A type of soluble, heat-resistant polyimide film and its preparation method

Abstract

This invention relates to the field of polymer materials technology, and discloses a type of soluble, high-heat-resistant polyimide film and its preparation method. The preparation method of this invention includes the following steps: mixing diamine, dianhydride, catalyst, and solvent, and reacting them in a gradient atmosphere under an inert gas atmosphere to obtain a polyimide solution; then precipitating the polyimide solution in a flocculant to obtain polyimide powder; dissolving the polyimide powder in a solvent to obtain a polyimide solution; then coating the polyimide solution onto a substrate surface and heating it to obtain a polyimide film; and crosslinking the polyimide film to obtain the soluble, high-heat-resistant polyimide film. The soluble, high-heat-resistant polyimide film disclosed in this invention has a glass transition temperature of up to 460℃ and a 5% thermogravimetric temperature of up to 545℃, exhibiting excellent heat resistance, solubility, and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a type of soluble, heat-resistant polyimide film and its preparation method. Background Technology

[0002] Polyimide (PI) is a high molecular weight polymer containing an imide ring structure in its main chain, polymerized from dianhydride and diamine monomers. As a special engineering material, polyimide possesses excellent electrical insulation properties, mechanical properties, chemical stability, aging resistance, radiation resistance, and low dielectric loss. Therefore, polyimide has been widely used in aerospace, microelectronics, nanotechnology, liquid crystals, separation membranes, lasers, and other fields.

[0003] Polyimide film is one of the earliest commercial products of polyimide. Major products include DuPont Kapton, Ube Industries' Upilex series, and Kanekachi Apical. Polyimide film has excellent overall performance, so it is known as "golden film" and has a wide range of applications in flexible printed circuit boards, solar cell substrates, motors, and wires and cables.

[0004] Despite the excellent overall properties of polyimide films, most commercially available and literature-reported polyimide films have glass transition temperatures below 400°C and poor solubility, making them difficult to process using solution methods. This fails to meet the high-performance requirements of polyimide film preparation processes in aerospace, microelectronics, and other fields. Therefore, developing novel polyimide film materials that combine good solubility, solution molding processing, and high heat resistance is an urgent need in the field of high-performance polymer materials.

[0005] From a molecular design perspective, introducing strongly polar groups and cross-linked structures can improve the heat resistance of polyimide films, while introducing sterically hindered side groups and twisted non-coplanar structures can improve 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] One study described a method for modifying polyimide films using cyano groups, including cyano end-capping and cyanoylation of the main chain benzene ring (a method for preparing and applying end-crosslinked high-temperature resistant polyimide films, application number: 2024103938597). However, when modifying polyimide films by cyano end-capping, the cyano content in the polymer chain is very low, and the crosslinking density of the cured product is low, which limits the improvement of the heat resistance of polyimide. While directly introducing cyano groups into the main chain benzene ring can significantly increase the glass transition temperature of polyimide films, the cyano-modified polyimide molecular chains are stacked in a crystalline aggregate state, and the dense molecular chain arrangement makes the solubility of polyetherimide less than ideal (see Facilesynthesis of soluble, self-crosslinkable and crystalline polyimides with ultrahigh thermal / chemical resistance, Polymer, 2023, 268, 125717).

[0007] Therefore, how to effectively improve the solubility of polyimide films while enhancing their heat resistance has become a technical challenge that urgently needs to be solved by those skilled in the art. Summary of the Invention

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

[0009] To achieve the above objectives, the present invention provides the following technical solution:

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

[0011] A method for preparing a type of soluble, highly heat-resistant polyimide film includes the following steps:

[0012] 1) Mix diamine, dianhydride, catalyst and solvent, and react them in a gradient under an inert gas atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in a precipitating agent to obtain polyimide powder.

[0013] 2) Dissolve the polyimide powder obtained in step 1) in a solvent and add a curing catalyst to obtain a polyimide solution. Then, coat the polyimide solution onto the substrate surface and heat it to obtain a polyimide film.

[0014] 3) Crosslink 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 benzidine, comprising: One or more of them.

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

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

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

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

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

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

[0022] Further, in step 1), the gradient reaction specifically refers to the following reactions: 0.5–8 h at 20–50 °C, 0.5–8 h at 50–80 °C, 0.5–10 h at 80–120 °C, 0.5–12 h at 120–150 °C, and 0.5–72 h at 150–200 °C.

