5-(4-benzocyclobutenyl)-1, 3-phenylenediamine compound, polyimide, polymer film and preparation method

Abstract

The invention discloses a 5-(4-benzocyclobutenyl)-1, 3-phenylenediamine compound, polyimide, a polymer film and a preparation method of the 5-(4-benzocyclobutenyl)-1, 3-phenylenediamine compound. A modified monomer with two active amino groups and a benzocyclobutene group capable of being directly heated and cross-linked is used as a diamine monomer to perform polymerization reaction, so that the benzocyclobutene group is introduced into a polymer molecule side chain, a four-membered ring of benzocyclobutene is subjected to ring opening cross-linking at high temperature to form an eight-membered ring structure, and the molecular weight of the polymer is reduced; according to the present invention, the low-molecular-weight by-product is not released during the curing, the catalyst or the initiator is not required to be added during the curing process, and other heteroatoms are not introduced, such that the prepared polymer film has characteristics of excellent heat resistance and excellent dielectric property, and has wide application prospects in the field of the dissolvable, easily-processed and low-water-absorption-rate target resin.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and more specifically to a 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, a polyimide, a polymer film and a preparation method thereof. Background Art

[0002] Aromatic diamine monomers are key monomers for preparing high-performance polymers such as polyimide, polyamide and other materials. Therefore, the structure of aromatic diamine monomers has an important influence on the thermal stability, mechanical properties and media resistance of the materials.

[0003] In order to meet the needs of materials used in high-temperature extreme environments, requirements are put forward for the heat resistance of materials. For example, heat-fixed polyimide is usually obtained by reacting cross-linkable groups at the end such as cyano, maleimide, norbornene, phenylethynyl, etc. After cross-linking, its molecules have a stable three-dimensional cross-linked network structure, and its heat resistance is excellent, and it can be used for a long time at high temperatures. If cross-linkable groups are introduced on the side groups or side chains of linear polyimide, the excellent solubility of linear polymers before cross-linking can be used to prepare film materials through solution processing first, and then cross-linking reactions can be carried out to further improve the heat resistance and medium resistance of the material, which will give the material more application fields.

[0004] Benzocyclobutene functional group (BCB) can be cross-linked by light or heat, has a wide processing window, and has excellent processing technology. In addition, BCB does not release low molecular byproducts during curing, and does not need to add catalysts or initiators during the curing process, and does not introduce other heteroatoms. At the same time, the BCB structure only contains carbon and hydrogen atoms, and the cross-linked polymer has good thermal stability, excellent dielectric properties and low hygroscopicity. However, it is difficult to introduce the BCB structure into aromatic diamine molecules and prepare it into diamine monomers, and there is no prior art report so far.

[0005] Patent application number WO2023182377 discloses a method for preparing a high molecular weight triarylamine compound, which synthesizes a monoamine intermediate containing benzocyclobutene, such as Formula II, through a 4-bromobenzocyclobutene coupling reaction, and then prepares an organic light-emitting material. In addition, some researchers have designed and synthesized an imide with a benzocyclobutene (BCB) structure, such as Formula III, and synthesized a benzocyclobutene-terminated liquid crystal polyester imide through solution polycondensation copolymerization. However, monoamine monomers can be used for end-capping, but cannot be introduced into the polymer side chain.

[0006] Therefore, there is an urgent need to develop a diamine monomer containing a benzocyclobutene structure, which can introduce the benzocyclobutene structure into the polymer side chain, thereby improving the heat resistance of the polymer.

[0007] Summary of the invention

[0008] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, a polyimide, a polymer film and a preparation method. The novel diamine monomer containing a benzocyclobutene directly heat-crosslinkable structure of the present invention can introduce the benzocyclobutene structure into the molecular side chain through copolymerization, and utilize the crosslinking regulation of the structure at high temperature to inhibit molecular motion, thereby obtaining a polyimide with excellent heat resistance and dielectric properties.

[0009] To achieve the above object, the technical solution of the present invention is as follows:

[0010] A 5(4-benzocyclobutenyl)-1,3-phenylenediamine compound having a structure shown in formula (I):

[0011]

[0012] The present invention also discloses a method for preparing the above-mentioned 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, comprising the following steps:

[0013] (1) mixing 1-bromo-3,5-dinitrobenzene and a reducing agent to react to obtain an intermediate S-1;

[0014] (2) dissolving the intermediate S-1 and an amino protecting agent in a protic solvent for amino protection to obtain an intermediate S-2;

[0015] (3) dissolving the intermediate S-2 in a solvent and mixing it with an arylboronic acid, and performing a Suzuki cross-coupling reaction under the action of a palladium catalyst to obtain an intermediate S-3;

[0016] (4) dissolving the intermediate S-3 in a solvent, and removing the protecting group under the action of a protonic acid to obtain the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound;

[0017]

[0018] Optionally, in step (1), the reducing agent includes iron powder, zinc powder or Pd / C; the reaction temperature is 80°C to 90°C; the reaction time is 3h to 5h; and the mass ratio of 1-bromo-3,5-dinitrobenzene to the reducing agent is 1 to 1.5:6 to 8.

[0019] Optionally, the purification method in step (1) is filtration and / or extraction.

[0020] Optionally, in step (2), the amino protecting agent is di-tert-butyl dicarbonate; the protic solvent is anhydrous ethanol; the reaction temperature is room temperature; the reaction time is 12h to 24h; and the mass ratio of the intermediate S-1 to di-tert-butyl dicarbonate is 1:2.

[0021] Optionally, the purification method in step (2) is dichloromethane column chromatography.

[0022] Optionally, in step (3), the aromatic boronic acid is benzocyclobutene-4-boric acid; the palladium catalyst is tetrakistriphenylphosphine palladium; the solvent includes one or more of toluene, ethanol and water; the base includes one or two of sodium carbonate, cesium carbonate and potassium carbonate; the reaction temperature is 100°C to 120°C; the reaction time is 12h to 24h; and the mass ratio of the intermediate S-2, benzocyclobutene-4-boric acid and tetrakistriphenylphosphine palladium is 1:1.2:0.1.

[0023] Optionally, the purification method in step (3) is column chromatography separation.

[0024] Optionally, in step (4), the protonic acid includes trifluoroacetic acid or hydrochloric acid; the solvent includes dichloromethane or ethyl acetate; the reaction temperature is room temperature; the reaction time is 12h to 24h; and the mass volume ratio of the protonic acid to the intermediate S-2 is 1 to 1.5:4 to 5.

[0025] The present invention also discloses a polyimide, wherein the raw materials of the polyimide include a dianhydride monomer, a diamine monomer 1 and a diamine monomer 2; the diamine monomer 2 is the above-mentioned 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, or the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound obtained by the above-mentioned preparation method.

[0026] Optionally, the molar ratio of the dianhydride monomer, the diamine monomer one and the diamine monomer two is 10:(7-6):(3-4).

[0027] Optionally, the dianhydride monomer is bisphenol A diether dianhydride; and the diamine monomer is meta-xylylenediamine.

[0028] The present invention also discloses a method for preparing the polyimide as described above, comprising the following steps: copolymerizing a dianhydride monomer with a first diamine monomer and a second diamine monomer in an organic solvent, performing an imidization reaction through dehydration cyclization, and then sequentially performing precipitation, washing, Soxhlet extraction, drying and high-temperature curing to obtain the polyimide.

[0029] Optionally, the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0030] Optionally, the reaction temperature of the copolymerization reaction is 15°C to 30°C; the reaction time of the copolymerization reaction is 12h to 24h.

[0031] Optionally, the reaction temperature of the dehydration cyclization imidization is 15° C. to 30° C.; the reaction time of the dehydration cyclization imidization is 24 h to 36 h.

[0032] Optionally, the precipitant used for the precipitation includes methanol and / or ethanol.

[0033] Optionally, the extractant used in the Soxhlet extraction includes methanol and / or ethanol.

[0034] Optionally, the temperature of the Soxhlet extraction is 110° C. to 140° C.; and the time of the Soxhlet extraction is 24 h to 48 h.

[0035] Optionally, the temperature of the high temperature curing is 220° C. to 260° C.; and the time of the high temperature curing is 7 hours.

[0036] The invention also discloses a polymer film, which is the polyimide mentioned above or the polyimide prepared by the preparation method mentioned above.

[0037] Optionally, the method for preparing the polymer film comprises the following steps: dissolving the polyimide in an organic solvent and casting the polyimide into a film, removing the organic solvent by gradient heating, and curing the film at high temperature to obtain the polymer film.

[0038] Optionally, the organic solvent includes one or more of m-cresol, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0039] Optionally, the mass concentration of the organic solution containing polyimide is 10% to 15%.

[0040] Optionally, the dissolving temperature is 100°C to 120°C.

[0041] Optionally, the gradient heating includes heating at 60°C for 12 hours, and then heating at 80°C, 100°C, 120°C, 150°C, 180°C and 200°C for 2 hours.

[0042] Optionally, the high temperature curing includes heating at 220° C. for 2 h, heating at 240° C. for 3 h, and heating at 260° C. for 2 h.

[0043] Optionally, the polymer film has a thickness of 60 to 80 μm.

[0044] Implementing the embodiments of the present invention will have the following beneficial effects:

[0045] The present invention utilizes a modified monomer having two active amino groups and a benzocyclobutene group that can be directly cross-linked by heating, which can be used as a diamine monomer for polymerization reaction, thereby introducing the benzocyclobutene group into the side chain of the polymer molecule. The four-membered ring of the benzocyclobutene undergoes ring-opening cross-linking at high temperature to form an eight-membered ring structure. No low-molecular by-products are released during curing, and no catalyst or initiator needs to be added during the curing process, and no other heteroatoms are introduced. The prepared polymer film has excellent heat resistance and dielectric properties, and has broad application prospects in the field of target resins that are soluble, easy to process, and have low water absorption.

[0046] The novel diamine monomer containing benzocyclobutene and capable of direct thermal crosslinking structure proposed by the present invention has simple raw material components required for preparation, mild reaction conditions for the synthesis process, simple and easy control, and green and environmentally friendly. Through precise control of the preparation process, the prepared product is easy to purify, has less impurities, and has a higher yield, and is therefore suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The 1HNMR spectrum of the intermediate S-1 of the present invention is shown in FIG.

[0048] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum (1HNMR) of the intermediate S-2 of Example 1 of the present invention.

[0049] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum (1HNMR) of the intermediate S-3 of Example 1 of the present invention.

[0050] Figure 4 This is a hydrogen nuclear magnetic resonance spectrum (1HNMR) of the diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine of Example 1 of the present invention.

[0051] Figure 5 It is a Fourier transform infrared spectrum (FT-IR) diagram of the polyimide PI-BP2 of Example 3 of the present invention and the diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB). DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0053] The instruments, reagents, materials, etc. involved in the following examples, unless otherwise specified, are all conventional instruments, reagents, materials, etc. in the prior art and can be obtained through regular commercial channels. The experimental methods, detection methods, etc. involved in the following examples, unless otherwise specified, are all conventional experimental methods, detection methods, etc. in the prior art.

[0054] Example 1

[0055] First, zinc powder (8.3 g) and water (80 ml) were added to a three-necked flask, stirred rapidly, and the pH was adjusted to 5 with acetic acid. The mixture was evacuated and nitrogen was passed through three times, and the mixture was heated to 80°C and reacted for 1 hour to activate the zinc powder. After cooling, 1-bromo-3,5-dinitrobenzene (3.7 g) and ethanol (150 ml) were added, and the temperature was raised to 80°C and the reaction was continued for 3 hours. Potassium hydroxide was added to adjust the pH to neutral, and the mixture was filtered while hot, and the solvent was removed under reduced pressure. The liquid was extracted and dried over anhydrous magnesium sulfate, and the solvent was spin-dried to obtain orange powder S-1,5-bromo-1,3-phenylenediamine with a yield of 90%.

[0056] 5-Bromo-1,3-phenylenediamine (4.0 g) and di-tert-butyl dicarbonate (10.26 g) were dissolved in anhydrous ethanol (30 mL), stirred at room temperature for 24 h, and then the reaction was stopped and the solvent was removed by rotary evaporation. The product was purified by chromatography on silica gel and the solvent was removed under reduced pressure to obtain yellow solid S-2 with a yield of 90%.

[0057] Add the monomer benzocyclobutene-4-boric acid (2.13g), intermediate S-2 (4.64g), cesium carbonate (8.6g) to a three-necked flask, catalyst tetrakistriphenylphosphine palladium (1.38g), then add toluene, ethanol, aqueous solution, evacuate and pass nitrogen three times, heat the flask under reflux at 110°C, stop the reaction after 24 hours, and the solution turns yellow. After cooling to room temperature, extract the reaction mixture, wash it with water three times, dry it with anhydrous magnesium sulfate, filter it, and remove the solvent under reduced pressure. Purify it by chromatography on silica gel to obtain yellow solid S-3 with a yield of 75%.

[0058] The intermediate S-3 (7.4 g) was placed in a three-necked flask, dichloromethane (50 ml) was added and stirred to dissolve, trifluoroacetic acid (20 ml) was slowly added dropwise, stirred at room temperature, reacted for 4 hours, sodium hydroxide was added to adjust the pH to neutral, washed three times with water, dried, the solvent was removed under reduced pressure, and purified by chromatography on silica gel to obtain a red-grey powder with a yield of 80%.

[0059] in, Figure 1-Figure 4 1HNMR chart of the compound obtained in Example 1 of the present invention.

[0060] Example 2

[0061] Under nitrogen protection, 1.0622 g (2 mmol) of bisphenol A diether dianhydride (BPADA), 0.1946 g (1.4 mmol) of m-xylenediamine (MXDA), 0.1326 g (0.6 mmol) of the diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB) prepared in Example 1, and 10 ml of N-methylpyrrolidone were added to a 50 mL reaction bottle, stirred at 25 ° C for 24 h, 0.64 ml of acetic anhydride and 0.64 ml of pyridine were slowly added, and the reaction was carried out at room temperature for 24 h to complete the imidization. The reaction solution was added dropwise to excess methanol to precipitate, filtered, and the filter cake was washed with methanol three times. Soxhlet extraction was carried out at 120 ° C for 24 h with ethanol as the extractant, and vacuum dried to obtain polyimide PI-BP1 as a light yellow fibrous solid.

[0062] Weigh 0.1g of PI-BP1 powder and add it to 2ml of m-cresol and heat it to 100℃ to fully dissolve it to obtain a yellow solution. The obtained solution was coated on a 60*60mm, 3mm thick glass plate, and the solvent was removed by heating at 60℃-12h, 80℃-2h, 100℃-2h, 120℃-2h, 150℃-2h, 180℃-2h, and 200℃-2h. After cooling to room temperature, the PI-BP1 film was removed by film removal.

[0063] Weigh 0.1g of PI-BP1 powder and add it to 2ml of m-cresol and heat it to 100℃ to fully dissolve it to obtain a yellow solution. The obtained solution was coated on a 60*60mm, 3mm thick glass plate, and the solvent was removed by heating at 60℃-12h, 80℃-2h, 100℃-2h, 120℃-2h, 150℃-2h, 180℃-2h, 200℃-2h; and cured by heating at 220℃-2h, 240℃-3h, and 260℃-2h. After cooling to room temperature, the p-PI-BP1 film was removed.

[0064] Example 3

[0065] The difference between this embodiment and embodiment 2 is that: 1.0622 g (2 mmol) of bisphenol A diether dianhydride (BPADA), 0.1668 g (1.2 mmol) of meta-xylenediamine (MXDA), 0.1768 g (0.8 mmol) of diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB) prepared in embodiment 1, and 10 ml of N-methylpyrrolidone are added to a 50 mL reaction bottle, and other conditions remain unchanged to obtain polyimide PI-BP2, which is a light yellow fibrous solid.

