WO2017057360A1

WO2017057360A1 - Novel tetracarboxylic dianhydride, polyimide derived from said tetracarboxylic dianhydride, and molded article produced from said polyimide

Info

Publication number: WO2017057360A1
Application number: PCT/JP2016/078448
Authority: WO
Inventors: 淳一石井; 長谷川　匡俊
Original assignee: 本州化学工業株式会社; 学校法人東邦大学
Priority date: 2015-09-30
Filing date: 2016-09-27
Publication date: 2017-04-06
Also published as: KR102619074B1; JP6715496B2; KR20180061248A; CN108137804B; KR102591070B1; KR20230066490A; TW201730172A; TWI708769B; CN108137804A; JPWO2017057360A1

Abstract

The present invention addresses the problem of providing: a polyimide which is derived from a novel tetracarboxylic dianhydride, has both excellent solubility in various types of organic solvents and thermoplasticity and therefore has excellent processability, and also has both a low linear thermal expansion coefficient and high light permeability (transparency); and a molded article produced from the polyimide. The problem can be solved by a polyimide derived from a tetracarboxylic dianhydride represented by formula (1).

Description

Novel tetracarboxylic dianhydride, polyimide derived from the tetracarboxylic dianhydride, and molded article comprising the polyimide

The present invention is a polyimide derived from a novel tetracarboxylic dianhydride, which is excellent in processability, has a low linear thermal expansion coefficient, and has a high light transmittance (transparency), and the polyimide. It relates to a molded body. Since the polyimide exhibits thermoplasticity in addition to excellent solution processability, it can be melt-molded as well as formed by a solution casting method. Furthermore, the molded body made of the polyimide exhibits a low linear thermal expansion coefficient and excellent transparency as compared with conventional solvent-soluble polyimides and thermoplastic polyimides. Because of these characteristics, transparency used in liquid crystal displays (LCD), organic electroluminescence (EL) displays, electronic paper, light emitting diode (LED) devices, solar cells, etc. that require dimensional stability and transparency to heat. It is useful as a substrate, transparent protective film material, and adhesive material.

As conventional transparent resins that can be molded, polyethylene terephthalate, polycarbonate, polyethersulfone, and the like are known. Although these resins are excellent in solution processability and melt moldability, dimensional changes due to heat (linear) Thermal expansion coefficient) is large. When the linear thermal expansion coefficient as a molded product is large, various problems may occur when laminated with low thermal expansion inorganic materials used in display devices and lighting devices such as LCDs, organic EL displays, electronic paper, and LEDs. Yes, not preferred. For example, the above-mentioned transparent resin molded body and a transparent electrode (ITO; Indium Tin Oxide), wiring such as copper, silver, and aluminum, or a thermal process at the time of forming an element such as a thin film transistor (TFT; Thin-Film Transistor), reduces the heat. There is a possibility that mismatch in the linear thermal expansion coefficient occurs between the expandable inorganic material and the conventional high thermal expansion resin, and distortion occurs at the interface, leading to delamination, substrate distortion, and element destruction.

On the other hand, aromatic polyimide is known as a resin having excellent thermal dimensional stability. Molded bodies made of aromatic polyimide with a rigid and straight chemical structure, such as polyimide films, require high dimensional stability (low linear thermal expansion coefficient) such as base films for flexible printed wiring boards and semiconductor interlayer insulating films. Widely used in the field. However, an aromatic polyimide having a low linear thermal expansion coefficient is strongly colored due to intramolecular conjugation and intramolecular / intermolecular charge transfer interaction, so that it is difficult to apply to the above optical use. Furthermore, since the intermolecular force of the polyimide is very strong, it is often poor in workability without exhibiting solubility in a solvent and thermoplasticity.
On the other hand, a polyimide that overcomes these disadvantages has been proposed. For example, a method of introducing a fluorine atom into a polyimide structure (Non-patent Document 1), or by using an alicyclic compound in one or both of a diamine component and a tetracarboxylic dianhydride component constituting a polyimide, Methods for suppressing conjugation and charge transfer interaction and increasing transparency have been proposed (Non-Patent Documents 2 and 3). Although polyimides having both transparency and solution processability have been developed by these prior arts, there are limited reports of polyimides that have low thermal expansion in addition to processability.
As a few reported examples, a specific polyimide having an ester group has been proposed (Patent Document 1). Although this polyimide has a low linear thermal expansion coefficient equivalent to that of inorganic materials in addition to transparency and heat resistance, it has insufficient solubility in various types of organic solvents, and there is room for improvement in this respect. .
Furthermore, there is no known polyimide having excellent processability that also has thermoplasticity.

JP2013-082876A

The present invention is a polyimide derived from a novel tetracarboxylic dianhydride, which has excellent solubility in various types of organic solvents, and also has thermoplasticity, so it has excellent processability and low linear thermal expansion. It aims at providing the molded object which consists of a polyimide which has a coefficient and high light transmittance (transparency), and this polyimide.

In view of the above technical background, the present inventors have conducted extensive research, and as a result, a polyimide having excellent processability can be obtained from the tetracarboxylic dianhydride represented by the following formula (1), which is extremely useful in this field. As a result, the present invention was completed.

The present invention is as follows.
1. Tetracarboxylic dianhydride represented by the following formula (1).

2. A polyimide having a repeating unit represented by the following formula (2).

3. 3. The polyimide according to 2, wherein the content of the repeating unit represented by the formula (2) is 55 mol% or more with respect to all the repeating units in the polyimide.
A polyimide solution comprising the polyimide according to 4.2 or 3 and an organic solvent, wherein the polyimide concentration is 5% by weight or more.
The polyimide molded body according to 5.2 or 3.

According to the present invention, characteristics that could not be obtained by the prior art, that is, excellent solubility in various types of organic solvents, and also excellent thermoplasticity, excellent workability, low linear thermal expansion coefficient, and A polyimide having all high light transmittance (transparency) and a molded body made of the polyimide use a tetracarboxylic dianhydride characterized in that a bulky cyclohexyl group is substituted on the central phenylene group. Can be obtained.

