JP2010092787A - Polyelectrolyte membrane including polyimide substrate containing cycloaliphatic hydrocarbon, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyelectrolyte membrane which includes superior proton conductivity, mechanical characteristics at high temperatures, durability such as hot water resistance when operated for a long period of time and fuel impermeability, and which is optimum for mobile equipment, co-generation for home or fuel cells of motor vehicles driven by methanol, hydrogen or the like as a fuel. <P>SOLUTION: The polyelectrolyte membrane is fabricated by introducing vinyl monomer as a graft chain by graft polymerization into a polyimide base material membrane containing cycloaliphatic hydrocarbon, then by chemical conversion of a part of the graft chain into a sulfonic acid group. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte membrane having excellent proton conductivity, mechanical properties, hydrothermal resistance, and fuel impermeability and a method for producing the same, and particularly for home cogeneration where long-term durability is desired and high temperature use The present invention relates to a polymer electrolyte membrane having excellent characteristics as a fuel cell for automobiles that can withstand heat resistance and a method for producing the same.

  Fuel cells using polymer electrolyte membranes have a low operating temperature of 150 ° C or less and high power generation efficiency and energy density. Therefore, power supplies for portable devices and cogeneration power supplies for homes that use methanol, hydrogen, etc. as fuel. It is expected as a power source for fuel cell vehicles. In such a fuel cell, there are important elemental technologies such as a polymer electrolyte membrane, an electrode catalyst, a gas diffusion electrode, and a membrane electrode assembly. Among them, the development of polymer electrolyte membranes having excellent characteristics for fuel cells is one of the most important elemental technologies.

  In a polymer electrolyte fuel cell, the electrolyte membrane functions as a so-called “electrolyte” for conducting hydrogen ions (protons), and also functions as a “membrane” for preventing direct mixing of hydrogen, methanol, and oxygen as fuel. To do. The polymer electrolyte membrane has a large ion exchange capacity, chemical stability that can withstand long-term use, in particular, at a battery operating temperature of 80 ° C. or higher, in any water-containing state from dry to flooded. It is required to be stable and to have a high water retention capacity in order to keep electric resistance low. On the other hand, due to the role as a diaphragm, it is required that the film has excellent mechanical strength and dimensional stability, and has low hydrogen, methanol and oxygen permeability.

  As an electrolyte membrane for a polymer electrolyte fuel cell, a perfluorosulfonic acid membrane “Nafion (registered trademark of DuPont)” developed by DuPont has been generally used. However, conventional fluorine-containing polymer electrolyte membranes such as Nafion are excellent in chemical durability and stability, but the ion exchange capacity is as small as around 1 mmol / g, and when hydrogen is used as fuel. In addition, hydrogen and oxygen crossover may occur. Furthermore, there was a drawback that the mechanical characteristics under operating conditions exceeding 100 ° C. required for the power source for automobiles were remarkably deteriorated. Furthermore, since the fluororesin-based polymer electrolyte membrane starts from the synthesis of the monomer, the number of manufacturing processes is increased, and thus it is expensive. It becomes an obstacle.

  Therefore, development of a low-cost polymer electrolyte membrane replacing the fluororesin polymer electrolyte membrane has been actively promoted. For example, a structure obtained by sulfonating an aromatic polymer membrane having excellent mechanical strength at a high temperature typified by engineering plastics and low fuel permeability such as methanol, hydrogen and oxygen has been proposed. The sulfonated aromatic polymer electrolyte membrane is obtained by synthesizing an aromatic monomer to which a sulfonic acid group responsible for proton conduction is bonded, synthesizing an aromatic polymer by the polymerization reaction, and then forming a film ( (See Patent Documents 1, 2, and 3).

On the other hand, as a development of a low-cost polymer electrolyte membrane, styrene monomer was introduced into a fluorine-based polymer membrane substrate such as polytetrafluoroethylene, polyvinylidene fluoride or ethylene-tetrafluoroethylene copolymer by graft polymerization, and then Attempts have been made to produce electrolyte membranes for polymer electrolyte fuel cells by sulfonation (see Patent Documents 4 and 5). However, since the fluoropolymer membrane substrate has a low glass transition temperature, the mechanical strength at a high temperature of 100 ° C or higher is significantly reduced, and the polystyrene graft chain is detached in high-temperature water. There is a drawback in that the fuel consumption significantly decreases, and further, crossover of hydrogen and oxygen as fuels occurs. Therefore, an attempt has been made to produce an electrolyte membrane by graft polymerization and sulfonation using a wholly aromatic engineering plastic excellent in mechanical properties and fuel barrier properties at high temperatures as a polymer substrate (see Patent Document 6). ).
JP 2004-288497 A JP 2004-346163 A JP 2006-12791 A JP 2001-348439 A JP 2004-246376 A JP 2008-53041 A

