JP2016033174A - Method for producing sulfonated polymer and polymer electrolyte, polymer electrolyte membrane, and polymer electrolyte fuel cell comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a sulfonated polymer for use in a polymer electrolyte film for a solid polymer electrolyte fuel cell.SOLUTION: The method for producing a sulfonated polymer is provided that comprises: a first step of reacting a block copolymer and a sulfonating agent in an organic solvent, the block copolymer containing a polymer block composed of a structural unit derived from an aromatic vinyl compound represented by a formula (1), an amorphous polymer block composed of a structural unit derived from an unsaturated aliphatic hydrocarbon, and a polymer block composed of a structural unit derived from another aromatic vinyl compound; a second step of washing solids which precipitated in the first step with water; and a third step of washing the solids washed in the second step with a C1-4 alcohol. (Ris H or a C1-4 alkyl group; Rto Rare each independently H or a C1-2 alkyl group; and at least two of Rto Rare H.)SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a sulfonated polymer that is useful as a polymer electrolyte membrane for a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as highly efficient power generation systems. Fuel cells are classified into molten carbonate type, solid oxide type, phosphoric acid type, solid polymer type, etc., depending on the type of electrolyte used. Among these, a polymer electrolyte membrane having a structure in which a polymer electrolyte membrane is sandwiched between electrodes (anode and cathode), a solid polymer fuel cell that generates electricity by supplying a fuel made of a reducing agent to the anode and an oxidant to the cathode, From the viewpoint of low-temperature operability, reduction in size and weight, etc., application to automobile power sources, portable device power sources, and household cogeneration systems that simultaneously use electricity and heat are being considered.

  The polymer electrolyte membrane used in the polymer electrolyte fuel cell is designed to increase the output of the polymer electrolyte fuel cell under low humidity and to withstand changes in humidity inside the polymer electrolyte fuel cell due to startup and shutdown ( It is required to achieve both dry and wet resistance. Such a demand is particularly strong in a polymer electrolyte fuel cell using hydrogen as a fuel.

  Examples of polymer electrolyte membranes that can increase the output of a polymer electrolyte fuel cell under low humidity include, for example, a polymer block (A) having an ion conductive group and a polymer block (B) having no ion conductive group (B And a polymer block (C) having a softening temperature higher than that of the polymer block (B) by 20 ° C. or more and having no ion-conducting group, in a specific order, a polymer electrolyte comprising a block copolymer A film has been proposed (see Patent Document 1). However, there is still room for improvement with respect to the wet and dry resistance of such a polymer electrolyte membrane.

International Publication No. 2011-122498

  Accordingly, an object of the present invention is to improve the output of a polymer electrolyte fuel cell under low humidity and to be excellent in moisture resistance when used as a polymer electrolyte membrane for a polymer electrolyte fuel cell. Another object of the present invention is to provide a method for producing a polymer.

According to the present invention, the above object is
[1] A polymer block composed of a structural unit derived from an aromatic vinyl compound (hereinafter referred to as “aromatic vinyl compound (1)”) represented by the following general formula (1) (hereinafter referred to as “polymer block ( _A0 ) ”), an amorphous polymer block composed of a structural unit derived from an unsaturated aliphatic hydrocarbon (hereinafter referred to as“ polymer block (B) ”), and the following general formula (2) And a polymer block (hereinafter referred to as “polymer block (C)”) composed of a structural unit derived from an aromatic vinyl compound (hereinafter referred to as “aromatic vinyl compound (2)”). A first step in which a block copolymer (hereinafter referred to as “block copolymer (Z ₀ )”) and a sulfonating agent are reacted in an organic solvent to obtain a reaction mixture;
A second step in which the reaction mixture obtained in the first step is brought into contact with water to precipitate a solid; and the solid precipitated in the second step is referred to as an alcohol having 1 to 4 carbon atoms (hereinafter referred to as “alcohol (X)”). The third step of washing with
A process for producing a sulfonated polymer comprising:
[2] A polymer electrolyte comprising a sulfonated polymer obtained by the method of [1] above;
[3] A polymer electrolyte membrane comprising a sulfonated polymer obtained by the method of [1] above;
[4] The polymer electrolyte membrane according to [3], which is for a polymer electrolyte fuel cell; and [5] a solid polymer fuel cell comprising the polymer electrolyte membrane according to 3 or 4 above;
Is achieved by providing

（式中、Ｒ^１は水素原子又は炭素数１〜４のアルキル基を表す。Ｒ^２〜Ｒ^４はそれぞれ独立に水素原子又は炭素数１〜２のアルキル基を表し、かつＲ^２〜Ｒ^４の少なくとも２つは水素原子を表す。）

(In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ^{2 to} R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R ^{2 to} R ^4. At least two of these represent hydrogen atoms.)

（式中、Ｒ^５は水素原子又は炭素数１〜４のアルキル基を表し、Ｒ^６〜Ｒ^８はそれぞれ独立に水素原子又は炭素数３〜８のアルキル基を表し、かつＲ^６〜Ｒ^８の少なくとも１つは炭素数３〜８のアルキル基を表す。）

(In the formula, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ^{6 to} R ⁸ each independently represents a hydrogen atom or an alkyl group having 3 to 8 carbon atoms, and R ^{6 to} R ^8. At least one of these represents an alkyl group having 3 to 8 carbon atoms.)

  The sulfonated polymer obtained by the production method of the present invention exhibits a high output under low humidity and is excellent in dry and wet resistance when used in a polymer electrolyte membrane for a polymer electrolyte fuel cell.

[First step]
The first step according to the production method of the present invention is a step of reacting the block copolymer (Z ₀ ) and the sulfonating agent in an organic solvent (sulfonation reaction). In the sulfonation reaction, a sulfonic acid group is selectively introduced into the polymer block (A ₀ ). As a result, in the polymer electrolyte membrane comprising the sulfonated polymer obtained in the present invention, a polymer block in which a sulfonic acid group is introduced into the polymer block (A ₀ ) (hereinafter referred to as “polymer block (A)”). ), The polymer block (B) and the polymer block (C) form a microphase separation structure. Thus, the polymer electrolyte membrane of the present invention is excellent in ion conductivity due to the ion conductive channel formed by the phase containing the polymer block (A), and the flexible phase and polymer block containing the polymer block (B) ( The phase with high binding force including C) is excellent in mechanical strength.
Here, “microphase separation” means phase separation in a microscopic sense, and more specifically, means phase separation in which the formed domain size is less than or equal to the wavelength of visible light (3800 to 7800 mm). It shall be.

(Block copolymer (Z ₀ ))
The block copolymer (Z ₀ ) used in the first step contains a polymer block (A ₀ ), a polymer block (B), and a polymer block (C).

The polymer block (A ₀ ) is composed of a structural unit derived from the aromatic vinyl compound (1).
Examples of the aromatic vinyl compound (1) include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, α-methylstyrene, α-methyl-4-methylstyrene, α- Examples thereof include methyl-2-methylstyrene, α-methyl-4-ethylstyrene, and styrene, 2-methylstyrene, 4-methylstyrene, α-methylstyrene, and α-methyl-4-methylstyrene are preferred and available. From the viewpoint of properties, styrene, α-methylstyrene and 4-methylstyrene are more preferable. The polymer block (A ₀ ) can be formed by polymerizing these aromatic vinyl compounds (1) as monomers. These aromatic vinyl compounds (1) may be used alone or in combination of two or more. The structural unit derived from the aromatic vinyl compound (1) with respect to all the structural units forming the polymer block (A ₀ ) is preferably 95 mol% or more.

The polymer block (A ₀ ) may contain a structural unit derived from another monomer other than the aromatic vinyl compound (1) as long as the effects of the present invention are not impaired. Examples of such other monomers include butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1, C4-C8 conjugated dienes such as 3-heptadiene; C2-C8 alkenes such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, 1-octene; (Meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate and butyl (meth) acrylate; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl pivalate; methyl vinyl ether, isobutyl Vinyl ethers such as vinyl ethers; aromatic vinyl compounds (2), vinyl naphthalene, vinyl biphenyl, etc. Aromatic vinyl compound (1) other than the aromatic vinyl compounds, and the like. These other monomers may be used alone or in combination of two or more. These other monomers can form a polymer block (A ₀ ) by mixing and copolymerizing with the aromatic vinyl compound (1).

The number average molecular weight (Mn) per polymer block (A ₀ ) is preferably in the range of 2,500 to 45,000, more preferably in the range of 4,000 to 34,000, and 7,000 to 20,000. The range of is more preferable. If the Mn is 2,500 or more, the polymer electrolyte fuel cell having a polymer electrolyte membrane made of a sulfonated polymer obtained tends to be excellent in output under low humidity, and if it is 45,000 or less, the resulting sulfone is obtained. The polymerized polymer tends to be excellent in coatability.
In addition, in this specification, Mn means the standard polystyrene conversion value measured by the gel permeation chromatography (GPC) method.

The total content of the polymer block in the polymer block _{(Z 0) (A 0)} is preferably in the range of 20 to 45 wt%, more preferably in the range of 25 to 40 mass%, further in the range of 30 to 40 wt% preferable. If the total content is 20% by mass or more, the obtained polymer electrolyte fuel cell having a polymer electrolyte membrane made of a sulfonated polymer tends to be excellent in output under low humidity, and can be obtained if it is 45% by mass or less. The polymer electrolyte membrane made of a sulfonated polymer tends to be excellent in water resistance.

The polymer block (B) is an amorphous polymer block composed of structural units derived from unsaturated aliphatic hydrocarbons. In addition, the amorphous property of the polymer block (B) can be confirmed by measuring the dynamic viscoelasticity of the block copolymer (Z ₀ ) and not having a change in the storage elastic modulus derived from the crystalline olefin polymer. .

  Examples of the unsaturated aliphatic hydrocarbon capable of forming the polymer block (B) include 2 carbon atoms such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. Alkene of ˜8; C7-10 vinylcycloalkane such as vinylcyclopentane, vinylcyclohexane, vinylcycloheptane, vinylcyclooctane; C7 such as vinylcyclopentene, vinylcyclohexene, vinylcycloheptene, vinylcyclooctene To 10 vinylcycloalkenes; butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-heptadiene And conjugated dienes having 4 to 8 carbon atoms such as C2-C8 alkene and butadiene such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1,3-pentadiene, isoprene, 1,3-hexadiene C4-C8 conjugated dienes such as 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, and 1,3-heptadiene are preferable, and conjugated dienes having 4 to 8 carbon atoms are preferable. More preferred are butadiene and isoprene. A polymer block (B) can be formed by polymerizing these unsaturated aliphatic hydrocarbons as monomers. These unsaturated aliphatic hydrocarbons may be used alone or in combination of two or more. It is preferable that the structural unit derived from the unsaturated aliphatic hydrocarbon with respect to all the structural units forming the polymer block (B) is 95 mol% or more.

  The polymer block (B) may contain a structural unit derived from a monomer other than the unsaturated aliphatic hydrocarbon as long as the effects of the present invention are not impaired. Examples of such other monomers include aromatic vinyl compounds such as styrene and vinyl naphthalene; halogen-containing vinyl compounds such as vinyl chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl pivalate; methyl vinyl ether And vinyl ethers such as isobutyl vinyl ether. These other monomers may be used alone or in combination of two or more. These other monomers can be mixed with the unsaturated aliphatic hydrocarbon and copolymerized to form a polymer block (B).

When the unsaturated aliphatic hydrocarbon has a plurality of carbon-carbon double bonds, any of them may be used for polymerization. For example, when the unsaturated aliphatic hydrocarbon is a conjugated diene, -It may be a binding unit or a 1,4-bond unit. A polymer block formed by polymerizing a conjugated diene usually retains a carbon-carbon double bond. However, after the polymerization, a hydrogenation reaction (hereinafter referred to as “hydrogenation reaction”) is performed, and the carbon-carbon double bond is formed. It is preferable to hydrogenate the heavy bond (hereinafter referred to as “hydrogenation”). The hydrogenation rate of such a carbon-carbon double bond (hereinafter referred to as “hydrogenation rate”) is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 97 mol% or more. By increasing the hydrogenation rate, when the block copolymer (Z ₀ ) is reacted with a sulfonating agent, introduction of sulfonic acid groups into the polymer block (B) tends to be inhibited. Further, the obtained sulfonated polymer tends to be excellent in heat resistance. The hydrogenation rate can be calculated by ¹ H-NMR measurement.

  The Mn per polymer block (B) is preferably in the range of 10,000 to 150,000, more preferably in the range of 17,500 to 100,000, and in the range of 28,000 to 75,000. More preferably. If such Mn is in the above range, the resulting sulfonated polymer tends to be excellent in coatability.

The total content of the polymer block (B) in the polymer block (Z ₀ ) is preferably in the range of 35 to 65% by mass, more preferably in the range of 35 to 55% by mass, and still more preferably in the range of 40 to 50% by mass. . When the total content is within the above range, the obtained polymer electrolyte membrane made of a sulfonated polymer tends to be excellent in mechanical strength.

The polymer block (C) is composed of structural units derived from the aromatic vinyl compound (2).
When the block copolymer (Z ₀ ) is reacted with a sulfonating agent, introduction of a sulfonic acid group into the polymer block (C) is inhibited, so that the polymer block (A ₀ ) can be selectively treated with sulfone. Acid groups can be introduced.

  Examples of the aromatic vinyl compound (2) include 4-propyl styrene, 4-isopropyl styrene, 4-butyl styrene, 4-isobutyl styrene, 4-tert-butyl styrene, 4-octyl styrene, α-methyl-4-tert. -Butyl styrene, α-methyl-4-isopropyl styrene and the like can be mentioned, and 4-tert-butyl styrene, 4-isopropyl styrene, α-methyl-4-tert-butyl styrene and α-methyl-isopropyl styrene are preferable. The polymer block (C) can be formed by polymerizing these aromatic vinyl compounds (2) as monomers. These aromatic vinyl compounds (2) may be used alone or in combination of two or more. The content of the structural unit derived from the aromatic vinyl compound (2) with respect to all the structural units forming the polymer block (C) is preferably 95 mol% or more.

  The polymer block (C) may contain a structural unit derived from another monomer other than the aromatic vinyl compound (2) as long as the present invention is not impaired. Examples of such other monomers include butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,4-hexadiene, 2,3-dimethyl-1,3-butadiene, and 2-ethyl-1. C4-C8 conjugated dienes such as 1,3-butadiene, 1,3-heptadiene; carbon numbers such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, 1-octene 2 to 8 alkenes; (meth) acrylate esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc. Vinyl esters; vinyl ethers such as methyl vinyl ether and isobutyl vinyl ether; styrene, α-methyl styrene, vinyl naphth Ren, aromatic vinyl compounds such as vinyl biphenyl (1) an aromatic vinyl compound other than thereof. These other monomers may be used alone or in combination of two or more. These other monomers can form a polymer block (C) by mixing and copolymerizing with the aromatic vinyl compound (2).

  The Mn per polymer block (C) is preferably in the range of 1,500 to 30,000, more preferably in the range of 2,000 to 25,000, and in the range of 3,500 to 15,000. More preferably. If the Mn is 1,500 or more, the resulting polymer electrolyte membrane made of a sulfonated polymer tends to be excellent in mechanical strength, and if it is 30,000 or less, the resulting sulfonated polymer tends to be excellent in coatability. Become.

The total content of the polymer block (C) in the polymer block (Z ₀ ) is preferably in the range of 5 to 30% by mass, more preferably in the range of 10 to 30% by mass, and still more preferably in the range of 20 to 30% by mass. . If the total content is 5% by mass or more, the resulting polymer electrolyte membrane composed of the sulfonated polymer tends to be excellent in mechanical strength, and if it is 30% by mass or less, the resulting sulfonated polymer has good coatability. It becomes.

The block copolymer (Z ₀ ) may contain a polymer block other than the polymer block (A ₀ ), the polymer block (B), and the polymer block (C). Although there is no restriction | limiting in particular in the monomer which can form such a polymer block, (meth) acrylic acid esters, such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate; vinyl acetate, propion Vinyl esters such as vinyl acid vinyl, vinyl butyrate and vinyl pivalate; Vinyl ethers such as methyl vinyl ether and isobutyl vinyl ether; Aromatic vinyl compounds other than aromatic vinyl compounds (1) and aromatic vinyl compounds (2) such as vinyl naphthalene and vinyl biphenyl Compounds and the like. These other polymer blocks may be one or plural. The content of these other polymer blocks in the block copolymer (Z ₀ ) is preferably 5% by mass or less in total.

The Mn of the block copolymer (Z ₀ ) is not particularly limited, but is usually preferably in the range of 30,000 to 200,000, more preferably in the range of 50,000 to 170,000, and 70,000 to 150,000. A range is further preferred. If the Mn is 30,000 or more, the resulting sulfonated polymer tends to be excellent in water resistance, and if it is 200,000 or less, the obtained sulfonated polymer tends to be excellent in coatability.

In the block copolymer (Z ₀ ), the mass ratio of the total amount of the polymer block (A ₀ ) to the total amount of the polymer block (C) (polymer block (A ₀ ): polymer block (C)) is 40. : 60 to 90:10 is preferable, 45:55 to 80:20 is more preferable, and 50:50 to 70:30 is still more preferable. When the ratio of the total amount of the polymer block (A ₀ ) is increased within the above mass ratio range, the polymer electrolyte fuel cell including the polymer electrolyte membrane using the obtained sulfonated polymer tends to be excellent in output under low humidity. It becomes. Moreover, when the ratio of the total amount of the polymer block (A ₀ ) is lowered within the above mass ratio range, the polymer electrolyte membrane using the resulting sulfonated polymer tends to be excellent in mechanical strength.

In the block copolymer (Z ₀ ), the mass ratio of the total amount of the polymer block (B) to the total amount of the polymer block (C) (polymer block (B): polymer block (C)) is 45: It is preferably 55 to 90:10, more preferably 50:50 to 85:15, and even more preferably 55:45 to 80:20. When the ratio of the total amount of the polymer block (B) is increased within the above mass ratio range, the resulting sulfonated polymer tends to be excellent in flexibility. Further, when the ratio of the total amount of the polymer block (B) is lowered within the above mass ratio range, the resulting polymer electrolyte membrane made of a sulfonated polymer tends to be excellent in mechanical strength.

As an example of the arrangement of the block copolymer (Z ₀ ), A ₀ -B-C type triblock copolymer (A ₀ , B and C are respectively a polymer block (A ₀ ) and a polymer block (B). , Polymer block (C), the same shall apply hereinafter), A ₀ -BCA ₀ type tetrablock copolymer, A ₀ -BA ₀ -C type tetrablock copolymer, BA ₀ -B-C-type tetrablock _copolymers, A 0 -B-C-B-type tetrablock _{copolymer, C-A 0 -B-A} 0 -C type pentablock copolymer, _{C-B-A 0} —B—C type pentablock copolymer, A ₀ —C—B—C—A ₀ type pentablock copolymer, A ₀ —C—B—A ₀ —C type pentablock copolymer, A ₀ — _{C-B-C-A 0} -C type hexamethylene block _{copolymer, C-A 0 -B-C} -A 0 -C type Hekisaburo Copolymer, A ₀ -C-A ₀ -CBC type hexablock copolymer, A ₀ -CA ₀ -C—B-C-A ₀ type heptablock copolymer, A _0- C—B—C—B—C—A _0- type heptablock copolymer, C—A ₀ —C—B—C—A ₀ —C-type hepta block copolymer, A ₀ —C—A ₀ —C—B—C—A ₀ —C type octablock copolymer, A ₀ —C—B—C—B—C—A ₀ —C type octablock copolymer, A ₀ —C—B—C -A ₀ -C—B—C type octablock copolymer and the like, and among them, from the viewpoint of ion conductivity and mechanical strength of the polymer electrolyte membrane, A ₀ -B—C—A ₀ type tetrablock _{copolymer, A} 0 _-B-A 0 -C-type tetrablock _copolymers, A 0 -B-C-B-type tetrablock _copolymers, A 0 -C-B-C- ₀ type pentablock _{copolymer, A 0 -C-B-A} 0 -C type pentablock _{copolymer, A 0 -C-B-C} -A 0 -C type hexamethylene block _copolymer, A 0 -C -A ₀ -C-B-C type hexablock copolymer, A ₀ -C-A ₀ -C-B-C-A ₀ type heptablock copolymer, A ₀ -C-B-C-B- C-A _0- type heptablock copolymer, A ₀ -C-A ₀ -C-B-C-A ₀ -C-type octa-block copolymer, A ₀ -C-B-C-B-C-A ₀ -C type oct block copolymer and _{A 0 -C-B-C-} A 0 -C-B-C type oct block copolymer are _{preferable, A 0 -C-B-C} -A 0 type pentablock _{copolymer, A 0 -C-B-A} 0 -C type pentablock _{copolymer, A 0 -C-B-C} -A 0 -C type hexamethylene block copolymer _{, A 0 -C-A 0 -C} -B-C type hexamethylene block _{copolymer, A 0 -C-A 0 -C} -B-C-
A ₀ -C type octablock copolymer, A ₀ -C—B—C—B—C—A ₀ —C type octablock copolymer and A ₀ —C—B—C—A ₀ —C—B -C-type oct block copolymer are more _{preferable, A 0 -C-B-C} -A 0 type pentablock copolymers and _{A 0 -C-A 0 -C-} B-C-A 0 -C type octa More preferred are block copolymers.

Although the production method of the block copolymer (Z ₀₎ can be selected as appropriate, a living radical polymerization method, after polymerizing the respective monomers described above by polymerization selected from a living anionic polymerization and living cationic polymerization method, needs The method of hydrogenating the carbon-carbon double bond of the polymer block (B) of the block copolymer obtained accordingly is preferable.

As specific examples of the method for producing the block copolymer (Z ₀ ), styrene is used as the aromatic vinyl compound (1), isoprene is used as the unsaturated aliphatic hydrocarbon, and 4-tert-butylstyrene is used as the aromatic vinyl compound (2). When used, styrene, isoprene and 4-tert-butylstyrene are sequentially added in a desired order in a solvent such as cyclohexane using an anionic polymerization initiator such as an organolithium compound at a temperature of 20 to 100 ° C. And sequentially polymerize. After polymerization, the obtained block copolymer is charged into a pressure vessel, a known hydrogenation catalyst is added, and a hydrogenation reaction is performed in a hydrogen atmosphere to obtain a block copolymer (Z ₀ ). be able to.

(Sulfonation reaction)
The sulfonation rate of the sulfonation reaction in the first step is 90% from the viewpoint of increasing the ionic conductivity and increasing the output of the solid polymer fuel cell comprising a polymer electrolyte membrane made of the resulting sulfonated polymer at low humidity. % Or more is preferable. In the present specification, the sulfonation rate means the molar fraction of the introduced sulfonic acid group with respect to the structural unit derived from the aromatic vinyl compound (1).
In addition, the content (ion exchange capacity) of the sulfonic acid group in the solid obtained in the second step described below and the sulfonated polymer obtained (ion exchange capacity) is preferably in the range of 1 to 3.5 meq / g, 1.5 to 3 meq / g. A range is more preferred. If the ion exchange capacity is 1 meq / g or more, the polymer electrolyte fuel cell including the polymer electrolyte membrane made of the sulfonated polymer tends to be excellent in output under low humidity, and if it is 3.5 meq / g or less. The sulfonated polymer tends to be excellent in water resistance. In addition, this content is calculated | required by neutralization titration.

Such sulfonation reaction is performed, for example, by preparing a solution or suspension from a block copolymer (Z ₀ ) and an organic solvent, adding a sulfonating agent to the solution or suspension, and mixing.
Sulfonating agents used in the sulfonation reaction include sulfuric acid, a mixture of acid anhydride and sulfuric acid, chlorosulfonic acid, a mixture of chlorosulfonic acid and trimethylsilyl chloride, sulfur trioxide, sulfur trioxide and triethyl phosphate. Examples thereof include a mixture system and aromatic organic sulfonic acid represented by 2,4,6-trimethylbenzenesulfonic acid. Among these, from the viewpoint of suppressing side reactions of sulfonation, a mixture system of acid anhydride and sulfuric acid is preferable.
Such a sulfonating agent may be purchased commercially or prepared by a known method.

  Examples of the organic solvent that can be used for the sulfonation reaction include halogenated hydrocarbons such as methylene chloride, linear aliphatic hydrocarbons such as hexane, cyclic aliphatic hydrocarbons such as cyclohexane, and aromatics having electron-withdrawing groups such as nitrobenzene. Group compounds and the like, and halogenated hydrocarbons such as methylene chloride are preferred.

The amount of the sulfonating agent used is preferably 0.9 to 10 mol times, more preferably 2 to 8 mol times with respect to the structural unit derived from the aromatic vinyl compound (1) in the block copolymer (Z ₀ ). Preferably, 3 to 5 mole times is more preferable from the viewpoint of washing efficiency of the solid after the sulfonation reaction. If the amount used is 0.9 mol times or more with respect to the structural unit derived from the aromatic vinyl compound (1) of the block copolymer (Z ₀ ), the sulfonation reaction tends to proceed rapidly. If it is less than mol times, it tends to be advantageous from the viewpoint of raw material cost.

As a specific example of the sulfonation reaction, a sulfonating agent is prepared in advance using acetic anhydride and sulfuric acid, and the block copolymer (Z ₀ ) and the sulfonating agent are reacted using methylene chloride as the organic solvent. The method for obtaining the mixture will be described below.

The methylene chloride to be used is dehydrated in advance with molecular sieves or the like.
While adding methylene chloride to a flask purged with nitrogen and stirring at 0 to 10 ° C., acetic anhydride and sulfuric acid were added dropwise while maintaining the liquid temperature at 20 to 30 ° C. To prepare.
Block copolymer (Z ₀₎ mass by adding 10 to 30 times by weight of methylene chloride respect of stirring at room temperature, to prepare a methylene chloride solution of the block copolymer (Z _0). Next, the previously prepared sulfonating agent is dropped while maintaining the liquid temperature at 20 to 30 ° C. while stirring the prepared methylene chloride solution. After the sulfonating agent is added, the mixture is stirred at room temperature and reacted until the desired sulfonation rate is obtained to obtain the desired reaction mixture. The sulfonation rate is obtained by sampling the reaction mixture and measuring ¹ H-NMR.

[Second step]
The second step according to the production method of the present invention is a step in which the reaction mixture obtained in the first step is brought into contact with water to precipitate a solid. Examples of the method of bringing into contact with water include a method of adding water to the reaction mixture and a method of adding the reaction mixture to water. From the viewpoint of suppressing mixing of water-soluble impurities into the resulting solid, water is added to the reaction mixture. The method of adding is preferable.
A solid can be precipitated by adding water while maintaining the liquid temperature of the reaction mixture obtained in the first step at 20 to 30 ° C.

The amount of water to be brought into contact with the reaction mixture is preferably 10 to 50 times by mass of the block copolymer (Z ₀ ) provided in the first step from the viewpoint of increasing the solid recovery efficiency. The temperature at which water is brought into contact with the reaction mixture is preferably in the range of 5 to 50 ° C, more preferably in the range of 10 to 40 ° C. The time for contacting the reaction mixture with water is preferably in the range of 0.1 to 30 hours, and more preferably in the range of 0.5 to 10 hours.

  The solid precipitated in the second step can be recovered by known means such as filtration and drying. Moreover, it is preferable to wash | clean the solid precipitated in the 2nd process with water in order to remove water-soluble impurities, such as an inorganic substance adhering to the solid surface, before using for a 3rd process. In the case of washing with water, it is preferable to stir the recovered solid in water, then remove the water by filtration and recover the solid again. Such washing with water may be performed only once or a plurality of times. The amount of water used in the water washing is preferably 10 to 50 times by mass of the solid obtained in the recovery step from the viewpoint of increasing the washing efficiency. The temperature for washing with water is preferably in the range of 5 to 80 ° C, more preferably in the range of 10 to 40 ° C. Washing with water is preferably repeated until the pH of the removed water does not change.

[Third step]
The third step according to the production method of the present invention is a step of washing the solid precipitated in the second step with alcohol (X).
Specific examples of alcohol (X) include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, and methanol is preferred from the viewpoint of the recovery efficiency of the sulfonated polymer. By washing the solid deposited in the second step using these alcohols (X), the resulting polymer electrolyte membrane made of a sulfonated polymer has high wet and dry resistance. The reason why such a polymer electrolyte membrane excellent in dry and wet resistance can be obtained is not clear, but it is estimated that the impurities causing the decrease in dry and wet resistance are estimated to be removed by alcohol, and the impurities causing the decrease in dry and dry resistance are not clear. Not intended, but assumes low molecular weight polymers.

  As for the usage-amount of alcohol (X), 20-70 mass times of the solid used for washing | cleaning is preferable. The washing time with alcohol (X) is preferably in the range of 20 minutes to 24 hours from the viewpoint of production efficiency, and more preferably in the range of 1 to 10 hours. The temperature for washing with alcohol (X) is preferably in the range of 0 to 60 ° C., and is usually carried out at room temperature. In washing with the alcohol (X), the solid is usually stirred in the alcohol (X), and then the alcohol (X) is removed by filtration to recover the sulfonated polymer. The recovered sulfonated polymer may be further washed with alcohol (X).

[Manufacture of polymer electrolyte and polymer electrolyte membrane]
Hereinafter, production of a polymer electrolyte and a polymer electrolyte membrane made of a sulfonated polymer obtained by the production method of the present invention will be described. Usually, a flowable composition comprising a sulfonated polymer dissolved or dispersed in a solvent is prepared, the flowable composition is formed into a desired shape, and the solvent is removed to form a molded body that is a polymer electrolyte ( For example, a polymer electrolyte membrane) is manufactured.

  The solvent that can be used in the fluid composition is not particularly limited as long as it does not destroy the structure of the sulfonated polymer. Specifically, it is a halogenated hydrocarbon such as methylene chloride; an aromatic such as toluene, xylene, or benzene. Hydrocarbons: Chain aliphatic hydrocarbons such as hexane, heptane, and octane; Cyclic aliphatic hydrocarbons such as cyclohexane; Ethers such as tetrahydrofuran, methanol, ethanol, propanol, 1-propanol, 1-butanol, 2-methyl- Examples thereof include alcohols such as 1-propanol. These solvents may be used alone or in combination of two or more, but from the viewpoint of solubility or dispersibility of the polymer block contained in the sulfonated polymer, toluene and 2-methyl-1 A mixed solvent of -propanol, a mixed solvent of xylene and 2-methyl-1-propanol, a mixed solvent of toluene and 2-propanol, a mixed solvent of cyclohexane and 2-propanol, a mixed solvent of cyclohexane and 2-methyl-1-propanol, A mixed solvent of tetrahydrofuran and methanol is preferable, a mixed solvent of toluene and 2-methyl-1-propanol, a mixed solvent of xylene and 2-methyl-1-propanol, and a mixed solvent of toluene and 2-propanol are more preferable.

  The flowable composition may contain various additives such as a softener, a stabilizer, an inorganic filler, an antistatic agent, a release agent, a flame retardant, a foaming agent, a pigment, a dye, a bleaching agent, and a fiber as necessary. Or may be dissolved or dispersed. The content of these additives in the components (solid content) other than the solvent in the fluid composition is preferably 25% by mass or less, more preferably 20% by mass or less, and more preferably 15% by mass. More preferably, it is as follows.

  Examples of the softener include petroleum-based softeners such as paraffinic, naphthenic, and aromatic process oils; paraffin, vegetable oil-based softeners, plasticizers, and the like. These may be used alone or in combination of two or more.

  Examples of the stabilizer include 2,6-ditert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-ditert-butyl-4-hydroxyphenyl) propionate], 1,3,5 Trimethyl-2,4,6-tris (3,5-ditert-butyl-4-hydroxybenzyl) benzene, octadecyl-3- (3,5-ditert-butyl-4-hydroxyphenyl) propionate, triethylene Glycol-bis [3- (3-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis (n-octylthio) -6- (4-hydroxy-3,5-ditert-butylanilino) -1 , 3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-ditert-butyl-4-hydroxyphen ) Propionate], N, N′-hexamethylenebis (3,5-ditert-butyl-4-hydroxy-hydrocinnamamide), 3,5-ditert-butyl-4-hydroxy-benzylphosphonate-diethyl Ester, tris (3,5-ditert-butyl-4-hydroxybenzyl) -isocyanurate, 3,9-bis [2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyl Phenol stabilizers such as oxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane; pentaerythrityltetrakis (3-laurylthiopropionate), di Stearyl 3,3′-thiodipropionate, dilauryl 3,3′-thiodipropionate, dimyristyl 3,3 ′ Sulfur stabilizers such as thiodipropionate; phosphorus stabilizers such as tris (nonylphenyl) phosphite, tris (2,4-ditert-butylphenyl) phosphite, distearyl pentaerythritol diphosphite It is done. These may be used alone or in combination of two or more.

  Examples of the inorganic filler include talc, calcium carbonate, silica, glass fiber, mica, kaolin, titanium oxide, montmorillonite, and alumina. These may be used alone or in combination of two or more.

  After the fluid composition is molded into a desired shape, the solvent is removed to obtain a molded body (for example, a polymer electrolyte membrane) that is a polymer electrolyte. The temperature at which the solvent is removed can be arbitrarily selected as long as the sulfonated polymer is not decomposed, and a plurality of temperatures may be arbitrarily combined. Solvent removal method is a method of removing the solvent by drying at 60 to 120 ° C. for 4 minutes or longer in a hot air dryer; removing the solvent by drying at 120 to 140 ° C. for 2 to 4 minutes in a hot air dryer. A method of pre-drying at 25 ° C. for 1 to 3 hours, and then drying in a hot air dryer at 80 to 120 ° C. for 5 to 10 minutes; Examples include a method of drying for 1 to 12 hours under reduced pressure under an atmosphere of 25 to 40 ° C., and from the viewpoint of increasing the mechanical strength of the obtained polymer electrolyte membrane, in a hot air dryer at 60 to 120 ° C. A method of drying over 4 minutes; a method of predrying at 25 ° C. for 1 to 3 hours and then drying in a hot air dryer at about 80 to 120 ° C. for 5 to 10 minutes; After pre-drying for a period of time, under an atmosphere of 25 to 40 ° C. 1.3. The method for drying 1 to 12 hours under a reduced pressure condition of at most Pa is preferred.

  Next, a method for producing a polymer electrolyte membrane will be described as an example of the molded body that is the polymer electrolyte. In the production of the polymer electrolyte membrane, the fluid composition is applied onto a substrate to form a membrane, and then the solvent is removed. Examples of the substrate on which the fluid composition is applied include a polymer film or a glass plate usually made of polyethylene terephthalate (PET) or the like. Examples of the coating method include a method of coating using a coater or an applicator. The polymer electrolyte membrane is usually used after being peeled from the substrate.

Further, a porous substrate may be used as the substrate. In this case, a porous substrate is usually impregnated with at least a part of the fluid composition, and a polymer electrolyte membrane using the porous substrate as a reinforcing material is obtained. That is, in this case, the porous substrate is used as a part of the polymer electrolyte membrane without peeling off. Examples of the porous substrate include fabrics such as woven fabrics and nonwoven fabrics; polymer films having fine through-holes, and the fabric is preferable from the viewpoint of mechanical strength. Examples of the fibers constituting the fabric include aramid fibers, glass fibers, cellulose fibers, nylon fibers, vinylon fibers, polyester fibers, polyolefin fibers, rayon fibers and the like. From the viewpoint of mechanical strength, all aromatic polyester fibers and Aramid fibers are preferred.
Examples of the method of applying the fluid composition on the porous substrate include a dip nip method, a method of laminating and applying to the substrate using a coater, an applicator, and the like.

  The polymer electrolyte membrane may be a multilayer membrane in which a plurality of polymer electrolytes are laminated in layers. As a method for producing a multilayer film, for example, after applying a fluid composition to a substrate, the solvent is removed to form a first layer, and then the same or another polymer is formed on the first layer. A fluid composition containing an electrolyte is applied and the solvent is removed to form a second layer. Similarly, the third and subsequent layers may be formed. Alternatively, the produced polymer electrolyte membranes may be bonded together to form a multilayer film.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not restrict | limited to these Examples.

(Measurement of ion exchange capacity)
The ion exchange capacity of the sulfonated polymer obtained in Examples and Comparative Examples was calculated by the following method.
In a glass container, a polymer electrolyte (a (g)) and an excess amount of a saturated aqueous solution of sodium chloride ((300 to 500) × a (ml)) are added, then the glass container is sealed and the contents are kept for 12 hours. Stir. Then, using phenolphthalein as an indicator, hydrogen chloride generated in water was titrated (titrated amount b (ml)) with a 0.01 N NaOH standard aqueous solution (titer f).
The ion exchange capacity was determined by the following formula.
Ion exchange capacity (meq / g) = (0.01 × b × f) / a

(Measurement of Mn of block copolymer (Z ₀ ))
It was measured by the GPC method under the following conditions and calculated in terms of standard polystyrene.
Device: manufactured by Tosoh Corporation, trade name: HLC-8220GPC
Eluent: Tetrahydrofuran Column: manufactured by Tosoh Corporation, trade name: TSK-GEL (TSKgel G3000HXL (inner diameter 7.8 mm, effective length 30 cm), TSKgel Super Multipore HZ-M (inner diameter 4.6 mm, effective length 15 cm) ) 2 in total 3 connected in series)
Column temperature: 40 ° C
Detector: RI
Feed rate: 0.35 ml / min

(Measurement of ¹ H-NMR)
The content of each structural unit of the block copolymer (Z ₀ ) and the block copolymer (Z ₀ ′) obtained in the production examples described later, and the 1,4-bond ratio and hydrogenation in the polymer block (B) The rate was calculated from the result of measuring ¹ H-NMR under the following conditions.
Solvent: Deuterated chloroform Measurement temperature: Room temperature Integration frequency: 32 times The sulfonation rate of the sulfonated polymer obtained in the examples and comparative examples was calculated from the results of ¹ H-NMR measurement under the following conditions.
Solvent: deuterated tetrahydrofuran / deuterated methanol (mass ratio 80/20) mixed solvent Measurement temperature: 50 ° C
Integration count: 32 times

(Measurement of storage modulus)
From the block copolymer (Z ₀ ) and the block copolymer (Z ₀ ′) obtained in the production example, a fluid composition containing a solvent is prepared in the same manner as in the method for producing the polymer electrolyte membrane, After the fluid composition was applied on the substrate, the solvent was removed to obtain a film.
The obtained film was measured in a tensile mode (frequency: 11 Hz) with a wide-range dynamic viscoelasticity measuring device (“DVE-V4FT Rheospectr” manufactured by Rheology) at a rate of temperature increase from 3 ° C./min, from −80 ° C. The temperature was raised to 250 ° C., and the storage elastic modulus (E ′), loss elastic modulus (E ″), and loss tangent (tan δ) were measured. Based on the fact that there was no change in the storage elastic modulus at 80 to 100 ° C. derived from the crystallized olefin polymer, the amorphous nature of the polymer block (B) was judged. As a result, for all the block copolymers (Z ₀ ) and block copolymers (Z ₀ ′) obtained in the production examples, the polymer block (B) was amorphous.

[Production Example 1]
(Production of block copolymer (Z ₀ -1))
After drying, 633 ml of dehydrated cyclohexane and 0.952 ml of sec-butyllithium (0.70 mol / L cyclohexane solution) were added to an autoclave with an internal volume of 1.4 L purged with nitrogen, and then stirred at 60 ° C. 29.3 ml, 4-tert-butylstyrene 14.9 ml, styrene 28.6 ml, 4-tert-butylstyrene 14.8 ml, isoprene 125 ml, 4-tert-butylstyrene 14.6 ml, styrene 27.8 ml and 4-tert -14.4 ml of butyl styrene was sequentially added and polymerized to obtain polystyrene-b-poly (4-tert-butylstyrene) -b-polystyrene-b-poly (4-tert-butylstyrene) -b-polyisoprene-b -Poly (4-tert-butylstyrene) -b- Polystyrene -b- obtain poly (4-tert-butylstyrene). The resulting block copolymer had an Mn of 110,000, a 1,4-bond ratio of the polyisoprene block of 93.7%, a content of structural units derived from styrene of 35.6% by mass, 4-tert- The content of the structural unit derived from butylstyrene was 24.6% by mass.

A cyclohexane solution of the above block copolymer is prepared, put into a pressure vessel that is purged with nitrogen, and a Ni / Al Ziegler catalyst is used at a hydrogen pressure of 0.5 to 1.0 MPa, 60 to 70 ° C. for 16 hours. A hydrogenation reaction was carried out, and a polystyrene polymer block (polymer block (A ₀ )), a hydrogenated polyisoprene polymer block (polymer block (B)) and a poly (4-tert-butylstyrene) polymer block (heavy Block copolymer (Z ₀ ) (polystyrene-b-poly (4-tert-butylstyrene) -b-polystyrene-b-poly (4-tert-butylstyrene) -b-water comprising a combined block (C)) Polyisoprene-b-poly (4-tert-butylstyrene) -b-polystyrene-b-poly (4-tert-butylstyrene) (hereinafter referred to as “ A block copolymer (referred to as Z ₀ -1))) was obtained.
The hydrogenation rate of the hydrogenated polyisoprene block of the obtained block copolymer (Z ₀ -1) was 99% or more.

[Production Example 2]
(Production of block copolymer (Z ₀ -2))
After drying, 688 ml of dehydrated cyclohexane and 1.96 ml of sec-butyllithium (0.70 mol / L cyclohexane solution) were added to a 2 L autoclave purged with nitrogen, and then stirred at 60 ° C. .6 ml, 4-tert-butylstyrene 10.9 ml, styrene 10.2 ml, 4-tert-butylstyrene 10.3 ml, isoprene 69.0 ml, 4-tert-butylstyrene 9.80 ml, styrene 9.20 ml, and 4 -9.55 ml of tert-butylstyrene was added in succession and polymerized to obtain polystyrene-b-poly (4-tert-butylstyrene) -b-polystyrene-b-poly (4-tert-butylstyrene) -b-polyisoprene. -B-poly (4-tert-butylstyrene) -b- Polystyrene -b- obtain poly (4-tert-butylstyrene). The resulting block copolymer had an Mn of 230,000, a 1,4-bond ratio of the polyisoprene block of 94.0%, a content of structural units derived from styrene of 27.8% by mass, 4-tert- The content of structural units derived from butylstyrene was 31.5% by mass.

A cyclohexane solution of the above block copolymer is prepared, put into a pressure vessel which is purged with nitrogen, and using a Ni / Al Ziegler catalyst at a hydrogen pressure of 0.5 to 1.0 MPa, 60 to 70 ° C. for 24 hours. A hydrogenation reaction was carried out to produce a polystyrene polymer block (polymer block (A ₀ )); a hydrogenated polyisoprene polymer block (polymer block (B)); and a poly (4-tert-butylstyrene) polymer block ( Block copolymer (Z ₀ ) (polystyrene-b-poly (4-tert-butylstyrene) -b-polystyrene-b-poly (4-tert-butylstyrene) -b -Hydrogenated polyisoprene-b-poly (4-tert-butylstyrene) -b-polystyrene-b-poly (4-tert-butylstyrene) (below) , Referred to as “block copolymer (Z ₀ -2)”).
The hydrogenation rate of the hydrogenated polyisoprene block of the obtained block copolymer (Z ₀ -2) was 99% or more.

[Production Example 3]
(Production of block copolymer (Z ₀ ′))
After drying, 461 ml of dehydrated cyclohexane and 2.18 ml of sec-butyllithium (1.0 mol / L cyclohexane solution) were added to an autoclave with an internal volume of 1.4 L substituted with nitrogen, and then stirred at 60 ° C. 19.8 ml, 123 ml of isoprene, and 19.8 ml of styrene were sequentially added and polymerized to synthesize polystyrene-b-polyisoprene-b-polystyrene. Mn of the obtained block copolymer was 66,000, the 1,4-bond ratio of the polyisoprene block was 94.0%, and the content of the structural unit derived from styrene was 30.0% by mass.

Prepare a cyclohexane solution of the above block copolymer, put it in a pressure vessel that is purged with nitrogen, and hydrogenate at a hydrogen pressure of 0.5 to 1.0 MPa and 70 ° C. for 15 hours using a Ni / Al Ziegler catalyst. A block copolymer (polystyrene-b-hydrogenated polyisoprene-b) comprising a polystyrene polymer block (polymer block (A ₀ )) and a hydrogenated polyisoprene polymer block (polymer block (B)) after reaction. -Polystyrene (hereinafter referred to as “block copolymer (Z ₀ ′)”) was obtained.
The hydrogenation rate of the hydrogenated polyisoprene block of the obtained block copolymer (Z ₀ ′) was 99% or more.

[Example 1]
(First step)
After drying, 62.7 ml of methylene chloride and 31.4 ml of acetic anhydride were added to a three-necked flask with an internal volume of 300 ml purged with nitrogen, and 15.2 ml of concentrated sulfuric acid was added dropwise with stirring at 0 ° C. A sulfonating agent was prepared by stirring for 60 minutes. On the other hand, 20 g of the block copolymer (Z ₀ -1) was placed in a 1 L glass reaction vessel equipped with a stirrer, and the inside of the system was purged with nitrogen. Then, 257 ml of methylene chloride was added and stirred at room temperature for 4 hours. And dissolved. To this solution, 109 ml of the sulfonating agent prepared previously was dropped over 5 minutes, and then stirred at room temperature for 48 hours to obtain a reaction mixture.
(Second step)
While stirring the reaction mixture, 1100 ml of distilled water was added dropwise while keeping the liquid temperature at 20 to 30 ° C. to precipitate a solid, and the solid was recovered by filtration under reduced pressure. The collected solid was stirred with 1000 ml of distilled water for 30 minutes and washed with water, and then the solid was collected again by filtration under reduced pressure. After repeating this water washing and vacuum filtration until there is no change in pH of the washing water, the collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 25 g of solid (hereinafter referred to as “solid (1)”). ").
(Third step)
7.0 g of solid (1) was put in a 1000 mL separable flask, 418 g of methanol was added, and the mixture was stirred for 2 hours, and then filtered under reduced pressure to collect the solid. The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 6.8 g of a sulfonated polymer which is the object of the present invention (hereinafter referred to as “sulfonated polymer (1)”). The resulting sulfonated polymer (1) had a sulfonation rate of 100 mol% and an ion exchange capacity of 2.2 meq / g.

(Production of polymer electrolyte membrane)
A 15.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the sulfonated polymer (1) obtained was prepared. Next, the fluid composition was applied to a release-treated PET film (Mitsubishi Resin Co., Ltd., trade name: MRV) with a thickness of about 200 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Example 2]
(Third step)
In the same manner as in Example 1, 7.0 g of the solid (1) obtained by performing the first step and the second step was put into a 1000 mL separable flask, 420 g of ethanol was added and stirred for 2 hours, and then centrifuged (2000 rpm 20 minutes). Thereafter, the supernatant was removed by decantation to collect a solid. The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 6.9 g of a sulfonated polymer which is the object of the present invention (hereinafter referred to as “sulfonated polymer (2)”). The resulting sulfonated polymer (2) had a sulfonation rate of 100 mol% and an ion exchange capacity of 2.2 meq / g.

(Production of polymer electrolyte membrane)
A 15.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the sulfonated polymer (2) obtained was prepared. Next, the fluid composition was applied to a release-treated PET film (Mitsubishi Resin Co., Ltd., trade name: MRV) with a thickness of about 200 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Example 3]
(Third step)
In the same manner as in Example 1, 7.1 g of the solid (1) obtained by performing the first step and the second step was put into a 1000 mL separable flask, 428 g of 2-propanol was added, and the mixture was stirred for 2 hours, and then centrifuged. The solid was recovered by separation (20000 rpm, 20 minutes). The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 7.0 g of a sulfonated polymer which is the object of the present invention (hereinafter referred to as “sulfonated polymer (3)”). The resulting sulfonated polymer (3) had a sulfonation rate of 100 mol% and an ion exchange capacity of 2.2 meq / g.

(Production of polymer electrolyte membrane)
A 15.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the resulting sulfonated polymer (3) was prepared. Next, the fluid composition was applied to a release-treated PET film (Mitsubishi Resin Co., Ltd., trade name: MRV) with a thickness of about 200 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Example 4]
(Third step)
In the same manner as in Example 1, 6.7 g of the solid (1) obtained by performing the first step and the second step was placed in a 1000 mL separable flask, 402 g of 2-methyl-1-propanol was added, and the mixture was stirred for 3 hours. Thereafter, the solid was recovered by centrifugation (2000 rpm, 40 minutes). The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 6.6 g of a sulfonated polymer as an object of the present invention (hereinafter referred to as “sulfonated polymer (4)”). The sulfonated polymer (4) obtained had a sulfonation rate of 100 mol% and an ion exchange capacity of 2.2 meq / g.

(Production of polymer electrolyte membrane)
A 15.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the sulfonated polymer (4) obtained was prepared. Next, the fluid composition was applied to a release-treated PET film (trade name: MRV, manufactured by Mitsubishi Plastics Co., Ltd.) with a thickness of about 200 μm, and then heated at 100 ° C. for 4 minutes with a hot air dryer. After drying, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Example 5]
(First step)
After drying, 72.9 ml of methylene chloride and 48.6 ml of acetic anhydride were added to a 1 L three-necked flask purged with nitrogen, and 21.7 ml of concentrated sulfuric acid was added dropwise with stirring at 0 ° C. A sulfonating agent was prepared by stirring for 60 minutes. On the other hand, 30 g of the block copolymer (Z ₀ -2) was placed in a 5 L glass reaction vessel equipped with a stirrer, and the inside of the system was purged with nitrogen. Then, 600 ml of methylene chloride was added and 4 hours at room temperature. Stir to dissolve. To this solution, 143 ml of the sulfonating agent prepared previously was dropped over 5 minutes, and then stirred at room temperature for 48 hours.
(Second step)
While stirring the reaction mixture, 1100 ml of distilled water was added dropwise while keeping the liquid temperature at 20 to 30 ° C. to precipitate a solid, and the solid was recovered by filtration under reduced pressure. The collected solid was stirred with 1000 ml of distilled water for 30 minutes and washed with water, and then the solid was collected again by filtration under reduced pressure. The solids collected after repeating this water washing and vacuum filtration until there was no change in the pH of the washing water were dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 36 g of solids (hereinafter referred to as “solid (2)”). Called).
(Third step)
7.0 g of solid (2) was put in a 1000 mL separable flask, 418 g of methanol was added, and the mixture was stirred for 2 hours, and then filtered under reduced pressure to collect the solid. The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 6.8 g of a sulfonated polymer which is the object of the present invention (hereinafter referred to as “sulfonated polymer (5)”). The resulting sulfonated polymer (5) had a sulfonation rate of 100 mol% and an ion exchange capacity of 1.9 meq / g.
(Production of polymer electrolyte membrane)
A 9.0% by mass toluene / 2-methyl-1-propanol (mass ratio 73/27) fluid composition of the obtained sulfonated polymer (5) was prepared. Next, the fluid composition was applied to a release-treated PET film (trade name: MRV, manufactured by Mitsubishi Plastics Co., Ltd.) at a thickness of about 450 μm, and then heated at 100 ° C. for 4 minutes with a hot air dryer. After drying, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Comparative Example 1]
(Production of polymer electrolyte membrane)
15.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the solid (1) obtained by performing the first step and the second step in the same manner as in Example 1. Was prepared. Next, the fluid composition was applied to a release-treated PET film (Mitsubishi Resin Co., Ltd., trade name: MRV) with a thickness of about 200 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Comparative Example 2]
(Production of polymer electrolyte membrane)
9.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the solid (2) obtained by performing the first step and the second step in the same manner as in Example 5. Was prepared. Next, the fluid composition was applied to a release-treated PET film (Mitsubishi Resin Co., Ltd., trade name: MRV) with a thickness of about 450 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Comparative Example 3]
In the same manner as in Example 1, 7.1 g of the obtained solid (1) obtained by performing the first step and the second step was put in a 1000 mL separable flask, 425 g of 1-hexanol was added, and the mixture was stirred for 2 hours. And centrifuged (20,000 rpm, 80 minutes). Thereafter, the supernatant was removed by decantation to collect a solid. The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 7.0 g of a sulfonated polymer. The resulting sulfonated polymer had a sulfonation rate of 100 mol% and an ion exchange capacity of 2.2 meq / g.
15.0 mass% toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the obtained sulfonated polymer was prepared. Next, the fluid composition was applied to a release-treated PET film (Mitsubishi Resin Co., Ltd., trade name: MRV) with a thickness of about 200 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Performance tests and results of polymer electrolyte membranes obtained in Examples and Comparative Examples]
The performance of the polymer electrolyte membrane used in each example and comparative example was evaluated by the following measurement / evaluation methods. The results are shown in Table 1.

[Comparative Example 4]
(First step)
In 242 ml of methylene chloride, 121 ml of acetic anhydride and 54 ml of sulfuric acid were mixed at 0 ° C. to prepare a sulfonating agent. On the other hand, 78 g of block copolymer (Z ₀ ′) was put in a glass reaction vessel equipped with a 3 L stirrer and the system was evacuated and introduced with nitrogen three times. Then, 846 ml of methylene chloride was introduced with nitrogen introduced. After stirring at room temperature for 4 hours to dissolve, 417 ml of the sulfonating agent was added dropwise over 5 minutes. After completion of dropping, the mixture was stirred at room temperature for 48 hours.
(Second step)
While stirring, 500 ml of distilled water was added dropwise to stop the reaction and solidify and precipitate the solid content.
Methylene chloride was removed by distillation under normal pressure, followed by filtration under reduced pressure. The resulting solid was transferred to a beaker, 1000 ml of distilled water was added and washed with stirring, and then the solid was recovered by filtration under reduced pressure. Such washing and vacuum filtration were repeated until there was no change in the pH of the washing water, and then the collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 80 g of a solid (sulfonated polymer). In the obtained sulfonated polymer, the ratio of the sulfonic acid group to the structural unit derived from styrene (sulfonation rate) was 100 mol%, and the ion exchange capacity was 2.3 meq / g.
(Production of polymer electrolyte membrane)
A 14.0% by mass toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the obtained sulfonated polymer was prepared. Next, the fluid composition was applied on a release-treated PET film (trade name: K1504, manufactured by Toyobo Co., Ltd.) to a thickness of about 250 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Then, it was cut into 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Comparative Example 5]
(Third step)
In the same manner as in Comparative Example 4, 7.0 g of the solid obtained by performing the first step and the second step was put into a 1000 mL separable flask, 418 g of methanol was added, and the mixture was stirred for 2 hours. It was collected. The collected solid was dried at 1.3 kPa and 30 ° C. for 24 hours to obtain 6.8 g of a sulfonated polymer. The resulting sulfonated polymer had a sulfonation rate of 100 mol% and an ion exchange capacity of 2.2 meq / g.
(Production of polymer electrolyte membrane)
A 14.0% by mass toluene / 2-methyl-1-propanol (mass ratio 77/23) fluid composition of the obtained sulfonated polymer was prepared. Next, the fluid composition was applied to a release-treated PET film (trade name: K1504, manufactured by Toyobo Co., Ltd.) with a thickness of about 250 μm, and then heated at 100 ° C. for 4 minutes with a hot air dryer. After drying, it was cut out to 9 cm × 9 cm to obtain a polymer electrolyte membrane having a thickness of 20 μm.