Infrared absorption spectrum of the polyimide film of Example 2 Dynamic viscoelastic curve of the polyimide film of Example 2 Infrared absorption spectrum of the polyimide film of Example 3 Dynamic viscoelastic curve of the polyimide film of Example 3 Infrared absorption spectrum of the polyimide film of Example 4 Dynamic viscoelastic curve of the polyimide film of Example 4 Dynamic viscoelastic curve of the polyimide film of Comparative Example 2

The tetracarboxylic dianhydride of the present invention has a structure represented by the following formula (1).

The chemical structural characteristics of the tetracarboxylic dianhydride represented by the formula (1) according to the present invention (hereinafter sometimes abbreviated as TACHQ) are as follows. Two phthalic anhydride structures are combined, and the central phenylene group is substituted with a bulky cyclohexyl group.

The method for synthesizing TACHQ represented by the formula (1) of the present invention is not particularly limited. For example, a diol represented by the following formula (3), that is, cyclohexylhydroquinone or a diacetate thereof, and the following formula (4) It is synthesize | combined by well-known esterification reaction from trimellitic acid represented by these, or its derivative (s).

Examples of trimellitic acid derivatives include trimellitic anhydride and trimellitic anhydride halide.

The polyimide of this invention has a repeating unit represented by following formula (2).

The first feature of the polyimide having a repeating unit represented by the formula (2) according to the present invention is that two ester bonds exist in the para position of the central phenylene group of the tetracarboxylic dianhydride moiety, Since it has a biphenylene structure bonded at the para position, the polyimide main chain structure forms a linear and rigid structure. Due to this characteristic, it is considered that the polyimide chain is highly oriented along the film plane direction (in-plane orientation) and exhibits excellent thermal dimensional stability (low linear thermal expansion coefficient). However, a low thermal expansion polyimide having such a linear and rigid structure has a strong cohesive force between polyimide chains, and thus is usually insoluble in an organic solvent, does not melt, and has poor workability. Therefore, in general, a method of bending a polyimide main chain structure by introducing a siloxane bond, an ether bond or a meta bond into the polyimide main chain, a method of reducing the imide group concentration in the polyimide repeating unit, and a bulky polyimide side chain. A method is adopted in which a substituent is introduced to weaken the cohesive force between polyimide chains and increase the workability. However, these methods inhibit the in-plane orientation in the polyimide molded body, particularly the film, and consequently increase the linear thermal expansion coefficient. That is, it is very difficult to achieve both workability and low thermal expansion.
Therefore, this problem can be solved by the second feature described next to the polyimide having the repeating unit represented by the formula (2) according to the present invention. That is, a bulky cyclohexyl group is substituted for the central phenylene group of the tetracarboxylic dianhydride moiety, and a side chain of the diamine moiety is substituted with a bulky trifluoromethyl group for electron withdrawing, so that between polyimide chains Only the cohesive force can be weakened without inhibiting the in-plane orientation. The polyimide having the repeating unit represented by the formula (2) that realizes this exquisite balance is excellent in solubility in various types of organic solvents, and also has excellent workability because it also has thermoplasticity, and A low coefficient of linear thermal expansion, which was originally difficult to achieve, is exhibited. Further, charge transfer interaction of polyimide is suppressed, and high transparency can be realized.

The polyimide which has a repeating unit represented by Formula (2) concerning this invention can synthesize | combine the polyimide which has the above outstanding characteristics by using TACHQ represented by Formula (1) as a raw material. it can. The method for producing the polyimide is not particularly limited. For example, TACHQ represented by the formula (1) and 2,2′-bis (trifluoromethyl) benzidine represented by the following formula (5) (hereinafter referred to as diamine) And may be abbreviated as TFMB) to obtain a polyimide precursor (polyamic acid) having a repeating unit represented by the formula (2) and imidizing the polyamic acid. Can do.

When polymerizing polyamic acid, an aromatic or aliphatic tetracarboxylic dianhydride other than TACHQ represented by formula (1) is used as a copolymerization component as long as the polymerization reactivity and the required properties of polyimide are not significantly impaired. can do.
The aromatic tetracarboxylic dianhydride that can be used in this case is not particularly limited. For example, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, hydroquinone -Bis (trimellitate anhydride), methylhydroquinone-bis (trimellitate anhydride), 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic acid Dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4 ′ -Biphenylsulfonetetracarboxylic dianhydride, 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride, 2,2'-bis (3,4-dicarboxypheny E) Propanoic acid dianhydride and the like.
The aliphatic tetracarboxylic dianhydride is not particularly limited. For example, as the alicyclic one, bicyclo [2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic Acid dianhydride, 5- (dioxotetrahydrofuryl-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride, 4- (2,5-dioxotetrahydrofuran-3-yl) tetralin-1,2 -Dicarboxylic anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride, bicyclo-3,3 ', 4,4'-tetracarboxylic dianhydride, 1,2,3,4 Examples thereof include cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, etc. Two or more of these may be used in combination.
From the viewpoint of further improving the solubility, heat resistance and transparency of the polyimide, 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride (hereinafter sometimes abbreviated as 6FDA), further lower heat of the polyimide molded body From the standpoint of expansibility, tetracarboxylic dianhydride having a rigid and linear structure, ie, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, Suitable as a polymerization component.
When an aromatic or aliphatic tetracarboxylic dianhydride other than TACHQ represented by the formula (1) is used as a copolymerization component, the ratio of TACHQ to all tetracarboxylic dianhydrides is preferably 55 mol. % Or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 90 mol% or more.

