JP7255488B2 - Polyimide, polyimide varnish, and polyimide film - Google Patents

Description

The present invention relates to polyimide, and polyimide varnish and polyimide film containing the polyimide.

In addition to its excellent heat resistance, polyimide has excellent mechanical properties, chemical resistance, and electrical properties. and widely used in fields such as display devices.
2. Description of the Related Art In the field of display devices, active studies are being made to realize lighter, thinner, and more flexible display devices by applying plastic substrates instead of glass substrates. However, for example, when an electronic element made of an inorganic material is formed on a film, the linear thermal expansion coefficient of the inorganic material and that of the film differ greatly, so the film on which the electronic element made of an inorganic material is formed may bend. In some cases, the electronic element made of the material was peeled off from the film. Therefore, polyimide films are also required to have a low coefficient of linear thermal expansion in addition to transparency and heat resistance.

It is generally known that the linear thermal expansion coefficient of polyimide decreases as the polymer chain becomes rigid and linear. Therefore, in order to lower the linear thermal expansion coefficient of polyimide and improve its dimensional stability, various structures have been proposed for both acid dianhydride and diamine, which are raw materials of polyimide.

For example, in Patent Document 1, 4,4′-(hexafluoroisopropylidene)diphthalic acid is used as an acid component, and 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl is used as a diamine component. A polyimide is disclosed.

Japanese Patent Application Publication No. 2012-503701

However, although the polyimide disclosed in Patent Document 1 is excellent in transparency and heat resistance, the coefficient of linear thermal expansion does not reach a satisfactory level, and there is a need for further improvement.
That is, the problem to be solved by the present invention is to provide a polyimide capable of forming a film having a low linear thermal expansion coefficient while maintaining high transparency and high heat resistance, and a polyimide varnish and a polyimide film containing the polyimide. That's what it is.

As a result of extensive studies, the inventors have found that a polyimide having a specific structural unit can form a film having a low coefficient of linear thermal expansion while maintaining high transparency and high heat resistance. Based on these findings, the inventors have completed the present invention. That is, the present invention relates to the following [1] to [3].
[1] A polyimide having a structural unit A derived from a tetracarboxylic acid or a derivative thereof and a structural unit B derived from a diamine,
Structural unit A is a structural unit (A-1) derived from a compound represented by the following formula (a-1), and a structural unit (A-2) derived from a compound represented by the following formula (a-2) ), including
Structural unit B is a structural unit (B-1) derived from a compound represented by the following formula (b-1), and a structural unit (B-2) derived from a compound represented by the following formula (b-2) ), including polyimides.

(In formula (b-1), each R independently represents a hydrogen atom, a fluorine atom or a methyl group.)
[2] A polyimide varnish obtained by dissolving the polyimide according to [1] above in an organic solvent.
[3] A polyimide film containing the polyimide according to [1] above.

ADVANTAGE OF THE INVENTION According to this invention, the polyimide which can form the film which has a low coefficient of linear thermal expansion, and the polyimide varnish and polyimide film containing this polyimide can be provided, maintaining high transparency and high heat resistance.

[Polyimide]
The polyimide of the present invention is a polyimide having a structural unit A derived from a tetracarboxylic acid or a derivative thereof and a structural unit B derived from a diamine,
Structural unit A is a structural unit (A-1) derived from the compound represented by the formula (a-1), and a structural unit (A-2) derived from the compound represented by the formula (a-2) ), including
The structural unit B is a structural unit (B-1) derived from the compound represented by the formula (b-1), and a structural unit (B-2) derived from the compound represented by the formula (b-2) ) is polyimide. The polyimide of the present invention has a specific structural unit (A-1), a structural unit (A-2), a structural unit (B-1), and a structural unit (B-2). can form a film having

[Constituent unit A]
The structural unit A contained in the polyimide of the present invention is a structural unit derived from tetracarboxylic acid or a derivative thereof. A tetracarboxylic acid or its derivative can be used individually or in combination of 2 or more types.
Derivatives of tetracarboxylic acids include anhydrides or alkyl esters of tetracarboxylic acids. As the alkyl ester of tetracarboxylic acid, the alkyl preferably has 1 to 3 carbon atoms, and examples thereof include dimethyl ester, diethyl ester and dipropyl ester of tetracarboxylic acid. As the tetracarboxylic acid or derivative thereof, tetracarboxylic dianhydride is preferred.
Structural unit A in the present invention includes a structural unit (A-1) derived from a compound represented by formula (a-1) below. The compound represented by formula (a-1) is biphenyltetracarboxylic dianhydride. Including the structural unit (A-1) in the structural unit A improves the heat resistance, mechanical properties (elastic modulus), and organic solvent resistance of the polyimide.

Examples of the compound represented by formula (a-1) include 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) represented by formula (a-1-1) below, 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) represented by the following formula (a-1-2), and represented by the following formula (a-1-3) 2,2′,3,3′-Biphenyltetracarboxylic dianhydride (i-BPDA), among which 3,3′,4,4′- represented by the following formula (a-1-1) Biphenyltetracarboxylic dianhydride is preferred. The compounds represented by formula (a-1) can be used alone or in combination of two or more.
s-BPDA is preferable from the viewpoint of organic solvent resistance, and a-BPDA and i-BPDA are preferable from the viewpoint of heat resistance and solution processability.

