide solvents, sulfone solvents. And sulfoxide solvents, among others, N, N-dimethylformamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N-methyl-2 are considered from the solubility of the polymer electrolyte produced. An amide solvent such as pyrrolidone, a halogen solvent such as dichlorobenzene and trichlorobenzene, and a sulfoxide solvent such as dimethyl sulfoxide are preferable. These may be used alone or in combination of two or more. What is necessary is just to set reaction temperature suitably, and is 20 to 200 degreeC, More preferably, it is 40 to 150 degreeC. If it is lower than 20 ° C, the reaction rate is slow, and if it is higher than 200 ° C, the main chain may be cleaved.

  Since the zerovalent nickel complex is unstable in water, the reaction system is preferably dehydrated. In addition to using a previously dehydrated solvent as a raw material, azeotropic dehydration using an azeotropic solvent such as toluene before addition of the zerovalent nickel compound is easy to operate and is preferably used. The reaction is preferably performed in an inert gas atmosphere.

  The time required for the reaction is not particularly limited, but is preferably 10 minutes to 10 hours, and more preferably 30 minutes to 3 hours. If it is shorter than 10 minutes, the reaction may not be completed, and if it is longer than 10 hours, productivity is unnecessarily lowered.

  To specifically illustrate the preferred embodiment of the production method of the present invention, first, a hydrophilic segment precursor, a hydrophobic segment precursor, a ligand, and a solvent (including a solvent for azeotropic dehydration) are charged. , Azeotropic dehydration of the system by heating. Thereafter, nitrogen bubbling is performed to remove dissolved oxygen, and then a zero-valent nickel compound is added to perform a coupling reaction to obtain a polymer electrolyte.

  The molecular weight of the polyelectrolyte thus obtained is preferably 10,000 to 300,000 g / mol in terms of number average molecular weight, and 30,000 to 150,000 g / mol from the balance of ease of synthesis and solubility in a solvent. Is more preferable. If the number average molecular weight is less than 10,000, the amount of sulfonic acid groups introduced is low, and sufficient proton conductivity tends to be not obtained or the strength as a membrane tends to be insufficient. When the number average molecular weight exceeds 300,000, handling tends to be difficult, for example, solubility in a solvent is lowered. The molecular weights of the hydrophobic segment precursor and the polymer electrolyte can be determined by the measurement methods described in the examples.

  The IEC of the polymer electrolyte is 1.5 to 3.5 meq. / G, the electrolyte membrane exhibits sufficiently high proton conductivity, and is 1.6 to 3.0 meq. / G is more preferable because it provides an excellent balance between proton conductivity and mechanical strength under low humidification. If the IEC is less than 1.5, the proton conductivity of the electrolyte membrane tends to be low, and if it is more than 3.5, the mechanical strength decreases due to swelling with water, and it tends to be difficult to have sufficient strength. is there.

The ion exchange capacity of the polymer electrolyte can be determined in the same manner as the method for measuring the ion exchange capacity of the polymer electrolyte membrane described in the Examples.
<2. Polymer electrolyte membrane>
The polymer electrolyte membrane of the present invention can be obtained by forming the polymer electrolyte obtained as described above. The method is not particularly limited, but the method of preparing the above polymer electrolyte solution, casting it on a substrate such as glass, and removing the solvent by heating can provide a uniform film thickness. preferable. Examples of the solvent used when the polymer electrolyte is used as a solution include dimethyl sulfoxide, N, N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, and N-methylpyrrolidone. Etc. The removal of the solvent is preferably performed by drying at a temperature of 10 to 200 ° C, more preferably 40 to 160 ° C. When the temperature is lower than 10 ° C, it takes a long time to remove the solvent. When the temperature is higher than 200 ° C, the polymer electrolyte may be decomposed.

 As the polymer electrolyte in the polymer electrolyte membrane of the present invention, the polymer electrolyte of the present invention may be used alone, or other polymer electrolytes may be mixed and used. In addition, the polymer electrolyte membrane of the present invention may contain additives other than the polymer electrolyte.

  From the viewpoint of proton conductivity, in the polymer electrolyte membrane of the present invention, the polymer electrolyte of the present invention is preferably the main component accounting for 70% by weight or more of the entire polymer electrolyte membrane. In addition, after obtaining the electrolyte membrane, a treatment such as biaxial stretching may be performed to control molecular orientation or the like, or a heat treatment may be performed to control crystallinity or residual stress. Furthermore, an appropriate chemical treatment may be performed during film formation. The chemical treatment includes, for example, addition of a protic compound for increasing conductivity and addition of a trace amount of polyvalent metal for improving durability. In any case, a polymer electrolyte membrane produced using the polymer electrolyte of the present invention in combination with a conventionally known technique is within the scope of the present invention.