When polymerizing the polyamic acid according to the present invention, an aromatic or aliphatic diamine other than TFMB represented by the formula (5) is used as a copolymerization component in a range that does not significantly impair the polymerization reactivity and the required characteristics of polyimide. be able to.
The aromatic diamine that can be used in this case is not particularly limited. For example, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,4-diaminoxylene, 2,4-diaminodurene, 4,4'-diaminodiphenylmethane, 4,4'-methylenebis (2-methylaniline), 4,4'-methylenebis (2-ethylaniline), 4,4'-methylenebis (2, 6-dimethylaniline), 4,4′-methylenebis (2,6-diethylaniline), 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 2, 4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone 4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzanilide, 4-aminophenyl-4'-aminobenzoate, benzidine, 3,3'-dihydroxybenzidine, 3,3 ' -Dimethoxybenzidine, o-tolidine, m-tolidine, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene 4,4′-bis (4-aminophenoxy) biphenyl, bis (4- (3-aminophenoxy) phenyl) sulfone, bis (4- (4-aminophenoxy) phenyl) sulfone, 2,2-bis (4 -(4-Aminophenoxy) phenyl) propane, 2,2-bis (4- (4-aminophenoxy) phenyl) hexaful Ropuropan, 2,2-bis (4-aminophenyl) hexafluoropropane, p- terphenyl-phenylenediamine, and the like.
The aliphatic diamine is a chain aliphatic to alicyclic diamine, and the alicyclic diamine is not particularly limited. For example, 4,4′-methylenebis (cyclohexylamine), isophoronediamine, trans- 1,4-diaminocyclohexane, cis-1,4-diaminocyclohexane, 1,4-cyclohexanebis (methylamine), 2,5-bis (aminomethyl) bicyclo [2.2.1] heptane, 2,6- Bis (aminomethyl) bicyclo [2.2.1] heptane, 3,8-bis (aminomethyl) tricyclo [5.2.1.0] decane, 1,3-diaminoadamantane, 2,2-bis (4 -Aminocyclohexyl) propane, 2,2-bis (4-aminocyclohexyl) hexafluoropropane, and chain aliphatic diamine Although not limited thereto, for example, 1,3-propanediamine, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8- Examples include octamethylene diamine, 1,9-nonamethylene diamine, and diaminosiloxane. Two or more of these may be used in combination.

In the polymerization reaction, the solvent used is preferably an aprotic solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, etc., but is formed with the raw material monomer. As long as the polyamic acid and the imidized polyimide are dissolved, any solvent can be used without any problem, and the structure of the solvent is not particularly limited. Specifically, for example, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ-butyrolactone, ester solvents such as butyl acetate, ethyl acetate and isobutyl acetate, carbonate solvents such as ethylene carbonate and propylene carbonate, glycols such as diethylene glycol dimethyl ether, triethylene glycol and triethylene glycol dimethyl ether Solvent, phenol solvents such as phenol, m-cresol, p-cresol, o-cresol, 3-chlorophenol, 4-chlorophenol, cyclopentanone, cyclohexanone, acetone, methyl Ketone solvents such as ethyl ketone, diisobutyl ketone and methyl isobutyl ketone, ether solvents such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane and dibutyl ether, and other general-purpose solvents include acetophenone, 1,3-dimethyl- 2-imidazolidinone, sulfolane, dimethyl sulfoxide, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butanol, ethanol, xylene, toluene, chlorobenzene, terpene, mineral spirit, Petroleum naphtha solvents can also be used, and two or more of these may be used in combination.

TACHQ represented by the formula (1) and TFMB represented by the formula (5) are polyaddition-reacted to obtain a polyamic acid, and then imidized to obtain a very useful industrially useful product of the present invention. A polyimide can be obtained.
The polyimide of the present invention is soluble in various kinds of organic solvents when used as a polyimide resin due to the linearity and rigidity of the polymer main chain and the chemical structural features of having bulky substituents in the side chain. In addition, it has excellent processability because it has both thermoplasticity and thermoplasticity. Further, a molded product of the polyimide, particularly a film, can be a material having both a low linear thermal expansion coefficient and high transparency.
Usually, the polymerization reactivity of tetracarboxylic dianhydride and diamine greatly affects the toughness of the finally obtained polyimide molded body. If the polymerization reactivity is not sufficiently high, a high polymer cannot be obtained, and as a result, the entanglement between polymer chains becomes low and the polyimide molded body may become brittle. The TACHQ of the formula (1) and the TFMB of the formula (5) used in the present invention show sufficiently high polymerization reactivity, so there is no such concern.

The method for producing the polyimide of the present invention is not particularly limited, and known methods can be appropriately applied. Specifically, for example, it can be synthesized by the following method. First, TFMB of formula (5) is dissolved in a polymerization solvent, and TACHQ powder of formula (1), which is substantially equimolar to TFMB of formula (5), is gradually added to this solution, and a mechanical stirrer or the like is used. Stir at a temperature in the range of -100 ° C, preferably 20-60 ° C for 0.5-150 hours, preferably 1-48 hours. In this case, the monomer concentration is usually in the range of 5 to 50% by weight, preferably in the range of 10 to 40% by weight. By carrying out polymerization in such a monomer concentration range, a polyamic acid having a uniform and high degree of polymerization can be obtained. When the polymerization degree of the polyamic acid increases too much and the polymerization solution becomes difficult to stir, it can be appropriately diluted with the same solvent. From the viewpoint of the toughness of the polyimide molded body, it is desirable that the degree of polymerization of the polyamic acid is as high as possible. By performing the polymerization in the above monomer concentration range, the degree of polymerization of the polymer is sufficiently high, and the solubility of the monomer and polymer can be sufficiently ensured. When the polymerization is performed at a concentration lower than the above range, the degree of polymerization of the polyamic acid may not be sufficiently high, and when the polymerization is performed at a concentration higher than the above monomer concentration range, the monomer and the polymer to be generated are not sufficiently dissolved. There is a case. In addition, when an aliphatic diamine is used, salt formation often occurs at the initial stage of polymerization and the polymerization is hindered. However, in order to increase the degree of polymerization as much as possible while suppressing salt formation, the monomer concentration during polymerization is preferably set as described above. It is preferable to manage the concentration range within a range.

