A benzimidazole transparent polyimide film and its preparation method and application

Abstract

The present application relates to the technical field of polyimide polymer materials, and discloses a benzimidazole transparent polyimide film, its preparation method, and application. The preparation method comprises: dissolving an N-substituted benzimidazole diamine monomer and a dianhydride monomer in a molar ratio of 1:(1-1.3) in a first solvent protected by an inert atmosphere, and carrying out a polymerization reaction at 180°C to 210°C under the action of a first catalyst; adding a precipitant to the reaction solution, collecting the solid phase, washing, and drying to obtain a benzimidazole transparent polyimide resin; preparing a solution of the benzimidazole transparent polyimide resin, standing, degassing, coating, and then drying to obtain a benzimidazole transparent polyimide film. The benzimidazole transparent polyimide film of the present application retains the high glass transition temperature performance of benzimidazole polyimide materials, while having the excellent optical transmittance of polyimide materials containing non-coplanar structures, and can be used in fields such as flexible solar cell baseboards and flexible displays.

Description

Technical Field

[0001] The present application relates to the technical field of polyimide polymer materials, and in particular to a benzimidazole transparent polyimide film and a preparation method and application thereof. Background Art

[0002] Polyimide film is an insulating material with excellent heat resistance, widely used in the electronics, electrical engineering, aerospace and other industries. Polyimide films used in optoelectronic materials, such as flexible substrates for solar cells and liquid crystal display materials, require high light transmittance and excellent mechanical properties in addition to excellent high-temperature resistance. However, traditional polyimide films generally appear light yellow or dark brown, which greatly limits the further application of polyimide in optoelectronic materials. This is mainly due to the electron-withdrawing effect of the carbonyl group in the dianhydride and the electron-donating effect of the diamine in the alternating polymer backbone, as well as the formation of intramolecular and intermolecular charge transfer complexes caused by the rigid conjugated structure of the entire polymer backbone.

[0003] By changing the molecular structure, high-temperature resistant and transparent polyimide film materials are developed, which can be used in fields such as flexible solar cell baseboards and flexible displays. Currently used methods for reducing the color of polyimides include: 1. Using fully fatty dianhydride or diamine monomers to obtain polyimides with fatty units, thereby destroying the conjugation of the structural molecules of the polyimide and inhibiting the formation of charge transfer complexes, such as the novel fluorinated copolymer polyimide and its preparation method disclosed in Patent Publication No. CN101831074A; 2. Using polyimides with large side groups or asymmetric structural units to hinder the conjugation of the electron cloud and inhibit charge transfer complexation, such as the polyimide containing phenolic hydroxyl groups disclosed in Patent Publication No. CN102516541A and the "Synthesis and Characterization of a Polyimide Containing a Phenolphthalein Structure" published in Acta Polymerica Sinica in 2012; 3. Using non-coplanar fully aromatic diamines to destroy the conjugation of the polyimide backbone and inhibit electron transfer complexation, such as the "Diamine architecture effects on glass transitions, relaxation processes and other material properties in organo-soluble aromatic diamines" published by F. Li et al. in Polymer in 1999. polyimide films". Through the above method, the optical transmittance of the polyimide film is improved.

[0004] However, although the above methods improve the optical transmittance of polyimide, the glass transition temperature of the prepared transparent polyimide film is generally lower than 350°C, which cannot fully meet the processing temperature of transparent polyimide films used in flexible solar cell substrates and flexible displays, such as lead-free reflow soldering (270°C) and silicon-based TFT manufacturing (short-term 400°C). Summary of the Invention

[0005] The present application provides a benzimidazole transparent polyimide film and its preparation method and application, aiming to solve the problem that the existing transparent polyimide film has a low glass transition temperature and is difficult to be applied to the field of flexible solar cell baseboards and flexible displays.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions.

[0007] In a first aspect of the present application, a benzimidazole transparent polyimide film is provided, wherein the benzimidazole transparent polyimide has a structure shown in formula (1):

[0008] (1)

[0009] wherein n≥20; R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives;

[0010] Ar1 is selected from at least one of the following substituents:

[0011] .

[0012] In some embodiments, the R1 is selected from any one of the following substituents:

[0013] .

[0014] In some embodiments, the R2 is selected from any one of the following substituents:

[0015] .

[0016] The second aspect of the present application provides a method for preparing the above-mentioned benzimidazole transparent polyimide film, comprising:

[0017] The N-substituted benzimidazole diamine monomer and the dianhydride monomer are dissolved in a first solvent protected by an inert atmosphere at a molar ratio of 1:1 to 1.3, and a polymerization reaction is carried out at 180° C. to 210° C. under the action of a first catalyst; a precipitant is added to the reaction solution, and the solid phase is collected, washed, and dried to obtain a benzimidazole transparent polyimide resin;

[0018] A benzimidazole transparent polyimide resin solution is prepared, and the solution is allowed to stand, degassed, coated, and then dried to obtain a benzimidazole transparent polyimide film.

[0019] In some embodiments, the N-substituted benzimidazole diamine monomer has a structure shown in formula (2):

[0020] (2)

[0021] wherein R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives;

[0022] and / or:

[0023] The dianhydride monomer includes at least one of the following compounds:

[0024] .

[0025] In some embodiments, the first solvent comprises at least one of ultra-dry benzonitrile, phenol, m-cresol, p-chlorophenol, nitrobenzene, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, gamma-butyrolactone, or sulfolane;

[0026] and / or:

[0027] The first catalyst is benzoic acid, p-hydroxybenzoic acid or isoquinoline;

[0028] and / or:

[0029] The precipitant is methanol, ethanol, ethyl acetate, acetone or water.

[0030] In some embodiments, the method for preparing the N-substituted benzimidazole diamine comprises:

[0031] The compound represented by the general formula (3) is subjected to a substitution reaction with the compound represented by the general formula (4) to obtain an intermediate product; the intermediate product is subjected to a first reduction reaction, an amidation reaction, a ring-closure reaction and a second reduction reaction in sequence to obtain an N-substituted benzimidazole diamine;

[0032] (3) (4)

[0033] The reaction formula is:

[0034]

[0035] Wherein, R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives.

