JP6980228B2 - Thermocrosslinkable polyimide, its thermosetting material and interlayer insulating film - Google Patents

Description

The present invention relates to a polyimide containing a heat-crosslinkable functional group, a thermosetting product obtained by heat-treating the polyimide at a high temperature, and its utilization.

Polyimide resin is used for various insulating members for electronics because it has excellent mechanical properties and electrical insulation in addition to extremely high heat resistance and flame retardancy. Generally used polyimide is insoluble in organic solvents and does not melt even at high temperatures, so it is difficult to process the polyimide itself.

Therefore, a polyimide precursor solution prepared by a double addition reaction of a tetracarboxylic acid dianhydride and a diamine in an amide-based solvent is applied onto a substrate and dried to form a film, and then molded at 350 ° C. or higher. Generally, a polyimide film is produced by heat treatment at a high temperature. This process, also referred to as a thermal imide process, is applied when manufacturing polyimide film roll products and copper-clad laminates.

However, when a thick-film polyimide film is produced, air bubbles tend to remain in the polyimide film due to the water desorbed in the thermal imide step and / or the evaporating solvent. Therefore, the form in which polyimide can be manufactured is limited to film-like products having a film thickness of less than about 100 μm.

Thermoplastic polyimides and solution-processable polyimides have been studied as measures to solve such problems. However, in order to impart thermoplasticity and solvent solubility to polyimide, it is necessary to introduce flexible linking groups, bulky substituents and irregular chains into the polyimide structure. As a result, the heat resistance, dimensional stability (low thermal expansion characteristic), flame retardancy and other characteristics of polyimide are deteriorated (see, for example, Non-Patent Document 1).

As a method for ensuring excellent heat resistance while maintaining melt processability, an imide oligomer represented by the following general formula (3) whose terminal is modified with a heat-crosslinkable functional group is known (for example, non-). See Patent Documents 2 and 3).

(In the formula (3), Ar ₁ represents a tetravalent aromatic group, Ar ₂ represents a divalent aromatic group, n represents the degree of polymerization, and X represents a monovalent thermobridgeable functional group).

In order to proceed with the cross-linking reaction of the heat-crosslinkable imide oligomer, the heat-crosslinkable functional groups X have sufficient molecular motion, that is, sufficient molecular motility to react between the molecules by causing large translational diffusion and collision with each other. It is necessary to ensure high melt fluidity. Therefore, in the formula (3), highly flexible structural units are used as _{Ar 1} and Ar _2.

Further, the polymerization in the formula (3) is carried out for the purpose of ensuring sufficient melt fluidity during the thermal cross-linking reaction and for the purpose of enhancing the solvent solubility and facilitating the compounding with the reinforcing fiber cloth such as carbon fiber. The degree n is usually controlled to 10 or less.

As described above, the imide oligomer having a thermosetting functional group at the terminal is subjected to a thermosetting reaction (also called a thermosetting reaction) in a molten state. Therefore, the thermosetting product obtained by high-temperature heat treatment of the imide oligomer is a crosslinked product in which the main chain has a three-dimensional random (isotropic) molecular orientation. Further, since this thermosetting product is three-dimensionally crosslinked, the polymer chains are poorly entangled with each other and have poor toughness. Therefore, the thermally crosslinkable imide oligomer is not used as a resin alone, but is usually used as a composite material with a reinforcing fiber cloth such as carbon fiber.

On the other hand, instead of an imide oligomer, a heat-crosslinkable polyimide having a repeating unit represented by the following formulas (4) and (5) in which a heat-crosslinkable functional group is introduced into a high-molecular-weight polyimide main chain has also been reported ( For example, see Non-Patent Document 4).

(In formulas (4) and (5), X ₃ represents a tetravalent aromatic group)
Further, various heat-resistant insulating film materials are used as constituent members of electronic devices. For example, a polyimide film showing a low coefficient of linear thermal expansion in the XY direction (film surface direction) is widely used for the purpose of reducing warpage during lamination with an inorganic material such as glass, copper, silicon, or stainless steel. Such a polyimide is referred to as a low thermal expansion polyimide. In order to reduce the coefficient of linear expansion in the film surface direction, the polyimide main chain needs to be highly oriented along the XY direction (see, for example, Non-Patent Document 5). In other words, the polyimide backbone needs to be in-plane oriented. However, the polyimide film exhibiting low thermal expansion in the XY direction exhibits extremely large thermal expansion in the Z direction (thickness direction) in principle (see, for example, Non-Patent Document 6).

Polymer, 37, 3683-3692 (1996) Journal of Textile Society, 50, 106-118 (1994) High Performance Polymers, 13, S61-S72 (2001) Journal of Polymer Science, Part A, 35, 2395-2402 (1997) Macromolecules, 29, 7897-7909 (1996) European Polymer Journal, 46, 681-693 (2010)

One aspect of the present invention is to provide a thermosetting polyimide and a thermosetting product thereof that can suppress thermal expansion in the Z direction while maintaining low thermal expansion in the XY direction.

As a result of diligent research to solve the above problems, the present inventors have obtained the polyimide shown below using a monomer having a heat-crosslinkable functional group, and the polyimide shown below sufficiently heat-crosslinks without requiring a melt-flow state. I found it to proceed. Based on this, the present inventors have found that a thermally cured product can be obtained in which thermal expansion in the Z direction is suppressed while maintaining low thermal expansion in the XY direction, and have completed the present invention. ..

That is, one aspect of the present invention includes the following configurations.
[1] The following general formula (1):

A repeating unit represented in, in the general formula (1), X ₁ represents a tetravalent aromatic or aliphatic group, X ₂ represents a divalent aromatic or aliphatic group, further X ₂ Medium, the following formula (2):

A heat-crosslinkable polyimide containing a structural unit represented by.
[2] the above formula wherein the structural unit represented by (2), thermally crosslinkable polyimide according to contain more than 1 mol% (1) for all X ₂ component.
[3] A thermosetting product obtained by heat-treating the heat-crosslinkable polyimide according to the above [1] or [2] at 330 ° C. or higher.
[4] An interlayer insulating film made of the thermosetting product according to the above [3].

