Aromatic diamine, polyimide film containing aromatic diamine and preparation method of polyimide film

Abstract

The invention discloses aromatic diamine, which has a structure shown in the following formula: # imgabs0 #, and Ar is a conjugated aromatic ring group. The aromatic diamine comprises pyridino-diimidazole and conjugated aromatic ring amido symmetrically connected to two ends of the pyridino-diimidazole, is a rigid linear group, and has a plurality of hydrogen bond donor-acceptor sites capable of effectively enhancing interaction between molecular chains. The invention also provides a polyimide film containing the aromatic diamine, the film not only has low thermal expansion coefficient, but also has excellent heat resistance, and particularly has excellent high heat resistance and low coefficient of expansion (lt; 5 ppm / K).

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and in particular relates to aromatic diamine, a polyimide film containing the aromatic diamine and a preparation method thereof. Background Art

[0002] Based on the pursuit of flexible screens in smart phones, smart wearables, VR / AR and automotive electronics, flexible displays are promoting the development of information visualization technology towards flexibility. Flexible screens have the advantages of being thin, durable, low power and retractable, and have huge potential and broad market prospects. In order to achieve the thinness and retractability of flexible screen devices, it is necessary to find polymer films with excellent comprehensive performance to replace traditional optical glass substrates.

[0003] Polyimide has high heat resistance, thermal stability and good mechanical properties. It is at the top of the material pyramid and is the most high-temperature resistant polymer material that can be actually applied. It has a wide range of applications in the field of flexible displays. Polyimide refers to a class of polymers containing imide groups on the main chain, which are usually divided into aromatic polyimide and alicyclic polyimide. Although the main chain contains aromatic rings or aromatic heterocycles with strong charge transfer effects, it has a high molecular chain interaction to a certain extent, which makes polyimide have a certain heat resistance and dimensional stability under temperature changes. However, it is difficult to meet the high temperature requirements of the subsequent process of flexible devices. In order to improve its performance, aromatic heterocycles, alicyclic rings, etc. are usually introduced into the molecular chain. These groups can increase the energy required for the movement of the chain segments to a certain extent. However, other properties such as thermal expansion coefficient are still high. By introducing amide bonds and other groups that can increase the interaction between molecules, hydrogen bonds can be formed between molecules to improve the regularity of the molecular chain under temperature changes, but it still cannot meet the requirements of comprehensive performance improvement. The performance of polyimide usually depends on the functional groups of diamine and dianhydride in the polycondensation reaction. The strength of their electron-withdrawing properties and steric hindrance effects will affect the comprehensive performance of polyimide.

[0004] The thermal expansion coefficient of traditional polyimide films is relatively high (>60ppm / K), which cannot meet the requirements of flexible display device substrates for low thermal expansion coefficient performance of substrate materials (<20ppm / K). In addition, the high thermal expansion coefficient of polyimide films can easily cause quality problems such as cracking and deformation of flexible devices. Therefore, the heat resistance and thermal dimensional stability of polyimide materials face challenges. For example, the glass transition temperature of polyimide film materials disclosed in patent application document CN118755087A exceeds 400°C, but its low expansion coefficient is still relatively large; the polyimide film materials disclosed in patent application document CN112029099B have good dimensional stability, but it is in a narrow temperature range (50-200°C) and its glass transition temperature is still relatively low.

[0005] In the process of realizing the present invention, the inventors found that there are at least the following problems in the prior art: the existing polyimide film has the problem that low expansion coefficient and high heat resistance cannot be achieved at the same time, especially the problem that low expansion and high heat resistance cannot be achieved at the same time within a wide temperature range (50-350°C). Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an aromatic diamine, a polyimide film containing the aromatic diamine and a preparation method thereof in view of the deficiencies of the above-mentioned prior art.

[0007] In order to solve the above technical problems, on the one hand, an aromatic diamine having a structure shown in Formula I is provided:

[0008]

[0009] Wherein, Ar is a conjugated aromatic ring group.

[0010] Some embodiments provide an aromatic diamine of the above structure, which is a linear rigid structure with a large aspect ratio and many hydrogen bond active sites.

[0011] On the other hand, a method for preparing the above-mentioned aromatic diamine is provided, comprising mixing tetraaminopyridine hydrochloride with an aromatic aminocarboxyl compound and a polyphosphoric acid solvent under an inert atmosphere, and reacting them under gradient temperature conditions to obtain the aromatic diamine of the structure.

[0012] Some embodiments provide a method for preparing the aromatic diamine of the above structure, with a yield of 70% to 90%, a high yield, and no other by-products.

[0013] On the other hand, a polyimide film comprising the above aromatic diamine is provided, wherein the main chain of the polyimide molecule has the above linear rigid structural unit containing the pyridodiimidazole group, the glass transition temperature of the polyimide film is 440-500°C, and the thermal expansion coefficient is <2.48ppm / °C.

