JP3327919B2 - Method for producing polyimide having good moldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polyimide resin for melt molding, and more particularly, to a polyimide resin having good heat stability and excellent moldability such as extrusion and injection molding. It relates to a manufacturing method.

[Conventional technology]

Conventionally, polyimide obtained by the reaction of tetracarboxylic dianhydride and diamine, in addition to its high heat resistance,
In order to have excellent mechanical strength and dimensional stability, flame retardancy, electrical insulation, etc., electrical and electronic equipment, aerospace equipment,
It is used in fields such as transportation equipment and is expected to be widely used in fields where co-heat resistance is required in the future.

Conventionally, various polyimides exhibiting excellent characteristics have been developed.

However, even if it is excellent in heat resistance, it does not have a clear glass transition temperature, so if it is used as a molding material, it must be processed using a method such as sintering molding, and the workability is excellent However, it has a low glass transition temperature, is soluble in halogenated hydrocarbons, and is not satisfactory in terms of heat resistance and solvent resistance, and has advantages and disadvantages in performance.

On the other hand, TLSt.Clair Proger and the like are polyimides having excellent mechanical properties, thermal properties, electrical properties, solvent resistance, etc., and having heat resistance as shown in the following general formulas (V) and (V).
I) (In the formula, R is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group, a monocyclic aromatic group, a condensed polycyclic aromatic group, or an aromatic group connected directly or by a crosslinking member. (Indicating a tetravalent group selected from the group consisting of non-fused polycyclic aromatic groups) (Int. J. Adhesion and Adhesive 4 , No 2, April) 198
4, and JP-A-62-53372).

The above polyimide is a novel heat resistant resin having many good physical properties.

However, the above-mentioned polyimide shows excellent fluidity and has good processability, but its melt viscosity is higher than that of engineering plastics which can be usually extruded and injection-molded, so that injection and extrusion molding can be performed. Have difficulty. For this reason, when producing a film or the like, there is no alternative but in the state of polyamic acid and the casting method.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for producing a polyimide having excellent moldability in addition to excellent characteristics inherent to polyimide.

[Means for solving the problem]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and achieved the present invention.

That is, the present invention relates to (a) the general formula (I) (Wherein, X represents a divalent group of —CO— or —SO ₂ —)
An aromatic diamine represented by the general formula (II): (Where R is A tetracarboxylic dianhydride represented by the formula (III): (Where Z is And (2) a dicarboxylic anhydride represented by the following formula: (d) a tetracarboxylic dianhydride in an amount of 0.9 to 1.0 mole per mole of aromatic diamine; General formula (IV) for thermally or chemically imidizing a polyamic acid obtained by reacting a dicarboxylic anhydride in a molar ratio of 0.001 to 1.0 per mole of aromatic diamine (Wherein, X and R have the same meanings as described above). A method for producing a polyimide for extrusion / injection molding, comprising a repeating structural unit represented by the formula:

The diamine used in the method of the present invention is an aromatic diamine compound represented by the general formula (I), that is, bis (3-
Aminophenyl) sulfone or 3,3'-diaminobenzophenone.

