JP4934822B2 - Polyimide resin and electrolyte membrane - Google Patents

Description

  The present invention relates to a polyimide resin and an electrolyte membrane.

  A fuel cell is a power generation device that directly converts the chemical reaction energy of fuel (eg, hydrogen, methanol, etc.) and oxygen into electrical energy, and is promising as a clean next-generation energy source that does not generate greenhouse gases or harmful substances. Has been. In particular, solid polymer electrolyte fuel cells (hereinafter referred to as PEFC) and methanol direct fuel cells (hereinafter referred to as DMFC) can be reduced in size and weight, and can be used as power sources for electric vehicles, homes, and portable devices. Because it is viewed as promising, research and development is actively underway. As an electrolyte membrane used for PEFC or DMFC, an electrolyte membrane that transmits only protons in a wet state is required. Currently, an electrolyte membrane mainly containing a perfluoroalkylsulfonic acid polymer is used.

  By the way, with respect to PEFC and DMFC, in order to improve the performance from the current level and to achieve a wide range of practical applications, the operating temperature may be higher (for example, 120 ° C. or higher) than the current temperature (for example, 80 ° C. or lower). It has been demanded. However, the electrolyte membrane containing the perfluoroalkylsulfonic acid polymer described above is difficult to be subjected to high-temperature operation at 100 ° C. or higher because proton conductivity and mechanical strength decrease under temperature conditions of 100 ° C. or higher. There is a problem that. In addition, there are problems such as easy permeation of fuel gas (hydrogen or methanol) and high cost.

  In order to solve such a problem, an electrolyte membrane including a polyimide resin in which a sulfonic acid group is introduced into a polymer has been proposed. An electrolyte membrane containing a polyimide resin having a sulfonic acid group introduced in the polymer has high heat resistance, oxidation resistance and mechanical strength, low manufacturing cost, easy introduction of substituents, and high proton conductivity. Therefore, it is considered as one of promising candidates for an electrolyte membrane for a fuel cell (see, for example, Patent Documents 1 to 4). Such an electrolyte membrane containing a polyimide resin in which a sulfonic acid group is introduced into a polymer has a proton conductivity and mechanical properties at 100 ° C. or higher as compared with the electrolyte membrane containing a perfluoroalkylsulfonic acid polymer. The problem that the mechanical strength is reduced is suppressed.

  Especially, the electrolyte membrane containing the polyimide resin described in Patent Documents 2 to 4 includes the polyimide resin in which a substituent containing a sulfonic acid group (for example, an acid alkoxy group) is introduced into the side chain of the polymer. Therefore, even when compared with an electrolyte membrane containing a polyimide resin described in Patent Document 1 in which a sulfonic acid group is directly introduced into an aromatic ring of a polymer main chain, proton conductivity and mechanical strength at 100 ° C. or higher Is further suppressed.

JP 2000-510511 A JP 2002-105199 A JP 2002-105200 A JP 2004-155998 A

However, the electrolyte membrane containing the polyimide resin described in Patent Documents 1 to 4 has a problem of low hydrolysis resistance.
That is, in order to increase the proton conductivity in the polyimide resin in order to improve the performance as an electrolyte membrane for a fuel cell, it is necessary to introduce a high concentration of sulfonic acid groups into the polyimide resin. However, since the sulfonic acid group has extremely high hydrophilicity, the introduction of the sulfonic acid group to the polyimide resin at a high concentration causes the entire polyimide resin to become hydrophilic, resulting in hydrolysis of the imide bond in the polyimide resin. It becomes easy to receive, and hydrolysis resistance falls.

  This problem is not only seen when a high concentration of sulfonic acid groups are introduced into the polyimide resin, but also when a strong acidic group other than a sulfonic acid group is introduced into the polyimide resin at a high concentration. Problem.

  Accordingly, an object of the present invention is to provide a polyimide resin having improved hydrolysis resistance. Moreover, it aims at providing the electrolyte membrane containing such the outstanding polyimide resin.

  As a result of intensive studies to achieve the above object, the present inventors have, as an acidic group to be introduced into the side chain of the polyimide resin, (a) an acid alkoxy group having 7 or more carbon atoms, and (b) an acid. It has been found that by using an acidic group of any one of a perfluoroalkoxy group, an (c) acid alkyl group, and a (d) acid alkylthio group, it is possible to improve hydrolysis resistance. It came to complete.

（一般式（１）中、Ａｒ^１は、炭素数６〜２０の芳香環であり、隣接するイミド基とともに原子数５又は６のイミド環を形成する。なお、この芳香環における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部又は全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。
また、Ａｒ^２は、炭素数６〜１３の芳香環であり、この芳香環における水素原子の少なくとも一部は炭素数７以上の酸アルコキシ基で置換されている。なお、この酸アルコキシ基における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部または全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。）(1) That is, the polyimide resin of this invention is characterized by including the structural unit shown by General formula (1).

(In General Formula (1), Ar ¹ is an aromatic ring having 6 to 20 carbon atoms, and forms an imide ring having 5 or 6 atoms with an adjacent imide group. In addition, some carbons in this aromatic ring The atoms may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms may be substituted with aliphatic groups, halogen atoms or perfluoroaliphatic groups. Good.
Ar ² is an aromatic ring having 6 to 13 carbon atoms, and at least a part of hydrogen atoms in the aromatic ring is substituted with an acid alkoxy group having 7 or more carbon atoms. In addition, some carbon atoms in this acid alkoxy group may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms are aliphatic groups, halogen atoms or It may be substituted with a perfluoroaliphatic group. )

  For this reason, in the polyimide resin of the present invention, a long-chain acid alkoxy group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are better separated. As a result, according to the polyimide resin of the present invention, since the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, the comparison has 6 or less carbon atoms. Compared with a polyimide resin having a short-chain acid alkoxy group, hydrolysis resistance is improved.