According to one aspect of the present invention, it is possible to provide a thermosetting polyimide and a thermosetting product thereof that can suppress thermal expansion in the Z direction while maintaining low thermal expansion in the XY direction. Therefore, according to one aspect of the present invention, it is possible to provide a thermosetting polyimide having excellent dimensional stability and a thermosetting product thereof.

It is a figure which shows the graph which plotted the relationship between the copolymerization composition of an Example and a comparative example, and a body expansion coefficient β. It is a figure which shows the DMA curve of Example 3 and the comparative example 4. FIG.

Hereinafter, embodiments of the present invention will be described in detail, but these are examples of embodiments and are not limited to these contents. Unless otherwise specified in the present specification, "A to B" representing a numerical range means "A or more and B or less".

The present inventors have found that thermal cross-linking is effective in order to suppress thermal expansion in the Z direction while maintaining a high degree of in-plane orientation in the XY direction, that is, low thermal expansion. However, in the heat-crosslinkable polyimide described in Non-Patent Document 4, in order to cause a cross-linking reaction, the acetylene groups need to be sufficiently translated and diffused to collide with each other. Due to the introduction of functional groups, it does not show sufficient melt fluidity as compared with imide oligomers. Therefore, in order for the thermally crosslinkable functional groups to react with each other and crosslink between the molecules, the content of the thermally crosslinkable functional groups is set to be considerably high in order to reduce the average distance between the thermally crosslinkable functional groups (acetylene groups). There is a need to. When the concentration of acetylene groups is low, the probability that acetylene groups are close to each other between molecules is low, so that the cross-linking reaction does not occur. Under these circumstances, in the above method of introducing a heat-crosslinkable functional group into the polyimide main chain, a small amount of a crosslinkable monomer is copolymerized with a specific polyimide to heat the polyimide while maintaining the characteristics of the original polyimide. It is difficult in principle to impart crosslinkability.

If it becomes possible to sufficiently proceed the thermal cross-linking reaction even in a situation where sufficient molecular motion cannot be secured, the thermal expansion in the Z direction will be suppressed while maintaining the high in-plane orientation in the XY direction, that is, the low thermal expansion. It will be possible, but there is no known way to achieve it. A heat-resistant insulating material capable of suppressing thermal expansion in the Z direction while maintaining low thermal expansion in the XY direction can be applied to the insulating layer of the multilayer electronic substrate.

The present inventors copolymerize 3,5-diaminobenzamide with a polyimide system originally exhibiting low thermal expansion characteristics in the XY direction to form a polyimide film, and then carry out an intermolecular cross-linking reaction by high-temperature heat treatment. It has been found that it is possible to suppress the thermal expansion in the Z direction while maintaining the low thermal expansion in the XY direction.

When producing the heat-crosslinkable polyimide according to the embodiment of the present invention, the following formula (6):

A monomer containing a thermally crosslinkable functional group represented by (3,5-diaminobenzamide, hereinafter also referred to as 35DABA) is used.

In 35DABA, 3- position and 5-position of the two amino groups (NH ₂ group) acts as a functional group at the time of polymerization of the polyimide precursor. On the other hand, the NH ₂ group in the amide group (CONH ₂ group) by electron-withdrawing effect of the neighboring C = O group, nucleophilic decreases. _{Therefore, the two} NH groups in the amide group do not participate in the polymerization reaction of the polyimide precursor, and therefore 35 DABA can be regarded as substantially a bifunctional diamine compound. The double addition reaction of 35DABA and tetracarboxylic dianhydride provides a solvent-soluble linear polymer without causing gelation defects.

On the other hand, in a solid phase and in a high temperature environment, the amide group introduced as a polyimide side chain can undergo a condensation reaction with an imide group originally present at an extremely high concentration in the vicinity thereof in the polyimide film. That is, an intermolecular cross-linking reaction can occur as shown by the following reaction formula (7). Therefore, intermolecular cross-linking is possible even if the melt-flow state is not reached.

(In the reaction formula (7), X ₁ represents a tetravalent aromatic or aliphatic group, and the wavy line represents a polymer chain).

As the side chain of polyimide, the amino group behaves as a heat-crosslinkable functional group by the same reaction mechanism as the above-mentioned amide group. However, the following formula (8): in which the amide group of 35 DABA was changed to an amino group:

When a monomer represented by (1,3,5-triaminobenzene) is used, it behaves as a trifunctional monomer. Therefore, a crosslinked product is generated during the polyimide precursor polymerization and the solubility is lowered, resulting in non-uniformity such as gelation and / or precipitation precipitation, and as a result, the next film forming step becomes impossible. ..

Furthermore, the bonding position of the amide group at 35 DABA is also extremely important for the effect of the present invention. For example, the following formula (9): in which the amide group is bonded to the amino group at the ortho position:

In the monomer represented by, the intramolecular cyclization reaction is prioritized over the intermolecular cross-linking reaction by the high-temperature heat treatment in the solid phase, as represented by the following reaction formula (10). Therefore, when the monomer represented by the formula (9) is used, the effect of improving the physical properties by the intermolecular cross-linking cannot be obtained.

(In the above reaction formula (10), X ₁ represents a tetravalent aromatic or aliphatic group, and the wavy line represents a polymer chain).

<Thermal crosslinkable polyimide>
The heat-crosslinkable polyimide according to the embodiment of the present invention has the following general formula (1):

It has a repeating unit represented by. The heat-crosslinkable polyimide preferably contains 70 mol% or more of the repeating unit represented by the general formula (1), more preferably 80 mol% or more, further preferably 90 mol% or more, and further preferably 100 mol% or more. There may be. In the general formula (1), X ₁ represents a tetravalent aromatic or aliphatic group, and X ₂ represents a divalent aromatic or aliphatic group. As the monomer of the heat-crosslinkable polyimide, tetracarboxylic dianhydride and diamine are used. That is, X ₁ is a structure derived from tetracarboxylic dianhydride, and X ₂ is a structure derived from diamine.

