JP2007126645A - Polymer having ion exchange group and use of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer capable of being used in preparing a polyelectrolyte membrane having a lower methanol permeability and a high ionic conductivity, to provide a polyelectrolyte membrane, a polyelectrolyte used in its preparation, and to provide use of the same. <P>SOLUTION: What is provided is: a polymer having ion exchange groups, wherein the branching number Bn as determined according to formula (1) is 10 or larger, and the ion exchange capacity is 1 meq/g or larger; a polyelectrolyte comprising the polymer, a polyelectrolyte membrane using the polyelectrolyte, a polyelectrolyte membrane obtained by the solution casting of the polyelectrolyte, a composite polyelectrolyte membrane prepared by using the polyelectrolyte membrane and a porous substrate, a catalyst composition containing the polyelectrolyte and a catalyst, and a polyelectrolyte type fuel cell using the polyelectrolyte. In formula (1), IV (M) is the limiting viscosity number of the polymer at a molecular weight M; and IVL (M) is the limiting viscosity number of a linear polymer at a molecular weight of M. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer having an ion-exchange group, a polymer electrolyte, a polymer electrolyte membrane, a polymer electrolyte composite membrane, a catalyst composition, and a polymer electrolyte fuel cell.

  In recent years, various attempts have been made to search for an energy source having a low environmental load. Among them, fuel cells, in particular solid polymer electrolyte fuel cells using a solid polymer electrolyte membrane, are expected to be applied as power sources for automobiles and the like because of the advantage that the exhaust material is only water.

  As a polymer electrolyte membrane for such a solid polymer electrolyte fuel cell, a perfluoroalkyl sulfone having a perfluoroalkyl sulfonic acid introduced into a perfluoroalkane main chain, as represented by Nafion (registered trademark of DuPont), is used. There are fluorine-based membranes obtained from polymer electrolytes such as acids, but the problem is that they are very expensive and have low heat resistance.

  In recent years, development of inexpensive polymer electrolytes that can replace the polymer electrolytes has been activated. Among them, a polymer obtained by introducing a sulfonic acid group into an aromatic polyether having excellent heat resistance and high film strength, that is, an aromatic polymer having a sulfonic acid group in the side chain and a main chain linked to an aromatic ring. For example, sulfonated polyetherketone polymers (Patent Document 1) and sulfonated polyethersulfone polymers (Patent Documents 2 and 3) have been proposed.

  By the way, an attempt to apply the above fuel cell to a power source of a notebook computer, a portable electronic device, etc. is also in progress. The application of is being considered. However, if the DMFC is used for a polymer electrolyte membrane made of the aromatic polymer electrolyte, methanol easily permeates the polymer electrolyte membrane during DMFC operation, and in such a case, power generation performance decreases. Problems arise. As a solution to this problem, the polymer electrolyte membrane applied to the DMFC is required to have low methanol permeability.

  As a method for lowering the methanol permeability, there is generally a method for lowering the ion exchange capacity of the polymer electrolyte itself. However, when this is done, only a polymer electrolyte membrane having low ion conductivity can be obtained at the same time. Reduce the power generation performance. As described above, it has been difficult for membranes obtained from conventionally known aromatic polymer electrolytes to achieve high levels of ionic conductivity related to power generation performance and low methanol permeability.

Japanese National Patent Publication No. 11-502249 (Claims) JP 10-45913 (Claims, paragraph [0010]) JP 10-211943 A (Claims)

  An object of the present invention is to provide a polymer that is suitable as a polymer electrolyte membrane for DMFC and that can be applied to a polymer electrolyte membrane that achieves low methanol permeability and ionic conductivity at high levels. Another object of the present invention is to provide a polymer electrolyte membrane using the polymer and its use.

（式中、IV(M)は該重合体の分子量Ｍにおける極限粘度であり、IVL(M)は分子量Ｍにおける直鎖状重合体の極限粘度である。） As a result of intensive studies on a polymer electrolyte that can solve the above-described problems using an inexpensive polymer electrolyte, the present inventors have generally considered that it depends on the affinity between the structural unit constituting the polymer electrolyte and methanol. The new knowledge that methanol permeability can be remarkably lowered by further branching the molecular chain of the polymer electrolyte has been obtained, and the present invention has been completed based on such knowledge.
That is, the present invention
[1] A polymer having an ion-exchange group, which has a degree of branching Bn calculated on the basis of the following formula of 10 or more and an ion-exchange capacity of 1 meq / g or more.

(In the formula, IV (M) is an intrinsic viscosity at a molecular weight M of the polymer, and IVL (M) is an intrinsic viscosity of a linear polymer at a molecular weight M.)

Furthermore, the present invention provides the following [2] to [5] as preferred embodiments according to the above [1].
[2] Polymer [1] which is soluble in solvent [3] The main chain is an aromatic polymer [1] or [2] polymer [4] The polymer has an ion-exchange group. [5] The polymer according to any one of [1] to [3], which is a block copolymer having a block having a block and a block having substantially no ion-exchange group [5] A block having an ion-exchange group and an ion exchange The weight composition ratio of the block having substantially no functional group is represented by (block having an ion-exchange group): (block having substantially no ion-exchange group) 3:97 to 70: 30. The polymer of [4]

Furthermore, the present invention provides the following [6] to [11] using any of the above polymers.
[6] A polymer electrolyte of a polymer electrolyte membrane [8] [6] comprising a polymer electrolyte [7] [6] comprising a polymer of any one of [1] to [5] Polymer electrolyte and catalyst of polymer electrolyte composite membrane [10] [6] using polymer electrolyte of polymer electrolyte membrane [9] [6] obtained by solution casting method and porous substrate Polymer electrolyte fuel cell comprising a polymer electrolyte of a catalyst composition [11] [6] containing

  According to the present invention, it is possible to easily obtain a polymer excellent in low methanol permeability while maintaining high ion conductivity and suitable as a polymer electrolyte membrane for DMFC. Moreover, when this polymer is used, DMFC excellent in power generation performance can be obtained.