Next, a method for imidizing polyamic acid will be described. The polyimide of the present invention can be imidized by a known method. For example, a chemical imidation method in which polyamic acid is imidized with a dehydrating cyclization reagent, polyamic acid is polymerized in a high-boiling solvent, and then heated to 150 ° C. or higher in the presence of an azeotropic agent such as xylene as a by-product. Solution heat imidation method that removes water from the system to obtain polyimide with a high degree of polymerization in solution, or polyamic acid obtained by casting and drying a polyamic acid solution on a support such as a glass substrate There is a thermal imidation method in which the film-like molded body is imidized by heating at 250 ° C. or higher, preferably 300 ° C. or higher in a heating furnace or the like. In order to obtain a highly transparent polyimide molded body, among these imidization methods, a chemical imidation method capable of imidization under mild conditions is preferable.

The chemical imidization method will be described in detail. The polyamic acid solution obtained by the method described above is diluted with the same solvent used in the polymerization. While stirring a polyamic acid solution diluted to an appropriate solution viscosity that is easy to stir with a mechanical stirrer, etc., a dehydrating ring-closing agent (chemical imidizing agent) consisting of an organic acid anhydride and a tertiary amine as a basic catalyst. Is dripped and stirred at 0 to 100 ° C., preferably 10 to 50 ° C. for 1 to 72 hours to complete imidation chemically. Although it does not specifically limit as an organic acid anhydride which can be used in that case, Acetic anhydride, propionic anhydride, etc. are mentioned. Acetic anhydride is preferably used because of easy handling and purification of the reagent. As the basic catalyst, pyridine, triethylamine, quinoline and the like can be used, but pyridine is preferably used because of easy handling and separation of the reagent, but is not limited thereto. The amount of the organic acid anhydride in the chemical imidizing agent is in the range of 1 to 10 times mol, more preferably 1 to 5 times mol of the theoretical dehydration amount of the polyamic acid. The amount of the basic catalyst is in the range of 0.1 to 2 moles, more preferably in the range of 0.1 to 1 moles, relative to the amount of the organic acid anhydride.

As mentioned above, chemical imidization agents and by-products such as carboxylic acids (hereinafter referred to as impurities) are mixed in the reaction solution after chemical imidation, so it is necessary to remove these and purify the polyimide. There is. A known method can be used for purification. For example, as the simplest method, after dripping in a large amount of poor solvent while stirring the imidized reaction solution to precipitate polyimide, the polyimide powder is recovered and repeatedly washed until impurities are removed, A method of obtaining polyimide powder by drying under reduced pressure can be applied. At this time, the poor solvent that can be used is not particularly limited as long as it is a solvent that allows polyimide to be precipitated and impurities can be efficiently removed and is easily dried. For example, alcohols such as water, methanol, ethanol, and isopropanol are suitable. There may be a mixture of these. When the concentration of the polyimide solution when it is dropped into a poor solvent and deposited is too high, the deposited polyimide becomes agglomerates, and impurities may remain in the coarse particles, and the obtained polyimide powder is used as a solvent. It may take a long time to dissolve. On the other hand, if the concentration of the polyimide solution is too thin, a large amount of poor solvent is required, which is not preferable because the environmental load increases due to waste solvent treatment and the production cost increases. Therefore, the concentration of the polyimide solution when dropped in the poor solvent is 20% by weight or less, more preferably 10% by weight or less. The amount of the poor solvent used at this time is preferably equal to or greater than that of the polyimide solution, and is preferably 5 to 100 times. The obtained polyimide powder is recovered, and the residual solvent is removed by vacuum drying or hot air drying. The drying temperature and time are not particularly limited as long as the polyimide does not change in quality and the residual solvent evaporates, and it is preferable to dry in a temperature range of 30 to 200 ° C. for 48 hours or less.

The polyimide of the present invention preferably has a polyimide intrinsic viscosity in the range of 0.1 to 10.0 dL / g, more preferably 0.3 to 5. The range is 0 dL / g.

Since the polyimide of the present invention is soluble in various types of organic solvents, the solvent can be selected according to the intended use and processing conditions. For example, in the case of continuous coating over a long period of time, the solvent in the polyimide solution may absorb moisture in the air and the polyimide may be deposited, so low moisture absorption such as triethylene glycol dimethyl ether, γ-butyrolactone or cyclopentanone. It is preferable to use an organic solvent. Therefore, various solvents and mixed solvents exhibiting low hygroscopicity can be selected for the polyimide of the present invention. The low hygroscopic solvent used is not particularly limited. For example, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ-butyrolactone, butyl acetate, acetic acid Ester solvents such as ethyl and isobutyl acetate, carbonate solvents such as ethylene carbonate and propylene carbonate, glycol solvents such as diethylene glycol dimethyl ether, triethylene glycol and triethylene glycol dimethyl ether, phenol, m-cresol, p-cresol, o-cresol, Phenolic solvents such as 3-chlorophenol and 4-chlorophenol, keto such as cyclopentanone, cyclohexanone, acetone, methyl ethyl ketone, diisobutyl ketone, methyl isobutyl ketone Solvents such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane, dibutyl ether, and other general-purpose solvents such as acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, Dimethyl sulfoxide, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, chloroform, butanol, ethanol, xylene, toluene, chlorobenzene, terpene, mineral spirit, petroleum naphtha solvents, etc. Two or more of these may be mixed and used. Also, amide solvents such as hygroscopic solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, and N-methyl-2-pyrrolidone can be mixed with the above low hygroscopic solvent to precipitate polyimide due to moisture absorption. Can also be suppressed.