Further, the heat crosslinkable polyimide, further in _{X 2,} the following formula (2):

Includes structural units represented by. The structural unit represented by the formula (2) is derived from the above-mentioned 35 DABA. Therefore, according to the heat-crosslinkable polyimide according to the embodiment of the present invention, it is possible to suppress the thermal expansion in the Z direction while maintaining the low thermal expansion in the XY direction.

Various aromatic diamines can be used as the diamine to be used in combination (copolymerization) with 35DABA as long as the reactivity when polymerizing the polyimide precursor and the required characteristics of the polyimide are not significantly impaired. At that time, the aromatic diamine that can be used as the copolymerization component is not particularly limited, and for example, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,4-diamino Xylene, 2,4-diaminodurene, 4,4'-methylenedianiline, 4,4'-methylenebis (3-methylaniline), 4,4'-methylenebis (3-ethylaniline), 4,4'-methylenebis (2-Methylaniline), 4,4'-methylenebis (2-ethylaniline), 4,4'-methylenebis (3,5-dimethylaniline), 4,4'-methylenebis (3,5-diethylaniline), 4,4'-Methylenebis (2,6-dimethylaniline), 4,4'-Methylenebis (2,6-diethylaniline), 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3' -Diaminodiphenyl ether, 2,4'-diaminodiphenyl ether, 2,2'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminobenzophenone, 3,3' -Diaminobenzophenone, 4,4'-diaminobenzaniline, benzidine, 3,3'-dihydroxybenzidine, 3,3'-dimethoxybenzidine, o-tridin, m-trizine, 2,2'-bis (trifluoromethyl) Benzidine, 1,4-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-amino) Phenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis (4- (3-aminophenoxy) phenyl) sulfone, bis (4- (4-aminophenoxy) phenyl) sulfone, 2,2- Bis (4- (4-aminophenoxy) phenyl) propane, 2,2-bis (4- (4-aminophenoxy) phenyl) hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane, p. -Terpheniline diamine and the like can be mentioned. Two or more kinds of the above-mentioned copolymerization components may be used.

Also, an aliphatic diamine can be used as a copolymerization component of 35 DABA. These are not particularly limited, but are, for example, 4,4'-methylenebis (cyclohexylamine), 4,4'-methylenebis (3-methylcyclohexylamine), 4,4'-methylenebis (3-ethylcyclohexylamine), 4,4. '-Methylenebis (3,5-dimethylcyclohexylamine), 4,4'-Methylenebis (3,5-diethylcyclohexylamine), isophoronediamine, trans-1,4-cyclohexanediamine, cis-1,4-cyclohexanediamine, 1,4-Cyclohexanebis (methylamine), 2,5-bis (aminomethyl) bicyclo [2.2.1] heptane, 2,6-bis (aminomethyl) bicyclo [2.2.1] heptane, 3 , 8-bis (aminomethyl) tricyclo [5.2.1.0] decane, 1,3-diaminoadamantan, 2,2-bis (4-aminocyclohexyl) propane, 2,2-bis (4-aminocyclohexyl) ) Hexafluoropropane, 1,3-propanediamine, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylene Examples include diamine, 1,9-nonamethylenediamine and the like. Two or more kinds of the above-mentioned copolymerization components may be used.

Various aromatic tetracarboxylic acid dianhydrides are used as the tetracarboxylic acid dianhydrides to be reacted with diamines as long as the reactivity when polymerizing the polyimide precursor and the required characteristics of the polyimide are not significantly impaired. The aromatic tetracarboxylic acid dianhydride that can be used is not particularly limited, and for example, pyromellitic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 3,3', 4,4'-Benzophenone tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyl ether tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyl sulfone tetracarboxylic acid dianhydride , 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropaneic acid dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) propanoic acid dianhydride, hydroquinone bis (trimeri) Tate anhydride), 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride and the like. These may be used alone or in two or more types.

Further, as the tetracarboxylic acid dianhydride, an aliphatic tetracarboxylic acid dianhydride can also be used, and is not particularly limited, but for example, Bicyclo [2.2.2] Oct-7-en-2,3,5. 6-Tetracarboxylic acid dianhydride, Bicyclo [2.2.2] octane-2,3,5,6-tetracarboxylic acid dianhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic acid dianhydride , Bicyclo-3,3', 4,4'-tetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride , 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride and the like. These can be used alone or in combination of two or more. Further, it may be used in combination with the above-mentioned aromatic tetracarboxylic dianhydride.

When the heat-crosslinkable polyimide according to the embodiment of the present invention is used as a film to exhibit low thermal expansion characteristics, the main chain of the polyimide is rigid and has a highly linear structure. preferable. For that purpose, it is preferable to use a tetracarboxylic dianhydride and a diamine that are both rigid and have a linear structure. Preferred tetracarboxylic acid dianhydrides from this point of view include, for example, pyromellitic acid dianhydride (PMDA), 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, hydroquinone bis (trimeritate hydride). ), 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride and the like.

Further, for the purpose of low thermal expansion of polyimide, diamines suitable as a copolymerization component to be used in combination with 35DABA include, for example, p-phenylenediamine, 4,4'-diaminobenzanilide, benzidine, 3,3'-dihydroxybenzidine, and the like. Examples thereof include 3,3'-dimethoxybenzidine, o-tridine, m-tridine, 2,2'-bis (trifluoromethyl) benzidine (TFMB), p-terphenylenediamine, trans-1,4-cyclohexanediamine and the like. ..

Among the above monomers, polyimide having a repeating unit represented by the following formula (11), which is a combination of PMDA as a tetracarboxylic dianhydride and TFMB as a diamine, is very effective in exhibiting low thermal expansion characteristics. be.

That is, for example, by using a polyimide having a repeating unit represented by the above formula (11) as a basic skeleton and copolymerizing and modifying 35 DABA in this system, the effect of thermal cross-linking results in low thermal expansion characteristics in the XY direction. It is possible to suppress thermal expansion in the Z direction while maintaining the above.