The ratio of the structural unit (A-1) to the structural unit A is preferably 50 mol% or more, more preferably 55 mol% or more, and still more preferably, from the viewpoints of heat resistance, mechanical properties (elastic modulus), and organic solvent resistance. is 60 mol% or more, more preferably 65 mol% or more, still more preferably 70 mol% or more, preferably 99 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less, and more More preferably 85 mol % or less, still more preferably 80 mol % or less.

Structural unit A includes a structural unit (A-2) derived from a compound represented by formula (a-2) below. The compound represented by formula (a-2) is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride. Including the structural unit (A-2) in the structural unit A improves the transparency of the film and improves the solubility of the polyimide in organic solvents.

The ratio of the structural unit (A-2) to the structural unit A is preferably 1 mol% or more, more preferably 5 mol% or more, still more preferably 10 mol% or more, from the viewpoint of solubility and high transparency. Preferably 15 mol% or more, more preferably 20 mol% or more, and from the viewpoint of high heat resistance, preferably 50 mol% or less, more preferably 45 mol% or less, still more preferably 40 mol% or less, and more More preferably 35 mol % or less, still more preferably 30 mol % or less.

The ratio of the structural unit (A-1) and the structural unit (A-2) to the structural unit A is preferably 50 to 99 mol% for the structural unit (A-1) and 1 to 50 for the structural unit (A-2). mol%, more preferably the structural unit (A-1) is 55 to 95 mol%, the structural unit (A-2) is 5 to 45 mol%, and more preferably the structural unit (A-1) is 60 to 90 mol%, the structural unit (A-2) is 10 to 40 mol%, more preferably the structural unit (A-1) is 65 to 85 mol%, and the structural unit (A-2) is 15 to 35 More preferably, the structural unit (A-1) is 70 to 80 mol% and the structural unit (A-2) is 20 to 30 mol%.
The molar ratio [(A-1)/(A-2)] between the structural unit (A-1) and the structural unit (A-2) is 50/50 from the viewpoint of low linear thermal expansion coefficient and high transparency. ~99/1 is preferable, 55/45 to 95/5 is more preferable, 60/40 to 90/10 is more preferable, 65/35 to 85/15 is more preferable, 70/30 to 80/20 is more preferable More preferred.

In the polyimide according to the present invention, in the structural unit A, as a structural unit other than the structural unit (A-1) and the structural unit (A-2), as long as the effects of the present invention are not impaired, the formula (a-1 ) and the compound represented by formula (a-2) may contain structural units derived from a tetracarboxylic acid or a derivative thereof other than the compound represented by formula (a-2), but it is preferable not to contain them.
The total proportion of the structural unit (A-1) and the structural unit (A-2) in the structural unit A is 70 mol% or more from the viewpoint of low linear thermal expansion coefficient, high transparency, and organic solvent resistance. is preferred, 85 mol% or more is more preferred, 99 mol% or more is even more preferred, and 100 mol% is even more preferred.

[Constituent unit B]
The structural unit B contained in the polyimide of the present invention is a structural unit derived from diamine.
The structural unit B contains a structural unit (B-1) derived from a compound represented by the following formula (b-1).

In formula (b-1) above, each R is independently selected from the group consisting of a hydrogen atom, a fluorine atom, and a methyl group, and is preferably a hydrogen atom.
Examples of the compound represented by the above formula (b-1) include 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(3-fluoro-4-aminophenyl)fluorene, and 9,9- Examples thereof include bis(3-methyl-4-aminophenyl)fluorene, etc., preferably at least one selected from the group consisting of these three compounds, and more preferably 9,9-bis(4-aminophenyl)fluorene.
By containing the structural unit (B-1), the polyimide of the present invention has improved transparency and heat resistance.
In the present invention, the ratio of the structural unit (B-1) to the structural unit B is preferably 50 mol% or less, more preferably 40 mol% or less, still more preferably 35 mol% or less, from the viewpoint of a low linear thermal expansion coefficient. , more preferably 30 mol% or less, still more preferably 25 mol% or less, and from the viewpoint of high transparency and high heat resistance, preferably 5 mol% or more, more preferably 10 mol% or more, More preferably 15 mol % or more, still more preferably 20 mol % or more.

The structural unit B in the present invention contains a structural unit (B-2) derived from a compound represented by the following formula (b-2).

The compound represented by the above formula (b-2) is 2,2′-bis(trifluoromethyl)benzidine (also known as 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl). be.
By including the structural unit (B-2), the polyimide of the present invention has improved mechanical properties (elastic modulus) and can form a film having a low coefficient of linear thermal expansion.
In the present invention, the ratio of the structural unit (B-2) to the structural unit B is preferably 50 mol from the viewpoint of forming a film having a low coefficient of linear thermal expansion while maintaining high transparency and high heat resistance. % or more, more preferably 60 mol% or more, still more preferably 65 mol% or more, still more preferably 70 mol% or more, still more preferably 75 mol% or more, and preferably 95 mol% or less, more preferably It is 90 mol % or less, more preferably 85 mol % or less, still more preferably 80 mol % or less.

The ratio of the structural units (B-1) and (B-2) to the structural unit B is preferably 5 to 50 mol% for the structural unit (B-1) and 50 to 95 mol% for the structural unit (B-2). , More preferably the structural unit (B-1) is 10 to 40 mol%, the structural unit (B-2) is 60 to 90 mol%, and more preferably the structural unit (B-1) is 15 to 35 mol%, the structural unit (B-2) is 65 to 85 mol%, more preferably the structural unit (B-1) is 15 to 30 mol%, the structural unit (B-2) is 70 to 85 mol% More preferably, the structural unit (B-1) is 20 to 25 mol% and the structural unit (B-2) is 75 to 80 mol%.
The molar ratio [(B-1)/(B-2)] between the structural unit (B-1) and the structural unit (B-2) is low linear thermal expansion while maintaining high transparency and high heat resistance. From the viewpoint of forming a film having a coefficient of Even more preferably, 25/75 to 20/80 is even more preferable.