Further, as long as the good physical properties of the polyimide obtained by the method of the present invention are not impaired, some of the above diamines may be used instead of other diamines. Examples of the diamine compound that can be used as a partial substitute include, for example, m-
Phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, bis (3-aminophenyl) ether, (3-aminophenyl) (4-aminophenyl)
Ether, bis (4-aminophenyl) ether, bis (3-aminophenyl) sulfide, (3-aminophenyl) (4-aminophenyl) sulfide, bis (4-aminophenyl) sulfide
Aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, (3-aminophenyl) (4-aminophenyl) sulfoxide, bis (4-aminophenyl) sulfoxide, (3-aminophenyl) (4-aminophenyl) sulfone , Bis (4-aminophenyl) sulfone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane,
3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-
Aminophenoxy) phenyl] methane, 1,1-bis [4
-(3-aminophenoxy) phenyl] ethane, 1,1-
Bis [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4-
(4-aminophenoxy) phenyl] propane, 2-
[4- (3-aminophenoxy) phenyl] -2- [4
-(3-Aminophenoxy) -3-methylphenyl] propane, 2,2-bis [4- (3-aminophenoxy)-
3-methylphenyl] propane, 2- [4- (3-aminophenoxy) phenyl-2- [4- (3-aminophenoxy-3,5-dimethylphenyl] propane, 2,2-bis [4- (3 -Aminophenoxy) -3,5-dimethylphenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] butane, 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,2-bis [4-
(3-Aminophenoxy) phenyl] -1,1,1,3,3,3-
Hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4
-Bis (4-aminophenoxy) benzene, 4,4'-bis (3-aminophenoxy) biphenyl, 4,4'-bis (4
-Aminophenoxy) biphenyl, 4,4'-bis (3-aminophenoxy) -3,3'-dimethylbiphenyl, 4,4'-
Bis (3-aminophenoxy) -3,5'-dimethylbiphenyl, 4,4'-bis' (3-aminophenoxy) -3,5'-
Dimethylbiphenyl, 4,4'-bis (3-aminophenoxy) -3,3 ', 5,5'-tetramethylbiphenyl, 4,4'-bis (3-aminophenoxy) -3,3'-dichlorobiphenyl , 4,4'-bis (3-aminophenoxy) -3,5'-dichlorobiphenyl, 4,4'-bis (3-aminophenoxy)
-3,3 ', 5,5'-tetrachlorobiphenyl, 4,4'-bis (3-aminophenoxy) -3,3'-dibromobiphenyl, 4,4'-bis (3-aminophenoxy) -3 , 5'-dibromobiphenyl, 4,4'-bis (3-aminophenoxy)
−3,3 ′, 5,5′-tetrabromobiphenyl, bis [4-
(4-aminophenoxy) phenyl] ketone, bis [4
-(3-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl ] -3-methoxyphenyl] sulfide, [4- (3
-Aminophenoxy) phenyl] [4- (3-aminophenoxy) -3,5-dimethoxyphenyl] sulfide,
Bis [4- (3-aminophenoxy) -3,5-dimethoxyphenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfoxide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [ 4-
(3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone,
Bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3- Bis [4- (3-aminophenoxy) benzoyl] benzene, 4,4'-bis [3-
(4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [3- (3-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-
Amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-
Dimethylbenzyl) phenoxy] diphenylsulfone,
Bis [4- {4- (4-aminophenoxy) phenoxy} phenyl] sulfone and the like are used, and these are used alone or in combination of two or more.

Examples of the tetracarboxylic dianhydride represented by the general formula (II) used in the method of the present invention include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid Acid dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3 -Hexafluoropropane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 4,4 '-(p- And phenylenedioxy) diphthalic dianhydride. These may be used alone or in combination of two or more.

Further, the dicarboxylic anhydride represented by the general formula (III) used in the method of the present invention includes, for example, malonic anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, pimelic acid Anhydride, suberic anhydride, azelaic anhydride, sebacic anhydride, methylmalonic anhydride, ethylmalonic anhydride, dimethylmalonic anhydride, methylsuccinic anhydride, 2,2-dimethylsuccinic anhydride , 2,3-dimethylsuccinic anhydride, tetramethylsuccinic anhydride, cyclohexanedicarboxylic anhydride and the like, and these may be used alone or as a mixture of two or more.

The molar ratio of the aromatic diamine, tetracarboxylic dianhydride and dicarboxylic anhydride used in the method of the present invention is 0.9 to 1.0 mol of tetracarboxylic dianhydride and 1 mol of dicarboxylic anhydride per 1 mol of aromatic diamine. Thing is 0.00
1 to 1.0 mol.

That is, in the production of polyimide, in order to adjust the molecular weight of the produced polyimide, it is customary to adjust the quantitative ratio of aromatic diamine and tetracarboxylic dianhydride. In the method of the present invention, in order to obtain a polyimide having good melt fluidity, the molar ratio of tetracarboxylic dianhydride to aromatic diamine is from 0.9 to 1.0.

The coexisting dicarboxylic anhydride is used in an amount of 0.001 to 1.0 mole ratio to the aromatic diamine. 0.00
If the molar ratio is less than 1, a polyimide having good moldability cannot be obtained. On the other hand, if the molar ratio exceeds 1.0, the mechanical properties of the resulting polyimide deteriorate. Preferred amounts are in the range of 0.01 to 0.5 molar ratio.

In the method for producing a polyimide according to the present invention, the reaction method is not particularly limited, and a known method is used. It is particularly preferable to carry out the reaction in an organic solvent.

As the organic solvent used in this reaction, for example, N, N-
Dimethylformamide, N, N-dimethylacetamide,
N, N-diethylacetamide, N, N-dimethylmethoxyacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, 1,2-dimethoxyethane, bis (2 -Methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, bis {2- (2-methoxyethoxy) ethyl} ether, tetrahydrofuran, 1,3-dioxane, 1,4-
Examples thereof include dioxane, pyridine, picoline, dimethyl sulfoxide, dimethyl sulfone, tetramethyl urea, hexamethyl phosphoramide, phenol, p-chlorophenol, m-cresol, p-cresol, o-cresol, cresylic acid, and anisole. These organic solvents may be used alone or in combination of two or more.

