Soluble high-heat-resistance polyimide film and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, and discloses a soluble high-heat-resistance polyimide film and a preparation method thereof. The preparation method of the soluble high-heat-resistance polyimide film comprises the following steps: mixing diamine, dianhydride, a catalyst and a solvent, carrying out gradient reaction in an inert gas atmosphere to obtain a polyimide solution, and then settling and separating out the polyimide solution in a settling agent to obtain polyimide powder; dissolving polyimide powder in a solvent to obtain a polyimide solution, then coating the surface of a substrate with the polyimide solution, and heating to obtain a polyimide film; and crosslinking the polyimide film to obtain the soluble high-heat-resistance polyimide film. The glass transition temperature of the soluble high-heat-resistance polyimide film can reach 460 DEG C, the 5% thermal weight loss temperature of the soluble high-heat-resistance polyimide film can reach 545 DEG C, and the soluble high-heat-resistance polyimide film has good heat resistance, solubility and mechanical performance.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, in particular to a soluble high-heat-resistant polyimide film and a preparation method thereof. Background Art

[0002] Polyimide (PI) is a high molecular polymer containing an imide ring structure in the main chain of the molecule, which is polymerized from dianhydride and diamine monomers. As a special engineering material, polyimide has good electrical insulation properties, mechanical properties, chemical stability, aging resistance, radiation resistance and low dielectric loss. Therefore, polyimide has been widely used in aviation, aerospace, microelectronics, nano, liquid crystal, separation membrane, laser and other fields.

[0003] Polyimide film is one of the earliest commodities of polyimide. The main products include DuPont Kapton, Ube Industries' Upilex series and Kaneka Apical. The comprehensive performance of polyimide film is very excellent. Therefore, polyimide film is known as "golden film" and is widely used in flexible printed circuit boards, solar cell base panels, motors, wires and cables and other fields.

[0004] Although polyimide films have excellent comprehensive properties, the glass transition temperature of most commercialized and reported polyimide films is still below 400°C, and their solubility is poor, making them difficult to process using solution methods. They cannot meet the requirements of aerospace, microelectronics and other fields for the preparation process and high performance of polyimide films. Therefore, the development of new polyimide film materials that have good solubility, solution molding and high heat resistance is an urgent need in the field of high-performance polymer materials.

[0005] From the perspective of molecular design, the introduction of strong polar groups and cross-linked structures is beneficial to improving the heat resistance of polyimide films, while the introduction of large steric side groups and twisted non-coplanar structures is beneficial to improving the transparency and solubility of polyimide films. However, overly complex molecular designs may significantly increase the cost of the synthesis process and also present many difficulties in industrial production.

[0006] A study has provided a method for modifying a polyimide film using a cyanide group, including cyanide end-capping and cyanation of the main chain benzene ring (a method for preparing a high-temperature resistant polyimide film with end-group cross-linking and its application, application number: 2024103938597); however, when the polyimide film is modified by cyanide end-capping, the cyanide content in the polymer chain is very low, and the cross-linking density of the cured product is low, which limits the improvement in the heat resistance of the polyimide; and directly introducing the cyanide group into the main chain benzene ring can greatly increase the glass transition temperature of the polyimide film, but the cyanide-modified polyimide molecular chain is stacked in a crystalline aggregate structure, and the dense molecular chain arrangement makes the solubility performance of the polyetherimide unsatisfactory (see Facile synthesis of soluble, self-crosslinkable and crystalline polyimides with ultrahigh thermal / chemical resistance, Polymer, 2023, 268, 125717).

[0007] Based on this, how to effectively improve the solubility of polyimide film while improving its heat resistance has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0008] The purpose of the present invention is to provide a type of soluble high-heat-resistant polyimide film and a preparation method thereof. The polyimide film has good heat resistance, solubility and mechanical properties, and has good application prospects in the field of high-performance polyimide-based composite materials and polyimide film materials.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] One of the technical solutions of the present invention:

[0011] A method for preparing a soluble high heat-resistant polyimide film comprises the following steps:

[0012] 1) mixing a diamine, a dianhydride, a catalyst and a solvent, and performing a gradient reaction in an inert gas atmosphere to obtain a polyimide solution, and then precipitating the polyimide solution in a precipitant to obtain a polyimide powder;

[0013] 2) dissolving the polyimide powder obtained in step 1) in a solvent, and adding a curing catalyst to obtain a polyimide solution, and then coating the polyimide solution on the surface of the substrate, heating, and obtaining a polyimide film;

[0014] 3) Cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film.

