KR102591070B1 - Novel tetracarboxylic dianhydride, polyimide derived from said tetracarboxylic dianhydride, and molded article produced from said polyimide - Google Patents

Abstract

A polyimide derived from a novel tetracarboxylic dianhydride that has excellent solubility in various types of organic solvents, has excellent processability because it is also thermoplastic, and has a low coefficient of linear thermal expansion and high light transmittance (transparency). and provision of molded articles of the polyimide. The above problem can be solved by a polyimide derived from tetracarboxylic dianhydride represented by the following formula (1).
[Formula 1]

Description

Novel tetracarboxylic dianhydride, polyimide derived from the tetracarboxylic dianhydride, and molded article made of the polyimide {Novel tetracarboxylic dianhydride, polyimide derived from said tetracarboxylic dianhydride, and molded article produced from said polyimide}

The present invention relates to a novel polyimide derived from tetracarboxylic dianhydride, which has excellent processability, a low linear thermal expansion coefficient, and high light transmittance (transparency), and a molded article made of the polyimide. Since this polyimide exhibits not only excellent solution processability but also thermoplasticity, it can be melt-molded as well as film-formed by the solution casting method. In addition, the molded body made of this polyimide exhibits a lower coefficient of linear thermal expansion compared to conventional solvent-soluble polyimide or thermoplastic polyimide and is also excellent in transparency. From these characteristics, transparent substrates and transparent protective films used in liquid crystal displays (LCDs), organic electroluminescence (EL) displays, electronic papers, light-emitting diode (LED) devices, and solar cells require dimensional stability and transparency against heat. It is useful as a material and adhesive material.

Polyethylene terephthalate, polycarbonate, polyethersulfone, etc. are known as conventional transparent resins that can be molded and processed. These resins have excellent solution processability and melt moldability, but have large dimensional changes (coefficient of linear thermal expansion) against heat. If the linear thermal expansion coefficient as a molded body is large, various problems may occur when laminated with low thermal expansion inorganic materials used in display devices or lighting devices such as LCDs, organic EL displays, electronic papers, and LEDs, so it is not preferable. For example, by a thermal process when forming the transparent resin molded body and elements such as transparent electrodes (ITO; Indium Tin Oxide), wiring of copper, silver, aluminum, etc., or thin film transistors (TFT; Thin-Film Transistor), A mismatch in linear thermal expansion coefficient may occur between a low thermal expansion inorganic material and a conventional high thermal expansion resin, and deformation may occur at the interface, which may lead to interlayer separation, deformation of the substrate, and destruction of the device.

On the other hand, aromatic polyimide is known as a resin with excellent thermal dimensional stability. Molded articles made of aromatic polyimide with a rigid and linear chemical structure, for example polyimide film, are widely used in fields that require high dimensional stability (low linear thermal expansion coefficient), such as base films for flexible printed wiring boards and interlayer insulating films for semiconductors. . However, aromatic polyimide with a low linear thermal expansion coefficient is strongly colored due to intramolecular conjugation and intra- and intermolecular charge transfer interactions, so it is difficult to apply it to the above optical applications. In addition, because polyimide has very strong intermolecular forces, it often does not exhibit solubility in solvents and thermoplasticity, resulting in poor processability.

On the other hand, polyimide that overcomes these drawbacks has 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 tetracarboxylic dianhydride component that make up the polyimide, A method to increase transparency by suppressing conjugate and charge transfer interactions has been proposed (Non-Patent Documents 2 and 3). Although polyimides that achieve both transparency and solution processability have been developed through these prior technologies, there are limited reported examples of polyimides that have not only processability but also low thermal expansion properties.

As one of the few reported examples, a specific polyimide having an ester group is proposed (Patent Document 1). This polyimide has not only transparency and heat resistance, but also a low linear thermal expansion coefficient equivalent to that of inorganic materials, but its solubility in various types of organic solvents is not sufficient, so there is room for improvement in this respect.

Additionally, there is no known polyimide that has excellent processability and is also thermoplastic.

Japanese Patent Publication No. 2013-082876

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

The present invention is a polyimide derived from a novel tetracarboxylic dianhydride, which has excellent solubility in various types of organic solvents, has excellent processability because it is also thermoplastic, and has a low linear thermal expansion coefficient and high light transmittance ( The purpose is to provide a polyimide that also has transparency, and a molded article made of the polyimide.

In view of the above background technology, the present inventors have conducted extensive research and discovered that a polyimide with excellent processability was obtained from tetracarboxylic dianhydride represented by the following formula (1), making it a very useful material in the field. , the present invention has been completed.

The present invention is as follows.

1. Tetracarboxylic dianhydride represented by the following formula (1).

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

3. The polyimide according to 2, wherein the content of the repeating unit represented by the formula (2) is 55 mol% or more for all repeating units in the polyimide.

4. A polyimide solution containing the polyimide according to 2 or 3 and an organic solvent, characterized in that the solid content concentration is 5% by weight or more.

