KR20150056779A - Polyimide and molded body thereof - Google Patents

Abstract

(화학식 중 R은 각각 독립적으로 수소 원자 또는 탄소 원자 수 1~6의 알킬기를 나타낸다. 단, 동일한 벤젠 고리에 결합하는 2개의 R 중 하나 이상은 알킬기이다.)An object of the present invention is to provide a polyimide having excellent transparency, high heat resistance and low coefficient of linear thermal expansion, exhibiting solvent processability (excellent solubility and film formability) by a low hygroscopic solvent, and a process for producing the same.
In order to solve the above problems, the polyimide of the present invention is characterized by containing a constituent unit represented by the following general formula (1).
[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

Description

TECHNICAL FIELD The present invention relates to a polyimide and a molded body thereof,

The present invention relates to a polyimide.

2. Description of the Related Art In the field of display devices such as liquid crystal displays, organic electroluminescence (EL) displays, and electronic papers, a transparent electrode (ITO), a thin-film transistor (TFT) An electrode or an electronic device is formed. In order to form these devices, high heat resistance and excellent dimensional stability (low linear thermal expansion coefficient) are required, so that it is difficult to apply a transparent material other than the glass substrate in the existing technology.

On the other hand, in recent years, there has been an increasing demand for lightweight and flexible display on these displays, making it difficult to cope with conventional glass substrates. As a substrate for replacing a glass substrate, more flexible and flexible resin substrates are attracting attention. However, a resin substrate having both high transparency, dimensional stability, heat resistance and excellent processability of a glass substrate is not known heretofore.

An engineering plastic is a candidate material for a resin substrate. However, polyether sulfone having the highest heat resistance among existing transparent engineering plastics has a glass transition temperature (Tg) of 225 DEG C, but has a problem in that it has a high linear thermal expansion coefficient.

On the other hand, there are wholly aromatic polyimides as materials having excellent properties such as high heat resistance, excellent dimensional stability, mechanical strength, insulation and flexibility, and these wholly aromatic polyimides are widely used in aerospace materials, heat resistant materials and electronic materials .

For example, polyimides obtained from ester group-containing tetracarboxylic dianhydrides and diamines represented by the following formulas (5) and (6) have been reported to exhibit high heat resistance and excellent dimensional stability (see Patent Document 1, Patent Document 2, 3).

However, many of the wholly aromatic polyimides including these polyimides are strongly colored due to intramolecular conjugates and intramolecular-molecular charge transfer interaction, making it difficult to realize transparency as high as that of glass.

Therefore, a polyimide having a high transparency by suppressing the coloring of the polyimide film has been proposed. For example, by introducing a fluorine atom into polyimide (see Non-Patent Document 1 and the like) or by using an alicyclic compound on one or both of the diamine component and the tetracarboxylic acid dianhydride component constituting the polyimide, A method of suppressing conjugation and charge transfer interaction to increase transparency has been proposed (see Patent Document 4, Patent Document 5, etc.).

However, the fluorine atom-introduced polyimide may have a high coefficient of linear thermal expansion. For example, it is known that the use of 4,4 '- (hexafluoroisopropylidene) diphthalic anhydride (hereinafter referred to as 6FDA) as the monomer improves the transparency of the polyimide film, but its coefficient of linear thermal expansion is very high Resulting in insufficient dimensional stability required for the device fabrication process. Therefore, when the above-mentioned fluorine-containing polyimide is used as a glass substitute substrate in this industrial field, a large coefficient of linear thermal expansion is generated between the electrode such as ITO and TFT formed on the polyimide film or between the electronic element and the polyimide film, There is a problem that the reliability of the electronic device is remarkably lowered.

Further, when a polyimide using an alicyclic compound as a diamine component, for example, a highly flexible alicyclic diamine such as 4,4'-methylenebis (cyclohexylamine) is used, a non-colored transparent polyimide film is obtained, And the coefficient of linear thermal expansion is increased. On the other hand, trans-1,4-diaminocyclohexane having a rigid structure as an alicyclic diamine was selected and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (hereinafter referred to as BPDA) Discloses a technique for producing a polyimide film having high transparency, a high glass transition temperature (345 占 폚), and a low thermal expansion coefficient (23 ppm / K) by combining a polyimide film (see Patent Document 6). However, this polyimide is insoluble in an organic solvent and therefore has a drawback that it lacks processability in solution.

As described above, many conventional polyimides are insoluble in organic solvents and it is not easy to mold and process the polyimide itself. For this reason, generally, tetramarboxylic acid dianhydride and diamine are equimolarly reacted in an aprotic polar solvent such as N-methyl-2-pyrrolidone (NMP) to polymerize a polyimide precursor (polyamide acid) The polyamic acid solution is cast on a substrate and dried to form a polyamic acid film, followed by heating and dehydrating ring closure (thermal imidization) at 300 ° C or higher to prepare a polyimide film.

However, thermal imidization at a high temperature is one of the factors causing the film to be colored. It is not suitable for applications requiring high transparency, and also causes residual deformation in the film due to large reaction shrinkage occurring at the time of thermal imidization, There is also a possibility of causing warpage. In addition, there is also a problem that haze due to film defects or bubbles is liable to occur due to the by-produced water at the time of thermal imidization.

Thus, a solvent-soluble polyimide has been proposed in order to avoid thermal imidization at a high temperature (see Patent Document 7, etc.). For example, it is possible to use 6FDA, 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride or the like as the tetracarboxylic acid dianhydride, 1,3-bis (3-aminophenoxy ) Benzene or bis [4- (3-aminophenoxy) phenyl] sulfone and the like show solubility in amide-based solvents and the like. The solvent-soluble polyimide commonly has a bending structure such as isopropylidene, sulfone, ether, or meta bond, or a bulky substituent represented by a trifluoromethyl group, thereby preventing aggregation or crystallization of the polyimide chain As a result, the solvent molecules are likely to penetrate between the polyimide chains.

In order to prepare these soluble polyimides, tetracarboxylic dianhydride and diamine are equimolarly reacted in a high boiling point solvent, and the solution is heated at 150 DEG C or higher in the presence of an azeotropic agent such as xylene to remove by- A method of obtaining a polyimide having a degree of polymerization can be used. Also, a method (chemical imidization method) of obtaining a polyimide without heating by adding a dehydrating / cyclizing reagent such as acetic anhydride / pyridine to a polyamic acid solution can be applied.

However, since most of the solvent-soluble polyimide has a very high coefficient of linear thermal expansion, it does not exhibit low thermal expansion characteristics (dimensional stability) required for substrates for image display devices. In order to lower the coefficient of linear thermal expansion, it is necessary to align the main chain of the polyimide in parallel to the film surface (in-plane orientation). For this purpose, it is essential that the linearity and rigidity of the main chain of the polyimide are sufficiently high. Such a molecular design contradicts the molecular design for improving the solubility of the solvent described above, so that compatibility between the solubility of the solvent and the low thermal expansion characteristics is a very difficult problem in principle.

(BPDA), pyromellitic dianhydride (hereinafter referred to as PMDA) and 2,2'-bis (trifluoromethyl) benzidine (hereinafter referred to as TFMB) having high linearity as a main raw material (Hereinafter referred to as " NMP "), and a cast film formed of the NMP solution exhibits a relatively low coefficient of linear thermal expansion 8).

As described above, most of the soluble polyimide is soluble only in an amide-based solvent such as NMP having a strong dissolving power and hardly dissolved in a non-amide-based solvent having a weak solubility, particularly, in a low hygroscopic solvent. However, a significant problem often arises when forming a film of polyimide varnish comprising an amide-based solvent.

That is, when continuous coating is performed for a long time, the polyimide varnish absorbs moisture from the atmosphere due to the high hygroscopicity of the amide-based solvent, causing clogging of the coating device due to thickening of the polyimide solution or precipitation of polyimide, Which may cause serious trouble. Therefore, from the viewpoint of solution processability, it is preferable that the polyimide has high solubility in a low hygroscopic solvent, but a low heat expandable polyimide which is soluble in a solvent having a lower polarity than an amide type solvent has not been known heretofore.

As described above, it has been difficult to design a wholly aromatic polyimide having both solution processability (low hygroscopic solvent availability), low linear thermal expansion coefficient, high heat resistance and high transparency, Practical transparent plastic substrate materials which satisfy both physical properties required as transparent substrates and transparent protective film materials such as substrates for electroluminescence (EL) substrates, substrates for image display devices such as electron source substrates, and solar cell substrates are known not.

