Diamine monomer containing all-trans-substituted cyclobutane structure and application of diamine monomer in high-performance transparent polyimide

Abstract

The invention provides a diamine monomer containing an all-trans-substituted cyclobutane structure and application of the diamine monomer in high-performance transparent polyimide, and belongs to the field of manufacturing of high-performance polymer materials and intermediates of the high-performance polymer materials. Starting from renewable biomass trans-anethole, the diamine monomer containing the all-trans-substituted cyclobutane structure provided by the invention has a structure as shown in a formula IV (the definition of each group is as shown in the specification), the preparation method of the diamine monomer is simple, green and efficient, and polyimide prepared from the diamine monomer is good in solubility, easy to process and suitable for industrial production. The method can be used for preparing the flexible transparent polyimide film with heat resistance, weather resistance, low water absorption and low dielectric constant, and is suitable for the fields of packaging materials in the electronic and electrical industry, flexible display and the like.

Description

Technical Field

[0001] The invention belongs to the field of manufacturing high-performance polymer materials and intermediates thereof, and specifically relates to a diamine monomer containing an all-trans-substituted cyclobutane structure and application thereof in high-performance transparent polyimide. Background Art

[0002] Polyimide is used in aerospace, electrical and electronic, microelectronics and many other fields due to its excellent heat resistance, film-forming properties, mechanical stability and electrical insulation. However, the formation of charge transfer complexes within and between polyimide molecular chains makes this material usually have a darker luster and poor transparency. In recent years, with the rapid development of emerging electronic technology industries such as high-frequency communication technology, flexible display, and smart wearables, higher requirements have been put forward for the transparency of polyimide dielectric film materials. The design and development of high-performance transparent polyimide has received extensive attention from scientific and technological workers. A large number of research results have shown that the introduction of rigid bulky side groups, fluorine-containing groups, alicyclic structures, etc. into polyimide molecular chains can help weaken the charge transfer interaction and thus improve the transparency of polyimide film materials. In addition, increasing the distortion of the polyimide molecular chain is conducive to reducing the stacking effect of the polymer molecular chain and improving the transparency and solubility of the polyimide material. Summary of the invention

[0003] The purpose of the present invention is to provide a diamine monomer containing a fully trans-substituted cyclobutane structure and an application thereof in a high-performance transparent polyimide. The polyimide prepared by a polycondensation reaction of the diamine monomer containing a fully trans-substituted cyclobutane structure provided by the present invention and a commercial dianhydride monomer exhibits high transparency and solubility, and has good film-forming properties, thermal stability and a low dielectric constant.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] In a first aspect of the present invention, a diamine monomer containing an all-trans-substituted cyclobutane structure is provided, having a structure as shown in Formula IV:

[0006]

[0007] The second aspect of the present invention provides a method for preparing a diamine monomer containing an all-trans-substituted cyclobutane structure, comprising the following steps:

[0008] (a) subjecting the following compound having a structure shown in Formula I to a nucleophilic substitution reaction with the following halogenated amide having a structure shown in Formula II in the presence of an inorganic base to form the following compound having a structure shown in Formula III;

[0009]

[0010] Wherein, R1 and R2 are each independently selected from the following group: H, methyl, and X is a halogen selected from the following group: Cl, Br, I.

[0011] (b) reacting a compound having a structure shown in Formula III in an organic solvent at a high temperature in the presence of a strong base to form a compound having a structure shown in Formula IV as follows;

[0012]

[0013] Preferably, the reaction in step (a) is carried out in the presence of an inorganic base selected from the group consisting of potassium carbonate, potassium hydroxide, cesium carbonate, sodium hydride, or a combination thereof; the molar ratio of the compound of the structure shown in formula I to the halogenated amide of the structure shown in formula II is 1:2-4; the molar ratio of the compound of the structure shown in formula I to the inorganic base is 1:2-5.

