JP6715496B2 - Novel tetracarboxylic dianhydride, polyimide derived from the tetracarboxylic dianhydride, and molded article made of the polyimide - Google Patents

Description

The present invention is a polyimide derived from a novel tetracarboxylic dianhydride, which is excellent in processability, has a low coefficient of linear thermal expansion, and has a high light transmittance (transparency), and the polyimide. Regarding a molded body. Since the polyimide exhibits not only excellent solution processability but also thermoplasticity, not only film formation by the solution casting method but also melt molding is possible. Further, the molded body made of the polyimide has a lower linear thermal expansion coefficient than the conventional solvent-soluble polyimide and the thermoplastic polyimide and is excellent in transparency. Due to these features, transparent materials used for liquid crystal displays (LCD), organic electroluminescence (EL) displays, electronic paper, light emitting diode (LED) devices, solar cells, etc., which require dimensional stability and transparency against heat. It is useful as a substrate, transparent protective film material, and adhesive material.

Polyethylene terephthalate, polycarbonate, polyether sulfone, etc. are known as conventional transparent resins that can be processed. Although these resins have excellent solution processability and melt moldability, they do not change in size due to heat (linear Large thermal expansion coefficient). When the molded product has a large linear thermal expansion coefficient, various problems may occur when laminated with a low thermal expansion inorganic material used for display devices such as LCDs, organic EL displays, electronic papers, LEDs, and lighting devices. Yes, it is not preferable. For example, the transparent resin molded body and a transparent electrode (ITO; Indium Tin Oxide), wiring of copper, silver, aluminum, or the like, or a thin-film transistor (TFT; Thin-Film Transistor) is used to form a device with a low heat A mismatch in the coefficient of linear thermal expansion occurs between the expansive inorganic material and the conventional high-thermal-expansion resin, and strain may occur at the interface, leading to delamination of the substrate, distortion of the substrate, and destruction of the element.

On the other hand, aromatic polyimide is known as a resin having excellent thermal dimensional stability. A molded article made of aromatic polyimide having a rigid and linear chemical structure, such as a polyimide film, is required to have high dimensional stability (low linear thermal expansion coefficient) such as a base film of a flexible printed wiring board or an interlayer insulating film of a semiconductor. Widely used in the field. However, an aromatic polyimide having a low coefficient of linear thermal expansion is strongly colored due to intramolecular conjugation and intramolecular/intermolecular charge transfer interaction, so that it is difficult to apply it to the above optical applications. Further, since polyimide has a very strong intermolecular force, it often shows no solubility in a solvent and no thermoplasticity and is poor in processability.
On the other hand, polyimides that overcome these drawbacks have been proposed. For example, by introducing a fluorine atom into the polyimide structure (Non-Patent Document 1), or by using an alicyclic compound in one or both of the diamine component and the tetracarboxylic dianhydride component that compose the polyimide, intramolecular Methods for suppressing conjugation and charge transfer interaction to improve 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 properties 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 transparency and heat resistance and a low linear thermal expansion coefficient equivalent to that of an inorganic material, its solubility in various kinds of organic solvents is not sufficient, and there was room for improvement in this respect. ..
Furthermore, a polyimide having excellent processability that also has thermoplasticity is not known.

Macromolecules, 24, 5001 (1991) J. Polym. Sci. , Part A, Polym. Chem. , 51,575 (2013) Polymer, 55, 4693 (2014)

JP, 2013-082876, A

The present invention is a polyimide derived from a novel tetracarboxylic dianhydride, excellent in solubility in various kinds of organic solvents, and also excellent in processability because it also has thermoplasticity, low linear thermal expansion An object of the present invention is to provide a polyimide having both a coefficient and a high light transmittance (transparency), and a molded body made of the polyimide.

In view of the above technical background, the inventors of the present invention have conducted intensive studies, and as a result, a polyimide having excellent processability was obtained from the tetracarboxylic dianhydride represented by the following formula (1), which is extremely useful in the field. The present invention has been completed by discovering that it can be used as a material.

The present invention is as follows.
1. A 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 based on all repeating units in the polyimide.
A polyimide solution containing the polyimide according to 4.2 or 3 and an organic solvent, wherein the solid content concentration is 5% by weight or more.
The polyimide molded product according to 5.2 or 3.