[0014] In some embodiments, the above-mentioned aromatic diamines have the same structure in the main chain of the polyimide molecule, such as the structure shown in Formula IA, and the number is one or more; in some embodiments, the aromatic diamines have different structures, such as the structure shown in Formula IA and the structure shown in Formula IB, and the number of aromatic diamines is two or more.

[0015] Some embodiments provide a polyimide film containing the above-mentioned aromatic diamine, which utilizes the large aspect ratio of the pyridodiimidazole group to enhance the chain rigidity of the polyimide molecular chain, and simultaneously utilizes the multiple hydrogen bond active sites of the pyridodiimidazole group to enhance the molecular bonds, thereby overcoming the defects of low molecular chain stacking density and uncertain orientation in the imidization process. The film has the characteristics of high heat resistance and low expansion coefficient in a wide temperature range, with a heat resistance temperature above 580°C, and has excellent heat resistance in a wide temperature range (50-350°C).

[0016] On the other hand, a method for preparing the above-mentioned polyimide film is provided, comprising: placing the aromatic diamine and aromatic dianhydride in an organic solvent under the protection of an inert gas, and obtaining a polyamic acid homogeneous solution through a condensation reaction; spin-coating the polyamic acid homogeneous solution on a substrate for thermal cyclization, and then obtaining a polyimide film through staged annealing and natural cooling.

[0017] Some embodiments provide a method for preparing the above-mentioned polyimide film, including thermal cyclization and stage annealing, which can fully promote the hydrogen bond donor and acceptor sites in the aromatic diamine molecular chain to play a role, forming a polyimide main chain with stronger intermolecular hydrogen bonding and more regular molecular chain arrangement, so as to overcome the current thermodynamic performance defects of polyimide.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The present invention provides an aromatic diamine of a novel structure as shown in the above formula I, comprising pyridodiimidazole and conjugated aromatic ring amine groups symmetrically connected to both ends of pyridodiimidazole, which is a rigid linear group having multiple hydrogen bond donor and acceptor sites that can effectively enhance the interaction between molecular chains.

[0020] 2. The present invention provides a polyimide film comprising the above aromatic diamine, with a glass transition temperature of 440-500°C and a thermal expansion coefficient of <2.48ppm / °C.

[0021] 3. The present invention provides a method for preparing a polyimide film. Preferably, one or more of N-methylpyrrolidone, N,N'-dimethylacetamide, N,N'-dimethylformamide and dimethyl sulfoxide are used as organic solvents for the polycondensation reaction, which can fully dissolve aromatic diamines and aromatic dianhydrides, promote the full stretching of molecular chains, obtain a uniform and stable polyamic acid homogeneous solution, and avoid the defect of poor comprehensive performance of the polyimide film.

[0022] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The aromatic diamine prepared in Example 11 H-NMR spectrum;

[0024] Figure 2 This is the infrared spectrum of the aromatic diamine prepared in Example 1;

[0025] Figure 3 This is a high-resolution mass spectrum of the aromatic diamine prepared in Example 1;

[0026] Figure 4 This is the infrared spectrum of the film prepared in Example 1;

[0027] Figure 5 The infrared spectrum of the film prepared by comparative example 1;

[0028] Figure 6 This is the infrared spectrum of the film prepared in Example 2;

[0029] Figure 7 This is the infrared spectrum of the film prepared in Example 3;

[0030] Figure 8 is the infrared spectrum of the film prepared in Application Example 4;

[0031] Fig. 9 This is the infrared spectrum of the film prepared in Application Example 5. DETAILED DESCRIPTION

[0032] 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.

[0033] In the following description, 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.

[0034] In the following description, the terms "include", "comprising", "having" and "containing" are open-ended terms, meaning including but not limited to.

[0035] 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.

[0036] Those skilled in the art will appreciate that the numerical ranges in the embodiments of the present application are to be understood as each intermediate value between the upper and lower limits of the scope also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the 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.

[0037] 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.

[0038] In some embodiments, an aromatic diamine of a novel structure as shown in Formula I above is provided. In some preferred embodiments, it has any structure of Formulas IA to ID, comprising pyridodiimidazole, and conjugated aromatic ring amine groups symmetrically connected to both ends of pyridodiimidazole, which are rigid linear groups and have multiple hydrogen bond accepting sites that can effectively enhance the interaction between molecular chains; the number of rings of the conjugated aromatic rings is ≥1, and in some preferred embodiments, the conjugated aromatic rings are benzene rings or naphthalene rings.