[Evaluation of polymer electrolyte membrane]
The polymer electrolyte membranes obtained in Examples and Comparative Examples were evaluated as follows.
(Production of single cell for polymer electrolyte fuel cell)
In the following tests, in order to evaluate the output of the polymer electrolyte membranes obtained in Examples and Comparative Examples and the wet and dry resistance and the polymer electrolyte fuel cell using the polymer electrolyte membrane under low humidity, A single cell for a molecular fuel cell was prepared by the following procedure. A 10 mass% aqueous dispersion of Nafion (registered trademark, hereinafter the same) is added to and mixed with Pt catalyst-supporting carbon so that the mass ratio of carbon to Nafion is 1: 1, and then 1-propanol is added. The mixture was added and mixed until the mass ratio of water / 1-propanol was 1/1 to prepare a uniformly dispersed paste. This paste was applied uniformly on one side of the carbon paper by spraying, then dried at 130 ° C. for 30 minutes, cut into 5.6 cm × 5.6 cm, and two electrodes were produced. Thereafter, two PET films of 9 cm × 9 cm (thickness 25 μm) provided with openings of 5 cm × 5 cm on the inner side are arranged on both surfaces of the polymer electrolyte membranes prepared in Examples and Comparative Examples, and the above 2 The electrodes were placed with the paste coating surface facing inward so as to cover the respective openings of the two PET films, and then sandwiched between two stainless plates to be hot pressed (115 ° C., 2 MPa, 8 minutes) to produce a membrane-electrode assembly. Next, the prepared membrane-electrode assembly is sequentially sandwiched between two conductive separators that also serve as two gas supply channels, two current collector plates, and two clamping plates with a rubber heater, and a solid polymer. A single cell for a fuel cell was prepared.

(Evaluation of dry and wet resistance and output under low humidity)
The power source of the single cell rubber heater for the polymer electrolyte fuel cell obtained above was connected to the fuel cell evaluation system (manufactured by NF Circuit Design Block Co., Ltd.), and the thermocouple of the fuel cell evaluation system was It connected to the separator of the single cell for molecular type fuel cells. Next, a fuel supply pipe and an exhaust pipe are connected to each of the two clamping plates with a rubber heater of the single cell for the polymer electrolyte fuel cell, and a load current control terminal and a voltage detection terminal are connected to each of the two current collecting plates. Connected terminals.
Using the solid polymer fuel cell unit connected as described above and the fuel cell evaluation system, the output under low humidity (30% RH) was evaluated according to the following operation.
Moreover, the hydrogen leak increase rate was calculated according to the following operation, and evaluated as an indicator of resistance to moisture.
<Operation 1>
While supplying nitrogen at 80 ° C. and 100% RH at 500 ml / min for 30 minutes to the anode and the cathode, the single cell for the polymer electrolyte fuel cell was heated to 80 ° C. Next, hydrogen at 80 ° C. and 100% RH was supplied to the anode at 100 ml / min, and air at 80 ° C. and 100% RH was supplied to the cathode at a rate of 100 ml / min for 30 minutes.
<Operation 2>
While maintaining the temperature of the unit cell for the polymer electrolyte fuel cell at 80 ° C., supplying 80 ° C. and 100% RH hydrogen to the anode, and supplying 80 ° C. and 100% RH air to the cathode, The voltage value at each current value was measured while gradually increasing from 1.25 A to 1.25 A, and when the voltage value became 0.01 V or less, the current value was returned to 0 A. The supply amount of hydrogen to the anode and the supply amount of air to the cathode are 46 ml / min and 168 ml / min at current values of 0 A, 1.25 A, and 2.5 A, respectively, and stoichiometric at 3.75 A and above. 1.5 and stoichiometric 2.0. Further, the current value was held for 1 minute at each current value.
Such an operation was repeated four times to make the polymer electrolyte membrane wet.
<Operation 3>
The temperature of the unit cell for the polymer electrolyte fuel cell is maintained at 80 ° C., the anode is 80 ° C., 80% RH hydrogen is 500 ml / min, the cathode is 80 ° C. and 80% RH nitrogen is 500 ml / min. After feeding for 1 hour, linear sweep voltammetry was performed. The voltage value was changed from 0.08 V to 0.50 V at a rate of 0.5 mV / second, the current value at each voltage value was measured, and the amount of hydrogen leak was evaluated by the current value at 0.4 V.
<Operation 4>
The polymer electrolyte membrane is dried by supplying non-humidified nitrogen to the single cell from the anode and cathode fuel supply pipes at a rate of 1000 ml / min for 12 hours while allowing the single cell for the polymer electrolyte fuel cell to cool. I made it.
<Operation 5>
The same operation as in the operation 1 was performed except that the humidity of hydrogen and air was changed to 30% RH.
<Operation 6>
The same operation as in the operation 2 was performed except that the humidity of hydrogen and air was changed to 30% RH and the number of repetitions was changed to 3.

The above operations 1 to 6 were performed in the order of operation 1, operation 2, operation 3, operation 4, operation 5, operation 6, operation 1, operation 2, operation 4, operation 5, operation 6, and operation 3. The current value at 0.4V obtained in the first operation 3 is L1, the current value at 0.4V obtained in the first operation 3 is L2, and L2 / L1 is the hydrogen leak increase rate. Defined and used as an indicator of resistance to moisture.
Further, the output under low humidity was calculated from the voltage value obtained when the current was 12.5 A in the third current insertion operation in the first operation 6.

Block copolymer (Z ₀ ) used in the first step of Examples 1 to 5 and Comparative Examples 1 to 5, alcohol used in the third step, ion exchange capacity of the sulfonated polymer obtained and the sulfonated polymer Table 1 shows the hydrogen leak increase rate and the output under low humidity of the polymer electrolyte membrane manufactured from the above.

From comparison between Examples 1 to 4 and Comparative Examples 1 and 3, it can be determined that the polymer electrolyte membrane of the present invention has a low hydrogen leak increase rate and is excellent in dry and wet resistance. Moreover, it can be seen from the comparison between Example 1 and Comparative Example 1 that the polymer electrolyte membrane of the present invention is superior in output under low humidity.
Similarly, the comparison between Example 5 and Comparative Example 2 shows that the polymer electrolyte membrane of the present invention has a lower hydrogen leak increase rate, better resistance to dryness and moisture, and better output under low humidity.
From the comparison between Example 1 and Comparative Example 5, the polymer electrolyte of the present invention was produced using a block copolymer (Z ₀ -1) containing a polymer block (C) as a raw material while having the same ion exchange capacity. It can be seen that the membrane has a higher output under low humidity.
In addition, as shown in Comparative Examples 4 and 5, in the polymer electrolyte membrane manufactured using the block copolymer (Z ₀ ′) not including the polymer block (C) as a raw material, the wet and dry resistance by the implementation of the third step The polymer electrolyte membrane is made of a sulfonated polymer produced by using a block copolymer (Z ₀ ) containing a polymer block (C) as a raw material for improving the wet and dry resistance by carrying out the third step. It is considered unique.

  When the sulfonated polymer obtained by the production method of the present invention is used in a polymer electrolyte membrane for a polymer electrolyte fuel cell, it exhibits a high output even at low humidity and is excellent in dry and moisture resistance. It is useful as a polymer electrolyte membrane for batteries.

Claims (5)

A polymer block composed of a structural unit derived from an aromatic vinyl compound represented by the following general formula (1), an amorphous polymer block composed of a structural unit derived from an unsaturated aliphatic hydrocarbon, and the following general formula A first step of obtaining a reaction mixture by reacting a block copolymer containing a polymer block composed of a structural unit derived from an aromatic vinyl compound represented by (2) with a sulfonating agent in an organic solvent;
A second step in which the reaction mixture obtained in the first step is brought into contact with water to precipitate a solid; and a third step in which the solid precipitated in the second step is washed with an alcohol having 1 to 4 carbon atoms;
A process for producing a sulfonated polymer.

(In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ^{2 to} R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R ^{2 to} R ^4. At least two of these represent hydrogen atoms.)

(In the formula, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ^{6 to} R ⁸ each independently represents a hydrogen atom or an alkyl group having 3 to 8 carbon atoms, and R ^{6 to} R ^8. At least one of these represents an alkyl group having 3 to 8 carbon atoms.) A polymer electrolyte comprising a sulfonated polymer obtained by the method of claim 1. A polymer electrolyte membrane comprising a sulfonated polymer obtained by the method of claim 1. The polymer electrolyte membrane according to claim 3, which is used for a polymer electrolyte fuel cell. A polymer electrolyte fuel cell comprising the polymer electrolyte membrane according to claim 3.