The heat cross-linkable polyimide, a structural unit represented by the above formula (2) preferably contains more than 1 mol% relative to the total X ₂ component. The upper limit of the content of the structural unit represented by the above formula (2) may be 100 mol%. Further, even when the content of 35DABA is low (for example, 1 to 10 mol%), since the imide group is present at a high concentration in the vicinity of the amide group of 35DABA, vigorous molecular motion (translational diffusion) accompanied by a melt-flow state. An intermolecular cross-linking reaction can occur between an amide group and an imide group without the need for special motion). From the viewpoint of the three-dimensional thermal dimensional stability is more improved, the heat crosslinkable polyimide, a structural unit represented by the above formula (2), include 20～100Mol% relative to the total X ₂ component Is more preferable, 50 to 100 mol% is more preferable, and 80 to 100 mol% is particularly preferable.

<Manufacturing method of 3,5-diaminobenzamide (35DABA)>
The method for synthesizing 35 DABA used in producing the heat-crosslinkable polyimide according to the embodiment of the present invention will be described below. First, the following formula (12):

3,5-Dinitrobenzoyl chloride (35DNBC) represented by is dissolved in a low-polarity solvent insoluble in water such as toluene.

After adding concentrated aqueous ammonia to the obtained solution, the mixture is vigorously stirred at 0 to 50 ° C. for 0.1 to 12 hours. By this operation, the following equation (13):

3,5-Dinitrobenzamide (35DNBA) represented by is obtained as a precipitate. This is filtered off, then thoroughly washed with water and then vacuum dried at 30-100 ° C. for 1-12 hours. Since the product is usually sufficiently pure, it can be used as it is in the next reduction step, but it may be further recrystallized from a suitable solvent or purified by column chromatography.

Next, the two nitro groups of 35DNBA are reduced to obtain the desired formula (14) :.

The method for obtaining the diamine represented by is described. The method of the reduction reaction is not particularly limited, and a known method can be applied. For example, a method using Pd / C as a hydrogenation reduction catalyst, a catalytic reduction method using a metal powder such as tin, zinc or iron in hydrochloric acid acidity, or a method using an ethanol solution of tin chloride dihydrate is also applicable. .. From the viewpoint of reaction efficiency and ease of post-treatment, a method using Pd / C as a hydrogenation reduction catalyst is preferably used.

Specifically, the catalytic reduction reaction using hydrogen gas and a Pd / C catalyst is carried out as follows. First, a dinitro compound (35DNBA) is dissolved in a solvent in a three-necked flask, and Pd / C powder is added thereto. Next, after introducing hydrogen into the flask, the mixture is stirred while heating to a predetermined temperature until the reaction is completed, and then cooled to room temperature. By selecting an appropriate solvent and solute concentration, it is possible to suppress the precipitation of the product (35 DABA) even when cooled to room temperature after the reaction. After the reaction, Pd / C is removed by filtration.

The recovery of the product can also be increased by concentrating the obtained filtrate using an evaporator. If a precipitate is precipitated by concentration, the product may be recovered by filtering the precipitate. Alternatively, the product may be precipitated by adding water as a precipitating agent to the concentrated filtrate. The obtained crude product is washed and filtered, and finally vacuum dried at a temperature below the melting point of the product, that is, in a temperature range of 50 to 120 ° C. for 5 to 12 hours to obtain a high-purity diamine. This diamine can be used in the next polymerization reaction step. If necessary, the product may be further purified by recrystallization, sublimation, column chromatography, or the like.

The solvent that can be used in the catalytic reduction reaction is not particularly limited as long as the dinitro compound and the reduced compound (diamine) are sufficiently dissolved, and the solvent containing sulfur or phosphorus, which is likely to be a catalytic poison, is excluded. .. Amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoramide; dimethylsulfoxide, sulfolane, etc. Pulmonate solvent; alcohol solvent such as methanol, ethanol, propanol; ether solvent such as tetrahydrofuran, 1,4-dioxane, diglime, triglime; ester solvent such as γ-butyrolactone and ethyl acetate; toluene, xylene and the like. Can be mentioned. Further, these solvents may be used alone or in combination of two or more. Ethanol or N, N-dimethylformamide is preferably used from the viewpoint of the solubility of the reaction raw material and the product and the ease of removal in the subsequent step.

The solvent used in the reduction reaction preferably has high solubility in the product diamine. If the solubility of the product is low, a part of the monoamine form produced during the reduction reaction may be precipitated as a precipitate, which may hinder the completion of the reaction to the diamine. Furthermore, if the solubility in the product diamine is good, the diamine remains dissolved in the solution even if the reaction solution is cooled to room temperature after the reduction reaction is completed, so it is necessary to remove the catalyst by hot filtration. It disappears. That is, the catalyst can be easily filtered and separated.

The catalytic reduction reaction may be carried out at room temperature, but the reaction solution may be heated in order to promote the dissolution and reaction of the dinitro compound. The reaction temperature at that time depends on the boiling point of the solvent used, but is usually in the range of 30 to 150 ° C., more preferably in the range of 30 to 120 ° C. The reaction time is usually in the range of 1 to 24 hours, but specifically, the reaction is continued until the reduction reaction is completed. The end point of the reduction reaction can be confirmed by the complete disappearance of the dinitro compound used as a raw material and the appearance of only one new spot in thin layer chromatography using a reaction solution sampled appropriately. can.

Since the obtained diamine has sufficiently high purity, it can be used as it is in the next polymerization step, but it may be further purified by a recrystallization method, a sublimation method, a column chromatography method or the like before use.

<Polymerization method of thermally crosslinkable polyimide precursor>
The heat-crosslinkable polyimide according to one embodiment of the present invention can be obtained by first polymerizing a precursor thereof and then subjecting the precursor to a heat dehydration ring closure reaction. The polyimide precursor refers to a polyamic acid. The dehydration ring closure reaction is also referred to as a thermal imidization reaction. The method for producing the precursor is not particularly limited, and a known method can be applied. For example, the polyimide precursor can be polymerized by the method shown below. As the diamine and the tetracarboxylic dianhydride, those described in the above-mentioned <heat-crosslinkable polyimide> can be used.