[0039]

[0040]

[0041] In some embodiments, a method for preparing the above aromatic diamine is provided, comprising: under an inert atmosphere, mixing tetraaminopyridine hydrochloride with an aromatic aminocarboxyl compound and a polyphosphoric acid solvent, and reacting them under gradient temperature conditions to obtain the aromatic diamine of the structure.

[0042] In some preferred embodiments, the gradient temperature increase includes reacting at 60°C for 1-2h, 80°C for 1-2h, 100°C for 1-2h, 120°C for 1-2h, 140°C for 1-2h, 160°C for 1-2h, and 190°C for 1-2h in sequence; the reaction of tetraaminopyridine hydrochloride with an aromatic aminocarboxyl compound to generate an aromatic diamine is a two-step reaction, the first step of the reaction generates an amide, and the second step of the reaction forms an imidazole ring structure, the amide formation temperature is generally 100-140°C, and the imidazole ring is generally formed at around 190°C. The inventors found that the reaction process of obtaining the final product imidazole ring with high selectivity is related to the degree of conversion of the amide group. In the art, the amide group is usually obtained by extending the amidation reaction time. The inventors unexpectedly found that by setting a buffer reaction stage between the amidation reaction and the cyclization reaction, that is, reacting at 160°C for 1-2h, the yield of the imidazole ring generated by the cyclization reaction can be as high as 90%, which may be attributed to the complete generation of the amide group in the buffer reaction stage, and the dehydration condensation of the amide and the amino group to obtain the imidazole ring reaction process without complex side reactions. Further, the inventors also found that the hydrogen chloride in tetraaminopyridine hydrochloride will affect the amidation reaction, resulting in the formation of ammonium salts as byproducts that affect the reaction balance. By setting the reaction at 60°C for 1-2h and 80°C for 1-2h, the hydrogen chloride in the reaction system is fully eliminated.

[0043] In some preferred embodiments, the P2O5 mass content of the polyphosphoric acid is 84%.

[0044] In some preferred embodiments, the aromatic amino-carboxyl compound is one or more of p-aminobenzoic acid, 3-aminobenzoic acid, 6-amino-2-naphthoic acid and 2-amino-1-naphthoic acid. The above aromatic amino-carboxyl compounds are used to introduce a rigid unit containing a pyridine diimidazole group into the main chain of the polyimide molecule.

[0045] In some preferred embodiments, the molar ratio of tetraaminopyridine hydrochloride to the aromatic aminocarboxyl compound is 1:2.05, and the sum of the masses of tetraaminopyridine hydrochloride and the aromatic aminocarboxyl compound / the mass of polyphosphoric acid = 20% to 30%; the aromatic diamine obtained according to the above ratio has high yield and purity; setting the ratio of the mass of polyphosphoric acid to the mass of the reactants can ensure that the polyphosphoric acid solvent can completely dissolve the reactants.

[0046] In some embodiments, a method for preparing a polyimide film using the above aromatic diamine as the main raw material is provided, wherein the aromatic diamine and aromatic dianhydride are placed in an organic solvent under the protection of an inert gas, and a polyamide acid homogeneous solution is obtained through a polycondensation reaction; the polyamide acid homogeneous solution is spin-coated on a substrate for thermal cyclization, and then subjected to stage annealing and natural cooling to obtain a polyimide film. In some embodiments, the substrates are all glass plates, stainless steel plates, silicon plates or polymer resin plates; in some preferred embodiments, the molar ratio of aromatic diamine to aromatic dianhydride is (0.95-1.05): 1, wherein the aromatic diamine is a combination of one or more of the aromatic diamines of the above structure; in some preferred embodiments, the solid content of the polyamide acid homogeneous solution is 10wt.%-20wt.%, when the solid content is less than 10wt.%, the polyamide acid homogeneous solution is difficult to be coated on the substrate, and when the solid content exceeds 20wt.%, the homogeneous solution is too viscous, and the obtained polyimide film is difficult to obtain a balanced and stable Heat resistance comprehensive performance; In some preferred embodiments, the organic solvent is one or more of N-methylpyrrolidone, N,N'-dimethylacetamide, N,N'-dimethylformamide and dimethyl sulfoxide. The above solvents are used as polycondensation reaction solvents to fully dissolve aromatic diamines and aromatic dianhydrides, achieve full stretching of molecular chains, and obtain a uniform and stable polyamic acid homogeneous solution; In some preferred embodiments, the temperature of the polycondensation reaction is 0-10°C. When the temperature is lower than 0°C, the polymerization reaction rate is too low to meet the film-forming molecular weight requirements. When the temperature is higher than 10°C, the heat of the polycondensation reaction process of aromatic diamines and aromatic dianhydrides is difficult to In order to obtain timely discharge, the reaction proceeds in the direction of depolymerization, the polyamide polymerization degree is too low, and by limiting the above-mentioned low temperature range, taking into account the reaction rate and reaction direction, the reaction is promoted to the direction of generating polyamic acid; in some preferred embodiments, the thermal cyclization includes thermal cyclization at 80-100°C for 1-2h, thermal cyclization at 150-180°C for 1-2h, thermal cyclization at 200-250°C for 1-2h, and thermal cyclization at 300-350°C for 1-2h; in this stage of thermal cyclization, thermal cyclization at 80-100°C for 1-2h and thermal cyclization at 150-180°C for 1-2h, the purpose is to Promote solvent volatilization to avoid the influence of solvent on the cyclization reaction. 200-250°C is the main temperature for polyamic acid cyclization. In order to further promote the cyclization, 300-350°C is set. The thermal cyclization at this stage can fully realize the solidification of the film, and the obtained film has a low thermal expansion coefficient and good heat resistance. In some preferred embodiments, the stage annealing specifically includes: cooling at a cooling rate of 50°C / h to 150°C, and then cooling at a cooling rate of 0.5°C / min to 100°C. Through stage annealing, breakage or uneven shrinkage can be prevented, and a film with better comprehensive performance can be obtained to avoid warping, deformation or cracking.