  In the sulfonated aromatic polymer electrolyte membrane described above, when the amount of sulfonic acid groups introduced is increased in order to increase electrical conductivity, the mechanical strength and handling properties are reduced with an increase in water solubility. Furthermore, since sulfonic acid groups are randomly present in the aromatic polymer chain, the separation of the hydrophobic portion maintaining mechanical strength and the electrolyte layer responsible for proton conduction is not clear. Long-term operation represented by proton conductivity, fuel impermeability and oxidation resistance compared to polymer electrolyte membranes that have a phase separation structure, such as molecular electrolyte membranes and commercially available fluoropolymer electrolyte membranes (Nafion, etc.) It was inferior in durability.

  In the polymer electrolyte membrane produced by graft polymerization and sulfonation using the above-mentioned wholly aromatic engineering plastic, in the case of wholly aromatic engineering plastic, since the diffusion of the monomer is low and radiation graft polymerization does not proceed sufficiently, There was a problem that ion exchange capacity, that is, proton conductivity was lowered.

  Accordingly, the object of the present invention is to have high proton conductivity, high mechanical properties at high temperatures, high durability in long-term operation such as hot water resistance, and low fuel barrier properties suitable for use in fuel cells. An object of the present invention is to provide a polymer electrolyte membrane and a method for producing the same.

  The present invention solves the problems of fluororesin-based electrolytes, such as a decrease in mechanical strength at high temperatures and crossover of fuel, as well as problems of sulfonated aromatic polymer electrolyte membranes and grafted wholly aromatic polymer electrolyte membranes. In order to solve this problem by combining the proton conductivity, mechanical strength, and handling properties, alicyclic hydrocarbons with excellent high temperature stability, mechanical strength, fuel barrier properties, and high graft polymerizability By introducing a graft chain into the polyimide base film containing it and then converting a part of the graft chain into a sulfonic acid group, it has excellent proton conductivity, fuel barrier properties, and durability in long-term operation such as hot water resistance. A polymer electrolyte membrane is obtained.

  More specifically, the polymer electrolyte membrane according to one aspect of the present invention is a polymer electrolyte membrane in which a vinyl monomer is graft-polymerized on a polyimide base film containing an alicyclic hydrocarbon, and a graft chain Is partially converted to a sulfonic acid group.

  A method for producing a polymer electrolyte membrane according to one aspect of the present invention includes a method in which a vinyl monomer is graft-polymerized on a polyimide base film containing an alicyclic hydrocarbon, and then a part of the graft chain is chemically converted into a sulfonic acid group. To make.

  In a more preferable method for producing a polymer electrolyte membrane, (1) a vinyl monomer having an aromatic ring capable of retaining a sulfonic acid group, (2) a sulfonic acid group by hydrolysis, on a polyimide base film containing an alicyclic hydrocarbon A vinyl monomer having a halogenated sulfonyl group or a sulfonic acid ester group that can be converted to (3), and (3) a vinyl monomer having a halogen or a carbonyl group into which a sulfonic acid group can be introduced by a sulfonation reaction. After graft polymerization of the vinyl monomer, a part of the graft chain is chemically converted into a sulfonic acid group.

  Although the polymer electrolyte membrane produced by the present invention can be produced at a very low cost as compared with the fluororesin polymer electrolyte membrane, it exhibits high mechanical properties at high temperatures and low fuel barrier properties. In addition, because of the high graft polymerizability, many graft chains can be introduced, so compared to conventional sulfonated aromatic polymer electrolyte membranes and grafted wholly aromatic polymer electrolyte membranes, high proton conductivity and durability at high temperatures Have both characteristics. For this reason, it is particularly suitable for use in household cogeneration where long-term durability is desired and for automobile fuel cells that can withstand high temperatures of 100 ° C. or higher.

  The polymer substrate membrane that can be used in the present invention is characterized in that the membrane shape can be maintained in the reaction solution in graft polymerization and sulfonation, and the obtained polymer electrolyte membrane exhibits high mechanical properties. And Therefore, the polymer substrate film may be a polyimide substrate film containing an alicyclic hydrocarbon, and the main chain structure is not particularly limited.

