JPS6262808A - Production of polyimide soluble in organic solvent - Google Patents

Abstract

PURPOSE:To obtain the titled polyimide having excellent heat-resistance and suitable as a film, adhesive, etc., by reacting plural kinds of specific aromatic diisocyanates with a benzophenonetetracarboxylic acid in an organic polar solvent in the presence of a catalyst. CONSTITUTION:The objective polyimide can be produced by mixing (A) two or more kinds of aromatic diisocyanates of formula (X is O, S, CONH, etc.) (e.g. 4,4'-diphenylmethane diisocyanate and 4,4'-diphenylsulfone diisocyanate) and (B) 3,3',4,4'-benzophenonetetracarboxylic acid (anhydride) in (C) an organic polar solvent (e.g. phenol) at a ratio (B/A) of 0.7-1.3 and a total concentration of 3-50wt%, adding (D) preferably 0.1-30mol of a catalyst (e.g. triethylamine) per 1mol of the component A and reacting the components with each other e.g. at 100-250 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing organic solvent-soluble polyimide, and more particularly, it relates to a method for producing organic solvent-soluble polyimide, and more specifically, it is a method for producing a substantially completely polyimide having a high glass transition temperature and a high thermal decomposition temperature, and particularly excellent heat resistance. This invention relates to a method for producing imidized organic solvent-soluble polyimide.

[Conventional technology]

In general, polyimide has excellent heat resistance, so it is very useful as a raw material for films used at high temperatures, wire coating materials, adhesives, paints, etc., and is used in advanced technology fields such as electronics and aerospace industries. There are high expectations for this as well.

Conventional polyimides are produced by polymerizing aromatic tetracarboxylic dianhydrides such as pyromellitic anhydride and aromatic amines in a polar solvent to obtain aromatic polyamic acids, and then using this solution as a base material. A film-like aromatic polyimide that is insoluble in a solvent is known, which is obtained by coating, forming into a film, and then dehydrating the polyimide by a method such as heating. but,
In conventional aromatic polyimide, its precursor, aromatic polyamic acid, has poor stability, and if left at room temperature, the viscosity of the polyamic acid solution decreases, and if left for a long time, part of it undergoes dehydration and ring closure to form polyimide. However, it has disadvantages such as becoming insolubilized and becoming cloudy. Therefore, conventional solutions of aromatic polyamic acids have to be stored at low temperatures and must be handled with care.

In addition, in the above polyimide production method, when imidizing the polyamic acid applied to the base material, it is usually necessary to heat it at a high temperature of 400°C or more for a long time, which is disadvantageous from an energy saving perspective. Since this method involves a dehydration reaction, defects such as voids and pinholes occur in the resulting film, making it difficult to obtain a smooth and homogeneous polyimide film.

By the way, polyimide is desired to have a high imidization rate due to various properties, especially for applications as electronic materials, such as IC, etc.
Glabella insulating film for transistors, magnetic heads, etc., semiconductor elements,
When used as a protective coating material for devices such as memory devices, or as a material for liquid crystal alignment films, it is desirable that imidization be substantially complete. However, the polyimide obtained by the above manufacturing method is incompletely imidized and the imidization rate is substantially less than 100%, so the dielectric constant is low.

It may have poor electrical properties such as dielectric loss tangent and insulation properties, increase leakage current when used as a protective coating material for devices, or have low adhesive strength with substrates and devices.
In addition, it has low heat resistance and is unsatisfactory as an electronic material. The reason why the imidization of the polyimide obtained by cyclizing this polyamic acid by heating is incomplete is because all the carboxy groups are imidized when the carboxyl groups contained in polyamic acid are ring-closed and imidized. This is thought to be due to the fact that the carboxy group remains unreacted without being cyclized because it is difficult to select the conditions, ie, appropriate temperature and necessary reaction time.

Therefore, if it were possible to easily produce a polyimide that is soluble in a certain organic solvent and has undergone substantially complete imidization, the polyimide solution could be cast, for example, on a smooth surface and the solvent removed. By simply removing it, a polyimide film with excellent properties can be obtained. Therefore,
Development of a method for producing such organic solvent-soluble polyimide (hereinafter referred to as "soluble polyimide") has been desired and attempts have been made.