Japanese Patent Laid-Open No. 10-070157 Japanese Patent Application Laid-Open No. 2006-013419 International Publication No. 2008/09110 Japanese Patent Laid-Open No. 07-56030 Japanese Patent Application Laid-Open No. 09-73172 Japanese Patent Application Laid-Open No. 2002-161136 Japanese Patent Application Laid-Open No. 2002-206057 Japanese Patent Application Laid-Open No. 2006-206756

 Macromolecules, 24, 5001 (1991)

The present invention relates to a polyimide having excellent transparency, high heat resistance and low coefficient of linear thermal expansion, exhibiting solvent processability (excellent solubility and film formability) by a low hygroscopic solvent, polyimide varnish obtained by dissolving it in a low hygroscopic solvent, A film having a low thermal expansion coefficient equivalent to that of an inorganic thin film obtained therefrom, high heat resistance and high transparency, and a method of producing them.

As a result of intensive studies to solve the above problems, the present inventors have found a polyimide comprising a constituent unit represented by the following formula (1), and the polyimide has excellent transparency, has a high heat resistance and a low coefficient of linear thermal expansion , A polyimide varnish with a low hygroscopic solvent is obtained easily with a low hygroscopic solvent (excellent solubility and film forming property), and a polyimide film having excellent transparency can be obtained, thus completing the present invention Respectively.

The present invention is as follows.

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

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

2. A polyimide comprising a structural unit represented by the following formula (2).

3. A polyimide according to 1, which comprises 70 mol% or more of a structural unit represented by the following formula (1).

[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

4. A polyimide varnish comprising the polyimide described in any one of 1 to 3 and an organic solvent.

Wherein the organic solvent is a low hygroscopic organic solvent selected from at least one selected from ester solvents, ether solvents, carbonate solvents, glycol solvents, phenol solvents and ketone solvents, and the solids concentration of the polyimide is 5 wt% %. ≪ / RTI >

6. A polyimide molded article comprising a structural unit represented by the following formula (1).

[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

7. A polyimide molded article according to 6, wherein the molded article is a film.

8. A polyimide film obtained by applying, drying and peeling off a polyimide varnish according to 4 or 5 onto a substrate.

9. The polyimide film according to 7 or 8, wherein the polyimide film has a total light transmittance of 80% or more when the film thickness is 10 占 퐉, the light transmittance at 400 nm is 45% or more, or the film thickness is 20 占 퐉.

10. A polyimide film according to 7 or 8, wherein the polyimide film has a light transmittance of at least 45% at 400 nm and a total light transmittance of at least 70% when the film thickness is 10 m, .

11. A method for synthesizing a polyimide comprising a structural unit represented by the following formula (1), wherein the polyimide precursor is imidized at a heating temperature of less than 150 deg.

[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

Since the polyimide of the present invention has two biphenylene structures bonded at the para position in the constituent unit, the main chain structure is very straight and rigid, and accordingly, the polyimide film obtained from the polyimide has a low And exhibits a coefficient of linear thermal expansion and a high heat resistance (high glass transition temperature).

Further, in the field of the art, it is known that the molecular design having two highly linear parabifenylene structures significantly lowers solvent solubility. However, the polyimide of the present invention has excellent solvent solubility and also excellent transparency. In the polyimide of the present invention, since the methyl group and the trifluoromethyl group are present at the 2,2 'position of the biphenylene group constituting the polyimide, the phenylene ring constituting biphenylene due to the steric hindrance effect is twisted, The aggregation of the polymer chains and the electron conjugation are suppressed. As a result, the solvent solubility is greatly improved and at the same time, the charge-transfer interaction peculiar to the polyimide, which is a cause of coloring, is suppressed. It is also believed that the alkyl groups at the 3-position, 3'-position, 5-position and / or 5'-position of the biphenylene group contribute to the same steric effect.

As described above, the polyimide of the present invention is soluble in various solvents, and in particular, when a low hygroscopic solvent is used as a solvent, the resulting polyimide varnish exhibits high solution stability. Therefore, It can be processed into a film. Further, the obtained polyimide film has high heat resistance, low coefficient of linear thermal expansion, and high light transmittance (transparency) of the polyimide. Therefore, a substrate for a liquid crystal display, a substrate for an organic electroluminescence (EL) , A transparent protective film material, a solar cell substrate, or the like, or a transparent protective film material.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing an infrared absorption spectrum of a polyimide obtained in Example 1. FIG.
2 is a diagram showing an infrared absorption spectrum of the polyimide obtained in Example 5. Fig.
3 is a diagram showing an infrared absorption spectrum of the polyimide obtained in Example 6. Fig.

The polyimide of the present invention is a polyimide including a structural unit represented by the following formula (1).

[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

In the formula, when R is an alkyl group, it is a linear or branched alkyl group having 1 to 6 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, an isopropyl group, a n-propyl group, N-hexyl group, n-pentyl group, and the like. Preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group. It is also preferable that all of the two Rs bonded to the same benzene ring are alkyl groups.

Therefore, a more preferable polyimide is a polyimide including a constitutional unit represented by the following formula (2).

(2)

As described above, in order to lower the thermal expansion of the conventional polyimide or polyimide film, it is generally necessary to make the main chain structure as straight as possible, to increase the rigidity, and to suppress the decrease of the linearity of the main chain accompanied by the structural change. However, such a molecular design is detrimental to solvent solubility.

On the other hand, the polyimide of the present invention has a low thermal expansion property, a high solvent solubility and a high solubility by introducing a parabiphenylene group having a greatly twisted back angle through the ester bond in order to enhance the solubility of the solvent in a straight- And solves the extremely difficult problem of realizing transparency at the same time.

The polyimide represented by the formula (1) or (2) of the present invention is not particularly limited in its production method. For example, the polyimide of the present invention can be obtained by reacting a tetracarboxylic acid dianhydride represented by the following formula (3) , 2'-bis (trifluoromethyl) benzidine (hereinafter may be abbreviated as TFMB in some cases) to obtain a polyamic acid containing a structural unit represented by the following formula (4) Followed by imidation.

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group, and the bonding position of the ester group is Meta position or para position.)

The tetracarboxylic acid dianhydride represented by the formula (3) is obtained by a known esterification reaction using biphenyl-4,4'diol and trimellitic acid represented by the following formula (8).

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

The polyimide including the constituent unit represented by the following general formula (2) in the case where all of R's in the general formula (1) are methyl groups will be described in further detail with reference to the production method of the polyimide of the present invention. When R is another alkyl group or hydrogen atom, it can be produced in the same manner as the polyimide including the constituent unit represented by the general formula (2).

(2)

The polyimide represented by the formula (2) is prepared by using a tetracarboxylic acid dianhydride represented by the following formula (9).

The tetracarboxylic acid dianhydride represented by the above formula (9) is a diol represented by the following formula (10): 2,2 ', 3,3', 5,5'-hexamethyl-biphenyl-4,4'-diol HM44BP), or a diacetate thereof and trimellitic acid, and they can be produced by a known esterification reaction.

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

The structural characteristic of the tetracarboxylic dianhydride (hereinafter sometimes abbreviated as TAHMBP) represented by the formula (9) as a raw material of the polyimide of the present invention is that the methyl substituent is bonded to the 2,2 'position of the central biphenylene group The point that the biphenylene group is largely twisted and the two ester groups which connect the biphenylene group and the phthalimide moiety are all bonded at the para position. This makes it possible to simultaneously realize heat resistance, solubility in a low hygroscopic solvent, transparency, and a linear thermal expansion coefficient equivalent to that of an inorganic thin film.

The polyimide precursor (polyamic acid) of the present invention may be copolymerized with an aromatic or aliphatic compound other than the tetracarboxylic acid dianhydride represented by the above formula (9) within a range that does not significantly impair the polymerization reactivity and the polyimide- Tetracarboxylic dianhydride can be used in combination as a copolymerization component.

The aromatic tetracarboxylic acid dianhydride that can be used at that time is not particularly limited, and examples thereof include pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, hydroquinone-bis (tri (Methylmethacrylate anhydride), methylhydroquinone-bis (trimellitate anhydride), 1,4,5,8-naphthalenetetracarboxylic acid 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 Bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) -biphenylsulfonetetracarboxylic dianhydride, 2,2'- Propanoic dianhydride and the like.

Examples of the aliphatic tetracarboxylic acid dianhydride include, but are not limited to, 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- -Dicarboxylic acid anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic acid dianhydride, bicyclo-3,3 ', 4,4'-tetracarboxylic acid dianhydride, 1,2, 3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, etc. These may be used in combination of two or more.