  In this invention, as an acid dianhydride which comprises the polyimide base film containing an alicyclic hydrocarbon, an alicyclic acid dianhydride or an aromatic acid dianhydride is represented. Examples of the alicyclic acid dianhydride include cyclobutanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene- 2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl ether tetracarboxylic dianhydride, dicyclohexylmethane tetracarboxylic dianhydride, dicyclohexyl sulfide tetracarboxylic dianhydride, dicyclohexylsulfone tetracarboxylic dianhydride 3-carboxymethylcyclopentane-1,2,4-tricarboxylic dianhydride, bicyclo [2.2.1] heptanetetracarboxylic dianhydride, bicyclo [2.2.1] heptane-5-carboxymethyl -2,3,6-tricarboxylic dianhydride, bicyclo [2.2.2 Octane-2,3,5,6-tetracarboxylic dianhydride, pentacyclo [8.2.14,7.02,9.03,8] tetradecane-5,6,11,12-tetracarboxylic acid Dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo [2.2.1] heptane-2-carboxymethyl- 2,5,6-tricarboxylic dianhydride, bicyclo [2.2.2] octane-2-carboxyethyl-2,5,6-tricarboxylic dianhydride, 3,3 ′, 4,4′-dicyclohexyl And tetracarboxylic dianhydride. Examples of the aromatic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic Acid dianhydride, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic Acid dianhydride, 2,2-bis (4- (3,4-dicarboxyphenoxy) phenyl) propane, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4 -Dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyl) Nyl) methane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (3,4 -Dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis ( 3,4-dicarboxyphenyl) ethane dianhydride, 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and the like.

  In the present invention, the diamine constituting the polyimide substrate film containing an alicyclic hydrocarbon compound represents an alicyclic diamine or an aromatic diamine. Examples of the alicyclic diamine include 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 4,4′-diaminodicyclohexylmethane, 2,2-bis (4,4′-diaminocyclohexyl) propane, 4 , 4′-diaminodicyclohexyl ether, 4,4′-diaminodicyclohexyl sulfide, 4,4′-diaminodicyclohexylsulfone, 2,3-diaminobicyclo [2.2.1] heptane, 2,5-diaminobicyclo [2. 2.1] heptane, 2,6-diaminobicyclo [2.2.1] heptane, 2,7-diaminobicyclo [2.2.1] heptane, 2,5- (bisaminomethyl) -bicyclo [2. 2.1] heptane, 2,3- (bisaminomethyl) -bicyclo [2.2.1] heptane, 2,6-bis (aminometh) Til) -bicyclo [2.2.1] heptane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 1,3-bisaminomethylcyclohexane, 1,4-bisaminomethylcyclohexane, etc. Can be mentioned. Examples of the aromatic diamine include 1,4-diaminobenzene, 1,3-diaminobenzene, 4,4′-diaminobiphenyl, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenyl ether, 4,4′- Diaminodiphenyl ether, 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, bis (4-aminophenyl) sulfide, bis (4-aminophenyl) sulfoxide, 4,4′-diaminodiphenylsulfone, 2,2- Bis (4-aminophenyl) propane, 2,2-bis (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 4,4′-diamino-2,2′-dimethyl Biphenyl, 1,3-bis (4-aminophenoxy) benzene, 2,2-bis (4- (4-aminophenoxy) Phenyl) propane, 1,1-bis (4-aminophenyl) ethane, 1,2-bis (4-aminophenyl) ethane, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (4 -Aminophenoxy) benzene, 1,4-bis [1- (4-aminophenyl) -1-methylethyl] benzene, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, bis [4- (4-aminophenoxy) phenyl] methane, 1,1-bis [4- (4-aminophenoxy) phenyl] ethane, 1,1-bis [3- (4-aminophenoxy) phenyl] ethane, 1,2- Bis [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [3- (4-aminophenoxy) phenyl] ethane, 2,2-bis [3- (4-aminophenoxy) Enyl] propane, 2,2-bis [4- (3-aminophenoxy) -3-methylphenyl] propane, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-amino) Phenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) -3,3′-methylbiphenyl, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl ] Sulfide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [3- (4-aminophenoxy) phenyl] sulfoxide, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [3- ( 4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-amino Phenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ketone, bis [3- (4-aminophenoxy) phenyl] ketone.

  In the present invention, due to the action of radiation, the hydrogen radicals of the alicyclic hydrocarbons present in the polyimide base film are extracted, and radicals that become the starting species of graft polymerization are generated. In order to generate radicals efficiently, the alicyclic hydrocarbon structure may be present in part or all of the diamine and / or alicyclic acid dianhydride. In the present invention, a monomer that has diffused through the amorphous layer of the aromatic polymer base material by the radical generated in the crystalline phase of the aromatic polymer film base material by the action of radiation is obtained by graft polymerization. An electrolyte membrane is prepared by sulfonating the graft membrane. That is, it is important to improve crystallinity in order to improve the graft ratio. Accordingly, it is desirable to select an aromatic acid dianhydride / alicyclic acid dianhydride composition and an aromatic diamine / alicyclic diamine composition that give higher crystallinity. The alicyclic hydrocarbon diamine and / or alicyclic acid dianhydride is preferably 1 to 90 mol% based on the total monomers. More desirably, it is 5 to 50 mol%.