  In the polyimide resin of the present invention, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are better separated. As a result, according to the polyimide resin of the present invention, protons generated in the hydrophilic region move well through the hydrophilic region that is unevenly distributed in the polyimide resin, so that the number of carbon atoms is relatively low. Compared with a polyimide resin having a short-chain acid alkoxy group, proton conductivity is improved.

  In the polyimide resin described in (1) above, it is of course preferable that the acid alkoxy group is an acid alkoxy group having 7 to 9 carbon atoms. However, in view of the above, the acid alkoxy group has 10 or more carbon atoms. More preferably, it is an acid alkoxy group.

In this specification, “may be substituted with S, N, O, SO ₂ or CO” means not only a case where only a carbon atom is substituted, but also a hydrogen atom bonded to the carbon atom. It is meant to include substitution. In addition, when N is substituted, the number of bonded hydrogen atoms may change.

（一般式（２）中、Ｘ^１及びＸ^２は、酸性基を含む置換基であり、同一であっても異なっていてもよい。ｌ^１及びｌ^２は、前記酸アルコキシ基の炭素数を表し、それぞれ７以上の整数である。また、ｌ^１及びｌ^２は、それぞれ同一であっても異なっていてもよい。）(2) In the polyimide resin described in (1) above, Ar ² is preferably a group having a structure represented by the general formula (2).

(In General Formula (2), X ¹ and X ² are substituents containing an acidic group and may be the same or different. L ¹ and l ² represent the number of carbon atoms of the acid alkoxy group. Each represents an integer greater than or equal to 7. In addition, l ¹ and l ² may be the same or different.

Thus, by using the group having a structure represented by the general formula (2) as Ar ² , hydrolysis resistance and proton conductivity in the polyimide resin are further improved.

（一般式（３）中、Ａｒ^１は、炭素数６〜２０の芳香環であり、隣接するイミド基とともに原子数５又は６のイミド環を形成する。なお、この芳香環における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部又は全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。
また、Ａｒ^３は、炭素数６〜１３の芳香環であり、この芳香環における水素原子の少なくとも一部は酸パーフルオロアルコキシ基で置換されている。なお、この酸パーフルオロアルコキシ基における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部または全部のフッ素原子は、脂肪族基、他のハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。）(3) The polyimide resin of this invention is characterized by including the structural unit shown by General formula (3).

(In General Formula (3), Ar ¹ is an aromatic ring having 6 to 20 carbon atoms and forms an imide ring having 5 or 6 atoms with an adjacent imide group. In addition, some carbons in this aromatic ring The atoms may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms may be substituted with aliphatic groups, halogen atoms or perfluoroaliphatic groups. Good.
Ar ³ is an aromatic ring having 6 to 13 carbon atoms, and at least a part of hydrogen atoms in the aromatic ring is substituted with an acid perfluoroalkoxy group. In addition, some carbon atoms in this acid perfluoroalkoxy group may be substituted with S, N, O, SO ₂ or CO, and some or all of the fluorine atoms may be aliphatic groups, other May be substituted with a halogen atom or a perfluoroaliphatic group. )

  For this reason, in the polyimide resin of the present invention, an acid perfluoroalkoxy group having high hydrophobicity exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The acidic acidic group and the main chain of the hydrophobic polyimide resin are well separated. As a result, according to the polyimide resin of the present invention, since the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, the acid alkoxy group having the same carbon number Hydrolysis resistance is improved as compared with a polyimide resin having.

  In the polyimide resin of the present invention, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, according to the polyimide resin of the present invention, protons generated in the hydrophilic region move well through the hydrophilic region unevenly distributed in the polyimide resin. Perfluoroalkoxy groups have higher electron withdrawing properties than alkoxy groups. As a result, according to the polyimide resin of the present invention, the acidity of the acidic group is increased, and protons are easily released from the acidic group. For this reason, according to the polyimide resin of this invention, proton conductivity improves compared with the polyimide resin which has the acid alkoxy group of the same carbon number.

(4) In the polyimide resin as described in (3) above, it is of course preferable that the acid perfluoroalkoxy group is an acid perfluoroalkoxy group having 6 or less carbon atoms, but the acid perfluoroalkoxy group has 7 carbon atoms. The acid perfluoroalkoxy group is more preferable.

  By configuring in this way, a long-chain acid perfluoroalkoxy group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. As a result, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, and therefore a relatively short-chain acid perfluoroalkoxy having 6 or less carbon atoms. Compared with a polyimide resin having a group, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. That is, the hydrophilic region and the hydrophobic region are more favorably separated. As a result, protons generated in the hydrophilic region move more favorably through the hydrophilic region unevenly distributed in the polyimide resin, and thus a relatively short-chain acid perfluoroalkoxy group having 6 or less carbon atoms. Compared with a polyimide resin having a proton conductivity, the proton conductivity is further improved.

  In addition, since a long-chain acid perfluoroalkoxy group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin, the carbon number is 6 or less. Compared with a relatively short chain, the electron withdrawing property by the perfluoroalkoxy group is further increased. As a result, since the acidity in the acidic group is further increased, protons are more easily released from the acidic group, and compared with a polyimide resin having a relatively short-chain acid perfluoroalkoxy group having 6 or less carbon atoms, Proton conductivity is further improved.

（一般式（４）中、Ｘ^１及びＸ^２は、酸性基を含む置換基であり、同一であっても異なっていてもよい。ｍ^１及びｍ^２は、前記酸パーフルオロアルコキシ基の炭素数を表し、それぞれ１以上の整数である。また、ｍ^１及びｍ^２は、それぞれ同一であっても異なっていてもよい。）(5) In the polyimide resin according to (3) it is preferably a group having a structure Ar ³ is represented by the general formula (4).

(In General Formula (4), X ¹ and X ² are substituents containing an acidic group and may be the same or different. M ¹ and m ² are carbon atoms of the acid perfluoroalkoxy group. Each represents an integer of 1 or more, and m ¹ and m ² may be the same or different.)

Thus, by using the group having the structure represented by the general formula (4) as Ar ³ , hydrolysis resistance and proton conductivity in the polyimide resin are further improved.