[0015] Further, in step 1), the diamine is a cyano-containing diphenyl diamine, comprising: One or more of .

[0016] Further, in step 1), the dianhydride comprises One or more of .

[0017] Further, in step 1), the catalyst comprises One or more of .

[0018] Furthermore, in step 1), the solvent is m-cresol or a mixed solvent obtained by mixing m-cresol with one or more of halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide in any proportion.

[0019] Furthermore, in step 1), the molar ratio of the diamine to the dianhydride is (0.9-1):(1-0.9).

[0020] Furthermore, in step 1), the amount of the catalyst used is 5 wt.% of the total amount of diamine and dianhydride.

[0021] Furthermore, in step 1), the mass volume ratio of the solvent to the total amount of diamine and dianhydride is 1 mL: (0.1-0.7) g.

[0022] Furthermore, in step 1), the gradient reaction is specifically: reaction at 20-50°C for 0.5-8h, reaction at 50-80°C for 0.5-8h, reaction at 80-120°C for 0.5-10h, reaction at 120-150°C for 0.5-12h, and reaction at 150-200°C for 0.5-72h.

[0023] Furthermore, in step 1), the sedimentation agent includes one or more of alkanes, acetone, ethanol, methanol and water.

[0024] Furthermore, in step 2), the solvent includes one or more of halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0025] Furthermore, in step 2), the mass concentration of the polyimide solution is 1 to 25%.

[0026] Furthermore, in step 2), the curing catalyst includes ferric chloride or cobalt acetylacetonate.

[0027] Furthermore, in step 2), the curing catalyst can be selectively added as needed.

[0028] Furthermore, in step 2), the substrate is a glass plate, an aluminum plate, a stainless steel plate or a copper plate.

[0029] Furthermore, in step 2), the heating is specifically: heating at 20-160° C. for 0.5-24 h.

[0030] Furthermore, in step 3), the cross-linking is specifically: keeping warm at 200-300°C for 0.5-10h, keeping warm at 300-380°C for 0.5-10h, and keeping warm at 380-420°C for 0.5-72h.

[0031] The second technical solution of the present invention:

[0032] The soluble high heat-resistant polyimide film is prepared by the method for preparing the above-mentioned soluble high heat-resistant polyimide film.

[0033] The third technical solution of the present invention:

[0034] The above soluble high heat-resistant polyimide film is used in the fields of aerospace, microelectronics and machinery.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention discloses a soluble high heat-resistant polyimide film, whose glass transition temperature can reach 460°C and 5% thermal weight loss temperature can reach 545°C, and has good heat resistance, solubility and mechanical properties, and has good application prospects in the fields of polyimide-based composite materials and polyimide film materials.

[0037] The polyimide disclosed in the present invention has an amorphous aggregate structure and can be dissolved in common organic solvents such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and tetrahydrofuran.

[0038] The invention suspends a cyano-containing benzene ring as a side group on the main chain of the polyimide, and each structural unit contains a cyano-containing benzene ring side group. The larger benzene ring side group hinders the orderly arrangement of the prepared polyimide, so that the polyimide presents an amorphous aggregate structure, and the solubility of the polyimide is significantly improved. In particular, the cyano-modified polyetherimide can also be dissolved in low-boiling point solvents such as tetrahydrofuran, chloroform or dichloromethane. At the same time, the high cyano content is beneficial to improving the cross-linking density of the film after the polyimide is cured, and the heat resistance of the polyimide is greatly improved. The glass transition temperature can reach 460°C, and the 5% thermal weight loss temperature can reach 545°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0040] Figure 1 The dynamic mechanical curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1;

[0041] Figure 2 is the Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1;

[0042] Figure 3 The XRD curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1;

[0043] Figure 4 Thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1;

[0044] Figure 5 is the Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-2 prepared in Example 2;

[0045] Figure 6 The XRD curve of the soluble high heat-resistant polyimide film PI-2 prepared in Example 2;

[0046] Figure 7 Thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-2 prepared in Example 2;

[0047] Figure 8 is the Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-3 prepared in Example 3;

[0048] Fig. 9 The XRD curve of the soluble high heat-resistant polyimide film PI-3 prepared in Example 3;

[0049] Fig.10 Thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-3 prepared in Example 3;

[0050] Fig.11 is the Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4;

[0051] Fig.12This is the XRD curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4;

[0052] Fig.13 This is the thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4. DETAILED DESCRIPTION

[0053] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0054] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0055] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0056] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0057] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0058] In the following examples, the room temperature is 25±2°C.