The ion-exchange groups which polymer has the present invention, is not particularly limited, for _{example, -SO 3 H, -COOH, -PO} (OH) 2, -SO 2 NHSO 2 -, - Ph (OH ) (Ph represents a phenylene group) and other cation exchange groups, -NH ₂ , -NHR, -NRR ', -NRR'R " ⁺ , -NH ₃ ⁺ (R, R', and R" are respectively Anion exchange groups such as independently representing an alkyl group, a cycloalkyl group, or an aryl group). Among them, a cation exchange group is preferable, and —SO ₃ H (sulfonic acid group) is particularly preferable. Some or all of these groups may form a salt with a counter ion, but when used as an ion conductive membrane of a fuel cell, such a salt is substantially formed. No ion exchange groups are preferred.

  The polymer of the present invention is a comb-type branched polymer or a random-type branched polymer having a repeating unit having the ion-exchange group and having a degree of branching Bn calculated on the basis of the above formula of 10 or more. Here, Bn is a known index indicating the degree of long-chain branching in a polymer. If the polymer is linear (does not have branching), Bn is 0, and the polymer is long-chain branching. Bn has a positive value, and as Bn increases, it means that there are more branch points per polymer chain, that is, more branch chains. The inventors have found that when a branched polymer having a high Bn is obtained, the branched polymer can achieve ion conductivity and low methanol permeability at a high level. It has been found that it is difficult to apply to DMFC due to the increase in properties. Bn is preferably 15 or more, more preferably 20 or more. Thus, the higher the Bn, the lower the methanol permeability. However, when the polymer of the present invention is applied to an ion conductive membrane for a fuel cell, it is preferable that it can be formed into a membrane by a solution casting method. If it is too large, the solubility in a solvent will be reduced, and film forming processability and recyclability may be inferior. The Bn is usually 250 or less, preferably 150 or less, more preferably 100 or less. Details of the solution casting method will be described later.

ここで、IV(M)は対象とする重合体の分子量Ｍにおける極限粘度であり、IVL(M)は分子量Ｍにおける直鎖状重合体の極限粘度である。なお、ｌｎは自然対数を表す。 The degree of branching Bn can be determined using a gel permeation chromatography (GPC) -triple detector method using a 90 ° light scattering detector in addition to a differential refractometer and a viscosity detector. Details are described in Carbohydrate Polymers, Vol. 45, pages 293-303 (2001). Recently, the branching degree Bn can be easily obtained by computer software attached to the apparatus.
In the present invention, when the branching degree Bn is calculated using such computer software, it is obtained based on the following equation.

Here, IV (M) is the intrinsic viscosity at the molecular weight M of the polymer of interest, and IVL (M) is the intrinsic viscosity of the linear polymer at the molecular weight M. Note that ln represents a natural logarithm.

In the GPC measurement of a polymer having a high ion exchange capacity such as the polymer of the present invention, a technique frequently used in the GPC measurement of a polymer having a high ion binding property is used. For example, the column uses a column in which the sample does not exceed the exclusion limit of the column and does not adsorb or repel the sample. The mobile phase is used under conditions where a salt such as lithium bromide is dissolved if necessary and eluted in descending order of molecular weight.
When a light scattering detector such as a fluorescent material cannot be used, Bn may be calculated by the viscosity-GPC method using GPC equipped with a differential refractometer and a viscosity detector. Details are described in Journal of the Japan Rubber Association, Vol. 45, No. 2, pp. 105-118 (1972).
As described above, the Bn of the polymer of the present invention can be easily obtained by using a commercially available GPC equipped with the above-described apparatus.

  In the polymer of the present invention, the molecular chain constituting the polymer may be any of an aliphatic polymer, an aromatic polymer, and a polymer having both an aliphatic chain and an aromatic chain. When used as, from the viewpoint of obtaining practical heat resistance, at least among the branched polymer chains, when the longest molecular chain is the main chain of the branched polymer, as the molecular chain forming the main chain, An aromatic polymer in which the aromatic rings are directly connected or connected with atoms or atomic groups as a connecting group is preferred, and the repeating unit having an ion-exchange group is preferably one having an aromatic ring.