5. The polyimide molded body according to 2 or 3.

According to the present invention, properties that could not be obtained in the prior art, namely, excellent solubility in various types of organic solvents, excellent processability due to thermoplasticity, low linear thermal expansion coefficient, and high light transmittance (transparency) are all achieved. Polyimide and a molded article made of the polyimide are obtained by using tetracarboxylic dianhydride, which is characterized in that the central phenylene group is substituted with a bulky cyclohexyl group.

1 is a diagram showing the infrared absorption spectrum of the polyimide film of Example 2.
Figure 2 is a diagram showing the dynamic viscoelastic curve of the polyimide film of Example 2.
Figure 3 is a diagram showing the infrared absorption spectrum of the polyimide film of Example 3.
Figure 4 is a diagram showing the dynamic viscoelastic curve of the polyimide film of Example 3.
Figure 5 is a diagram showing the infrared absorption spectrum of the polyimide film of Example 4.
Figure 6 is a diagram showing the dynamic viscoelastic curve of the polyimide film of Example 4.
Figure 7 is a diagram showing the dynamic viscoelastic curve of the polyimide film of Comparative Example 2.

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

[Formula 1]

The chemical structural characteristic of tetracarboxylic dianhydride (hereinafter sometimes abbreviated as TACHQ) represented by Formula 1 of the present invention is that two phthalic anhydride structures are formed at the para position of the central phenylene group through an ester bond. It is bonded, and a bulky cyclohexyl group is substituted on the central phenylene group.

The method for synthesizing TACHQ represented by Formula 1 of the present invention is not particularly limited, but for example, a diol represented by Formula 3 below, that is, cyclohexylhydroquinone or its diacetate form and trimellitic acid represented by Formula 4 below, or It is synthesized from its derivatives by a known esterification reaction.

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

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

[Formula 2]

The first characteristic of the polyimide having a repeating unit represented by Formula 2 of the present invention is that two ester bonds exist in the para position of the central phenylene group in the tetracarboxylic dianhydride portion, and a bond is bonded in the para position in the diamine portion. Because it has a biphenylene structure, the polyimide main chain structure forms a straight and rigid structure. Due to this characteristic, the polyimide chains are highly oriented along the film plane direction (in-plane orientation), and it is believed that excellent thermal dimensional stability (low linear thermal expansion coefficient) is exhibited. However, low thermal expansion polyimide, which has such a straight and rigid structure, usually does not dissolve or melt in organic solvents due to the strong cohesion between polyimide chains, and thus lacks processability. Accordingly, in general, there is a method of bending the polyimide main chain structure by introducing a siloxane bond, an ether bond, and a meta bond into the polyimide main chain, a method of reducing the concentration of imide groups in the polyimide repeating unit, and a method of adding a bulky substituent to the polyimide side chain. A method of increasing processability by introducing a weakening of the cohesion between polyimide chains is adopted. However, these methods inhibit the in-plane orientation of the polyimide molded body, especially the film, and consequently increase the coefficient of linear thermal expansion. In other words, it is very difficult to achieve both processability and low thermal expansion properties.

Accordingly, it becomes possible to solve this problem by the second feature described below of the polyimide having a repeating unit represented by the formula (2) of the present invention. That is, by substituting a bulky cyclohexyl group on the central phenylene group of the tetracarboxylic dianhydride site and also substituting an electron-withdrawing and bulky trifluoromethyl group on the side chain of the diamine site, the in-plane between polyimide chains It can only weaken cohesion without impairing orientation. Polyimide, which has a repeating unit represented by Chemical Formula 2, which achieves this exquisite balance, has excellent solubility in various types of organic solvents, and also has thermoplasticity, so it has excellent processability and low linear thermal expansion, which was originally difficult to achieve. coefficient, and furthermore, the charge transfer interaction of polyimide is suppressed, making it possible to realize high transparency.

The polyimide having the repeating unit represented by Formula 2 of the present invention can be synthesized using TACHQ represented by Formula 1 as a raw material and having the excellent properties described above. There are no particular limitations on the production method of this polyimide, but for example, TACHQ represented by the formula (1) and 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as TFMB) represented by the following formula (5) as a diamine. It can be produced through a process of reacting with (sometimes abbreviated) to obtain a polyimide precursor (polyamic acid) having a repeating unit represented by Formula 2 and a process of imidizing the polyamic acid.

[Formula 2]

[Formula 1]

When polymerizing polyamic acid, an aromatic or aliphatic tetracarboxylic dianhydride other than TACHQ represented by Formula 1 can be used together as a copolymerization component to the extent that the polymerization reactivity and the required properties of the polyimide are not significantly impaired.

The aromatic tetracarboxylic dianhydride that can be used at this time is not particularly limited, but examples include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and hydroquinone-bis(tri). mellitate anhydride), methylhydroquinone-bis(trimellitate anhydride), 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic 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, and 2,2'-bis(3,4-dicarboxyphenyl)propanoic acid dianhydride.

There are no particular limitations on the aliphatic tetracarboxylic dianhydride, but examples of alicyclic dianhydrides include bicyclo [2. 2. 2] Octo-7-N-2,3,5,6-tetracarboxylic dianhydride, 5-(dioxotetrahydrofuryl-3-methyl-3-cyclohexene-1,2-dicarboxyl 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 dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentane Examples include tetracarboxylic dianhydride, etc. It is also possible to use two or more types of these in combination.