  In the present invention, (1) vinyl monomer having an aromatic ring capable of retaining a sulfonic acid group, and (2) halogenation capable of being converted into a sulfonic acid group by hydrolysis. Examples thereof include vinyl monomers having a sulfonyl group and a sulfonic acid ester group, and (3) vinyl monomers having a halogen or a carbonyl group into which a sulfonic acid group can be introduced by a sulfonation reaction.

  (1) As vinyl monomers having an aromatic ring capable of retaining a sulfonic acid group, alkyl styrene such as styrene, α-methylstyrene, 4-vinyltoluene, 4-tert-butylstyrene, 2-chlorostyrene, 4-chlorostyrene, Halogenated styrene such as 2-bromostyrene, 3-bromostyrene, 4-bromostyrene, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 4-methoxystyrene, 4-methoxymethylstyrene, 2,4- Alkoxy styrene such as dimethoxy styrene, vinyl phenyl allyl ether, 4-hydroxy styrene, 4-acetoxy styrene, 4-tert-butoxy styrene, 4-tert-butyloxy carbonyloxy styrene, 4-vinyl benzyl alkyl ether which hydroxy Examples thereof include styrene derivatives.

(2) 4-vinylbenzenesulfonic acid sodium salt, 4-vinylbenzylsulfonic acid sodium salt as vinyl monomers having a sulfonyl halide group, a sulfonic acid ester group, and a sulfonic acid group that can be converted into a sulfonic acid group by hydrolysis, 4-methoxy sulfonyl styrene, 4-ethoxy sulfonyl styrene, 4-styrene sulfonyl _{fluoride, CF 2 = CF-O- (} CF 2) n-SO 2 F ( _{wherein, n = 1~5), CF 2} = CF _{-O-CF2-CF (CF 3} ) -O- (CF 2) n-SO 2 F ( wherein, n = 1 to 5) perfluoro (fluorosulfonyl vinyl ether) derivatives such as, CF ₂ = CF-SO _And fluorosulfonyltetrafluorovinyl derivatives such as ₂ F.

(3) As the vinyl monomer having a halogen sulfonic acid group can be introduced by sulfonation reaction, 4-chloromethyl _{styrene, CH 2 = CH-O- (} CH 2) nX ( wherein, n 1-5. X is a halogen group, chlorine or fluorine), CF ₂ = CF—O— (CH ₂ ) nX (where n is 1 to 5, X is a halogen group, chlorine or fluorine), CH _{2 = CH-O- (CF 2)} nX ( wherein, n 1~5.X a halogen group, chlorine or _{fluorine), CF 2 = CF-O-} (CF 2) nX ( in wherein, n 1 to 5. X is a halogen group, which is chlorine or fluorine), CF ₂ = CF—O—CF ₂ —CF (CF ₃ ) —O— (CF ₂ ) nX (where n is 1 to 5). X is a halogen group, chlorine or fluorine). Examples of the vinyl monomer having a carbonyl group into which a sulfonic acid group can be introduced by a sulfonation reaction include acrylic acid, acrylic acid salt, acrylic acid ester, alkyl vinyl ketone, allyl vinyl ketone, and alkyl (2-propenyl) ketone. It is done. Specifically, acrylic acid, sodium acrylate, potassium acrylate, trimethylammonium acrylate, triethylammonium acrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, phenyl acrylate, acrylic Naphthyl acid, benzyl acrylate, methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, butyl vinyl ketone, phenyl vinyl ketone, benzyl vinyl ketone, methyl (2-propenyl) ketone, ethyl (2-propenyl) ketone, propyl (2 -Propenyl) ketone, butyl (2-propenyl) ketone, benzyl (2-propenyl) ketone and the like. These monomers may be used not only as a single species but also as a mixture of a plurality of species, or may be used by diluting in a solvent.