According to the present invention, characteristics not obtained in the prior art, namely, excellent solubility in various kinds of organic solvents, and also excellent in processability because it also has thermoplasticity, low linear thermal expansion coefficient, and A polyimide having all of high light transmittance (transparency), and a molded body made of the polyimide use a tetracarboxylic dianhydride characterized in that a central phenylene group is substituted with a bulky cyclohexyl group. It is obtained by

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 feature of the tetracarboxylic acid dianhydride represented by the formula (1) according to the present invention (hereinafter, sometimes abbreviated as TACHQ) is that it is bonded to the para-position of the central phenylene group via an ester bond. The point is that two phthalic anhydride structures are bonded 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 synthesized by a known esterification reaction from trimellitic acid or its derivative represented by
Examples of the trimellitic acid derivative include trimellitic anhydride, trimellitic anhydride halide and the like.

The polyimide of the present invention has a repeating unit represented by the 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 are present in the para position of the central phenylene group of the tetracarboxylic dianhydride site, and the diamine site is 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 feature, it is considered that the polyimide chains are highly oriented along the plane direction of the film (in-plane orientation) and exhibit excellent thermal dimensional stability (low linear thermal expansion coefficient). However, the low thermal expansion polyimide having such a linear and rigid structure is generally insoluble in an organic solvent, does not melt, and has poor processability because of strong cohesive force between polyimide chains. Therefore, generally, a method of introducing a siloxane bond, an ether bond, or a meta bond into the polyimide main chain to bend the polyimide main chain structure, 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 to improve workability. However, these methods hinder the in-plane orientation in the polyimide molded body, especially in the film, and consequently increase the coefficient of linear thermal expansion. That is, it is very difficult to achieve both workability and low thermal expansion.
Then, this problem can be solved by the second feature described below of 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 with an electron-withdrawing property, so that the polyimide chain 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 has excellent solubility in various kinds of organic solvents and also has thermoplasticity, and thus has excellent processability, and It exhibits a low coefficient of linear thermal expansion, which was originally difficult to achieve, and further suppresses the charge transfer interaction of the polyimide, thus achieving high transparency.

The polyimide having the repeating unit represented by the formula (2) according to the present invention can synthesize the polyimide having the above excellent properties by using the TACHQ represented by the 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) as a diamine (hereinafter , TFMB in some cases) to obtain a polyimide precursor (polyamic acid) having a repeating unit represented by the formula (2), and a step of imidizing the polyamic acid. You can

When polymerizing a polyamic acid, an aromatic or aliphatic tetracarboxylic acid dianhydride other than TACHQ represented by the formula (1) is used as a copolymerization component in a range that does not significantly impair the polymerization reactivity and the required properties of the polyimide. can do.
The aromatic tetracarboxylic dianhydride that can be used in that case is not particularly limited, but examples thereof include pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and hydroquinone. -Bis(trimeritate hydride), methylhydroquinone-bis(trimeritate hydride), 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid Dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4' -Biphenyl sulfone tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 2,2'-bis(3,4-dicarboxyphenyl)propanoic dianhydride, etc. ..
The aliphatic tetracarboxylic dianhydride is not particularly limited, but for example, as an alicyclic compound, 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 acid anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic acid dianhydride, bicyclo-3,3',4,4'-tetracarboxylic acid dianhydride, 1,2,3,4- Examples thereof include cyclobutanetetracarboxylic acid dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, etc. Also, two or more of these may be used in combination.
From the viewpoint of further increasing the solubility, heat resistance, and transparency of the polyimide, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (hereinafter sometimes abbreviated as 6FDA), further low heat of the polyimide molded body From the viewpoint of expansivity, a tetracarboxylic dianhydride having a rigid and linear structure, that is, pyromellitic dianhydride and 3,3′,4,4′-biphenyltetracarboxylic dianhydride, It is suitable as a polymerization component.
When an aromatic or aliphatic tetracarboxylic dianhydride other than TACHQ represented by the formula (1) is used in combination as a copolymerization component, the ratio of TACHQ to all tetracarboxylic dianhydrides is preferably 55 mol. % Or more, more preferably 70 mol% or more, further 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 properties of the polyimide. be able to.
The aromatic diamine that can be used in that case is not particularly limited, but examples thereof include 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(2,2 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) ) Hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, p-terphenylenediamine and the like.
The aliphatic diamine is a chain aliphatic or alicyclic diamine, and the alicyclic diamine is not particularly limited, and examples thereof include 4,4′-methylenebis(cyclohexylamine), isophoronediamine, and trans-diamine. 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 are not particularly limited, and examples thereof include 1,3-propanediamine and 1,4-tetramethylenediamine. 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, diaminosiloxane and the like. Also, two or more of these may be used in combination.