The polyimide of the present invention contains a structural unit derived from a diamine other than the compounds represented by the formulas (b-1) to (b-2) in the structural unit B as long as the effects of the present invention are not impaired. may be present, but preferably not.
The total proportion of the structural unit (B-1) and the structural unit (B-2) in the structural unit B forms a film having a low coefficient of linear thermal expansion while maintaining high transparency and high heat resistance. 70 mol % or more is preferable, 85 mol % or more is more preferable, 99 mol % or more is still more preferable, and 100 mol % is even more preferable, from the viewpoint of

[Method for producing polyimide]
The polyimide of the present invention is obtained by reacting a tetracarboxylic acid component that provides the structural unit A and a diamine component that provides the structural unit B.

A tetracarboxylic acid or its derivative is mentioned as a tetracarboxylic acid component. A tetracarboxylic acid component can be used individually or in combination of 2 or more types.
Derivatives of tetracarboxylic acids include anhydrides and alkyl esters of the tetracarboxylic acids.
As the alkyl ester of tetracarboxylic acid, the alkyl preferably has 1 to 3 carbon atoms, and examples thereof include dimethyl ester, diethyl ester and dipropyl ester of tetracarboxylic acid.
The tetracarboxylic acid component used in the present invention includes biphenyltetracarboxylic acid or derivatives thereof and 4,4'-(hexafluoroisopropylidene)diphthalic acid or derivatives thereof. Among them, it is preferable to include biphenyltetracarboxylic dianhydride [the above formula (a-1)] and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride [the above formula (a-2)], and 3 ,3′,4,4′-biphenyltetracarboxylic dianhydride [the above formula (a-1-1)] and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride are more preferable. .

The amount of biphenyltetracarboxylic acid or derivative thereof used is preferably 50 to 99 mol%, more preferably 55 to 95 mol%, still more preferably 60 to 90 mol%, and even more preferably, the total tetracarboxylic acid component. is 65 to 85 mol %, more preferably 70 to 80 mol %.
The amount of 4,4'-(hexafluoroisopropylidene)diphthalic acid or a derivative thereof used is preferably 1 to 50 mol%, more preferably 5 to 45 mol%, and still more preferably 10 to 40 mol %, more preferably 15 to 35 mol %, and even more preferably 20 to 30 mol %.
The total amount of biphenyltetracarboxylic acid, 4,4'-(hexafluoroisopropylidene)diphthalic acid, and derivatives thereof used is preferably 70 to 100 mol%, more preferably 70 to 100 mol%, based on the total tetracarboxylic acid component. 85 to 100 mol %, more preferably 99 to 100 mol %, still more preferably 100 mol %.

Furthermore, the tetracarboxylic acid component used in the present invention may contain tetracarboxylic acid components other than biphenyltetracarboxylic acid and 4,4′-(hexafluoroisopropylidene)diphthalic acid, or derivatives thereof. . The tetracarboxylic acid component includes at least one selected from the group consisting of tetracarboxylic acids containing aromatic rings or derivatives thereof, and tetracarboxylic acids containing alicyclic hydrocarbon structures or derivatives thereof. The tetracarboxylic acid component can be used alone or in combination of two or more.

Tetracarboxylic acids containing aromatic rings or derivatives thereof include pyromellitic acid, 3,3′,4,4′-diphenylsulfonetetracarboxylic acid, 3,3′,4,4′-benzophenonetetracarboxylic acid, 4, 4'-oxydiphthalic acid, 2,2',3,3'-benzophenonetetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, 2,2-bis(2,3-dicarboxyphenyl ) propane, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane, 1,1-bis(2,3-dicarboxyphenyl)ethane, 1,2-bis(2,3-dicarboxyphenyl) ethane, 1,1-bis(3,4-dicarboxyphenyl)ethane, 1,2-bis(3,4-dicarboxyphenyl)ethane, bis(2,3-dicarboxyphenyl)methane, bis(3, 4-dicarboxyphenyl)methane, 4,4'-(p-phenylenedioxy)diphthalic acid, 4,4'-(m-phenylenedioxy)diphthalic acid, 2,3,6,7-naphthalenetetracarboxylic acid , 1,4,5,8-naphthalenetetracarboxylic acids and derivatives thereof.

Tetracarboxylic acids containing an alicyclic hydrocarbon structure or derivatives thereof include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,4,5-cyclopentanetetracarboxylic acid, 1,2,4, 5-cyclohexanetetracarboxylic acid, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid, dicyclohexyltetracarboxylic acid, cyclopentanonebisspironorbornanetetracarboxylic acid or these Positional isomers and their derivatives are included.
Examples of tetracarboxylic acids or derivatives thereof that contain neither an alicyclic hydrocarbon structure nor an aromatic ring include 1,2,3,4-butanetetracarboxylic acid, 1,2,3,4-pentanetetracarboxylic acid, etc. or Derivatives thereof are included.

The amount of tetracarboxylic acid component other than biphenyltetracarboxylic acid or its derivative and 4,4'-(hexafluoroisopropylidene)diphthalic acid or its derivative is preferably 30 mol% of the total tetracarboxylic acid component. Below, it is more preferably 15 mol % or less, still more preferably 1 mol % or less, and still more preferably 0 mol %.