  Further, in the polymer electrolyte membrane of the present invention, various commonly used additives, antioxidants for preventing resin deterioration, antistatic agents and lubricants for improving handling in molding as a film are electrolyte membranes. As long as it does not affect the processing and performance as described above, it can be used as appropriate.

  As thickness of the polymer electrolyte membrane of this invention, arbitrary thickness can be selected according to a use. For example, when considering reducing the resistance of the polymer electrolyte membrane when used as a fuel cell, the thinner the polymer electrolyte membrane, the better. On the other hand, considering the gas barrier properties, handling properties, and resistance to tearing when bonded to the electrode, the polymer electrolyte membrane may be undesirably too thin. Considering these, the thickness of the polymer electrolyte membrane is preferably 5 μm or more and 300 μm or less, more preferably 10 μm or more and 100 μm or less, and 10 μm or more and 50 μm or less is particularly preferable when the output is important as a fuel cell. If the thickness of the polymer electrolyte membrane is 5 μm or more and 300 μm or less, the production is easy, the membrane resistance and mechanical properties are balanced, and the handling property when processing as a fuel cell material is excellent. The thickness of the polymer electrolyte membrane can be determined by the measurement method described in the examples.

The ion exchange equivalent (IEC) of the polymer electrolyte membrane of the present invention can be adjusted by the IEC of the polymer electrolyte. For example, when the polymer electrolyte membrane includes a material other than the polymer electrolyte, the IEC as the polymer electrolyte membrane is thereby lowered, and therefore, the IEC of the polymer electrolyte membrane can be set to a higher value or the like. . The IEC as the polymer electrolyte membrane is 1.0 to 3.5 meq. / G, preferably 1.5 to 3.0 meq. / G is more preferable. IEC is 1.0 eq. If it is smaller than / g, there is a tendency that preferable proton conductivity is hardly expressed, and 3.5 meq. When it is larger than / g, mechanical strength decreases due to swelling with water, and it tends to be difficult to have sufficient strength.
<3. Membrane / electrode assembly, fuel cell>
The membrane / electrode assembly according to the present invention (hereinafter referred to as “MEA”) is obtained by applying an electrode catalyst to the polymer electrolyte membrane of the present invention. The electrode catalyst used in the present invention may literally be a conventionally known electrode catalyst for those skilled in the art, as long as it contains a conductive catalyst carrier and a catalytically active substance supported on the conductive catalyst carrier. Other specific configurations are not particularly limited. Specifically, a catalyst active for the electrode reaction of the fuel cell is used. On the anode side, a catalyst having the ability to oxidize fuel (hydrogen, methanol, etc.) is used. On the cathode side, a catalyst for the reaction of generating water from supplied oxygen, protons generated at the anode, and electrons is used.

  Specific examples of the conductive catalyst carrier include carbon carriers having a high surface area such as carbon black, ketjen black, activated carbon, carbon nanohorn, and carbon nanotube, and include catalyst supporting ability, electronic conductivity, and electrochemical stability. Therefore, these materials are preferable.

  Specific examples of the catalytically active substance include platinum, cobalt, ruthenium, and the like, and these may be used alone or as an alloy containing at least one of them or as an arbitrary mixture. In particular, when considering the oxidizing ability of the fuel, the reducing ability of the oxidizing agent, and durability, platinum or an alloy containing platinum is preferable. If necessary, these may be composed of three or more components using iron, tin, rare earth elements, etc. for stabilization and long life.

  The electrode catalyst layer can be prepared by applying a catalyst ink containing a polymer electrolyte, an electrode catalyst and a solvent on a support and removing the solvent. The solvent can be used without any limitation as long as it can dissolve the polymer electrolyte and does not poison the fuel cell catalyst.

  The catalyst ink may contain additives such as a non-electrolyte binder, a water repellent, a dispersant, a thickener, and a pore former as necessary. In addition, those additives conventionally known to those skilled in the art can be used, and other specific configurations are not particularly limited.

The catalyst ink prepared by the above composition and method can be applied by the following coating method depending on the viscosity and the type of substrate. As a method for applying the catalyst ink to the base material, any method known to those skilled in the art may be used, and other specific configurations are not particularly limited. For example, methods using a knife coater, bar coater, spray, dip coater, spin coater, roll coater, die coater, curtain coater, screen printing, etc. can be listed, but are not limited to these. When the film is used, the fuel cell catalyst layer transfer sheet can be produced. When the conductive porous sheet is used as the substrate, the fuel cell gas diffusion electrode can be produced. The methods for producing MEA are conventionally studied polymer electrolyte membranes made of perfluorocarbon sulfonic acid and other hydrocarbon polymer electrolyte membranes (for example, sulfonated polyetheretherketone, sulfonated polyethersulfone, sulfone). A known method performed with oxidized polysulfone, sulfonated polyimide, sulfonated polyphenylene sulfide, or the like is applicable. Such an MEA can be used, for example, in a fuel cell, in particular, a polymer electrolyte fuel cell.

  Hereinafter, examples will be shown, and the embodiment of the present invention will be described in more detail. The present invention is not limited to the following examples.

  Each measurement was performed as follows.

(Measurement of molecular weight)
The molecular weight was measured by GPC method. The conditions are as follows.
GPC measuring device: HLC-8220 (manufactured by Tosoh Corporation)
Column: SuperAW4000 and SuperAW2500 (made by Showa Denko KK) connected in series Column temperature: 40 ° C
Mobile phase solvent: NMP (N-methylpyrrolidone, LiBr added to 10 mmol / dm ³ )
Solvent flow rate: 0.3 mL / min
Standard material: TSK standard polystyrene (manufactured by Tosoh Corporation)
Hereinafter, the number average molecular weight converted with standard polystyrene is expressed as Mn, and the weight average molecular weight converted with standard polystyrene is expressed as Mw.
(Measurement of ion exchange equivalent (IEC))
As a measurement sample, 10 to 20 mg of the membrane after acid treatment was cut out and dried under reduced pressure at 80 ° C., and the dry weight (W _dry ) was measured. This membrane was immersed in a saturated aqueous NaCl solution (30 mL) at room temperature for 24 hours to convert the ionic group from H ⁺ type to Na ⁺ type. Thereafter, HCl contained in the obtained solution was quantified with a 0.01 M NaOH aqueous solution using an automatic potentiometric titrator AT-510 (manufactured by Kyoto Electronics Industry Co., Ltd.), and the ion exchange capacity IEC value was calculated using the following equation. Calculated. Two samples were prepared for the same membrane, and the average value of the two measurements was taken as the calculated IEC value by titration.

(Production Example 1)
To a 500 mL three-necked flask equipped with a thermometer and a stir bar, 4,4-dichlorobenzophenone (75 g, 300 mmol) and 30% fuming sulfuric acid (400 g, 1.5 mol) were added. The mixture was heated to 130 ° C. and stirring was continued for 6 hours. After cooling to room temperature, the reaction solution was added to ice water little by little. After neutralizing with an aqueous NaOH solution, the precipitated white solid was collected by filtration. By drying at 105 ° C. under reduced pressure, 112 g of a sulfonic acid group-containing monomer represented by the following formula (Formula 6) was obtained.

(Production Example 2)
A 500 mL four-necked flask equipped with a reflux tube and a DeanStark tube was charged with 4,4′-dichlorodiphenylsulfone (31.6 g, 110 mmol), 4,4′-dihydroxybenzophenone (21.4 g, 100 mmol), potassium carbonate ( 20.7 g, 150 mmol), dimethylacetamide (200 mL), and toluene (50 mL) were added. The mixture was heated to 170 ° C. and stirring was continued for 35 hours while removing generated water. 4,4′-Dichlorodiphenylsulfone (0.5 g) was added, and the mixture was further stirred for 5 hours. The mixture was filtered using filter paper to remove excess potassium carbonate, and then the filtrate was poured into 500 mL of methanol to reprecipitate the product. The product was dried under reduced pressure at 70 ° C. for 4 hours, washed with 500 mL of pure water twice at 60 ° C., further washed with 500 mL of methanol once at 60 ° C., and then at 70 ° C. under reduced pressure. By drying overnight, 41.5 g of a hydrophobic moiety oligomer of the following formula (Chemical Formula 7) was obtained. The molecular weight by GPC was Mn = 5400 and Mw = 13900.