[0036] In some embodiments, the method for preparing the N-substituted benzimidazole diamine comprises:

[0037] S1, dissolving 1 eq of 3,4-dinitrofluorobenzene and 1.1 eq of 4-nitroaniline in 10 eq of a second solvent, heating to 60-90°C for reaction; collecting the solid phase, slurrying and purifying it with the second solvent, and drying to obtain an intermediate product A;

[0038] S2, dissolving 1 eq of intermediate product A, 1.2-3 eq of sodium sulfide nonahydrate, and 1.2-3 eq of the second catalyst in a solution of 10 eq of ethanol and water in a volume ratio of 2:1, heating to 60-80°C for reduction reaction; after the reaction, adding water to precipitate the solid phase, slurrying with water for purification, and drying to obtain intermediate product B;

[0039] S3, dissolving 1 eq of intermediate product B and 1.2-3 eq of acid-binding agent in 5-15 eq of tetrahydrofuran to prepare solution A; dissolving 1.2-2 eq of acyl chloride monomer in a small amount of tetrahydrofuran to prepare solution B, slowly adding solution B dropwise to solution A, controlling the temperature at 0-5°C to carry out chlorination reaction; after the reaction, remove tetrahydrofuran, precipitate the solid phase with methanol or dichloromethane, and dry to obtain intermediate product C;

[0040] S4, dispersing 1 eq of intermediate product C and 1-3 eq of the third catalyst in 5-15 eq of an acid solution, heating to 80-180°C for a ring-closure reaction; after the reaction, adding water to precipitate a solid phase, drying and then recrystallizing to obtain intermediate product D;

[0041] S5, dissolving 1 eq of the intermediate product D in 5-15 eq of a third solvent, adding 0.1-1 eq of a hydrogenation catalyst, heating to 60-80° C. to carry out a reduction reaction with hydrogen, and after the reaction, adding water to precipitate a solid phase to obtain an N-substituted benzimidazole diamine.

[0042] In some embodiments, the second solvent comprises at least one of methanol, ethanol, propanol, or isopropanol;

[0043] The second catalyst comprises at least one of sodium bicarbonate, sodium carbonate, potassium bicarbonate or potassium carbonate;

[0044] The acid binding agent includes at least one of triethylamine, diisopropylethylamine, pyridine, sodium carbonate, sodium bicarbonate or potassium carbonate;

[0045] The acyl chloride monomer includes benzoyl chloride, 4-phenylbenzoyl chloride, 3-phenylbenzoyl chloride or acetyl chloride;

[0046] The third catalyst comprises at least one of p-toluenesulfonic acid, acetic anhydride or pyridine;

[0047] The acid solution includes at least one of acetic acid, sulfuric acid or acetic anhydride;

[0048] The third solvent includes at least one of tetrahydrofuran, ethanol, methanol, isopropanol, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, 1,4-dioxane, ethyl acetate, benzene, toluene or xylene;

[0049] The hydrogenation catalyst includes at least one of palladium carbon, platinum carbon, activated nickel or rhodium carbon.

[0050] The third aspect of the present application provides the use of the above-mentioned benzimidazole transparent polyimide film or the benzimidazole transparent polyimide film prepared by the above-mentioned preparation method in flexible solar cell base plates and flexible displays.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] The benzimidazole transparent polyimide film of the present application retains the high glass transition temperature performance of benzimidazole polyimide materials, and at the same time has the excellent optical transmittance of polyimide materials containing non-coplanar structures, and can be used in flexible solar cell baseboards and flexible displays and other fields.

[0053] The benzimidazole transparent polyimide film of this application has a glass transition temperature of 310-420°C, a 5% thermal decomposition temperature of 470-530°C, a light transmittance greater than 80% at 500nm, a cutoff wavelength of 290-360nm, and is self-supporting. The benzimidazole transparent polyimide film of this application is used in fields such as flexible solar cell baseboards and flexible displays. It can withstand the high-temperature processing environment of flexible substrates during the manufacturing process, reducing quality defects such as panel explosion and delamination, and improving the performance and quality of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0055] Figure 1 This is the H NMR spectrum of 2,4-dinitrobenzene-N-(4-nitrophenyl)aniline prepared in Example 1;

[0056] Figure 2This is the H-NMR spectrum of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline prepared in Example 1;

[0057] Figure 3 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-phenylbenzimidazole prepared in Example 1;

[0058] Figure 4 This is the H NMR spectrum of 5-amino-1-(4-aminophenyl)-2-phenylbenzimidazole prepared in Example 1;

[0059] Figure 5 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-(4-phenylbenzene)benzimidazole prepared in Example 2;

[0060] Figure 6 This is the H NMR spectrum of 5-amino-1-(4-aminobenzene)-2-(4-phenylbenzene)benzimidazole prepared in Example 2;

[0061] Figure 7 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3;

[0062] Figure 8 This is the H NMR spectrum of 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3;

[0063] Figure 9 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole prepared in Example 4;

[0064] Figure 10 This is the H NMR spectrum of 5-amino-1-(4-aminophenyl)-2-methylbenzimidazole prepared in Example 4;

[0065] Figure 11 This is the infrared test spectrum of the benzimidazole transparent polyimide film of this application;

[0066] Figure 12 This is a test chart of the thermal stability (Td) of the benzimidazole transparent polyimide film of the present application;

[0067] Figure 13 This is a test chart of the glass transition temperature (Tg) of the benzimidazole transparent polyimide film of the present application;

[0068] Figure 14 This is a test chart of the light transmittance and cutoff wavelength of the benzimidazole transparent polyimide film of this application. DETAILED DESCRIPTION

[0069] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0070] In the following description of this embodiment, the terms "include", "comprising", "having" and "containing" are open-ended terms, meaning including but not limited to.

[0071] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, B exists alone, and both A and B exist. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0072] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0073] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0074] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0075] It will be understood by those skilled in the art that the numerical ranges in the examples of the present application are to be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also included in the present application. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0076] Unless otherwise indicated, the technical / scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs. Although this application 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 this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0077] In a first aspect, the present application provides a benzimidazole transparent polyimide film, wherein the benzimidazole transparent polyimide has a structure shown in formula (1):

[0078] (1)

[0079] wherein n≥20; R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; preferably, R1 is selected from any one of the following substituents:

[0080] .

[0081] R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives; preferably R2 is selected from any one of the following substituents:

[0082]

[0083] Ar1 is selected from at least one of the following substituents:

[0084] .