In a three-necked flask, diamine is dissolved in a sufficiently dehydrated polymerization solvent, and tetracarboxylic dianhydride powder is gradually added thereto, and the temperature is 0 to 100 ° C, preferably 20 to 60 ° C, 0.5 to 100. Stir with a mechanical stirrer for an hour, preferably 1-80 hours. At that time, the content of 35 DABA with respect to the total amount of diamine is 1 to 100 mol%.

During the above polymerization reaction, the total monomer concentration in the solvent is 5 to 50% by weight, preferably 10 to 40% by weight. By polymerizing in this monomer concentration range, a uniform and highly polymerizable polyimide precursor solution can be obtained. In addition, in this specification, a polyimide precursor solution is also referred to as a polyimide precursor varnish. If the degree of polymerization of the polyimide precursor increases too much and it becomes difficult to stir the polymerization solution, it can be diluted with a solvent.

If the polymerization is carried out at a concentration lower than the above-mentioned monomer concentration range, the degree of polymerization of the polyimide precursor may not be sufficiently high, and the finally obtained polyimide film may become fragile. On the other hand, if the polymerization is carried out at a concentration higher than the above concentration range, the monomer may not be sufficiently dissolved, or the reaction solution may become non-uniform, resulting in gelation, which is not preferable. Further, when 35 DABA and an aliphatic diamine are used in combination (copolymerization), the degree of polymerization may decrease if the polymer is polymerized at a concentration lower than the above concentration range. Further, when 35 DABA and an aliphatic diamine are used in combination, polymerization at a concentration higher than the above concentration range forms a strong salt, so that a long polymerization reaction time is required for the salt to be completely dissolved, and as a result, a long polymerization reaction time is required. It may lead to a decrease in productivity.

The solvent used when polymerizing the precursor of the heat-crosslinkable polyimide according to the embodiment of the present invention may be a solvent that sufficiently dissolves the monomer and the polyimide precursor to be produced and does not react with them, particularly. Not limited. As a solvent that can be used, for example, an amide solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone; γ -Cyclic ester solvent such as butyrolactone; Cyclic ketone solvent such as cyclopentanone and cyclohexanone; Symphonic solvent such as sulfolane and dimethylsulfoxide; Glycol solvent such as triethyleneglycol; Phenol such as m-cresol and p-cresol A system solvent can be mentioned. These solvents may be used alone or in combination of two or more. Usually, NMP is preferably used in terms of dissolving power, low toxicity and cost.

Further, when polymerizing the polyimide precursor, the charge ratio (molar ratio) of the tetracarboxylic acid dianhydride and the diamine that can be applied is in the range of tetracarboxylic acid dianhydride: diamine = 90: 100 to 100: 90. It is preferable to have. From the viewpoint of increasing the degree of polymerization of the polyimide precursor as much as possible, the charging ratio is more preferably in the range of 95: 100 to 100: 95, further preferably 98: 100 to 100: 98, and preferably 100: 100. Especially preferable.

Further, from the viewpoint of the toughness of the polyimide film and the handling of the polyimide precursor varnish according to the embodiment of the present invention, the intrinsic viscosity of the polyimide precursor is preferably in the range of 0.3 to 10.0 dL / g, and 0. More preferably, it is in the range of 5 to 5.0 dL / g.

After polymerizing the polyimide precursor, the reaction solution is appropriately diluted with the same solvent, and then dropped, filtered and dried in a large amount of water or a poor solvent such as methanol, and the polyimide precursor can be isolated as a powder. Is.

<Method of imidization, film formation and thermal cross-linking>
The heat-crosslinkable polyimide according to one embodiment of the present invention is obtained by subjecting the polyimide precursor obtained by the above method to a dehydration ring closure reaction (imidization reaction). Examples of the form of the heat-crosslinkable polyimide that can be used include films, laminates with various substrates, powders and molded bodies. If the base polyimide before being modified with 35 DABA has high solvent solubility, it can also be obtained in the form of a polyimide solution, that is, a polyimide varnish.

First, a method for forming a polyimide film by a thermal imidization reaction will be described. A solution of the polyimide precursor is cast on a substrate made of inorganic glass, copper, aluminum, stainless steel, or silicon and then dried in a hot air circulation dryer at 40 to 150 ° C., preferably 50 to 120 ° C. to perform polyimide. Form a precursor film. A polyimide film that is not thermally crosslinked can be produced by subjecting it to a thermal imidization reaction while heating it on a substrate in a vacuum or in an inert gas atmosphere such as nitrogen at 200 to 400 ° C, preferably 250 to 300 ° C. .. The thermal imidization reaction is preferably carried out in vacuum or in an inert gas, but may be carried out in air if the reaction temperature is not too high.

A polyimide can be obtained by appropriately diluting the solution of the polyimide precursor as it is or with the same solvent and then heating it to 150 to 200 ° C., depending on the boiling point of the solvent. When the polyimide is dissolved in the solvent used, a polyimide varnish is obtained. On the other hand, when the polyimide is insoluble in a solvent, it precipitates as a precipitate and a polyimide powder is obtained. At this time, toluene, xylene, or the like may be added in order to azeotropically distill off water, which is a by-product of the imidization reaction. Further, a base such as γ-picoline can be added as an imidization catalyst. Polyimide can also be isolated as a powder by dropping and filtering a uniform polyimide varnish in a poor solvent such as water or methanol. A polyimide varnish can also be obtained by redissolving the polyimide powder in various solvents.

The heat-crosslinkable polyimide according to one embodiment of the present invention is polymerized in one step (one-pot polymerization) by reacting a tetracarboxylic acid dianhydride with a diamine at a high temperature in a solvent without isolating the polyimide precursor. )can do. At this time, the reaction temperature is usually in the range of 150 to 250 ° C., although it depends on the boiling point of the solvent. When the polyimide is insoluble in the solvent used, the polyimide is obtained as a precipitate, and when the polyimide is soluble in the solvent, it is obtained as a polyimide varnish.

The solvent that can be used for one-pot polymerization is not particularly limited, but is an aprotic solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and γ-butyrolactone. Can be mentioned. Toluene, xylene, or the like can be added to these solvents in order to azeotropically distill off water, which is a by-product of the imidization reaction. Further, a base such as γ-picoline can be added as an imidization catalyst.

A polyimide film that has not been thermally crosslinked can also be formed by applying the polyimide varnish obtained as described above onto a substrate and then drying it at 40 to 300 ° C., preferably 100 to 300 ° C.

The polyimide film obtained as described above is heat-treated at 330 to 450 ° C., more preferably 350 to 400 ° C. in a vacuum or in an atmosphere of an inert gas such as nitrogen to obtain a polyimide film undergoing a thermal cross-linking reaction. Can be done. Further, the polyimide precursor film can be heat-treated under the same conditions to perform imidization and thermal cross-linking at the same time.

Inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents on the polyimide precursor varnish or polyimide varnish obtained as described above, as long as the required characteristics of the polyimide film are not impaired. , Various additives such as defoaming agent, fluorescent whitening agent, polymerization initiator, and photosensitive agent may be added.

One embodiment of the present invention includes a thermosetting product obtained by heat-treating a thermosetting polyimide at 330 ° C. or higher as described above. The polyimide thermally crosslinked in this way becomes a three-dimensional crosslinked body. Therefore, the thermosetting product obtained by thermally cross-linking the thermosetting polyimide according to the embodiment of the present invention is also referred to as a three-dimensional cross-linked product. Further, since this thermosetting product has a three-dimensional crosslinked structure, it has a very complicated structure. Since the cross-linking reaction proceeds while maintaining the molecular orientation, the three-dimensional cross-linked product is superior in toughness to the three-dimensional cross-linked product of the imide oligomer described in Non-Patent Documents 2 and 3.

Further, the film made of such a thermosetting product can be used as an interlayer insulating film, a coverlay film, a glass substitute film, or the like.

Although the polyimide film is mainly exemplified above, the three-dimensional crosslinked body may be in the form of powder, fiber or molded body.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The physical property values in the following examples were measured by the following method.

[Confirmation of molecular structure and evaluation of membrane physical properties]
<Infrared absorption spectrum>
An infrared absorption spectrum of 35 DABA was measured by the KBr plate method using a Fourier transform infrared spectrophotometer (FT-IR4100 manufactured by JASCO Corporation). Moreover, the infrared absorption spectrum of the polyimide thin film was measured by the transmission method.

< ^{1 1} H-NMR spectrum>
Using an NMR spectrophotometer (ECP400) manufactured by JEOL Ltd. ^{, a 1} H-NMR spectrum of _{35 DABA was measured using deuterated dimethyl sulfoxide (DMSO-d 6} ) as a solvent.

<Differential Scanning Calorimetry (DSC)>
Using a differential scanning calorimetry device (DSC3100) manufactured by Netch Japan, differential scanning calorimetry was performed in a nitrogen atmosphere at a heating rate of 5 ° C./min, and the melting point of 35 DABA was obtained from the obtained endothermic peak temperature of melting. ..

<Reduced viscosity, intrinsic viscosity (η _inh )>
The varnish of the polyimide precursor polymerized in NMP was diluted with the same solvent to obtain a 0.5% by weight solution. The reduced viscosity of this solution was measured at 30 ° C. using an Ostwald viscometer. This value can be regarded as substantially the intrinsic viscosity, and the higher the value, the higher the molecular weight of the polyimide precursor.

<Dynamic mechanical analysis, glass transition temperature (T _g )>
Dynamic dynamic analysis using TA Instruments' dynamic dynamics measuring device (Q-800) in tensile mode under the conditions of nitrogen, frequency 0.1 Hz, heating rate 5 ° C / min, room temperature to 450 ° C ( By performing DMA), the storage elastic modulus (E') and the loss elastic modulus (E ") of the polyimide film (thickness of about 20 μm) were measured. From the peak temperature of the loss elastic modulus curve to the glass transition temperature (T) of the polyimide. _g ) was determined. The _{higher the T g} , the higher the physical heat resistance. Further, the storage elastic modulus _{gradually decreases immediately after exceeding T g} in the temperature rise process, and the smaller the decrease is, the more the storage elastic modulus is determined. It indicates that softening (thermal deformation) in a temperature range of T _{g or higher is suppressed, that is, dimensional stability is high.}

<Coefficient of thermal expansion in XY direction (CTE in XY direction)>
Using a thermomechanical analyzer (TMA4000) manufactured by Netch Japan Co., Ltd., polyimide is used as an average value in the range of 100 to 200 ° C. from the elongation of the test piece at a load of 0.5 g / film thickness of 1 μm and a heating rate of 5 ° C./min. The XY-direction CTE (α _XY ) of the film (thickness of about 20 μm) was determined. The lower this value is, the better the thermal dimensional stability in the XY direction is.

<5% weight loss temperature (T _d ⁵ )>
Using a thermogravimetric analyzer (TG-DTA2000) manufactured by Netch Japan Co., Ltd., the initial weight of the polyimide film (thickness about 20 μm) is 5 in the temperature rise process in nitrogen or air at a temperature rise rate of 10 ° C./min. The temperature when it decreased by% was measured. The _{higher the value of T d} ^5, the higher the thermal stability.

<Z-direction linear thermal expansion coefficient (Z-direction CTE), body expansion coefficient (β)>
The polyimide film was placed on a silicon wafer, set in a METTLER TOLEDO hot stage (FP90 / 82), and then heated to 200 ° C by repeating temperature raising and holding in steps from 100 ° C to 20 ° C. .. During the temperature hold, the film thickness at each temperature was measured using an interference type thin film measuring device (F20) manufactured by Philmetrics, and the Z-direction CTE (α _Z ) was obtained from the obtained gradient of the temperature-film thickness curve. rice field.

In addition, the coefficient of thermal expansion (β) was obtained from the relational expression: β = (2α _XY + α _{Z ) / 3, which is generally established, using α XY} and α _Z actually measured as described above.

[Example 1]
<Synthesis of thermally crosslinkable functional group-containing diamine (35DABA)>
The heat-crosslinkable functional group-containing diamine (35DABA) was synthesized as follows.