During the polymerization reaction, aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethylsulfoxide are preferable as the solvent used, but they are formed with the raw material monomer. Any solvent can be used without any problem as long as the polyamic acid and the imidized polyimide are dissolved, 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, Ester solvent such as ε-caprolactone, α-methyl-γ-butyrolactone, butyl acetate, ethyl acetate and isobutyl acetate, carbonate solvent such as ethylene carbonate and propylene carbonate, glycol system such as diethylene glycol dimethyl ether, triethylene glycol and triethylene glycol dimethyl ether. Solvents, phenolic solvents such as phenol, m-cresol, p-cresol, o-cresol, 3-chlorophenol, 4-chlorophenol and the like, ketones such as cyclopentanone, cyclohexanone, acetone, methyl ethyl ketone, diisobutyl ketone and methyl isobutyl ketone. System solvents, tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane, ether solvents such as 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, butanol, ethanol, xylene, toluene, chlorobenzene, terpenes, mineral spirits, petroleum naphtha solvent, etc. can also be used. You may use it in mixture of 2 or more types.

After polyaddition reaction of TACHQ represented by the formula (1) and TFMB represented by the formula (5) to obtain a polyamic acid, and then imidizing the polyamic acid, the present invention, which is extremely useful in the industry, can be obtained. A polyimide can be obtained.
The polyimide of the present invention is characterized by the linearity of the polymer main chain, rigidity, and the chemical structural characteristics that bulky substituents are present on the side chain, and when made into a polyimide resin, it dissolves in various types of organic solvents. In addition to being excellent in processability and thermoplasticity, it is excellent in processability, and the polyimide molded body, particularly the film, can be a material having a low linear thermal expansion coefficient and high transparency.
Usually, the polymerization reactivity of tetracarboxylic dianhydride and diamine has a great influence on 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 of polymer chains becomes low, and the polyimide molded body may become brittle. Since the TACHQ of the formula (1) and the TFMB of the formula (5) used in the present invention exhibit sufficiently high polymerization reactivity, there is no such concern.

The method for producing the polyimide of the present invention is not particularly limited, and a known method can be appropriately applied. Specifically, for example, it can be synthesized by the following method. First, TFMB of the formula (5) is dissolved in a polymerization solvent, and TACHQ powder of the formula (1), which is substantially equimolar to the TFMB of the formula (5), is gradually added to this solution, and a mechanical stirrer or the like is used. To 100° C., preferably 20 to 60° C. for 0.5 to 150 hours, preferably 1 to 48 hours. In this case, the monomer concentration is usually in the range of 5 to 50% by weight, preferably 10 to 40% by weight. By carrying out the polymerization in such a monomer concentration range, a uniform polyamic acid having a high degree of polymerization can be obtained. When the degree of polymerization of the polyamic acid is excessively increased and it becomes difficult to stir the polymerization solution, it may 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 carrying out the polymerization in the above monomer concentration range, the polymerization degree of the polymer is sufficiently high, and the solubility of the monomer and the polymer can be sufficiently ensured. When the polymerization is carried out 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 carried out at a higher concentration than the above monomer concentration range, the monomer and the polymer to be formed are insufficiently dissolved. May be. Further, when an aliphatic diamine is used, salt formation often occurs at the initial stage of the polymerization, which hinders the polymerization. It is preferable to control the concentration within a range.

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

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 as that used for the polymerization. Agitating a polyamic acid solution diluted to an appropriate solution viscosity that is easy to stir with a mechanical stirrer, etc., while adding an anhydride of an organic acid and a tertiary amine as a basic catalyst to this dehydration ring closure agent (chemical imidizing agent) Is added dropwise and stirred at 0 to 100°C, preferably 10 to 50°C for 1 to 72 hours to chemically complete imidization. The organic acid anhydride that can be used in that case is not particularly limited, and examples thereof include acetic anhydride and propionic anhydride. Acetic anhydride is preferably used because of the ease of handling and purification of reagents. As the basic catalyst, pyridine, triethylamine, quinoline and the like can be used, but pyridine is preferably used because of the ease of handling and separation of the reagent, but it 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, and more preferably 1 to 5 times the molar amount of the theoretical dehydration amount of the polyamic acid. The amount of the basic catalyst is in the range of 0.1 to 2 times, and more preferably 0.1 to 1 times the mol of the organic acid anhydride.

As described above, since byproducts (hereinafter referred to as impurities) such as chemical imidizing agent and carboxylic acid are mixed in the reaction solution after chemical imidization, it is necessary to remove them to purify the polyimide. There is. A known method can be used for purification. For example, the simplest method is to drop an imidized reaction solution into a large amount of a poor solvent while stirring to precipitate a polyimide, and then repeatedly wash until the polyimide powder is recovered and impurities are removed, A method for obtaining a 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 precipitates polyimide, can efficiently remove impurities, and is easy to dry, but, for example, water, methanol, ethanol, alcohols such as isopropanol are preferable. Yes, these may be mixed and used. The concentration of the polyimide solution when dropped and deposited in a poor solvent is agglomerates of polyimide that precipitates when it is too high, and impurities may remain in the coarse particles, or the obtained polyimide powder may be 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 increases the environmental load due to waste solvent treatment and increases the manufacturing cost, which is not preferable. Therefore, the concentration of the polyimide solution when dropped into 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 more than the amount of the polyimide solution, and is preferably 5 to 100 times. The obtained polyimide powder is collected, and the residual solvent is removed by vacuum drying, hot air drying, or the like. There is no limitation on the drying temperature and time as long as the polyimide does not deteriorate and the residual solvent evaporates, and it is preferable to dry within 48 hours or less in the temperature range of 30 to 200°C.

From the viewpoint of the toughness of the polyimide molded body and the handling of the solution, the polyimide of the present invention has an intrinsic viscosity of the polyimide of preferably 0.1 to 10.0 dL/g, more preferably 0.3 to 5. It is in the range of 0 dL/g.

Since the polyimide of the present invention is soluble in various kinds of organic solvents, the solvent can be selected according to the intended use and processing conditions. For example, when continuously coating over a long period of time, the solvent in the polyimide solution absorbs moisture in the air, and polyimide may precipitate, so low moisture absorption of triethylene glycol dimethyl ether, γ-butyrolactone, cyclopentanone, etc. It is preferable to use an organic solvent. Therefore, various solvents or mixed solvents having 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. Ethyl, ester solvents such as 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, Phenol solvents such as 3-chlorophenol and 4-chlorophenol, ketone solvents such as cyclopentanone, cyclohexanone, acetone, methyl ethyl ketone, diisobutyl ketone and methyl isobutyl ketone, tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxy Ether-based solvents such as ethane and 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, and 2-methyl. Cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, chloroform, butanol, ethanol, xylene, toluene, chlorobenzene, terpene, mineral spirits, petroleum naphtha-based solvents and the like can be used, and two or more kinds of them may be mixed and used. In addition, even an amide solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, or N-methyl-2-pyrrolidone, which is a hygroscopic solvent, is mixed with the low hygroscopic solvent to precipitate polyimide by moisture absorption. Can also be suppressed.

The solid content concentration when the polyimide of the present invention is dissolved in a solvent to form a solution is preferably 5% by weight or more, though it depends on the molecular weight of the polyimide, the production method and the thickness of the produced film. If the solid content concentration is too low, it becomes 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 the temperature is from room temperature to a boiling point of the solvent or lower in the air in an inert gas. It can be dissolved into a polyimide solution by dissolving it for 48 hours.
Further, in the polyimide of the present invention, if necessary, a release agent, a filler, a dye, a pigment, a silane coupling agent, a crosslinking agent, an end capping agent, an antioxidant, an antifoaming agent, an additive such as a leveling agent. Can be added.
The obtained polyimide solution can be formed into a film by a known method to form a polyimide molded body or a film. For example, a polyimide solution is cast on a support such as a glass substrate by using a doctor blade or the like, and a hot air drier, an infrared drying furnace, a vacuum drier, an inert oven or the like is used, and usually in the range of 40 to 300°C. Preferably, the polyimide film can be formed by drying in the range of 50 to 250°C.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
The physical property values in the following examples were measured by the following methods.
<Infrared absorption spectrum>
An infrared absorption spectrum of tetracarboxylic dianhydride was measured by a KBr transmission method using a Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by JASCO Corporation). 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 spectra of tetracarboxylic dianhydride and polyimide powder chemically imidized in deuterated dimethyl sulfoxide were measured.
<Differential scanning calorimetry (melting point)>
The melting point of the tetracarboxylic dianhydride was measured by using a differential scanning calorimeter DSC3100 (Netch Co.) 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 the 0.5 wt% polyamic acid solution or the 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 polyimide powder, 1 g of the organic solvent described in Table 1 (solid content concentration 1% by weight) was put into a sample tube and stirred for 5 minutes using a test tube mixer to visually confirm the dissolved state. 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, dimethylsulfoxide (DMSO), γ-butyrolactone (GBL), triethylene glycol dimethyl ether (Tri-GL) are used. did.
The evaluation results are ++ when dissolved at room temperature, + when dissolved by heating and kept uniform even after cooling to room temperature, +, when swelled/partially dissolved, ±, and when insoluble. Was 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 dynamic viscoelasticity measuring device (Q800) manufactured by TA Instruments. Further, the thermoplasticity was evaluated from the steepness of the decrease of 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 with TMA4000 manufactured by Netti Co., Ltd. (sample size width 5 mm, length 15 mm), the load was film thickness (μm)×0.5 g. After the temperature was raised (first heating), the temperature was cooled to 20° C., the temperature was further raised at 5° C./min (second heating), and the TMA curve at the second heating was calculated. The linear thermal expansion coefficient was determined as an average value between 100 and 200°C.
<Transmittance of polyimide film: T ₄₀₀ >
The light transmittance at 200-700 nm of the polyimide film (20 μm thick) was measured using an ultraviolet-visible near-infrared spectrophotometer (V-650) manufactured by JASCO Corporation, and the light transmittance at a wavelength of 400 nm was measured as a transparency. It was used as an index. Further, the wavelength (cutoff wavelength) at which the transmittance is 0.5% or less was also obtained.
<Yellowness index (Yellowness index): YI>
Using an ultraviolet-visible spectrophotometer V-530 (manufactured by JASCO Corporation), from the light transmittance (T%) of the polyimide film at a wavelength of 380 to 780 nm, a VWCT-615 type color diagnostic program (manufactured by JASCO Corporation) was used to determine JISK77373. The yellowness index (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 according to JIS K7361 and the haze (turbidity) according to JIS K7136 were determined.
<Birefringence: Δn>
Using an Abbe refractometer (Abbe 1T) manufactured by Atago Co., the refractive index in a direction (n _in ) parallel to the polyimide film surface and a direction (film thickness direction) (n _out ) perpendicular to the polyimide film surface is measured by an Abbe refractometer (using a sodium lamp, The wavelength was 589 nm), and the birefringence (Δn=n _in −n _out ) was determined from the difference between these refractive indices. The higher the birefringence value, the higher the degree of in-plane orientation of the polymer chains.

<Synthesis example 1>
A. Synthesis of TAHQ Tetracarboxylic acid dianhydride (TAHQ) represented by the following formula (6) was synthesized as follows. Into a round bottom flask, 12.6751 g (60.1940 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 a solution A. 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 to seal the septum to prepare a solution B. While cooling and stirring in an ice bath, Solution B was gradually added dropwise to Solution A by a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After the reaction was completed, the white precipitate was filtered off and washed with THF and ion-exchanged water. The removal of pyridine hydrochloride was confirmed by the addition of an aqueous silver nitrate solution to the washing solution and the disappearance of white precipitation. The washed product was collected and vacuum dried 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 of TAHQ The product was obtained by Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by JASCO Corporation) at 3082 cm ⁻¹ with an aromatic C—H stretching vibration absorption band, and with 1847 cm ⁻¹ and 1781 cm ⁻¹ an acid anhydride. A group C=O stretching vibration absorption band and an ester group C=O stretching vibration absorption band at 1742 cm ^-1 were confirmed.
In addition, 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), Attribution of 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) It was confirmed that the elemental analysis values were estimated C: 62.89%, H: 2.20%, actual measurement C: 62.69%, H: 2.42%, and the product was confirmed to be TAHQ. It was
When the melting point was measured by a differential scanning calorimeter DSC3100 (Netch Co.), a sharp melting peak was found at 272.4° C., suggesting that this product has high purity.

<Synthesis example 2>
A. Synthesis of tetracarboxylic dianhydride TAPh Tetracarboxylic dianhydride (TAPh) represented by the following formula (7) was synthesized as follows. To a recovery flask, 15.116 g (71.8 mmol) of trimellitic anhydride chloride was put, dissolved in 16.5 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealed with a septum to prepare a solution A. In another 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 to seal the septum to prepare a solution B. While cooling and stirring in an ice bath, Solution B was gradually added dropwise to Solution A by a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After the reaction was completed, the white precipitate was filtered off and washed with THF and ion-exchanged water. The removal of pyridine hydrochloride was confirmed by the addition of an aqueous silver nitrate solution to the washing solution and the disappearance of white precipitation. The washed product was collected and vacuum dried at 80° C. for 1 hour and then 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 of TAPh The product was obtained by Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by JASCO Corporation) at 3092,3065 cm ⁻¹ with an aromatic C—H stretching vibration absorption band, and at 1847 cm ⁻¹ and 1775 cm ⁻¹ with an acid. An anhydride group C=O stretching vibration absorption band and an ester group C=O stretching vibration absorption band at 1752 cm ^-1 were confirmed.
In addition, 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=7.8Hz, 1H), 8.29-8.32 (m, 1H), 8.50-8. .56 (m, 2H), 8.66-8.70 (m, 2H), and the elemental analysis values were estimated C: 67.42%, H: 2.64%, and measured C: 67. It was 49% and H:2.82%, and the product was confirmed to be TAPh.
When the melting point was measured by a differential scanning calorimeter DSC3100 (Netch Co.), it showed a sharp melting peak at 198.4° C., suggesting that this product has high purity.

<Example 1>
A. Synthesis of tetracarboxylic dianhydride TACHQ represented by formula (1) TACHQ represented by formula (1) was synthesized as follows. Into a round bottom flask, 12.7033 g (60.3137 mmol) of trimellitic anhydride chloride was put, dissolved in 33 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealed with a septum to prepare a solution A. In another flask, 3.8551 g (20.0661 mmol) of 2-cyclohexylhydroquinone (CHQ) was added with 6.5 mL of dehydrated THF and 9.7 mL (120 mmol) of pyridine to seal the septum to prepare a solution B.
While cooling and stirring in an ice bath, Solution B was gradually added dropwise to Solution A by a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After the reaction was completed, the white precipitate was filtered off and washed with THF and ion-exchanged water. The removal of pyridine hydrochloride was confirmed by the addition of an aqueous silver nitrate solution to the washing solution and the disappearance of white precipitation. 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 naturally cooled and allowed to stand for 72 hours. The precipitated white powder was filtered off and dried in vacuum 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 by 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 at ¹ and an ester group C=O stretching vibration absorption band at 1745 cm ^-1 .
In addition, 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=12Hz, 1H), 7.50-7.18(m, 3H), 8.33-8.29(m, 2H), 8.71-8.65. (M, 4H), the elemental analysis values were theoretical value C: 66.67%, H: 3.73%, measured value C: 66.27%, H: 3.78%, and the product was It was confirmed to be TACHQ.
When the melting point was measured by a differential scanning calorimeter DSC3100 (Netch Co.), a sharp melting peak was found at 229.1° C., suggesting that this product has high purity.

<Example 2>
A. Synthesis of polyimide of repeating unit represented by formula (8) (polymerization of polyamic acid) TACHQ/TFMB
3 mmol of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved in dehydrated N,N-dimethylacetamide (DMAc). 3 mmol of TACHQ powder described in Example 1 was slowly added thereto, and the mixture was 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 intrinsic viscosity of the obtained polyamic acid was 1.72 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 2.8 mL (30 mmol) of acetic anhydride and 1.2 mL (15 mmol) of pyridine was stirred with stirring. The mixture was slowly added dropwise at room temperature, and the mixture was further stirred for 24 hours after completion of the addition. The resulting polyimide solution was slowly dropped into a large amount of methanol to precipitate the polyimide. The obtained 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 (δ=about 13 ppm) and NHCO protons (δ=about 11 ppm) peculiar to polyamic acid were not observed. It was suggested that the chemical reaction was completed. The intrinsic viscosity of the obtained polyimide was 2.55 dL/g, which was a high molecular weight substance. Table 1 shows the solubility of the polyimide powder in the solvent. It can be seen from Table 1 that the solvent solubility is excellent.

B. Preparation of Polyimide Solution and Formation of Polyimide Film The above polyimide powder was redissolved in γ-butyrolactone (GBL) while heating to prepare a uniform solution of 6.0% by weight. This polyimide solution was cast on a glass substrate and dried in a hot air dryer at 80° C. for 2 hours. Then, the 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 again heat-treated in vacuum at 200° C. for 1 hour to remove residual strain.
The infrared absorption spectrum of the obtained polyimide film is shown in FIG. 1, the dynamic viscoelastic curve is shown in FIG. 2, and the thermal and optical characteristics are shown in Table 2. It can be identified from FIG. 1 that the target polyimide. It can be seen from FIG. 2 that a sharp decrease in storage elastic modulus is observed at around 225° C., indicating high thermoplasticity. From Table 2, it can be seen that the film has a low coefficient of linear thermal expansion (CTE) of 11.9 ppm/K and is a colorless transparent film. These excellent properties are an effect of the structure of formula (2).

<Example 3>
A. Synthesis of polyimide of 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). 2.4 mmol of the TACHQ powder described in Example 1 and 0.6 mmol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) powder described in Example 1 were slowly added thereto, and the mixture was stirred at room temperature for 72 hours, and DMAc was appropriately added. Polyamic acid, which is a polyimide precursor, was obtained (solid content concentration 22.7% by weight). The intrinsic viscosity of the obtained polyamic acid was 0.91 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 2.8 mL (30 mmol) of acetic anhydride and 1.2 mL (15 mmol) of pyridine was stirred with stirring. The mixture was slowly added dropwise at room temperature, and the mixture was further stirred for 24 hours after completion of the addition. The resulting polyimide solution was slowly dropped into a large amount of methanol to precipitate the polyimide. The obtained 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 (δ=about 13 ppm) and NHCO protons (δ=about 11 ppm) peculiar to polyamic acid were not observed. It was suggested that the chemical reaction was completed. The intrinsic viscosity of the obtained polyimide was 1.75 dL/g, which was a high molecular weight substance. Table 1 shows the solubility of the polyimide powder in the solvent. It can be seen from Table 1 that the solvent solubility is excellent.

B. Preparation of Polyimide Solution and Formation of Polyimide Film The above polyimide powder was redissolved in cyclopentanone (CPN) while being heated to prepare a uniform solution of 8.0% by weight. This polyimide solution was cast on a glass substrate and dried by a hot air dryer at 60° C. for 2 hours. Then, the 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 again heat-treated in vacuum at 200° C. for 1 hour to remove residual strain. The infrared absorption spectrum of the obtained polyimide film is shown in FIG. 3, the dynamic viscoelastic curve is shown in FIG. 4, and the thermal and optical characteristics are shown in Table 2. It can be identified from FIG. 3 that the target polyimide. It can be seen from FIG. 4 that a sharp decrease in storage elastic modulus is observed at around 225° C., indicating high thermoplasticity. From Table 2, it can be seen that the film has a low coefficient of linear thermal expansion (CTE) of 24.7 ppm/K and is a colorless and transparent film. These excellent properties are an effect of the structure of formula (2).

<Example 4>
A. Synthesis of polyimide of 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). 1.0 mmol of TACHQ powder and 1.0 mmol of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) powder described in Example 1 were slowly added thereto, and the mixture was stirred at room temperature for 72 hours, and DMAc was appropriately added. In addition, a polyamic acid as a polyimide precursor was obtained (solid content concentration 30% by weight).
The intrinsic viscosity of the obtained polyamic acid was 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 stirred while stirring the solution. The mixture was slowly added dropwise at room temperature, and the mixture was further stirred for 24 hours after completion of the addition. The resulting polyimide solution was slowly dropped into a large amount of methanol to precipitate the polyimide. The obtained 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 (δ=about 13 ppm) and NHCO protons (δ=about 11 ppm) peculiar to polyamic acid were not observed. It was suggested that the chemical reaction was completed. 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 excellent.

B. Preparation of polyimide solution and formation of polyimide film The above polyimide powder was redissolved in cyclopentanone (CPN) at room temperature to prepare a uniform solution of 23% by weight. This polyimide solution was cast on a glass substrate and dried by a hot air dryer at 60° C. for 2 hours. Then, the 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 again heat-treated in vacuum at 200° C. for 1 hour to remove residual strain.
The infrared absorption spectrum of the obtained polyimide film is shown in FIG. 5, the dynamic viscoelastic curve is shown in FIG. 6, and the thermal and optical characteristics are shown in Table 2. From FIG. 5, it can be identified that the target polyimide. It can be seen from FIG. 6 that a sharp decrease in storage elastic modulus is observed at around 230° C., high thermoplasticity is exhibited, and further from Table 2 that the film is colorless and transparent.

<Comparative Example 1>
A. Synthesis of polyimide of repeating unit represented by the following formula (11) (polymerization of polyamic acid) TAPh(100)/TFMB
3 mmol of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was dissolved in dehydrated N-methyl-2-pyrrolidone (NMP). 3 mmol of TAPh powder described in Synthesis Example 2 was slowly added thereto 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. Then, the substrate was heat-imidized in vacuum at 250° C. for 1 hour and 350° C. for 1 hour, and then the polyimide film was peeled from the glass substrate. This polyimide film was again heat-treated in vacuum at 200° C. for 1 hour to remove residual strain.
Table 2 shows the thermal and optical characteristics of the obtained polyimide film. From Table 2, it can be seen that the light transmittance is low, and that there is severe yellowing and cloudiness. It is considered that since the cyclohexyl group in the polyimide of the repeating unit of formula (8) was changed to a phenyl group, the optical properties of the polyimide film of the repeating unit of formula (11) were significantly deteriorated. In other words, it can be seen that the cyclohexyl group structure is extremely useful even if it has the same bulky structure.

<Comparative example 2>
A. Synthesis of polyimide of repeating unit represented by formula (12) (polymerization of polyamic acid) TAHQ/TFMB
2 mmol of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved in dehydrated N,N-dimethylacetamide (DMAc). 2 mmol of TAHQ powder described in Synthesis Example 1 was slowly added thereto, and the mixture was 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% by weight). The intrinsic viscosity of the obtained polyamic acid was 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 stirred while stirring the solution. The solution was slowly added dropwise at room temperature, and the fluidity of the solution disappeared and gelled 3 hours after the completion of the addition. From the comparison of the polyimides of the repeating units of the formulas (8) and (12), it can be seen that the bulky cyclohexyl group extremely enhances the solubility in the solvent.

B. Formation of Polyimide Film The above polyamic acid solution was cast onto a glass substrate and dried at 60° C. for 2 hours with a hot air dryer. Then, the substrate was heat-imidized in vacuum 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 again heat-treated in vacuum at 300° C. for 1 hour to remove residual strain.
The dynamic viscoelastic curve of the obtained polyimide film is shown in FIG. 7, and the thermal and optical characteristics are shown in Table 2. It can be seen from FIG. 7 that the temperature at which the decrease in storage elastic modulus starts is as high as 375° C., and thus the thermal processability is inferior to the polyimide of the repeating unit of the formula (8). The yellowness and haze are also high, and the optical properties are inferior.
That is, it can be seen that the cyclohexyl group of formula (2) plays an extremely important role.

Claims (5)

The following formula (1):
The tetracarboxylic dianhydride represented by. Formula (2) below:
A polyimide having a repeating unit represented by: Content 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. It is a polyimide solution containing the polyimide of Claim 2 or 3, and an organic solvent, Comprising: Solid content concentration is 5 weight% or more, The polyimide solution characterized by the above-mentioned. The polyimide molded body according to claim 2 or 3.