[0047] In some embodiments, the method for preparing a polyimide film also includes a benzimidazole compound, and the molar ratio of the benzimidazole compound to the aromatic diamine is (0.2 to 4):1; the polyimide film is prepared by combining 2-(4-aminophenyl)-5-aminobenzimidazole and aromatic diamine, and the two diamine structures cooperate synergistically, so that the film has relatively higher heat resistance and lower thermal expansion coefficient in a wide temperature range.

[0048] The present invention has been subjected to a series of experiments before the application is filed. A part of the experimental results are now cited to further describe the invention in detail, and the following is a detailed description in conjunction with the embodiments.

[0049] Example 1

[0050] This embodiment provides an aromatic diamine, whose structural formula is shown in Formula IA, specifically:

[0051]

[0052] This embodiment also provides a method for preparing the above aromatic diamine, comprising:

[0053] Under the protection of inert gas, 1 mol of tetraaminopyridine hydrochloride, 2 mol of p-aminobenzoic acid and polyphosphoric acid are placed in a three-necked flask equipped with a mechanical stirrer, the temperature is raised from room temperature to 60°C and maintained for 1.5 hours of reaction, the temperature is raised to 80°C and maintained for 1.5 hours of reaction, the temperature is raised to 100°C for 1.5 hours of reaction, the temperature is raised to 120°C for 1.5 hours of reaction, the temperature is raised to 140°C for 1.5 hours of reaction, the temperature is raised to 160°C for 2 hours of reaction, the temperature is raised to 190°C for 2 hours of reaction, after the reaction is completed, the reaction is washed with deionized water, the pH value is adjusted to 7.5 with a saturated sodium carbonate solution, the system after the pH adjustment is filtered, the filter residue is dried to obtain an aromatic diamine; the mass of the polyphosphoric acid is 4 times the sum of the masses of tetraaminopyridine hydrochloride and p-aminobenzoic acid.

[0054] The above method for preparing aromatic diamines has the following specific route:

[0055]

[0056] The yield of the aromatic diamine prepared in this example is 90%.

[0057] Example 2

[0058] This embodiment provides an aromatic diamine, whose structural formula is shown in Formula IB, specifically:

[0059]

[0060] This embodiment also provides a method for preparing the above aromatic diamine, comprising:

[0061] Under the protection of inert gas, 1 mol of tetraaminopyridine hydrochloride, 2 mol of 3-aminobenzoic acid and polyphosphoric acid are placed in a three-necked flask equipped with a mechanical stirrer, and the temperature is raised from room temperature to 60°C and maintained for 1 hour, the temperature is raised to 80°C and maintained for 1 hour, the temperature is raised to 100°C for 1 hour, the temperature is raised to 120°C for 2 hours, the temperature is raised to 140°C for 1 hour, the temperature is raised to 160°C for 2 hours, the temperature is raised to 190°C for 2 hours, after the reaction, the reaction is washed with deionized water, and the pH value is adjusted to 7.5 with a saturated sodium carbonate solution, the system after the pH adjustment is filtered, and the filter residue is dried to obtain an aromatic diamine; the mass of the polyphosphoric acid is 4 times the sum of the masses of tetraaminopyridine hydrochloride and 3-aminobenzoic acid.

[0062] The above method for preparing aromatic diamines has the following specific route:

[0063]

[0064] The yield of the aromatic diamine prepared in this example is 85%.