One method for producing soluble polyimide in which imidization is substantially complete is to use a monomer that has been imidized in advance, and to use an imide group (or another functional group that can be converted into an imide group) that the monomer has. ) is known to produce soluble polyimide by reacting functional groups other than those of For example,
No. 4056 and No. 58-4057 disclose that, as shown in the following formula, the reaction between the nitro group of imidized monomer (i) and the phenoxyto moiety of monomer (ii) A method for producing a soluble polyimide whose molecular weight is increased by ether bonds is described. This soluble polyimide is soluble in organic solvents due to the high mobility of its structural units, especially around the ether bonds, and moreover, imidization is virtually impossible. However, the glass transition temperature is 217°C, which is considerably lower than that of conventional aromatic polyimide obtained from doromellitic dianhydride and aromatic diamine (250 to 400°C), so it is difficult to mechanically It has the disadvantage of poor heat resistance in terms of reduced strength.

Another method for preparing soluble polyimides in which the imidization is substantially complete includes at least 30 mole percent of 3.3', 4
．． 4'-benzophenone tetracarboxylic acid and an aromatic diisocyanate containing at least 30 mol % of an aromatic diisocyanate represented by the following general formula (iii), or the following general formula (iii), (i
A method is known in which one or more of the aromatic diisocyanates represented by (v), (v) and (vi) are reacted together with a diisocyanate containing a small amount (both containing 30 mol%) in an organic solvent. [wherein, X is -CH2-, -0-, -sow-].

CHl ■ CI(.

Lower alkoxyl group, halogen atom, -coon.

-OH or -503H. 〕 (〕Unexamined Japanese Patent Publication 1973-
Publication No. 48196. In order to make the polyimide obtained by this production method soluble in organic solvents, especially phenolic solvents, the polyimide has a lower symmetry than p,p'-diisocyanatodiphenylene compound.
a todifoxynylene compound (the above general formula (V)), a compound in which a substituent group R is further bonded to the two phenylene groups (the above general formula (iii)), or m, at having an m'-substituent R '-Disubstituted p,p'-diisocyana-todiphenylene compound (the above general formula (iv)) at 30
It is essential to use mol% or more. As a result, while this polyimide is soluble in phenolic solvents, it has a lower thermal decomposition temperature and lower glass transition temperature than conventional polyimides using p, p'-diaminodiphenylene compounds (and has poor heat resistance). It has its drawbacks.

[Problem that the invention seeks to solve]

As mentioned above, there is a need for soluble polyimides that have been substantially completely imidized; The problem is that the temperature and/or the glass transition temperature are low and the heat resistance is insufficient.

The object of the present invention is to solve such problems, to achieve substantially complete imidization, to have excellent electrical properties, to have high thermal decomposition temperature and high glass transition temperature, and to have good heat resistance. An object of the present invention is to provide an excellent method for producing soluble polyimide.

Means for Solving Problem C] According to the present invention, 3.3',4.4'-benzophenonetetracarboxylic acids and general formula (I); [wherein, X is -o-, -s -, -co-.

-3ot-, -CONH-, -(CH,), 1- (
n is an integer from 1 to Z4) and -C-(R'' and R3 are
which may be the same or different and represent a divalent group selected from a lower alkyl group, a fluorine-substituted lower alkyl group, or a halogen atom) in an organic polar solvent, A method of making a soluble polyimide is provided comprising heating in the presence of a catalyst.

3,3',4.4'-benzophenonetetracarboxylic acids in the present invention are 3.3', 4.4'
-benzophenonetetracarboxylic acid and 3.3'
, 4.4'-benzophenonetetracarboxylic acid dianhydrides, dialkyl esters and tetraalkyl esters, where the alkyl group is, for example, methyl, ethyl.

3.3', 4.4'-benzophenonetetracarboxylic dianhydride is particularly preferred because of its high reactivity with aromatic diisocyanates.

In the production method of the present invention, specific examples of aromatic diisocyanates of general formula (I) used in the reaction with 3.3',4.4'-benzophenonetetracarboxylic acids include diphenylmethane-4,4'- Diisocyanate, diphenyl ether-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, -diphenylsulfide-4,4'-diisocyanate, 1,2-diphenylethane-p, p '-diisocyanate, 2,2-diphenylpropane-p,p'-diisocyanate, 2,2-diphenyl-1.1.1.3,3.3-hexafluoropropane-1)+P'-diisocyanate isocyanate,
2.2-diphenylbutane-p,p'-diisocyanate, diphenylated chloromethane-4,,4'-diisocyanate, diphenyldifluoromethane-4,4'-diisocyanate, benzophenone-4,4'- Examples include diisocyanate, N-phenylbenzoic acid amide-4,4'-diisocyanate, and the like. Among these aromatic diisocyanates, diphenylmethane-4 is preferred.
, 4'-diisocyanate, diphenyl ether-4,
4'-diisocyanate, diphenylsulfone-4,4
'-Diisocyanate, diphenyl sulfide-4,4
'-diisocyanates may be mentioned.

In the production method of the present invention, it is essential to use two or more of the above-mentioned aromatic diisocyanates in combination in order for the resulting polyimide to become soluble in organic solvents.

There is no particular restriction on the combination of aromatic diisocyanates of general formula (1). For example, a combination of two types is diphenyl ether-4,4'-diisocyanate and diphenylsulfone-4,4'-diisocyanate. Isocyanate; diphenylmethane-4,4'-diisocyanate and diphenylsulfone-4,4'-diisocyanate;benzophenone-4,4'-diisocyanate and diphenyl ether-4,4'-diisocyanate; benzophenone- 4,4'-diisocyanate and diphenylmethane-4,4'-diisocyanate; benzophenone-4
, 4'-diisocyanate and diphenylsulfone-4,
4'-diisocyanate; 2,2-diphenyl-1,1
, 3,3-hexafluoropropane-p,p'-diisocyanate and diphenyl ether-4,4'-diisocyanate;2,2-diphenyl-1,L3,3-hexafluoropropane-p,p' -Diisocyanate and diphenylmethane-4,4'-diisocyanate; 2.2-
Diphenyl-1,1,3,3-hexafluoropropane-p,p'-diisocyanate and diphenylsulfone-
4,4'-diisocyanate; 2,2-bis(4-isocyanatophenyl)hexafluoropropane and 4.4
'-benzophenone diisocyanate; 2,2-his(4-isocyanatophenyl)propane and 4,4'-diphenyl ether diisocyanate; 2
, 2-bis(4-isocyanatophenyl)propane and 4,4'-diphenylmethane diisocyanate; 2.2-bis(4-incyanatophenyl)propane and 414'-diphenylsulfone diisocyanate; 2.2 - His(4-isocyanatophenyl)propane and 4,4'-benzophenone diisocyanate; 2.2
-bis(4-isocyanatophenyl)propane and 2.
Examples include 2-bis(4-isocyanatophenyl)hexafluoropropane.

Further, as a combination of three aromatic diisocyanates of general formula (1), 4.4'-diphenyl ether diisocyanate and 4.
4'-diphenylmethane diisocyanate and 4,4'-
Diphenylsulfone diisocyanate; 4.4'-diphenyl ether diisocyanate, 4.4'-diphenylmethane diisocyanate, and 4.4'-benzophenone diisocyanate; 4.4'-diphenyl ether diisocyanate;
4'-diphenylmethane diisocyanate and 2,2-bis(4-isocyanatophenyl)propane; 4.4'
-diphenyl ether diisocyanate and -4,4'
-benzophenone diisocyanate and 4,4'-diphenylsulfone diisocyanate; enylsulfone diisocyanate; 4,4'-diphenylmethane diisocyanate and 4,4
'-diphenylsulfone diisocyanate and 4.4'-
Benzophenone diisocyanate; 4.4'-diphenylmethane diisocyanate and 2.2
-bis(4-isocyanatophenyl)propane and 2.
2-bis(4-isocyanatophenyl)hexafluoropropane; 4.4'-diphenyl ether diisocyanate; 2.
2-bis(4-isocyanatophenyl)propane and 2
．． 2-bis(4-isocyanatophenyl)hexafluoropropane; 4.4'-diphenyl ether diisocyanate; and 4.
4'-diphenylsulfone diisocyanate and 4.4'
-benzophenone diisocyanate; 4.4'-diphenylmethane diisocyanate and 4.4'-diaminosulfone diisocyanate 4I4'-benzophenone diisocyanate; 4.4'-diphenylmethane diisocyanate and 4,4
'-Diphenylsulfone diisocyanate and 2.2-bis(4-isocyanatophenyl)hexafluoropropane; 4.4'-diphenylmethane diisocyanate and 4.4
'-Diphenylsulfone diisocyanate and 2,2-bis(4-isocyanatophenyl)propane; 4.4'
- diphenylsulfone diisocyanate and 2.2-bis(4-isocyanatophenyl)propane and 2.2-bis(4-isocyanatophenyl)hexafluoropropane; 4.4'-benzophenone diisocyanate and 2. 2-
Bis(4-isocyanatophenyl)propane and 2.2
-bis(4-isocyanatophenyl)hexafluoropropane and the like.