[0085] In the benzimidazole transparent polyimide of the present application, the structure of benzimidazole diamine is "V-shaped", which is beneficial for increasing the interchain distance between molecular chains, inhibiting the formation of charge transfer complexes (CTCs), and improving the transparency of the polyimide film. The benzimidazole transparent polyimide of the present application retains the high glass transition temperature performance of benzimidazole polyimide materials while possessing the excellent optical transmittance of polyimide materials containing non-coplanar structures. The material can be used in fields such as flexible solar cell substrates and flexible displays. In the present application, the molecular weight of the benzimidazole transparent polyimide is preferably greater than 10,000 to achieve a better film-forming effect, that is, the number of repeating units n is ≥20, and more preferably n ≥40.

[0086] In a second aspect, the present application provides a method for preparing a benzimidazole transparent polyimide film, comprising:

[0087] The N-substituted benzimidazole diamine monomer and the dianhydride monomer are dissolved in a first solvent protected by an inert atmosphere at a molar ratio of 1:1 to 1.3, and a polymerization reaction is carried out at 180° C. to 210° C. under the action of a first catalyst; a precipitant is added to the reaction solution, and the solid phase is collected, washed, and dried to obtain a benzimidazole transparent polyimide resin;

[0088] Among them, the first solvent is used to dissolve the N-substituted benzimidazole diamine monomer and the dianhydride monomer, which includes at least one of ultra-dry benzonitrile, phenol, m-cresol, p-chlorophenol, nitrobenzene, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone or cyclopentane sulfone; the first catalyst is used to promote the reaction of the N-substituted benzimidazole diamine monomer and the dianhydride monomer, and in this application, the first catalyst is selected from benzoic acid, p-hydroxybenzoic acid or isoquinoline; the precipitant is used to precipitate the reaction product from the reaction solution, and the precipitant is methanol, ethanol, ethyl acetate, acetone or water.

[0089] A benzimidazole transparent polyimide resin solution is prepared, and the solution is allowed to stand, degassed, coated, and then dried to obtain a benzimidazole transparent polyimide film.

[0090] Specifically, a benzimidazole transparent polyimide resin is dissolved in N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, butyrolactone, or sulfolane to prepare a polyimide solution. The polyimide solution is allowed to stand at -20°C to 0°C for 24 to 30 hours to remove air bubbles. The debubbled polyimide solution is then applied to a film, preferably with a wet film thickness of 20 to 400 μm. The film is then dried at 100 to 250°C for 3 to 12 hours to remove the solvent.

[0091] In the present application, the dianhydride monomer includes at least one of the following compounds:

[0092] .

[0093] The N-substituted benzimidazole diamine monomer has a structure shown in formula (2):

[0094] (2)

[0095] Specifically, the structure of the N-substituted benzimidazole diamine monomer is:

[0096]

[0097] Wherein, R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; preferably, R1 is selected from any one of the following substituents:

[0098] .

[0099] R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives; preferably R2 is selected from any one of the following substituents:

[0100]

[0101] In the present application, the preparation method of the N-substituted benzimidazole diamine comprises:

[0102] Fluorobenzenes substituted with different nitro groups are subjected to a substitution reaction with m-nitroaniline or p-nitroaniline substituted with different groups to obtain an intermediate product; the intermediate product is subjected to a first reduction reaction, an amidation reaction, a ring-closure reaction, and a second reduction reaction in sequence to obtain an N-substituted benzimidazole diamine;

[0103] Among them, the structures of fluorobenzene substituted with different nitro groups are shown in formula (3), and the structures of meta-nitroaniline or para-nitroaniline substituted with different groups are shown in formula (4):

[0104] (3) (4)

[0105] The reaction formula is:

[0106]

[0107] Wherein, R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives.

[0108] Specifically, the fluorobenzene substituted with different nitro groups may be 2,4-dinitrofluorobenzene or 2,5-dinitrofluorobenzene; the m-nitroaniline or p-nitroaniline substituted with different groups may be 3-nitroaniline, 4-nitroaniline, 2-methyl-3-nitroaniline or 2-methyl-4-nitroaniline.

[0109] Taking 3,4-dinitrofluorobenzene and 4-nitroaniline as examples, the preparation method of N-substituted benzimidazole diamine includes:

[0110] S1, dissolving 1 eq of 3,4-dinitrofluorobenzene and 1.1 eq of 4-nitroaniline in 10 eq of a second solvent, heating to 60-90°C for reaction; collecting the solid phase, slurrying and purifying it with the second solvent, and drying to obtain an intermediate product A;

[0111] The second solvent includes at least one of methanol, ethanol, propanol or isopropanol, preferably methanol or ethanol; the number of times of pulping and purification is 3-5 times.

[0112] S2, dissolving 1 eq of intermediate product A, 1.2-3 eq of sodium sulfide nonahydrate, and 1.2-3 eq of the second catalyst in a solution of 10 eq of ethanol and water in a volume ratio of 2:1, heating to 60-80°C for reduction reaction; after the reaction, adding water to precipitate the solid phase, slurrying with water for purification, and drying to obtain intermediate product B;

[0113] The second catalyst comprises at least one of sodium bicarbonate, sodium carbonate, potassium bicarbonate or potassium carbonate, preferably sodium bicarbonate or sodium carbonate. The amount of water added for precipitation is 4 to 6 times the volume of the reaction solution, and the amount of water added for slurrying is 4 to 6 times the mass of the solid phase.

[0114] S3, dissolving 1 eq of intermediate product B and 1.2-3 eq of acid-binding agent in 5-15 eq of tetrahydrofuran to prepare solution A; dissolving 1.2-2 eq of acyl chloride monomer in a small amount of tetrahydrofuran to prepare solution B, slowly adding solution B dropwise to solution A while controlling the temperature at 0-5°C to carry out an amidation reaction; after the reaction, remove the tetrahydrofuran, precipitate the solid phase with methanol or dichloromethane, and dry it to obtain intermediate product C;

[0115] The acid binding agent is used to absorb the acid generated during the reaction and promote the reaction. The acid binding agent includes at least one of triethylamine, diisopropylethylamine, pyridine, sodium carbonate, sodium bicarbonate or potassium carbonate, preferably triethylamine, pyridine or sodium carbonate. The amount of the acid binding agent is preferably 1.4 to 1.8 eq.