[0059] In the following embodiments, the method for preparing the soluble high heat-resistant polyimide film comprises the following steps:

[0060] 1) mixing a diamine, a dianhydride, a catalyst and a solvent, and performing a gradient reaction in an inert gas atmosphere to obtain a polyimide solution, and then precipitating the polyimide solution in a precipitant to obtain a polyimide powder;

[0061] Wherein, the diamine is a cyano-containing diphenyl diamine, including: One or more of;

[0062] Wherein, the dianhydride comprises One or more of;

[0063] Wherein, the catalyst comprises One or more of;

[0064] Wherein, the solvent is m-cresol or a mixed solvent obtained by mixing m-cresol with one or more of halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide in any proportion;

[0065] Wherein, the molar ratio of the diamine to the dianhydride is (0.9-1): (1-0.9);

[0066] Wherein, the amount of the catalyst is 5wt.% of the total amount of diamine and dianhydride;

[0067] Wherein, the mass volume ratio of the solvent to the total amount of diamine and dianhydride is 1mL: (0.1-0.7)g;

[0068] The gradient reaction is specifically: reacting at 20-50°C for 0.5-8h, reacting at 50-80°C for 0.5-8h, reacting at 80-120°C for 0.5-10h, reacting at 120-150°C for 0.5-12h, and reacting at 150-200°C for 0.5-72h;

[0069] Wherein, the sedimentation agent includes one or more of alkanes, acetone, ethanol, methanol and water;

[0070] 2) dissolving the polyimide powder obtained in step 1) in a solvent to obtain a polyimide solution, and then coating the polyimide solution on the surface of the substrate and heating to obtain a polyimide film;

[0071] Wherein, the solvent includes one or more of halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide;

[0072] Wherein, the mass concentration of the polyimide solution is 1 to 25%;

[0073] Wherein, the coating is performed by casting, spin coating, brush coating or scraping;

[0074] Wherein, the substrate is a glass plate, an aluminum plate, a stainless steel plate or a copper plate;

[0075] The heating is specifically: heating at 20-160° C. for 0.5-24 hours;

[0076] 3) cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film;

[0077] The cross-linking is specifically: keeping warm at 200-300°C for 0.5-10h, keeping warm at 300-380°C for 0.5-10h, and keeping warm at 380-420°C for 0.5-72h.

[0078] Example 1

[0079] A soluble high heat-resistant polyimide film PI-1

[0080] 1) 0.4185 g of 2',4'-diamino-[1,1'-biphenyl]-4-benzonitrile, 0.8884 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 0.06 mL of isoquinoline and 6 mL of m-cresol were mixed, and gradient reaction was carried out in a nitrogen atmosphere to obtain a polyimide solution, and then the polyimide solution was precipitated in anhydrous ethanol, filtered, and dried to obtain a polyimide powder;

[0081] The gradient reaction is specifically: reaction at room temperature for 2 hours, reaction at 50°C for 12 hours, reaction at 80°C for 12 hours, reaction at 120°C for 12 hours, reaction at 150°C for 4 hours, reaction at 180°C for 4 hours, and reaction at 200°C for 4 hours;

[0082] 2) dissolving the polyimide powder obtained in step 1) in N,N-dimethylacetamide according to the mass concentration of the polyimide solution being 10% to obtain a polyimide N,N-dimethylacetamide solution, and then coating the polyimide N,N-dimethylacetamide solution on the surface of a stainless steel plate and heating to obtain a polyimide film;

[0083] The heating is specifically: heating at 60°C for 4 hours and heating at 120°C for 3 hours;

[0084] 3) cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, which is recorded as PI-1;

[0085] The cross-linking is specifically as follows: keeping warm at 300°C for 6 hours, keeping warm at 380°C for 36 hours, and then cooling to room temperature.

[0086] The dynamic mechanical curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1 was measured (measurement conditions: nitrogen atmosphere, heating rate of 2°C / min, frequency of 1Hz, single cantilever beam mode), and the measurement results are as follows: Figure 1 As shown;

[0087] The Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1 was measured (measurement conditions: KBr tablet method, measurement range: 4000 cm -1 ~500cm -1 ), the measurement results are as follows Figure 2 As shown;

[0088] The XRD curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1 was measured (measurement conditions: Cu target as X-ray light source, scanning speed 6° / min, scanning range 5°~50°), and the measurement results are as follows: Figure 3 As shown;

[0089] The thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-1 prepared in Example 1 was measured (measurement conditions: nitrogen atmosphere, heating rate 10°C / min, test range 60-800°C), and the measurement results are as follows: Figure 4 shown.