Among these combinations, a particularly preferable combination is 4.4'-diphenylmethane diisocyanate and 4.4
'-Diphenylsulfone diisocyanate; 4.41-
Diphenyl ether diisocyanate and 4.4'-diphenylsulfone diisocyanate; 4.4'-diphenylmethane diisocyanate and 4.4'-benzophenone diisocyanate: 4.4'-diphenylmethane diisocyanate and 4.4
'-diphenyl ether diisocyanate and 4.4'-
Diphenylsulfone diisocyanate; 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-benzophenone diisocyanate, etc. can be mentioned.

The production method of the present invention is carried out in a solvent in the presence of a catalyst. Catalysts used in this production method include triethylamine, tri-n-propylamine, tri-1so-propylamine, tri-n-butylamine, N, N, N'
, N'-tetramethylethylenediamine, N, N, N
', N'-tetramethyl-1,3-diaminobutane, 1,4-diazabicyclo(2,2,2)octane,
1,8-diazabicyclo(5,4,0)? - undecene, 1,5-diazabicyclo(4,3,0) 5-nonene, N,N-diethylpiperazine, N-ethylmorpholine, pyridine, quinoline, isoquinoline, γ-picoline, N,N-dimethylaniline, N, N-',; ethylaniline, N, N-dimethylbenzylamine, N-
Tertiary amines such as methylimidazole can be mentioned, and the amount of the catalyst used is usually 0.1 to 30 mol per mol of aromatic diisocyanate of general formula (1),
In particular, it is preferable to use 0.5 to 20 moles because the molecular weight of the resulting soluble polyimide can be increased.

The method for producing the soluble polyimide of the present invention is 3.3'.

4. It is carried out by heating 4'-benzophenone tetracarboxylic acids and two or more aromatic diisocyanates of general formula (1) in an organic polar solvent in the presence of the catalyst, and these The monomer reaction proceeds in one step to obtain the desired soluble polyimide.

Specific examples of organic polar solvents used as reaction solvents include phenol, 0-cresol, m-cresol, p-cresol, 2.3-dimethylphenol, 2.
4-dimethylphenol, 2,5-dimethylphenol, 2,6-dimethylphenol.

3.4-dimethylphenol, 3.5-dimethylphenol, 0-chlorophenol, m-chlorophenol,
Phenolic solvents such as p-chlorophenol, O-bromophenol, m-bromophenol, p-bromophenol, and N-methyl-2-pyrrolidone, N,N-
Dimethylacetamide.

N,N-dimethylformamide and hexamethylphos are produced.

Among the above organic polar solvents, m-cresol and 2,
Since 4-dimethylphenol is liquid at room temperature, it is convenient to handle, and it also has the economical advantage of being inexpensive. When using a phenolic solvent that is solid at room temperature, use m-cresol.

It can also be used as a solvent when mixed with 2,4-dimethylphenol or the like to lower the melting point.

In addition, organic solvents that do not impair the reaction, such as toluene, xylene, and ethylbenzene, may be mixed as a diluent, etc., to the extent that the soluble polyimide produced by the reaction does not precipitate.

Molar ratio of aromatic diisocyanate of general formula (1) to 3,3',4.4'-benzophenonetetracarboxylic acids/aromatic 3. diisocyanates) are useful in obtaining high molecular weight soluble polyimides.
7 to 1.3 is preferred, and approximately 1 is particularly preferred.

Further, the molecular weight of the obtained soluble polyimine P can be adjusted in 3.
Either change the molar ratio of 3', 4.4'-benzophenone tetracarboxylic acids and aromatic diisocyanate, or use aromatic monoisocyanates such as phenylisocyanate or aromatic dicarboxylic anhydrides such as phthalic anhydride. This can be done by adding.