[0116] The acyl chloride monomer is used for performing addition reaction with an amino group to form an amide; the acyl chloride monomer includes benzoyl chloride, 4-phenylbenzoyl chloride, 3-phenylbenzoyl chloride or acetyl chloride.

[0117] The amount of methanol or dichloromethane used is 1 to 10 eq, preferably 3 to 5 eq.

[0118] S4, dispersing 1 eq of intermediate product C and 1-3 eq of the third catalyst in 5-15 eq of an acid solution, heating to 80-180°C for a ring-closure reaction; after the reaction, adding water to precipitate a solid phase, drying and then recrystallizing to obtain intermediate product D;

[0119] The third catalyst comprises at least one of p-toluenesulfonic acid, acetic anhydride or pyridine, and the amount of the third catalyst is preferably 1.3 to 1.8 eq. The acid solution comprises at least one of acetic acid, sulfuric acid or acetic anhydride, preferably acetic acid or acetic anhydride.

[0120] After the solid phase is dried, a recrystallization reagent is added for recrystallization, wherein the recrystallization reagent includes at least one of 1,4-dioxane, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, m-cresol or cyclopentane sulfone, preferably 1,4-dioxane, dimethylacetamide, N-methylpyrrolidone or 1,3-dimethyl-2-imidazolidinone.

[0121] S5, dissolving 1 eq of the intermediate product D in 5-15 eq of a third solvent, adding 0.1-1 eq of a hydrogenation catalyst, heating to 60-80° C. to carry out a reduction reaction with hydrogen, and after the reaction, adding water to precipitate a solid phase to obtain an N-substituted benzimidazole diamine.

[0122] The pressure of the hydrogen in the reaction is 0.7-0.8 MPa; the hydrogenation catalyst includes at least one of palladium carbon, platinum carbon, activated nickel or rhodium carbon.

[0123] The third solvent includes at least one of tetrahydrofuran, ethanol, methanol, isopropanol, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, 1,4-dioxane, ethyl acetate, benzene, toluene, or xylene, preferably methanol, ethanol, 1,4-dioxane, dimethylacetamide, or N-methylpyrrolidone. The drying temperature is preferably 40-80°C.

[0124] Thirdly, the benzimidazole transparent polyimide film of the present application has a high glass transition temperature and high optical transmittance. Its glass transition temperature is 310~420℃, its 5% thermal decomposition temperature is 470~530℃, its light transmittance at 500nm is greater than 80%, its cut-off wavelength is 290~360nm, and it is self-supporting. The benzimidazole transparent polyimide film of the present application can be applied to flexible solar cell base plates and flexible displays. It can withstand the high-temperature processing environment of the flexible substrate during the manufacturing process, reduce the occurrence of quality defects such as panel explosion and delamination, and improve the performance and quality of the substrate.

[0125] The present application is further described below through examples.

[0126] Example 1

[0127] This embodiment provides an N-substituted benzimidazole diamine, which is 5-amino-1-(4-aminophenyl)-2-phenylbenzimidazole, and its structure is as follows:

[0128]

[0129] The preparation method thereof comprises:

[0130] Step 1: In a 3000 mL three-necked flask, add 0.54 mol of 3,4-dinitrofluorobenzene, 0.59 mol of 4-nitroaniline, and 1000 mL of ethanol. Set the oil bath temperature to 80°C and react with mechanical stirring for 24 hours. The reaction progress was determined by TLC. After the reaction, the mixture was filtered with ethanol. The filter cake was slurried five times with 500 mL of ethanol, filtered, and dried in a vacuum oven at 80°C for 48 hours. The final product was 128 g of a yellow powder, 2,4-dinitrobenzene-N-(4-nitrophenyl)aniline, with a yield of 78%.

[0131] Step 2: In a 500 mL three-necked flask, add 0.16 mol of 2,4-dinitrobenzene-N-(4-nitrophenyl)aniline, 0.25 mol of sodium sulfide nonahydrate, 0.33 mol of sodium bicarbonate and 500 mL of ethanol / water mixed solution (V 乙醇 :V 水 =2:1), set the oil bath temperature to 80°C, and react for 24 hours with mechanical stirring. The reaction progress was confirmed by TLC. After the reaction was completed, the mixture was poured into 1500 mL of water to precipitate and filtered. The filter cake was slurried with 500 mL of water 3-5 times, filtered, and dried in a vacuum oven at 80°C for 48 hours. The final product was 42 g of a red powder, 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, with a yield of 93%.

[0132] Step 3: In a 1000mL single-necked flask, add 0.12mol of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, 0.18mol of triethylamine, and 270mL of THF. Stir and cool in an ice-water bath. When the reaction solution temperature drops below 5°C, slowly add 30mL of a 6M solution of benzoyl chloride in THF dropwise to the reaction solution, ensuring that the reaction solution temperature does not exceed 5°C. After the addition is complete, remove the ice-water bath, and continue the reaction at room temperature for 24 hours. Monitor the reaction progress by TLC. After the reaction is complete, the solvent is dried and 100mL of methanol is added. A large amount of solid precipitates and is filtered. After drying, the product, N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)benzamide, is obtained as a yellow powder.

[0133] Step 4: To a 500 mL single-necked flask, add 79.29 mmol of N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)benzamide, 118.94 mmol of p-toluenesulfonic acid monohydrate, and 300 mL of acetic acid. The mixture was stirred magnetically at 100°C for 12 hours, and the reaction progress was monitored by TLC. Upon completion of the reaction, the reaction solution was poured into 1000 mL of water, filtered, and the filter cake dried to obtain a crude product. The crude product was then recrystallized from dioxane, filtered, and dried to obtain 25 g of the product, 5-nitro-1-(4-nitrobenzene)-2-phenylbenzimidazole, with a yield of 87%.

[0134] Step 5: In a 100 mL single-necked flask, 13.88 mmol of 5-nitro-1-(4-nitrobenzene)-2-phenylbenzimidazole, 0.5 g of palladium on carbon, and 50 mL of ethanol were added. The atmosphere was replaced with nitrogen three times, and then hydrogen was introduced to a pressure of 0.8 MPa. The temperature was controlled at 80°C and the reaction was maintained at this temperature and pressure for 5 h. The reaction progress was determined by TLC. After the reaction, the catalyst was filtered and recovered, and the filtrate was poured into water for precipitation. After filtration and drying, 3.7 g of a white solid, i.e., 5-amino-1-(4-aminobenzene)-2-phenylbenzimidazole, was obtained with a yield of 90%, which was recorded as monomer 1.