The diamine component used in the present invention includes the compound represented by formula (b-1) above and 2,2'-bis(trifluoromethyl)benzidine [formula (b-2) above]. The diamine component that provides the structural unit B is not limited to diamine, and may be a derivative thereof (diisocyanate, etc.) as long as the same structural unit is formed, but diamine is preferred.
The amount of the compound represented by the formula (b-1) used is preferably 5 to 50 mol%, more preferably 10 to 40 mol%, still more preferably 10 to 35 mol%, based on the total diamine component. %, more preferably 15 to 30 mol %, even more preferably 15 to 25 mol %, still more preferably 20 to 25 mol %.
The amount of 2,2'-bis(trifluoromethyl)benzidine to be used is preferably 50 to 95 mol%, more preferably 60 to 90 mol%, still more preferably 65 to 90 mol%, based on the total diamine component. %, more preferably 70 to 85 mol %, even more preferably 75 to 85 mol %, still more preferably 75 to 80 mol %.
The total amount of the compound represented by the above formula (b-1) and 2,2'-bis(trifluoromethyl)benzidine used is preferably 70 to 100 mol%, more preferably 85 to 100 mol %, more preferably 99 to 100 mol %, still more preferably 100 mol %.

Furthermore, the diamine component used in the present invention may contain a diamine component other than the compound represented by the above formula (b-1) and 2,2'-bis(trifluoromethyl)benzidine. The diamine component includes at least one selected from the group consisting of aromatic diamines and aliphatic diamines. The diamine component can be used alone or in combination of two or more.
The term "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and part of its structure includes an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. , and other substituents (eg, halogen atoms, sulfonyl groups, carbonyl groups, oxygen atoms, etc.). "Aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and part of its structure includes an aromatic hydrocarbon group and an aliphatic hydrocarbon group. , an alicyclic hydrocarbon group, and other substituents (eg, halogen atoms, sulfonyl groups, carbonyl groups, oxygen atoms, etc.).

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, benzidine, o-tolidine, m-tolidine, octafluorobenzidine, 3,3'- Dihydroxy-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4 '-diaminobiphenyl, 2,6-diaminonaphthalene, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl Sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzophenone, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 2,2-bis[4-(2-methyl- 4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2,6-dimethyl-4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexa Fluoropropane, 2,2-bis[4-(2-methyl-4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2,6-dimethyl-4-aminophenoxy)phenyl]hexa Fluoropropane, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(2-methyl-4-aminophenoxy)biphenyl, 4,4'-bis(2,6-dimethyl-4- aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(2-methyl-4-aminophenoxy)phenyl]sulfone , bis[4-(2,6-dimethyl-4-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(2-methyl-4-aminophenoxy)phenyl ] ether, bis[4-(2,6-dimethyl-4-aminophenoxy)phenyl]ether, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(2-methyl-4-aminophenoxy ) benzene, 1,4-bis(2,6-dimethyl-4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(2-methyl-4-aminophenoxy) benzene, 1,3-bis(2,6-dimethyl-4-aminophenoxy)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene,

2,2-bis(4-aminophenyl)propane, 2,2-bis(2-methyl-4-aminophenyl)propane, 2,2-bis(3-methyl-4-aminophenyl)propane, 2,2 -bis(3-ethyl-4-aminophenyl)propane, 2,2-bis(3,5-dimethyl-4-aminophenyl)propane, 2,2-bis(2,6-dimethyl-4-aminophenyl) Propane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(2-methyl-4-aminophenyl)hexafluoropropane, 2,2-bis(2,6-dimethyl-4- aminophenyl)hexafluoropropane, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(2-methyl-4-aminophenyl)-1,4-diisopropylbenzene , α,α'-bis(2,6-dimethyl-4-aminophenyl)-1,4-diisopropylbenzene, α,α'-bis(3-aminophenyl)-1,4-diisopropylbenzene, α,α '-Bis(4-aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(2-methyl-4-aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(2, 6-dimethyl-4-aminophenyl)-1,3-diisopropylbenzene, α,α'-bis(3-aminophenyl)-1,3-diisopropylbenzene, 9,9-bis(2-methyl-4-amino phenyl)fluorene, 9,9-bis(2,6-dimethyl-4-aminophenyl)fluorene, 5-amino-1,3,3-trimethyl-1-(4-aminophenyl)-indane, 1,1- bis(4-aminophenyl)cyclopentane, 1,1-bis(2-methyl-4-aminophenyl)cyclopentane, 1,1-bis(2,6-dimethyl-4-aminophenyl)cyclopentane, 1, 1-bis(4-aminophenyl)cyclohexane, 1,1-bis(2-methyl-4-aminophenyl)cyclohexane, 1,1-bis(2,6-dimethyl-4-aminophenyl)cyclohexane, 1,1 -bis(4-aminophenyl)4-methyl-cyclohexane, 1,1-bis(4-aminophenyl)norbornane, 1,1-bis(2-methyl-4-aminophenyl)norbornane, 1,1-bis( 2,6-dimethyl-4-aminophenyl)norbornane, 1,1-bis(4-aminophenyl)adamantane, 1,1-bis(2-methyl-4-aminophenyl)adamantane, 1,1-bis(2 ,6-dimethyl-4-aminophenyl)adamantane and the like. These can be used individually or in combination of 2 or more types.