From the viewpoint of further improving the solubility, heat resistance, and transparency of polyimide, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (hereinafter sometimes abbreviated as 6FDA) was used to develop additional low thermal expansion properties of polyimide molded products. From this point of view, tetracarboxylic dianhydrides having a rigid and linear structure, namely pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride, are preferred as copolymerization components.

When aromatic or aliphatic tetracarboxylic dianhydrides other than TACHQ represented by Formula 1 are used together as copolymerization components, the ratio of TACHQ to all tetracarboxylic dianhydrides is preferably 55 mol% or more, more preferably It may be 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 90 mol% or more.

When polymerizing the polyamic acid of the present invention, aromatic or aliphatic diamines other than TFMB represented by the formula (5) can be used together as a copolymerization component to the extent that the polymerization reactivity and the required properties of the polyimide are not significantly impaired.

The aromatic diamine that can be used at this time is not particularly limited, but examples 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(2,6-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-amino) Phenoxy)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, etc. are mentioned.

In addition, aliphatic diamines include chain aliphatic to alicyclic diamines, and alicyclic diamines are not particularly limited, but examples include 4,4'-methylenebis(cyclohexylamine), isophorone diamine, and trans-1,4-diamino. Cyclohexane, 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, chain aliphatic The diamine is not particularly limited, but examples include 1,3-propanediamine, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1 , 8-octamethylenediamine, 1,9-nonamethylenediamine, diaminosiloxane, etc. It is also possible to use two or more of these together.

The solvent used during the polymerization reaction is preferably an aprotic solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, or dimethyl sulfoxide. The raw material monomer and Once the resulting polyamic acid and imidized polyimide are dissolved, any solvent can be used without any problem, and the solvent structure 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- Ester solvents such as valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ-butyrolactone, butyl acetate, ethyl acetate, and isobutyl acetate, carbonate solvents such as ethylene carbonate and propylene carbonate, and diethylene. Glycol-based solvents such as glycol dimethyl ether, triethylene glycol, triethylene glycol dimethyl ether, phenol-based solvents such as phenol, m-cresol, p-cresol, o-cresol, 3-chlorophenol, and 4-chlorophenol, cyclopenta Ketone solvents such as rice paddy, cyclohexanone, acetone, methyl ethyl ketone, diisobutyl ketone, methyl isobutyl ketone, tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane, dibutyl ether, etc. Ether-based solvents and other general-purpose solvents include 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, butanol, ethanol, xylene, toluene, chlorobenzene, turpentine, mineral spirits, petroleum naphtha-based solvents, etc. can also be used, and two or more types of these can be mixed. It's okay too.

The polyimide of the present invention, which is very useful in the industry, can be obtained by performing a polyaddition reaction between TACHQ represented by Formula 1 and TFMB represented by Formula 5 to obtain polyamic acid, and then imidizing this.

The polyimide of the present invention has excellent solubility in various types of organic solvents when used as a polyimide resin due to its chemical structural characteristics such as the linearity and rigidity of the polymer main chain and the presence of bulky substituents in the side chains, and also has thermoplasticity. Because it has both properties, it has excellent processability, and the polyimide molded product, especially the film, can be made of a material that has both a low coefficient of linear thermal expansion 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 degree of entanglement between polymer chains may decrease, making the polyimide molded article vulnerable. There is no such concern because TACHQ of Chemical Formula 1 and TFMB of Chemical Formula 5 used in the present invention exhibit sufficiently high polymerization reactivity.

The method for producing the polyimide of the present invention is not particularly limited, and known methods can be appropriately applied. Specifically, it can be synthesized by, for example, the following method. First, TFMB of Formula 5 is dissolved in a polymerization solvent, and TFMB of Formula 5 and substantially equimolar TACHQ powder of Formula 1 are gradually added to this solution, and the mixture is stirred in the range of 0 to 100° C. using a mechanical stirrer, etc. is stirred at 20 to 60°C for 0.5 to 150 hours, preferably 1 to 48 hours. At this time, 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 performing polymerization in this monomer concentration range, a polyamic acid with a uniform and high degree of polymerization can be obtained. If the degree of polymerization of the polyamic acid increases too much and the polymerization solution becomes difficult to stir, it is also possible to dilute it with the same solvent as appropriate. From the viewpoint of the toughness of the polyimide molded body, it is preferable that the degree of polymerization of the polyamic acid is as high as possible. By performing polymerization in the above monomer concentration range, the polymerization degree is sufficiently high and the solubility of the monomer and polymer can also be sufficiently ensured. If 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 if polymerization is performed at a concentration higher than the above monomer concentration range, dissolution of the monomer or the resulting polymer may become insufficient. In addition, when aliphatic diamine is used, salt formation often occurs in the early stages of polymerization, hindering polymerization. In order to increase the degree of polymerization as much as possible while suppressing salt formation, it is desirable to manage the monomer concentration during polymerization within the above-mentioned preferable concentration range. do.

