JP4608363B2 - Phenoxysulfonated aromatic polyimide and polymer electrolyte membrane - Google Patents

Description

  The present invention relates to a novel sulfonated aromatic polyimide, and more particularly to a phenoxysulfonated aromatic polyimide used for a polymer electrolyte membrane and a polymer electrolyte membrane obtained by forming the same.

  A fuel cell is a device that obtains electrical energy according to an operating principle based on the reverse operation of water electrolysis. In a fuel cell, in general, water is generated and direct current power is obtained by feeding hydrogen obtained by reforming a fuel such as natural gas, methanol, and coal, and oxygen in the air. Thus, fuel cell power generation is attracting attention because it has high power generation efficiency and can supply clean energy.

  Among the fuel cells, the polymer electrolyte fuel cell (PEFC) uses a solid polymer electrolyte membrane (proton exchange membrane) as the electrolyte, which causes problems with dissipation and retention of the electrolyte. Power supply for automobiles, because it has the advantages of being able to operate at a low temperature of 100 ° C. or less, having a very short start-up time, being capable of high energy density and being small and light. Development is progressing as a distributed power source for homes and buildings, a power source for spacecraft, a portable power source. In particular, from the viewpoint of environmental problems such as global warming and vehicle exhaust gas countermeasures, polymer electrolyte fuel cells have been expected as fuel cells for automobiles.

  Solid polymer electrolytes have the property of binding tightly to specific ions or selectively permeating cations or anions, and electrolyte groups such as sulfonic acid groups in polymer chains. A solid polymer material is known. Specifically, a perfluorosulfonic acid membrane having high proton conductivity and high oxidation resistance is used. Although this perfluorosulfonic acid group-containing polymer membrane is attracting attention due to its extremely high chemical stability, it is difficult to manufacture and is expensive, and because it is a fluorine-based material, consideration for environmental issues during synthesis and disposal Is also necessary.

  Further, in order to reduce the size and weight of the polymer electrolyte fuel cell, the output is not sufficient in the operation at a low temperature of 100 ° C. or less, and the high output by the operation in the range of 100 to 120 ° C. is required. . However, since the conventional perfluorosulfonic acid group-containing polymer film has a softening point in the vicinity of 100 ° C., there is a high possibility that the film will be deformed under the temperature condition exceeding 100 ° C. and the function cannot be fully exhibited. On the other hand, the hydrocarbon-based electrolyte membrane has advantages that it is easy to manufacture and low in cost, has a high degree of freedom in molecular design, and can easily adjust the ion exchange capacity.

  Aromatic polyimide is generally obtained by polycondensation of an aromatic diamine such as oxydianiline and an aromatic tetracarboxylic acid such as pyromellitic anhydride, and between the diamine residue and the acid anhydride residue. Due to strong intermolecular interaction based on charge transfer interaction, it has excellent thin film forming ability, mechanical strength, heat resistance, solvent resistance, and chemical stability, so super engineering plastics, interlayer insulation materials, etc. It is used in electronic materials or hollow fiber gas separation membranes. These excellent characteristics are also necessary for ion exchange membranes and electrolyte membranes for fuel cells. Particularly, polyimides having ion exchange groups such as sulfonic acid groups (also referred to as sulfo groups) and phosphoric acid groups are good. It is expected as an electrolyte membrane for fuel cells.

  However, polyimide has the disadvantage that the imide ring is easily hydrolyzed in an acidic aqueous solution, and is inferior to other sulfonated aromatic hydrocarbon polymers such as sulfonated polyphenylene and sulfonated polyethersulfone. It was.

Special Table 2000-510511 Japanese Patent Laid-Open No. 2003-64181 JP 2002-110174 A Japanese Patent Laid-Open No. 2004-155998 JP 2004-35891 A JP 2004-107484 A Polymer vol.42, p5097-5105 (2001) Journal Membrane Science vol.230, p111-120 (2004) Solid State Ionics vol.147, p189-194 (2002) Macromolecular Rapid Communications vol.23, p896-900 (2002) Journal Membrane Science vol.230, p61-70 (2004) Journal Materials Chemistry vol.14, p1062-1070 (2004) Transaction Materials Research Society Japan vol.29, p2541-2546 (2004)

Therefore, a polyimide having a six-membered ring imide ring from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) is more resistant to hydrolysis than a five-membered imide ring from phthalic anhydride. (Non-Patent Document 1). For example, in Patent Document 1, a copolymerized polyimide membrane of NTDA, a sulfonated diamine represented by the following formulas (11) to (13), and a non-sulfonated diamine (for example, oxydianiline) is an electrolyte membrane for a fuel cell. As good as it is.