[0090] Example 2

[0091] A soluble high heat-resistant polyimide film PI-2

[0092] 1) 0.4185 g of 2',4'-diamino-[1,1'-biphenyl]-4-benzonitrile, 0.6204 g of 4,4'-oxydiphthalic anhydride, 0.06 mL of isoquinoline and 6 mL of m-cresol were mixed, and gradient reaction was carried out in a nitrogen atmosphere to obtain a polyimide solution, and then the polyimide solution was precipitated in anhydrous ethanol, filtered, and dried to obtain a polyimide powder;

[0093] The gradient reaction is specifically: reaction at room temperature for 2 hours, reaction at 50°C for 12 hours, reaction at 80°C for 12 hours, reaction at 120°C for 12 hours, reaction at 150°C for 4 hours, reaction at 180°C for 4 hours, and reaction at 200°C for 4 hours;

[0094] 2) dissolving the polyimide powder obtained in step 1) in N,N-dimethylacetamide according to the mass concentration of the polyimide solution being 20% ​​to obtain a polyimide N,N-dimethylacetamide solution, and then coating the polyimide N,N-dimethylacetamide solution on the surface of the aluminum plate and heating to obtain a polyimide film;

[0095] The heating is specifically: heating at 80°C for 4 hours and heating at 160°C for 6 hours;

[0096] 3) cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, which is recorded as PI-2;

[0097] The cross-linking is specifically carried out as follows: keeping the temperature at 200° C. for 2 hours, keeping the temperature at 400° C. for 48 hours, and then cooling to room temperature.

[0098] The Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-2 prepared in Example 2 was measured (measurement conditions: KBr tablet method, measurement range: 4000 cm -1 ~500cm -1 ), the measurement results are as follows Figure 5 As shown;

[0099] The XRD curve of the soluble high heat-resistant polyimide film PI-2 prepared in Example 2 was measured (measurement conditions: Cu target as X-ray light source, scanning speed 6° / min, scanning range 5°~50°), and the measurement results are as follows: Figure 6 As shown;

[0100] The thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-2 prepared in Example 2 was measured (measurement conditions: nitrogen atmosphere, heating rate 10°C / min, test range 60-800°C), and the measurement results are as follows: Figure 7 shown.

[0101] Example 3

[0102] A soluble high heat-resistant polyimide film PI-3

[0103] 1) 0.4685 g of 2',4'-diamino-[1,1'-biphenyl]-3,5-dinitrile, 0.8884 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 0.06 mL of isoquinoline and 6 mL of m-cresol were mixed, and gradient reaction was carried out in a nitrogen atmosphere to obtain a polyimide solution, and then the polyimide solution was precipitated in anhydrous ethanol, filtered, and dried to obtain a polyimide powder;

[0104] The gradient reaction is specifically: reaction at room temperature for 2 hours, reaction at 80°C for 4 hours, reaction at 120°C for 4 hours, reaction at 150°C for 4 hours, and reaction at 180°C for 12 hours;

[0105] 2) dissolving the polyimide powder obtained in step 1) in N,N-dimethylformamide at a mass concentration of 10%, and adding ferric chloride as a curing catalyst at a mass concentration of 0.5% to obtain a polyimide N,N-dimethylformamide solution, and then coating the polyimide N,N-dimethylacetamide solution on the surface of the glass plate, heating, and obtaining a polyimide film;

[0106] The heating is specifically: heating at 60°C for 4 hours and heating at 100°C for 2 hours;

[0107] 3) cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, which is recorded as PI-3;

[0108] The cross-linking is specifically as follows: keeping warm at 250°C for 2 hours, keeping warm at 380°C for 10 hours, keeping warm at 420°C for 2 hours, and then cooling to room temperature.

[0109] The Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-3 prepared in Example 3 was measured (measurement conditions: KBr tablet method, measurement range: 4000 cm -1 ~500cm -1 ), the measurement results are as follows Figure 8 As shown;

[0110] The XRD curve of the soluble high heat-resistant polyimide film PI-3 prepared in Example 3 was measured (measurement conditions: Cu target as X-ray light source, scanning speed 6° / min, scanning range 5°~50°), and the measurement results are as follows: Fig. 9 As shown;

[0111] The thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-3 prepared in Example 3 was measured (measurement conditions: nitrogen atmosphere, heating rate 10°C / min, test range 60-800°C), and the measurement results are as follows: Fig.10 shown.