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, the chemical imidization method of imidizing polyamic acid using a dehydration cyclization reagent, polymerizing polyamic acid in a high boiling point solvent and then heating it to 150°C or higher in the presence of an azeotrope such as xylene, resulting in water by-produced. A film-shaped molded body of polyamic acid obtained by removing a polyimide with a high degree of polymerization in a solution state by removing it from the system, or by casting and drying a polyamic acid solution on a support such as a glass substrate. A thermal imidization method of imidizing by heating at 250°C or higher, preferably 300°C or higher, using a heating furnace or the like, may be included. In order to obtain a highly transparent polyimide molded body, among these imidization methods, the chemical imidization method, which allows 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 as the solvent used during polymerization. While stirring the polyamic acid solution diluted to an appropriate solution viscosity that is easy to stir with a mechanical stirrer, a dehydrating ring-closing agent (chemical imidizing agent) consisting of an anhydride of an organic acid and a tertiary amine as a basic catalyst is added dropwise to 0~ Imidization is completed chemically by stirring at 100°C, preferably 10 to 50°C, for 1 to 72 hours. The organic acid anhydride that can be used at this time is not particularly limited, but includes acetic anhydride, propionic anhydride, and the like. Acetic anhydride is preferably used because of the ease of handling and purification of the reagent. In addition, as a basic catalyst, pyridine, triethylamine, quinoline, etc. can be used. Pyridine is preferably used because of the ease of handling and separation of reagents, but is not limited to these. The amount of organic acid anhydride in the chemical imidizing agent is in the range of 1 to 10 times the mole of the theoretical dehydration amount of polyamic acid, and is more preferably 1 to 5 times the mole. Additionally, the amount of the basic catalyst is in the range of 0.1 to 2 times the mole relative to the amount of the organic acid anhydride, and more preferably in the range of 0.1 to 1 times the mole.

As described above, since by-products (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 purify the polyimide by removing these. For purification, known methods can be used. For example, in the simplest method, the imidized reaction solution is dropped dropwise into a large amount of poor solvent while stirring to precipitate the polyimide, and then the polyimide powder is recovered and washed repeatedly until the impurities are removed. A method of obtaining polyimide powder by drying under reduced pressure can be applied. The poor solvent that can be used at this time is not particularly limited as long as it can efficiently remove impurities by precipitating polyimide and is easy to dry, but for example, alcohols such as water, methanol, ethanol, and isopropanol are preferred, and these are preferred. You may mix and use them. If the concentration of the polyimide solution when deposited dropwise in a poor solvent is too high, the precipitated polyimide may become a lump of particles, and impurities may remain in the coarse particles, and the time required to dissolve the obtained polyimide powder in the solvent may increase. There are concerns that it may take a long time. On the other hand, excessively diluting the concentration of the polyimide solution is undesirable because a large amount of poor solvent is required, which increases the environmental load due to waste solvent treatment and increases manufacturing costs. Therefore, the concentration of the polyimide solution when dropped into a poor solvent is 20% by weight or less, more preferably 10% by weight or less. At this time, the amount of poor solvent used is preferably equal to or greater than that of the polyimide solution, and 5 to 100 times the amount is highly preferable. The obtained polyimide powder is recovered and the residual solvent is removed by vacuum drying, hot air drying, etc. There is no limit to the drying temperature and time as long as the polyimide is not deteriorated and the residual solvent is evaporated, and it is preferable to dry for 48 hours or less in the temperature range of 30 to 200 ° C.

The polyimide of the present invention has an intrinsic viscosity of preferably 0.1 to 10.0 dL/g, and more preferably 0.3 to 5.0 dL/g, from the viewpoint of the toughness of the polyimide molded body and the handleability of the solution. am.

Since the polyimide of the present invention is highly soluble in various types of organic solvents, the solvent can be selected according to the intended use or processing conditions. For example, in the case of continuous coating over a long period of time, there is a risk that the solvent in the polyimide solution will absorb moisture in the air and cause the polyimide to precipitate, so use a solvent such as triethylene glycol dimethyl ether, γ-butyrolactone, or cyclopentanone. It is preferable to use a low hygroscopic solvent. Therefore, the polyimide of the present invention can be selected from various solvents or mixed solvents that exhibit low hygroscopicity. The low hygroscopic solvent used is not particularly limited, but examples include γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone. Ester solvents such as lactone, butyl acetate, ethyl acetate, and isobutyl acetate, carbonate solvents such as ethylene carbonate and propylene carbonate, glycol-based solvents such as diethylene glycol dimethyl ether, triethylene glycol, and triethylene glycol dimethyl ether, phenol, m Phenolic solvents such as -cresol, p-cresol, o-cresol, 3-chlorophenol, 4-chlorophenol, cyclopentanone, cyclohexanone, acetone, methyl ethyl ketone, diisobutyl ketone, methyl isobutyl ketone, etc. ketone-based solvents, ether-based solvents such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane, and dibutyl ether, and other general-purpose solvents such as acetophenone and 1,3-dimethyl-2-imida. Zolidinone, 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, turpentine, mineral spirits, petroleum naphtha-based solvents, etc. can also be used, and two or more types of these can be mixed. In addition, even if it is an amide solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, or N-methyl-2-pyrrolidone, which is a hygroscopic solvent, precipitation of polyimide by moisture absorption occurs when mixed with the low hygroscopic solvent. It is also possible to suppress.