From the viewpoint of the low thermal expansion property of the polyimide film in the tetracarboxylic acid dianhydride, tetracarboxylic acid dianhydride having a rigid and linear structure, namely, pyromellitic acid dianhydride, 3,3 ', 4,4'- Phenyltetracarboxylic acid dianhydride is suitable as a copolymerization component and particularly 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is more preferable as a tetracarboxylic acid dianhydride because of its polymerization reactivity and easy availability. Do.

The content of the aromatic or aliphatic tetracarboxylic acid dianhydride used in combination with the tetracarboxylic dianhydride represented by the formula (9) is in the range of 0 to 30 mol% of the total amount of the tetracarboxylic acid dianhydride.

The polyimide containing the constituent unit represented by the above formula (2) of the present invention is obtained by reacting 2,2'-bis (trifluoromethyl) benzidine (TFMB) with such a tetracarboxylic acid dianhydride.

As described above, in the polyimide of the present invention, when the raw diamine is TFMB, the presence of the trifluoromethyl group at the 2,2 'position in the TFMB lowers the intermolecular force and increases the solubility of the polyimide in the low hygroscopic solvent. Further, the trifluoromethyl group also functions as an electron-withdrawing group, thereby contributing to enhancement of the transparency of the polyimide film by suppressing the charge transfer interaction which is a cause of coloring. It is also believed that the rigid parabiphenylene group in the TFMB contributes to the low thermal expansion of the polyimide.

An aromatic or aliphatic diamine other than TFMB can be used as a copolymerization component in a range that does not significantly impair the polymerization reactivity and polyimide required properties when the precursor (polyamic acid) of the polyimide of the present invention is polymerized.

The aromatic diamine which can be used at this time is not particularly limited, and examples thereof include aromatic diamines such as p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,4-diaminodurane, 4,4'-diaminodiphenylmethane, 4,4'-methylenebis (2-methylaniline), 4,4'-methylenebis -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'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4 ' - diaminobenzophenone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzanilide, 4-aminophenyl-4'-aminobenzoate, benzidine, 3,3'-dihydroxybenzidine, (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, 1, 3-dimethoxybenzidine, o-tolidine, m- Bis (4-aminophenoxy) phenylsulfone, bis (4- (4-aminophenoxy) (4- (4-aminophenoxy) phenyl) hexafluoropropane, 2,2-bis (4- 2,2-bis (4-aminophenyl) hexafluoropropane, p-terphenylenediamine, and the like.

Examples of the aliphatic diamines include chain aliphatic or alicyclic diamines. The alicyclic diamines are not particularly limited, and examples thereof include 4,4'-methylenebis (cyclohexylamine), isophoronediamine, trans-1,4-diaminocyclo Cyclohexane bis (methylamine), 2,5-bis (aminomethyl) bicyclo [2.2.1] heptane, 2,6-bis Methyl) bicyclo [2.2.1] heptane, 3,8-bis (aminomethyl) tricyclo [5.2.1.0] decane, 1,3-diaminoamantane, 2,2- Propane, 2,2-bis (4-aminocyclohexyl) hexafluoropropane and chain aliphatic diamines are not particularly limited, and examples thereof include 1,3-propanediamine, 1,4-tetramethylenediamine, 1,5- Hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, diaminosilylamine, And the like. It is also possible to use two or more of them in combination. In this case, the content of the diamine is in the range of 0 to 30 mol% of the total amount of the diamine.

Examples of the solvent used for polymerizing the precursor (polyamic acid) of the polyimide of the present invention include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylsulfoxide Aprotic solvent is preferable. However, any solvent may be used without any problem as long as the raw material monomer, the polyimide precursor to be produced, and the imidized polyimide are dissolved, and the structure of the solvent is not particularly limited.

Specific examples include amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methyl-2-pyrrolidone,? -Butyrolactone,? -Valerolactone, Ester solvents such as butyl acetate, ethyl acetate and isobutyl acetate; carbonate solvents such as ethylene carbonate and propylene carbonate; ketone solvents such as diethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether, Glycols such as glycol dimethyl ether, triethylene glycol and triethylene glycol dimethyl ether, phenol-based solvents such as phenol, m-cresol, p-cresol, o-cresol, 3-chlorophenol and 4-chlorophenol, Ketone solvents such as acetone, methyl ethyl ketone, diisobutyl ketone and methyl isobutyl ketone; ketone solvents such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane and dibutyl ether Ether solvents as acetone, other general solvents such as acetophenone, 1, Dimethyl sulfoxide, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve, Solvent acetate, butanol, ethanol, xylene, toluene, chlorobenzene, turpentine oil, mineral spirit, and petroleum naphtha solvent may be used, or a mixture of two or more thereof may be used.

The polyimide precursor of the present invention can be obtained by subjecting the tetracarboxylic dianhydride (TAHMBP) represented by the formula (9) and TFMB to a partial reaction to obtain a polyimide precursor, followed by imidation thereof.

The polyimide of the present invention has a high solubility in solution (low hygroscopic solvent) as a polyimide resin, a low coefficient of linear thermal expansion equivalent to that of an inorganic thin film, and a high coefficient of linear expansion similar to that of an inorganic thin film from the chemical structural features of linearity, rigidity, It is possible to use a material having physical properties that can not be obtained with conventional materials that have both heat resistance and high transparency.

Generally, the polymerization reactivity of the tetracarboxylic dianhydride and the diamine greatly affects the toughness of the finally obtained polyimide film. If the polymerization reactivity is not sufficiently high, a high polymer can not be obtained, and as a result, entanglement between the polymer chains is lowered, which may cause the polyimide film to become fragile. In this respect, TAHMBP and TFMB used in the present invention exhibit sufficiently high polymerization reactivity, so that there is no such concern.

The method for synthesizing the polyimide of the present invention is not particularly limited, and a known method can be suitably applied. Specifically, it can be synthesized by, for example, the following method. As a step of obtaining a polyimide precursor (polyamic acid), TFMB is first dissolved in a polymerization solvent in a reaction vessel, TAHMBP powder substantially equimolar with TFMB is slowly added to this solution, and the mixture is heated at a temperature of 0 to 100 ° C Deg.] C, preferably 20 to 60 [deg.] C for 0.5 to 150 hours, preferably 1 to 48 hours.

In this case, the concentration of the raw material monomer is usually in the range of 5 to 50 wt%, preferably in the range of 10 to 40 wt%. By performing polymerization in such a monomer concentration range, a polyimide precursor (polyamic acid) having uniform and high polymerization degree can be obtained. When the degree of polymerization of the polyimide precursor is excessively increased to make it difficult for the polymerization solution to be stirred, it is also possible to appropriately dilute the polyimide precursor with the same solvent. From the viewpoint of toughness of the polyimide film, the polymerization degree of the polyimide precursor is preferably as high as possible. By conducting the polymerization in the above monomer concentration range, the degree of polymerization of the polymer is sufficiently high, and the solubility of the raw material monomer and the produced polymer can be sufficiently secured.

If the polymerization is carried out at a concentration lower than the above range, the degree of polymerization of the polyimide precursor may not be sufficiently increased. If the polymerization is carried out at a concentration higher than the monomer concentration range, the solubility of the monomer or the resulting polymer may be insufficient. When an aliphatic diamine is used, salt formation often occurs at the initial stage of polymerization to hinder the polymerization. In order to increase the degree of polymerization so as to suppress salt formation, it is preferable to control the concentration of the monomer at the time of polymerization to a suitable concentration range.

Next, the step of imidizing the obtained polyimide precursor (polyamic acid) will be described. The imidization method of the polyimide precursor for obtaining the polyimide of the present invention can be carried out by known methods such as a thermal imidization method for thermal dehydration ring closure and a chemical imidization method using a dehydrating agent.

However, it is preferable to imidize in a mild condition such as chemical imidization which does not require high temperature heat treatment. In a method other than chemical imidization, for example, in the case of a thermal imidation method, tetracarboxylic acid dianhydride and diamine are equimolarly reacted in a high boiling solvent and heated at 150 ° C or higher in the presence of an azeotropic agent such as xylene to form by- The polyimide having a high degree of polymerization can be obtained in a solution state. However, when heated at 150 占 폚 or more, a solvent or the like is colored and this colored component may cause coloring of the film.

That is, the imidization method of the polyimide precursor (polyamic acid) of the present invention is specifically exemplified by a method in which the solution of the polyimide precursor obtained above is mixed with a polyimide precursor solution having a proper solution viscosity, As a precursor solution, a dehydrating ring closure agent (chemical imidization agent) composed of an anhydride of an organic acid and a tertiary amine as a basic catalyst is dropped while stirring with a mechanical stirrer or the like, and the solution is heated at a temperature of 0 to 100 캜, preferably 10 to 50 캜 For 1 to 72 hours to complete the imidization chemically.