In the method of the present invention, a method of adding and reacting an aromatic diamine, tetracarboxylic dianhydride, and dicarboxylic anhydride as starting materials to an organic solvent includes: (a) aromatic diamine and tetracarboxylic dianhydride After the reaction, the reaction is continued by adding dicarboxylic anhydride. (B) After reacting by adding dicarboxylic anhydride to aromatic diamine, adding tetracarboxylic dianhydride and further reacting And (c) simultaneous addition and reaction of aromatic diamine, tetracarboxylic dianhydride, and dicarboxylic anhydride.

The reaction temperature is usually from 0 ° C. to 250 ° C., and preferably not more than 60 ° C.

The reaction pressure is not particularly limited, and the reaction can be sufficiently performed at normal pressure.

The reaction time varies depending on the aromatic diamine, tetracarboxylic dianhydride, dicarboxylic anhydride, type of solvent and reaction temperature used, and usually 4 to 24 hours is sufficient.

By such a reaction, a polyimide acid which is a repeating structural unit represented by the following general formula (VII) is generated.

(Wherein X and R are the same as described above). The polyamic acid is dehydrated by heating to 100 to 400 ° C., or chemically treated with a commonly used imidizing agent such as triethylamine and acetic anhydride. By imidization, a corresponding polyimide which is a repeating structural unit represented by the general formula (IV) is obtained.

(In the formula, X and R are the same as described above.) In general, after a polyimide acid is formed at a low temperature, it is further thermally or chemically imidized.

As another method, a polyimide can be obtained by simultaneously performing the production of the polyimide acid and the thermal imidization reaction at a temperature of 60 ° C. to 250 ° C.

That is, aromatic diamine, tetracarboxylic dianhydride, aliphatic or cycloaliphatic dicarboxylic anhydride is suspended or dissolved in an organic solvent, and then reacted under heating to produce polyamic acid and dehydrated imide. Can be obtained simultaneously to obtain a polyimide comprising a repeating structural unit represented by the general formula (IV).

When subjecting the polyimide obtained by the method of the present invention to melt molding, other thermoplastic resins, for example, polyethylene, polypropylene, polycarbonate, polyallylate, polyamide, polysulfone, polyethersulfone, and polyether are used within a range that does not impair the purpose of the present invention. An appropriate amount of ether ketone, polyphenylene sulfide, polyamide imide, polyether imide, modified polyphenylene oxide or the like can be blended according to the purpose. In addition, the following fillers and the like used in ordinary resin compositions,
It may be used to the extent that the object of the invention is not impaired. That is, abrasion resistance improvers such as graphite, carborundum, silica stone powder, molybdenum disulfide, and fluororesin, reinforcement of glass fiber, carbon fiber, boron fiber, silicon carbide fiber, carbon whisker, asbestos, metal fiber, ceramic fiber, etc. Material, flame retardant improver such as antimony trioxide, magnesium carbonate, calcium carbonate, electric property improver such as clay and mica, tracking resistance improver such as asbestos, silica, graphite, barium sulfate,
Acid-resistance improvers such as silica and calcium metasilicate, thermal conductivity improvers such as iron powder, zinc powder, aluminum powder, and copper powder, and other glass beads, glass spheres, talc, diatomaceous earth, alumina, silica balun, and hydration Alumina, metal oxides, coloring agents and the like.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1 A reaction vessel equipped with a stirrer, a reflux condenser and a nitrogen inlet tube was charged with 212 g (1.0 mol) of 3,3′-diaminobenzophenone and 2970 g of N, N-dimethylacetamide, and the mixture was stirred at room temperature under a nitrogen atmosphere. Then, 312 g (0.97 mol) of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride was added in portions while paying attention to the rise in solution temperature, and the mixture was stirred at room temperature for about 20 hours. In this polyamic acid solution at room temperature under a nitrogen atmosphere,
Add 13.6 g (0.12 mol) of glutaric anhydride and add
Stir for hours. Then, to this solution, 202 g (2 mol) of triethylamine and 306 g (3 mol) of acetic anhydride were added dropwise. About one hour after the completion of the dropping, yellow polyimide powder began to precipitate. The mixture was further stirred at room temperature for 10 hours and filtered.
Further, the mixture was dispersed and washed in methanol, filtered, and dried at 180 ° C. for 2 hours to obtain 470 g of a polyimide powder. This polyimide powder had a glass transition temperature of 250 ° C. and a melting point of 298 ° C. (by the DSC method; the same applies hereinafter). The logarithmic viscosity of this polyimide powder was 0.52 d / g. Here, the logarithmic viscosity is a value measured at 35 ° C. using a mixed solvent of parachlorophenol and phenol (weight ratio 90:10) with a concentration of 0.5 g / 100 m solvent.