The total concentration of 3,3',4,4'-benzophenonetetracarboxylic acids and aromatic diisocyanate in the reaction solvent is 3 to 50% by weight, more preferably 5 to 30% by weight.
Weight percent is preferred.

The reaction temperature when carrying out the present invention is usually higher than 100°C, preferably higher than 100°C and lower than 250°C, particularly preferably higher than 120°C and lower than 230°C. In the production method of the present invention, imidization proceeds in one step, but in order to promote imidization, a temperature of over 100°C is desirable;
At temperatures below 0°C, it is difficult for imidization to proceed smoothly. Under such reaction conditions, the reaction is usually completed in 10 minutes to 50 hours.

Further, this reaction is preferably carried out under a dry nitrogen atmosphere in order to prevent deactivation of the reaction due to moisture absorption and oxidative deterioration of the polymer during the reaction.

Intrinsic viscosity η of the soluble polyimide thus obtained
inh (concentration 0-5 g/100 ml, solvent m
-cresol, 30°C) is preferably 0.05 dl/g or more, particularly 0.05 to 20 dl/g. Intrinsic viscosity. −′
0.05d! If it is less than /g, the moldability as a soluble polyimide will be insufficient. Note that the intrinsic viscosity ηinh is a viscosity expressed as 0.5 (t is the flow rate of the polymer solution, and to is the flow rate of m-cresol).

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 3.3', 4.4'-
Benzophenone tetracarboxylic dianhydride 40.28g
(0,125 mol), diphenylmethane-4,4'-diisocyanate 7.76 g (0,031 mol) and diphenylsulfone-4,4'-diisocyanate 2
8.23 g <0.094 mol) was charged, and 465.0 g of m-cresol was added as a reaction solvent to disperse the above components in m-cresol.

Next, as a catalyst, 1,4-diazabicyclo(2,2,2
) 1.26 s (0.0125 mol) of octane was added, and the mixture was heated from room temperature with stirring under a nitrogen atmosphere.

At about 100° C., carbon dioxide began to be generated and the reaction was observed to start, and a homogeneous reaction solution was obtained. After that, 1
The temperature was raised to 80° C., and the reaction was continued for an additional 5 hours to obtain a reddish-brown, transparent, and viscous soluble polyimide solution.

The obtained soluble polyimide was soluble in phenolic solvents, N-methylpyrrolidone, and the like.

Further, the infrared absorption spectrum of the soluble polyimide is shown in FIG.

The following properties of the obtained soluble polyimide were measured.

(11 Intrinsic viscosity: Intrinsic viscosity was measured to be 0.48 d1/g under the conditions described above.

(2) Glass transition temperature: Measured to be 251°C by scanning thermogravimetry (DSC).

+3110% thermal decomposition temperature: 1% under nitrogen atmosphere using thermogravimetric analysis (TGA) equipment
The temperature was increased at a rate of 0°C/min, and the temperature was determined as the point at which the weight loss was 10% relative to the original weight, and the temperature was determined to be 545°C.

The above results are summarized in Table 1.

Example 2 Diphenyl ether-4,4 was used in place of diphenylmethane-4,4'-diisocyanate used in Example 1.
'-diisocyanate 7.82 g (0,031 mol)
A soluble polyimide solution was obtained in the same manner as in Example 1 except that .

The obtained soluble polyimide solution was a uniform reddish-brown transparent viscous solution, and this soluble polyimide was soluble not only in m-cresol but also in N-methylpyrrolidone and dimethylacetamide.

The properties of the obtained soluble polyimide were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 3 Catalyst used in Example 1 1.4-diazabicyclo(2,2
,2) Instead of octane, 1,8-diazabicyclo(
5,4,0) ・7-Undecene 1.90g (0,0
A soluble polyimide solution was obtained in the same manner as in Example 1 except that 125 mol) was used. The obtained soluble polyimide solution was a uniform reddish-brown transparent viscous solution, and the obtained soluble polyimide was soluble in m-cresol.