[0135] Example 2

[0136] This embodiment provides an N-substituted benzimidazole diamine, which is 5-amino-1-(4-aminobenzene)-2-(4-phenylbenzene)benzimidazole, and its structure is as follows:

[0137]

[0138] The preparation method thereof comprises:

[0139] Step 1: Same as step 1 of Example 1;

[0140] Step 2: Same as step 1 in Example 2;

[0141] Step 3: In a 1000mL single-necked flask, 0.15mol of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, 0.22mol of triethylamine, and 370mL of THF were added. The mixture was stirred and cooled in an ice-water bath. When the reaction temperature dropped below 5°C, 30mL of a 7.3M THF solution of 4-phenylbenzoyl chloride was slowly added dropwise to the reaction solution. The temperature of the reaction solution was maintained at 5°C. After the addition was complete, the ice-water bath was removed and the reaction was continued at room temperature for 24 hours. The reaction progress was monitored by TLC. After the reaction was completed, the solvent was dried and 200mL of methanol was added. A large amount of solid precipitated and was filtered. After drying, the product, N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)-4-phenylbenzamide, was obtained as a yellow powder.

[0142] Step 4: In a 1000 mL single-necked flask, add 0.13 mol of N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)-4-phenylbenzamide, 0.2 mol of p-toluenesulfonic acid monohydrate, and 600 mL of acetic acid. The mixture was stirred magnetically at 100°C for 12 hours, and the reaction progress was monitored by TLC. After the reaction was completed, the reaction solution was poured into 2000 mL of water, filtered, and the filter cake was dried to obtain a crude product. The crude product was then recrystallized from dioxane, filtered, and dried to obtain 42 g of the product, 5-nitro-1-(4-nitrobenzene)-2-(4-phenylbenzene)benzimidazole, with a yield of 73%.

[0143] Step 5: In a 100 mL single-necked flask, 11.46 mmol of 5-nitro-1-(4-nitrobenzene)-2-(4-phenylbenzene)benzimidazole, 0.5 g of palladium on carbon, and 50 mL of ethanol were added. The atmosphere was replaced with nitrogen three times, and then hydrogen was introduced to a pressure of 0.8 MPa. The temperature was controlled at 80°C and the reaction was maintained at this temperature and pressure for 5 h. The reaction progress was determined by TLC. After the reaction, the catalyst was filtered and recovered, and the filtrate was poured into water for precipitation. After filtration and drying, 4.0 g of a white solid, i.e., 5-amino-1-(4-aminobenzene)-2-(4-phenylbenzene)benzimidazole, was obtained in a yield of 93%, which was recorded as monomer 2.

[0144] Example 3

[0145] This embodiment provides an N-substituted benzimidazole diamine, which is 5-amino-1-(4-aminophenyl)-2-(3-phenylbenzene)benzimidazole, and its structure is as follows:

[0146]

[0147] The preparation method thereof comprises:

[0148] Step 1: Same as step 1 of Example 1;

[0149] Step 2: Same as step 1 in Example 2;

[0150] Step 3: In a 1000mL single-necked flask, 0.1mol of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, 0.15mol of triethylamine, and 270mL of THF were added. The mixture was stirred and cooled in an ice-water bath. When the reaction temperature dropped below 5°C, 30mL of a 5M solution of 3-phenylbenzoyl chloride in THF was slowly added dropwise to the reaction solution, ensuring that the reaction temperature did not exceed 5°C. After the addition was complete, the ice-water bath was removed and the reaction was continued at room temperature for 24 hours. The reaction progress was monitored by TLC. After the reaction was completed, the solvent was dried and 100mL of methanol was added. A large amount of solid precipitated and was filtered. After drying, the product, N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)-3-phenylbenzamide, was obtained as a yellow powder.

[0151] Step 4: In a 1000 mL single-necked flask, add 0.1 mol of N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)-3-phenylbenzamide, 0.15 mol of p-toluenesulfonic acid monohydrate, and 500 mL of acetic acid. The mixture was stirred magnetically at 100°C for 12 hours, and the reaction progress was monitored by TLC. After the reaction was completed, the reaction solution was poured into 1500 mL of water, filtered, and the filter cake was dried to obtain a crude product. The crude product was then recrystallized from dioxane, filtered, and dried to obtain 35 g of the product, 5-nitro-1-(4-nitrobenzene)-2-(3-phenylbenzene)benzimidazole, with a yield of 78%.

[0152] Step 5: In a 100 mL single-necked flask, 11.46 mmol of 5-nitro-1-(4-nitrobenzene)-2-(3-phenylbenzene)benzimidazole, 0.5 g of palladium on carbon, and 50 mL of ethanol were added. The atmosphere was replaced with nitrogen three times, and then hydrogen was introduced to a pressure of 0.8 MPa. The temperature was controlled at 80°C and the reaction was maintained at this temperature and pressure for 5 h. The reaction progress was determined by TLC. After the reaction, the catalyst was filtered and recovered, and the filtrate was poured into water for precipitation. After filtration and drying, 4.2 g of a white solid, i.e., 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole, was obtained with a yield of 98%, which was recorded as monomer 3.

[0153] Example 4

[0154] This embodiment provides an N-substituted benzimidazole diamine, which is 5-amino-1-(4-aminophenyl)-2-methylbenzimidazole, and its structure is as follows:

[0155]

[0156] The preparation method thereof comprises:

[0157] Step 1: Same as step 1 of Example 1;

[0158] Step 2: Same as step 1 in Example 2;

[0159] Step 3: In a 1000mL single-necked flask, add 0.2mol of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, 0.3mol of triethylamine, and 500mL of THF. Stir and cool in an ice-water bath. When the reaction solution temperature drops below 5°C, slowly add 50mL of a 6M solution of acetyl chloride in THF dropwise, ensuring that the reaction solution temperature does not exceed 5°C. After the addition is complete, remove the ice-water bath and continue the reaction at room temperature for 24 hours. Monitor the reaction progress by TLC. After the reaction is complete, the solvent is dried and 200mL of methanol is added. A large amount of solid precipitates and is filtered. After drying, the product, N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)formamide, is obtained as a yellow powder.