（一般式（５）中、Ａｒ^１は、炭素数６〜２０の芳香環であり、隣接するイミド基とともに原子数５又は６のイミド環を形成する。なお、この芳香環における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部又は全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。
また、Ａｒ^４は、炭素数６〜１３の芳香環であり、この芳香環における水素原子の少なくとも一部は酸アルキル基で置換されている。なお、この酸アルキル基における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部又は全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。）(6) The polyimide resin of this invention is characterized by including the structural unit shown by General formula (5).

(In General Formula (5), Ar ¹ is an aromatic ring having 6 to 20 carbon atoms, and forms an imide ring having 5 or 6 atoms with an adjacent imide group. In addition, some carbons in this aromatic ring The atoms may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms may be substituted with aliphatic groups, halogen atoms or perfluoroaliphatic groups. Good.
Ar ⁴ is an aromatic ring having 6 to 13 carbon atoms, and at least a part of hydrogen atoms in the aromatic ring is substituted with an acid alkyl group. In addition, some carbon atoms in this acid alkyl group may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms are aliphatic groups, halogen atoms or It may be substituted with a perfluoroaliphatic group. )

  For this reason, in the polyimide resin of the present invention, a hydrophobic acidic alkyl group exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. And the main chain of the hydrophobic polyimide resin are well separated. As a result, according to the polyimide resin of the present invention, since the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, the acid alkoxy group having the same carbon number Hydrolysis resistance is improved as compared with a polyimide resin having.

  In the polyimide resin of the present invention, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, according to the polyimide resin of the present invention, protons generated in the hydrophilic region move well through the hydrophilic region that is unevenly distributed in the polyimide resin. Compared with the polyimide resin having, proton conductivity is improved.

(7) In the polyimide resin as described in (6) above, it is naturally preferable that the acid alkyl group is an acid alkyl group having 6 or less carbon atoms, but the acid alkyl group is an acid alkyl group having 7 or more carbon atoms. More preferably.

  By comprising in this way, a long-chain acid alkyl group having 7 or more carbon atoms is present between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. As a result, since the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, a relatively short-chain acid alkyl group having 6 or less carbon atoms is formed. Compared with the polyimide resin it has, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. That is, the hydrophilic region and the hydrophobic region are more favorably separated. As a result, protons generated in the hydrophilic region move more favorably through the hydrophilic region unevenly distributed in the polyimide resin, and thus have a relatively short-chain acid alkyl group having 6 or less carbon atoms. Compared with polyimide resin, proton conductivity is further improved.

(8) In the polyimide resin according to the above (6), the acid alkyl group is preferably not perfluorinated, but the acid alkyl group is more preferably an acid perfluoroalkyl group. .

  By comprising in this way, there exists an acid perfluoroalkyl group having high hydrophobicity between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The groups and the main chain of the hydrophobic polyimide resin can be separated more satisfactorily. As a result, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from hydrophilic acidic groups, so it is compared with polyimide resins that have non-perfluorinated acid alkyl groups. Thus, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. That is, the hydrophilic region and the hydrophobic region are more favorably separated. As a result, protons generated in the hydrophilic region move better through the hydrophilic region unevenly distributed in the polyimide resin. In addition, the perfluoroalkyl group has a higher electron withdrawing property than the alkyl group. As a result, the acidity of the acidic group is further increased, and protons are more easily released from the acidic group. For these reasons, proton conductivity is further improved as compared with a polyimide resin having an acid alkyl group that is not perfluorinated.

（一般式（６）中、Ｘ^１及びＸ^２は、酸性基を含む置換基であり、同一であっても異なっていてもよい。ｎ^１及びｎ^２は、前記酸アルキル基の炭素数を表し、それぞれ１以上の整数である。また、ｎ^１及びｎ^２は、それぞれ同一であっても異なっていてもよい。）(9) In the polyimide resin as described in (6) above, Ar ⁴ is preferably a group having a structure represented by the general formula (6).

(In General Formula (6), X ¹ and X ² are substituents containing an acidic group and may be the same or different. N ¹ and n ² represent the number of carbon atoms of the acid alkyl group. Each represents an integer of 1 or more, and n ¹ and n ² may be the same or different.

Thus, by using the group having the structure represented by the general formula (6) as Ar ⁴ , hydrolysis resistance and proton conductivity in the polyimide resin are further improved.

（一般式（７）中、Ａｒ^１は、炭素数６〜２０の芳香環であり、隣接するイミド基とともに原子数５又は６のイミド環を形成する。なお、この芳香環における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部又は全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。
また、Ａｒ^５は、炭素数６〜１３の芳香環であり、この芳香環における水素原子の少なくとも一部は酸アルキルチオ基で置換されている。なお、この酸アルキルチオ基における一部の炭素原子は、Ｓ、Ｎ、Ｏ、ＳＯ_２又はＣＯで置換されていてもよく、また、一部又は全部の水素原子は、脂肪族基、ハロゲン原子又はパーフルオロ脂肪族基で置換されていてもよい。）(10) The polyimide resin of the present invention is characterized by including a structural unit represented by the general formula (7).

(In General Formula (7), Ar ¹ is an aromatic ring having 6 to 20 carbon atoms and forms an imide ring having 5 or 6 atoms together with an adjacent imide group. In addition, some carbons in this aromatic ring The atoms may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms may be substituted with aliphatic groups, halogen atoms or perfluoroaliphatic groups. Good.
Ar ⁵ is an aromatic ring having 6 to 13 carbon atoms, and at least a part of hydrogen atoms in the aromatic ring is substituted with an acid alkylthio group. In addition, some carbon atoms in this acid alkylthio group may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms are aliphatic groups, halogen atoms or It may be substituted with a perfluoroaliphatic group. )

  For this reason, in the polyimide resin of the present invention, an acid alkylthio group having a sulfur atom larger than an oxygen atom exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. As a result, according to the polyimide resin of the present invention, due to the steric hindrance of the sulfur atom, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, Compared with a polyimide resin having an acid alkoxy group having the same carbon number, hydrolysis resistance is improved.