[0065] Example 3

[0066] This embodiment provides an aromatic diamine, whose structural formula is shown in Formula IC, specifically:

[0067]

[0068] This embodiment also provides a method for preparing the above aromatic diamine, comprising:

[0069] Under the protection of inert gas, 1 mol of tetraaminopyridine hydrochloride, 2 mol of 6-amino-2-naphthoic acid and polyphosphoric acid are placed in a three-necked flask equipped with a mechanical stirrer, and the temperature is raised from room temperature to 60°C and maintained for 2 hours, the temperature is raised to 80°C and maintained for 2 hours, the temperature is raised to 100°C for 2 hours, the temperature is raised to 120°C for 1 hour, the temperature is raised to 140°C for 2 hours, the temperature is raised to 160°C for 2 hours, the temperature is raised to 190°C for 2 hours, after the reaction, the reaction is washed with deionized water, the pH value is adjusted to 8 with a saturated sodium carbonate solution, the system after the pH adjustment is filtered, and the filter residue is dried to obtain an aromatic diamine; the mass of the polyphosphoric acid is 4 times the sum of the masses of tetraaminopyridine hydrochloride and 6-amino-2-naphthoic acid.

[0070] The above method for preparing aromatic diamines has the following specific route:

[0071]

[0072] The yield of the aromatic diamine prepared in this example is 80%.

[0073] Example 4

[0074] This embodiment provides an aromatic diamine, whose structural formula is shown in Formula ID, specifically:

[0075]

[0076] This embodiment also provides a method for preparing the above aromatic diamine, comprising:

[0077] Under the protection of inert gas, 1 mol of tetraaminopyridine hydrochloride, 2 mol of 2-amino-1-naphthoic acid and polyphosphoric acid are placed in a three-necked flask equipped with a mechanical stirrer, and the temperature is raised from room temperature to 60°C and maintained for 2 hours, the temperature is raised to 80°C and maintained for 1 hour, the temperature is raised to 100°C for 2 hours, the temperature is raised to 120°C for 1 hour, the temperature is raised to 140°C for 2 hours, the temperature is raised to 160°C for 2 hours, the temperature is raised to 190°C for 2 hours, after the reaction, the reaction is washed with deionized water, the pH value is adjusted to 7 with a saturated sodium carbonate solution, the system after the pH adjustment is filtered, and the filter residue is dried to obtain an aromatic diamine; the mass of the polyphosphoric acid is 4 times the sum of the masses of tetraaminopyridine hydrochloride and 2-amino-1-naphthoic acid.

[0078] The above method for preparing aromatic diamines has the following specific route:

[0079]

[0080] The yield of the aromatic diamine prepared in this example is 70%.

[0081] Application Example 1

[0082] This application example provides a polyimide film, comprising the aromatic diamine described in Example 1. This application example also provides a method for preparing the polyimide film, comprising:

[0083] (1) Under inert gas protection, 17.07 g (0.05 mol) of the aromatic diamine (Formula IA) described in Example 1, 92 ml of N,N'-dimethylacetamide (DMAC) and 92 ml of dimethyl sulfoxide (DMSO) were added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet and a thermometer, and stirred at room temperature until completely dissolved. Then, the system temperature was lowered to 0° C., and 14.72 g (0.05 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After complete dissolution, stirring was continued for 16 hours to carry out a polycondensation reaction to obtain a polyamic acid homogeneous solution having a solid content of about 15 wt.%;

[0084] (2) filtering the polyamic acid homogeneous solution obtained in step (1), defoaming it, coating it on a flat and smooth dry glass plate by spin coating, placing it in an oven under a vacuum atmosphere for thermal cyclization, the thermal cyclization being specifically 100°C / 2 hours, 150°C / 2 hours, 250°C / 2 hours, and 350°C / 1 hour, and then performing gradient annealing, that is, slowly cooling from 350°C to 150°C at a cooling rate of 50°C / h, and then slowly cooling from 150°C to 100°C at a cooling rate of 0.5°C / min, then turning off the power, opening the cavity, and naturally cooling to room temperature to obtain a polyimide film.

[0085] The main properties of the polyimide film prepared in this application example are shown in Table 1. The infrared analysis data of the film (FT-IR, cm -1 )like Figure 4 shown.

[0086] Application Comparative Example 1

[0087] This comparative example of application provides a polyimide film, comprising an aromatic diamine (2-(4-aminophenyl)-5-aminobenzimidazole) as shown in the following structure, wherein the aromatic diamine is commercially available.