The solid concentration when the polyimide of the present invention is dissolved in a solvent to form a solution depends on the molecular weight of the polyimide, the production method and the thickness of the film to be produced, but is preferably 5% by weight or more. If the solid content concentration is too low, it is difficult to form a film having a sufficient film thickness. As a method for dissolving the polyimide of the present invention in a solvent, for example, the polyimide powder of the present invention is added while stirring the solvent, and 1 in the air or in an inert gas at a temperature range from room temperature to the boiling point of the solvent. It can be dissolved over ˜48 hours to make a polyimide solution.
In addition, the polyimide of the present invention may contain additives such as mold release agents, fillers, dyes, pigments, silane coupling agents, crosslinking agents, end-capping agents, antioxidants, antifoaming agents, and leveling agents as necessary. Can be added.
The obtained polyimide solution can be formed into a film by a known method to form a polyimide molded body or film. For example, a polyimide solution is cast on a support such as a glass substrate using a doctor blade or the like, and usually in the range of 40 to 300 ° C. using a hot air dryer, an infrared drying furnace, a vacuum dryer, an inert oven, or the like. Preferably, the polyimide film can be formed by drying in the range of 50 to 250 ° C.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, it is not limited to these Examples.
The physical property values in the following examples were measured by the following methods.
<Infrared absorption spectrum>
Using a Fourier transform infrared spectrophotometer FT / IR4100 (manufactured by JASCO Corporation), the infrared absorption spectrum of tetracarboxylic dianhydride was measured by the KBr transmission method. Moreover, the infrared absorption spectrum of the polyimide thin film was measured by the transmission method.
< ¹ H-NMR spectrum>
Using a Fourier transform nuclear magnetic resonance spectrophotometer JNM-ECP400 (manufactured by JEOL), ¹ H-NMR spectrum of tetracarboxylic dianhydride and chemically imidized polyimide powder in deuterated dimethyl sulfoxide was measured.
<Differential scanning calorimetry (melting point)>
The melting point of tetracarboxylic dianhydride was measured using a differential scanning calorimeter DSC3100 (Netch Co., Ltd.) in a nitrogen atmosphere at a temperature rising rate of 5 ° C./min. The higher the melting point and the sharper the melting peak, the higher the purity.
<Intrinsic viscosity>
The reduced viscosity of a 0.5% by weight polyamic acid solution or polyimide solution was measured at 30 ° C. using an Ostwald viscometer. This value was regarded as the intrinsic viscosity.
<Solubility test of polyimide powder in organic solvent>
With respect to 10 mg of the polyimide powder, 1 g of an organic solvent shown in Table 1 (solid content concentration 1% by weight) was placed in a sample tube, stirred for 5 minutes using a test tube mixer, and the dissolved state was visually confirmed. As a solvent, chloroform (CF), acetone, tetrahydrofuran (THF), 1,4-dioxane (DOX), ethyl acetate, cyclopentanone (CPN), cyclohexanone (CHN), N, N-dimethylformamide (DMF), N , N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), m-cresol, dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), triethylene glycol dimethyl ether (Tri-GL) did.
The evaluation results are ++ when dissolved at room temperature, + when dissolved by heating and maintaining uniformity after being allowed to cool to room temperature, ± when swollen / partially dissolved, and − Is displayed.
<Glass transition temperature: T _g , thermoplasticity>
The glass transition temperature of the polyimide film was determined from the loss peak at a frequency of 0.1 Hz, an amplitude of 0.1%, and a heating rate of 5 ° C./min using a TA Instruments dynamic viscoelasticity measuring device (Q800). Further, the thermoplasticity was evaluated from the steepness of the decrease in the storage elastic modulus curve immediately after the glass transition temperature.
<Linear thermal expansion coefficient: CTE>
The linear thermal expansion coefficient of the polyimide film was once increased to 150 ° C. at 5 ° C./min using TMA4000 manufactured by Netch Co. (sample size: width 5 mm, length 15 mm) with a load of film thickness (μm) × 0.5 g. The temperature was raised (first temperature increase), then cooled to 20 ° C., further heated at 5 ° C./min (second temperature increase), and calculated from the TMA curve at the second temperature increase. The linear thermal expansion coefficient was determined as an average value between 100 and 200 ° C.
<Transmissivity of polyimide membrane: _T400 >
Using a UV-Vis near-infrared spectrophotometer (V-650) manufactured by JASCO Corporation, the light transmittance at 200-700 nm of a polyimide film (20 μm thick) is measured, and the light transmittance at a wavelength of 400 nm is determined to be transparent. Used as an indicator. Further, the wavelength (cutoff wavelength) at which the transmittance was 0.5% or less was also determined.
<Yellowness (Yellowness Index): YI>
Using a UV-visible spectrophotometer V-530 (manufactured by JASCO Corp.), the light transmittance (T%) of the polyimide film at a wavelength of 380 to 780 nm was determined from JISK77373 by the VWCT-615 type color diagnostic program (manufactured by JASCO Corporation). The yellowness (YI) was calculated according to the above.
<Total light transmittance and haze>
Using Haze Meter NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), the total light transmittance of the polyimide film based on JISK7361 and the haze (turbidity) based on JISK7136 were determined.
<Birefringence: Δn>
Using an Abbe refractometer (Abbe 1T) manufactured by Atago Co., Ltd., the refractive index _{in the} direction parallel to the polyimide film surface (n _in ) and _{in the} direction perpendicular to the film thickness (n _out ) (n _out ) is measured using an Abbe refractometer (using a sodium lamp, The birefringence (Δn = n _in −n _out ) was determined from the difference in refractive index. The higher the birefringence value, the higher the in-plane orientation degree of the polymer chain.

<Synthesis Example 1>
A. Synthesis of TAHQ Tetracarboxylic dianhydride (TAHQ) represented by the following formula (6) was synthesized as follows. 12.6751 g (60.1940 mmol) of trimellitic anhydride chloride was placed in an eggplant flask, dissolved in 33 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealed with a septum to prepare solution A. Further, in another flask, 2.2209 g (20.1700 mmol) of hydroquinone (HQ) was added to 8.2 mL of dehydrated THF and 9.7 mL (120 mmol) of pyridine, followed by septum sealing to prepare Solution B. While cooling and stirring in an ice bath, solution B was gradually added dropwise to solution A with a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After completion of the reaction, the white precipitate was filtered off and washed with THF and ion exchange water. Removal of pyridine hydrochloride was confirmed by adding a silver nitrate aqueous solution to the washing solution and no white precipitate was observed. The washed product was collected and dried in vacuum at 100 ° C. for 12 hours. The obtained product was a white powder, and the yield was 8.0287 g and the yield was 87.6%.