(11) In the polyimide resin as described in (10) above, it is naturally preferable that the acid alkylthio group is an acid alkylthio group having 6 or less carbon atoms, but the acid alkylthio group is an acid alkylthio group having 7 or more carbon atoms. More preferably.

  By comprising in this way, a long-chain acid alkylthio group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The acidic group and the main chain of the hydrophobic polyimide resin are well separated. As a result, since the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, it has a relatively short-chain acid alkylthio group having 6 or less carbon atoms. Compared with a polyimide resin, hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, since the proton generated in the hydrophilic region moves well through the hydrophilic region unevenly distributed in the polyimide resin, the polyimide having a relatively short-chain acid alkylthio group having 6 or less carbon atoms. Compared with resin, proton conductivity is improved.

(12) In the polyimide resin according to (10), the acid alkylthio group is preferably not perfluorinated, but the acid alkylthio group is more preferably an acid perfluoroalkylthio group. .

  By comprising in this way, since the acid perfluoroalkylthio group which has high hydrophobicity exists between a hydrophilic acidic group and the principal chain of hydrophobic polyimide resin, hydrophilic acidic group The group and the main chain of the hydrophobic polyimide resin are well separated. As a result, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from hydrophilic acidic groups, so it is compared with polyimide resins that have non-perfluorinated acid alkylthio groups. Thus, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, according to the polyimide resin of the present invention, protons generated in the hydrophilic region move well through the hydrophilic region unevenly distributed in the polyimide resin. In addition, the perfluoroalkylthio group has a higher electron withdrawing property than the alkylthio group. As a result, the acidity of the acidic group is increased, and protons are easily released from the acidic group. For these reasons, proton conductivity is improved as compared with a polyimide resin having an alkylthio group that is not perfluorinated.

（一般式（８）中、Ｘ^１及びＸ^２は、酸性基を含む置換基であり、同一であっても異なっていてもよい。ｏ^１及びｏ^２は、前記酸アルキルチオ基の炭素数を表し、それぞれ１以上の整数である。また、ｏ^１及びｏ^２は、それぞれ同一であっても異なっていてもよい。）(13) In the polyimide resin as described in (10) above, Ar ⁵ is preferably a group having a structure represented by the general formula (8).

(In the general formula (8), X ¹ and X ² are substituents containing an acidic group and may be the same or different. O ¹ and o ² represent the number of carbon atoms of the acid alkylthio group. Each represents an integer of 1 or more, and o ¹ and o ² may be the same or different.)

Thus, by using the group having the structure represented by the general formula (8) as Ar ⁵ , hydrolysis resistance and proton conductivity in the polyimide resin are further improved.

  In the polyimide resin described in the above (1), (3), (6) or (10), the acid alkoxy group, the acid perfluoroalkoxy group, the acid alkyl group or the acid alkylthio group has 20 or less carbon atoms. Preferably there is.

  By comprising in this way, acquisition and manufacture of a raw material become easy and manufacturing cost will also become cheap. In addition, the ratio of acidic groups contained per certain weight of the polyimide resin is not reduced, and high proton conductivity can be realized.

(14) In the polyimide resin as described in (2), (5), (9) or (13) above, X ¹ and X ² are sulfonic acid groups, phosphonic acid groups, carboxylic acid groups or phenolic hydroxyl groups. It is preferable that it is a substituent to contain.

  By comprising in this way, the acid dissociation degree of an acidic group becomes high and it becomes easy to discharge | release a proton from an acidic group, Therefore Proton conductivity further improves.

(15) In the polyimide resin according to the above (1) to (14), the structural unit includes a diamine compound containing an acid alkoxy group having 7 or more carbon atoms, an acid perfluoroalkoxy group, an acid alkyl group, or an acid alkylthio group. And a structural unit obtained by polycondensation with tetracarboxylic dianhydride.

  By comprising in this way, the synthesis | combination of a polyimide resin is easy and the manufacturing cost becomes cheap.

(16) The electrolyte membrane of the present invention includes the polyimide resin according to any one of (1) to (15) above.

  For this reason, since the electrolyte membrane of the present invention is an electrolyte membrane containing an excellent polyimide resin having high hydrolysis resistance and high proton conductivity as described above, the operating temperature of the fuel cell can be set to 100 ° C. or higher. It becomes possible, and it becomes possible to improve the performance of the fuel cell than at present and to achieve wide practical use.

  In addition, it can be produced at a lower cost than conventional perfluoroalkylsulfonic acid polymers.

  The polyimide resin and electrolyte membrane of this invention are demonstrated in detail based on embodiment.

[Embodiment 1]
(Polyimide resin)
The polyimide resin according to Embodiment 1 is a polyimide resin including the structural unit represented by the above general formula (1).

  In the polyimide resin according to Embodiment 1, as described above, a long-chain acid alkoxy group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. Therefore, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. As a result, according to the polyimide resin according to the first embodiment, the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, and thus has 6 or less carbon atoms. Compared with a polyimide resin having a relatively short-chain acid alkoxy group, hydrolysis resistance is improved.

  Further, in the polyimide resin according to Embodiment 1, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, according to the polyimide resin according to the first embodiment, protons generated in the hydrophilic region move well through the hydrophilic region unevenly distributed in the polyimide resin, and therefore the number of carbon atoms is 6 or less. Compared with a polyimide resin having a relatively short-chain acid alkoxy group, proton conductivity is improved.

  In addition, in the polyimide resin which concerns on Embodiment 1, it is further more preferable that an acid alkoxy group is a C10 or more acid alkoxy group.

As Ar ¹ in the above general formula (1), for example, the following substituents can be preferably used.

(Ar ¹ )

Moreover, as Ar < ² > in above-mentioned General formula (1), the substituent shown below can be used preferably, for example.