The organic acid anhydride which can be used at this time is not particularly limited, and examples thereof include acetic anhydride and propionic anhydride. Acetic anhydride is suitably used for ease of handling or purification of reagents. As the basic catalyst, pyridine, triethylamine, quinoline, or the like can be used. However, pyridine is suitably used for handling or separating the reagent, but is not limited thereto. The amount of the organic acid anhydride in the chemical imidization 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 polyimide precursor. The amount of the basic catalyst is in the range of 0.1 to 2 times by mole, more preferably 0.1 to 1 time by mole, based on the amount of the organic acid anhydride.

In addition, chemical imidization agents and by-products such as carboxylic acid (hereinafter referred to as impurities) are mixed in the reaction solution after the chemical imidization, and therefore it is necessary to remove them to purify the polyimide. For purification, known methods can be used. For example, as the simplest method, the imidized reaction solution is dropped into a large amount of a poor solvent while stirring to precipitate the polyimide. The polyimide powder is recovered, washed repeatedly until the impurities are removed, and dried under reduced pressure to obtain polyimide A method of obtaining a powder can be applied.

As the solvent that can be used at this time, polyimide may be precipitated to efficiently remove impurities, and there is no particular limitation as long as it is a solvent that is easy to dry. For example, water or alcohols such as methanol, ethanol and isopropanol are suitable, May be used. If the concentration of the polyimide solution is too high when the polyimide solution is dripped into the poor solvent, the precipitated polyimide becomes a lump of particles and the impurities may remain in the coarse particles. The time of dissolving the obtained polyimide powder in the solvent For a long time.

On the other hand, if the concentration of the polyimide solution is too low, a large amount of poor solvent is required, which increases the environmental load due to the waste solvent treatment and increases the manufacturing cost, which is not preferable. Therefore, the concentration of the polyimide solution when dropped into a poor solvent is 20 wt% or less, more preferably 10 wt% or less. The amount of the poor solvent to be used is preferably equal to or more than the equivalent amount of the polyimide solution, and 1.5 to 3 times the amount is suitable. The obtained polyimide powder is recovered and the residual solvent is removed by vacuum drying, hot air drying or the like. The drying temperature and the time are not limited as long as the polyimide is not deteriorated and the residual solvent is not decomposed. It is preferable that the drying is carried out at a temperature of 30 to 200 DEG C for not more than 48 hours.

The intrinsic viscosity of the polyimide of the present invention is not particularly limited as long as it can be appropriately selected depending on the application. For example, when used as a polyimide film, the intrinsic viscosity of the polyimide is preferably 0.1 To 10.0 dL / g, more preferably from 0.5 to 5.0 dL / g.

In the reaction, the tetracarboxylic acid dianhydride other than the tetracarboxylic dianhydride, which is a raw material of the present invention, and / or the diamine component other than the diamine as the raw material of the present invention, Unit, a polyimide copolymer containing 70 mol% or more of the structural unit represented by the general formula (1) or (2) is preferable.

Further, since the polyimide of the present invention has excellent solubility in a solvent, it can be converted into a polyimide varnish by dissolving in various organic solvents. The obtained varnish can be used, for example, as a molded article such as a polyimide film or a laminate.

Further, since the polyimide of the present invention is usually obtained as a powder, it can be molded as a resin itself, and can be used as various molded articles such as electronic parts, connectors, films, and laminated bodies by suitably employing a known molding method .

When the polyimide of the present invention is dissolved in an organic solvent to be used as a varnish, the organic solvent may be appropriately selected in accordance with the application and processing conditions of the varnish. For example, when a continuous coating is performed over a long period of time, since the solvent in the polyimide solution absorbs moisture in the air, polyimide may be precipitated. Therefore, triethyleneglycol dimethylether,? -Butyrolactone, or cyclopentanone It is preferable to use a hygroscopic solvent. Therefore, the polyimide of the present invention can be selected from various solvents or mixed solvents exhibiting low hygroscopicity.

The low-hygroscopic solvent to be used is not particularly limited, and examples thereof include gamma -butyrolactone, gamma -valerolactone, delta-valerolactone, gamma -caprolactone, epsilon -caprolactone, Ester solvents such as lactone, butyl acetate, ethyl acetate and isobutyl acetate; carbonate solvents such as ethylene carbonate and propylene carbonate; glycol solvents such as diethylene glycol dimethyl ether, triethylene glycol and triethylene glycol dimethyl ether; , phenol solvents such as m-cresol, p-cresol, o-cresol, 3-chlorophenol and 4-chlorophenol, cyclopentanone, cyclohexanone, acetone, methyl ethyl ketone, diisobutyl ketone, methyl isobutyl Ether solvents such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane, diethoxyethane and dibutyl ether, and other general-purpose solvents such as acetophenone, 1,3-dimethyl-2- Imidazolidinone, sulfolane, dime Butanol, ethanol, xylenes, toluene, chlorobenzene, toluene, and the like may be used in combination with one or more solvents selected from the group consisting of methanol, ethanol, propanol, , Turpentine oil, mineral spirit, and petroleum naphtha solvent may be used, or two or more of these solvents may be used in combination. Also, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methyl-2-pyrrolidone which are hygroscopic solvents can also inhibit the precipitation of polyimide by combining with the low hygroscopic solvent Do.

Next, the polyimide varnish of the present invention and a process for producing the polyimide film obtained by molding the same are described in more detail.

When the polyimide of the present invention is dissolved in a solvent to prepare a varnish, the solid content concentration thereof can be appropriately selected depending on the use of the varnish and is not particularly limited. For example, in the case of a film, it is preferable to set the solid content concentration to 5 wt% or more, although it depends on the molecular weight of the polyimide, the production method and the thickness of the film to be produced. If the solid content concentration is too low, it becomes difficult to form a film having a sufficient film thickness. On the other hand, when the solid content concentration is high, the solution viscosity is too high, and the coating may become difficult. 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 to the polyimide powder in an air or inert gas at a temperature ranging from room temperature to the boiling point of the solvent, It is dissolved over 48 hours to obtain a polyimide solution.

As the most preferable form for producing a film using the polyimide of the present invention, for example, a polyimide varnish is coated on a support such as a glass substrate by a known method such as a doctor blade, A film is produced. The coefficient of linear thermal expansion of the polyimide film obtained thereby is preferably 30 ppm / K or less, and more preferably 25 ppm / K or less. The glass transition temperature as an index of heat resistance is preferably 250 DEG C or more, and more preferably 270 DEG C or more from the film formation condition of an inorganic thin film such as ITO.

With respect to the transparency of the polyimide film of the present invention, the total light transmittance when the film thickness is 20 m is preferably 80% or more, more preferably 85% or more.

In addition, when the film thickness is 10 탆, the light transmittance at 400 nm is preferably 45% or more, more preferably 50% or more, further preferably 60% or more, particularly preferably 80% or more, For excellent reasons, the total light transmittance when the film thickness is 10 [micro] m is preferably 70% or more, more preferably 80% or more, further preferably 85% or more.

The preferable range of the transmittance of 400 nm or the total light transmittance in the case where the film thickness is 10 占 퐉 or 20 占 퐉 means that the transmittance at a film thickness of a polyimide film not having a thickness of 10 占 퐉 or 20 占 퐉 is changed to the Lambert- On the basis of the transmittance in terms of the film thickness of 10 mu m or 20 mu m or the transmittance in the case where the transmittance measured by processing the film thickness to 10 mu m or 20 mu m falls within the above preferable range, such a polyimide film is also included .

Further, in the case of a polyimide film of the same quality, the transmittance of the film is improved as the film thickness is decreased. Therefore, even when the transmittance of the polyimide film having a thickness larger than the film thickness of 10 탆 or 20 탆 is within the above- And it is included in a preferable polyimide film without necessity of measurement.

As a conversion method, for example, assuming that the light transmittance at 400 nm of the polyimide film having a thickness of 21 탆 obtained in Example 2 described later is 69.5%, it is assumed that the product of the molar extinction coefficient and the concentration is constant, Based on the law, the conversion value in the case of 10 占 퐉 is calculated to be 84.0%.

In the polyimide varnish of the present invention, additives such as a releasing agent, a filler, a silane coupling agent, a crosslinking agent, a terminal sealing agent, an antioxidant, a defoaming agent, and a leveling agent may be added as necessary.

The obtained polyimide varnish is used to form a film by a known method and then dried to form a polyimide film. For example, the polyimide varnish may be cast on a support such as a glass substrate using a doctor blade or the like, and dried in a hot air drier, an infrared drier, a vacuum drier, an inert oven, , Preferably 50 to 250 ° C, to form a polyimide film.