[0014] Preferably, the reaction in step (b) is carried out in the presence of a strong base selected from the group consisting of potassium carbonate, potassium hydroxide, cesium carbonate, sodium hydride, or a combination thereof; the organic solvent is dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone; and the molar ratio of the compound of the structure shown in formula III to the base is 1:2-5.

[0015] The third aspect of the present invention provides a polyimide having a structure as shown in Formula V:

[0016]

[0017] The value range of n is n≥10;

[0018] X is One or more of .

[0019] A fourth aspect of the present invention provides a method for preparing a polyimide film, comprising the following steps:

[0020] (1) In an inert gas atmosphere, a diamine monomer having a structure represented by Formula IV, a dianhydride monomer, and an organic solvent are mixed to undergo a polycondensation reaction to obtain a homogeneous and transparent polyamic acid solution;

[0021] (2) adding acetic anhydride and triethylamine to the polyamic acid solution obtained in step (1), and obtaining a homogeneous and transparent polyimide solution through a dehydration reaction;

[0022] (3) The polyimide solution obtained in step (2) is precipitated in a large amount of methanol to obtain a polyimide having a structure represented by formula IV.

[0023] (4) dissolving the polyimide obtained in step (3) in an organic solvent to obtain a polyimide solution, casting the polyimide solution onto a glass plate, and slowly removing the solvent at a certain temperature to obtain a polyimide film.

[0024] Preferably, the molar ratio of the diamine monomer having the structure represented by Formula IV to the dianhydride monomer in step (1) is 1:1-1.02.

[0025] Preferably, the organic solvent in step (1) is one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone, and the dianhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 4,4'-oxydiphthalic anhydride, 4,4'-benzophenonetetracarboxylic anhydride.

[0026] Preferably, the organic solvent in step (4) is N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone.

[0027] The present invention also provides application of the polyimide film in transparent dielectric materials.

[0028] Beneficial effects of the present invention

[0029] The present invention provides a diamine monomer containing a fully trans-substituted cyclobutane structure and its application in high-performance transparent polyimide. The diamine monomer provided by the present invention contains a fully trans-substituted cyclobutane structure and has a large torsion dihedral angle. The polyimide prepared by using the diamine monomer with this special structure shows a highly twisted molecular chain structure, which reduces the molecular chain stacking effect, thereby significantly improving the solubility and transparency of the polyimide material. At the same time, this twisted structure increases the free volume of the polymer chain and significantly reduces the dielectric constant and dielectric loss of the polymer at high frequencies. Experimental results show that the diamine monomer containing a fully trans-substituted cyclobutane structure provided by the present invention is used to prepare a transparent polyimide film with low dielectric constant, low dielectric loss and good thermal stability. For example, the dielectric constant of polyimide 6FDA-PI at 10GHz is 2.43, the dielectric loss factor is 0.003, the transmittance at 400nm is as high as 92%, the 5% thermal weight loss temperature in nitrogen reaches 490°C, and the linear thermal expansion coefficient below 300°C is as low as 56ppm / °C.

[0030] The polyimide film provided by the invention has good solubility and is easy to process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Attached Figure 1 The product obtained by implementing example 3 of the present invention 1 H NMR spectrum. DETAILED DESCRIPTION

[0033] The present invention provides a diamine monomer containing an all-trans-substituted cyclobutane structure, having a structure as shown in Formula IV:

[0034]

[0035] The present invention provides a method for preparing a diamine monomer containing an all-trans-substituted cyclobutane structure, comprising the following steps:

[0036] (a) In an acetonitrile solvent, a compound having a structure shown in Formula I and a halogenated amide having a structure shown in Formula II are subjected to a nucleophilic substitution reaction at 80° C. in the presence of an inorganic base, wherein the base is preferably potassium iodide, potassium carbonate, potassium hydroxide, cesium carbonate, sodium hydride, or a combination thereof; the reaction time is preferably 12-24 hours, and the crude product is purified by recrystallization using dichloromethane and petroleum ether to form a compound having a structure shown in Formula III;

[0037]

[0038] Wherein, R1 and R2 are each independently selected from the following group: H, methyl, and X is a halogen selected from the following group: Cl, Br, I.