B. Identification product TAHQ, from a Fourier transform infrared spectrophotometer FT / IR4100 (manufactured by JASCO Corporation), aromatic C-H stretching vibration absorption band at 3082cm ^-1, acid anhydrides 1847Cm ^-1 and 1781cm ^-1 The group C═O stretching vibration absorption band was confirmed, and the ester group C═O stretching vibration absorption band was confirmed at 1742 cm ⁻¹ .
As a result of ¹ H-NMR measurement using a Fourier transform nuclear magnetic resonance spectrophotometer JNM-ECP400 (manufactured by JEOL), (DMSO-d ₆ , δ, ppm): 7.54 (s, 4H), Assigned as 8.30 (d, J = 7.9 Hz, 2H), 8.65 (sd, J = 0.72 Hz, 2H), 8.67 (dd, J = 8.0 Hz, 1.3 Hz, 2H) The elemental analysis values are estimated values C: 62.89%, H: 2.20%, measured values C: 62.69%, H: 2.42%, and the product was confirmed to be TAHQ. It was.
Further, when the melting point was measured by a differential scanning calorimeter DSC3100 (Netch Co., Ltd.), a sharp melting peak was observed at 272.4 ° C., suggesting that this product was of high purity.

<Synthesis Example 2>
A. Synthesis of tetracarboxylic dianhydride TAPh A tetracarboxylic dianhydride (TAPh) represented by the following formula (7) was synthesized as follows. Trimellitic chloride 15.1116 g (71.8 mmol) was placed in an eggplant flask, dissolved in 16.5 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealed with a septum to prepare solution A. Further, in a separate flask, 6.2721 g (34 mmol) of 2-phenylhydroquinone was added with 23.5 mL of dehydrated THF and 8.7 mL (108 mmol) of pyridine, and a septum was sealed to prepare solution B. While cooling and stirring in an ice bath, solution B was gradually added dropwise to solution A with a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After completion of the reaction, the white precipitate was filtered off and washed with THF and ion exchange water. Removal of pyridine hydrochloride was confirmed by adding a silver nitrate aqueous solution to the washing solution and no white precipitate was observed. The washed product was collected and vacuum-dried at 80 ° C. for 1 hour and further at 100 ° C. for 12 hours. The obtained product was a white powder, and the yield was 17.93 g and the yield was 98.7%.

B. Identification product TAPh the acid Fourier transform infrared spectrophotometer FT / IR4100 from (manufactured by JASCO Corporation), aromatic C-H stretching vibration absorption band at 3092,3065Cm ^-1, to 1847cm ^-1 and 1775 cm ^-1 An anhydride group C═O stretching vibration absorption band was confirmed, and an ester group C═O stretching vibration absorption band was confirmed at 1752 cm ⁻¹ .
Further, as a result of ¹ H-NMR measurement using a Fourier transform nuclear magnetic resonance spectrophotometer JNM-ECP400 (manufactured by JEOL), (DMSO-d ₆ , δ, ppm): 7.30-7.40 (m 3H), 7.55-7.66 (m, 5H), 8.23 (d, J = 7.8 Hz, 1H), 8.29-8.32 (m, 1H), 8.50-8 .56 (m, 2H), 8.66-8.70 (m, 2H), and the elemental analysis values are estimated C: 67.42%, H: 2.64%, measured C: 67. 49%, H: 2.82%, and the product was confirmed to be TAPh.
Further, when the melting point was measured with a differential scanning calorimeter DSC3100 (Netch Co., Ltd.), a sharp melting peak was observed at 198.4 ° C., suggesting that this product was of high purity.

<Example 1>
A. Synthesis of tetracarboxylic dianhydride TACHQ represented by formula (1) TACHQ represented by formula (1) was synthesized as follows. Into an eggplant flask, 12.7003 g (60.3137 mmol) of trimellitic anhydride chloride was placed, dissolved in 33 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealed with a septum to prepare solution A. Further, in a separate flask, 3.8551 g (20.0661 mmol) of 2-cyclohexylhydroquinone (CHQ) was added to 6.5 mL of dehydrated THF and 9.7 mL (120 mmol) of pyridine, followed by septum sealing to prepare solution B.
While cooling and stirring in an ice bath, solution B was gradually added dropwise to solution A with a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After completion of the reaction, the white precipitate was filtered off and washed with THF and ion exchange water. Removal of pyridine hydrochloride was confirmed by adding a silver nitrate aqueous solution to the washing solution and no white precipitate was observed. The washed crude product was collected and vacuum-dried at 100 ° C. for 12 hours. The obtained crude product was a white powder, and the yield was 6.54 g and the yield was 87.6%.
(Purification)
After 2.5526 g of the obtained crude product was dissolved in a mixed solvent of acetic anhydride and toluene (volume ratio 1:10) at 90 ° C., it was allowed to cool naturally and allowed to stand for 72 hours. The precipitated white powder was separated by filtration and vacuum dried at 160 ° C. for 12 hours. The yield of the obtained white powder was 1.3602 g, and the recrystallization yield was 53.3%.

B. Identification of TACHQ The product purified by recrystallization was obtained from a Fourier transform infrared spectrophotometer FT / IR4100 (manufactured by JASCO Corporation) at 2928 cm ⁻¹ with an aliphatic C—H stretching vibration absorption band, 1861 cm ⁻¹ and 1778 cm ^{−. An} acid anhydride group C═O stretching vibration absorption band was confirmed in ¹ and an ester group C═O stretching vibration absorption band was confirmed in 1745 cm ⁻¹ .
Further, as a result of ¹ H-NMR measurement using a Fourier transform nuclear magnetic resonance spectrophotometer JNM-ECP400 (manufactured by JEOL), (DMSO-d ₆ , δ, ppm): 1.80-1.23 (m , 10H), 2.69 (t, J = 12 Hz, 1H), 7.50-7.18 (m, 3H), 8.33-8.29 (m, 2H), 8.71-8.65. (M, 4H), the elemental analysis values were the theoretical value C: 66.67%, H: 3.73%, the actual measurement value C: 66.27%, H: 3.78%, and the product was It was confirmed to be TACHQ.
Further, when the melting point was measured with a differential scanning calorimeter DSC3100 (Netch Co., Ltd.), a sharp melting peak was observed at 229.1 ° C., suggesting that this product was of high purity.

<Example 2>
A. Synthesis of Polyimide of Repeating Unit Represented by Formula (8) (Polyamide Acid Polymerization) TACHQ / TFMB
3 mmol of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was dissolved in dehydrated N, N-dimethylacetamide (DMAc). To this, 3 mmol of TACHQ powder described in Example 1 was slowly added and stirred at room temperature for 72 hours, and DMAc was appropriately added to obtain a polyamic acid as a polyimide precursor (solid content concentration 16.7% by weight). The obtained polyamic acid had an intrinsic viscosity of 1.72 dL / g.
(Chemical imidization reaction)
The resulting polyamic acid solution was diluted with dehydrated DMAc to a solid content concentration of about 10.0% by weight, and a mixed solution of 2.8 mL (30 mmol) of acetic anhydride and 1.2 mL (15 mmol) of pyridine was then stirred. The solution was slowly added dropwise at room temperature, and stirred for another 24 hours after completion of the addition. The obtained polyimide solution was slowly dropped into a large amount of methanol to precipitate the polyimide. The resulting white precipitate was sufficiently washed with methanol and vacuum dried at 100 ° C. for 12 hours. When ¹ H-NMR measurement was performed on the obtained fibrous polyimide powder, COOH protons (near δ = 13 ppm) and NHCO protons (near δ = 11 ppm) characteristic of polyamic acid were not observed. It was suggested that the chemical reaction was complete. The obtained polyimide had an intrinsic viscosity of 2.55 dL / g and was a high molecular weight product. Table 1 shows the solubility of the polyimide powder in the solvent. It can be seen from Table 1 that the solvent solubility is superior.

B. Preparation of polyimide solution and film formation of polyimide film The above polyimide powder was redissolved in γ-butyrolactone (GBL) while heating to prepare a 6.0 wt% uniform solution. This polyimide solution was cast on a glass substrate and dried in a hot air dryer at 80 ° C. for 2 hours. Thereafter, the whole substrate was dried in vacuum at 200 ° C. for 1 hour, allowed to cool to room temperature, and then the polyimide film was peeled off from the glass substrate. This polyimide film was once again heat treated in vacuum at 200 ° C. for 1 hour to remove residual strain.
FIG. 1 shows an infrared absorption spectrum of the obtained polyimide film, FIG. 2 shows a dynamic viscoelastic curve, and Table 2 shows thermal characteristics and optical characteristics. From FIG. 1, it can identify that it is the target polyimide. As can be seen from FIG. 2, a sharp decrease in storage modulus is observed around 225 ° C., indicating high thermoplasticity. From Table 2, it can be seen that the linear thermal expansion coefficient (CTE) is as low as 11.9 ppm / K and is a colorless and transparent film. These excellent characteristics are the effects of the structure of formula (2).

<Example 3>
A. Synthesis of polyimide having a repeating unit represented by the following formula (9) (polymerization of polyamic acid) TACHQ (80) 6FDA (20) / TFMB
3 mmol of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was dissolved in dehydrated N, N-dimethylacetamide (DMAc). To this, 2.4 mmol of TACHQ powder described in Example 1 and 0.6 mmol of 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) powder were slowly added and stirred at room temperature for 72 hours. In addition, a polyamic acid as a polyimide precursor was obtained (solid content concentration 22.7% by weight). The obtained polyamic acid had an intrinsic viscosity of 0.91 dL / g.
(Chemical imidization reaction)
The resulting polyamic acid solution was diluted with dehydrated DMAc to a solid content concentration of about 10.0% by weight, and a mixed solution of 2.8 mL (30 mmol) of acetic anhydride and 1.2 mL (15 mmol) of pyridine was then stirred. The solution was slowly added dropwise at room temperature, and stirred for another 24 hours after completion of the addition. The obtained polyimide solution was slowly dropped into a large amount of methanol to precipitate the polyimide. The resulting white precipitate was thoroughly washed with methanol and vacuum dried at 100 ° C. for 12 hours. When ¹ H-NMR measurement was performed on the obtained fibrous polyimide powder, COOH protons (near δ = 13 ppm) and NHCO protons (near δ = 11 ppm) characteristic of polyamic acid were not observed. It was suggested that the chemical reaction was complete. The obtained polyimide had an intrinsic viscosity of 1.75 dL / g and was a high molecular weight product. Table 1 shows the solubility of the polyimide powder in the solvent. It can be seen from Table 1 that the solvent solubility is superior.

B. Preparation of polyimide solution and film formation of polyimide film The above polyimide powder was redissolved while heating in cyclopentanone (CPN) to prepare a 8.0 wt% uniform solution. This polyimide solution was cast on a glass substrate and dried with a hot air dryer at 60 ° C. for 2 hours. Thereafter, the whole substrate was dried in vacuum at 200 ° C. for 1 hour and allowed to cool to room temperature, and then the polyimide film was peeled from the glass substrate. This polyimide film was once again heat treated in vacuum at 200 ° C. for 1 hour to remove residual strain. FIG. 3 shows the infrared absorption spectrum of the obtained polyimide film, FIG. 4 shows the dynamic viscoelasticity curve, and Table 2 shows the thermal characteristics and optical characteristics. From FIG. 3, it can identify that it is the target polyimide. As can be seen from FIG. 4, a steep decrease in storage elastic modulus is observed around 225 ° C., indicating high thermoplasticity. From Table 2, it can be seen that the linear thermal expansion coefficient (CTE) is as low as 24.7 ppm / K and is a colorless and transparent film. These excellent characteristics are the effects of the structure of formula (2).