The properties of the obtained soluble polyimide were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 4 The amounts of diphenyl ether-4,4'-diisocyanate and diphenylsulfone-4,4'-diisocyanate used in Example 2 were 15 and 78 g, respectively.
(0,0625 mol) and 18.78 g (0,062 mol)
A reddish-brown transparent soluble polyimide solution was obtained in the same manner as in Example 2, except that the amount was changed to 5 mol). The obtained soluble polyimide was soluble not only in m-cresol but also in N-methylpyrrolidone.

Various properties of the obtained soluble polyimide were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 5 Catalyst used in Example 4 1,4-diazabicyclo(2,2
, 2) 1.94 g of isoquinoline (0
A reddish-brown, transparent, and viscous soluble polyimide solution was obtained in the same manner as in Example 4, except that 0.0150 mol) was used.

Is the obtained soluble polyimide compatible with m-cresol? It was accommodating.

Various properties of the obtained soluble polyimide were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 6 The amounts of diphenyl ether-4,4'-diisocyanate and diphenylsulfone-4,4'-diisocyanate used in Example 2 were each 4.80 g (
A reddish-brown transparent polyimide solution was obtained in the same manner as in Example 2, except that the amounts were changed to 0,019 mol) and 31.85 g (0,106 mol).

The obtained soluble polyimide is composed of m-cresol.
-It was also soluble in methylpyrrolidone.

Various properties of the obtained soluble polyimide were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 7 In place of diphenylmethane-4,4'-diisocyanate used in Example 1, diphenyl ether-4,4'-
diisocyaner) 7.90 g (0,0313 mol),
Diphenylmethane-4,4'-diisocyanate 3.1
3 g (0,0125 mol), and diphenylsulfone-4,4'-diisocyanate 28.19 go, 0
A reddish-brown transparent soluble polyimide solution was obtained in the same manner as in Example 1 except that 938 mol) was used.

This soluble polyimide includes m-cresol and N
-It was also soluble in methylpyrrolidone.

The various properties of the obtained soluble polyimide were measured in the same manner as in Example 1, and the results are shown in Table 1.

Table 1 Comparative Examples 1 to 3 As a reaction component, 40.28 g (0,1
25 mol) and equimolar amounts of diphenylmethane-4,4
'-diisocyanate (Comparative Example 1), diphenylsulfone-4,4'-diisocyanate (Comparative Example 2) or diphenyl ether-4,4'-diisocyanate (Comparative Example 3). Polyimide was obtained in the same manner as in Example 1. The reaction proceeded in a heterogeneous system, and a polyimide solution uniformly dissolved in the organic solvent could not be obtained. The obtained polyimide was insoluble in any organic solvent.

〔Effect of the invention〕

The soluble polyimide obtained by the production method of the present invention is easy to handle because it is soluble in organic solvents and obtained as a relatively low-viscosity solution that is fluid at room temperature. Therefore, in addition to extremely high workability when creating polyimide films, it is possible to create homogeneous films without defects such as pinholes by simply drying them after forming them using conventional methods such as casting or spin coating. .

Moreover, this soluble polyimide has high stability in a solution state and can be stored stably for a long period of time without causing deterioration such as a decrease in viscosity or insoluble analysis.

Furthermore, this soluble polyimide has a high thermal decomposition temperature and a high glass transition temperature, and has excellent heat resistance comparable to conventional solvent-insoluble polyimides.

The soluble polyimide of the present invention also has particularly excellent mechanical properties, electrical properties, chemical resistance, etc., and is useful for, for example, high-temperature films, adhesives, paints, etc. Specifically, it is useful for printed wiring. It is useful for substrates, flexible wiring boards, surface protection films or interlayer insulating films for semiconductor integrated circuit elements, liquid crystal alignment films, covering materials for enameled electric wires, various laminates, scallop baskets, and the like.

[Brief explanation of drawings]

FIG. 1 shows the infrared absorption spectrum of the soluble polyimide prepared in Examples t-'c'.

Claims (1)

[Claims] 3,3',4,4'-benzophenonetetracarboxylic acids and general formula (I): ▲There are numerical formulas, chemical formulas, tables, etc.▼(I) [In the formula, X is -O -, -S-, -CO-, -SO_2
-, -CONH-, -(CH_2)_n- (n is 1 to 4
(is an integer of A method for producing an organic solvent-soluble polyimide, which comprises heating two or more aromatic diisocyanates represented by [representing a selected divalent group] in an organic polar solvent in the presence of a catalyst.