Examples of aliphatic diamines include ethylenediamine, hexamethylenediamine, polyethylene glycol bis(3-aminopropyl) ether, polypropylene glycol bis(3-aminopropyl) ether, 1,3-bis(aminomethyl)cyclohexane, 1,4- Bis(aminomethyl)cyclohexane, metaxylylenediamine, paraxylylenediamine, 1,4-bis(2-amino-isopropyl)benzene, 1,3-bis(2-amino-isopropyl)benzene, isophoronediamine, norbornane Diamine, siloxane diamine, 4,4'-diaminodicyclohexylmethane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 3,3'-diethyl-4,4'-diaminodicyclohexylmethane, 3,3' , 5,5′-tetramethyl-4,4′-diaminodicyclohexylmethane, 2,3-bis(aminomethyl)-bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)-bicyclo[ 2.2.1]heptane, 2,6-bis(aminomethyl)-bicyclo[2.2.1]heptane, 2,2-bis(4,4′-diaminocyclohexyl)propane, 2,2-bis( 4,4'-diaminomethylcyclohexyl)propane and the like.

The amount of the diamine component other than the compound represented by formula (b-1) and 2,2'-bis(trifluoromethyl)benzidine used is preferably 30 mol% or less, more preferably 30 mol% or less, based on the total diamine component. is 15 mol % or less, more preferably 1 mol % or less, and even more preferably 0 mol %.

When producing the polyimide according to the present invention, the ratio of the amount of the tetracarboxylic acid component and the diamine component charged is preferably 0.9 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component.

When producing the polyimide of the present invention, a terminal blocking agent may be used in addition to the tetracarboxylic acid component and the diamine component. Monoamines or dicarboxylic acids are preferable as the terminal blocking agent. The amount of the terminal blocker to be introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per 1 mol of the tetracarboxylic acid component. Monoamine terminal blockers include, for example, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3- Ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline and the like are recommended. Among these, benzylamine and aniline are preferably used. Dicarboxylic acids are preferable as the dicarboxylic acid end blocking agent, and a part of them may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2 -dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid and the like are recommended. Among these, phthalic acid and phthalic anhydride can be preferably used.

The method for reacting the tetracarboxylic acid component and the diamine component described above is not particularly limited, and a known method can be used.
As a specific reaction method, (1) a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, stirred at room temperature to 80° C. for 0.5 to 30 hours, and then heated to imidize. (2) After charging the diamine component and the reaction solvent into a reactor and dissolving them, charging the tetracarboxylic acid component, stirring at room temperature to 80° C. for 0.5 to 30 hours, and then and (3) a method in which a tetracarboxylic acid component, a diamine component and a reaction solvent are charged into a reactor and the temperature is immediately raised to carry out the imidization reaction.

Any solvent may be used as long as it can dissolve the resulting polyimide without interfering with the imidization reaction. Examples include aprotic solvents, phenolic solvents, ether solvents, carbonate solvents and the like.

Specific examples of aprotic solvents include N,N-dimethylisobutyramide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethyl amide solvents such as imidazolidinone and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoricamide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethylsulfoxide and sulfolane; ketone solvents such as acetone, cyclohexanone and methylcyclohexanone; amine solvents such as picoline and pyridine; and ester solvents such as acetic acid (2-methoxy-1-methylethyl). mentioned.

Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4 -xylenol, 3,5-xylenol, and the like.
Specific examples of ether solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl] ether, tetrahydrofuran, 1,4-dioxane and the like.
Specific examples of carbonate-based solvents include diethyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, and the like.
Among the above reaction solvents, aprotic solvents are preferable, and amide solvents or lactone solvents are more preferable. Moreover, the above reaction solvents may be used alone or in combination of two or more.

In the imidization reaction, it is preferable to carry out the reaction while removing water produced during production using a Dean-Stark apparatus or the like. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

A known imidization catalyst can be used in the above imidization reaction. Examples of imidization catalysts include base catalysts and acid catalysts.
Base catalysts include pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, imidazole, N,N-dimethylaniline. , N,N-diethylaniline and the like, and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium hydrogencarbonate and sodium hydrogencarbonate.
Acid catalysts include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, and the like. is mentioned. You may use said imidization catalyst individually or in combination of 2 or more types.
Among the above, from the viewpoint of handleability, a base catalyst is preferred, an organic base catalyst is more preferred, and triethylamine is even more preferred.

When the above catalyst is used, the imidization reaction temperature is preferably 120 to 250°C, more preferably 160 to 190°C, and still more preferably 180 to 190°C, from the viewpoint of the reaction rate and suppression of gelation. be. Moreover, the reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water.
The temperature of the imidization reaction when no catalyst is used is preferably 200 to 350°C.
In the reaction of the diamine component and the tetracarboxylic acid component, a polyimide solution containing at least the polyimide and the reaction solvent can be obtained after the imidization reaction is completed.

[Polyimide]
The weight average molecular weight of the polyimide of the present invention is preferably 500 to 1,000,000, more preferably 5,000 to 100,000, from the viewpoint of mechanical strength of the resulting polyimide film. The weight average molecular weight of polyimide can be measured by gel filtration chromatography or the like.
As an example of measuring the weight average molecular weight, there is a method of measuring the absolute molecular weight with a light scattering detector using N,N-dimethylformamide as a developing solvent.