Using the polyimide powder obtained in the present example, a Koka type flow tester (Shimadzu Corporation, CFT-500, orifice diameter 0.
(1 cm, length 1 cm), the relationship between melt viscosity and pressure (shear rate) was measured. FIG. 1 shows the relationship between the melt viscosity and the shear rate measured after variously changing the shear rate after maintaining the temperature at 380 ° C. for 5 minutes.

Comparative Example 1 464 g of a polyimide powder was obtained in exactly the same manner as in Example 1 except that the operation of reacting glutaric anhydride was not performed.

The logarithmic viscosity of the obtained polyimide powder was 0.52 d / g.

Using this polyimide powder, the melt viscosity was measured with a flow tester in the same manner as in Example 1, and the results shown in FIG. 1 were obtained.

Compared with the polyimide powder obtained in Example 1, the melt viscosity in the low shear rate region was higher, indicating that the processability was poor.

Example 2 In a reaction apparatus similar to that of Example 1, 212 g (1,0 mol) of 3,3'-diaminobenzophenone and N, N-dimethylacetamide were added.
Under nitrogen atmosphere at room temperature, 9.22 g (0.66 mol) of 1,2-cyclohexanedicarboxylic anhydride and 312 g were charged.
g (0.97 mol) of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride are added, being careful to increase the solution temperature,
Stir at room temperature for about 20 hours.

Then, to this solution, 202 g (2 mol) of triethylamine and 306 g (3 mol) of acetic anhydride were added dropwise. The mixture was stirred for 20 hours to obtain a pale yellow slurry.

The slurry is filtered, washed with methanol, and
For 8 hours to obtain 486 g of a pale yellow polyimide powder. The glass transition temperature of this polyimide powder was 250 ° C., the melting point was 298 ° C., and the logarithmic viscosity was 0.50 d / g.

The molding stability of the polyimide obtained in this example was measured by changing the residence time in the cylinder of the flow tester. Cylinder temperature was 380 ° C. and pressure was 100 kg / cm ² .

The results are shown in FIG. Even if the residence time in the cylinder becomes longer, the melt viscosity hardly changes, indicating that the molding stability is good.

Comparative Example 2 A pale yellow polyimide powder was obtained in exactly the same manner as in Example 2, except that 1,2-cyclohexanedicarboxylic anhydride was not used.

Glass transition temperature of polyimide powder is 250 ° C, logarithmic viscosity is 0.5
It was 0d / g.

When the residence time in the flow tester cylinder was changed and the melt viscosity was measured in the same manner as in Example 2, the melt viscosity increased as the residence time became longer, and the molding stability was higher than that of the polyimide obtained in Example 2. Showed inferiority.
The results are shown in FIG.

Example 3 The same reaction apparatus as in Example 1 was used except that 3,3 ′ in Example 1 was used.
-212 g (1.0 mol) of diaminobenzophenone was added to bis (3
-Aminophenyl) sulfone was replaced with 248 g (1.0 mol) of the same reaction to obtain a polyamic acid solution. Glutaric anhydride 17.03 (0.15 mol) was added to the polyamic acid solution at room temperature under a nitrogen atmosphere, and the mixture was further stirred for 1 hour. Then, to this solution, 202 g (2 mol) of triethylamine and 306 g (3 mol) of acetic anhydride were added dropwise. About one hour after the completion of the dropping, yellow polyimide powder began to precipitate. The mixture was further stirred at room temperature for 10 hours and filtered. Further, it was dispersed and washed in methanol, filtered and dried at 180 ° C. for 2 hours to obtain 506 g of a polyimide powder. The glass transition temperature of this polyimide powder was 269 ° C. The glass transition temperature of this polyimide powder was 269 ° C. (according to DSC; the same applies hereinafter). Also, the logarithmic viscosity of this polyimide powder is 0.
It was 51 d / g.