[0088]

[0089] This comparative example provides a method for preparing the above-mentioned polyimide film, comprising:

[0090] (1) Under the protection of inert gas, 11.21 g (0.05 mol) of the above aromatic diamine and 126.1 ml of N,N'-dimethylacetamide (DMAC) were added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet, and a thermometer, and stirred at room temperature until completely dissolved. Then, the system temperature was lowered to 0° C., and 14.72 g (0.05 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After complete dissolution, stirring was continued for 16 hours to carry out a polycondensation reaction, thereby obtaining a polyamic acid homogeneous solution having a solid content of about 18 wt.%;

[0091] (2) filtering the polyamic acid homogeneous solution obtained in step (1), defoaming it, coating it on a flat and smooth dry glass plate by spin coating, placing it in an oven under a vacuum atmosphere for thermal cyclization, the thermal cyclization being specifically 100°C / 2 hours, 150°C / 2 hours, 250°C / 2 hours, and 350°C / 1 hour, and then performing gradient annealing, that is, slowly cooling from 350°C to 150°C at a cooling rate of 50°C / h, and then slowly cooling from 150°C to 100°C at a cooling rate of 0.5°C / min, then turning off the power, opening the cavity, and naturally cooling to room temperature to obtain a polyimide film.

[0092] The main properties of the polyimide film prepared in this application example are shown in Table 1. The infrared analysis data of the film (FT-IR, cm -1 )like Figure 5 shown.

[0093] Application Example 2

[0094] This application example provides a polyimide film, comprising the aromatic diamine described in Example 1. This application example also provides a method for preparing the polyimide film, comprising:

[0095] (1) Under inert gas protection, 11.83 g (0.052 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole, 4.5 g (0.013 mol) of the aromatic diamine described in Example 1, 92 ml of N,N'-dimethylacetamide (DMAC) and 92 ml of dimethyl sulfoxide (DMSO) were added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet and a thermometer, and stirred at room temperature until completely dissolved. Then, the system temperature was lowered to 5° C., and 19.4 g (0.066 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After complete dissolution, stirring was continued for 10 hours to carry out a polycondensation reaction to obtain a polyamic acid homogeneous solution having a solid content of about 16 wt.%;

[0096] (2) filtering the polyamic acid homogeneous solution obtained in step (1), defoaming it, coating it on a flat and smooth dry glass plate by spin coating, placing it in an oven under a vacuum atmosphere for thermal cyclization, the thermal cyclization being specifically 100°C / 2 hours, 150°C / 2 hours, 250°C / 2 hours, and 350°C / 1 hour, and then performing gradient annealing, that is, slowly cooling from 350°C to 150°C at a cooling rate of 50°C / h, and then slowly cooling from 150°C to 100°C at a cooling rate of 0.5°C / min, then turning off the power, opening the cavity, and naturally cooling to room temperature to obtain a polyimide film.

[0097] The main properties of the polyimide film prepared in this application example are shown in Table 1. The infrared analysis data of the film (FT-IR, cm -1 )like Figure 6 shown.

[0098] Application Example 3

[0099] This application example provides a polyimide film, comprising the aromatic diamine described in Example 1. This application example also provides a method for preparing the polyimide film, comprising:

[0100] (1) Under inert gas protection, 8.87 g (0.039 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole, 9.0 g (0.026 mol) of the aromatic diamine described in Example 1, 103.5 ml of N,N'-dimethylacetamide (DMAC) and 95.6 ml of dimethyl sulfoxide (DMSO) were added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet and a thermometer, and stirred at room temperature until completely dissolved. Then, the system temperature was lowered to 5° C., and 19.41 g (0.065 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After complete dissolution, stirring was continued for 10 hours to carry out a polycondensation reaction to obtain a polyamic acid homogeneous solution having a solid content of about 15 wt.%;

[0101] (2) filtering the polyamic acid homogeneous solution obtained in step (1), defoaming it, coating it on a flat and smooth dry glass plate by spin coating, placing it in an oven under a vacuum atmosphere for thermal cyclization, the thermal cyclization being specifically 100°C / 2 hours, 150°C / 2 hours, 250°C / 2 hours, and 350°C / 1 hour, and then performing gradient annealing, that is, slowly cooling from 350°C to 150°C at a cooling rate of 50°C / h, and then slowly cooling from 150°C to 100°C at a cooling rate of 0.5°C / min, then turning off the power, opening the cavity, and naturally cooling to room temperature to obtain a polyimide film.

[0102] The main properties of the polyimide film prepared in this application example are shown in Table 1. The infrared analysis data of the film (FT-IR, cm -1 )like Figure 7 shown.