Specific examples of the repeating unit having an ion exchange group include the following (1). In addition, the ion-exchange group in the exemplified repeating unit includes a repeating unit in the form of a so-called free acid in which the sulfonic acid group, which is the preferred ion-exchange group, does not form a salt with a counter ion, The sulfonic acid group may be a repeating unit in which another ion exchange group such as a phosphonic acid group or a carboxylic acid group is substituted, and the other ion exchange group may form a salt with a counter ion.
(1) Repeating unit having an ion-exchange group:

Further, the polymer of the present invention is obtained from such a polymer electrolyte as a copolymer having both a repeating unit having an ion-exchange group exemplified above and a repeating unit having no ion-exchange group. The polymer electrolyte membrane to be obtained is preferable because it is more excellent in mechanical strength, and the following (2) illustrates a repeating unit having no ion-exchange group.
(2) Repeating units based on monomers substantially having no ion-exchange groups:

  In the present invention, the repeating unit constituting the main chain and / or the branched chain branched from the main chain in the polymer is a repeating unit having an ion-exchange group exemplified above (hereinafter referred to as “repeating unit 1”). ) And a repeating unit having no ion-exchange group (hereinafter referred to as “repeating unit 2”), and each copolymerization mode is random copolymerization, alternating copolymerization, or repeating unit 1 is linked. Any block copolymer having both a block formed by repeating unit 2 and a block formed by connecting repeating unit 2 may be used, and a main chain (or branched chain) formed by connecting repeating unit 1 and repeating unit 2 may be connected. A copolymerization mode consisting of a branched chain (or main chain) may also be used.

このように、２つの脱離基（塩素原子）を有するモノマーと、２つの求核基（フェノール性水酸基）を有するモノマーとを縮合させることで、エーテル基を有する繰り返し単位からなる線状高分子（重合度ｊ）が得られる。
分岐高分子を得るためには、繰り返し単位１および繰り返し単位２を誘導しうる、２つの反応基（脱離基または求核基）を有するモノマーに加え、該反応基を分子内に３つ以上有するモノマー（以下、「多官能性モノマー」と呼ぶ）を用いることにより、分岐高分子を得ることができる。 Here, as a typical example of the production method for obtaining the polymer of the present invention, the production method of the branched polymer having the above repeating unit 1 and repeating unit 2 exemplified as suitable repeating units will be described.
The above repeating unit 1 and repeating unit 2 are divalent groups having an oxygen atom as a linking group via an ether bond, and usually a halogen atom when linking aromatic rings via an ether bond. A leaving group represented by a mesyl group or a tosyl group and a nucleophilic group represented by a phenolic hydroxyl group or a metal phenolate group in which the phenolic hydroxyl group forms a salt with an alkali metal ion or the like to form an ether The polymerization can be advanced by making the reaction for forming a bond a unit reaction. Specifically, an example of this reaction is shown below.

Thus, a linear polymer comprising a repeating unit having an ether group by condensing a monomer having two leaving groups (chlorine atoms) and a monomer having two nucleophilic groups (phenolic hydroxyl groups). (Polymerization degree j) is obtained.
In order to obtain a branched polymer, in addition to a monomer having two reactive groups (leaving group or nucleophilic group) capable of deriving the repeating unit 1 and the repeating unit 2, three or more reactive groups are present in the molecule. A branched polymer can be obtained by using a monomer having the same (hereinafter referred to as “polyfunctional monomer”).

  Examples of the compound having three or more leaving groups in the molecule that are the above polyfunctional monomers include hexafluorobenzene and decafluorobiphenyl, and examples of the compound having three or more nucleophilic groups in the molecule include Loglucinol, 4,4 ′, 4 ″ -trihydroxytriphenylmethane.

  In addition, a linear polymer constituting the main chain is prepared in advance with a monomer having two leaving groups and a monomer having two nucleophilic groups, and the resulting aromatic polymer in the linear polymer By introducing a leaving group or a nucleophilic group, a linear polymer having a reactive group in the side chain is newly obtained, and a branched polymer is also obtained by reacting a monomer with the reactive group in the side chain. be able to.

  Further, after obtaining a linear polymer in the same manner as described above, the linear polymer is irradiated with a high energy beam such as an electron beam or radiation to cause the linear polymer to undergo a rearrangement reaction or the high molecular beam. A branched polymer can also be obtained by generating radicals in the linear polymer chain by irradiation with energy rays and using these radicals as reaction base points.

From the viewpoint of not requiring industrially complicated equipment, a method for producing a branched polymer using the above polyfunctional monomer is preferred. From the viewpoint of simplifying the production, repeating unit 1 and / or repeating unit 2 are preferred. Are prepared in advance, and the polyfunctional monomer is bonded to at least one end, preferably both ends of the linear polymer, so that three or more reactive base points are formed at the ends. The branched polymer precursor is obtained, and the branched polymer precursor is reacted with a monomer that induces a branched chain, or two or more kinds of the branched polymer precursors are produced, and the plurality of types of branched polymer precursors are prepared. A branched polymer can also be produced by bonding bodies together.
More preferably, a branched polymer precursor mainly composed of repeating units 2 (or repeating units 1) is obtained, and after a multifunctional monomer is bonded to the terminal of the branched polymer precursor, such a branched polymer precursor is obtained. When polymerizing a molecular precursor and a monomer mainly containing a monomer that induces repeating unit 1 (or repeating unit 2), the resulting branched polymer has a block having an ion-exchange group mainly having repeating unit 1. A block polymer having a block mainly having an ion-exchange group mainly having the repeating unit 2, the block copolymer having a high level of low methanol permeability and ion conductivity, and The polymer electrolyte is excellent in mechanical strength and heat resistance.
In addition, the block having the ion exchange group means a block having 0.5 or more expressed by the average number of ion exchange groups per repeating unit constituting the block, and the block having one or more blocks. preferable. On the other hand, the block having substantially no ion-exchange group means a block having an average number of ion-exchange groups per repeating unit constituting the block of 0.1 or less, More preferred is a block of 0.05 or less.

  A known reaction is applied to obtain the branched polymer precursor. Specifically, the methods described in the above Patent Documents 1 to 3 can be used. When obtaining a linear polymer from a monomer having two leaving groups and a monomer having two nucleophilic groups, either the number of equivalents of the leaving group or the number of equivalents of the nucleophilic group is excessive. By this, since the kind of the reactive group remaining at the terminal of the obtained branched polymer precursor can be controlled, it is possible to easily obtain the terminal having a desired reactive group at the terminal. Next, the reactive group at the terminal is reacted with a polyfunctional monomer to obtain a branched polymer precursor having three or more reactive groups at the terminal, and the reactive group at the terminal of the branched polymer precursor is set as the reactive base point. As described above, another monomer or another branched polymer precursor is reacted in the presence of a reaction solvent, the reaction solution is sampled every predetermined time, and Bn is obtained from the analysis by GPC described above. The reaction is terminated when the desired branched polymer is obtained. In the case of a branched polymer composed of the repeating unit 1 and the repeating unit 2 exemplified as preferred repeating units, the reaction conditions can be appropriately optimized depending on the type of reactive group (leaving group, nucleophilic group) in the monomer used. The reaction temperature is usually 80 to 180 ° C., preferably 100 to 150 ° C., and the reaction time is 10 hours or more. In order to improve the reactivity of the phenolic hydroxyl group that is a nucleophilic group, it is preferable to use an alkali such as potassium carbonate as a deoxidizing agent, and it is preferable to remove by-product water by azeotropic dehydration or the like. In order to obtain higher Bn, the reaction temperature is preferably set to a higher temperature for a long time. In addition, when Bn becomes high, a cross-linking reaction may occur as a side reaction, but the polymer in which such a cross-linking reaction has occurred is a polymer called a gel, which has a significantly reduced solubility in a solvent. If solid-liquid separation is used, it can be easily removed.

Furthermore, the polymer of the present invention is a polymer having an ion exchange capacity of 1 meq / g or more. When the ion exchange capacity is small, it is not preferable because the ion conductivity is lowered when used as an ion conductive membrane for a fuel cell. The ion exchange capacity is preferably 1.5 meq / g or more, more preferably 1.6 meq / g or more. If the ion exchange capacity is too large, the water resistance tends to be poor, and the ion exchange capacity is preferably 4 meq / g or less, more preferably 3 meq / g or less.
The ion exchange capacity is the equivalent number of ion exchange groups per unit weight of the polymer, and the ion exchange capacity can be controlled by controlling the amount of ion exchange groups introduced into the polymer. Specifically, the copolymerization ratio between the repeating unit having an ion-exchange group and the repeating unit having no ion-exchange group may be controlled from the amount of the monomer that derives each repeating unit. When the polymer of the present invention is a block copolymer described as a preferred copolymerization mode, also depending on a copolymerization ratio of a block having an ion-exchange group and a block having substantially no ion-exchange group. Can be controlled.
The block copolymer has a weight composition ratio of a block having an ion-exchange group and a block having substantially no ion-exchange group (a block having an ion-exchange group): (substantially containing an ion-exchange group) It is preferably from 3:97 to 70:30, more preferably from 5:95 to 60:40, still more preferably from 10:90 to 50:50, and from 20:80 to 40:60 is particularly preferred. When the weight composition ratio is within this range, the water resistance can be improved while maintaining a high level of ionic conductivity.

Among the combinations of the repeating unit 1 and the repeating unit 2 exemplified above, as a more preferable block copolymer, specifically, combinations of repeating units constituting each block are the following (I) to (IV): Any one is more preferable.

  As described above, the polymer of the present invention has solvent solubility enough to be applied to GPC analysis, but is preferably soluble in a solvent at a concentration of 1% by weight. The solvent is not particularly limited, such as an organic solvent or water. Furthermore, it is not necessary to be a single solvent, and it may be soluble in two or more mixed solvents. The term “soluble” means that when 1% by weight of the polymer is dissolved in a solvent, the residue when filtered through a 1 μm filter is usually based on the total weight of the polymer mixed with the solvent. It means 10% by weight or less. The residue is preferably 8% by weight or less and particularly preferably 5% by weight or less. Such a solvent-soluble polymer has an advantage that the polymer once in the form of a film can be recycled again. In addition, the polymer is preferably 1% by weight or more and soluble in a solvent. However, when the polymer is soluble in a solvent at a concentration of about 2 to 30% by weight, There is also an advantage that the film forming processability is excellent.

The average molecular weight of the polymer of the present invention is preferably 5,000 to 1,000,000, more preferably 10,000 to 500,000, especially 15,000 to the number average molecular weight in terms of polystyrene. 300,000 is particularly preferred.
Further, the average molecular weight of the block having an ion-exchange group when the polymer of the present invention is a block copolymer is preferably 2,000 to 200,000 in terms of polystyrene-equivalent number average molecular weight. The average molecular weight of the block having substantially no ion-exchange group is preferably 5,000 to 400,000 in terms of polystyrene-equivalent number average molecular weight. 000 to 200,000 is particularly preferred. The molecular weight for each block is determined from the block composition ratio specified by NMR or the like and the molecular weight of the entire polymer, or each block is prepared by stepwise polymerization, that is, using the branched polymer precursor, When obtaining a copolymer, the molecular weight of each block may be determined by measuring the molecular weight of the precursor that induces each block and performing differential processing.

  In the polymer of the present invention, the copolymer having the repeating unit 1 and the repeating unit 2 which are the above preferred repeating units has been described. However, by changing the type of the leaving group or nucleophilic group, oxygen The present invention can also be easily carried out in the case of polymers having various specifications in which aromatic rings are connected by atoms or atomic groups other than atoms.

Next, the use according to the polymer of the present invention, particularly application to a fuel cell will be described.
A polymer electrolyte membrane of a fuel cell is usually used by being sandwiched between a separator, a gasket, a gas diffusion layer, and the like in a fuel cell stack and applied with a high surface pressure. If a film having a high water absorption rate is used under such conditions, the film may swell so much that it cannot withstand the surface pressure, causing deformation, bleeding, or partial dissolution. Therefore, it is better that the polymer electrolyte membrane does not have a too high water absorption rate. Since the polymer of the present invention can be converted into a polymer electrolyte membrane having excellent water resistance, it can be suitably used for this purpose.

  Since the polymer of the present invention is excellent in low methanol permeability, it is particularly suitable for a DMFC that directly supplies methanol as a fuel, but can also be applied to a solid polymer fuel cell using hydrogen gas as a fuel.

When used as such a polymer electrolyte membrane, the polymer of the present invention is usually used in the form of a film. Although there is no restriction | limiting in particular in the method to convert into a film, The method (solution casting method) which forms into a film from a solution state is used preferably.
Specifically, the polymer is formed by dissolving the polymer in a suitable solvent, casting the solution on a glass plate, and removing the solvent. The solvent used for film formation is not particularly limited as long as it can dissolve the polymer and can be removed thereafter, and N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), Aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO); Chlorinated solvents such as dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene and dichlorobenzene; Methanol, ethanol, propanol and the like Alcohol glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether are preferably used. These can be used singly, but two or more solvents can be mixed and used as necessary. Considering the environment, an aprotic polar solvent, alcohol or alkylene glycol monoalkyl ether is more preferably used. Among them, N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), or dimethyl sulfoxide (DMSO) is more preferable because of high polymer solubility.

  Although there is no restriction | limiting in particular in the thickness of a film, 10-300 micrometers is preferable and 20-100 micrometers is especially preferable. If the film is too thin, the practical strength may not be sufficient. If the film is too thick, the membrane resistance tends to increase and the characteristics of the electrochemical device tend to deteriorate. The film thickness can be controlled by the concentration of the solution and the coating thickness on the substrate.

For the purpose of improving various physical properties of the film, plasticizers, stabilizers, mold release agents, and the like used in ordinary polymers can be used. In addition, other polymers can be combined with the polymer of the present invention by a method such as mixing in the same solvent and co-casting.
In addition to fuel cell applications, it is also known to add inorganic or organic fine particles as a water retention agent in order to facilitate the water content control. Any of these known methods can be used as long as they are not contrary to the object of the present invention.
If recyclability is not required, crosslinking can be performed by irradiating with an electron beam or radiation for the purpose of improving the mechanical strength of the film.

  In addition, in order to further improve the strength, flexibility and durability of the polymer electrolyte membrane, the polymer of the present invention is impregnated into a porous base material and combined to form a composite membrane for use in the polymer electrolyte membrane. It is also possible. A known method can be used as the compounding method. The porous substrate is not particularly limited as long as it satisfies the above-mentioned purpose of use, and examples thereof include porous membranes, woven fabrics, nonwoven fabrics, fibrils, and the like, which can be used regardless of their shapes and materials.

When the polymer electrolyte composite membrane using the polymer of the present invention is used as a diaphragm of a polymer electrolyte fuel cell, the thickness of the porous substrate is usually 1 to 100 μm, preferably 3 to 30 μm, more preferably The pore diameter is usually 0.01 to 100 μm, preferably 0.02 to 10 μm, and the porosity is usually 20 to 98%, preferably 40 to 95%.
If the film thickness of the porous substrate is too thin, the effect of reinforcing the strength after the combination or the reinforcing effect of imparting flexibility and durability may be insufficient. On the other hand, if the film thickness is too thick, the electric resistance becomes high, and the obtained composite film becomes insufficient as a diaphragm of the polymer electrolyte fuel cell. If the pore size is too small, it is difficult to fill the polymer electrolyte, and if it is too large, the reinforcing effect on the polymer electrolyte is weakened. If the porosity is too small, the resistance as a solid electrolyte membrane is increased. If it is too large, the strength of the porous substrate itself is generally weakened and the reinforcing effect is reduced.
From the viewpoint of heat resistance and the effect of reinforcing physical strength, the porous base material is preferably an aliphatic or aromatic polymer, or a fluorine-containing polymer.

  The polymer electrolyte membrane and / or the polymer electrolyte composite membrane thus obtained are joined to the membrane layer-electrode assembly, membrane-electrode-gas diffusion layer by joining the catalyst layer and the gas diffusion layer on both sides. A layered assembly can be produced. A known material can be used for the gas diffusion layer, but a porous carbon woven fabric, carbon non-woven fabric or carbon paper is preferable because the raw material gas is efficiently transported to the catalyst.

  Here, the catalyst is not particularly limited as long as it can activate the oxidation-reduction reaction of hydrogen or oxygen, and a known catalyst can be used, but a known catalyst for a fuel cell is preferably used. It is particularly preferable to use the fine particles. Platinum fine particles are often used by being supported on particulate or fibrous carbon such as activated carbon or graphite. Such a catalyst is usually mixed with an alcohol solution of a polymer electrolyte such as a perfluoroalkyl sulfonic acid resin to obtain a catalyst composition, which is pasted into a gas diffusion layer and / or a polymer electrolyte membrane and It is used by forming a catalyst layer by applying to a polymer electrolyte composite membrane and / or drying. As a specific method, for example, J. Org. Electrochem. Soc. : Known methods such as those described in Electrochemical Science and Technology, 1988, 135 (9), 2209 can be used.