Example

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples. The physical properties in the following examples were measured by the following methods.

(Assessment Methods)

Material property values and the like described in this specification are obtained by the following evaluation method.

≪ Infrared absorption spectrum &

Infrared absorption spectrum of the tetracarboxylic dianhydride was measured by the KBr method using a Fourier transform infrared spectrophotometer FT / IR 350 (manufactured by Jasco). For the infrared absorption spectrum of polyimide, a thin film sample (thickness of about 5 mu m) was prepared and measured.

< ¹ H-NMR spectrum>

¹ H-NMR spectrum of tetracarboxylic acid dianhydride and chemically imidized polyimide powder in deuterated dimethyl sulfoxide was measured by using Fourier transform nuclear magnetic resonance JNM-ECP400 (manufactured by JEOL). Tetramethylsilane was used as the reference material.

&Lt; Differential scanning analysis (melting point) &gt;

The melting point of tetracarboxylic dianhydride was measured at a heating rate of 2 ° C / min in a nitrogen atmosphere using a differential scanning calorimeter DSC3100 (Bruker AXS). The higher the melting point and the sharpened melting peak, the higher the purity.

<Intrinsic Viscosity>

A 0.5 wt% polyimide precursor solution or polyimide solution was measured for reduced viscosity at 30 DEG C using an Ostwald viscometer. This value was regarded as a unique point.

<Solubility test of polyimide powder in organic solvent>

To 0.1 g of the polyimide powder, 9.9 g of the organic solvent described in Table 2 (solid content concentration: 1% by weight) was placed in a sample tube and stirred for 5 minutes using a test tube mixer to visually confirm the dissolution state. Examples of the solvent include chloroform (CF), acetone, tetrahydrofuran (THF), 1,4-dioxane (DOX), ethyl acetate, cyclopentanone (CPN), cyclohexanone (CHN), N, (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), m-cresol, dimethylsulfoxide (DMSO), gamma -butyrolactone Glycol dimethyl ether (Tri-GL) was used. The results of the evaluation are expressed as ++ when dissolved at room temperature, + when swelling / partially dissolved, ± when insoluble, and - when dissolving by heating and maintaining the uniformity even after cooling to room temperature. .

&Lt; Evaluation of moisture absorption stability of polyimide varnish &

The concentration of the polyimide solution was adjusted to 9 to 13% by weight, 2 mL of the solution was dropped on a glass substrate, and the solution was allowed to stand for 24 hours under an environment of 40% relative humidity. After the solution was allowed to stand for 24 hours, the polyimide solution had no change compared to immediately after the dropwise addition, and the polyimide precipitated and the solution was whitened. When there is no change in the polyimide solution even after 24 hours under an environment of relative humidity of 40%, it shows that the coating property when the polyimide film is produced is excellent.

<Glass transition temperature: Tg>

Using a thermomechanical analyzer (TMA4000) manufactured by Bruker AXS, the glass transition temperature of the polyimide film was determined from the loss peak at a frequency of 0.1 Hz and a temperature rise rate of 5 deg. C / min by dynamic viscoelasticity measurement.

<Linear Thermal Expansion Coefficient: CTE>

The coefficient of linear thermal expansion of the polyimide film was measured using TMA4000 manufactured by Bruker AXS (sample size width 5 mm, length 15 mm), and the load was set at a film thickness (占 퐉) 占 0.5 g at 150 占 폚 at 5 占 폚 / After the temperature was elevated (first elevated temperature), the temperature was cooled to 20 deg. C, and the temperature was further increased at 5 deg. C / min (second elevated temperature) and calculated from the TMA curve at the second elevated temperature. The coefficient of linear thermal expansion was obtained as an average value between 100 and 200 ° C.

<5% weight reduction temperature: Td ⁵ >

(Tg-DTA2000) manufactured by Bruker AXS, the temperature at the time when the initial weight of the polyimide film (thickness 20 占 퐉) was reduced by 5% in the temperature raising process at a temperature raising rate of 10 占 폚 / Respectively. The higher the value, the higher the thermal stability.

<Transmittance of polyimide film: T ₄₀₀ >

The light transmittance of a polyimide film (thickness of 20 mu m) at 200-700 nm was measured using an ultraviolet visible infrared spectrophotometer (V-650) manufactured by JASCO Corporation to determine the light transmittance at a wavelength of 400 nm as a transparency And used as an indicator. The wavelength (cutoff wavelength) at which the transmittance was 0.5% or less was also determined.

&Lt; Birefringence:? N>

Using a Abbe refractometer (using a sodium lamp, at a wavelength of 589 nm (nm)), a refractive index of a direction (n _in ) parallel to the polyimide film plane and a direction perpendicular to the film thickness direction (n _out ) ), And the birefringence (? N = n _in- n _out ) was determined from the refractive index difference between them. The higher the birefringence value, the higher the in-plane orientation of the polymer chain.

<Water absorption rate>

The polyimide film (film thickness 20 to 30 占 퐉) vacuum-dried at 50 占 폚 for 24 hours was immersed in water at 24 占 폚 for 24 hours, and the excess moisture was completely wiped with Kimwipes and water absorption rate %). For most applications, the lower this value is, the better.

<Permittivity: ε _opt >

Atta apoptosis prepared Abbe refractometer average refractive index of the polyimide film by using the (Abe 1T) _{[n av = (2n in + n} out) / 3 ] the following equation based on: ε _cal = 1.1 × n polyimide film by a _av ² the dielectric constant (ε _opt) was calculated.

&Lt; Tensile modulus (Young's modulus), breaking strength, breaking elongation &gt;

A tensile test (stretching speed: 8 mm / min) was performed on a test piece (3 mm × 30 mm) of a polyimide film using TENSILON UTM-2 (manufactured by A & D Co.) (%) From the elongation at break of the film. The higher the elongation at break, the higher the toughness of the film. The breaking strength was obtained from the stress when the test piece was broken.

&Lt; Synthesis Example 1 &

Synthesis of tetracarboxylic dianhydride represented by the formula (9)

(synthesis)

The tetracarboxylic dianhydride (TAHMBP) represented by the formula (9) was synthesized as follows. 8.8493 g (42.0 mmol) of anhydrous trimellitic acid chloride was added to 30 mL of dehydrated tetrahydrofuran (THF) at room temperature, and the solution A was adjusted by septum sealing (solute concentration: 24.9 wt% ). 5.4044 g (20.0 mmol) of 2,2 ', 3,3', 5,5'-hexamethyl-biphenyl-4,4'-diol (HM44BP) was further added to 38 mL of dehydrated THF in a separate flask at room temperature (Solute concentration 14.5 wt%), to which 3.9 mL (48 mmol) of pyridine was added and the solution B was adjusted by septum sil.

While cooling and stirring in an ice bath, Solution B was slowly added dropwise to the solution A with a syringe, followed by stirring at room temperature for 24 hours. After completion of the reaction, the white precipitate was separated by filtration and washed with THF and ion exchange water. The removal of pyridine hydrochloride was confirmed by the addition of an aqueous solution of silver nitrate to the cleaning solution, resulting in no white precipitation. The washed crude product was recovered and vacuum dried at 150 ° C for 12 hours. The obtained crude product was a pale yellowish white powder, yield 6.1984 g, and yield of 50.1%.

(refine)

The obtained crude product was purified by recrystallization. To 5.9905 g of the crude product was added 88 mL of? -Butyrolactone (GBL), dissolved by heating at 150 占 폚, left to stand overnight, and allowed to stand overnight. The precipitated yellowish white powder was recovered by filtration and vacuum-dried at 180 DEG C for 12 hours. The yield of pale yellowish white powder obtained was 3.6974 g, and the yield of recrystallization was 66.2%. The product purified by recrystallization was purified by Fourier transform infrared spectrophotometer FT / IR 350 (manufactured by JASCO Corporation) at 1,861 cm ^-1 and 1,772 cm ^-1 , using acid anhydride C = O stretching vibration absorption band, 1745 cm ^-1 The ester group C = O stretching vibration absorption band was confirmed. In addition, result of the proton NMR measurement using a Fourier transform NMR JNM-ECP400 (JEOL _{manufacture), (DMSO-d 6,} δ, ppm): 1.98 (s, -CH 3, 6H), 2.08-2.15 (m , a _{-CH 3, 12H), 6.98 (} brs, ArH, 2H), 8.33 (d, J = 7.9Hz, ArH, 2H), 8.71-8.76 (m, ArH, 4H) attributed to the possible, and the product is TAHMBP . The melting point was measured by a differential scanning calorimetry analyzer DSC3100 (Bruker AXS), and a sharp melting peak was observed at 309.4 DEG C, suggesting that the product had a high purity.