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

[0024] Further, in step 2), the solvent includes one or more of the following: haloalkanes, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

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

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

[0029] Further, in step 2), the heating specifically refers to heating at 20–160°C for 0.5–24 hours.

[0030] Further, in step 3), the crosslinking specifically involves: holding at 200-300℃ for 0.5-10 hours, holding at 300-380℃ for 0.5-10 hours, and holding at 380-420℃ for 0.5-72 hours.

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

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

[0033] The third technical solution of this invention:

[0034] The above-mentioned soluble, heat-resistant polyimide films have applications in aerospace, microelectronics, and machinery fields.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] The present invention discloses a type of soluble high heat-resistant polyimide film with a glass transition temperature of up to 460°C and a 5% thermal weight loss temperature of up to 545°C. It 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 this invention has an amorphous aggregated structure and is soluble in common organic solvents, such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran.

[0038] This invention uses cyano-containing benzene rings as side groups suspended on the polyimide backbone, and each structural unit contains a cyano-containing benzene ring side group. The large benzene ring side groups hinder the orderly arrangement of the prepared polyimide, resulting in an amorphous aggregated structure. This significantly improves the solubility of the polyimide, especially the cyano-modified polyetherimide, which 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 increasing the crosslinking density of the polyimide film after curing, greatly improving the heat resistance of the polyimide. The glass transition temperature can reach 460℃, and the 5% thermal weight loss temperature can reach 545℃. Attached Figure Description

[0039] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the 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 Fourier transform infrared spectrum 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 is shown.

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

[0044] Figure 5 Fourier transform infrared spectrum of the soluble, 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 is shown.

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

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

[0048] Figure 9 The XRD curve of the soluble, high-heat-resistant polyimide film PI-3 prepared in Example 3 is shown.

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

[0050] Figure 11 Fourier transform infrared spectrum of the soluble, heat-resistant polyimide film PI-4 prepared in Example 4;

[0051] Figure 12The XRD curve of the soluble, high-heat-resistant polyimide film PI-4 prepared in Example 4 is shown.

[0052] Figure 13 The thermogravimetric analysis curve of the soluble high heat-resistant polyimide film PI-4 prepared in Example 4 is shown. Detailed Implementation

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0054] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0055] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0056] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

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

[0058] In the following embodiments, the room temperature is 25±2℃.

[0059] In the following embodiments, the method for preparing a type of soluble, highly heat-resistant polyimide film includes the following steps:

[0060] 1) Mix diamine, dianhydride, catalyst and solvent, and react them in a gradient under an inert gas atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in a precipitating agent to obtain polyimide powder.

[0061] Wherein, the diamine is a cyano-containing benzidine, comprising: One or more of the following;

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

[0063] The catalyst includes One or more of the following;

[0064] The solvent is m-cresol or a mixed solvent obtained by mixing m-cresol with one or more of the following in any proportion: halogenated hydrocarbon, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0065] The molar ratio of the diamine to the dianhydride is (0.9–1):(1–0.9).

[0066] The catalyst is used in an amount of 5 wt.% of the total amount of diamine and dianhydride;

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

[0068] Specifically, the gradient reaction is carried out at 20–50°C for 0.5–8 h, at 50–80°C for 0.5–8 h, at 80–120°C for 0.5–10 h, at 120–150°C for 0.5–12 h, and at 150–200°C for 0.5–72 h.

[0069] The settling agent includes one or more of alkanes, acetone, ethanol, methanol, and water;

[0070] 2) Dissolve the polyimide powder obtained in step 1) in a solvent to obtain a polyimide solution, then coat the polyimide solution onto the substrate surface and heat it to obtain a polyimide film;

[0071] The solvent includes one or more of the following: haloalkanes, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide;

[0072] The mass concentration of the polyimide solution is 1-25%.

[0073] The coating process includes casting, spin coating, brush coating, or scraping coating.

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

[0075] Specifically, the heating process involves heating at 20–160°C for 0.5–24 hours.

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

[0077] Specifically, the crosslinking process involves: maintaining a temperature of 200–300℃ for 0.5–10 hours, maintaining a temperature of 300–380℃ for 0.5–10 hours, and maintaining a temperature of 380–420℃ for 0.5–72 hours.