Example 1
In a 500 mL four-necked flask equipped with a reflux tube and a DeanStark tube, sodium 2,5-dichlorobenzenesulfonate (7.84 g, 31.5 mmol), the oligomer obtained in Production Example 2 (4 g, 0.876 mmol) , 2,2′-bipyridyl (11.92 g, 76.4 mmol), dimethyl sulfoxide (176 mL), and toluene (44 mL) were added. Under a nitrogen atmosphere, the mixture was heated to 170 ° C. for 3 hours for azeotropic dehydration. After toluene was distilled off at 170 ° C., the mixture was cooled to 80 ° C., and nitrogen was bubbled for 30 minutes. The flow rate of nitrogen was adjusted to be about 500 mL per minute. Bis (1,5-cyclooctadiene) nickel (10 g, 36.4 mmol) was added and stirred at that temperature for 2 hours. The reaction solution was poured into 1 L of methanol and reprecipitated, and the solid content was washed twice with 6N hydrochloric acid (1 L), and further washed with pure water until the pH of the washing solution became 7. The solid content was dried overnight at 105 ° C. under reduced pressure to obtain a polymer electrolyte (7.49 g) of the following formula (Chemical Formula 8). The yield was 85%. Moreover, the molecular weight by GPC was Mn = 68,000 and Mw = 166,000.

 The polymer electrolyte was pulverized using a pulverizer, washed with methylene chloride and methanol, and dissolved in dimethyl sulfoxide to obtain a polymer electrolyte solution having a solid content concentration of about 10%. The solution was applied onto a PET film (Toler mirror 188 μm) affixed on a glass plate using an applicator with a clearance set to 15 mil. The obtained coated film was dried at 120 ° C. for 12 hours using a hot plate, and then washed with 6N hydrochloric acid and further distilled water to obtain an electrolyte membrane. The electrolyte membrane was peeled from the PET film, and the IEC was measured, and 2.30 meq. / G.

(Comparative Example 1)
In the same manner as in Example 1 except that nitrogen bubbling was not performed, 7.13 g of a polymer electrolyte was obtained. The yield was 80%. The molecular weight by GPC was Mn = 49,700 and Mw = 154,000. A polymer electrolyte membrane was prepared in the same manner as in Example 1, and the IEC was measured. The result was 2.21 meq. / G.
(Comparative Example 2)
The same as Comparative Example 1 except that the amount of bis (1,5-cyclooctadiene) nickel used was 15 g (54.6 mmol) and the amount of 2,2′-bipyridyl used was 8.94 g (57.3 mmol). Thus, 3.45 g of a polymer electrolyte was obtained. The yield was 39%. The molecular weight by GPC was Mn = 37,400 and Mw = 90,600. When a polymer electrolyte membrane was prepared in the same manner as in Example 1 and IEC was measured, it was 1.56 meq. / G.
(Example 2)
In a 1 L four-necked flask equipped with a reflux tube and a DeanStark tube, the sulfonic acid group-containing monomer obtained in Production Example 1 (24 g, 52.8 mmol), the oligomer obtained in Production Example 2 (16 g, 3.50 mmol). ), 2,2′-bipyridyl (23.12 g, 148 mmol), dimethyl sulfoxide (480 mL), and toluene (120 mL). Under a nitrogen atmosphere, the mixture was heated to 170 ° C. for 3 hours for azeotropic dehydration. After toluene was distilled off at 170 ° C., the mixture was cooled to 80 ° C., and nitrogen was bubbled for 30 minutes. The flow rate of nitrogen was adjusted to be about 1 L per minute. Bis (1,5-cyclooctadiene) nickel (20 g, 72.8 mmol) was added and stirred at that temperature for 2 hours. The reaction solution was poured into 1 L of methanol and reprecipitated, and the solid content was washed twice with 6N hydrochloric acid (1 L), and further washed with pure water until the pH of the washing solution became 7. The solid content was dried overnight at 105 ° C. under reduced pressure to obtain a polymer electrolyte (33.2 g) of the following formula (Chemical Formula 9). The yield was 99%. Moreover, the molecular weight by GPC was Mn = 134,000 and Mw = 413,000.

 The polymer electrolyte was pulverized using a pulverizer, washed with methylene chloride and methanol, and dissolved in dimethyl sulfoxide to obtain a polymer electrolyte solution having a solid concentration of about 12%. The solution was applied onto a PET film (Toler mirror 188 μm) affixed on a glass plate using an applicator with a clearance set to 15 mil. The obtained coated film was dried at 120 ° C. for 12 hours using a hot plate, and then washed with 6N hydrochloric acid and further distilled water to obtain an electrolyte membrane. The electrolyte membrane was peeled from the PET film, and the IEC was measured and found to be 2.58.