&Lt; Synthesis Example 2 &

Synthesis of tetracarboxylic dianhydride represented by the formula (5)

(synthesis)

The tetracarboxylic acid dianhydride (hereinafter referred to as TA44BP) represented by the formula (5) was synthesized as follows. 16.8457 g (80.0 mmol) of anhydrous trimellitic acid chloride was dissolved in 71 mL of dehydrated N, N-dimethylformamide (DMF) at room temperature to prepare a solution A, which was adjusted to a solute concentration of 20 wt% ). 7.4483 g (40.0 mmol) of 4,4'-biphenol was further dissolved in 32 mL of dehydrated DMF at room temperature (solute concentration 20% by weight), and 19.3 mL (240 mmol) of pyridine was added thereto &Lt; / RTI &gt; and the solution B was adjusted. While cooling and stirring in an ice bath, Solution B was slowly dropped into Solution A with a syringe and then stirred at room temperature for 12 hours. After completion of the reaction, the yellow precipitate was separated by filtration and washed with DMF and ion exchange water. The removal of pyridine hydrochloride was confirmed by the addition of an aqueous solution of silver nitrate to the cleaning solution, resulting in no white precipitation. The washed crude product was recovered and vacuum-dried at 180 DEG C for 12 hours. The obtained crude product was yellow powder, yield 9.6930 g, and yield of 38.5%.

(refine)

The obtained crude product was purified by recrystallization. To 7.9956 g of the crude product was added 120 mL of? -Butyrolactone (GBL), dissolved by heating, and allowed to stand for 12 hours. The precipitated yellowish plate crystals were collected by filtration and vacuum-dried at 200 ° C for 12 hours. The yield of pale yellow white powder obtained was 6.3165 g, and the yield of recrystallization was 79%. The product purified by recrystallization was purified from a Fourier transform infrared spectrophotometer FT / IR 350 (manufactured by Jasco) at 1861 cm ^-1 and 1782 cm ^-1 Acid anhydride C = O stretching vibration absorption band, at 1730 cm ^-1 The ester C = O stretching vibration absorption band was confirmed. (DMSO-d ₆ , 隆, ppm): 7.52 (d, ArH, 4H), 7.58 (d, ArH, 4H ), 8.51 (d, ArH, 2H), 8.6 (m, ArH, 4H), 8.71-8.76 (m, ArH, 4H) and the product was TA44BP. The melting point was measured by a differential scanning calorimetry analyzer DSC3100 (Bruker AXS), and a sharp melting peak was observed at 326 DEG C, suggesting that the product had a high purity.

&Lt; Synthesis Example 3 &

Synthesis of tetracarboxylic dianhydride represented by the following formula (11)

(synthesis)

The tetracarboxylic acid dianhydride (TA23X-BP) represented by the formula (11) was synthesized as follows. 6.3207 g (30.0170 mmol) of anhydrous trimellitic acid chloride was added to an eggplant-shaped flask and dissolved in 13.0 mL of dehydrated GBL at room temperature to prepare a solution A by sephtamycin. Further, 2.4239 g (10.0032 mmol) of 2,2 ', 3,3'-tetramethyl-biphenyl-4,4'-diol (23X-BP) was dissolved in 37.3 mL of dehydrated GBL in a separate flask at room temperature , To which 4.85 mL (59.9656 mmol) of pyridine was added and the solution B was adjusted by septum sil.

While cooling and stirring in an ice bath, Solution B was dropped into Solution A over about 20 minutes by a syringe, and then stirred at room temperature overnight.

After completion of the reaction, the white precipitate was separated by filtration and washed with ion-exchanged water. The removal of pyridine hydrochloride was confirmed by the addition of an aqueous solution of silver nitrate to the cleaning solution, resulting in no white precipitation. The washed crude product was recovered and vacuum dried at 80 DEG C for 1 hour and at 100 DEG C for 12 hours. The obtained crude product was white powder, yield 5.6107 g, and yield of 95.0%.

(refine)

The obtained crude product was purified by recrystallization. To 3.6411 g of the crude product, 210 mL of GBL was added and dissolved by heating at 100 DEG C, followed by natural cooling and standing overnight. The precipitate was collected by filtration and vacuum-dried at 160 DEG C for 12 hours. The yield of the obtained white powder was 2.8178 g, and the yield of recrystallization was 77.3%.

The product was purified by re-crystallization was confirmed that the acid anhydride C = O stretching vibration absorption band, ester C = O stretching vibration absorption band in 1741 to result ㎝ ^-1, 1780 ㎝ ^-1 measured by infrared absorption spectrum. (DMSO-d ₆ , delta, ppm): 2.02 (s, -CH3, 6H), 2.17 (s, -CH3, 6H), 7.07-7.09 ArH, 2H), 7.24-7.26 (d, J = 8.2 Hz, ArH, 2H), 8.31-8.33 (d, J = 7.96 Hz, ArH, 2H), 8.70-8.72 , ArH, 2H), 8.67 (s, ArH, 2H), and it was confirmed that the product was TA23X-BP. Further, the melting point was measured by differential scanning calorimetry analysis, and a sharp melting peak was observed at 309.1 DEG C, suggesting that the product had a high purity.

&Lt; Example 1 &gt;

(Polymerization of polyimide precursor)

0.9607 g (3 mmol) of 2,2'-bis (trifluoromethyl) benzidine (TFMB) was dissolved in 11.3 g of dehydrated N, N-dimethylacetamide (DMAc). 1.8558 g (3 mmol) of the TAHMBP powder described in Synthesis Example 1 was slowly added thereto and stirred at room temperature for 96 hours to obtain a polyamic acid as a polyimide precursor (solid concentration 20.0 wt%). The intrinsic viscosity of the obtained polyamic acid was 1.84 dL / g.

(Chemical imidization reaction)

The obtained polyamic acid solution was diluted with dehydrated DMAc to a solid concentration of 10.0 wt%, and then a mixed solution of 2.8 mL (30 mmol) of anhydrous acetic acid and 1.2 mL (15 mmol) of pyridine was slowly added dropwise at room temperature After completion of dropwise addition, the mixture was further stirred for 24 hours. The obtained polyimide solution was slowly dropped into a large amount of methanol to precipitate polyimide. The obtained white precipitate was thoroughly washed with methanol, and vacuum-dried at 160 DEG C for 12 hours. The obtained fibrous polyimide powder was 2.5130 g. Proton NMR measurement was performed on this powder, and it was suggested that the chemical imidization reaction was completed because no COOH proton (close to 13 ppm) and NHCO proton (close to 11 ppm) peculiar to polyamic acid were observed. The intrinsic viscosity of the obtained polyimide was 3.16 dL / g, and it was a high molecular weight substance.

(Adjustment of polyimide solution and film formation of polyimide film)

The above polyimide powder was redissolved in cyclopentanone (CPN) at room temperature to prepare a homogeneous solution of 11.4 wt%. This polyimide solution was cast on a glass substrate and dried in a hot air drier at 60 DEG C for 2 hours. Thereafter, the substrate was subjected to heat treatment at 250 deg. C in a vacuum for 1 hour to cool to room temperature, and then the polyimide film was peeled off from the glass substrate. This polyimide film was further subjected to heat treatment in a vacuum at 250 캜 for 1 hour to remove residual strain. The obtained polyimide film was colorless and transparent. The mechanical properties of the polyimide film (film thickness: 32 탆) were measured. The average elongation of 20 test pieces was 10.7%, the maximum elongation was 20.0%, the tensile elastic modulus was 4.5 GPa, and the breaking strength was 0.19 GPa. Further, the thermal characteristics were measured. The coefficient of linear thermal expansion was 21.7 ppm / K in the polyimide film having a thickness of 24 탆, the glass transition temperature was 272 캜, and the thermogravimetric reduction temperature was 437 캜 (in air). The permittivity calculated from the refractive index of the polyimide film was 2.80 and the water absorption rate was 0.04%. The characteristics are shown in Table 1 together with other evaluation results. Further, the moisture absorption stability of the polyimide solution adjusted to 11.4 wt% by CPN was evaluated, and no change was observed even in an environment of 24 hours relative humidity of 40%. In addition, solvent solubility was good for various solvents, and it showed excellent solubility in low hygroscopic solvents such as CPN, GBL and Tri-GL. This is due to the dense molecular design of the polyimide of the present invention. The results of the dissolution test are shown in Table 2. The infrared absorption spectrum of the polyimide thin film is also shown in Fig.