[0039] (b) reacting the compound having the structure shown in Formula III in an organic solvent at 140° C. in the presence of a strong base, wherein the strong base is potassium carbonate, potassium hydroxide, cesium carbonate, sodium hydride, or a combination thereof; the organic solvent is dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone; the reaction time is preferably 24-48 hours to form the following compound having the structure shown in Formula IV;

[0040]

[0041] Wherein, R1 and R2 are each independently selected from the following group: H, methyl, and X is a halogen selected from the following group: Cl, Br, I.

[0042]

[0043] The present invention also provides a polyimide having a structure as shown in Formula V:

[0044]

[0045] In formula V, the value range of n is n≥20;

[0046] X is One or more of .

[0047] Preferably, the structural formula of the polyimide is as follows:

[0048]

[0049] The present invention also provides a method for preparing a polyimide film, comprising the following steps:

[0050] (1) In an inert gas atmosphere, a diamine monomer having a structure shown in Formula IV, a dianhydride monomer and an organic solvent are mixed and subjected to a condensation reaction. The reaction temperature is preferably 20-40° C. and the reaction time is preferably 12-48 hours to obtain a homogeneous and transparent polyamic acid solution. The molar ratio of the diamine monomer having a structure shown in Formula IV to the dianhydride monomer is 1:1-1.02. The sum of the molar amounts of the diamine monomer having a structure shown in Formula IV and the dianhydride monomer is 20%-50% of the volume of the solvent used. The organic solvent is preferably one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone. The dianhydride monomer is preferably 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 4,4'-oxydiphthalic anhydride, and 4,4'-benzophenonetetracarboxylic anhydride.

[0051] (2) adding acetic anhydride and triethylamine to the polyamic acid solution obtained in step (1), and subjecting the polyamic acid solution to a dehydration reaction, wherein the reaction temperature is preferably 20-40° C. and the reaction time is preferably 12-48 hours, to obtain a homogeneous and transparent polyimide solution; the amount of acetic anhydride is 1-2 times the sum of the amounts of the diamine monomer and the dianhydride monomer; and the amount of triethylamine is 1-2 times the sum of the amounts of the diamine monomer and the dianhydride monomer.

[0052] (3) The polyimide solution obtained in step (2) is precipitated in a large amount of methanol to obtain a polyimide having a structure represented by formula V.

[0053] (4) dissolving the polyimide obtained in step (3) in an organic solvent to obtain a polyimide solution, wherein the organic solvent is preferably N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone; casting the polyimide solution onto a glass plate, slowly removing the solvent at a certain temperature, preferably 60-100° C., and preferably for 12-48 hours, and naturally cooling to room temperature to obtain a polyimide film.

[0054] The polyimide film is immersed in deionized water to separate from the glass plate to obtain a polymer film, and vacuum dried to obtain a transparent polyimide film; the vacuum drying temperature is preferably 60-100° C., and the time is preferably 6-8 hours.

[0055] The present invention also provides application of the polyimide film in high-frequency and low-dielectric-constant materials.

[0056] The present invention is further described in detail below with reference to specific examples, in which the raw materials involved are all commercially available.

[0057] Example 1 Preparation of diamine monomer containing dipropionamide structure

[0058]

[0059] In a 250ml round-bottom flask equipped with a magnetic, (1S,2S,3R,4R)1,2-bis(4-hydroxyphenyl)-3,4-dimethylcyclobutane (4.4362g, 0.0165mol, 1equirv) and 2-bromopropionamide (5.0251g, 0.033mol, 2equirv) were dissolved in acetonitrile (150ml), and potassium iodide (0.2744g, 0.1equirv) and potassium carbonate (6.8488g, 0.496mol, 3equirv) were added. The reactants were heated to 80°C, refluxed for 36h, cooled to room temperature, and the solvent was removed by vacuum distillation. Extracted twice with ethyl acetate and washed with saturated brine. Drying over anhydrous sodium sulfate, filtering, and removing the solvent gave a crude product. The product was recrystallized with dichloromethane / petroleum ether (DCM:Pe=1:20) to obtain a diamine monomer containing a dipropionamide structure (6.43 g, yield 95%).

[0060] Example 2 Preparation of diamine monomer containing dibutylamide structure

[0061]

[0062] In a 250ml round-bottom flask equipped with a magnetic, (1S,2S,3R,4R)1,2-bis(4-hydroxyphenyl)-3,4-dimethylcyclobutane (2.6836g, 0.01mol, 1equirv) and 2-bromoisobutyramide (3.3204g, 0.02mol, 2equirv) were dissolved in acetonitrile (100ml), and potassium iodide (0.166g, 0.1equirv) and potassium carbonate (3.3204g, 0.03mol, 3equirv) were added. The reactants were heated to 80°C, refluxed for 36h, cooled to room temperature, and the solvent was removed by vacuum distillation. Extracted twice with ethyl acetate and washed with saturated brine. Drying over anhydrous sodium sulfate, filtering, and removing the solvent gave a crude product. Recrystallize with dichloromethane / petroleum ether (DCM:Pe=1:20) to obtain a diamine monomer containing a dibutylamide structure (6.43 g, yield 95%)

[0063] Example 3 Preparation of diamine monomer containing all-trans-substituted cyclobutane structure

[0064]

[0065] The four-membered ring aromatic derivative (6.8680g, 1equirv) and potassium hydroxide (2.2526g, 40.15mmol, 2.4equirv) were dissolved in DMSO (58ml). The reactants were heated to 140°C, refluxed for 18h, cooled to room temperature, and diluted with water. Extracted with ethyl acetate three times and washed with saturated brine. Drying with anhydrous magnesium sulfate, filtering, and removing the solvent to obtain a crude product. Column chromatography using dichloromethane / methanol (DCM:MeOH=50:1) as the eluent obtained a diamine monomer containing a fully trans-substituted cyclobutane structure (after column chromatography and recrystallization (1.10104g, yield 22.39%).

[0066] Example 4 Preparation of 6FDA-PI

[0067] Under argon protection, a mixture of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) (223.9 mg, 0.5 mmol) and a diamine monomer containing a fully trans-substituted cyclobutane structure (134.1 mg, 0.5 mmol) and N-methylpyrrolidone (1.5 mL) was reacted at 25°C for 24 hours, and then acetic anhydride (0.4 mL) and triethylamine (0.2 mL) were added. After stirring at 25°C for 24 hours, the reaction solution was slowly dripped into methanol (400 mL) to obtain a white filamentous solid after filtration. After vacuum drying at 70°C for 6 hours, polyimide 6FDA-PIA was obtained.

[0068] The structure of the polyimide 6FDA-PI containing an all-trans-substituted cyclobutane structure is as follows:

[0069]

[0070] Example 5 Preparation of ODPA-PI

[0071] Under argon protection, a mixture of 4,4'-oxydiphthalic anhydride (ODPA) (310.21 mg, 1 mmol), a diamine monomer containing a fully trans-substituted cyclobutane structure (268.2 mg, 1 mmol) and N-methylpyrrolidone (3 mL) was reacted at 25°C for 24 hours, and then acetic anhydride (0.8 mL) and triethylamine (0.4 mL) were added. After stirring at 25°C for 24 hours, the reaction solution was slowly dripped into methanol (600 mL). A white filamentous solid was obtained by filtration. After vacuum drying at 70°C for 6 hours, polyimide ODPA-PI was obtained.

[0072] The structure of the polyimide ODPA-PI containing an all-trans-substituted cyclobutane structure is as follows:

[0073]

[0074] Example 6 Preparation of PMDA-PI

[0075] Under argon protection, a mixture of pyromellitic dianhydride (PMDA) (218.12 mg, 1 mmol), a diamine monomer containing a fully trans-substituted cyclobutane structure (268.2 mg, 1 mmol) and N-methylpyrrolidone (3 mL) was reacted at 25°C for 24 hours, and then acetic anhydride (0.8 mL) and triethylamine (0.4 mL) were added. After stirring at 25°C for 24 hours, the reaction solution was slowly dripped into methanol (600 mL). A white filamentous solid was obtained by filtration. After vacuum drying at 70°C for 6 hours, polyimide PMDA-PI was obtained.

[0076] The structure of the polyimide PMDA-PI containing an all-trans-substituted cyclobutane structure is as follows:

[0077]

[0078] Example 7 Preparation of HPMDA-PI

[0079] Under argon protection, a mixture of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) (224.17 mg g, 1 mmol), a diamine monomer containing a fully trans-substituted cyclobutane structure (268.2 mg, 1 mmol) and N-methylpyrrolidone (3 mL) was reacted at 25 ° C for 24 hours, and then acetic anhydride (0.8 mL) and triethylamine (0.4 mL) were added. After stirring at 25 ° C for 24 hours, the reaction solution was slowly dripped into methanol (600 mL) and filtered to obtain a white filamentous solid. After vacuum drying at 70 ° C for 6 hours, polyimide HPMDA-PI was obtained.

[0080] The structure of the polyimide HPMDA-PI containing an all-trans-substituted cyclobutane structure is as follows:

[0081]

[0082] Example 8 Preparation of BTDA-PI

[0083] Under argon protection, a mixture of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) (224.17 mg g, 1 mmol), a diamine monomer containing an all-trans-substituted cyclobutane structure (268.2 mg, 1 mmol) and N-methylpyrrolidone (3 mL) was reacted at 25 ° C for 24 hours, and then acetic anhydride (0.8 mL) and triethylamine (0.4 mL) were added. After stirring at 25 ° C for 24 hours, the reaction solution was slowly dripped into methanol (600 mL) to obtain a white filamentous solid after filtration. After vacuum drying at 70 ° C for 6 hours, polyimide BTDA-PI was obtained.

[0084] The structure of the polyimide BTDA-PI containing an all-trans-substituted cyclobutane structure is as follows:

[0085]

[0086] Example 9 Preparation of BPDA-PI

[0087] Under argon protection, a mixture of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (294.88 mg g, 1 mmol), a diamine monomer containing a fully trans-substituted cyclobutane structure (268.2 mg, 1 mmol) and N-methylpyrrolidone (3 mL) was reacted at 25 ° C for 24 hours, and then acetic anhydride (0.8 mL) and triethylamine (0.4 mL) were added. After stirring at 25 ° C for 24 hours, the reaction solution was slowly dripped into methanol (600 mL) to obtain a white filamentous solid after filtration. After vacuum drying at 70 ° C for 6 hours, polyimide BPDA-PI was obtained.

[0088] The structure of the polyimide BPDA-PI containing an all-trans-substituted cyclobutane structure is as follows:

[0089]

[0090] Example 10

[0091] 6FDA-PI (1 g) was dissolved in 15 mL of N, N-dimethylacetamide to form a homogeneous transparent solution. The obtained solution was cast onto a clean glass plate, dried at 80° C. for 12 h, and naturally cooled to room temperature to obtain a 6FDA-PI film.

[0092] ODPA-PI (1 g) was dissolved in 15 mL N, N-dimethylacetamide to form a homogeneous transparent solution. The obtained solution was cast onto a clean glass plate, dried at 80° C. for 12 h, and naturally cooled to room temperature to obtain an ODPA-PI film.

[0093] BPDA-PI (1 g) was dissolved in 15 mL N, N-dimethylacetamide to form a homogeneous transparent solution. The obtained solution was cast onto a clean glass plate, dried at 80° C. for 12 h, and naturally cooled to room temperature to obtain a BPDA-PI film.