[0160] Step 4: In a 1000 mL single-necked flask, add 0.12 mol of N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)formamide, 0.18 mol of p-toluenesulfonic acid monohydrate, and 400 mL of acetic acid. The mixture was stirred magnetically at 100°C for 12 hours, and the reaction progress was monitored by TLC. After the reaction was completed, the reaction solution was poured into 1200 mL of water, filtered, and the filter cake was dried to obtain a crude product. The crude product was then recrystallized from dioxane, filtered, and dried to obtain 26.8 g of the product, 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole, with a yield of 75%.

[0161] Step 5: In a 100 mL single-necked flask, 16.76 mmol of 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole, 0.5 g of palladium on carbon, and 50 mL of ethanol were added. The atmosphere was initially replaced with nitrogen three times, and then hydrogen was introduced to a pressure of 0.7 MPa. The temperature was controlled at 60°C and the reaction was maintained at this temperature and pressure for 5 h. The reaction progress was determined by TLC. After the reaction, the catalyst was filtered and recovered, and the filtrate was poured into water for precipitation. After filtration and drying, 3.8 g of a white solid, i.e., 5-amino-1-(4-aminophenyl)-2-methylbenzimidazole, was obtained with a yield of 95%, which was recorded as monomer 4.

[0162] The intermediate product prepared in Example 1 and monomers 1-4 prepared in Examples 1-4 were subjected to proton nuclear magnetic resonance spectroscopy to determine the shift and amount of active hydrogen atoms in the compounds and the purity of the monomers. Instrument model: Bruker 400 AVANCE III, Germany; test solvent: deuterated dimethyl sulfoxide (d6-DMSO).

[0163] The test results are as follows Figures 1-10 As shown. Among them, Figure 1 This is the H NMR spectrum of 2,4-dinitrobenzene-N-(4-nitrophenyl)aniline prepared in Example 1; Figure 2 This is the H NMR spectrum of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline prepared in Example 1; Figure 3 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-phenylbenzimidazole prepared in Example 1; Figure 4 This is the H NMR spectrum of monomer 1 prepared in Example 1, namely 5-amino-1-(4-aminophenyl)-2-phenylbenzimidazole.

[0164] Figure 5 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-(4-phenylbenzene)benzimidazole prepared in Example 2; Figure 6 This is the H NMR spectrum of 5-amino-1-(4-aminobenzene)-2-(4-phenylbenzene)benzimidazole prepared in Example 2.

[0165] Figure 7This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3; Figure 8 This is the H NMR spectrum of 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3.

[0166] Figure 9 This is the H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole prepared in Example 4; Figure 10 This is the H NMR spectrum of 5-amino-1-(4-aminophenyl)-2-methylbenzimidazole prepared in Example 4.

[0167] from Figure 1 and Figure 2 It can be seen that the intermediate product monomer obtained in step 1 and step 2 of Example 1 has high yield and high purity, and almost no impurity peaks, which is conducive to the subsequent reaction and lays the foundation for the high yield and high purity of the subsequent reaction products. Figure 3 、 Figure 5 、 Figure 7 and Figure 9 It can be seen that according to the designed reaction steps, the target dinitro monomer was successfully obtained with high purity, which is conducive to obtaining high-purity diamine monomer after the nitro group is reduced. The reduction reaction is simple and the diamine monomer can be obtained without purification. Figure 4 、 Figure 6 、 Figure 8 and Figure 10 It can be seen that, given the high purity of the dinitro monomer, the purity of the diamine monomer is also high. High-purity diamine monomers facilitate polymerization, resulting in higher molecular weight polyimide resins. The higher the purity of the diamine monomer, the better the optical properties and overall performance of the resulting polyimide film.

[0168] Example 5

[0169] The present application provides a benzimidazole transparent polyimide film, the structural formula of the benzimidazole transparent polyimide is as follows:

[0170]

[0171] The preparation method of the benzimidazole transparent polyimide film comprises:

[0172] S1. 10 g of 5-amino-1-(4-aminophenyl)-2-phenylbenzimidazole prepared in Example 1 was dissolved in 140.0 g of m-cresol, nitrogen was introduced, and mechanical stirring was performed. 7.43 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) was then added and dissolved. 2.8 g of isoquinoline was then added, and the mixture was reacted at 200° C. for 8 h. After the reaction system was cooled, it was poured into ethanol. The precipitate was collected, washed thoroughly with ethanol and water, and dried to obtain a benzimidazole transparent polyimide resin.

[0173] S2, 10.0g of benzimidazole transparent polyimide resin was dissolved in 56.7g of N,N-dimethylacetamide. After complete dissolution, the bottle was sealed and placed in a refrigerator at -20°C for degassing for 24 hours to obtain a uniform polyimide solution. The polyimide solution was returned to room temperature, and a clean, flat glass sheet was placed on a table for coating. The thickness of the coating device was controlled to 40 μm. The coated glass sheet was transferred to a muffle furnace and heated at 80°C, 150°C, and 250°C for 1 hour respectively to remove the solvent. After the muffle furnace was cooled to room temperature, the glass plate was removed and placed in 50°C hot water. The film was peeled off from the glass plate to obtain a self-supporting transparent polyimide film, recorded as CPI-1.

[0174] Example 6

[0175] The present application provides a benzimidazole transparent polyimide film, the structural formula of the benzimidazole transparent polyimide is as follows:

[0176]

[0177] The preparation method of the benzimidazole transparent polyimide film comprises:

[0178] S1. Take 10 g of 5-amino-1-(4-aminophenyl)-2-phenylbenzimidazole prepared in Example 1, dissolve it in 150.0 g of m-cresol, introduce nitrogen and mechanically stir; then add 14.79 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA), and after dissolution, add 2.8 g of isoquinoline, and react at 200 ° C for 8 h; after the reaction system is cooled, pour it into ethanol, collect the precipitate, wash it thoroughly with ethanol and water, and dry it to obtain a benzimidazole transparent polyimide resin.

[0179] S2 is the same as step S2 of Example 5. The benzimidazole transparent polyimide film prepared in Example 6 is denoted as CPI-2.