The solid content concentration when the polyimide of the present invention is dissolved in a solvent to form a solution varies depending 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 becomes difficult to form a film with 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 polyimide powder of the present invention is added in the air or in an inert gas at a temperature range from room temperature to the boiling point of the solvent or less. It can be dissolved over 48 hours to form a polyimide solution.

Additionally, additives such as release agents, fillers, dyes, pigments, silane coupling agents, crosslinking agents, end capping agents, antioxidants, antifoaming agents, and leveling agents may be added to the polyimide of the present invention as needed.

The obtained polyimide solution can be formed into a film by a known method to form a polyimide molded body or film. For example, the polyimide solution is spread on a support such as a glass substrate using a doctor blade, etc., and is dried using a hot air dryer, infrared dryer, vacuum dryer, inner oven, etc., usually in the range of 40 to 300°C, preferably. A polyimide film can be formed by drying in the range of 50 to 250°C.

Example

The present invention will be described in detail below by way of examples, but is not limited to these examples.

In addition, the physical properties in the examples below were measured by the following method.

＜Infrared absorption spectrum＞

The infrared absorption spectrum of tetracarboxylic dianhydride was measured by the KBr transmission method using a Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by Nippon Spectrophotometer). Additionally, the infrared absorption spectrum of the polyimide thin film was measured using a transmission method.

＜ ^1H -NMR spectrum＞

The ¹ H-NMR spectrum of tetracarboxylic dianhydride and chemically imidized polyimide powder in deuterated dimethyl sulfoxide was measured using a Fourier transform nuclear magnetic resonance spectrophotometer JNM-ECP400 (manufactured by JEOL).

＜Differential scanning calorimetry (melting point)＞

The melting point of tetracarboxylic dianhydride was measured using a differential scanning calorimeter DSC3100 (Nechi) in a nitrogen atmosphere at a temperature increase 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 Oswald viscometer. This value was regarded as the intrinsic viscosity.

＜Solubility test of polyimide powder in organic solvents＞

For 10 mg of polyimide powder, 1 g (solid concentration 1% by weight) of the organic solvent shown in Table 1 was added to a sample tube, stirred for 5 minutes using a test tube mixer, and the dissolution state was visually confirmed. Solvents include chloroform (CF), acetone, tetrahydrofuran (THF), 1,4-dioxane (DOX), ethyl acetate, cyclopentanone (CPN), cyclohexanone (CHN), and 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) was used.

The evaluation results were indicated as ++ when dissolved at room temperature, + when dissolved by heating and maintaining uniformity even after cooling to room temperature, ± when swollen/partially dissolved, and - when not dissolved.

＜Glass transition temperature: T _g , thermoplastic＞

Using a dynamic viscoelasticity measuring device (Q800) manufactured by TA Instruments, 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 temperature increase rate of 5°C/min. In addition, thermoplasticity was evaluated from the steepness of the decline in the storage modulus curve immediately after the glass transition temperature.

＜Coefficient of linear thermal expansion: CTE＞

The linear thermal expansion coefficient of the polyimide film was determined using TMA4000 manufactured by Nechi (sample size width 5 mm, length 15 mm), the load was set to film thickness (μm) x 0.5 g, and the temperature was raised to 150°C at 5°C/min. After (the first temperature increase), it was cooled to 20°C, and the temperature was further raised at 5°C/min (the second temperature increase), and the temperature was calculated from the TMA curve at the second temperature increase. The linear thermal expansion coefficient was obtained as the average value between 100 and 200°C.

＜Transmittance of polyimide film: T ₄₀₀ ＞

The light transmittance at 200-700 nm of polyimide film (20 ㎛ thickness) was measured using an ultraviolet-visible/near-infrared spectrophotometer (V-650) manufactured by Nippon Spectrophotometer, and the light transmittance at a wavelength of 400 nm was measured. It was used as an indicator of transparency. Additionally, the wavelength (cutoff wavelength) at which the transmittance is 0.5% or less was also determined.

＜Yellowness Index：YI＞

Using an ultraviolet-visible spectrophotometer V-530 (manufactured by Nippon Spectrophotometer), the light transmittance (T%) of the polyimide film at a wavelength of 380 to 780 nm was measured using the VWCT-615 type color diagnostic program (manufactured by Nippon Spectrophotometer). The yellowness (YI) was calculated based on JISK77373.

＜Total light transmittance and haze＞

Using Haze Meter NDH4000 (manufactured by Nippon Denshoku Industries), the total light transmittance of the polyimide film based on JISK7361 and the haze (turbidity) based on JISK7136 were determined.

＜Double refraction: Δn＞

Using an Abbe refractometer (Abbe 1T) manufactured by Atago, the refractive index in the direction parallel to the polyimide film surface (n _in ) and the direction perpendicular to the film thickness (n _out ) was measured using an Abbe refractometer (using a sodium lamp, wavelength 589 nm). ) was measured, and the birefringence (Δn=n _in -n _out ) was obtained from the difference in these refractive indices. A higher birefringence value means a higher degree of in-plane orientation of the polymer chain.

<Synthesis Example 1>

A. Synthesis of TAHQ

Tetracarboxylic dianhydride (TAHQ) represented by the following formula (6) was synthesized as follows. Solution A was prepared by adding 12.6751 g (60.1940 mmol) of anhydrous trimellitic acid chloride to a eggplant-shaped flask, dissolving it in 33 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealing it with a septum. Additionally, in a separate 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 and sealed with a septum to prepare solution B. While cooling and stirring in an ice bath, solution B was slowly added dropwise to solution A using a syringe over about 5 minutes, and then stirred at room temperature for 24 hours. After completion of the reaction, the white precipitate was separated by filtration and washed with THF and ion-exchanged water. Removal of pyridine hydrochloride was confirmed by adding an aqueous solution of silver nitrate to the cleaning solution so that no white precipitate was visible. The washed product was recovered and vacuum dried at 100°C for 12 hours. The obtained product was a white powder, the quantity was 8.0287 g, and the yield was 87.6%.

B. TAHQ’s Sympathy

The product was measured using a Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by Nippon Spectrophotometer), showing an aromatic CH stretching vibration absorption band at 3082 cm ^-1 , an acid anhydride group C=O stretching vibration absorption band at 1847 cm ^-1 and 1781 cm ^-1 , and 1742 The ester group C=O stretching vibration absorption band was confirmed at 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): 7.54 (s, 4H), 8.30 (d, J = 7.9Hz, 2H), 8.65 (sd, J = 0.72Hz, 2H), 8.67 (dd, J = 8.0Hz, 1.3Hz, 2H), and the elemental analysis values are estimated values C: 62.89%, H: It was confirmed that the actual values were 2.20%, C: 62.69%, H: 2.42%, and the product was TAHQ.

Additionally, the melting point was measured using a differential scanning calorimeter DSC3100 (Nechi), and 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

Tetracarboxylic dianhydride (TAPh) represented by the following formula (7) was synthesized as follows. Solution A was prepared by adding 15.1116 g (71.8 mmol) of anhydrous trimellitic acid chloride to a eggplant-shaped flask, dissolving it in 16.5 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealing it with a septum. Additionally, in a separate flask, 6.2721 g (34 mmol) of 2-phenylhydroquinone was added to 23.5 mL of dehydrated THF and 8.7 mL (108 mmol) of pyridine and sealed with a septum to prepare solution B. While cooling and stirring in an ice bath, solution B was slowly added dropwise to solution A using a syringe over about 5 minutes, and the solution was then stirred at room temperature for 24 hours. After completion of the reaction, the white precipitate was separated by filtration and washed with THF and ion-exchanged water. Removal of pyridine hydrochloride was confirmed by adding an aqueous solution of silver nitrate to the cleaning solution so that no white precipitate was visible. The washed product was recovered and vacuum dried at 80°C for 1 hour and further at 100°C for 12 hours. The obtained product was a white powder, the quantity was 17.93 g, and the yield was 98.7%.

B. Identification of TAPh

The product was measured using a Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by Nippon Spectrophotometer), with aromatic C-H stretching vibration absorption bands at 3092 and 3065 cm ^-1 , and acid anhydride group C=O stretching at 1847 cm ^-1 and 1775 cm ^-1. Vibration absorption band, ester group C=O stretching vibration absorption band was confirmed at 1752 cm ^-1 .

Additionally, as a result of ¹ H-NMR measurement using Fourier transform nuclear magnetic resonance spectrophotometer JNM-ECP400 (manufactured by JEOL), (DMSO-d ₆ , δ, ppm): 7.30-7.40 (m, 3H), 7.55- It is attributed to 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), element The analysis values were estimated values of C: 67.42%, H: 2.64%, actual values of C: 67.49%, H: 2.82%, and the product was confirmed to be TAPh.

Additionally, the melting point was measured using a differential scanning calorimeter DSC3100 (Nechi), and 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. Solution A was prepared by adding 12.7003 g (60.3137 mmol) of anhydrous trimellitic acid chloride to a eggplant-shaped flask, dissolving it in 33 mL of dehydrated tetrahydrofuran (THF) at room temperature, and sealing it with a septum. Additionally, in a separate flask, 3.8551 g (20.0661 mmol) of 2-cyclohexylhydroquinone (CHQ), 6.5 mL of dehydrated THF, and 9.7 mL (120 mmol) of pyridine were added and sealed with a septum to prepare solution B.

While cooling and stirring in an ice bath, solution B was slowly added dropwise to solution A using a syringe over about 5 minutes, and the solution was then stirred at room temperature for 24 hours. After completion of the reaction, the white precipitate was separated by filtration and washed with THF and ion-exchanged water. Removal of pyridine hydrochloride was confirmed by adding an aqueous solution of silver nitrate to the cleaning solution so that no white precipitate was visible. The washed crude product was recovered and dried under vacuum at 100°C for 12 hours. The obtained crude product was a white powder, the quantity was 6.54 g, and the yield was 87.6%.

(refine)

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, then allowed to cool naturally and left to stand for 72 hours. The precipitated white powder was filtered and dried under 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%.

[Formula 1]

B. Sympathy of TACHQ

The product purified by recrystallization was measured by Fourier transform infrared spectrophotometer FT/IR4100 (manufactured by Nippon Spectrophotometer), showing an aliphatic C-H stretching vibration absorption band at 2928 cm ^-1 and an acid anhydride group C at 1861 cm ^-1 and 1778 cm ^-1 . =O stretching vibration absorption band, ester group C=O stretching vibration absorption band was confirmed at 1745 cm ^-1 .

Additionally, as a result of ¹ H-NMR measurement using 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), and the elemental analysis values are theoretical value C: 66.67%, H: 3.73%, actual value C: 66.27%, H: 3.78%, and the product was confirmed to be TACHQ.

In addition, the melting point was measured using a differential scanning calorimeter DSC3100 (Nechi) and showed a sharp melting peak at 229.1°C, suggesting that this product was of high purity.

<Example 2>

A. Synthesis of polyimide of the 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 the TACHQ powder described in Example 1 was slowly added here, stirred at room temperature for 72 hours, and DMAc was added appropriately to obtain polyamic acid, 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)

After diluting the obtained polyamic acid solution with dehydrated DMAc to a solid content concentration of about 10.0% by weight, a mixed solution of 2.8 mL (30 mmol) acetic anhydride and 1.2 mL (15 mmol) pyridine was slowly added dropwise while stirring. and stirred for an additional 24 hours after the dropwise addition was completed. The obtained polyimide solution was slowly added dropwise to a large amount of methanol to precipitate polyimide. The obtained white precipitate was thoroughly washed with methanol and dried under vacuum at 100°C for 12 hours. As a result of ¹ H-NMR measurement on the obtained fibrous polyimide powder, COOH protons (near δ = 13 ppm) and NHCO protons (near δ = 11 ppm), which are characteristic of polyamic acid, were not observed, indicating a chemical image. It was suggested that the dehydration reaction was complete. The obtained polyimide had an intrinsic viscosity of 2.55 dL/g and was a high molecular weight material. Additionally, the solubility of polyimide powder in solvents is shown in Table 1. From Table 1, it can be seen that it exhibits excellent solvent solubility.

B. Preparation of polyimide solution and film formation of polyimide film

The polyimide powder was re-dissolved in γ-butyrolactone (GBL) while heating to prepare a 6.0% by weight homogeneous solution. This polyimide solution was spread on a glass substrate and dried in a hot air dryer at 80°C for 2 hours. After that, the entire 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.

The infrared absorption spectrum of the obtained polyimide film is shown in Figure 1, the dynamic viscoelastic curve is shown in Figure 2, and the thermal and optical properties are shown in Table 2. From Figure 1, it can be identified that it is the target polyimide. From Figure 2, it can be seen that a sharp decrease in storage modulus is observed around 225°C, indicating high thermoplasticity. From Table 2, it can be seen that the coefficient of linear thermal expansion (CTE) is low at 11.9 ppm/K and that it is a colorless and transparent film. Their excellent properties are an effect of the structure of Chemical Formula 2.

<Example 3>

A. Synthesis of polyimide with 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). Here, 2.4 mmol of TACHQ powder and 0.6 mmol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) powder described in Example 1 were slowly added and stirred at room temperature for 72 hours, and DMAc was added as appropriate. By addition, polyamic acid, 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)

After diluting the obtained polyamic acid solution with dehydrated DMAc to a solid content concentration of about 10.0% by weight, a mixed solution of 2.8 mL (30 mmol) acetic anhydride and 1.2 mL (15 mmol) pyridine was slowly added dropwise while stirring. and stirred for an additional 24 hours after the dropwise addition was completed. The obtained polyimide solution was slowly added dropwise to a large amount of methanol to precipitate polyimide. The obtained white precipitate was thoroughly washed with methanol and dried under vacuum at 100°C for 12 hours. As a result of ¹ H-NMR measurement on the obtained fibrous polyimide powder, COOH protons (near δ = 13 ppm) and NHCO protons (near δ = 11 ppm), which are characteristic of polyamic acid, were not observed, indicating a chemical image. It was suggested that the dehydration reaction was complete. The obtained polyimide had an intrinsic viscosity of 1.75 dL/g and was a high molecular weight material. Additionally, the solubility of polyimide powder in solvents is shown in Table 1. From Table 1, it can be seen that it exhibits excellent solvent solubility.

B. Preparation of polyimide solution and film formation of polyimide film

The polyimide powder was re-dissolved in cyclopentanone (CPN) while heating to prepare an 8.0% by weight homogeneous solution. This polyimide solution was spread on a glass substrate and dried with a hot air dryer at 60°C for 2 hours. After that, the entire substrate was dried in vacuum at 200°C for 1 hour and left 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. The infrared absorption spectrum of the obtained polyimide film is shown in Figure 3, the dynamic viscoelastic curve is shown in Figure 4, and the thermal and optical properties are shown in Table 2. From Figure 3, it can be identified that it is the target polyimide. From Figure 4, it can be seen that a sharp decrease in storage modulus is observed around 225°C, indicating high thermoplasticity. From Table 2, it can be seen that the coefficient of linear thermal expansion (CTE) is low at 24.7 ppm/K and that it is a colorless and transparent film. Their excellent properties are an effect of the structure of Chemical Formula 2.