[0103] Application Example 4

[0104] This application example provides a polyimide film, comprising the aromatic diamine described in Example 1. This application example also provides a method for preparing the polyimide film, comprising:

[0105] (1) Under inert gas protection, 5.38 g (0.024 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole, 12.3 g (0.036 mol) of the aromatic diamine described in Example 1, 103.5 ml of N,N'-dimethylacetamide (DMAC) and 95.6 ml of dimethyl sulfoxide (DMSO) were added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet and a thermometer, and stirred at room temperature until completely dissolved. Subsequently, the system temperature was lowered to 5° C., 17.68 g (0.06 mol) of pyromellitic dianhydride (PMDA) was added, and after complete dissolution, stirring was continued for 24 hours to carry out a polycondensation reaction to obtain a polyamic acid homogeneous solution having a solid content of about 15 wt.%;

[0106] (2) filtering the polyamic acid homogeneous solution obtained in step (1), defoaming it, coating it on a flat and smooth dry glass plate by spin coating, placing it in an oven under a vacuum atmosphere for thermal cyclization, the thermal cyclization being specifically 100°C / 2 hours, 180°C / 2 hours, 250°C / 2 hours, and 350°C / 1 hour, and then performing gradient annealing, that is, slowly cooling from 350°C to 150°C at a cooling rate of 50°C / h, and then slowly cooling from 150°C to 100°C at a cooling rate of 0.5°C / min, then turning off the power, opening the cavity, and naturally cooling to room temperature to obtain a polyimide film.

[0107] The main properties of the polyimide film prepared in this application example are shown in Table 1. The infrared analysis data of the film (FT-IR, cm -1 )like Figure 8 shown.

[0108] Application Example 5

[0109] This application example provides a polyimide film, comprising the aromatic diamine described in Example 1. This application example also provides a method for preparing the polyimide film, comprising:

[0110] (1) Under inert gas protection, 2.76 g (0.012 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole, 16.8 g (0.05 mol) of the aromatic diamine described in Example 1, 114 ml of N,N'-dimethylacetamide (DMAC) and 104 ml of dimethyl sulfoxide (DMSO) were added to a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet and a thermometer, and stirred at room temperature until completely dissolved. Subsequently, the system temperature was lowered to 10° C., and 18.11 g (0.061 mol) of pyromellitic dianhydride (PMDA) was added. After complete dissolution, stirring was continued for 24 hours to carry out a polycondensation reaction to obtain a polyamic acid homogeneous solution having a solid content of about 15 wt.%;

[0111] (2) filtering the polyamic acid homogeneous solution obtained in step (1), defoaming it, coating it on a flat and smooth dry glass plate by spin coating, placing it in an oven under a vacuum atmosphere for thermal cyclization, the thermal cyclization being specifically 100°C / 2 hours, 180°C / 2 hours, 250°C / 2 hours, and 350°C / 1 hour, and then performing gradient annealing, that is, slowly cooling from 350°C to 150°C at a cooling rate of 50°C / h, and then slowly cooling from 150°C to 100°C at a cooling rate of 0.5°C / min, then turning off the power, opening the cavity, and naturally cooling to room temperature to obtain a polyimide film.

[0112] The main properties of the polyimide film prepared in this application example are shown in Table 1. The infrared analysis data of the film (FT-IR, cm -1 )like Fig. 9 shown.

[0113] Performance Evaluation

[0114] The thermodynamic properties of the polyimide films obtained in Example 1 to Example 5 and Comparative Example 1 were evaluated. The dimensional stability of the films was measured using a static mechanical analyzer (TMA) in a nitrogen atmosphere, the heat resistance was measured using a dynamic analyzer (DMA) in a nitrogen atmosphere, and the thermal decomposition temperature was measured using a thermal gravimetric analyzer (TGA) in a nitrogen atmosphere. 5％ is the temperature at which the weight loss is 5%. The results are shown in Table 1.

[0115] Table 1 Thermodynamic properties of polyimide films obtained from application examples 1 to 5 and application comparative example 1

[0116]

[0117]

[0118] As can be seen from Table 1, the thermal expansion coefficient of the polyimide film of the present invention is below 2.48ppm / K in a wide temperature range of 50-350°C, and the glass transition temperature is basically between 440-500°C. It has the characteristics of high heat resistance and low expansion coefficient in a wide temperature range. The thermal decomposition temperature exceeds 580°C, and it has enhanced high-temperature stability, indicating that the polyimide film structure of the present invention has stronger interchain interaction, which may be due to the presence of more imidazole groups in the molecular chain, which makes the hydrogen bond interaction between polymer chains stronger.

[0119] Compared with the comparative example 1, the thermal expansion coefficient of the polyimide film of the present invention is significantly reduced in a wide temperature range, and the glass transition temperature and the thermal decomposition temperature are significantly increased, indicating that the polyimide introduced with pyridodiimidazole groups can achieve both low expansion coefficient and high heat resistance.

[0120] Furthermore, compared with the application of comparative example 1, the polyimide film prepared by combining 2-(4-aminophenyl)-5-aminobenzimidazole and aromatic diamine (application examples 2 to 5) can maintain relatively higher heat resistance and lower thermal expansion coefficient in a wide temperature range.