(Ar ² )

Among them, it is preferred that Ar ² is a group having the structure represented by the general formula described above (2).

The chemical structures represented by Ar ¹ and Ar ² are not necessarily the same, and may be a copolymer or a mixture in which a plurality of substituents are mixed.

As X ¹ or X ² in the above general formula (2), the following substituents can be preferably used.

(X ¹ , X ² )

  In the polyimide resin according to Embodiment 1, the molecular weight is not particularly limited, but the polymerization average molecular weight is preferably at least 5000 or more from the viewpoint of maintaining the mechanical strength of the electrolyte membrane.

  In addition, although the structure of a polyimide resin contains the structural unit shown by above-mentioned General formula (1), it may contain the other structural unit (copolymerization component). In this case, any of a block copolymer, an alternating copolymer, or a random copolymer may be used.

  Next, a method for producing the polyimide resin according to Embodiment 1 will be described with an example. In addition, the manufacturing method of the polyimide resin which concerns on Embodiment 1 is not limited to this.

  The polyimide resin according to Embodiment 1 is obtained by polymerizing a plurality of monomers composed of a diamino compound containing an acid alkoxy group and a tetracarboxylic dianhydride compound in the presence of an organic acid, a tertiary amine, and an organic solvent. Can be manufactured.

  In this production method, the amino group portion of the diamino compound reacts with the acid anhydride portion of the tetracarboxylic dianhydride compound, whereby the polymerization reaction proceeds, and a polyimide resin having an imide bond is formed.

  As the diamino compound containing an acid alkoxy group, for example, the following compounds can be preferably used.

(Diamino compounds containing acid alkoxy groups)

  The diamino compound may be used as a single compound or a mixture of a plurality of compounds.

  As a crosslinking agent for improving the stability of the obtained polyimide resin, for example, the following diamino compound, triamino compound, tetraamino compound and the like can be appropriately added.

(Diamino compound)

(Triamino compound)

(Tetraamino compound)

  As the tetracarboxylic dianhydride compound, for example, the following compounds can be preferably used.

(Tetracarboxylic dianhydride compound)

  Among the tetracarboxylic dianhydride compounds described above, naphthalene-1,8: 4,5-tetracarboxylic dianhydride can be particularly preferably used from the viewpoint of the stability of the resulting polyimide resin.

  The tetracarboxylic dianhydride compound may be used as a single compound or a mixture of a plurality of compounds.

  The diamino compound and the tetracarboxylic dianhydride compound react at a molar ratio of 1: 1. Therefore, the amount of the diamino compound and the tetracarboxylic dianhydride compound is adjusted so that the molar ratio is about 1: 1.

  The method for producing a polyimide resin according to Embodiment 1 includes a dissolution process, a polymerization process, and a modification process. In addition, the process according to need can be included.

  The dissolution step is a step of heating and dissolving a mixture of a diamino compound (0.1 mM to 5 M), a tertiary amine (0.1 mM to 20 M), and an organic solvent. The tertiary amine is used for dissolving a diamino compound having an acidic group in an organic solvent. Although it does not specifically limit as temperature which heats a mixture, A monomer can be easily melt | dissolved in a solvent easily by setting it as about 20-150 degreeC.

  The tertiary amine is not particularly limited, and trimethylamine, triethylamine, tripropylamine, diazabicycloundecene and the like can be preferably used. Of these, triethylamine can be particularly preferably used. These tertiary amines may be used alone or as a mixture of two or more tertiary amines.

  As the organic solvent, those having a high boiling point and a high polarity are preferable. Phenol, m-cresol, m-chlorophenol, p-chlorophenol, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methyl-2-pyrrolidinone, N- Cyclohexyl-2-pyrrolidinone and the like can be preferably used. Of these, m-cresol, dimethyl sulfoxide and N-methyl-2pyrrolidinone can be particularly preferably used. These organic solvents may be used alone or as a mixture of two or more organic solvents.

  In the polymerization step, a tetracarboxylic dianhydride compound (0.1 mM to 5 M) is added to a solution obtained by uniformly dissolving a diamino compound in a solvent, and in the presence of an organic acid (0.01 mM to 20 M). This is a step of polymerizing by heating. The organic acid serves as a polymerization / ring-closure reaction catalyst, and promotes the formation of a polyamic acid and the formation of an imide ring by the ring closure.

  As the organic acid, a compound having a high boiling point and high solubility in the above organic solvent is preferable, and benzoic acid, methylbenzoic acid, dimethylbenzoic acid, salicylic acid and the like can be preferably used. Of these, benzoic acid can be particularly preferably used. If the organic acid is present in the polymerization step, it may be added in the dissolution step described above. The amount of the organic acid to be added is not particularly limited, but in the case of benzoic acid, it is preferable to add about 1 to 6 moles relative to the tetracarboxylic dianhydride compound. Moreover, as temperature which heats a mixture, it is at least 40 degreeC or more, Preferably a polymerization reaction advances efficiently by setting it as about 150-180 degreeC, and can obtain a high molecular weight polyimide resin.

  The modification step is a step of correcting physical defects in the mixture (polymerized polyimide resin) and improving physical, chemical, and thermal characteristics of the polyimide resin. The structural defect is a defect based on an unclosed portion (amic acid) in the polyimide resin. In the reforming step, the mixture is heated at a temperature higher than that in the polymerization step to perform a dehydration reaction, thereby causing imidation of the unclosed portion. The temperature for heating the mixture is preferably at least 150 ° C or higher, more preferably 190 to 220 ° C. With such a temperature, the ring closure reaction proceeds efficiently, and a polyimide resin free of structural defects can be obtained.

(Electrolyte membrane)
The electrolyte membrane according to Embodiment 1 can be manufactured by forming the polyimide resin according to Embodiment 1 by a known method. As the film forming method, for example, a general method such as a casting method in which a solution is cast on a flat plate, a method in which a solution is applied on a flat plate by a die coater, a comma coater, or a method in which a melt is stretched is preferably used. it can. In this case, the polyimide resin can be used alone or in combination with other polymer compounds, polymer electrolytes, low molecular plasticizers and the like.

[Embodiment 2]
(Polyimide resin)
The polyimide resin according to Embodiment 2 is a polyimide resin including the structural unit represented by the general formula (3).

  In the polyimide resin according to the second embodiment, an acid perfluoroalkoxy group having high hydrophobicity exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The acidic group and the main chain of the hydrophobic polyimide resin are well separated. As a result, according to the polyimide resin according to the second embodiment, the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group. Compared with a polyimide resin having an alkoxy group, hydrolysis resistance is improved.

  Moreover, in the polyimide resin which concerns on Embodiment 2, as mentioned above, a hydrophilic acidic group and the principal chain of hydrophobic polyimide resin come to be isolate | separated favorably. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, according to the polyimide resin according to the second embodiment, protons generated in the hydrophilic region move well through the hydrophilic region unevenly distributed in the polyimide resin. Perfluoroalkoxy groups have higher electron withdrawing properties than alkoxy groups. As a result, according to the polyimide resin according to Embodiment 2, the acidity of the acidic group is increased, and protons are easily released from the acidic group. For this reason, according to the polyimide resin which concerns on Embodiment 2, proton conductivity improves compared with the polyimide resin which has the acid alkoxy group of the same carbon number.

  In the polyimide resin according to Embodiment 2, the acid perfluoroalkoxy group is preferably an acid perfluoroalkoxy group having 6 or less carbon atoms, but more preferably an acid perfluoroalkoxy group having 7 or more carbon atoms. preferable.

  By configuring in this way, a long-chain acid perfluoroalkoxy group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. As a result, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, and therefore a relatively short-chain acid perfluoroalkoxy having 6 or less carbon atoms. Compared with a polyimide resin having a group, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. That is, the hydrophilic region and the hydrophobic region are more favorably separated. As a result, protons generated in the hydrophilic region move more favorably through the hydrophilic region unevenly distributed in the polyimide resin, and thus a relatively short-chain acid perfluoroalkoxy group having 6 or less carbon atoms. Compared with a polyimide resin having a proton conductivity, the proton conductivity is further improved.

  In addition, since a long-chain acid perfluoroalkoxy group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin, the carbon number is 6 or less. Compared with a relatively short chain, the electron withdrawing property by the perfluoroalkoxy group is further increased. As a result, since the acidity in the acidic group is further increased, protons are more easily released from the acidic group, and compared with a polyimide resin having a relatively short-chain acid perfluoroalkoxy group having 6 or less carbon atoms, Proton conductivity is further improved.

As Ar ¹ in the above general formula (3), the same substituents as Ar ¹ in the above general formula (1) can be preferably used as in the case of the first embodiment.

As Ar ³ in the above general formula (3), the following substituents can be preferably used.

(Ar ³ )

The chemical structures represented by Ar ¹ and Ar ³ do not have to be the same, and may be a copolymer or a mixture in which a plurality of substituents are mixed.

  As the diamino compound containing an acid perfluoroalkoxy group, for example, the following compounds can be preferably used.

(Diamino compound containing acid perfluoroalkoxy group)

(Electrolyte membrane)
The electrolyte membrane according to Embodiment 2 can be manufactured by forming the polyimide resin according to Embodiment 2 by a known method. This is similar to the case of the electrolyte membrane according to the first embodiment.

[Embodiment 3]
(Polyimide resin)
The polyimide resin according to Embodiment 3 is a polyimide resin including the structural unit represented by the general formula (5).

  In the polyimide resin according to Embodiment 3, since a hydrophobic acid alkyl group is present between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin, the hydrophilic acidic group and The main chain of the hydrophobic polyimide resin is well separated. As a result, according to the polyimide resin according to the third embodiment, the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group. Compared with a polyimide resin having an alkoxy group, hydrolysis resistance is improved.

  Moreover, in the polyimide resin which concerns on Embodiment 3, as mentioned above, a hydrophilic acidic group and the principal chain of hydrophobic polyimide resin come to be isolate | separated favorably. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, according to the polyimide resin according to the third embodiment, protons generated in the hydrophilic region move well through the hydrophilic region that is unevenly distributed in the polyimide resin. For this reason, according to the polyimide resin which concerns on Embodiment 3, a proton conductivity improves compared with the polyimide resin which has the acid alkoxy group of the same carbon number.

  In the polyimide resin according to Embodiment 3, the acid alkyl group is preferably an acid alkyl group having 6 or less carbon atoms, but more preferably an acid alkyl group having 7 or more carbon atoms.

  By comprising in this way, a long-chain acid alkyl group having 7 or more carbon atoms is present between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. As a result, since the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, a relatively short-chain acid alkyl group having 6 or less carbon atoms is formed. Compared with the polyimide resin it has, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. That is, the hydrophilic region and the hydrophobic region are more favorably separated. As a result, protons generated in the hydrophilic region move more favorably through the hydrophilic region unevenly distributed in the polyimide resin, and thus have a relatively short-chain acid alkyl group having 6 or less carbon atoms. Compared with polyimide resin, proton conductivity is further improved.

  In the polyimide resin according to Embodiment 3, the acid alkyl group is preferably an acid perfluoroalkyl group.

  By comprising in this way, there exists an acid perfluoroalkyl group having high hydrophobicity between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The groups and the main chain of the hydrophobic polyimide resin can be separated more satisfactorily. As a result, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from hydrophilic acidic groups, so it is compared with polyimide resins that have non-perfluorinated acid alkyl groups. Thus, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are more favorably separated. That is, the hydrophilic region and the hydrophobic region are more favorably separated. As a result, protons generated in the hydrophilic region move better through the hydrophilic region unevenly distributed in the polyimide resin. In addition, since the perfluoroalkyl group has higher electron withdrawing properties than the alkyl group, the acidity of the acidic group is further increased, and protons are more easily released from the acidic group. For this reason, proton conductivity is further improved as compared with a polyimide resin having an acid alkyl group that is not perfluorinated.

As Ar < ¹ > in above-described General formula (5), the substituent similar to Ar < ¹ > in above-mentioned General formula (1) can be used preferably similarly to the case of Embodiment 1-2.

As Ar ⁴ in the above general formula (5), for example, the following substituents can be preferably used.

(Ar ⁴ )

The chemical structures represented by Ar ¹ and Ar ⁴ do not have to be the same, and may be a copolymer or a mixture in which a plurality of substituents are mixed.

  As the diami compound containing an acid alkyl group, for example, the following compounds can be preferably used.

(Diamino compounds containing acid alkyl groups)

(Electrolyte membrane)
The electrolyte membrane according to Embodiment 3 can be manufactured by forming the polyimide resin according to Embodiment 3 by a known method. This is similar to the case of the electrolyte membrane according to the first embodiment.

[Embodiment 4]
(Polyimide resin)
The polyimide resin according to Embodiment 4 is a polyimide resin including the structural unit represented by the general formula (7).

  In the polyimide resin according to Embodiment 4, an acid alkylthio group having a sulfur atom larger than an oxygen atom exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. As a result, according to the polyimide resin according to Embodiment 4, the imide bond present in the main chain of the hydrophobic polyimide resin is not easily attacked by water molecules from the hydrophilic acidic group due to the steric hindrance of the sulfur atom. Therefore, compared with the polyimide resin which has the acid alkoxy group of the same carbon number, hydrolysis resistance improves.

  In the polyimide resin according to Embodiment 4, the acid alkylthio group is naturally preferably an acid alkylthio group having 6 or less carbon atoms, but more preferably an acid alkylthio group having 7 or more carbon atoms.

  By comprising in this way, a long-chain acid alkylthio group having 7 or more carbon atoms exists between the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin. The acidic group and the main chain of the hydrophobic polyimide resin are well separated. As a result, since the imide bond existing in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from the hydrophilic acidic group, it has a relatively short-chain acid alkylthio group having 6 or less carbon atoms. Compared with a polyimide resin, hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, since the proton generated in the hydrophilic region moves well through the hydrophilic region unevenly distributed in the polyimide resin, the polyimide having a relatively short-chain acid alkylthio group having 6 or less carbon atoms. Compared with resin, proton conductivity is improved.

  In the polyimide resin according to Embodiment 4, the acid alkylthio group is preferably an acid perfluoroalkylthio group.

  By comprising in this way, since the acid perfluoroalkylthio group which has high hydrophobicity exists between a hydrophilic acidic group and the principal chain of hydrophobic polyimide resin, hydrophilic acidic group The group and the main chain of the hydrophobic polyimide resin are well separated. As a result, the imide bond present in the main chain of the hydrophobic polyimide resin is less susceptible to attack by water molecules from hydrophilic acidic groups, so it is compared with polyimide resins that have non-perfluorinated acid alkylthio groups. Thus, the hydrolysis resistance is further improved.

  Further, as described above, the hydrophilic acidic group and the main chain of the hydrophobic polyimide resin are well separated. That is, the hydrophilic region and the hydrophobic region are well separated. As a result, protons generated in the hydrophilic region move well through the hydrophilic region unevenly distributed in the polyimide resin. In addition, the perfluoroalkylthio group has a higher electron withdrawing property than the alkylthio group. As a result, the acidity of the acidic group is increased, and protons are easily released from the acidic group. For these reasons, proton conductivity is improved as compared with a polyimide resin having an alkylthio group that is not perfluorinated.

As Ar < ¹ > in above-described General formula (7), the substituent similar to Ar < ¹ > in General formula (1) mentioned above can be used preferably similarly to the case of Embodiment 1-3.

As Ar ⁵ in the general formula (7), for example, the following substituents can be preferably used.

(Ar ⁵ )

The chemical structures represented by Ar ¹ and Ar ⁵ do not have to be the same, and may be a copolymer or a mixture in which a plurality of substituents are mixed.

  As the diamino compound containing an acid alkylthio group, for example, the following compounds can be preferably used.

(Diamino compound containing an alkylthio group)

(Electrolyte membrane)
The electrolyte membrane according to Embodiment 4 can be manufactured by forming the polyimide resin according to Embodiment 4 by a known method. This is similar to the case of the electrolyte membrane according to the first embodiment.

Example 1
[Monomer Synthesis 1: Synthesis of 3,3′-bis (sulfodecyloxy) benzidine]
To a 300 mL eggplant-shaped flask, 150 mL of anhydrous acetonitrile, 50 g of 1,10-dibromodecane and 10 g of potassium carbonate were added and stirred while heating under reflux. A total of 4.0 g of 0.54 g of 4,4′-bis (acetamido) -3,3′-dihydroxybiphenyl was added every 6 hours, and the mixture was stirred for 12 hours while heating under reflux. The reaction mixture was poured into chloroform and then washed three times with pure water. The organic layer was concentrated and precipitated in hexane to obtain 4,4′-bis (acetamido) -3,3′-bis (10-bromodecyloxy) biphenyl as a yellow powder.

  In a 100 mL eggplant-shaped flask, 50 g of anhydrous 1,1,2,2-tetrachloroethane, 2.0 g of 4,4′-bis (acetamido) -3,3′-bis (10-bromodecyloxy) biphenyl, tetrabromide Butylammonium 0.2g and saturated sodium sulfite aqueous solution 40mL were added. The mixture was stirred with heating at reflux for 4 days. The reaction mixture was acidified with concentrated hydrochloric acid, and the organic components were extracted with chloroform. The chloroform layer was washed 3 times with pure water and evaporated to dryness to obtain 4,4'-bis (acetamido) -3,3'-bis (10-sulfodecyloxy) biphenyl.

  Add 2 g of 4,4′-bis (acetamido) -3,3′-bis (10-sulfodecyloxy) biphenyl, 6 mL of concentrated hydrochloric acid, 50 mL of methanol and 20 mL of pure water to a 20 mL eggplant-shaped flask, and heat to reflux for 12 hours. While stirring. After completion of the reaction, the mixture was heated to dryness. The obtained pale yellow powder was recrystallized and purified using methanol / water and methanol / chloroform to obtain 3,3'-bis (sulfodecyloxy) benzidine as white crystals.

[Production of polyimide resin]
In a 100 mL four-necked flask equipped with a mercury thermometer with a seal, a nitrogen inlet and a reflux tube, 1.314 g (2.0 mmol) of 3,3′-bis (sulfodecyloxy) benzidine and 0.38 mL ( 3 mmol) of triethylamine and 7.5 mL of m-cresol (manufactured by Kanto Chemical Co., Inc.) were added and heated at 140 ° C. for 10 minutes under a nitrogen stream. This mixture was vigorously stirred to obtain a transparent homogeneous solution (dissolution step).

  0.536 g (2.00 mmol) of naphthalene-1,8: 4,5-tetracarboxylic dianhydride, 1.000 g (8.18 mmol) of benzoic acid, 15 mL of m-cresol and Was added. The reaction solution became reddish brown. Then, it heated for 15 hours, stirring at 175 degreeC under nitrogen stream. The reaction solution became viscous (polymerization step).

  Subsequently, it heated at 195 degreeC under nitrogen stream for 5 hours. Heating was stopped and cooled to 60 ° C. A red-brown and viscous polyimide polymer solution was obtained (reforming step).

[Manufacture of electrolyte membrane]
The obtained polyimide polymer solution was formed into a film by a casting method. In the casting method, the copolymer solution produced on a glass plate was poured as it was, and then the film was naturally dried at 60 ° C. for one day to form a film. Then, after performing normal-pressure drying at 80 degreeC for 12 hours, the reduced pressure drying was further performed at 80 degreeC for 12 hours.

  And the obtained film | membrane was immersed in 400 mL of 1N nitric acid ethanol solution, and was stirred for 12 hours (acid treatment process). This acid treatment step was repeated two more times. Thereafter, it was washed with ethanol. Then, it dried under reduced pressure at 60 degreeC for 12 hours, and was set as the test sample.

(Example 2)
A test sample was obtained according to the method of Example 1 except that 3,3′-bis (sulfotetrafluoroethyloxy) benzidine was used instead of 3,3′-bis (sulfodecyloxy) benzidine.

(Example 3)
A test sample was obtained according to the method of Example 1 except that 3,3′-bis (sulfomethyl) benzidine was used instead of 3,3′-bis (sulfodecyloxy) benzidine.

Example 4
A test sample was obtained according to the method of Example 1 except that 3,3′-bis (sulfoethylthio) benzidine was used instead of 3,3′-bis (sulfodecyloxy) benzidine.

(Comparative Example 1)
A test sample was obtained according to the method of Example 1 except that 3,3′-bis (sulfopropyloxy) benzidine was used instead of 3,3′-bis (sulfodecyloxy) benzidine.

(Oxidation resistance)
Each test sample according to Examples 1 to 4 and Comparative Example 1 was heated at 80 ° C. in Fenton reagent (3% hydrogen peroxide aqueous solution containing 2 ppm of iron sulfate). The appearance of each test sample was observed over time. The time at which the sample film began to dissolve and the time at which it completely dissolved was recorded.

(Hydrolysis resistance)
Each test sample according to Examples 1 to 4 and Comparative Example 1 was exposed to an atmosphere of high temperature and high humidity (140 ° C., humidity 100%) for 24 hours. After the test, the appearance of each test sample was observed.

(Proton conductivity)
Each test sample according to Examples 1 to 4 and Comparative Example 1 was cut into a size of 5 × 40 mm, and the AC impedance was measured by the 4-terminal method. The measurement was performed under the conditions of 80 ° C. or 100 ° C., a relative humidity of 65%, a constant current of 0.005 mA as a current value, and 10 to 20000 Hz as a sweep frequency. The proton conductivity was calculated from the obtained impedance, distance between membrane terminals (10 mm), and film thickness (50 μm).

(result)
Table 1 shows the evaluation results for the test samples according to Examples 1 to 4 and Comparative Example 1.

  As is clear from Table 1, each test sample according to Examples 1 to 4 has higher oxidation resistance, higher hydrolysis resistance and higher proton conductivity than the test sample according to Comparative Example 1. It became clear.

Claims (4)

A polyimide resin comprising a structural unit represented by the general formula (1).

(In General Formula (1), Ar ¹ is an aromatic ring having 6 to 20 carbon atoms, and forms an imide ring having 5 or 6 atoms with an adjacent imide group. In addition, some carbons in this aromatic ring The atoms may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms may be substituted with aliphatic groups, halogen atoms or perfluoroaliphatic groups. Good.
Ar ² is a group having a structure represented by the general formula (2) in which two hydrogen atoms in an aromatic ring are substituted with an acid alkoxy group having 7 or more carbon atoms. In addition, some carbon atoms in this acid alkoxy group may be substituted with S, N, O, SO ₂ or CO, and some or all of the hydrogen atoms are aliphatic groups, halogen atoms or It may be substituted with a perfluoroaliphatic group. )

(In General Formula (2), X ¹ and X ² are substituents containing an acidic group and may be the same or different. L ¹ and l ² represent the number of carbon atoms of the acid alkoxy group. Each represents an integer greater than or equal to 7. In addition, l ¹ and l ² may be the same or different. The polyimide resin according to claim ^1, wherein X ¹ and X ² are substituents containing a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, or a phenolic hydroxyl group.   The structural unit is a structural unit obtained by polycondensation of a tetracarboxylic dianhydride with a diamine compound containing an acid alkoxy group having 7 or more carbon atoms, an acid perfluoroalkoxy group, an acid alkyl group or an acid alkylthio group. The polyimide resin according to claim 1 or 2, wherein   An electrolyte membrane comprising the polyimide resin according to claim 1, 2 or 3.