Melt viscosity and pressure (shear rate) in the same manner as in Example 1.
Was measured. FIG. 3 shows the relationship between the melt viscosity and the shear rate measured at various temperatures with a shear rate of 5 minutes after the temperature was maintained at 380 ° C. for 5 minutes.

Comparative Example 3 496 g of polyimide powder was obtained in exactly the same manner as in Example 3, except that the operation of reacting glutaric anhydride was not performed.

The logarithmic viscosity of the obtained polyimide powder was 0.51 d / g.

Using this polyimide powder, the melt viscosity was measured with a flow tester in the same manner as in Example 1, and the results shown in FIG. 3 were obtained.

It can be seen that the melt viscosity is high in the low shear rate region as compared with the polyimide obtained in Example 3, and the molding processability is inferior to the polyimide obtained in Example 3.

Example 4 A reaction apparatus similar to that of Example 1 was charged with 212 g (1.0 mol) of bis (3-aminophenyl) sulfone and 3170 g of N, N-dimethylacetamide.
(0.06 mol) of 1,2-cyclohexanedicarboxylic anhydride and 312 g (0.97 mol) of 3,3 ′, 4,4′-benzophenonedicarboxylic dianhydride were added while paying attention to the rise of the solution temperature. And stirred for about 20 hours.

Then, to this solution, 202 g (2 mol) of triethylamine and 306 g (3 mol) of acetic anhydride were added dropwise. The mixture was stirred for 20 hours to obtain a pale yellow slurry. This slurry was separated by filtration, washed with methanol, and dried under reduced pressure at 180 ° C. for 8 hours to obtain 475 g of a pale yellow polyimide powder. The glass transition temperature of this polyimide powder is 250 ° C, the melting point is 298 ° C, and the logarithmic viscosity is
It was 0.50 d / g.

The molding stability of the polyimide obtained in this example was measured by changing the residence time in the cylinder of the flow tester. The temperature was 380 ° C. and the pressure was 100 kg / cm ² .

The results are shown in FIG. Even if the residence time in the cylinder becomes longer, the melt viscosity hardly changes, indicating that the thermal stability is good.

Comparative Example 4 A pale yellow polyimide powder was obtained in exactly the same manner as in Example 4, except that 1,2-cyclohexanedicarboxylic anhydride was not used.

Glass transition temperature of polyimide powder is 250 ℃, logarithmic viscosity is
It was 0.50 d / g.

When the residence time in the flow tester cylinder was changed and the melt viscosity was measured in the same manner as in Example 4, the melt viscosity increased as the residence time became longer.
Was inferior in thermal stability to the polyimide obtained in 1. The results are shown in FIG.

〔The invention's effect〕

According to the method of the present invention, there is provided a polyimide having excellent mechanical properties, thermal properties, electrical properties, solvent resistance, heat resistance, thermal stability for a long time, and excellent moldability. be able to.

[Brief description of the drawings]

FIGS. 1 and 3 show the relationship between the melt viscosity and the shear rate of the polyimide produced by the method of the present invention. FIG. 1 shows the measurement results for the polyimides obtained in Example 1 and Comparative Example 1. FIG. 3 shows the measurement results for the polyimides obtained in Example 3 and Comparative Example 3. 2 and 4 show the relationship between the melt viscosity of the polyimide produced by the method of the present invention and the residence time in a sininder, and FIG. 2 shows the measurement of the polyimide obtained in Example 2 and Comparative Example 2. As a result, FIG. 4 shows the measurement results for the polyimides obtained in Example 4 and Comparative Example 4.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-95030 (JP, A) JP-A-60-258229 (JP, A) JP-A-1-131239 (JP, A) 95029 (JP, A) JP-A-61-78834 (JP, A) JP-A-1-138226 (JP, A)

Claims (1)

(57) [Claims] (1) General formula (I) (Wherein, X represents a divalent group of —CO— or —SO ₂ —)
An aromatic diamine represented by the general formula (II): (Where R is A tetracarboxylic dianhydride represented by the formula (III): (Where Z is And (2) a dicarboxylic anhydride represented by the following formula: (d) a tetracarboxylic dianhydride in an amount of 0.9 to 1.0 mole per mole of aromatic diamine; General formula (IV) for thermally or chemically imidizing a polyamic acid obtained by reacting a dicarboxylic anhydride in a molar ratio of 0.001 to 1.0 per mole of aromatic diamine (Wherein, X and R have the same meanings as described above). A method for producing a polyimide for extrusion / injection molding, comprising a repeating structural unit represented by the formula: