Benzimidazole transparent polyimide film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polyimide polymer materials, and discloses a benzimidazole transparent polyimide film as well as a preparation method and application thereof. The preparation method comprises the following steps: 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 180-210 DEG C under the action of a first catalyst; adding a precipitant into the reaction liquid, collecting a solid phase, washing and drying to obtain the benzimidazole transparent polyimide resin. And preparing the benzimidazole transparent polyimide resin into a solution, standing, defoaming, coating, and drying to obtain the benzimidazole transparent polyimide film. The benzimidazole transparent polyimide film provided by the invention not only retains the performance of high glass transition temperature of a benzimidazole polyimide material, but also has excellent optical permeability of a polyimide material containing a non-coplanar structure, and can be used in the fields of flexible solar cell bottom plates, flexible display and the like.

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, which is widely used in electronics, electrical engineering, aerospace and other industries. Polyimide films used in the field of optoelectronic materials, such as flexible substrates for solar cells and liquid crystal display materials, require high light transmittance and excellent mechanical properties on the basis of 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. The main reason is the electron-withdrawing effect of the carbonyl group in the dianhydride that appears alternately in the polymer main chain, the electron-donating effect of the diamine, and the formation of intramolecular and intermolecular charge transfer complexes generated by the rigid conjugated structure of the entire polymer main chain.

[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 base panels and flexible displays. The methods currently used to reduce the color of polyimide are: 1. Using dianhydride or diamine monomers with a full fat structure to obtain polyimide with fat units, destroying the conjugation of the structural molecules of the polyimide and inhibiting the formation of charge transfer complexes, such as the novel fluorine-containing copolymer polyimide and its preparation method disclosed in the patent with publication number CN101831074A; 2. Using polyimide with large side groups or asymmetric structural units to hinder the conjugation of the electron cloud and inhibit the charge transfer complex, such as the polyimide containing phenolic hydroxyl groups disclosed in the patent with publication number CN102516541A, and "Synthesis and Performance Characterization of a Polyimide Containing Phenolphthalein Structure" published in "Journal of Polymer Science" in 2012; 3. Using non-coplanar fully aromatic diamines to destroy the conjugation of the polyimide main chain and inhibit electron transfer complexation, such as "Diamine architecture effects on glass transitions, relaxation processes and other material properties in organo-soluble aromatic" 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 the transparent polyimide film 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 a preparation method and application thereof, 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 base plates and flexible displays.

[0006] In order to achieve the above objectives, the present 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]

[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]

[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 includes at least one of ultra-dry benzonitrile, phenol, m-cresol, p-chlorophenol, nitrobenzene, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, γ-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-closing reaction and a second reduction reaction in sequence to obtain an N-substituted benzimidazole diamine;

[0032]

[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 it to obtain an intermediate product A;

[0038] S2, dissolving 1 eq of the 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 the intermediate product B;

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

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

[0041] S5, dissolving 1 eq of the intermediate product D in 5-15 eq of the 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 a flexible solar cell base plate and a flexible display.

[0051] Compared with the prior art, the beneficial effects of this application are:

[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 the fields of flexible solar cell baseboards and flexible displays.

[0053] The benzimidazole transparent polyimide film of the present application has a glass transition temperature of 310-420°C, a 5% thermal decomposition temperature of 470-530°C, a light transmittance of more than 80% at 500nm, a cut-off wavelength of 290-360nm, and is self-supporting. The benzimidazole transparent polyimide film of the present application is applied to the fields of flexible solar cell base plates and flexible displays, and can withstand the high-temperature processing environment of the flexible substrate during the manufacturing process, reduce the occurrence of quality defects such as bursting and delamination, and improve the performance and quality of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

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

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

[0058] Figure 4 The H NMR spectrum of 5-amino-1-(4-aminobenzene)-2-phenylbenzimidazole prepared in Example 1;

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

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

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

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

[0063] Fig. 9 The H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole prepared in Example 4;

[0064] Fig.10 The H NMR spectrum of 5-amino-1-(4-aminobenzene)-2-methylbenzimidazole prepared in Example 4;

[0065] Fig.11 This is the infrared test spectrum of the benzimidazole transparent polyimide film of the present application;

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

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

[0068] Fig.14 This is a test chart of light transmittance and cut-off wavelength of the benzimidazole transparent polyimide film of the present application. DETAILED DESCRIPTION

[0069] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work 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 all open 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 of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after 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, c can be single or multiple, respectively.

[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 other meanings.

[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] Those skilled in the art will appreciate that the numerical ranges in the embodiments of the present application are to be construed as specifically disclosing each intermediate value between the upper and lower limits of the scope. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present application. The upper and lower limits of these smaller ranges may be independently included or excluded in the scope.

[0076] Unless otherwise specified, the technical / scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs. Although this application only describes 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 a 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]

[0079] Wherein, n≥20; R1 is selected from hydrogen, halogen, C1-C3 alkyl and halogenated alkyl, phenyl or phenyl derivative; 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 to increase the chain spacing between molecular chains, inhibit the formation of charge transfer complexes (CTC), and improve the transparency of polyimide films. The benzimidazole transparent polyimide of the present application not only retains the high glass transition temperature performance of benzimidazole polyimide materials, but also has the excellent optical transmittance of polyimide materials containing non-coplanar structures. The material can be used in the fields of flexible solar cell base plates and flexible displays. In the present application, it is preferred that the molecular weight of the benzimidazole transparent polyimide is 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 the first catalyst in this application is 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, benzimidazole transparent polyimide resin is dissolved in N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, butyrolactone or cyclopentane sulfone to prepare a polyimide solution; the polyimide solution is allowed to stand at -20 to 0°C for 24 to 30 hours to remove bubbles therein. The defoamed polyimide solution is coated, preferably with a wet film thickness of 20 to 400 μm, and after coating, the film is 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]

[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] The fluorobenzene substituted with different nitro groups is subjected to a substitution reaction with the meta-nitroaniline or para-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-closing 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]

[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 meta-nitroaniline or para-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 it to obtain an intermediate product A;

[0111] Wherein, 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 the 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 the intermediate product B;

[0113] The second catalyst includes 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 pulping is 4 to 6 times the mass of the solid phase.

[0114] S3, dissolving 1eq of the intermediate product B and 1.2-3eq of the acid-binding agent in 5-15eq of tetrahydrofuran to prepare solution A; dissolving 1.2-2eq of the 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 perform an amidation reaction; after the reaction, removing tetrahydrofuran, precipitating a solid phase with methanol or dichloromethane, and drying to obtain an intermediate product C;

[0115] Wherein, the acid binding agent is used to absorb the acid generated in 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 addition reaction with amino group to form 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 the intermediate product C and 1 to 3 eq of the third catalyst in 5 to 15 eq of an acid solution, heating to 80 to 180° C. for a ring-closing reaction; after the reaction, adding water to precipitate a solid phase, drying and then recrystallizing to obtain an intermediate product D;

[0119] The third catalyst includes 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 includes 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 the 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] Wherein, 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] On the third aspect, 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°C, the 5% thermal decomposition temperature is 470-530°C, the light transmittance at 500nm is greater than 80%, the 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 bursting and delamination, and improve the performance and quality of the substrate.

[0125] The present application is further described below by way of examples.

[0126] Example 1

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

[0128]

[0129] The preparation method thereof comprises:

[0130] Step 1: In a 3000mL three-necked flask, add 0.54mol of 3,4-dinitrofluorobenzene, 0.59mol of 4-nitroaniline and 1000mL of ethanol, set the oil bath temperature to 80°C, react for 24h under mechanical stirring, and determine the reaction progress by TLC. After the reaction is completed, ethanol is used for leaching and filtration, the filter cake is slurried with 500mL of ethanol for 5 times, filtered and dried in a vacuum oven at 80°C for 48h. Finally, 128g of yellow powder is obtained, namely 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, react for 24 hours under mechanical stirring, and determine the reaction progress by TLC. After the reaction is completed, pour into 1500mL of water to precipitate and filter. Slurry the filter cake with 500mL of water for 3 to 5 times, filter and dry in a vacuum oven at 80°C for 48 hours. Finally, 42g of red powder, i.e. 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, is obtained with a yield of 93%.

[0132] Step 3: In a 1000mL single-mouth bottle, 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 liquid temperature is lower than 5°C, slowly drop 30mL of 6M benzoyl chloride THF solution into the reaction liquid, ensure that the reaction liquid temperature does not exceed 5°C during the dropwise addition, remove the ice-water bath, continue to react at room temperature for 24h, and monitor the reaction progress by TLC. After the reaction is completed, spin-dry the solvent, add 100mL of methanol, and a large amount of solid precipitates and is filtered. After drying, a yellow powder product is obtained, i.e., N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)benzamide.

[0133] Step 4: In a 500mL single-necked flask, add 79.29mmol of N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)benzamide, 118.94mmol of p-toluenesulfonic acid monohydrate and 300mL of acetic acid, stir magnetically at 100°C for 12h, and monitor the reaction progress by TLC. After the reaction is completed, the reaction solution is poured into 1000mL of water, filtered and the filter cake is dried to obtain a crude product. The crude product is then recrystallized in dioxane, filtered, and dried to obtain 25g of product, i.e., 5-nitro-1-(4-nitrobenzene)-2-phenylbenzimidazole, with a yield of 87%.

[0134] Step 5: In a 100mL single-necked flask, add 13.88mmol of 5-nitro-1-(4-nitrobenzene)-2-phenylbenzimidazole, 0.5g of palladium carbon and 50mL of ethanol, replace with nitrogen three times, then fill with hydrogen to a pressure of 0.8MPa, control the temperature at 80°C, keep the temperature and pressure for 5h, and determine the progress of the reaction by TLC. After the reaction is completed, filter and recover the catalyst, pour the filtrate into water for precipitation, filter and dry to obtain 3.7g of white solid, i.e. 5-amino-1-(4-aminobenzene)-2-phenylbenzimidazole, with a yield of 90%, 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-mouth bottle, add 0.15mol of 2-amino-4-nitrobenzene-N-(4-nitrophenyl) aniline, 0.22mol of triethylamine and 370mL of THF, stir and cool in an ice-water bath, when the reaction liquid temperature is lower than 5°C, slowly drop 30mL of a THF solution of 4-phenylbenzoyl chloride with a molar concentration of 7.3M into the reaction liquid, ensure that the reaction liquid temperature does not exceed 5°C during the dropwise addition, remove the ice-water bath, continue to react at room temperature for 24h, and monitor the reaction progress by TLC. After the reaction is completed, spin-dry the solvent, add 200mL of methanol, and a large amount of solid precipitates and is filtered. After drying, a yellow powder product is obtained, i.e., N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)-4-phenylbenzamide.

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

[0143] Step 5: In a 100mL single-necked flask, add 11.46mmol of 5-nitro-1-(4-nitrobenzene)-2-(4-phenylbenzene)benzimidazole, 0.5g of palladium carbon and 50mL of ethanol, replace with nitrogen three times, then fill with hydrogen to a pressure of 0.8MPa, control the temperature at 80°C, keep the temperature and pressure for 5h, and determine the progress of the reaction by TLC. After the reaction is completed, filter and recover the catalyst, pour the filtrate into water for precipitation, filter and dry to obtain 4.0g of white solid, i.e. 5-amino-1-(4-aminobenzene)-2-(4-phenylbenzene)benzimidazole, with a yield of 93%, recorded as monomer 2.

[0144] Example 3

[0145] This embodiment provides an N-substituted benzimidazole diamine, which is 5-amino-1-(4-aminobenzene)-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-mouth bottle, add 0.1mol of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline, 0.15mol of triethylamine and 270mL of THF, stir and cool in an ice-water bath, when the reaction liquid temperature is lower than 5°C, slowly drop 30mL of 5M 3-phenylbenzoyl chloride THF solution into the reaction liquid, ensure that the reaction liquid temperature does not exceed 5°C during the dropwise addition, remove the ice-water bath, continue to react at room temperature for 24h, and monitor the reaction progress by TLC. After the reaction, spin-dry the solvent, add 100mL of methanol, and a large amount of solid precipitates and is filtered. After drying, a yellow powder product is obtained, i.e., N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)-3-phenylbenzamide.

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

[0152] Step 5: In a 100mL single-necked flask, add 11.46mmol of 5-nitro-1-(4-nitrobenzene)-2-(3-phenylbenzene)benzimidazole, 0.5g of palladium carbon and 50mL of ethanol, replace with nitrogen three times, then fill with hydrogen to a pressure of 0.8MPa, control the temperature at 80°C, keep the temperature and pressure for 5h, and determine the progress of the reaction by TLC. After the reaction is completed, filter and recover the catalyst, pour the filtrate into water for precipitation, filter and dry to obtain 4.2g of white solid, i.e. 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole, with a yield of 98%, recorded as monomer 3.

[0153] Example 4

[0154] This embodiment provides an N-substituted benzimidazole diamine, which is 5-amino-1-(4-aminobenzene)-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-mouth bottle, 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 temperature of the reaction solution is lower than 5°C, slowly drop 50mL of 6M acetyl chloride THF solution into the reaction solution, ensure that the temperature of the reaction solution does not exceed 5°C during the dropwise addition, remove the ice-water bath, continue to react at room temperature for 24h, and monitor the reaction progress by TLC. After the reaction, spin dry the solvent, add 200mL of methanol, and a large amount of solid precipitates and is filtered. After drying, a yellow powder product is obtained, i.e., N-(5-nitro-2-((4-nitrophenyl)amino)phenyl)formamide.

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

[0161] Step 5: In a 100 mL single-necked flask, add 16.76 mmol of 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole, 0.5 g of palladium carbon and 50 mL of ethanol, replace with nitrogen three times, then fill with hydrogen to a pressure of 0.7 MPa, control the temperature at 60°C, keep the temperature and pressure for 5 hours, and determine the progress of the reaction by TLC. After the reaction is completed, filter and recover the catalyst, pour the filtrate into water for precipitation, filter and dry to obtain 3.8 g of white solid, i.e., 5-amino-1-(4-aminobenzene)-2-methylbenzimidazole, with a yield of 95%, recorded as monomer 4.

[0162] The intermediate product prepared in Example 1 and the monomers 1-4 prepared in Examples 1-4 were subjected to H NMR analysis to determine the displacement and quantity of active hydrogen in the compound and the purity of the monomer. Instrument model: German Bruker 400AVANCEⅢ; test solvent: deuterated dimethyl sulfoxide (d6-DMSO).

[0163] Test results such as Figure 1-Figure 10 As shown. Among them, Figure 1 The H NMR spectrum of 2,4-dinitrobenzene-N-(4-nitrophenyl)aniline prepared in Example 1; Figure 2 The H NMR spectrum of 2-amino-4-nitrobenzene-N-(4-nitrophenyl)aniline prepared in Example 1; Figure 3 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-aminobenzene)-2-phenylbenzimidazole.

[0164] Figure 5 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 7The 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] Fig. 9 The H NMR spectrum of 5-nitro-1-(4-nitrobenzene)-2-methylbenzimidazole prepared in Example 4; Fig.10 This is the H NMR spectrum of 5-amino-1-(4-aminobenzene)-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 not only high yield but also high purity, and almost no impurity peak, 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 Fig. 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 a 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 Fig.10 It can be seen that under the premise of high purity of dinitro monomer, the purity of diamine monomer is also high. High-purity diamine monomer is conducive to polymerization reaction, thereby obtaining polyimide resin with higher molecular weight. The higher the purity of diamine monomer, the better the optical properties of the obtained polyimide film and its performance.

[0168] Example 5

[0169] The present application provides a benzimidazole transparent polyimide film, and 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, take 10g of 5-amino-1-(4-aminobenzene)-2-phenylbenzimidazole prepared in Example 1, dissolve it in 140.0g of m-cresol, pass nitrogen and stir mechanically; then add 7.43g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), add 2.8g of isoquinoline after dissolution, and react at 200°C for 8h; 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.

[0173] S2, dissolve 10.0g of benzimidazole transparent polyimide resin in 56.7g of N,N-dimethylacetamide, and after it is completely dissolved, seal the bottle mouth and stand in a refrigerator at -20℃ for degassing for 24h to obtain a uniform polyimide solution. The polyimide solution is restored to room temperature, and a clean and flat glass sheet is placed on the table for coating. The thickness of the coating device is controlled at 40μm. The coated glass sheet is transferred to a muffle furnace and heated at 80℃, 150℃ and 250℃ for 1h respectively to remove the solvent. After the muffle furnace is cooled to room temperature, the glass plate is taken out and placed in hot water at 50℃. The film is 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, and 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 10g of 5-amino-1-(4-aminobenzene)-2-phenylbenzimidazole prepared in Example 1, dissolve it in 150.0g of m-cresol, introduce nitrogen and stir mechanically; then add 14.79g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA), add 2.8g of isoquinoline after dissolution, and react at 200°C for 8h; 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, and 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 10g of 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3, dissolve it in 120g of m-cresol, introduce nitrogen and stir mechanically; then add 5.955g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), add 2.3g of isoquinoline after dissolution, and react at 200°C for 10h; 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.

[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, and 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 10g of 5-amino-1-(4-aminobenzene)-2-(3-phenylbenzene)benzimidazole prepared in Example 3, dissolve it in 130g of m-cresol, introduce nitrogen and stir mechanically; then add 11.80g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA), add 2.3g of isoquinoline after dissolution, and react at 200°C for 12h; 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.

[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, and 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, take 10g of 5-amino-1-(4-aminobenzene)-2-methylbenzimidazole prepared in Example 4, dissolve it in 150g of m-cresol, pass nitrogen and stir mechanically; then add 9.41g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), add 3.6g of isoquinoline after dissolution, and react at 200°C for 12h; 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.

[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, and 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 10g of 5-amino-1-(4-aminobenzene)-2-methylbenzimidazole prepared in Example 4, dissolve it in 200g of m-cresol, pass nitrogen and stir mechanically; then add 18.64g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA), add 3.6g of isoquinoline after dissolution, and react at 200°C for 12h; 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.

[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 benzimidazole transparent polyimide films CPI-1 to CPI-6 prepared in Examples 5-10 were subjected to infrared testing, and the test results are as follows: Fig.11 shown.

[0205] Depend on Fig.11 It can be seen that CPI-1 to CPI-6 are at 1770cm -1 (symmetric stretching peak of imide carbonyl), 1700 cm -1 (imide carbonyl asymmetric stretching peak), 1371 cm -1 The typical characteristic imide and benzimidazole absorption peaks are shown at 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] project Tg / ℃ <![CDATA[T d5％ / ℃]]> <![CDATA[T 400nm / %]]> <![CDATA[T 500nm / %]]> <![CDATA[λ cutoff / nm]]> CPI-1 414 487 83 87 308 CPI-2 371 531 13 85 364 CPI-3 354 477 83 87 300 CPI-4 314 526 20 85 356 CPI-5 411 475 82 88 291 CPI-6 386 526 19 86 358

[0209] The thermal stability (Td) was tested using a thermogravimetric analyzer TGA 550 in a nitrogen atmosphere at a heating rate of 10°C / min. Fig.12 As shown. Fig.12 It can be seen that CPI-1 to CPI-6 have no obvious thermal weight loss steps before the thermal decomposition temperature, proving that the prepared transparent polyimide films have been completely imidized. From Table 1, it can be seen that the 5% thermal weight loss temperature of the benzimidazole transparent polyimide film is between 470 and 530°C, which has good heat resistance.

[0210] The glass transition temperature (Tg) was measured using a TARSA-G2 dynamic thermomechanical analyzer (solid analyzer) at a heating rate of 5°C / min. Fig.13 As shown. Fig.13 As shown in Table 1, the glass transition temperature of the benzimidazole transparent polyimide film is between 310 and 420°C, which is relatively high. Among them, the glass transition temperatures of CPI-1, CPI-2, CPI-3, CPI-5 and CPI-6 are all higher than 350°C, while the glass transition temperatures of CPI-1 and CPI-5 reach 414°C and 411°C, which fully meet the processing temperature requirements of transparent polyimide films used in flexible solar cell substrates and flexible displays.

[0211] The light transmittance and cut-off wavelength were tested using the UV-Vis 2501 instrument in the transmittance mode at room temperature. The test results are as follows: Fig.14 As shown. Fig.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 cut-off wavelength of 290 to 360 nm, and has excellent optical transmittance.

[0212] The present application provides a transparent polyimide with a novel structure of benzimidazole structure, wherein the structure of benzimidazole diamine is "V-shaped", which is significantly different from the existing "linear" benzimidazole diamine monomer. The transparent polyimide prepared from the "V-shaped" diamine of the present application is beneficial to increase the chain spacing between molecular chains, inhibit the formation of charge transfer complexes (CTC), and improve the transparency of the polyimide film. The test results show that the transparency of the benzimidazole transparent polyimide provided by the present application is significantly improved, and at the same time, its thermal properties, such as 5% thermal weight loss temperature and glass transition temperature, are almost not sacrificed, proving that the transparent polyimide film provided by this patent not only has good thermal properties, but also has excellent optical properties.

[0213] Although the present application has been described in detail in general terms and in specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements may be made to the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed in the present 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 includes 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-closing 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 a first solvent, and drying it to obtain an intermediate product A; S2, dissolving 1 eq of the 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 the intermediate product B; S3, dissolving 1eq of the intermediate product B and 1.2-3eq of the acid-binding agent in 5-15eq of tetrahydrofuran to prepare solution A; dissolving 1.2-2eq of the acyl chloride monomer in a small amount of tetrahydrofuran to prepare solution B, slowly dropping solution B into solution A, controlling the temperature at 0-5°C to carry out acyl chlorination reaction; after the reaction, removing tetrahydrofuran, precipitating the solid phase with methanol or dichloromethane, and drying to obtain the intermediate product C; S4, dispersing 1 eq of the intermediate product C and 1 to 3 eq of the third catalyst in 5 to 15 eq of an acid solution, heating to 80 to 180° C. for a ring-closing reaction; after the reaction, adding water to precipitate a solid phase, drying and then recrystallizing to obtain an intermediate product D; S5, dissolving 1 eq of the intermediate product D in 5-15 eq of the 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.

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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