First, 13.86 g (60 mmol) of 3,5-dinitrobenzoyl chloride (35DNBC) was dissolved in 144 mL of toluene in an eggplant-shaped flask. After adding 100 mL of 28% aqueous ammonia to this solution, the mixture was vigorously stirred at room temperature for 1 hour. The precipitated precipitate was separated by filtration, washed thoroughly with water until the washing liquid became neutral, and then vacuum dried at 100 ° C. for 12 hours to obtain a white powder with a yield of 77%. The analysis results of this product are shown below.

Melting point: 183 ° C
FT-IR spectrum ^{(KBr, cm -1): 3350/3168} ( amide group, NH stretching vibration), 1676 (amide group, C = O stretching vibration), 1631 (NH ₂ deformation vibration), 1550 (amide Group, C = O expansion and contraction vibration + nitro group, inverse symmetric expansion and contraction vibration), 1345 (nitro group, symmetric expansion and contraction vibration)
^{1 1} H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 9.07 (sd, 2H, J = 2.0 Hz, 2,6-ArH), 8.96 (st, 1H, J = 2) .0Hz, 4-ArH), 8.67 (s, 1H, CONH ₂ ), 8.03 (s, 1H, CONH ₂ )
From the results of this analysis, it was confirmed that the product was 3,5-dinitrobenzamide (35DNBA).

Next, the reduction of the two nitro groups of 35DNBA was carried out as follows.

In a three-necked flask, 35 DNBA (3.05 g, 14.43 mmol) was dissolved in 60 mL of ethanol, then Pd / C (0.33 g) was added as a catalyst, and then reflux was performed at 80 ° C. for 8 hours while hydrogen bubbling. did. Completion of the reaction was confirmed by thin layer chromatography. After completion of the reaction, the catalyst residue was removed by filtering the reaction mixture. The filtrate was allowed to stand at room temperature for 12 hours, and then the precipitated precipitate was filtered off. In addition, in order to increase the yield, the precipitate was recovered by concentrating the filtrate side with an evaporator. The whole precipitate obtained was vacuum dried at 100 ° C. for 12 hours to obtain a reddish brown product in a yield of 60%. The analysis results of this product are shown below.

Melting point: 151.4 ° C
FT-IR spectrum (KBr, cm ^-1 ): 3409/3213 (NH ₂ group, stretching vibration), 1648 (amide group, C = O stretching vibration)
¹ H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 7.44 (s, 1H, CONH ₂ ), 6.90 (s, 1H, CONH ₂ ), 6.23 (sd, 2H, J = 2.0Hz, 2,6-ArH), 5.93 (st, 1H, J = 2.0Hz, 4-ArH), 4.81 (s, 4H, 3,5-NH ₂ )
Elemental analysis (C ₇ H ₉ ON ₃ , molecular weight 151.17): Estimated value (%) C; 55.62, H; 6.00, N; 27.80, Analytical value C; 55.67, H; 5 .97, N; 27.73
From these analysis results, the product is the following formula (6):

It was confirmed that it was a high-purity 35 DABA represented by.

<Polyimide precursor polymerization, polyimide film fabrication and characterization>
A polyimide copolymer having a diamine component copolymerization composition of 35 DABA (20 mol%): TFMB (80 mol%) was prepared as follows. TFMB (1.60 mmol) and 35 DABA (0.40 mmol) were placed in a well-dried closed reaction vessel, followed by NMP fully dehydrated with Molecular Sieves 4A to dissolve TFMB and 35 DABA. The polymerization reaction was started while adding PMDA powder (2.00 mmol) little by little to this solution. Polymerization was started with the initial total solute concentration set to 30% by weight, but since the solution viscosity became too high during the polymerization reaction, the mixture was stirred at room temperature for 72 hours while adding the minimum necessary solvent stepwise as appropriate. did. The final solute concentration was 19% by weight. No gelation was observed during the polymerization reaction, and a completely uniform and viscous polyimide precursor solution was obtained. The reduced viscosity of the polyimide precursor measured with an Ostwald viscometer at a concentration of 0.5% by weight at 30 ° C. in NMP was 1.20 dL / g, which was a result showing a sufficient high molecular weight.

Next, in order to determine the thermal crosslinking temperature conditions, a thin film of a polyimide precursor was prepared and heat-treated at 250 ° C. in vacuum for 1 hour to obtain a polyimide thin film. When the infrared absorption spectrum of the polyimide thin film was measured, an NH expansion and contraction vibration absorption band of an amide group, which is a side chain of 35 DABA ^{, was found at 3370 cm-1.} When this polyimide thin film was further heat-treated in vacuum at 350 ° C. for 1 hour, this absorption band was greatly reduced. It is considered that this is because the amide group of the side chain undergoes a condensation reaction (crosslinking) between the molecules and the imide group present at a high concentration in the vicinity thereof. From this result, the heat treatment temperature for thermal cross-linking was set to 350 ° C., and thereafter, a polyimide film (film thickness of about 20 μm) for evaluation of physical properties was produced as follows. The polymerized polyimide precursor varnish was applied to a glass substrate and then dried in a hot air dryer at 80 ° C. for 3 hours. Then, the substrate was heat-treated at 250 ° C. in vacuum for 1 hour and then at 350 ° C. in vacuum for 1 hour to obtain a polyimide film. In order to remove the residual strain of the polyimide film, the polyimide film was peeled off from the glass substrate, and then heat-treated in vacuum at 340 ° C. for 1 hour. With respect to the obtained polyimide film, CTE in the XY direction (α _XY ) and CTE in the Z direction (α _Z ) were measured, and the coefficient of thermal expansion (β) was determined. _{In addition, T g was} measured by dynamic viscoelasticity measurement, temperature change of storage elastic modulus (E'), and 5% weight loss temperature in nitrogen atmosphere and air atmosphere were measured by thermogravimetric analysis.

[Example 2]
By polymerizing the polyimide precursor in the same manner as in Example 1 except that the copolymerization composition of the diamine component was changed to 35 DABA (50 mol%): TFMB (50 mol%), uniform without gelation. I got a nice varnish. Further, a polyimide film was produced in the same manner as in the method described in Example 1, and the physical properties were evaluated.