&Lt; Example 2 &gt;

(Adjustment of polyimide solution and film formation of polyimide film)

The polyimide powder obtained by the method described in Example 1 was redissolved in? -Butyrolactone (GBL) at room temperature to prepare a solution of 9.9 wt%. This polyimide solution was cast on a glass substrate and dried in a hot-air drier at 80 DEG C for 2 hours. Thereafter, the substrate was subjected to heat treatment at 250 deg. C in a vacuum for 1 hour to cool to room temperature, and then the polyimide film was peeled off from the glass substrate. This polyimide film was further subjected to heat treatment in a vacuum at 250 캜 for 1 hour to remove residual strain. The obtained polyimide film was colorless and transparent. The mechanical properties of the polyimide film (film thickness 22 탆) were measured. The average elongation of the test pieces was 7.1%, the maximum elongation was 9.0%, the tensile elastic modulus was 4.4 GPa, and the breaking strength was 0.18 GPa. The thermal characteristics were also measured. The coefficient of linear thermal expansion was 25.1 ppm / K in a polyimide film having a thickness of 23 占 퐉, 274 占 폚 in a glass transition temperature, and 437 占 폚 (in air). The dielectric constant calculated from the refractive index of the polyimide film was 2.80, and the water absorption rate was 0.05%. The characteristics are shown in Table 1 together with other evaluation results. Also, the stability of the polyimide solution adjusted to 9.9 wt% by GBL was evaluated. As a result, no change in the solution was observed even in an environment of 40% relative humidity for 24 hours.

&Lt; Example 3 &gt;

(Adjustment of polyimide solution and film formation of polyimide film)

The polyimide powder obtained by the method described in Example 1 was redissolved in triethylene glycol dimethyl ether (TriGL) at room temperature to prepare a 10 wt% solution. This polyimide solution was cast on a glass substrate and dried in a hot air drier at 100 DEG C for 2 hours. Thereafter, the substrate was subjected to heat treatment at 250 deg. C in a vacuum for 1 hour to cool to room temperature, and then the polyimide film was peeled off from the glass substrate. This polyimide film was further subjected to heat treatment in a vacuum at 250 캜 for 1 hour to remove residual strain. The obtained polyimide film was colorless and transparent. The mechanical properties of the polyimide film (film thickness: 30 탆) were measured. The average elongation of 20 test pieces was 10.2%, the maximum elongation was 25.5%, the tensile elastic modulus was 4.2 GPa, and the breaking strength was 0.18 GPa. The thermal characteristics were also measured. The coefficient of linear thermal expansion was 25.7 ppm / K in a polyimide film having a thickness of 23 占 퐉 and the glass transition temperature was 280 占 폚. The permittivity calculated from the refractive index of the polyimide film was 2.79 and the water absorption rate was below the detection limit (&lt; 0.01%). The characteristics are shown in Table 1 together with other evaluation results. In addition, the stability of the polyimide solution adjusted to 10 wt% with TriGL was evaluated. As a result, no change was observed even in an environment of 40% relative humidity for 24 hours.

<Example 4>

(Adjustment of polyimide solution and film formation of polyimide film)

The polyimide powder obtained by the method described in Example 1 was redissolved in tetrahydrofuran (THF) at room temperature to prepare a solution of 11.5% by weight. A polyimide film was produced in the same manner as in Example 1 except that the solvent was changed. The obtained polyimide film was colorless and transparent, and the coefficient of linear thermal expansion was 22.3 ppm / K in a polyimide film having a thickness of 12 탆. The stability of the polyimide solution adjusted to 11.5% by weight in terms of THF was evaluated, and no change was observed even in an environment of 40% relative humidity for 24 hours.

&Lt; Example 5 &gt;

(Polymerization of polyimide precursor)

0.9607 g (3 mmol) of TFMB was dissolved in 14.3 g of dehydrated DMAc. To this solution was slowly added 1.2990 g (2.1 mmol) of the TAHMBP powder described in Synthesis Example 1 and 0.2648 g (0.9 mmol) of 3,3 ', 4,4'-diphenyltetracarboxylic dianhydride (BPDA) powder And stirred at room temperature for 72 hours to obtain a polyamic acid (solid content concentration: 15% by weight). The intrinsic viscosity of the obtained polyamic acid was 1.46 dL / g.

(Chemical imidization reaction)

The polyamic acid solution was diluted with dehydrated DMAc to a solid concentration of 9.6 wt%, and then a mixed solution of 2.8 mL (30 mmol) of acetic anhydride and 1.2 mL (15 mmol) of pyridine was slowly added dropwise at room temperature , And then stirred for 24 hours. The obtained polyimide solution was added to a large amount of methanol to precipitate. The obtained fibrous white precipitate was thoroughly washed with methanol and vacuum-dried at 160 DEG C for 12 hours.

Proton NMR measurement was performed on this powder, and it was suggested that the chemical imidization reaction was completed because no COOH proton (close to 13 ppm) and NHCO proton (close to 11 ppm) peculiar to polyamic acid were observed. The intrinsic viscosity of the obtained polyimide was 2.96 dL / g.

(Adjustment of polyimide solution and film formation of polyimide film)

The polyimide powder was redissolved in cyclopentanone (CPN) at room temperature to prepare a 12.5 wt% solution. This polyimide solution was cast on a glass substrate and dried in a hot air drier at 60 DEG C for 2 hours. Thereafter, the substrate was subjected to heat treatment at 250 deg. C in a vacuum for 1 hour to cool to room temperature, and then the polyimide film was peeled off from the glass substrate.

This polyimide film was further subjected to heat treatment in a vacuum at 250 캜 for 1 hour to remove residual strain. The obtained polyimide film was colorless and transparent. The mechanical properties of the polyimide film (film thickness: 25 mu m) were measured. The average elongation of 20 test pieces was 11.2%, the maximum elongation was 17.7%, the tensile elastic modulus was 4.5 GPa, and the breaking strength was 0.19 GPa. Further, the thermal characteristics were measured. The coefficient of linear thermal expansion was 22.5 ppm / K in a polyimide film having a thickness of 22 탆, the glass transition temperature was 273 캜, and the thermogravimetric reduction temperature was 449 캜 (in air).

Further, the dielectric constant calculated from the refractive index of the polyimide film was 2.84 and the water absorption rate was 0.05%. The characteristics are shown in Table 1 together with other evaluation results. In addition, the stability of the polyimide solution adjusted to 12.5 wt% by CPN was evaluated. As a result, no change was observed even in an environment of 40% relative humidity for 24 hours. In addition, solvent solubility was good for various solvents, and it showed excellent solubility in low hygroscopic solvents such as CPN, GBL and Tri-GL. Normally, when a monomer having a rigid structure such as BPDA is used as a copolymerization component, the solubility of the solvent of the polyimide is usually lowered even if the amount thereof is used in a small amount, but the polyimide copolymer of the present invention still maintains excellent solubility . This is due to the dense molecular design of the polyimide of the present invention. The results of the dissolution test are shown in Table 2. The infrared absorption spectrum of the polyimide copolymer thin film is shown in Fig.

&Lt; Example 6 &gt;

(Polymerization of polyimide precursor)

0.32 g (1 mmol) of TFMB was dissolved in 2.12 g of dehydrated DMAc. 0.59 g (1 mmol) of the TA23X-BP powder described in Synthesis Example 3 was added slowly and stirred at room temperature for 72 hours to obtain a polyamic acid as a polyimide precursor (solid content concentration: 30% by weight).

The intrinsic viscosity of the obtained polyamic acid was 1.18 dL / g.

(Chemical imidization reaction)

The obtained polyamic acid solution was diluted with dehydrated DMAc to a solid concentration of 12.0 wt%, and then a mixed solution of 1.0 g (10 mmol) of acetic anhydride and 0.4 mL (5 mmol) of pyridine was slowly added dropwise at room temperature After completion of dropwise addition, the mixture was further stirred for 24 hours. The obtained polyimide solution was slowly dropped into a large amount of methanol to precipitate polyimide. The obtained white precipitate was thoroughly washed with methanol, and vacuum-dried at 100 占 폚 for 12 hours. The obtained polyimide powder was 0.819 g. Proton NMR measurement was performed on this powder, and it was suggested that the chemical imidization reaction was completed because no COOH proton (close to 13 ppm) and NHCO proton (close to 11 ppm) peculiar to polyamic acid were observed. The intrinsic viscosity of the obtained polyimide was 1.81 dL / g.