[0066] Weigh 0.1 g of PI-BP2 powder, prepare the solution and apply film according to Example 2, and obtain PI-BP2 film and p-PI-BP2 film in sequence, wherein: Figure 5 This is the Fourier transform infrared spectra of PI-BP2 and MPDA-BCB obtained in Example 3 of the present invention.

[0067] The reaction formula in Examples 2 to 3 is shown in Formula IV:

[0068]

[0069] Comparative Example 1:

[0070] The only difference between this comparative example and Example 2 is that: MPDA-BCB is not added, the amount of meta-xylylenediamine added is adjusted to 2 mmol, and polyimide PI-BP0 is prepared as a white fibrous solid.

[0071] Weigh 0.1g of PI-BP0 powder and add it to 2ml of m-cresol and heat it to 100℃ to fully dissolve it to obtain a colorless solution. The obtained solution was coated on a 60*60mm, 3mm thick glass plate, and the solvent was removed by heating at 60℃-12h, 80℃-2h, 100℃-2h, 120℃-2h, 150℃-2h, 180℃-2h, and 200℃-2h. After cooling to room temperature, the PI-BP0 film was removed by film removal.

[0072] The reaction formula in Comparative Example 1 is shown in Formula V:

[0073]

[0074] The structures of Examples 1 to 3 and Comparative Example 1 were characterized by nuclear magnetic resonance and infrared absorption spectra, verifying that the structures of the products were consistent with expectations. The products of Examples 2-3 and Comparative Example 1 were used in the preparation of thin films.

[0075] Heat resistance test

[0076] The heat resistance of the PI resins obtained in Examples 2-3 and Comparative Example 1 was evaluated using DSC and DMA. The test results are shown in Table 1.

[0077] Table 1. DSC and DMA data of polyimide before and after crosslinking

[0078]

[0079] Note: a is measured by DSC, b is measured by DMA.

[0080] From the data in Table 1, it can be seen that the heat resistance of Examples 2-3 is better than that of Comparative Example 1 of PI without adding modified monomers, especially when the modified diamine monomer in Example 3 is added to 40%, the glass transition temperature of the modified polyimide is increased from 169°C to 233°C.

[0081] As the proportion of cross-linkable modified monomers increases, the glass transition temperature of cross-linked polyimide shows an upward trend. This may be attributed to the increase in cross-linkable modified monomers, which leads to an increase in the degree of cross-linking after the ring opening of benzocyclobutene, a decrease in the distance between molecules, and an increase in the degree of entanglement of the molecular chain, which restricts the movement of the polyimide molecular chain segments. As a result, a higher temperature is required for the molecular chain to move. Macroscopically, the glass transition temperature gradually increases, and the heat resistance is significantly improved.

[0082] In summary, the present invention utilizes the synthesized diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB), and copolymerizes it with diamine monomers and dianhydride monomers, introduces the benzocyclobutene group into the polyimide side chain through copolymerization, utilizes the cross-linking regulation of the benzocyclobutene structure, inhibits the molecular motion, and obtains a polyimide with excellent comprehensive performance. The heat resistance of the polymer film made of the polyimide prepared by the present invention is effectively improved. At the same time, the preparation of the monomers involved in the present invention is highly repeatable, and can meet the actual needs of synthesizing polymers such as polyimide and polyamide.

[0083] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, characterized in that: It has the structure shown in formula (I):