（Ｄ₂はＯ、Ｓ、ＣＨ₂又はＣ（ＣＦ₃）₂等、Ｒ₄〜Ｒ₇は水素原子又はアルキル基、Ａｒはスルホ基を有する芳香環残基） However, the water resistance of these sulfonated polyimide membranes is not sufficient, and in Patent Document 2, a sulfonated copolymer polyimide membrane from a sulfonated diamine represented by the following formula (14) has a further excellent water resistance. It is disclosed. This is because the electron-withdrawing sulfo group is bonded to the phenyl ring away from the phenyl ring to which the amino group is bonded, so that the basicity of the amine is high and the hydrolysis resistance of the imide ring is increased ( For example, it is considered Non-Patent Document 2).

(D ₂ is O, S, CH ₂ or C (CF ₃ ) ₂ etc., R _{4 to} R ₇ are hydrogen atoms or alkyl groups, Ar is an aromatic ring residue having a sulfo group)

  All of the sulfonated polyimides described above are cases in which the sulfo group is directly bonded to the polymer main chain. In a perfluorosulfonic acid polymer electrolyte membrane, a sulfo group is bonded to the fluoroether end of the side chain, and the hydrophilic sulfo group part is microphase-separated from the hydrophobic main chain part to form a hydrophilic ion channel. It is thought that

  With the expectation of the same effect, a side chain type sulfonated aromatic hydrocarbon polymer film in which a sulfo group is introduced into a side chain of an aromatic hydrocarbon polymer has been reported so far. For example, poly-1,4-phenylene having a 4- (4-sulfophenoxy) benzoyl group represented by the following formula (15) (Non-patent Document 3), having a 2-sulfobenzoyl group represented by the formula (16) Aromatics such as polysulfone (Non-Patent Document 4), polysulfone having an ω-sulfoalkylsulfonyl group represented by Formula (17) (Non-Patent Document 5), polysulfone having an ω-sulfoalkyl group represented by Formula (18) A hydrocarbon polymer (patent document 3) is mentioned.

  Synthesis of a diamine having a ω-sulfoalkoxy group represented by formula (19) (Non-patent Documents 6 and 4) and a diamine having a sulfophenoxy group represented by Formula (20) (Non-patent Document 7) in polyimide And the synthesis and physical properties of its polyimide have been reported. These side-chain sulfonated polyimide membranes have a microphase separation structure and have been shown to have relatively good high temperature water resistance.

In addition, a polyimide having a sulfo group in the side chain and a sulfonated aromatic group bonded to the aromatic ring of the main chain via an alkylene ether bond (Patent Document 5) or the following formula (21)
-R-SO ₃ H (21)
A polyimide having a sulfonic acid group in the side chain shown in (R represents alkylene, halogenated alkylene, arylene, halogenated arylene, or ether bond) is disclosed (Patent Document 6). Some of these ion exchangers have durability at relatively high temperatures and hydrolysis resistance, but further hydrolysis resistance is desired.

  Utilizing the excellent properties based on the strong intermolecular interaction of polyimide, it is a tough and flexible sulfonated polyimide thin film, and the electrolyte membrane with excellent high temperature water resistance with improved imide ring hydrolysis resistance Development is required. When sulfonated polyimide membranes developed so far are used for a long period of time, hydrolysis of the imide ring occurs and the molecular weight decreases, so the membrane may lose mechanical properties. In addition, during use at a high temperature, there may be a phenomenon that the sulfo group is eliminated over time, the ion exchange capacity is lowered, and the performance is lowered. Since these phenomena become particularly noticeable at high temperatures exceeding 100 ° C, they have long-term durability and mechanical strength even when used at temperatures above 100 ° C, and can be used in a wide range of temperatures. Development of a polymer electrolyte membrane that can withstand use as an electrolyte membrane for a fuel cell with little decrease in proton conductivity under humidity is desired. Another object of the present invention is to provide a sulfonated polyimide suitable as a polymer electrolyte membrane.

  In order to solve the above problems, the present inventors have conducted extensive research. As a result, a sulfonated polyimide using a specific diamine compound as a monomer has high heat resistance and high mechanical properties even at a temperature of 100 to 120 ° C. The inventors have found that a cation exchange membrane that maintains strength and has little deterioration with time, particularly a sulfonated polyimide membrane suitable for a polymer electrolyte membrane for fuel cells, has been completed, and the present invention has been completed.

（但し、Ａｒ₁は少なくとも１つの芳香環を有する４価の基であり、Ａｒ₂は下記式（２）で示される２価の基である。）

（但し、Ｘは水素原子、アルカリ金属、アンモニウム又は４級アミンである。）
また、本発明は、上記式（１）で表される構造単位を５〜１００モル％、下記式（３）で表される構造単位を０〜９５モル％有するフェノキシスルホン化芳香族ポリイミドである。

（但し、Ａｒ₃は少なくとも１つの芳香環を有する４価の基であり、Ａｒ₄はＡｒ₂とは異なる少なくとも１つの芳香環を有し、-SO₃Xを有しない２価の基である。）
上記式（１）及び（３）において、Ａｒ₁及びＡｒ₃が下記式（４）又は（５）で示される４価の基であるとより良好な物性を示すフェノキシスルホン化芳香族ポリイミドとなる。

（但し、Z及びYは直結合、CO、O、CH₂又はSOである。） That is, the present invention is a phenoxysulfonated aromatic polyimide characterized by having a structural unit represented by the following formula (1).