  It is also possible to crosslink the graft chain by using a crosslinking agent such as a polyfunctional monomer in combination with the vinyl monomer. Further, after graft polymerization, graft chains, aromatic polymer chains, and graft chains and aromatic polymer chains can be cross-linked by addition of a polyfunctional monomer or irradiation with radiation. Polyfunctional monomers used as crosslinking agents include bis (vinylphenyl) ethane, divinylbenzene, 2,4,6-triallyloxy-1,3,5-triazine (triallyl cyanurate), triallyl-1,2,4 -Benzene tricarboxylate (triallyl trimellitate), diallyl ether, bis (vinylphenyl) methane, divinyl ether, 1,5-hexadiene, butadiene and the like. The crosslinking agent is preferably used in an amount of 10% or less by weight with respect to the vinyl monomer. If used over 10%, the polymer electrolyte membrane becomes brittle.

As the polymer electrolyte membrane has a higher electrical conductivity having a positive correlation with the ion exchange capacity, the performance as the polymer electrolyte membrane is better. Here, the ion exchange capacity is the amount of ion exchange groups (g / g) per gram of dry electrolyte membrane. However, when the electric conductivity of the ion exchange membrane at 25 ° C is 0.02 ([Ω · cm] ^-1 ) or less, the output performance as a fuel cell often decreases significantly. In many cases, the conductivity is designed to be 0.02 ([Ω · cm] ⁻¹ ) or more, and higher performance polymer electrolyte membranes are designed to be 0.10 ([Ω · cm] ⁻¹ ) or more.

  In the present invention, a polymer electrolyte membrane is produced by graft polymerization of a vinyl monomer using a radical generated on an aromatic polymer membrane substrate by the action of radiation and then chemical conversion to a sulfonic acid group. . Therefore, by controlling the graft rate and the sulfonation rate, the ion exchange capacity and thus the electrical conductivity of the resulting membrane can be controlled.

In the present invention, the radiation is applied to the aromatic polymer membrane substrate at 1 to 1000 kGy at room temperature to 150 ° C. in an inert gas or in the presence of oxygen. More preferably, irradiation is performed at 10 to 500 kGy. If it is 10 kGy or less, it is difficult to obtain a graft ratio necessary for obtaining an electric conductivity of 0.02 ([Ω · cm] ⁻¹ ) or more, and if it is 500 kGy or more, the polymer film substrate becomes brittle. Graft polymerization is a simultaneous irradiation method in which an aromatic polymer membrane substrate and a monomer are simultaneously irradiated and graft polymerized, and an aromatic polymer membrane substrate is irradiated with radiation and then contacted with a vinyl monomer for graft polymerization. It can be performed by any of the pre-irradiation methods.

  For graft polymerization of a polymer film substrate, a method of immersing the polymer film substrate in a vinyl monomer liquid is generally used. In the present invention, in the graft polymerization of the vinyl monomer to the aromatic polymer membrane substrate, the graft polymerizability of the polymer substrate, the membrane in the polymerization solution of the graft polymer membrane substrate obtained by graft polymerization From the viewpoint of shape maintenance, dichloroethane, chloroform, N-methylformamide, N-methylacetamide, N-methylpyrrolidone, γ-ptyrolactone, n-hexane, methanol, ethanol, 1-propanol, t-butanol, toluene, cyclohexane, cyclohexanone It is also possible to use a method of immersing the polymer membrane substrate in a vinyl monomer solution diluted with a solvent such as dimethyl sulfoxide.

In the present invention, the graft ratio is 2 to 120% by weight, more preferably 4 to 80% by weight, based on the polymer membrane substrate. If it is 4% by weight or less, it is difficult to obtain an electric conductivity of 0.02 ([Ω · cm] ⁻¹ ) or more, and if it is 80% by weight or more, the mechanical strength of the graft polymer film cannot be obtained.

In the present invention, the method for introducing a sulfonic acid group differs depending on the vinyl monomers (1) to (3) used for graft polymerization. In the graft polymer membrane obtained from the vinyl monomer (1), sulfonation to the aromatic ring in the graft chain is carried out by reacting concentrated sulfuric acid, fuming sulfuric acid, or dichloroethane solution or chloroform solution of chlorosulfonic acid. be able to. Depending on the graft rate of the graft polymer membrane, the sulfonation rate for showing electrical conductivity applicable to the polymer electrolyte membrane varies. Here, the sulfonation rate is 100% when one molecule of sulfonic acid is introduced per vinyl monomer unit of the graft chain. The sulfonation rate is preferably adjusted to 10 to 150% by changing the reaction time and the reaction temperature. More preferably, it is 30 to 100%. If it is 30% or less, it is difficult to obtain an electric conductivity of 0.02 ([Ω · cm] ⁻¹ ) or more, and if it is 100% or more, the heat resistance and oxidation resistance of the graft chain are remarkably lowered.