<Example 4>

A. Synthesis of polyimide with 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). Here, 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 and stirred at room temperature for 72 hours, and DMAc was added as appropriate. By addition, polyamic acid, a polyimide precursor, was obtained (solid concentration 30% by weight). The intrinsic viscosity of the obtained polyamic acid was 0.56 dL/g.

(Chemical imidization reaction)

After diluting the obtained polyamic acid solution with dehydrated DMAc to a solid content concentration of about 10.0% by weight, a mixed solution of 1.9 mL (20 mmol) acetic anhydride and 0.8 mL (10 mmol) pyridine was slowly added dropwise while stirring. and stirred for an additional 24 hours after the dropwise addition was completed. The obtained polyimide solution was slowly added dropwise to a large amount of methanol to precipitate polyimide. The obtained white precipitate was thoroughly washed with methanol and dried under vacuum at 100°C for 12 hours. As a result of ¹ H-NMR measurement on the obtained fibrous polyimide powder, COOH protons (near δ = 13 ppm) and NHCO protons (near δ = 11 ppm), which are characteristic of polyamic acid, were not observed, indicating a chemical image. It was suggested that the dehydration reaction was complete. The intrinsic viscosity of the obtained polyimide was 0.76 dL/g. Additionally, the solubility of polyimide powder in solvents is shown in Table 1. From Table 1, it can be seen that it exhibits excellent solvent solubility.

B. Preparation of polyimide solution and film formation of polyimide film

The polyimide powder was re-dissolved in cyclopentanone (CPN) at room temperature to prepare a 23% by weight homogeneous solution. This polyimide solution was spread on a glass substrate and dried with a hot air dryer at 60°C for 2 hours. After that, the entire substrate was dried in vacuum at 200°C for 1 hour and left 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.

The infrared absorption spectrum of the obtained polyimide film is shown in Figure 5, the dynamic viscoelastic curve is shown in Figure 6, and the thermal and optical properties are shown in Table 2. From Figure 5, it can be identified that it is the target polyimide. From Figure 6, a steep decrease in storage elastic modulus is observed around 230°C, showing high thermoplasticity, and further, from Table 2, it can be seen that it is a colorless and transparent film.

<Comparative Example 1>

A. Synthesis of polyimide with a 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). Here, 3 mmol of the TAPh powder described in Synthesis Example 2 was slowly added and stirred at room temperature for 72 hours to obtain polyamic acid, a polyimide precursor (solid content concentration: 20% by weight). The intrinsic viscosity of the obtained polyamic acid was 1.6 dL/g.

B. Deposition of polyimide film

The polyamic acid solution was spread on a glass substrate and dried in a hot air dryer at 80°C for 3 hours. After that, the substrate was thermally imidized in a vacuum at 250°C for 1 hour and at 350°C for 1 hour, 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.

The thermal properties and optical properties of the obtained polyimide film are shown in Table 2. From Table 2, it can be seen that there is low light transmittance and severe yellowing and cloudiness. Since the cyclohexyl group in the polyimide of the repeating unit of Formula 8 was replaced with a phenyl group, the optical properties of the polyimide film of the repeating unit of Formula 11 are thought to have significantly deteriorated. In other words, even if the structure has the same large volume, it can be seen that the structure of the cyclohexyl group is very useful.

<Comparative Example 2>

A. Synthesis of polyimide of the 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 the TAHQ powder described in Synthesis Example 1 was slowly added here, stirred at room temperature for 72 hours, and DMAc was added appropriately to obtain polyamic acid, 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)

After diluting the obtained polyamic acid solution with dehydrated DMAc to a solid content concentration of about 10.0% by weight, a mixed solution of 1.9 mL (20 mmol) acetic anhydride and 0.8 mL (10 mmol) pyridine was slowly added dropwise while stirring. After the dropwise addition was completed, the fluidity of the solution was lost and gelled over an additional 3 hours. From a comparison of the polyimides of the repeating units of Formula 8 and Formula 12, it can be seen that the bulky cyclohexyl group greatly increases the solubility in solvents.

B. Deposition of polyimide film

The polyamic acid solution was spread on a glass substrate and dried in a hot air dryer at 60°C for 2 hours. After that, the substrate was thermally imidized in a vacuum at 200°C for 0.5 hours and at 250°C for 2 hours, and then the polyimide film was peeled from the glass substrate. This polyimide film was once again heat-treated at 300°C in vacuum for 1 hour to remove residual strain.

The dynamic viscoelasticity curve of the obtained polyimide film is shown in Figure 7, and the thermal properties and optical properties are shown in Table 2. From Figure 7, it can be seen that since the temperature at which the storage modulus decreases begins is as high as 375°C, the heat processability is inferior to that of the polyimide of the repeating unit of Chemical Formula 8. Additionally, the optical properties are poor due to high yellowness and haze.

In other words, it can be seen that the cyclohexyl group of Formula 2 has a very important function.

Claims (5)

Formula 1 below:
[Formula 1]

Tetracarboxylic dianhydride, represented by . delete delete delete delete