(However, Ar ₁ is a tetravalent group having at least one aromatic ring, and Ar ₂ is a divalent group represented by the following formula (2).)

(However, X is a hydrogen atom, an alkali metal, ammonium, or a quaternary amine.)
Moreover, this invention is a phenoxy sulfonated aromatic polyimide which has 5-100 mol% of structural units represented by the said Formula (1), and 0-95 mol% of structural units represented by following formula (3). .

(However, Ar ₃ is a tetravalent group having at least one aromatic ring, Ar ₄ is a divalent group having at least one aromatic ring different from Ar ₂ and having no —SO ₃ X. .)
In the above formulas (1) and (3), when Ar ₁ and Ar ₃ are a tetravalent group represented by the following formula (4) or (5), a phenoxysulfonated aromatic polyimide having better physical properties is obtained. .

(However, Z and Y are a direct bond, CO, O, CH ₂ or SO.)

Furthermore, the present invention is a polymer electrolyte membrane obtained by forming the above phenoxysulfonated aromatic polyimide.
The polymer electrolyte membrane preferably satisfies one or more of the following requirements.
1) A 30 μm-thick polymer electrolyte membrane is immersed in pressurized hot water at a temperature of 130 ° C. for 190 hours, and is not broken even if it is bent by 180 °, and the breaking stress is 50 MPa or more.
2) Proton conductivity is 0.10 S / cm or higher at 60 ° C. and 100% relative humidity, proton conductivity is 0.004 S / cm or higher at 50% relative humidity, and proton conductivity at 120 ° C. and 50% relative humidity. Is immersed in pressurized hot water at 0.03 S / cm or more and 130 ° C. for 190 hours, and no decrease in proton conductivity is observed before and after that.

（但し、Ｘは水素原子、アルカリ金属、アンモニウム又は４級アミンである。） In addition, in the method for producing a phenoxysulfonated aromatic polyimide of the present invention, a phenoxy group-containing aromatic diamine represented by the following formula (6) is used as an aromatic diamine when synthesizing from an aromatic diamine and an aromatic tetracarboxylic acid. It is characterized by using 5 to 100 mol% and 0 to 95 mol% of another aromatic diamine.

(However, X is a hydrogen atom, an alkali metal, ammonium, or a quaternary amine.)

  The present invention will be further described below.

The phenoxysulfonated aromatic polyimide of the present invention has a structural unit represented by the formula (1) or the formula (1) and the formula (3). This polyimide can be synthesized by reacting an aromatic diamine and an aromatic tetracarboxylic acid (preferably an aromatic tetracarboxylic dianhydride). In formula (1) or formula (3), since aromatic diamine gives Ar ₂ or Ar ₄ and aromatic tetracarboxylic acids give Ar ₁ or Ar ₃ , preferred Ar _{1 to} Ar ₄ are diamine components shown below. And aromatic tetracarboxylic acids.

As the diamine component forming the structural unit represented by the formula (1), a phenoxy group-containing aromatic diamine represented by the above formula (6) is used, and obtained by reacting this with an aromatic tetracarboxylic acid. be able to. In formula (6), X is a hydrogen atom, an alkali metal, ammonium or a quaternary amine, preferably a hydrogen atom. C ₆ H ₄ is a phenylene group and can be o-, m- or p-phenylene, preferably p-phenylene.

The aromatic tetracarboxylic acids used in the synthesis of the phenoxysulfonated aromatic polyimide of the present invention are not particularly limited, and examples thereof include 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3 ', 3,4'-biphenyltetracarboxylic acid, 3,3', 4,4'-benzophenone tetracarboxylic acid, 3,3 ', 4,4'-diphenyl ether tetracarboxylic acid, bis (3,4-di Carboxyphenyl) methane, 2,2-bis (3,4-dicarboxyphenyl) propane, pyromellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 3,4,9,10-perylenetetracarboxylic acid 4,4 '-(hexafluoroisopropylidene) diphthalic acid, m- (terphenyl) 3,4,3 ", 4" -tetracarboxylic acid, or their acid dianhydrides and esterified products. In particular, an acid dianhydride having a naphthalene ring represented by the following formula (7) or (8) and capable of forming a six-membered imide is preferred from the water resistance of the sulfonated polyimide. In the formula (8), Z and Y are selected from a direct bond, CO, O, CH ₂ and SO, and may be the same or different. A direct bond is preferable.

Therefore, the preferable sulfonated polyimide of the present invention has a structural unit represented by the following formula (9) or (10). Here, Z and Y are as defined above.

The phenoxysulfonated aromatic polyimide of the present invention uses a diamine component not having a sulfo group (SO ₃ X) as a substituent together with a phenoxy group-containing aromatic diamine component represented by the formula (6) as a diamine component. May be. That is, the phenoxysulfonated aromatic polyimide of the present invention may include a structural unit represented by the formula (3) and a structural unit represented by the formula (1).

In Formula (3), Ar ₃ is a tetravalent group having at least one or more aromatic rings, Ar ₄ is a divalent group having at least one or more aromatic rings, and a sulfo group is substituted as a substituent. It does not have. Ar ₁ and Ar ₃ may be the same or different.

As the aromatic tetracarboxylic acids forming Ar ₃ in the formula (3), the same aromatic tetracarboxylic acids as described above can be suitably used. Preferably, Ar ₃ in formula (3) gives a residue of formula (4) or (5).
The aromatic diamine forming Ar ₄ in the formula (3) is an aromatic diamine having no sulfo group as a substituent, and examples thereof include paraphenylene diamine, metaphenylene diamine, and 4,4′-oxydianiline. , 3,4'-oxydianiline, 9,9-bis (4-aminophenyl) fluorene, 3,3'-bis (3-aminophenyl) sulfone, 4,4'-bis (3-aminophenoxy) diphenyl Sulfone, 2,2'-trifluoromethylbenzidine, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene 4,4′-bis (4-aminophenoxy) biphenyl and the like can be preferably mentioned.

  The phenoxysulfonated aromatic polyimide of the present invention can be easily performed by a known method using an aromatic tetracarboxylic acid and an aromatic diamine. Aromatic tetracarboxylic acids and aromatic diamines may each be one kind or two or more kinds, but at least a phenoxy group-containing aromatic diamine represented by the formula (6) is used.

  For example, in a polar solvent, an aromatic diamine, an aromatic tetracarboxylic dianhydride, a tertiary amino compound, toluene or xylene as an azeotropic solvent is added, and the resulting water is azeotropically heated by heating at 140 to 220 ° C. This can be easily achieved by performing a polycondensation reaction for 0.5 to 100 hours while removing together with the solvent. Here, examples of the tertiary amino compound include trimethylamine and triethylamine. If necessary, benzoic acid, isoquinoline and the like may be added as a catalyst. The molar ratio of the amino group of the aromatic diamine to the acid dianhydride group of the aromatic tetracarboxylic dianhydride is preferably in the range of 0.95 to 1.05, and if it is out of this range, the molecular weight of the polyimide becomes low. This is not preferable because the strength of the resulting film is reduced. Depending on the type of phenoxy group-containing aromatic diamine used by the above condensation polymerization method, an amine salt type sulfonated polyimide can be obtained. By immersing this in a hydrochloric acid aqueous solution and performing ion exchange, the proton type sulfonated polyimide can be obtained. Easy to obtain. Further, by immersing an amine salt type or proton type sulfonated polyimide in an alkali metal salt or ammonium salt aqueous solution and performing ion exchange, an alkali metal salt or ammonium salt type sulfonated polyimide can be easily obtained.

  The phenoxy sulfonated aromatic polyimide of the present invention can have the structural unit represented by the formula (3) in addition to the structural unit represented by the formula (1), and also does not impair the effects of the present invention. It can have small amounts of other structural units. The structural unit represented by the formula (1) may be contained in a range of 5 to 100 mol%, preferably 50 to 100 mol%. In addition, the polyimide terminal is excluded from the calculation of the content.

  When the structural unit represented by Formula (3) is included, the molar ratio of Formula (1) / Formula (3) is in the range of 5/95 to 95/5, preferably 10/90 to 95/5. More preferably, it is 50/50 to 95/5, and particularly preferably 70/30 to 95/5. In the copolymerized phenoxysulfonated aromatic polyimide, it is not preferable that the unit represented by the formula (1) is less than 5 mol% with respect to the total weight, since it becomes difficult to develop characteristics such as ion exchange capacity and proton conductivity. The structure of the copolymerized phenoxysulfonated aromatic polyimide may be either a random copolymer or a block copolymer.

  The phenoxysulfonated aromatic polyimide of the present invention has a film forming property that its solution viscosity (35 ° C., 0.5 wt% solution) is in the range of 0.7 to 20 dl / g, preferably 2.0 to 10 dl / g. And preferred in terms of film properties. Although there are no restrictions on the use of this phenoxysulfonated aromatic polyimide, it can be formed into membranes, particles and fibers due to its electrolyte, ion exchange and conductivity, and used for electrodialysis, diffusion dialysis, battery membranes, etc. Suitable. When forming a film, it is obtained by applying a solution of phenoxysulfonated aromatic polyimide or a precursor thereof (polyamic acid) to a predetermined thickness on a substrate, and drying or curing.

  The film made of the phenoxysulfonated aromatic polyimide of the present invention has very good water resistance. Specifically, a film having a thickness of 30 μm is immersed in pressurized hot water at a temperature of 130 ° C. for 190 hours, and is not broken even when bent by 180 °, and the breaking stress can be 50 MPa or more. Excellent for applications such as battery diaphragms. On the other hand, a sulfonated aromatic polyimide film synthesized from a sulfonated aromatic diamine in which a sulfo group such as 2,2′-benzidinedisulfonic acid or the like described in conventional patent documents is directly bonded to an aromatic ring of the main chain is Since the imide ring of the aromatic ring to which the sulfo group is bonded easily undergoes hydrolysis, depending on the copolymer composition with the non-sulfonated diamine, it dissolves or breaks in about 1 minute to several hours under the same conditions. . Note that 180 ° bending means that the fold angle is 0 °.

  In addition, the polymer electrolyte membrane made of the phenoxysulfonated aromatic polyimide of the present invention preferably has a proton conductivity of 0.10 S / cm or more at a temperature of 60 ° C. and a relative humidity of 100%. It is particularly preferable to be in the range of 5 S / cm. Moreover, in relative humidity 50%, it is preferable that it is 0.004 S / cm or more, and it is especially preferable that it exists in the range of 0.006-0.05 S / cm. More preferably, it exhibits an extremely high proton conductivity of 0.03 S / cm or more at a temperature of 120 ° C. and a relative humidity of 50%. Further, it is preferable that substantially no decrease in proton conductivity is observed (within a range of ± 5%) before and after immersion in pressurized hot water at 130 ° C. for 190 hours.

The polyimide of the present invention has excellent mechanical strength and is a polyimide in which a sulfonic acid group is directly bonded to an aromatic ring constituting the main chain, a polyimide in which a sulfonic acid group is bonded to an alkyl group through an ether bond, or 3 Compared to polyimides with, 3 '-(4-sulfophenoxy) benzidine as one component, polymer chain scission and sulfone by hydrolysis when used under harsh conditions such as in acidic aqueous solution at high temperature Little degradation over time, such as elimination of acid groups, and little decrease in proton conductivity under low humidity. When used as a fuel cell electrolyte membrane, it has high barrier properties against liquids such as fuel hydrogen gas and methanol. Thus, an excellent electrolyte membrane can be obtained. That is, in the case of the polyimide of the present invention, there is no sulfonic acid group which is a hydrophilic group in the portion constituting the main chain, and the side chain aromatic ring having a sulfonic acid group constitutes the main chain via an ether group. Since it is bonded to the phenyl ring and the hydrophilic sulfonic acid group-containing side chain aromatic ring is separated from the imide ring, the hydrophobic main chain part and the hydrophilic side chain base part have a microphase separation structure. It is easy to take. Therefore, the water sorption amount is small in the hydrophobic domain of the polyimide main chain part, and the main chain becomes difficult to undergo hydrolysis when used as an electrolyte membrane. In addition, compared to polyimides with 3,3 '-(4-sulfophenoxy) benzidine as one component, it has excellent water vapor sorption, especially under low humidity, and high proton conductivity. is there.
The phenoxysulfonated aromatic polyimide of the present invention is practically very suitable as an electrolyte membrane, and can be suitably used for ion exchange, for polymer electrolyte membrane for fuel cell, for gas sensor and the like. Polyimide is a solid electrolyte with high proton conductivity, high heat resistance, and high mechanical strength. When used as a cation exchanger or various diaphragms for electrolysis, it has a high barrier property against gases and liquids. It has excellent properties as an electrolyte membrane for batteries.

Hereinafter, the present invention will be described specifically by way of examples.
H-NMR data were measured by JEOL EX-270 using deuterated dimethyl sulfoxide (DMSO-d ₆ ) as a solvent.
The evaluation methods and evaluation criteria are as follows.