[0078] Example 1

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

[0080] 1) Mix 0.4185g of 2',4'-diamino-[1,1'-biphenyl]-4-benzonitrile, 0.8884g of 4,4'-(hexafluoroisopropene)phthalic anhydride, 0.06mL of isoquinoline and 6mL of m-cresol, and react them in a gradient under a nitrogen atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in anhydrous ethanol, filter it, and dry it to obtain polyimide powder.

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

[0082] 2) Dissolve the polyimide powder obtained in step 1) in N,N-dimethylacetamide according to the mass concentration of the polyimide solution of 10% to obtain an N,N-dimethylacetamide solution of polyimide. Then, coat the surface of a stainless steel plate with the N,N-dimethylacetamide solution of polyimide and heat it to obtain a polyimide film.

[0083] Specifically, the heating process involves heating at 60°C for 4 hours and heating at 120°C for 3 hours.

[0084] 3) Crosslink the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, denoted as PI-1;

[0085] Specifically, the crosslinking process involves maintaining the temperature at 300°C for 6 hours, maintaining the temperature at 380°C for 36 hours, and then cooling to room temperature.

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

[0087] The Fourier transform infrared spectrum of the soluble high-heat-resistant polyimide film PI-1 prepared in Example 1 was determined (determination conditions: KBr pellet method, measurement range: 4000 cm⁻¹). -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 source, scanning speed 6° / min, scanning range 5°~50°), and the 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 determined (measurement conditions: nitrogen atmosphere, heating rate 10℃ / min, test range 60~800℃), and the results are as follows. Figure 4 As shown.

[0090] Example 2

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

[0092] 1) Mix 0.4185g of 2',4'-diamino-[1,1'-biphenyl]-4-benzonitrile, 0.6204g of 4,4'-oxobisphthalic anhydride, 0.06mL of isoquinoline and 6mL of m-cresol, and react them in a gradient under a nitrogen atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in anhydrous ethanol, filter it, and dry it to obtain polyimide powder.

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

[0094] 2) Dissolve the polyimide powder obtained in step 1) in N,N-dimethylacetamide according to the mass concentration of the polyimide solution being 20% ​​to obtain an N,N-dimethylacetamide solution of polyimide. Then, coat the N,N-dimethylacetamide solution of polyimide onto the surface of an aluminum plate and heat it to obtain a polyimide film.

[0095] Specifically, the heating process involves heating at 80°C for 4 hours and heating at 160°C for 6 hours.

[0096] 3) Crosslink the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, denoted as PI-2;

[0097] Specifically, the crosslinking process involves maintaining the temperature at 200°C for 2 hours, maintaining the temperature at 400°C for 48 hours, and then cooling to room temperature.

[0098] The Fourier transform infrared spectrum of the soluble, high-heat-resistant polyimide film PI-2 prepared in Example 2 was determined (determination conditions: KBr pellet method, measurement range: 4000 cm⁻¹). -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 source, scanning speed 6° / min, scanning range 5°~50°), and the 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 determined (measurement conditions: nitrogen atmosphere, heating rate 10℃ / min, test range 60~800℃), and the results are as follows. Figure 7 As shown.

[0101] Example 3

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

[0103] 1) Mix 0.4685g of 2',4'-diamino-[1,1'-biphenyl]-3,5-dionitrile, 0.8884g of 4,4'-(hexafluoroisopropene)phthalic anhydride, 0.06mL of isoquinoline and 6mL of m-cresol, and react them in a gradient under a nitrogen atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in anhydrous ethanol, filter it, and dry it to obtain polyimide powder.

[0104] Specifically, the gradient reaction is as follows: reacting at room temperature for 2 hours, at 80°C for 4 hours, at 120°C for 4 hours, at 150°C for 4 hours, and at 180°C for 12 hours.

[0105] 2) Dissolve the polyimide powder obtained in step 1) in N,N-dimethylformamide at a mass concentration of 10%, and add ferric chloride as a curing catalyst at a mass concentration of 0.5% to obtain an N,N-dimethylformamide solution of polyimide. Then, coat the N,N-dimethylacetamide solution of polyimide onto the surface of a glass plate and heat it to obtain a polyimide film.

[0106] Specifically, the heating process involves heating at 60°C for 4 hours and heating at 100°C for 2 hours.

[0107] 3) Crosslink the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, denoted as PI-3;

[0108] Specifically, the crosslinking process involves: holding at 250°C for 2 hours, holding at 380°C for 10 hours, holding at 420°C for 2 hours, and then cooling to room temperature.