In the graft polymer membrane obtained from the vinyl monomer (2), hydrolysis of a sulfonyl halide group, a sulfonate group, and a sulfonate group in the graft chain into a sulfonate group is carried out by using a neutral aqueous solution, an alkaline aqueous solution, Or it can process by processing with acidic aqueous solution. In graft copolymerization with vinyl monomers other than vinyl monomer (2), the sulfonation rate is preferably adjusted to 10 to 100% by changing the composition ratio. More preferably, it is 30 to 100%. If it is 30% or less, it is difficult to obtain an electric conductivity of 0.02 ([Ω · cm] ⁻¹ ) or more, and if it is 100% or more, the heat resistance and oxidation resistance of the graft chain are remarkably lowered.

In the graft polymer membrane obtained from the vinyl monomer (3), the chemical conversion of the halogen atom in the graft chain to the sulfonate is carried out by using a sodium sulfite aqueous solution, a sodium hydrogen sulfite aqueous solution, or a mixture thereof with dimethylsulfoxide Can be treated with a solution. Also, chemical conversion of hydrogen atom on carbon to which carbonyl group in the graft chain is bonded to sulfonic acid can be treated with dichloroethane solution of chlorosulfonic acid or a complex of sulfur trioxide and Lewis base such as dioxane. . In graft copolymerization with vinyl monomers other than the vinyl monomer (3), the sulfonation rate is preferably adjusted to 10 to 100% by changing the composition ratio. More preferably, it is 30 to 100%. If it is 30% or less, it is difficult to obtain an electric conductivity of 0.02 ([Ω · cm] ⁻¹ ) or more, and if it is 100% or more, the heat resistance and oxidation resistance of the graft chain are remarkably lowered.

  In the present invention, in order to increase the electric conductivity of the polymer electrolyte membrane, it is also conceivable to make the polymer electrolyte membrane thin. However, at present, an excessively thin polymer electrolyte membrane is easily damaged, and it is difficult to manufacture the membrane itself. Therefore, in the present invention, a polymer electrolyte membrane of 5 to 200 μm is preferable. More preferred is a polymer electrolyte membrane in the range of 10 to 100 μm.

In the present invention, the energy imparted by radiation acts on the aromatic polymer chain to generate an active species such as a radical that initiates graft polymerization of the vinyl monomer on the polymer chain. Therefore, radiation is not particularly limited as long as it is an energy source that causes a reaction that generates active species such as radicals on the polymer chain. Specific examples include γ rays, electron beams, ion rays, and X-rays.
(Example)

Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to this. In addition, each measured value was calculated | required by the following measurements.
(1) Graft rate (%)

（２）イオン交換容量（mmol/g） When the polymer membrane substrate is the main chain part and the graft polymerized part with the vinyl monomer is the graft chain part, the weight ratio of the graft chain part to the main chain part is the graft ratio (X _dg [wt%]) Represented as:

(2) Ion exchange capacity (mmol / g)

[n（酸性基）_obs]の測定は、高分子電解質膜を1M硫酸溶液中に50℃で4時間浸漬し、完全にプロトン型（H型）とした後、50℃の3M NaCl水溶液中に4時間浸漬することで再度-SO₃Na型とする。高分子電解質膜を取り出した後、残存のNaCl水溶液を0.2M NaOHで中和滴定することで、高分子電解質膜の酸性基濃度を、置換されたプロトン（H⁺）として求めた。
（３）含水率（%） The ion exchange capacity (IEC) of the polymer electrolyte membrane is expressed by the following equation.

[n (acidic group) _obs ] is measured by immersing the polymer electrolyte membrane in a 1M sulfuric acid solution at 50 ° C for 4 hours to form a complete proton type (H type), and then in a 3M NaCl aqueous solution at 50 ° C. Re-SO ₃ Na type by immersion for 4 hours. After removing the polymer electrolyte membrane, the remaining NaCl aqueous solution was neutralized and titrated with 0.2 M NaOH to obtain the acidic group concentration of the polymer electrolyte membrane as a substituted proton (H ⁺ ).
(3) Moisture content (%)

（４）電気伝導度（[Ω・cm]^-1） Remove the H-type polymer electrolyte membrane stored in water at room temperature, gently wipe off the water on the surface (after about 1 minute), and then measure the weight (W (g)). This membrane is vacuum-dried at 60 ° C. for 16 hours and then weighed to obtain the dry weight W _d (g) of the polymer electrolyte membrane, and the moisture content is calculated from W _s and W _d by the following formula.