[Water absorption]
About 80 mg of a sample of a membrane made of sulfonated polyimide was vacuum-dried at 120 ° C. for 2 hours, measured for dry weight W _d , and then immersed in water at 30 ° C. and 100 ° C. for 2 to 4 hours. The sample was taken out of the water, the water adhering to the surface quickly was wiped off, the membrane weight Ws during swelling was measured, and the water absorption rate (WU) was determined from the following equation.
WU = [(Ws−W _d ) / W _d ] × 100

〔water resistant〕
A film sample having a film thickness of about 30 μm was immersed in hot water at 130 ° C. under pressure for 192 hours, and then evaluated from the viewpoint of the film shape and strength in the following five stages. In addition, the film piece used by II-V is made into the shape of width 5mm and length 2cm after immersion treatment and air drying.
I: The film shape is not maintained.
II: The film breaks when both ends of the film piece are gripped (the gripping margin is 5 mm) and bent.
III: Breaks when the film piece is bent and bent so that the angle of the crease is 0 degrees.
IV: Does not break even when bent with a crease, but breaks when bent back.
V: Even if it is bent with a crease or bent back, it does not break.
In addition, after the membrane subjected to the pressure water immersion treatment was air-dried, the proton conductivity was measured at 60 ° C. and 100 to 80% RH, and evaluated from the viewpoint of proton conductivity in the following three stages.
A: Proton conductivity decreases by 20% or more due to treatment.
B: 5-19% decrease.
C: Within ± 5%.

[Mechanical strength]
A film sample (width 5 mm, length 4 cm) having a film thickness of about 30 μm was subjected to a tensile test using a Tensilon universal testing machine (RTC-1150A, load cell UR-50N-D) manufactured by Orientec Co., Ltd. The measurement was performed on the untreated film and the film which was air-dried after being immersed in hot water under pressure of 130 ° C. for 48 hours and 192 hours.

[Proton conductivity]
A membrane sheet (1.0 cm x 0.5 cm) and four platinum black electrode plates are attached to a proton conductivity measurement cell and set in temperature-controlled water or a temperature / humidity-controlled chamber, manufactured by Hioki Electric Co., Ltd. The electrical resistance R was measured by the complex impedance method in the frequency range of 100 Hz to 100 kHz using an LCR meter (HIOKI 3552-80), and the proton conductivity σ at 60 ° C. was calculated from the following equation.
σ = d / (t _s w _s R)
Here, d is the distance between two electrodes (0.5 cm), and t _s and w _s are the thickness and width of the film sheet at 70% RH at room temperature. For calculation of proton conductivity in water, t _s and w _s values in water were used.

[Methanol permeability coefficient]
A membrane sheet is sandwiched between a supply side cell (capacity 350 ml) and a permeation side cell (capacity 100 ml) of the liquid permeation measurement cell via a fluororubber seal plate. Put 30 wt% methanol aqueous solution on the membrane supply side, add distilled water on the permeate side, measure the liquid composition on the supply side and the permeate side at arbitrary time intervals using a gas chromatograph, and permeate methanol at 50 ° C. The coefficient P _M was determined. Note with swollen film thickness in the calculation of P _M.
[Solution viscosity η _SP / c]
Solvent: m-cresol; 0.5 wt%; measured at 35 ° C.

The abbreviations of the compounds used in the following Examples and Comparative Examples are as follows.
NTDA: 1,4,5,8-naphthalenetetracarboxylic dianhydride 2,2′-BSPB: 2,2′-bis (3-sulfopropoxy) benzidine 2,2′-BSPOB: 2,2′-bis (3-sulfophenoxy) benzidine 3,3′-BSPOB: 3,3′-bis (3-sulfophenoxy) benzidine BAPB: 4,4′-bis (4-aminophenoxy) biphenyl BAPBDS: 3,3 ′-( 4,4'-Diaminophenoxy) biphenylsulfonic acid DMF: N, N-dimethylformamide DMSO: dimethyl sulfoxide

Synthesis example 1
6.001 g (16.3 mmol) of 2,2′-diphenoxy-4,4′-diaminobiphenyl (m-PHOB) was placed in a 100 ml three-necked flask, cooled in an ice bath, and then 9 ml of concentrated sulfuric acid was stirred. Slowly added. After complete dissolution of m-PHOB, 3 ml of fuming sulfuric acid (SO ₃ 60%) was slowly added. After complete addition of fuming sulfuric acid, the mixture was held at 0 ° C. with stirring for 0.5 hours. Then it was slowly warmed to 40 ° C. and kept at 40 ° C. for 2 hours. Then, after cooling to room temperature, the mixture was poured into 100 g of crushed ice to precipitate a white solid. The solid was filtered off and dried under reduced pressure at 60 ° C. for 15 hours to obtain 6.04 g of a white solid product (yield 70%). The melting point of this product was 300 ° C. or higher. This compound was obtained by ¹ HNMR (270 MHz, DMSO-d ₆ ), δ: 6.04-6.05 ppm (2H, S), 6.28-6.32 (2H, D), 6.75-6.79 (4H, D), 6.92.-6.95. The peak of (2H, D), 7.51-7.54 (4H, D) was shown, and from the assignment and integral intensity ratio, it was confirmed that the product was 2,2′-BSPOB represented by the following formula. The IR spectrum measured by the KBr tablet method is shown in FIG.