[0180] Example 7

[0181] The present application provides a benzimidazole transparent polyimide film, the structural formula of the benzimidazole transparent polyimide is as follows:

[0182]

[0183] The preparation method of the benzimidazole transparent polyimide film comprises:

[0184] S1. Take 10 g of 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3 and dissolve it in 120 g of m-cresol. Pour nitrogen into the solution and stir mechanically. Then add 5.955 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA). After the solution is dissolved, add 2.3 g of isoquinoline and react at 200°C for 10 h. After the reaction system is cooled, pour it into ethanol. The precipitate is collected, washed thoroughly with ethanol and water, and dried to obtain a benzimidazole transparent polyimide resin.

[0185] S2 is the same as step S2 of Example 5. The benzimidazole transparent polyimide film prepared in Example 7 is denoted as CPI-3.

[0186] Example 8

[0187] The present application provides a benzimidazole transparent polyimide film, the structural formula of the benzimidazole transparent polyimide is as follows:

[0188]

[0189] The preparation method of the benzimidazole transparent polyimide film comprises:

[0190] S1. Take 10 g of 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3 and dissolve it in 130 g of m-cresol. Pour nitrogen into the solution and stir mechanically. Then add 11.80 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA). After dissolution, add 2.3 g of isoquinoline and react at 200°C for 12 h. After the reaction system is cooled, pour it into ethanol. After collecting the precipitate, wash it thoroughly with ethanol and water, and dry it to obtain a benzimidazole transparent polyimide resin.

[0191] S2 is the same as step S2 of Example 5. The benzimidazole transparent polyimide film prepared in Example 8 is denoted as CPI-4.

[0192] Example 9

[0193] The present application provides a benzimidazole transparent polyimide film, the structural formula of the benzimidazole transparent polyimide is as follows:

[0194]

[0195] The preparation method of the benzimidazole transparent polyimide film comprises:

[0196] S1. 10 g of 5-amino-1-(4-aminophenyl)-2-methylbenzimidazole prepared in Example 4 was dissolved in 150 g of m-cresol, nitrogen was introduced, and mechanical stirring was performed. 9.41 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) was then added and dissolved. 3.6 g of isoquinoline was then added, and the mixture was reacted at 200°C for 12 h. After the reaction system was cooled, it was poured into ethanol. The precipitate was collected, washed thoroughly with ethanol and water, and dried to obtain a benzimidazole transparent polyimide resin.

[0197] S2 is the same as step S2 of Example 5. The benzimidazole transparent polyimide film prepared in Example 9 is denoted as CPI-5.

[0198] Example 10

[0199] The present application provides a benzimidazole transparent polyimide film, the structural formula of the benzimidazole transparent polyimide is as follows:

[0200]

[0201] The preparation method of the benzimidazole transparent polyimide film comprises:

[0202] S1. Take 10 g of 5-amino-1-(4-aminophenyl)-2-methylbenzimidazole prepared in Example 4 and dissolve it in 200 g of m-cresol. Pour nitrogen into the mixture and stir mechanically. Then add 18.64 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA). After dissolution, add 3.6 g of isoquinoline and react at 200°C for 12 h. After the reaction system is cooled, pour it into ethanol. After collecting the precipitate, wash it thoroughly with ethanol and water, and dry it to obtain a benzimidazole transparent polyimide resin.

[0203] S2 is the same as step S2 of Example 5. The benzimidazole transparent polyimide film prepared in Example 10 is denoted as CPI-6.

[0204] The infrared test was performed on the benzimidazole transparent polyimide films CPI-1 to CPI-6 prepared in Examples 5-10. The test results are as follows: Figure 11 shown.

[0205] Depend on Figure 11 It can be seen that CPI-1 to CPI-6 are at 1770cm -1 (symmetric stretching peak of imide carbonyl group), 1700 cm -1 (imide carbonyl asymmetric stretching peak), 1371 cm -1 (CN stretching peak) show typical characteristic imide and benzimidazole absorption peaks, and 1660 cm -1There is no absorption peak at (carboxyl absorption peak), which proves that the prepared transparent polyimide has been completely imidized, indicating that the benzimidazole transparent polyimide film with the structure shown is successfully prepared.

[0206] The benzimidazole transparent polyimide films CPI-1 to CPI-6 prepared in Examples 5-10 were tested for thermal stability (Td), glass transition temperature (Tg), light transmittance and cutoff wavelength. The test results are shown in Figure 2. Figure 12-14 The test data is shown in Table 1.

[0207] Table 1 Performance test results of benzimidazole transparent polyimide film

[0208]

[0209] The thermal stability (Td) was determined by thermogravimetric analysis using a TGA 550 instrument in a nitrogen atmosphere at a heating rate of 10 o The test was carried out under C / min conditions. The test results are as follows Figure 12 As shown. Figure 12 As can be seen, CPI-1 to CPI-6 show no obvious thermal weight loss step before the thermal decomposition temperature, demonstrating that the prepared transparent polyimide films have all been fully imidized. Table 1 shows that the 5% thermal weight loss temperature of the benzimidazole transparent polyimide films is between 470 and 530°C, demonstrating excellent heat resistance.

[0210] The glass transition temperature (Tg) was measured using a TA RSA-G2 dynamic thermomechanical analyzer (solid analyzer) at a heating rate of 5°C / min. Figure 13 As shown. Figure 13 As shown in Table 1, the glass transition temperatures of benzimidazole transparent polyimide films range from 310°C to 420°C, indicating relatively high glass transition temperatures. CPI-1, CPI-2, CPI-3, CPI-5, and CPI-6 all have glass transition temperatures above 350°C, while CPI-1 and CPI-5 reach 414°C and 411°C, respectively. These temperatures fully meet the processing temperature requirements for transparent polyimide films used in flexible solar cell substrates and flexible displays.

[0211] The light transmittance and cut-off wavelength were measured using the UV-Vis 2501 instrument in transmittance mode at room temperature. The test results are as follows: Figure 14 As shown. Figure 14 As shown in Table 1, the benzimidazole transparent polyimide film prepared in the present application has a light transmittance of more than 80% at 500 nm and a cutoff wavelength of 290-360 nm, and has excellent optical transmittance.

[0212] This application provides a novel transparent polyimide with a benzimidazole structure, wherein the benzimidazole diamine has a "V-shaped" structure, which is significantly different from the existing "linear" benzimidazole diamine monomer. The transparent polyimide prepared from the "V-shaped" diamine of this application is beneficial for increasing the interchain distance between molecular chains, inhibiting the formation of charge transfer complexes (CTCs), and improving the transparency of the polyimide film. Test results show that the transparency of the benzimidazole transparent polyimide provided by this application is significantly improved, while its thermal properties, such as the 5% thermal weight loss temperature and glass transition temperature, are hardly compromised. This demonstrates that the transparent polyimide film provided by this patent not only has good thermal properties but also excellent optical properties.

[0213] Although this specification has been used to fully describe the present application using general descriptions and specific embodiments, it is obvious to those skilled in the art that modifications or improvements may be made based on the present application. Therefore, such modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed in this application.

Claims

1. A benzimidazole transparent polyimide film, characterized in that: The benzimidazole transparent polyimide has a structure shown in formula (1): wherein n≥20; R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives; Ar1 is selected from at least one of the following substituents:

2. The benzimidazole transparent polyimide film according to claim 1, characterized in that: The R1 is selected from any one of the following substituents:

3. The benzimidazole transparent polyimide film according to claim 1, characterized in that: The R2 is selected from any one of the following substituents:

4. The method for preparing the benzimidazole transparent polyimide film according to any one of claims 1 to 3, characterized in that: include: The N-substituted benzimidazole diamine monomer and the dianhydride monomer are dissolved in a first solvent protected by an inert atmosphere at a molar ratio of 1: (1 to 1.3), and a polymerization reaction is carried out at 180° C. to 210° C. under the action of a first catalyst; a precipitant is added to the reaction solution, and the solid phase is collected, washed, and dried to obtain a benzimidazole transparent polyimide resin; A benzimidazole transparent polyimide resin solution is prepared, and the solution is allowed to stand, degassed, coated, and then dried to obtain a benzimidazole transparent polyimide film.

5. The preparation method according to claim 4, characterized in that The N-substituted benzimidazole diamine monomer has a structure shown in formula (2): wherein R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives; and / or: The dianhydride monomer includes at least one of the following compounds:

6. The preparation method according to claim 4, characterized in that The first solvent comprises at least one of ultra-dry benzonitrile, phenol, m-cresol, p-chlorophenol, nitrobenzene, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone or sulfolane; and / or: The first catalyst is benzoic acid, p-hydroxybenzoic acid or isoquinoline; and / or: The precipitant is methanol, ethanol, ethyl acetate, acetone or water.

7. The preparation method according to claim 5, characterized in that The preparation method of the N-substituted benzimidazole diamine comprises: The compound represented by the general formula (3) is subjected to a substitution reaction with the compound represented by the general formula (4) to obtain an intermediate product; the intermediate product is subjected to a first reduction reaction, an amidation reaction, a ring-closure reaction and a second reduction reaction in sequence to obtain an N-substituted benzimidazole diamine; The reaction formula is: Wherein, R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivatives; R2 is selected from C1-C5 alkyl and halogenated alkyl, phenyl or phenyl derivatives.

8. The preparation method according to claim 7, characterized in that The preparation method of the N-substituted benzimidazole diamine comprises: S1, dissolving 1 eq of 3,4-dinitrofluorobenzene and 1.1 eq of 4-nitroaniline in 10 eq of a second solvent, heating to 60-90° C. for reaction; collecting the solid phase, slurrying and purifying it with the first solvent, and drying it to obtain an intermediate product A; S2, dissolving 1 eq of intermediate product A, 1.2-3 eq of sodium sulfide nonahydrate, and 1.2-3 eq of the second catalyst in a solution of 10 eq of ethanol and water in a volume ratio of 2:1, heating to 60-80°C for reduction reaction; after the reaction, adding water to precipitate the solid phase, slurrying with water for purification, and drying to obtain intermediate product B; S3, dissolving 1 eq of intermediate product B and 1.2-3 eq of acid-binding agent in 5-15 eq of tetrahydrofuran to prepare solution A; dissolving 1.2-2 eq of acyl chloride monomer in a small amount of tetrahydrofuran to prepare solution B, slowly adding solution B dropwise to solution A, controlling the temperature at 0-5°C to carry out acyl chlorination reaction; after the reaction, remove tetrahydrofuran, precipitate the solid phase with methanol or dichloromethane, and dry to obtain intermediate product C; S4, dispersing 1 eq of intermediate product C and 1-3 eq of the third catalyst in 5-15 eq of an acid solution, heating to 80-180° C. for a ring-closure reaction; after the reaction, adding water to precipitate a solid phase, drying, and then recrystallizing to obtain intermediate product D; S5, dissolving 1 eq of the intermediate product D in 5-15 eq of a third solvent, adding 0.1-1 eq of a hydrogenation catalyst, heating to 60-80° C. to carry out a reduction reaction with hydrogen, and adding water after the reaction to precipitate a solid phase to obtain an N-substituted benzimidazole diamine.

9. The preparation method according to claim 8, characterized in that: The second solvent comprises at least one of methanol, ethanol, propanol or isopropanol; The second catalyst comprises at least one of sodium bicarbonate, sodium carbonate, potassium bicarbonate or potassium carbonate; The acid binding agent includes at least one of triethylamine, diisopropylethylamine, pyridine, sodium carbonate, sodium bicarbonate or potassium carbonate; The acyl chloride monomer includes benzoyl chloride, 4-phenylbenzoyl chloride, 3-phenylbenzoyl chloride or acetyl chloride; The third catalyst comprises at least one of p-toluenesulfonic acid, acetic anhydride or pyridine; The acid solution includes at least one of acetic acid, sulfuric acid or acetic anhydride; The third solvent includes at least one of tetrahydrofuran, ethanol, methanol, isopropanol, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, 1,4-dioxane, ethyl acetate, benzene, toluene or xylene; The hydrogenation catalyst includes at least one of palladium carbon, platinum carbon, activated nickel or rhodium carbon.

10. Use of the benzimidazole transparent polyimide film according to any one of claims 1 to 3 or the benzimidazole transparent polyimide film prepared by the preparation method according to any one of claims 4 to 9 in flexible solar cell base plates and flexible displays.

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