[Example 3]
By polymerizing the polyimide precursor in the same manner as in Example 1 except that the copolymerization composition of the diamine component was changed to 35 DABA (80 mol%): TFMB (20 mol%), uniform without gelation. I got a nice varnish. Further, a polyimide film was produced in the same manner as in the method described in Example 1, and the physical properties were evaluated.

[Comparative Example 1]
Polymerization, film formation, thermal imidization, and film property evaluation were carried out in the same manner as in Example 1 except that 35 DABA was not used as the diamine and TFMB was used alone.

[Comparative Example 2]
Polymerization, film formation, thermal imidization, and film property evaluation were carried out in the same manner as in Example 1 except that the copolymerization composition of the diamine component was changed to m-PDA (20 mol%): TFMB (80 mol%). gone.

[Comparative Example 3]
Polymerization, film formation, thermal imidization, and film property evaluation were carried out in the same manner as in Example 1 except that the copolymerization composition of the diamine component was changed to m-PDA (50 mol%): TFMB (50 mol%). gone.

[Comparative Example 4]
Polymerization, film formation, thermal imidization, and film property evaluation were carried out in the same manner as in Example 1 except that the copolymerization composition of the diamine component was changed to m-PDA (80 mol%): TFMB (20 mol%). gone.

[result]
Table 1 summarizes the physical property values.

In addition, the relationship between the copolymerization composition and β is plotted in FIG. In FIG. 1, as a comparative example, a polymer obtained by using TFMB alone without using 35 DABA, and m-phenylenediamine (m-PDA) containing no amide group instead of 35 DABA are shown. The results of the copolymer obtained by using (corresponding to Comparative Examples 1 to 4 described later) were also overwritten.

In FIG. 1, circles represent Examples 1 to 3 using 35 DABA, and squares represent Comparative Examples 1 to 4 using 35 DABA. The horizontal axis of FIG. 1 shows the ratio of 35 DABA or m-PDA. The square with X = 0 represents Comparative Example 1. It can be seen that the β of the polyimide copolymer film of Example 1 having 35 DABA = 20 mol% is lower than the β of the corresponding copolymer of m-PDA = 20 mol% (Comparative Example 2). This indicates that the three-dimensional thermal dimensional stability was improved as a result of the thermal cross-linking in the polyimide of Example 1.

The polyimide film of Example 2 gave β lower than that of Comparative Example 3 with m-PDA = 50 mol%, and the difference between these β values, that is, Δβ = β (m-PDA system) -β (35DABA system) was. It was further expanded than the case of Example 1. This is considered to reflect the result that the three-dimensional crosslink density further increased with the increase of the 35 DABA content.

The polyimide film of Example 3 gave β lower than that of Comparative Example 4 in which m-PDA = 80 mol%, and the difference between these β values, that is, Δβ = β (m-PDA system) -β (35DABA system) was. It was further expanded as compared with the case of Example 2. This is considered to reflect the result that the three-dimensional crosslink density further increased with the increase of the 35 DABA content.

Further, FIG. 2 shows the DMA curves of Example 3 and Comparative Example 4. In FIG. 2, black circles represent Example 3 and white circles represent Comparative Example 4. In Comparative Example 4 with m-PDA = 80 mol%, a relatively clear glass transition was observed at around 400 ° C. as a decrease in storage elastic modulus. On the other hand, in the polyimide film of Example 3 (35 DABA = 80 mol%), the decrease in the storage elastic modulus at around 400 ° C. slowed down and the glass transition became unclear. This indicates that as a result of thermal cross-linking, thermal deformation (softening) at _{T g} is suppressed, resulting in a dramatic improvement in thermal dimensional stability in the temperature range above _{T g.} In addition, the polyimide film of Example 3 clearly increased the storage elastic modulus (E') as compared with the corresponding Comparative Example 4 (the former was E'= 4.0 GPa near room temperature, and the latter was E'= 2. 2GPa). Since the DMA measurements were performed in tensile mode, this result indicates that the storage modulus in the XY direction was increased by cross-linking. That is, it means that the thermal cross-linking occurs not only in the Z direction but also in the XY direction, in other words, the thermal cross-linking occurs three-dimensionally.

The polyimide film of Comparative Example 1 showed an extremely low XY direction CTE (α _XY = −0.7 ppm / K), but a Z direction CTE (α _Z = 162.8 ppm / K) was very large. As a result, the polyimide film of Comparative Example 1 had a very large coefficient of thermal expansion (β = 161.4 ppm / K).

The polyimide film of Comparative Example 2 showed a higher β value than the polyimide film of Example 1. This indicates that the polyimide of Comparative Example 2 is inferior in thermal dimensional stability to the polyimide of Example 1 because it does not have an amide group in the side chain and cannot be thermally crosslinked.

The polyimide film of Comparative Example 3 showed a higher β value than the polyimide film of Example 2. This indicates that, as in the case of Comparative Example 2, since the polyimide of Comparative Example 3 cannot be thermally crosslinked, it is inferior in thermal dimensional stability to the polyimide of Example 2.

The polyimide film of Comparative Example 4 showed a higher β value than the polyimide film of Example 3. This indicates that the polyimide of Comparative Example 4 is inferior in thermal dimensional stability to the polyimide of Example 3 because the polyimide of Comparative Example 4 cannot be thermally crosslinked as in Comparative Examples 2 and 3.

The present invention can be widely used in industries in the electric and electronic fields.

Claims (3)

The following general formula (1):

A repeating unit represented in, in the general formula (1), X ₁ represents a tetravalent aromatic or aliphatic group, X ₂ represents a divalent aromatic or aliphatic group, further X ₂ Medium, the following formula (2):

A thermosetting product obtained by heat-treating a thermosetting polyimide containing a structural unit represented by (1) at 330 ° C. or higher. The heat-crosslinkable polyimide has a structural unit represented by the formula (2) in all X. ₂ The thermosetting product according to claim 1, which contains 1 mol% or more of the components. An interlayer insulating film comprising the thermosetting product according to claim 1 or 2.

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