The polyimide of the present invention may be further mixed with various additives as long as the effects of the present invention are not impaired. Examples of additives include antioxidants, light stabilizers, surfactants, flame retardants, plasticizers, inorganic fillers, and polymer compounds other than the polyimide.
Examples of polymer compounds include polyimides other than the polyimide of the present invention, polycarbonates, polystyrenes, polyamides, polyamideimides, polyesters such as polyethylene terephthalate, polyethersulfones, polycarboxylic acids, polyacetals, polyphenylene ethers, polysulfones, polybutylenes, polypropylene, and polyacrylamides. , polyvinyl chloride, and the like.

[Polyimide varnish]
The polyimide varnish of the present invention is obtained by dissolving the polyimide of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide of the present invention and an organic solvent, and the polyimide is dissolved in the organic solvent.
The organic solvent is not particularly limited as long as it dissolves the polyimide, but it is preferable to use the compounds described above as the reaction solvent used in the production of the polyimide singly or in combination of two or more.
Since the polyimide of the present invention has solvent solubility, it can be made into a highly concentrated varnish that is stable at room temperature.

The polyimide varnish may be a polyimide solution itself in which polyimide obtained by a polymerization method is dissolved in a reaction solvent. Further, the polyimide solution may be mixed with at least one solvent selected from the solvents exemplified above as a solvent in which the polyimide dissolves.
The solid content concentration of the polyimide varnish of the present invention can be appropriately selected according to the workability and the like when forming the polyimide film described later, and the reaction solvent used in the production of the polyimide of the present invention is volatilized and condensed. Alternatively, the solid content concentration and viscosity of the polyimide varnish of the present invention may be adjusted by adding an organic solvent as a diluent. The organic solvent is not particularly limited as long as it can dissolve polyimide.
The solid content concentration of the polyimide varnish of the present invention is preferably 5 to 45% by mass, more preferably 5 to 35% by mass, even more preferably 5 to 25% by mass. The viscosity of the polyimide varnish of the present invention is preferably 0.1 to 200 Pa·s, more preferably 0.5 to 180 Pa·s, even more preferably 1 to 150 Pa·s. The viscosity of the polyimide varnish is a value measured at 25° C. using an E-type viscometer.

[Polyimide film]
The polyimide film of the present invention contains the polyimide of the present invention, and has a low coefficient of linear thermal expansion while maintaining high transparency and high heat resistance. The polyimide film of the present invention preferably comprises the polyimide of the present invention.
The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, a polyimide varnish containing the polyimide of the present invention, or a polyimide varnish containing the polyimide of the present invention and the various additives described above, is coated on a smooth support such as a glass plate, a metal plate, a plastic, or a film A method of removing solvent components such as a reaction solvent and a diluting solvent contained in the varnish after molding into a shape may be mentioned.
By adjusting the solid content concentration and viscosity of the polyimide varnish as described above, the thickness of the polyimide film of the present invention can be easily controlled.

A release agent may be applied to the surface of the support, if necessary. As a method of applying the polyimide varnish to the support and then heating to evaporate the solvent component, the following method is preferable. That is, after evaporating the solvent at a temperature of 120° C. or less to form a self-supporting film, the self-supporting film is peeled off from the support, and the ends of the self-supporting film are fixed. It is preferable to produce a polyimide film by drying at a temperature of not less than the boiling point and not more than 350°C. Moreover, it is preferable to dry in a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or increased pressure.

The thickness of the polyimide film of the present invention can be appropriately selected depending on the application, etc., preferably 1 to 250 μm, more preferably 5 to 100 μm, still more preferably 7 to 90 μm, still more preferably 10 to 80 μm. is. A thickness of 1 to 250 μm enables practical use as a self-supporting film.

In the present invention, a polyimide film having a total light transmittance of preferably 80% or more, more preferably 85% or more, still more preferably 88% or more, and even more preferably 89% or more at a thickness of 10 μm can be formed.
In the present invention, a polyimide film having a yellow index (YI value) of preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.5 or less can be formed.
In the present invention, a polyimide film having a haze of preferably 1.0 or less, more preferably 0.8 or less, and even more preferably 0.5 or less can be formed.
In the present invention, a polyimide film having a glass transition temperature of preferably 250° C. or higher, more preferably 300° C. or higher, and even more preferably 350° C. or higher can be formed.

In the present invention, a polyimide film having a linear thermal expansion coefficient of preferably 40 ppm/°C or less, more preferably 35 ppm/°C or less, and even more preferably 30 ppm/°C or less can be formed.
In the present invention, it is possible to form a polyimide film having a tensile modulus (measurement temperature 23° C., humidity 50% RH) of preferably 3.0 GPa or more, more preferably 3.5 GPa or more.
The total light transmittance, YI value, haze, glass transition temperature, linear thermal expansion coefficient, and tensile elastic modulus of the polyimide film can be specifically measured by the methods described in Examples.

The polyimide film containing the polyimide of the present invention is excellent in transparency and heat resistance, and has a low linear thermal expansion coefficient, so that there is little dimensional change due to heat, and it is a film for various members such as color filters, flexible displays, semiconductor parts, and optical members. It is preferably used as. Since the polyimide film of the present invention has high dimensional stability, it can withstand high-temperature processes in the manufacturing process of image display devices. Therefore, for example, the polyimide film of the present invention can be used for at least a part of image display devices such as liquid crystal displays and organic EL displays.

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is by no means limited to these examples.
The physical properties of the polyimide varnishes, polyimide precursor varnishes and polyimide films obtained in the following Examples and Comparative Examples were measured by the following methods.

(1) Solid content concentration:
The solid content concentration of the polyimide varnish or polyimide precursor varnish was measured by heating the sample at 320° C.×120 min in a small electric furnace MMF-1 manufactured by AS ONE CORPORATION, and calculating from the difference in mass of the sample before and after heating.
(2) Film thickness:
The thickness of the polyimide film was measured using a micrometer manufactured by Mitutoyo Corporation.

(3) Tensile modulus Measurement was performed in accordance with JIS K7127, using a tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd., measurement temperature 23 ° C., humidity 50% RH, distance between chucks 50 mm, tensile speed A tensile test was performed at 50 mm/min to determine the tensile modulus.
(4) Glass transition temperature (Tg)
Using a differential scanning calorimeter "DSC6200" manufactured by Hitachi High-Tech Science Co., Ltd., DSC measurement was performed at a heating rate of 10°C/min to determine the glass transition temperature.

(5) Total light transmittance, yellow index (YI), haze Measured using a simultaneous color/turbidity measuring instrument "COH400" manufactured by Nippon Denshoku Industries Co., Ltd. Total light transmittance and YI were measured according to JIS K7361-1:1997, and haze was measured according to JIS K7136:2000.
(6) Linear thermal expansion coefficient (CTE)
Using a thermomechanical analyzer (TMA/SS6100) manufactured by Hitachi High-Tech Science Co., Ltd., TMA measurement was performed in tensile mode under the conditions of a sample size of 2 mm × 20 mm, a load of 0.1 N, and a heating rate of 10 ° C./min. A CTE of 100-250° C. was determined. The closer the CTE value is to 0, the better the dimensional stability.

<Example 1>
2,2'-Bis(trifluoromethyl)benzidine was added to a 5-necked round-bottomed flask equipped with a stainless steel half-moon stirrer, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a condenser, a thermometer, and a glass end cap. (manufactured by Wakayama Seika Kogyo Co., Ltd.) 29.462 g (0.092 mol), 9,9-bis(4-aminophenyl)fluorene (manufactured by Taoka Chemical Co., Ltd.) 8.014 g (0.023 mol), N 111.263 g of -methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Corporation) was added, and the system was stirred at a temperature of 70°C under a nitrogen atmosphere at a rotation speed of 200 rpm to obtain a solution.
To this solution were added 27.066 g (0.092 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation) and 4,4′-(hexafluoroisopropylidene)diphthalate. After adding 10.218 g (0.023 mol) of acid anhydride (manufactured by Daikin Industries, Ltd.) and 27.816 g of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Corporation) at once, triethylamine ( 0.582 g of Kanto Kagaku Co., Ltd.) was added, heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the mixture was refluxed for 1 hour and 30 minutes while maintaining the temperature in the reaction system at 190° C. while adjusting the number of revolutions according to the increase in viscosity.
After that, 512.54 g of N-methyl-2-pyrrolidone (Mitsubishi Chemical Co., Ltd.) was added, and the temperature in the reaction system was cooled to 120°C, and then stirred for about 3 hours to homogenize the solid content to a concentration of 10. A solution (polyimide varnish) containing 10% by mass of polyimide was obtained. Subsequently, the resulting polyimide varnish is applied onto a glass plate, held on a hot plate at 80° C. for 30 minutes, and then heated in a hot air dryer at 300° C. for 30 minutes under a nitrogen purge to evaporate the solvent. A 10 μm film was obtained. Table 1 shows the results.

<Example 2>
2,2'-Bis(trifluoromethyl)benzidine was added to a 5-necked round-bottomed flask equipped with a stainless steel half-moon stirrer, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a condenser, a thermometer, and a glass end cap. (manufactured by Wakayama Seika Kogyo Co., Ltd.) 19.685 g (0.061 mol), 9,9-bis(4-aminophenyl)fluorene (manufactured by Taoka Chemical Co., Ltd.) 5.343 g (0.015 mol), N -Methyl-2-pyrrolidone (Mitsubishi Chemical Co., Ltd.) 75.897 g was added and stirred at a system temperature of 70°C under a nitrogen atmosphere at a rotation speed of 200 rpm to obtain a solution.
To this solution were added 15.789 g (0.054 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation) and 4,4′-(hexafluoroisopropylidene)diphthalate. After adding 10.218 g (0.023 mol) of acid anhydride (manufactured by Daikin Industries, Ltd.) and 18.974 g of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Corporation) at once, triethylamine ( 0.388 g of Kanto Kagaku Co., Ltd.) was added, heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the mixture was refluxed for 3 hours and 10 minutes while maintaining the temperature in the reaction system at 190° C. while adjusting the number of revolutions according to the increase in viscosity.
After that, 349.97 g of N-methyl-2-pyrrolidone (Mitsubishi Chemical Co., Ltd.) is added, the temperature inside the reaction system is cooled to 120° C., and the mixture is stirred for about 3 hours to homogenize the solid content to a concentration of 10. % by weight polyimide varnish was obtained. Subsequently, the resulting polyimide varnish is applied onto a glass plate, held on a hot plate at 80° C. for 30 minutes, and then heated in a hot air dryer at 300° C. for 30 minutes under a nitrogen purge to evaporate the solvent. A 10 μm film was obtained. Table 1 shows the results.

<Comparative Example 1>
9,9-bis(4-aminophenyl)fluorene was added to a 5-necked round-bottomed flask equipped with a stainless steel half-moon stirrer, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a condenser, a thermometer, and a glass end cap. 24.392 g (0.070 mol) (manufactured by Taoka Chemical Co., Ltd.) and 66.786 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Co., Ltd.) were added, and the system was stirred at a temperature of 70° C. under a nitrogen atmosphere at a rotation speed of 200 rpm. to obtain a solution.
To this solution, 31.097 g (0.070 mol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (manufactured by Daikin Industries, Ltd.) and 16.697 g of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation) were added. After adding all at once, 0.212 g of triethylamine (manufactured by Kanto Kagaku Co., Ltd.) was added as an imidization catalyst, heated with a mantle heater, and the temperature in the reaction system was raised to 190° C. over about 20 minutes. The components to be distilled off were collected, and the mixture was refluxed for 1 hour while maintaining the temperature in the reaction system at 190° C. while adjusting the number of revolutions according to the increase in viscosity.
After that, 394.709 g of γ-butyrolactone (Mitsubishi Chemical Co., Ltd.) is added, and the temperature in the reaction system is cooled to 120 ° C., and then stirred for about 3 hours to homogenize the polyimide with a solid content concentration of 10% by mass. Got varnish. Subsequently, the resulting polyimide varnish was applied onto a glass plate, held on a hot plate at 80°C for 20 minutes, and then heated in a hot air dryer at 400°C for 30 minutes under a nitrogen purge to evaporate the solvent. A 10 μm film was obtained. Table 1 shows the results.

<Comparative Example 2>
9,9-bis(4-aminophenyl)fluorene was added to a 5-necked round-bottomed flask equipped with a stainless steel half-moon stirrer, a nitrogen inlet tube, a Dean-Stark apparatus equipped with a condenser, a thermometer, and a glass end cap. (manufactured by Taoka Chemical Co., Ltd.) 34.845 g (0.100 mol) and N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Co., Ltd.) 120.202 g were added, and the temperature in the system was 50 ° C., under a nitrogen atmosphere, rotation was performed. A solution was obtained by stirring at several hundred rpm.
To this solution, 29.420 g (0.100 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation) and N,N-dimethylacetamide (Mitsubishi Gas Chemical Co., Ltd.) After confirming dissolution, the temperature was returned to room temperature, and stirring was continued for 5 hours while adjusting the number of revolutions in accordance with the increase in viscosity.
Then, N,N-dimethylacetamide (manufactured by Mitsubishi Gas Chemical Co., Ltd.) 92.91 g was added, stirred for about 1 hour to homogenize, and a polyimide precursor (polyamic acid) solution (polyimide precursor varnish) was obtained. Subsequently, the resulting polyimide precursor varnish was applied onto a glass plate, held on a hot plate at 80°C for 20 minutes, and then heated in a hot air dryer at 400°C for 30 minutes under a nitrogen purge to evaporate the solvent. , to obtain a polyimide film having a thickness of 10 μm. Table 1 shows the results.

Abbreviations in the table are as follows.
s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride [compound represented by formula (a-1-1)]
6FDA: 4,4'-(hexafluoroisopropylidene) diphthalic anhydride [compound represented by formula (a-2)]
BAFL: 9,9-bis(4-aminophenyl)fluorene [compound represented by formula (b-1) (R: hydrogen atom)]
TFMB: 2,2'-bis(trifluoromethyl)benzidine [compound represented by formula (b-2)]

From Table 1, the polyimide films of Examples 1 and 2 have high transparency, high heat resistance, and low coefficients of linear thermal expansion, so that all these properties are well balanced. On the other hand, although the polyimide films of Comparative Examples 1 and 2 have excellent heat resistance, they have a high coefficient of linear thermal expansion, and the polyimide film of Comparative Example 2 is also inferior in transparency. It was not possible to obtain a film with a low coefficient of linear thermal expansion in addition to the strength and high heat resistance.

Claims (5)

A polyimide having a structural unit A derived from a tetracarboxylic acid or a derivative thereof and a structural unit B derived from a diamine,
Structural unit A is a structural unit (A-1) derived from a compound represented by the following formula (a-1), and a structural unit (A-2) derived from a compound represented by the following formula (a-2) ), including
Structural unit B is a structural unit (B-1) derived from a compound represented by the following formula (b-1), and a structural unit (B-2) derived from a compound represented by the following formula (b-2) ) , including
The ratio of the structural unit (A-1) to the structural unit A is 55 to 95 mol%, the ratio of the structural unit (A-2) is 5 to 45 mol%,
The total ratio of the structural unit (A-1) and the structural unit (A-2) to the structural unit A is 85% or more,
The compound represented by formula (a-1) is a compound represented by the following formula (a-1-1),
The ratio of the structural unit (B-1) to the structural unit B is 10 to 40 mol%, and the ratio of the structural unit (B-2) is 60 to 90 mol%,
A polyimide in which the total ratio of the structural unit (B-1) and the structural unit (B-2) to the structural unit B is 99 mol% or more.

(In formula (b-1), each R independently represents a hydrogen atom, a fluorine atom or a methyl group.) 2. The polyimide according to claim 1 , wherein the ratio of the structural unit (A-1) to the structural unit A is 60 to 90 mol %, and the ratio of the structural unit (A-2) is 10 to 40 mol %. 3. The polyimide according to claim 1, wherein the ratio of the structural unit (B-1) to the structural unit B is 15 to 30 mol %, and the ratio of the structural unit (B-2) is 70 to 85 mol %. A polyimide varnish obtained by dissolving the polyimide according to any one of claims 1 to 3 in an organic solvent. A polyimide film comprising the polyimide according to any one of claims 1 to 3 .