(4) Electrical conductivity ([Ω · cm] ^-1 )

（５）熱水耐性（重量残存率％） In accordance with the measurement by the alternating current method (New Experimental Chemistry Course 19, Polymer Chemistry (II), p998, Maruzen), using a normal membrane resistance measurement cell, Hewlett-Packard LCR meter, E-4925A, polymer electrolyte membrane The film resistance (Rm) was measured. The cell was filled with a 1M aqueous sulfuric acid solution, the resistance between two platinum electrodes (distance 5 mm) was measured, and the electrical conductivity of the polymer electrolyte membrane was calculated using the following equation.

(5) Hot water resistance (weight residual rate%)

The weight of the polymer electrolyte membrane after vacuum drying at 60 ° C. for 16 hours is W _3, and the dry weight of the electrolyte membrane immersed in water at 95 ° C. for 24 hours is W ₄ .

3 cm x 5 cm pyromellitic dianhydride / 4,4'-diaminodicyclohexylmethane alicyclic hydrocarbon polyimide film (hereinafter abbreviated as PI film 1) (film thickness 25μm) made of glass with cock After deaeration in a separable container, the inside of the glass container was replaced with argon gas. In this state, the polyimide film 1 was irradiated with γ rays from a ⁶⁰ Co source at 220 kGy at room temperature. Subsequently, styrene degassed by bubbling argon gas was added to the glass container so that the irradiated PI film 1 was immersed. After replacing with argon gas, the glass container was sealed and left at 60 ° C. for 24 hours. The obtained graft polymer membrane was washed with toluene and dried. A polymer electrolyte membrane was obtained by leaving it to stand in a 1,2-dichloroethane solution of 0.05 M chlorosulfonic acid at 30 ° C. for 4 hours, followed by washing with water. Table 1 shows the graft ratio, ion exchange capacity, electrical conductivity, elastic modulus at break, and hot water resistance of the polymer electrolyte membrane obtained in this example.

An alicyclic hydrocarbon polyimide film composed of 3 cm x 5 cm pyromellitic dianhydride / 4,4'-diaminodicyclohexylmethane / 4,4'-diaminodiphenyl ether (molar ratio: 10/1/9) (hereinafter referred to as PI The film was abbreviated as “film 2” (film thickness: 25 μm) in a separable container made of glass with a cock, and after deaeration, the inside of the glass container was replaced with argon gas. In this state, the polyimide film 2 was irradiated with γ rays from a ⁶⁰ Co source at 220 kGy at room temperature. Subsequently, styrene degassed by bubbling argon gas was added to the glass container so that the irradiated PI film 2 was immersed. After replacing with argon gas, the glass container was sealed and left at 60 ° C. for 24 hours. The obtained graft polymer membrane was washed with toluene and dried. A polymer electrolyte membrane was obtained by leaving it to stand in a 1,2-dichloroethane solution of 0.05 M chlorosulfonic acid at 30 ° C. for 4 hours, followed by washing with water. Table 1 shows the graft ratio, ion exchange capacity, electrical conductivity, elastic modulus at break, and hot water resistance of the polymer electrolyte membrane obtained in this example.

3 cm x 5 cm 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride / 4,4'-diaminodicyclohexylmethane / 4,4'-diaminodiphenyl ether (molar ratio: 10/1/9) An alicyclic hydrocarbon polyimide film (hereinafter abbreviated as PI film 3) (film thickness: 25 μm) was placed in a separable container made of glass with a cock, and after deaeration, the inside of the glass container was replaced with argon gas. In this state, the polyimide film 3 was irradiated with 220 kGy of γ rays from a ⁶⁰ Co ray source at room temperature. Subsequently, styrene degassed by bubbling argon gas was added to the glass container so that the irradiated PI film 3 was immersed. After replacing with argon gas, the glass container was sealed and left at 60 ° C. for 24 hours. The obtained graft polymer membrane was washed with toluene and dried. A polymer electrolyte membrane was obtained by leaving it to stand in a 1,2-dichloroethane solution of 0.05 M chlorosulfonic acid at 30 ° C. for 4 hours, followed by washing with water. Table 1 shows the graft ratio, ion exchange capacity, electrical conductivity, elastic modulus at break, and hot water resistance of the polymer electrolyte membrane obtained in this example.