[0094] PMDA-PI (1 g) was dissolved in 15 mL N, N-dimethylacetamide to form a homogeneous transparent solution. The obtained solution was cast onto a clean glass plate, dried at 80° C. for 12 h, and naturally cooled to room temperature to obtain a PMDA-PI film.

[0095] The thermal stability of the obtained film was tested by TGA, with nitrogen as the carrier gas and a heating rate of 10°C / min; the linear thermal expansion coefficient was tested by thermomechanical analysis, with a heating rate of 5°C / min; the transmittance of the film was tested by UV-visible spectrophotometer; and the dielectric properties were tested by Agilent impedance meter and network spectrum analyzer.

[0096]

[0097] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as reference individually. In addition, it should be understood that after reading the above content of the present invention, various changes made by those skilled in the art to the technical solution of the present invention should be within the scope of protection determined by the claims of the present invention.

Claims

1. A diamine monomer containing an all-trans-substituted cyclobutane structure, characterized in that: It has a structure as shown in Formula IV:

2. The method for preparing a diamine monomer containing an all-trans-substituted cyclobutane structure according to claim 1, characterized in that: The following steps are involved: (a) subjecting the following compound having a structure shown in Formula I to a nucleophilic substitution reaction with the following halogenated amide having a structure shown in Formula II in the presence of an inorganic base to form the following compound having a structure shown in Formula III; Wherein, R1 and R2 are each independently selected from the following group: H, methyl, and X is a halogen selected from the following group: Cl, Br, I. (b) reacting a compound having a structure shown in Formula III in an organic solvent at a high temperature in the presence of a strong base to form a compound having a structure shown in Formula IV as follows; 3. The method for preparing a diamine monomer containing an all-trans-substituted cyclobutane structure as claimed in claim 2, characterized in that: The reaction in step (a) is carried out in the presence of an inorganic base selected from the group consisting of potassium carbonate, potassium hydroxide, cesium carbonate, sodium hydride, or a combination thereof; the molar ratio of the compound of the structure shown in formula I to the halogenated amide of the structure shown in formula II is 1:2-4; the molar ratio of the compound of the structure shown in formula I to the inorganic base is 1:2-5.

4. The method for preparing a diamine monomer containing an all-trans-substituted cyclobutane structure according to claim 2, characterized in that: The reaction in step (b) is carried out in the presence of a strong base selected from the group consisting of potassium carbonate, potassium hydroxide, cesium carbonate, sodium hydride, or a combination thereof; the organic solvent is dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone; and the molar ratio of the compound of the structure shown in formula III to the base is 1:2-5.

5. A polyimide, characterized in that: It has the structure shown in Formula V: The value range of n is n≥10; X is One or more of .

6. The method for preparing a polyimide and a film thereof according to claim 5, characterized in that: The following steps are involved: (1) In an inert gas atmosphere, a diamine monomer having a structure represented by Formula IV, a dianhydride monomer, and an organic solvent are mixed to undergo a polycondensation reaction to obtain a homogeneous and transparent polyamic acid solution; (2) adding acetic anhydride and triethylamine to the polyamic acid solution obtained in step (1), and obtaining a homogeneous and transparent polyimide solution through a dehydration reaction; (3) The polyimide solution obtained in step (2) is precipitated in a large amount of methanol to obtain a polyimide having a structure represented by formula IV. (4) dissolving the polyimide obtained in step (3) in an organic solvent to obtain a polyimide solution, casting the polyimide solution onto a glass plate, and slowly removing the solvent at a certain temperature to obtain a polyimide film.

7. The method for preparing a polyimide and a film thereof according to claim 6, characterized in that: The molar ratio of the diamine monomer having the structure shown in Formula IV to the dianhydride monomer in the step (1) is 1:1-1.02; the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone.

8. The method for preparing a polyimide and a film thereof according to claim 6, characterized in that: The organic solvent in step (4) is N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone.

9. Use of the polyimide film according to claim 6 in transparent dielectric materials.

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