Example 1
In a dry 100 ml four-necked flask 1.053 g (1.99 mmol) 2,2'-BSPOB and 0.67 ml triethylamine (TEA) were dissolved in 9 ml m-cresol and then 0.532 g ( 1.99 mmol) NTDA and 0.337 g benzoic acid were added and the mixture was stirred at 80 ° C. for 4 hours and 180 ° C. for 15 hours under nitrogen gas atmosphere. The polymerization reaction solution was cooled to 80 ° C., diluted with 25 ml of m-cresol, poured into a large amount of acetone, the precipitated solid was filtered off, washed with acetone and dried. The solution viscosity η _SP / c of the obtained product was 4.1 dl / g. The product was dissolved in m-cresol, cast onto a glass plate, and dried at 100 ° C. for 1 hour and 120 ° C. for 10 hours to obtain a TEA salt type sulfonated polyimide membrane. This was immersed in methanol for 1 day, then immersed in a 0.5 M sulfuric acid solution for 3 days to exchange protons, washed with water and vacuum dried at 150 ° C. for 10 hours to form a proton-type sulfonation composed of structural units represented by the following formula: A polyimide NTDA-2,2'-BSPOB film was obtained. The IR measurement results are shown in FIG.

Example 2
In a dry 100 ml four-necked flask, 2.534 g (4.78 mmol) 2,2'-BSPOB and 1.61 ml TEA were dissolved in 24.5 ml m-cresol and then 0.877 g ( 2.38 mmol) of BAPB was added and dissolved, then 1.918 g (7.15 mmol) of NTDA and 1.212 g of benzoic acid were added and the mixture was stirred at 80 ° C. for 4 hours at 180 ° C. under a nitrogen gas atmosphere. After stirring for 15 hours, the polymerization reaction solution was cooled to 80 ° C., diluted with 65 ml of m-cresol, poured into a large amount of acetone, the precipitated solid was filtered off, washed with acetone and dried. The solution viscosity η _SP / c of the obtained product was 3.9 dl / g. The product was dissolved in m-cresol, cast on a glass plate, and dried at 100 ° C. for 1 hour and 120 ° C. for 10 hours to obtain a TEA salt type copolymer sulfonated polyimide membrane. This was immersed in methanol for 1 day, then immersed in a 0.5 M sulfuric acid solution for 3 days to exchange protons, washed with water, and vacuum dried at 150 ° C. for 10 hours to obtain proton type random copolymer sulfonated polyimide NTDA-2,2 A '-BSPOB / BAPB (2/1) -r film was obtained. The IR measurement results are shown in FIG.

Comparative Example 1
In a dry 100 ml four-necked flask, 2.248 g (4.24 mmol) of 3,3′-BSPOB and 1.57 ml of TEA were dissolved in 22 ml of m-cresol and then 0.781 g (2.12 mmol). ) BAPB was added and dissolved, 1.702 g (6.35 mmol) of NTDA and 1.081 g of benzoic acid were added and the mixture was stirred at 80 ° C. for 4 hours and at 180 ° C. for 20 hours. The polymerization reaction solution was cooled to 80 ° C., diluted with 45 ml of m-cresol, poured into a large amount of acetone, the precipitated solid was filtered off, washed with acetone and dried. The solution viscosity η _SP / c of the obtained product was 2.1 dl / g. The product was dissolved in m-cresol, cast on a glass plate, and dried at 100 ° C. for 1 hour and 120 ° C. for 10 hours to obtain a TEA salt type copolymer sulfonated polyimide membrane. This was immersed in methanol for 1 day, then immersed in a 0.5 M sulfuric acid solution for 3 days to exchange protons, washed with water, and vacuum dried at 150 ° C. for 10 hours to obtain proton type random copolymer sulfonated polyimide NTDA-3,3 A '-BSPOB / BAPB (2/1) -r film was obtained.

Comparative Example 2
The same procedure as in Comparative Example 1 was performed except that BAPBDS was used instead of 3,3′-BSPOB. After obtaining a resin having a solution viscosity η _SP / c of 2.0 dl / g, a proton type random copolymer sulfonated polyimide NTDA-BAPBDS / BAPB (2/1) -r membrane was obtained by the same procedure.

Comparative Example 3
The same procedure as in Comparative Example 1 was performed except that 2,2′-BSPB was used instead of 3,3′-BSPOB. After obtaining a resin having a solution viscosity η _SP / c of 5.7 dl / g, a proton type random copolymer sulfonated polyimide NTDA-2,2'-BSPB / BAPB (2/1) -r membrane is obtained by the same procedure. Got.