[0109] The Fourier transform infrared spectrum of the soluble, high-heat-resistant polyimide film PI-3 prepared in Example 3 was determined (measurement conditions: KBr pellet method, measurement range: 4000 cm⁻¹). -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 source, scanning speed 6° / min, scanning range 5°~50°), and the results are as follows. Figure 9 As shown;

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

[0112] Example 4

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

[0114] 1) Mix 0.4685g of 2',4'-diamino-[1,1'-biphenyl]-3,5-dinitrile, 0.6204g of 4,4'-oxophthalic anhydride, 0.06mL of isoquinoline and 6mL of m-cresol, and react them in a gradient under a nitrogen atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in anhydrous ethanol, filter it, and dry it to obtain polyimide powder.

[0115] Specifically, the gradient reaction is as follows: reacting at room temperature for 2 hours, at 80°C for 4 hours, at 120°C for 4 hours, at 150°C for 4 hours, and at 180°C for 12 hours.

[0116] 2) Dissolve the polyimide powder obtained in step 1) in N,N-dimethylformamide at a mass concentration of 12%, and add cobalt acetylacetone curing catalyst at a mass concentration of 1% to obtain an N,N-dimethylformamide solution of polyimide. Then, coat the N,N-dimethylformamide solution of polyimide onto the surface of a glass plate and heat it to obtain a polyimide film.

[0117] Specifically, the heating process involves heating at 70°C for 4 hours and heating at 110°C for 3 hours.

[0118] 3) Crosslink the polyimide film obtained in step 2) to obtain the soluble high heat-resistant polyimide film, denoted as PI-4;

[0119] Specifically, the crosslinking process involves: maintaining a temperature of 200°C for 5 hours, maintaining a temperature of 350°C for 10 hours, maintaining a temperature of 400°C for 4 hours, and then cooling to room temperature.

[0120] The Fourier transform infrared spectrum of the soluble, high-heat-resistant polyimide film PI-4 prepared in Example 4 was determined (measurement conditions: KBr pellet method, measurement range: 4000 cm⁻¹). -1 ~500cm -1 The measurement results are as follows: Figure 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 source, scanning speed 6° / min, scanning range 5°~50°), and the results are as follows. Figure 12 As shown;

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

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do 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 type of soluble, high-heat-resistant polyimide film, characterized in that, Includes the following steps: 1) Mix diamine, dianhydride, catalyst and solvent, and react them in a gradient under an inert gas atmosphere to obtain a polyimide solution. Then, precipitate the polyimide solution in a precipitating agent to obtain polyimide powder. 2) Dissolve the polyimide powder obtained in step 1) in a solvent and add a curing catalyst to obtain a polyimide solution. Then, coat the polyimide solution onto the substrate surface and heat it to obtain a polyimide film. 3) Crosslink the polyimide film obtained in step 2) to obtain the soluble, high-heat-resistant polyimide film; In step 1), the diamine is a cyano-containing benzidine, comprising: One or more of the following; the dianhydrides include One or more of the following; the catalyst includes One or more of the following: the solvent is m-cresol or a mixed solvent obtained by mixing m-cresol with one or more of the following: halogenated hydrocarbons, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide in any proportion; the settling agent includes one or more of the following: alkanes, acetone, ethanol, methanol, and water.

2. The method for preparing a type of 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 5 wt.% of the total amount of the diamine and dianhydride; and the mass-volume ratio of the solvent to the total amount of the diamine and dianhydride is 1 mL:(0.1-0.7) g.

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

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

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

6. The method for preparing a type of soluble, high-heat-resistant polyimide film according to claim 1, characterized in that, In step 2), the heating specifically refers to heating at 20–160°C for 0.5–24 hours.

7. The method for preparing a type of soluble, high-heat-resistant polyimide film according to claim 1, characterized in that, In step 3), the crosslinking specifically involves: holding at 200-300℃ for 0.5-10 hours, holding at 300-380℃ for 0.5-10 hours, and holding at 380-420℃ for 0.5-72 hours.

8. A soluble high heat-resistant polyimide film prepared by a method for preparing a type of soluble high heat-resistant polyimide film as described in any one of claims 1 to 7.

9. The application of a soluble, high-heat-resistant polyimide film as described in claim 8 in the fields of aerospace, microelectronics, and machinery.

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