2. A method for preparing the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound as claimed in claim 1, characterized in that: The following steps are involved: (1) mixing 1-bromo-3,5-dinitrobenzene and a reducing agent to react to obtain an intermediate S-1; (2) dissolving the intermediate S-1 and an amino protecting agent in a protic solvent for amino protection to obtain an intermediate S-2; (3) dissolving the intermediate S-2 in a solvent and mixing it with an arylboronic acid, and performing Suzuki cross-coupling under the action of a palladium catalyst to obtain an intermediate S-3; (4) dissolving the intermediate S-3 in a solvent, and removing the protecting group under the action of a protonic acid to obtain the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound; 3. The preparation method according to claim 2, characterized in that: In the step (1), the reducing agent includes iron powder, zinc powder or Pd / C; the reaction temperature is 80°C to 90°C; the reaction time is 3h to 5h; the mass ratio of 1-bromo-3,5-dinitrobenzene to the reducing agent is 1 to 1.5:6 to 8; In the step (2), the amino protecting agent is di-tert-butyl dicarbonate; the protic solvent is anhydrous ethanol; the reaction temperature is room temperature; the reaction time is 12h to 24h; the mass ratio of the intermediate S-1 to di-tert-butyl dicarbonate is 1:2; In the step (3), the aryl boronic acid is benzocyclobutene-4-boric acid; the palladium catalyst is tetrakistriphenylphosphine palladium; the solvent includes one or more of toluene, ethanol and water; the base includes one or two of sodium carbonate, cesium carbonate and potassium carbonate; the reaction temperature is 100°C to 120°C; the reaction time is 12h to 24h; the mass ratio of the intermediate S-2, benzocyclobutene-4-boric acid and tetrakistriphenylphosphine palladium is 1:1.2:0.1; In the step (4), the protonic acid includes trifluoroacetic acid or hydrochloric acid; the solvent includes dichloromethane or ethyl acetate; the reaction temperature is room temperature; the reaction time is 12h to 24h; and the mass volume ratio of the protonic acid to the intermediate S-3 is 1 to 1.5:4 to 5.

4. A polyimide, characterized in that: The raw materials of the polyimide include dianhydride monomer, diamine monomer one and diamine monomer two; The diamine monomer 2 is the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound described in claim 1, or the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound obtained by the preparation method described in any one of claims 2-3.

5. The polyimide according to claim 4, characterized in that The mass ratio of the dianhydride monomer, the diamine monomer 1 and the diamine monomer 2 is 10:(7-6):(3-4); The dianhydride monomer is bisphenol A type diether dianhydride; The first diamine monomer is meta-xylylenediamine.

6. A method for preparing a polyimide as claimed in any one of claims 4 to 5, characterized in that: The following steps are involved: The polyimide is obtained by copolymerizing the dianhydride monomer with the first diamine monomer and the second diamine monomer in an organic solvent, performing a dehydration cyclization imidization reaction, and then sequentially performing precipitation, washing, Soxhlet extraction, drying and high-temperature curing.

7. The preparation method according to claim 6, characterized in that: The organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The reaction temperature of the copolymerization reaction is 15°C to 30°C; the reaction time of the copolymerization reaction is 12h to 24h; The reaction temperature of the dehydration cyclization imidization is 15°C to 30°C; the reaction time of the dehydration cyclization imidization is 24h to 36h; The precipitation agent used in the precipitation includes methanol and / or ethanol; The extractant used in the Soxhlet extraction includes methanol and / or ethanol; The temperature of the Soxhlet extraction is 110°C to 140°C; the time of the Soxhlet extraction is 24h to 48h; The temperature of the high temperature curing is 220° C. to 260° C.; the time of the high temperature curing is 7 hours.

8. A polymer film, characterized in that The polymer film is the polyimide described in any one of claims 4-5 or the polyimide prepared by the preparation method described in any one of claims 6-7.

9. The polymer film according to claim 8, characterized in that The method for preparing the polymer film comprises the following steps: The polyimide is dissolved in an organic solvent and cast into a film, and then the organic solvent is removed by gradient heating, and the polymer film is obtained by high-temperature curing.

10. The polymer film according to claim 9, characterized in that The organic solvent includes one or more of m-cresol, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The dissolving temperature is 100°C to 120°C; The gradient temperature increase includes heating at 60°C for 12 hours, and then heating at 80°C, 100°C, 120°C, 150°C, 180°C and 200°C for 2 hours in sequence; The high temperature curing includes heating at 220°C for 2h, heating at 240°C for 3h, and heating at 260°C for 2h in sequence; The thickness of the polymer film is 60-80 μm.

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