  The polymer of the present invention can also be used as a polymer electrolyte in such a catalyst composition. Specifically, in place of the perfluoroalkyl sulfonic acid resin exemplified as the polymer electrolyte constituting the above-described catalyst composition. The polymer of the present invention may be used for the above. Examples of the solvent used in obtaining the catalyst composition using the polymer of the present invention include the same solvents as those mentioned as the solvent used for film formation of the polymer. When the catalyst composition using the polymer of the present invention is used, the polymer electrolyte membrane in the fuel cell is not limited to the membrane using the polymer of the present invention, and a known polymer electrolyte membrane is used. Can do.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

Measurement of molecular weight The number average molecular weight (Mn) in terms of polystyrene was measured by gel permeation chromatography (GPC) under the following conditions.
Column Tosoh TSKgel GMH _HR -M
Column temperature 40 ° C
Mobile phase solvent DMF (LiBr added to 10 mmol / dm ³ )
Solvent flow rate 0.5 ml / min Sample concentration 0.05% (W / V)
Injection volume 200 μl

Calculation of Bn In addition to the differential refractive index detector as a detector in the above GPC measurement, a detector (model 270 manufactured by Viscotek) equipped with a viscosity detector and a 90 ° light scattering detector is used to make a GPC-triple detector. Based on the results, Bn was calculated based on the formula described in this specification using the computer software Omnisec Ver.3.1 attached to the apparatus.

A polymer electrolyte membrane to be measured is sandwiched in the center of an H-shaped diaphragm cell consisting of a methanol permeability test cell A and a cell B, a 10% by weight aqueous methanol solution is added to the cell A, and pure water is added to the cell B. The amount of methanol permeating per unit time and unit film thickness was measured, and the methanol permeation coefficient D (cm ² / s) was determined.

The ion exchange capacity was determined by a titration method.

The proton conductivity was measured by an alternating current method at a temperature of 80 ° C. and a relative humidity of 90%.

The polymer electrolyte membrane (about 200 mg) to be measured for water absorption was immersed in hot water at 100 ° C. for 2 hours, and was determined from the weight change before and after that.

Reference example 1
Production of polyethersulfone (fluorine-terminated type) In a flask equipped with an azeotropic distillation apparatus, under a nitrogen atmosphere, 1000 g of Sumika Excel PES4003P (manufactured by Sumitomo Chemical Co., Ltd., hydroxyl-terminated polyethersulfone), 7.59 g of potassium carbonate, 2,500 ml of DMAc and 500 ml of toluene were added, and azeotropic dehydration was performed by heating and stirring at 160 ° C. After allowing to cool at room temperature, 53.6 g of decafluorobiphenyl was added and the mixture was heated and stirred at 80 ° C. for 3.5 hours. The reaction solution was dropped into a large amount of water, and the resulting precipitate was collected by filtration, washed with a methanol / acetone mixed solvent, dried at 80 ° C., and the following oligomer (hereinafter referred to as P1) in which a linking agent was bonded to the terminal. Got.
Mn = 3.2 × 10 ⁴

Example 1
1) Production of polymer electrolyte In a flask equipped with an azeotropic distillation apparatus, 130.00 g of potassium 2,5-dihydroxybenzenesulfonate, 4,4′-difluorodiphenylsulfone-3,3′-disulfonic acid in an Ar atmosphere Dipotassium (278.17 g) and potassium carbonate (81.86 g) were added, and DMSO (1200 mL) and toluene (240 mL) were added. Thereafter, toluene was distilled off by heating at a bath temperature of 130 ° C. to azeotropically dehydrate water in the system, and the mixture was stirred while keeping at 170 ° C. for 4 hours. Subsequently, the reaction solution was sufficiently cooled to room temperature to obtain a hydrophilic oligomer solution. Further, 420.0 g of fluorine-terminated polyethersulfone (P1) synthesized according to Reference Example 1, 2000 mL of DMSO, and 250 mL of toluene were added to a flask equipped with an azeotropic distillation apparatus under an Ar atmosphere. Thereafter, toluene was distilled off by heating at a bath temperature of 130 ° C. to azeotropically dehydrate water in the system, allowed to cool to room temperature, and then added to the hydrophilic oligomer solution and mixed. Thereafter, 2.32 g of potassium carbonate was added, and the mixture was heated and stirred for a total of 47 hours while raising the temperature to 150 ° C. The reaction solution was allowed to cool and then added dropwise to a large amount of hydrochloric acid, and the resulting precipitate was collected by filtration. Further, filtration and washing with water was repeated until the washing solution became neutral, and then dried under reduced pressure at 60 ° C. to obtain a block copolymer A1. After 1% by weight of A1 was dissolved in DMF, the residue when filtered through a 1 μm filter was 0.1% by weight or less.
Mn = 4.0 × 10 ⁴
Branch degree Bn = 22.3
Ion exchange capacity = 1.68 meq / g
From the ion exchange capacity, the weight composition ratio of the segment having an ion exchange group (segment based on a hydrophilic oligomer) and the segment having substantially no ion exchange group (segment based on a hydrophobic oligomer) is 32:68. Calculated.
Assumed structure of block copolymer A1: Hydrophobic oligomer and hydrophilic oligomer are considered to be linked via a linking group, and have a branch because Bn is 22.3. In particular, it seems that the linking group is linked to the hydrophobic oligomer or the hydrophilic oligomer at positions other than the 4,4′-position.

2) Production of polymer electrolyte membrane The obtained polymer electrolyte A1 was dissolved in N-methyl-2-pyrrolidone (NMP) to form a solution, which was applied using a bar coater, and dried at 80 ° C. and normal pressure for 2 hours. . Thereafter, the polymer electrolyte membrane (film thickness = 34 μm) was obtained by immersing in 1.5 mol / L hydrochloric acid and further washing with ion exchange water. The methanol permeability coefficient and proton conductivity of the obtained polymer electrolyte membrane were as follows.
Methanol permeability coefficient = 4.0 × 10 ⁻⁷ cm ² / s
Proton conductivity = 1.3 × 10 ⁻¹ S / cm
Water absorption rate = 97%

Example 2
In the same manner as in Example 1, 140.00 g of potassium 2,5-dihydroxybenzenesulfonate, 300.03 g of dipotassium 4,4′-difluorodiphenylsulfone-3,3′-disulfonate, and 88.16 g of potassium carbonate were used. A hydrophilic oligomer solution was obtained, the amount of fluorine-terminated polyethersulfone (P1) was changed to 452.1 g, and then the same operation as in Example 1 was performed. However, the time for stirring while keeping the temperature up to 150 ° C. was changed to a total of 60 hours. The post-process similar to Example 1 was performed and the 520-g copolymer A2 was obtained. After 1% by weight of A2 was dissolved in DMF, the residue when filtered through a 1 μm filter was 0.1% or less.
Mn = 4.7 × 10 ⁴
Branch degree Bn = 23.6
Ion exchange capacity = 1.53 meq / g
From the ion exchange capacity, the weight composition ratio of the segment having an ion exchange group and the segment having substantially no ion exchange group was calculated to be 29:71.
A polymer electrolyte membrane (film thickness = 37 μm) was obtained in the same manner as in Example 1. The methanol permeability coefficient and proton conductivity of the obtained polymer electrolyte membrane were as follows.
Methanol permeability coefficient = 4.4 × 10 ⁻⁷ cm ² / s
Proton conductivity = 8.7 × 10 ⁻² S / cm
Water absorption rate = 84%

Comparative Example 1
In the same manner as in Example 1, 138.34 g of potassium 2,5-dihydroxybenzenesulfonate, 289.88 g of dipotassium 4,4′-difluorodiphenylsulfone-3,3′-disulfonate, and 87.95 g of potassium carbonate were used. A hydrophilic oligomer solution was obtained. The mixture was mixed with 500.0 g of fluorine-terminated polyethersulfone (P1) and stirred while keeping the temperature up to 140 ° C. for a total of 46 hours. The post-process similar to Example 1 was performed and the 550-g copolymer B1 was obtained. After 1% by weight of B1 was dissolved in DMF, the residue when filtered through a 1 μm filter was 0.1% or less.
Mn = 3.2 × 10 ⁴
Branch degree Bn = 8.5
Ion exchange capacity = 1.50 meq / g
From the ion exchange capacity, the weight composition ratio of the segment having an ion exchange group and the segment having substantially no ion exchange group was calculated as 28:72.
A polymer electrolyte membrane (film thickness = 49 μm) was obtained in the same manner as in Example 1. The methanol permeability coefficient of the obtained polymer electrolyte membrane was as follows.
Methanol permeability coefficient = 8.6 × 10 ⁻⁷ cm ² / s
Proton conductivity = 1.2 × 10 ⁻¹ S / cm
Water absorption rate = 74%

Ｍｎ＝ ４．６×１０⁴
分岐度Ｂｎ＝ ０．０
イオン交換容量 １．６３ ｍｅｑ／ｇ
イオン交換容量から、イオン交換性基を有するセグメントとイオン交換性基を実質的に有さないセグメントの重量組成比は３１：６９と算出された。
実施例１と同様の方法にて高分子電解質膜（膜厚＝４４μｍ）を得た。得られた高分子電解質膜のメタノール透過係数は以下の通りであった。
メタノール透過係数＝ ６．７×１０^-7ｃｍ²／ｓ
プロトン伝導度＝ １．６×１０^-1Ｓ／ｃｍ
吸水率＝ １３３％ Comparative Example 2
In a flask equipped with an azeotropic distillation apparatus, in an Ar atmosphere, 40.0 g of potassium 2,5-dihydroxybenzenesulfonate, 94.2 g of dipotassium 4,4′-difluorodiphenylsulfone-3,3′-disulfonate, potassium carbonate 25.5 g was added and 585 mL DMSO and 92 mL toluene were added. Thereafter, toluene was distilled off by heating at a bath temperature of 140 ° C. to azeotropically dehydrate water in the system, and the mixture was stirred while keeping at 150 ° C. for 15 hours. Subsequently, the reaction solution was sufficiently cooled to room temperature to obtain a hydrophilic oligomer solution. In addition, 81.4 g of 4,4′-dihydroxydiphenylsulfone, 79.4 g of 4,4′-difluorodiphenylsulfone, and 49.5 g of potassium carbonate were added to a flask equipped with an azeotropic distillation apparatus under an Ar atmosphere. Toluene 111 mL was added. Thereafter, toluene was distilled off by heating at a bath temperature of 140 ° C. to azeotropically dehydrate the water in the system, and the mixture was stirred at 150 ° C. for 6 hours to obtain a hydrophobic oligomer solution. Subsequently, the hydrophobic oligomer solution was allowed to cool to room temperature, and then the hydrophilic oligomer solution was added to the hydrophobic oligomer solution and stirred while keeping the temperature up to 150 ° C. for a total of 24 hours. The reaction solution was allowed to cool and then added dropwise to a large amount of hydrochloric acid, and the resulting precipitate was collected by filtration. Further, filtration and washing were repeated with water until the washing solution became neutral, and then dried under reduced pressure at 60 ° C. to obtain 211.6 g of the following block copolymer B2. After 1% by weight of B2 was dissolved in DMF, the residue when filtered through a 1 μm filter was 0.1% or less.

Mn = 4.6 × 10 ⁴
Branch degree Bn = 0.0
Ion exchange capacity 1.63 meq / g
From the ion exchange capacity, the weight composition ratio of the segment having an ion exchange group and the segment having substantially no ion exchange group was calculated to be 31:69.
A polymer electrolyte membrane (film thickness = 44 μm) was obtained in the same manner as in Example 1. The methanol permeability coefficient of the obtained polymer electrolyte membrane was as follows.
Methanol permeability coefficient = 6.7 × 10 ⁻⁷ cm ² / s
Proton conductivity = 1.6 × 10 ⁻¹ S / cm
Water absorption rate = 133%

Comparative Example 3
In the same manner as in Comparative Example 2, 45.1 g of potassium 2,5-dihydroxybenzenesulfonate, 119.5 g of 4,4′-difluorodiphenylsulfone-3,3′-disulfonate dipotassium, and 28.80 g of potassium carbonate were used. A hydrophilic oligomer solution was obtained. Further, in the same manner as in Comparative Example 2, a hydrophobic oligomer solution was obtained using 118.0 g of 4,4′-dihydroxydiphenylsulfone, 110.3 g of 4,4′-difluorodiphenylsulfone, and 75.0 g of potassium carbonate. After mixing these in the same manner as in Comparative Example 2, the mixture was stirred while keeping the temperature up to 150 ° C. for a total of 17.5 hours, and 292.0 g of block copolymer B3 was obtained by the same post treatment as in Comparative Example 2. . After 1% by weight of B3 was dissolved in DMF, the residue when filtered through a 1 μm filter was 0.1% or less.
Mn = 4.7 × 10 ⁴
Branch degree Bn = 0.0
Ion exchange capacity = 1.72 meq / g
From the ion exchange capacity, the weight composition ratio of the segment into which the ion exchange group was introduced and the segment into which the ion exchange group was not substantially introduced was calculated as 32:68.
A polymer electrolyte membrane (film thickness = 35 μm) was obtained in the same manner as in Example 1. The methanol permeability coefficient of the obtained polymer electrolyte membrane was as follows.
Methanol permeability coefficient = 8.7 × 10 ⁻⁷ cm ² / s
Proton conductivity = 1.2 × 10 ⁻¹ S / cm
Water absorption rate = 194%

  The copolymer of Example 1 and Comparative Examples 2 and 3, and the copolymer of Example 2 and Comparative Example 1 are copolymers having the same degree of ion exchange capacity, but Examples 1-2 having a higher degree of branching are more permeable to methanol. The coefficient was small.

As described above in detail, according to the present invention, a polymer used for the preparation of a polymer electrolyte membrane having a lower methanol permeability and a higher proton conductivity is provided. A polymer electrolyte membrane having high conductivity, a polymer electrolyte used for the preparation thereof, and a polymer electrolyte membrane, a polymer electrolyte composite membrane, a catalyst composition, and a polymer electrolyte fuel cell are provided as their uses. Further, according to the present invention, it is possible to obtain a polymer electrolyte membrane having a water absorption rate that is not too high. Therefore, the industrial utility value of the present invention is very large.

Claims (11)

A polymer having an ion-exchange group, wherein the degree of branching Bn calculated based on the following formula is 10 or more and the ion-exchange capacity is 1 meq / g or more.

(In the formula, IV (M) is the intrinsic viscosity at the molecular weight M of the polymer, and IVL (M) is the intrinsic viscosity of the linear polymer at the molecular weight M.   The polymer according to claim 1, which is soluble in a solvent.   The polymer according to claim 1 or 2, wherein the main chain is an aromatic polymer.   The polymer according to any one of claims 1 to 3, wherein the polymer is a block copolymer having a block having an ion-exchange group and a block having substantially no ion-exchange group.   The weight composition ratio of the block having an ion-exchange group and the block having substantially no ion-exchange group is (block having an ion-exchange group): (block having substantially no ion-exchange group) The polymer according to claim 4, wherein the polymer is 3:97 to 70:30.   A polymer electrolyte comprising the polymer according to claim 1.   A polymer electrolyte membrane using the polymer electrolyte according to claim 6.   A polymer electrolyte membrane obtained by a solution casting method using the polymer electrolyte according to claim 6.   A polymer electrolyte composite membrane comprising the polymer electrolyte according to claim 6 and a porous substrate.   A catalyst composition comprising the polymer electrolyte according to claim 6 and a catalyst. A polymer electrolyte fuel cell comprising the polymer electrolyte according to claim 6.