<Example 4>
A. Synthesis of polyimide having a repeating unit represented by the following formula (10) (polymerization of polyamic acid) TACHQ (50) 6FDA (50) / TFMB
2 mmol of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was dissolved in dehydrated N, N-dimethylacetamide (DMAc). To this, 1.0 mmol of TACHQ powder described in Example 1 and 1.0 mmol of 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) powder were slowly added and stirred at room temperature for 72 hours. In addition, polyamic acid as a polyimide precursor was obtained (solid content concentration 30% by weight).
The resulting polyamic acid had an intrinsic viscosity of 0.56 dL / g.
(Chemical imidization reaction)
The obtained polyamic acid solution was diluted with dehydrated DMAc to a solid content concentration of about 10.0% by weight, and a mixed solution of 1.9 mL (20 mmol) of acetic anhydride and 0.8 mL (10 mmol) of pyridine was then stirred. The solution was slowly added dropwise at room temperature, and stirred for another 24 hours after completion of the addition. The obtained polyimide solution was slowly dropped into a large amount of methanol to precipitate the polyimide. The resulting white precipitate was sufficiently washed with methanol and vacuum dried at 100 ° C. for 12 hours. When ¹ H-NMR measurement was performed on the obtained fibrous polyimide powder, COOH protons (near δ = 13 ppm) and NHCO protons (near δ = 11 ppm) characteristic of polyamic acid were not observed. It was suggested that the chemical reaction was complete. The intrinsic viscosity of the obtained polyimide was 0.76 dL / g. Table 1 shows the solubility of the polyimide powder in the solvent. It can be seen from Table 1 that the solvent solubility is superior.

B. Preparation of polyimide solution and film formation of polyimide film The above polyimide powder was redissolved in cyclopentanone (CPN) at room temperature to prepare a 23 wt% uniform solution. This polyimide solution was cast on a glass substrate and dried with a hot air dryer at 60 ° C. for 2 hours. Thereafter, the whole substrate was dried in vacuum at 200 ° C. for 1 hour and allowed to cool to room temperature, and then the polyimide film was peeled from the glass substrate. This polyimide film was once again heat treated in vacuum at 200 ° C. for 1 hour to remove residual strain.
FIG. 5 shows an infrared absorption spectrum of the obtained polyimide film, FIG. 6 shows a dynamic viscoelastic curve, and Table 2 shows thermal characteristics and optical characteristics. From FIG. 5, it can identify that it is the target polyimide. From FIG. 6, it can be seen that a steep decrease in storage elastic modulus is observed at around 230 ° C. and shows high thermoplasticity, and further, from Table 2, it is clear that the film is colorless and transparent.

<Comparative Example 1>
A. Synthesis of polyimide having a repeating unit represented by the following formula (11) (polyamide acid polymerization) TAPh (100) / TFMB
3 mmol of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was dissolved in dehydrated N-methyl-2-pyrrolidone (NMP). To this, 3 mmol of TAPh powder described in Synthesis Example 2 was slowly added and stirred at room temperature for 72 hours to obtain a polyamic acid as a polyimide precursor (solid content concentration 20% by weight). The intrinsic viscosity of the obtained polyamic acid was 1.6 dL / g.
B. Formation of Polyimide Film A polyamic acid solution was cast on a glass substrate and dried with a hot air dryer at 80 ° C. for 3 hours. Thereafter, the whole substrate was heat imidized at 250 ° C. for 1 hour and 350 ° C. for 1 hour, and then the polyimide film was peeled off from the glass substrate. This polyimide film was once again heat treated in vacuum at 200 ° C. for 1 hour to remove residual strain.
Table 2 shows the thermal characteristics and optical characteristics of the obtained polyimide film. From Table 2, it can be seen that there is low light transmittance, and severe yellowing and turbidity. Since the cyclohexyl group in the polyimide of the repeating unit of the formula (8) was changed to a phenyl group, it is considered that the optical properties of the polyimide film of the repeating unit of the formula (11) were significantly deteriorated. That is, it can be seen that the structure of the cyclohexyl group is extremely useful even with a similar bulky structure.

<Comparative Example 2>
A. Synthesis of Polyimide of Repeating Unit Represented by Formula (12) (Polyamide Acid Polymerization) TAHQ / TFMB
2 mmol of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was dissolved in dehydrated N, N-dimethylacetamide (DMAc). Here, 2 mmol of TAHQ powder described in Synthesis Example 1 was slowly added and stirred at room temperature for 72 hours, and DMAc was appropriately added to obtain a polyamic acid as a polyimide precursor (solid content concentration 11.4 wt%). The obtained polyamic acid had an intrinsic viscosity of 4.45 dL / g.
(Chemical imidization reaction)
The obtained polyamic acid solution was diluted with dehydrated DMAc to a solid content concentration of about 10.0% by weight, and a mixed solution of 1.9 mL (20 mmol) of acetic anhydride and 0.8 mL (10 mmol) of pyridine was then stirred. The solution was slowly added dropwise at room temperature, and the fluidity of the solution disappeared and gelled in another 3 hours after completion of the addition. From comparison of the polyimides of the repeating units of formula (8) and formula (12), it can be seen that the bulky cyclohexyl group has extremely enhanced solubility in the solvent.

B. Formation of Polyimide Film The above polyamic acid solution was cast on a glass substrate and dried with a hot air dryer at 60 ° C. for 2 hours. Thereafter, the whole substrate was thermally imidized at 200 ° C. for 0.5 hours and 250 ° C. for 2 hours, and then the polyimide film was peeled from the glass substrate. This polyimide film was once again heat treated in vacuum at 300 ° C. for 1 hour to remove residual strain.
FIG. 7 shows the dynamic viscoelasticity curve of the obtained polyimide film, and Table 2 shows the thermal characteristics and optical characteristics. From FIG. 7, it can be seen that the temperature at which the storage elastic modulus begins to decrease is as high as 375 ° C., so that it is inferior in thermal workability to the repeating unit polyimide of formula (8). Moreover, yellowness and haze are also high and optical characteristics are also inferior.
That is, it can be seen that the cyclohexyl group of the formula (2) plays an extremely important role.

Claims

Following formula (1):

Tetracarboxylic dianhydride represented by
Following formula (2):

The polyimide which has a repeating unit represented by these.
The content rate of the repeating unit represented by Formula (2) is 55 mol% or more with respect to all the repeating units in a polyimide, The polyimide of Claim 2 characterized by the above-mentioned.
A polyimide solution comprising the polyimide according to claim 2 or 3 and an organic solvent, wherein the polyimide solution has a solid content concentration of 5% by weight or more.
The polyimide molded body according to claim 2 or 3.