[Evaluation of polyimide film]
The polyimide membranes prepared in the above examples and comparative examples were evaluated for water resistance, water absorption, proton conductivity and methanol permeability. The results are shown in Table 1. In addition, Table 2 shows the tensile test results of the membrane before and after immersion in the water of Example 2 and Comparative Example 1. FIG. 4 shows the temperature dependence of proton conductivity of the membranes of Example 2 and Comparative Example 1, and FIG. 5 shows the humidity dependence of proton conductivity at 60 ° C. of Examples 1-2 and Comparative Examples 1-3. Shown in In Table 1, φ represents proton conductivity / methanol permeability coefficient (50 ° C., 30 wt% methanol concentration, unit is 10 ⁴ Ss / cm ³ ).

From the above results, the following can be understood.
1) The film | membrane of Examples 1-2 is excellent in the high temperature water resistance of the film | membrane from a viewpoint of mechanical strength compared with the film | membrane of Comparative Examples 2-3. 2) Compared with the film of Comparative Example 1, the film of Example 2 has a breaking stress 1.5 to 2 times greater in the tensile test after immersion in pressurized water, and is excellent in the high temperature water resistance of the film. 3) Compared to the membrane of Comparative Example 1, the membrane of Example 2 has high proton conductivity despite having the same ion exchange capacity. In particular, the difference becomes large at low humidity, and is 4 times larger at 60 ° C. and 50% RH. 4) The membrane of Example 2 has a high proton conductivity of 0.05 S / cm at 120 ° C. and 50% RH. 5) The membrane of Example 2 has a very low methanol permeability coefficient, and the ratio of proton conductivity to methanol permeability coefficient φ has a relatively large value for a 30 wt% methanol solution at 50 ° C.

  The polyimide of the present invention shows a very low methanol permeability coefficient like the polyimide of the comparative example, while 2,2′-BSPOB has a 4-sulfophenoxy group bonded to the meta position relative to the amino group. Polyimide with a property that is significantly different from 3,3'-BSPOB bonded to the position was given, and it was found that it was excellent in high-temperature water resistance and proton conductivity at all humidity. In addition, it was found that the characteristics in the future are much better than the polyimide from 2,2'-BSPB. Therefore, the sulfonated polyimide membrane in this patent is suitable as a polymer electrolyte membrane for a solid polymer fuel cell at high temperature and humidification, and as a polymer electrolyte membrane for a direct methanol fuel cell.

IR spectrum of the compound obtained in Synthesis Example 1 IR spectrum of the polyimide obtained in Example 1 IR spectrum of the polyimide obtained in Example 2 Temperature dependence of proton conductivity of polyimide membranes. Humidity dependence of proton conductivity of polyimide membrane at 60 ℃

Claims (7)

A phenoxysulfonated aromatic polyimide having a structural unit represented by the following formula (1):

(However, Ar ₁ is a tetravalent group having at least one aromatic ring, and Ar ₂ is a divalent group represented by the following formula (2).)

(However, X is a hydrogen atom, an alkali metal, ammonium, or a quaternary amine.) 2. The phenoxysulfonated aromatic polyimide according to claim 1, comprising 5 to 100 mol% of a structural unit represented by the formula (1) and 0 to 95 mol% of a structural unit represented by the following formula (3).

(However, Ar ₃ is a tetravalent group having at least one aromatic ring, and Ar ₄ is a divalent group having at least one aromatic ring and not —SO ₃ X.) The phenoxysulfonated aromatic polyimide according to claim 1 or 2, wherein Ar ₁ and Ar ₃ are represented by the following formula (4) or (5).

(However, Z and Y are a direct bond, CO, O, CH ₂ or SO.)   A polymer electrolyte membrane obtained by forming the phenoxysulfonated aromatic polyimide according to claim 1.   5. The polymer electrolyte membrane according to claim 4, wherein the polymer electrolyte membrane having a thickness of 30 μm is immersed in pressurized hot water at a temperature of 130 ° C. for 190 hours, and is not broken even when bent by 180 °, and the breaking stress is 50 MPa or more.   At a temperature of 60 ° C. and a relative humidity of 100%, the proton conductivity is 0.10 S / cm or higher, and at a relative humidity of 50%, the proton conductivity is 0.004 S / cm or higher, and the temperature is 120 ° C. and the relative humidity is 50%. The high conductivity according to claim 4 or 5, wherein the proton conductivity is substantially not decreased before and after being immersed in pressurized hot water at a temperature of 0.03 S / cm or more and further at 130 ° C for 190 hours. Molecular electrolyte membrane. In producing the phenoxysulfonated aromatic polyimide according to claim 1 from an aromatic diamine and an aromatic tetracarboxylic acid, 5 to 100 mol of a phenoxy group-containing aromatic diamine represented by the following formula (6) as an aromatic diamine. % And other aromatic diamines 0 to 95 mol%, a method for producing a phenoxysulfonated aromatic polyimide.

(However, X is a hydrogen atom, an alkali metal, ammonium, or a quaternary amine.)

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