[0121] In Table 1, the possible reason for the negative thermal expansion coefficient is that the pyridodiimidazole unit accounts for a large proportion in the polyimide main chain. The mobility of the molecular chain segments of polyimide becomes stronger during the heating process. Within a certain temperature range, the ordered arrangement occurs as the temperature rises. The volume shrinkage caused by the ordered arrangement of the structural units with a small aspect ratio during this transformation process is not obvious, while the volume shrinkage of the structural units with a large aspect ratio is obvious. Compared with the benzimidazole group, the pyridodiimidazole group with a planar rigid ring structure has a larger aspect ratio.

[0122] Comparative Example 1

[0123] This comparative example examines the effect of annealing conditions on the polyimide film. The method is the same as that of Application Example 1, except that the power is directly turned off without gradient annealing, the cavity is opened, and the temperature is naturally cooled to room temperature.

[0124] The polyimide film obtained in this comparative example has quality problems, which are manifested in local warping and cracking.

[0125] Comparative Example 2

[0126] This comparative example examines the effects of the molar ratio of aromatic diamine to aromatic dianhydride and the solid content in the polyamic acid homogeneous solution on the polyimide film. The method is the same as that in Application Example 1, except that the solid content is 5wt.%, and the molar ratio is 1.5:1.

[0127] In this comparative example, the polyamic acid homogeneous solution could not be successfully coated on the substrate.

[0128] Comparative Example 3

[0129] This comparative example is the same as comparative example 2, except that the solid content is 25% and the molar ratio is 0.5:1.

[0130] In this comparative example, the polyamic acid homogeneous solution is too viscous and difficult to be evenly coated to obtain a polyimide film.

Claims

1. An aromatic diamine, characterized in that It has the structure shown in formula I: Wherein, Ar is a conjugated aromatic ring group.

2. The aromatic diamine according to claim 1, characterized in that The aromatic diamine is selected from one or more of Formula IA to Formula ID:

3. A method for preparing the aromatic diamine according to any one of claims 1 to 2, characterized in that: include: Under an inert atmosphere, tetraaminopyridine hydrochloride is mixed with an aromatic amino carboxyl compound and a polyphosphoric acid solvent, and reacted under a gradient temperature increase condition to obtain the aromatic diamine.

4. The method according to claim 3, characterized in that The gradient temperature increase includes reacting at 60° C. for 1-2 h, 80° C. for 1-2 h, 100° C. for 1-2 h, 120° C. for 1-2 h, 140° C. for 1-2 h, 160° C. for 1-2 h, and 190° C. for 1-2 h in sequence; And / or, the aromatic aminocarboxyl compound is one or more of p-aminobenzoic acid, 3-aminobenzoic acid, 6-amino-2-naphthoic acid and 2-amino-1-naphthoic acid.

5. A polyimide film, characterized in that: The polyimide film comprises the aromatic diamine according to any one of claims 1 to 2, wherein the glass transition temperature of the polyimide film is 440 to 500° C. and the thermal expansion coefficient is less than 2.48 ppm / ° C.

6. A method for preparing the polyimide film as claimed in claim 5, characterized in that: include: Under the protection of inert gas, the aromatic diamine and aromatic dianhydride are placed in an organic solvent to undergo polycondensation reaction to obtain a polyamic acid homogeneous solution; The polyamic acid homogeneous solution is spin-coated on a substrate for thermal cyclization, followed by stage annealing and natural cooling to obtain a polyimide film.

7. The method according to claim 6, characterized in that The molar ratio of the aromatic diamine to the aromatic dianhydride is (0.95-1.05):1; and / or the solid content of the polyamic acid homogeneous solution is 10wt.%-20wt.%; and / or the organic solvent is one or more of N-methylpyrrolidone, N,N'-dimethylacetamide, N,N'-dimethylformamide and dimethyl sulfoxide; and / or the temperature of the polycondensation reaction is 0-10°C.

8. The method according to claim 6, characterized in that The thermal cyclization includes thermal cyclization at 80-100°C for 1-2h, thermal cyclization at 150-180°C for 1-2h, thermal cyclization at 200-250°C for 1-2h, and thermal cyclization at 300-350°C for 1-2h. And / or, the stage annealing includes: cooling the thermal cyclization temperature of the last stage to 150°C at a cooling rate of 50°C / h, and then cooling to 100°C at a cooling rate of 0.5°C / min.

9. The method according to claim 6, characterized in that The raw materials for obtaining the polyamic acid homogeneous solution also include a benzimidazole compound, and the molar ratio of the benzimidazole compound to the aromatic diamine is (0.2-4):

1.

10. Use of the polyimide film as claimed in claim 5 in the field of flexible display.

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