[0112] Example 4

[0113] A soluble high heat-resistant polyimide film PI-4

[0114] 1) 0.4685 g of 2',4'-diamino-[1,1'-biphenyl]-3,5-dicarbonitrile, 0.6204 g of 4,4'-oxydiphthalic anhydride, 0.06 mL of isoquinoline and 6 mL of m-cresol were mixed, and gradient reaction was carried out in a nitrogen atmosphere to obtain a polyimide solution, and then the polyimide solution was precipitated in anhydrous ethanol, filtered, and dried to obtain a polyimide powder;

[0115] The gradient reaction is specifically: reaction at room temperature for 2 hours, reaction at 80°C for 4 hours, reaction at 120°C for 4 hours, reaction at 150°C for 4 hours, and reaction at 180°C for 12 hours;

[0116] 2) dissolving the polyimide powder obtained in step 1) in N,N-dimethylformamide at a mass concentration of 12%, and adding a curing catalyst, cobalt acetylacetonate, at a mass concentration of 1%, to obtain a polyimide N,N-dimethylformamide solution, and then coating the polyimide N,N-dimethylformamide on the surface of a glass plate, and heating to obtain a polyimide film;

[0117] The heating is specifically: heating at 70°C for 4 hours and heating at 110°C for 3 hours;

[0118] 3) cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, which is recorded as PI-4;

[0119] The cross-linking is specifically carried out as follows: keeping warm at 200°C for 5 hours, keeping warm at 350°C for 10 hours, keeping warm at 400°C for 4 hours, and then cooling to room temperature.

[0120] The Fourier transform infrared spectrum curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4 was measured (measurement conditions: KBr tablet method, measurement range: 4000 cm -1 ~500cm -1 ), the measurement results are as follows Fig.11 As shown;

[0121] The XRD curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4 was measured (measurement conditions: Cu target as X-ray light source, scanning speed 6° / min, scanning range 5°~50°), and the measurement results are as follows: Fig.12 As shown;

[0122] The thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4 was measured (measurement conditions: nitrogen atmosphere, heating rate 10°C / min, test range 60-800°C), and the measurement results are as follows: Fig.13 shown.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a soluble high heat-resistant polyimide film, characterized in that: The following steps are involved: 1) mixing a diamine, a dianhydride, a catalyst and a solvent, and performing a gradient reaction in an inert gas atmosphere to obtain a polyimide solution, and then precipitating the polyimide solution in a precipitant to obtain a polyimide powder; 2) dissolving the polyimide powder obtained in step 1) in a solvent, and adding a curing catalyst to obtain a polyimide solution, and then coating the polyimide solution on the surface of the substrate, heating, and obtaining a polyimide film; 3) Cross-linking the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film.

2. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 1), the diamine is a cyano-containing diphenyl diamine, comprising: One or more of; the dianhydride comprises One or more of; the catalyst includes The solvent is m-cresol or a mixed solvent obtained by mixing m-cresol with one or more of halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide in any proportion; the precipitant includes one or more of alkanes, acetone, ethanol, methanol, and water.

3. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 1), the molar ratio of the diamine to the dianhydride is (0.9-1):(1-0.9); the amount of the catalyst is 5wt.% of the total amount of the diamine and the dianhydride; the mass volume ratio of the solvent to the total amount of the diamine and the dianhydride is 1mL:(0.1-0.7)g.

4. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 1), the gradient reaction is specifically: reaction at 20-50°C for 0.5-8h, reaction at 50-80°C for 0.5-8h, reaction at 80-120°C for 0.5-10h, reaction at 120-150°C for 0.5-12h, and reaction at 150-200°C for 0.5-72h.

5. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 2), the solvent includes one or more of halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

6. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 2), the mass concentration of the polyimide solution is 1 to 25%.

7. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 2), the heating is specifically: heating at 20-160° C. for 0.5-24 h.

8. The method for preparing a soluble high heat-resistant polyimide film according to claim 1, characterized in that: In step 3), the cross-linking is specifically carried out as follows: keeping warm at 200-300°C for 0.5-10h, keeping warm at 300-380°C for 0.5-10h, and keeping warm at 380-420°C for 0.5-72h.

9. A soluble high heat-resistant polyimide film prepared by the method for preparing a soluble high heat-resistant polyimide film as claimed in any one of claims 1 to 8.

10. Use of the soluble high heat-resistant polyimide film according to claim 9 in the fields of aerospace, microelectronics and machinery.

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