(Adjustment of polyimide solution and film formation of polyimide film)

The above polyimide powder was redissolved in cyclopentanone (CPN) at room temperature to prepare a homogeneous solution of 8.0 wt%. This polyimide solution was cast on a glass substrate and dried by a hot-air drier at 60 占 폚 for 2 hours. Thereafter, the substrate was subjected to heat treatment at 200 占 폚 in vacuum for 1 hour and cooled to room temperature, and then the polyimide film was peeled off from the glass substrate. This polyimide film was subjected to heat treatment in vacuum at 200 캜 for one hour to remove residual strain. The polyimide film obtained was slightly turbid, but colorless and transparent. The polyimide film had a coefficient of linear thermal expansion of 15.5 ppm / K and a film thickness of 13.0 占 퐉 in a polyimide film having a film thickness of 28.6 占 퐉 and a glass transition temperature of 211 占 폚 and 5% The reduction temperature was 437 DEG C (in air) in the polyimide film of 20.0 mu m.

The infrared absorption spectrum of the polyimide thin film is shown in Fig.

&Lt; Reference Example 1 &

(Adjustment of polyimide solution and film formation of polyimide film)

The polyimide powder obtained by the method described in Example 1 was redissolved in N, N-dimethylacetamide (DMAc) at room temperature to prepare a solution of 11.1 wt%. A polyimide film was prepared in the same manner as in Example 1 except that the solvent was changed. The obtained polyimide film was colorless transparent and had a coefficient of linear thermal expansion of 27.1 ppm / K in a polyimide film having a thickness of 15 μm. The stability of the polyimide solution adjusted to 11.1 wt% by DMAc was evaluated, and the solution was clouded and the polyimide precipitated under an environment of 40% relative humidity for 24 hours. This indicates that the solution absorbs moisture under an environment of relative humidity of 40% for 24 hours because DMAc is highly hygroscopic.

<Reference Example 2>

(Adjustment of polyimide solution and film formation of polyimide film)

The polyimide powder obtained by the method described in Example 1 was redissolved in N-methyl-2-pyrrolidone (NMP) at room temperature to prepare a 9.8 wt% solution. A polyimide film was prepared in the same manner as in Example 1 except that the solvent was changed. The obtained polyimide film was colorless transparent and had a coefficient of linear thermal expansion of 26.7 ppm / K in a polyimide film having a thickness of 17 탆. The stability of the polyimide solution adjusted to 9.8 wt% by NMP was evaluated. The solution was clouded and the polyimide precipitated under an environment of relative humidity of 40% for 24 hours. This is because the hygroscopicity of NMP is high as in the case of the result of Reference Example 1.

<Reference Example 3>

(Polymerization of polyimide precursor)

0.9607 g (3 mmol) of TFMB was dissolved in 6.6 g of dehydrated DMAc. To this solution, 1.8558 g (3 mmol) of TAHMBP powder was added slowly (solid concentration 30.0 wt%), further dehydrated DMAc was added and the mixture was stirred at room temperature for 11 days (solid concentration 20.0 wt%). The intrinsic viscosity of the obtained polyimide precursor (polyamic acid) was 1.26 dL / g.

(Formation of polyimide precursor film and production of polyimide film)

The resulting polyamic acid solution was cast on a glass substrate and dried in a hot air drier at 60 DEG C for 2 hours. Thereafter, the substrate was thermally imidized in a vacuum at 200 캜 for 0.5 hour and subsequently at 350 캜 for 1 hour. After cooling to room temperature, the polyimide film was peeled from the glass substrate. This polyimide film was further subjected to heat treatment in vacuum at 320 DEG C for 1 hour to remove residual strain. The obtained polyimide film was whitish.

The coefficient of linear thermal expansion of this polyimide film was 66.5 ppm / K in a polyimide film having a film thickness of 26 탆. The values of the coefficient of linear thermal expansion of the polyimide film produced by the thermal imidization reaction as described above were chemically imidized as described in Examples 1 to 4. The linear thermal expansion coefficient of the polyimide film of the copper composition produced through the cast film formation of the polyimide varnish, And since the film is opaque, the conventional two-step process of forming a film at the stage of polyamic acid and thermally imidizing it is not preferable. The characteristics are shown in Table 1 together with other evaluation results.

&Lt; Comparative Example 1 &

(Polymerization of polyimide precursor)

0.9607 g (3 mmol) of TFMB was dissolved in 10.3 g of dehydrated NMP. 1.6033 g (3 mmol) of the TA44BP powder described in Synthesis Example 2 was slowly added thereto and stirred at room temperature for 5 days to obtain a polyamic acid (solid content concentration: 20.0 wt%). The intrinsic viscosity of the polyamic acid was 1.99 dL / g.

(Chemical imidization reaction)

The obtained polyamic acid solution was diluted with dehydrated NMP to a solid concentration of 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 slowly dropped at room temperature Bar, reaction solution became gelled and it was impossible to complete the chemical imidization reaction. This is because the solvent solubility of the polyimide is insufficient. This result is due to the fact that there is no substituent on the central biphenylene group of the used TA44BP, indicating how the substituent in TAHMBP plays an important role in solvent solubility.

&Lt; Comparative Example 2 &

(Thermal imidization of the polyimide precursor)

The polyamic acid solution polymerized in Comparative Example 1 was cast on a glass substrate and dried by a hot air drier at 80 DEG C for 2 hours. Thereafter, the substrate was thermally imidized in a vacuum at 250 ° C for 1 hour and then at 350 ° C for 1 hour. After cooling to room temperature, the polyimide film was peeled from the glass substrate.

This polyimide film was subjected to heat treatment in vacuum at 350 캜 for one hour. The obtained polyimide film was strongly colored yellow.

This result is attributed to the structure in which no substituent is present on the central biphenylene group of the used TA44BP, showing how the substituent in TAHMBP plays an important role in suppressing the coloring of the film.

++: soluble at room temperature, +: soluble by heating to near boiling point, -: insoluble,

±: swelling, partially dissolved,

b) gelation after a few days, c) homogenous solution

(Total light transmittance and haze value of the polyimide film)

With respect to the polyimide films of Examples 1 to 3, Example 5, and Example 6 and Comparative Example 2, haze Meter NDH 4000 manufactured by Nippon Denshoku Industries Co., Ltd. was used to measure the total light transmittance according to JIS K 7361 and the haze Value was measured five times each, and an average value was obtained and used as an index of transparency. According to these results, the total light transmittance of the polyimides of Examples 1 to 3 and 5 was sufficiently high and the haze value was low. However, it was found that the polyimide film of Comparative Example 2 was inferior in these values and the coloring could not be inhibited due to the structure in which no substituent was present on the central biphenylene group of TA44BP used in the synthesis of polyimide.

In addition, the polyimide film of Example 6 had a total light transmittance, a light transmittance of 400 nm, and a cut-off wavelength much better than that of the polyimide film of Comparative Example 2, 2 &lt; / RTI &gt; Further, since the haze value of the polyimide film of Example 6 was measured to be twice the film thickness of the polyimide film of Comparative Example 2, the haze value was slightly larger than that of Comparative Example 2. However, considering the film thickness of each example film, The polyimide film of Example 6 is superior.

Claims (11)

1. A polyimide comprising a structural unit represented by the following formula (1).
[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.) A polyimide comprising a structural unit represented by the following formula (2).
(2)

The method according to claim 1,
A polyimide comprising at least 70 mol% of a structural unit represented by the following formula (1).
[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.) A polyimide varnish containing the polyimide according to any one of claims 1 to 3 and an organic solvent. 5. The method of claim 4,
Wherein the organic solvent is a low hygroscopic organic solvent selected from at least one selected from an ester solvent, an ether solvent, a carbonate solvent, a glycol solvent, a phenol solvent and a ketone solvent, and the solids concentration of the polyimide is 5 wt% Polyimide varnish. 1. A polyimide molded article comprising a constituent unit represented by the following formula (1).
[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.) The method according to claim 6,
Wherein the molded article is a film. A polyimide film obtained by applying, drying and peeling off the polyimide varnish according to claim 4 or 5 onto a substrate. 9. The method according to claim 7 or 8,
The polyimide film has a total light transmittance of 80% or more when the film thickness is 10 占 퐉, the light transmittance at 400 nm is 45% or more, or the film thickness is 20 占 퐉. 9. The method according to claim 7 or 8,
Wherein the polyimide film has a light transmittance of at least 45% at 400 nm and a total light transmittance of at least 70% when the film thickness is 10 占 퐉 and the film thickness is 10 占 퐉. A method for synthesizing a polyimide comprising a structural unit represented by the following formula (1), wherein the polyimide precursor is imidized at a heating temperature of less than 150 ° C.
[Chemical Formula 1]

(In the formula, each R independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that at least one of the two Rs bonded to the same benzene ring is an alkyl group.)

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