Glass separable container with cock of alicyclic hydrocarbon polyimide film (hereinafter abbreviated as PI film 4) consisting of 3cm x 5cm cyclobutanetetracarboxylic dianhydride / 4,4'-diaminodiphenyl ether (hereinafter abbreviated as PI film 4) After deaeration by putting in, the inside of the glass container was replaced with argon gas. In this state, the polyimide film 1 was irradiated with γ rays from a ⁶⁰ Co source at 220 kGy at room temperature. Subsequently, styrene degassed by bubbling with argon gas was added to the glass container so that the irradiated polyimide film 4 was immersed. After replacing with argon gas, the glass container was sealed and left at 60 ° C. for 24 hours. The obtained graft polymer membrane was washed with toluene and dried. A polymer electrolyte membrane was obtained by leaving it to stand in a 1,2-dichloroethane solution of 0.05 M chlorosulfonic acid at 30 ° C. for 4 hours, followed by washing with water. Table 1 shows the graft ratio, ion exchange capacity, electrical conductivity, elastic modulus at break, and hot water resistance of the polymer electrolyte membrane obtained in this example.
(Comparative Example 1)

3 cm x 5 cm of pyromellitic dianhydride / 4, 4'-diaminodiphenyl ether wholly aromatic polyimide film (hereinafter abbreviated as Kapton film) (thickness 25 μm) graft polymerized under the same conditions as in Example 1 No weight increase was observed, and no graft membrane was obtained.
(Comparative Example 2)

3 cm x 5 cm 2,2-bis (4- (3,4-dicarboxyphenoxy) phenyl) propane / 4,4'-diaminodiphenyl ether wholly aromatic polyimide film (hereinafter referred to as PEI (polyetherimide) film) (Omitted) (film thickness 50 μm) was placed in a glass separable container with a cock and deaerated, and the inside of the glass container was replaced with argon gas. In this state, the PEI film was irradiated with 220 kGy of γ rays from a ⁶⁰ Co source at room temperature. Subsequently, styrene degassed by bubbling argon gas was added to the glass container so that the irradiated PEI film was immersed. After replacing with argon gas, the glass container was sealed and left at 60 ° C. for 24 hours. The obtained graft polymer membrane was washed with toluene and dried. A polymer electrolyte membrane was obtained by leaving it to stand in a 1,2-dichloroethane solution of 0.05 M chlorosulfonic acid at 30 ° C. for 4 hours and then performing a hydrolysis treatment by washing with water. Comparative Example 2 in Table 1 shows the graft ratio, ion exchange capacity, electrical conductivity, elastic modulus at break, and hot water resistance of the polymer electrolyte membrane obtained in this example.
(Comparative Example 3)

  The ion exchange capacity, electrical conductivity, elastic modulus at break, and hot water resistance measured for Nafion 112 (manufactured by DuPont) are shown in Comparative Example 3 in Table 1.

  Since the polymer electrolyte membrane of the present invention can introduce many graft chains into an alicyclic polyimide membrane base material excellent in mechanical properties and fuel impermeability at high temperatures due to high graft polymerizability, Compared to aromatic polymer electrolyte membranes and grafted wholly aromatic polymer electrolyte membranes, it exhibits higher proton conductivity, durability, and fuel impermeability. As a result, this polymer is excellent in proton conductivity, durability, and fuel impermeability, ideal for portable devices powered by methanol, hydrogen, etc., fuel cells expected as power sources for household cogeneration and automobiles. An electrolyte membrane can be provided.

Claims (6)

  A polymer electrolyte membrane in which a vinyl monomer is graft-polymerized on a polyimide base membrane containing an alicyclic hydrocarbon, wherein a part of the graft chain is chemically converted to a sulfonic acid group. film.   2. The polymer electrolyte membrane according to claim 1, wherein the polyimide base film containing the alicyclic hydrocarbon has an alicyclic hydrocarbon structure on one of diamine or acid dianhydride constituting the polyimide. A polymer electrolyte membrane.   2. The polymer electrolyte membrane according to claim 1, wherein the polyimide base film containing the alicyclic hydrocarbon has an alicyclic hydrocarbon structure in each of the diamine or acid dianhydride constituting the polyimide. A polymer electrolyte membrane.   A method for producing a polymer electrolyte membrane, which is produced by graft-polymerizing a vinyl monomer to a polyimide substrate membrane containing an alicyclic hydrocarbon and then chemically converting a part of the graft chain to a sulfonic acid group.   (1) Vinyl monomer having an aromatic ring capable of retaining a sulfonic acid group, (2) Halogenated sulfonyl group or sulfonic acid ester that can be converted to a sulfonic acid group by hydrolysis. After graft polymerization of a vinyl monomer having a group and (3) a vinyl monomer having a halogen or a carbonyl group capable of introducing a sulfonic acid group by a sulfonation reaction, A method for producing a polymer electrolyte membrane, wherein the part is chemically converted to a sulfonic acid group.   6. The method for producing a polymer electrolyte membrane according to claim 4, wherein a polyfunctional monomer having a weight ratio of 10% or less to the vinyl monomer is added together with the vinyl monomer.