(Comparative Example 3)
28.5g of polymer electrolyte was obtained like Example 2 except not performing nitrogen bubbling. The yield was 85%. The molecular weight by GPC was Mn = 92,000 and Mw = 199,000. A polymer electrolyte membrane was prepared in the same manner as in Example 1, and the IEC was measured and found to be 2.30 meq. / G.

  The above conditions and results are summarized in Table 1.

  As is apparent from Table 1, the polymer electrolytes of Examples 1 and 2 use 2,2′-bipyridyl at least twice as much mole as the nickel atom, satisfy the 18-electron rule, and perform nitrogen bubbling. As a result, the number average molecular weight and IEC were higher than those of the polymer electrolytes of Comparative Examples 1 and 3 in which nitrogen bubbling was not performed. The yield was also high. In Comparative Example 2, although the amount of zero-valent nickel used is larger than the others, the amount of 2,2′-bipyridyl used is about 1 time mole with respect to nickel atoms, and does not satisfy the 18-electron rule. The yield was significantly low, and the average molecular weight and IEC were also low.

Claims (7)

A method for producing a polymer electrolyte composed of a hydrophilic segment and a hydrophobic segment,
Hydrophilic segment precursor containing an aromatic ring having a sulfonic acid group and having 2 or more halogen atoms as a main chain, and a hydrophobic segment having an aromatic ring having substantially no sulfonic acid group and having 2 or more halogen atoms as a main chain When producing from a functional segment precursor, a complex comprising a zero-valent nickel compound and a ligand is 0.5 molar equivalent to the sum of halogen atoms contained in the hydrophilic segment precursor and the hydrophobic segment precursor. More than 0.75 molar equivalents are used, and the complex is used, and the use ratio of the zerovalent nickel compound and the ligand is adjusted so that the nickel atom has an electron configuration satisfying the 18-electron rule,
A method for producing a polymer electrolyte, comprising a step of removing oxygen dissolved in a reaction system.   The method for producing a polymer electrolyte according to claim 1, wherein the ligand is 2,2'-bipyridyl.   The method for producing a polymer electrolyte according to claim 2, wherein the 2,2'-bipyridyl is used in an amount of 2 to 3 molar equivalents relative to the zerovalent nickel compound.   The method for producing a polymer electrolyte according to claim 1, wherein the zero-valent nickel compound is bis (1,5-cyclooctadiene) nickel.   The method for producing a polymer electrolyte according to any one of claims 1 to 4, wherein the step of removing oxygen present in the reaction system is bubbling nitrogen into the reaction system. The method for producing a polymer electrolyte according to any one of claims 1 to 5, wherein the hydrophilic segment precursor has a structure represented by any one of the following general formula group 1 (chemical formula 1).

(In the formula, m represents an integer of 1 to 4, k and l represent an integer of 0 to 4, k + 1 represents an integer of 1 or more, p represents an integer of 0 to 10, q represents an integer of 0 to 10, r Represents an integer of 1 to 4. Hal represents halogen, X represents at least one structure selected from the group consisting of —CO—, —SO ₂ —, and —C (CF ₃ ) ₂ —; Consists of —CO—, —SO ₂ —, —SO—, —CONH—, —COO—, — (CF ₂ ) _t — (t is an integer of 1 to 10), —C (CF ₃ ) ₂ —. Represents at least one structure selected from the group, Z is a direct bond, or — (CH ₂ ) _o — (where o is an integer of 1 to 10), —C (CH ₃ ) ₂ —, —O—, — Represents at least one structure selected from the group consisting of S—, Ar ¹ is a substituent represented by —SO ₃ H or O (CH ₂ ) _s SO ₃ H (s is an integer of 1 to 12); Have It represents an aromatic group.) The method for producing a polymer electrolyte according to any one of claims 1 to 6, wherein the precursor of the hydrophobic segment has any structure of the following general formula group 2 (Chemical formula 2).

(In the formula, Hal represents halogen, Ar represents a divalent aromatic group, n represents an integer of 1 to 50, a, b, and c represent integers of 0 to 50, provided that 2 ≦ a + b + c ≦ 50 is satisfied. To do.)