Novel heterocyclic diamine monomers, colorless polyimides and methods of preparation

Abstract

The application relates to the technical field of polyimide synthesis, and discloses a novel aromatic heterocyclic diamine monomer, colorless polyimide and a preparation method. The preparation method comprises the following steps: under a nitrogen atmosphere, pyridine or pyrazine monomers containing amino groups and 4-nitro-2-(trifluoromethyl) benzoyl chloride are dissolved in an organic solvent, and an acylation condensation reaction is carried out under the action of a first catalyst; the reaction product is added into water, an inorganic salt is further added to precipitate, and the precipitate is washed and dried to obtain a crude product; the crude product is purified to obtain a dinitro monomer; under a nitrogen atmosphere, the dinitro monomer and a second catalyst are dissolved in an alcohol solvent, heated to a predetermined temperature, and a reducing agent is slowly added to carry out a reduction reaction; the reaction product is added into water, an inorganic salt is further added to precipitate, and the precipitate is washed and dried to obtain a novel aromatic heterocyclic diamine monomer. The colorless polyimide prepared from the novel aromatic heterocyclic diamine monomer has excellent thermal performance and optical performance.

Description

Technical Field

[0001] This application relates to the field of polyimide synthesis technology, and in particular to a novel aromatic heterocyclic diamine monomer, a colorless polyimide, and a method for its preparation. Background Technology

[0002] Colorless polyimide (CPI) films are key substrates for next-generation flexible optoelectronic displays and high-frequency communication devices. In high-end applications such as flexible OLEDs, foldable screens, and advanced packaging, CPI materials must simultaneously meet stringent standards of high visible light transmittance, extremely low coefficient of thermal expansion (CTE), and high glass transition temperature. Overcoming the performance bottlenecks that constrain these three aspects is crucial for achieving long-term device stability. Research on the precise structure-property relationship between the microscopic molecular structure and macroscopic comprehensive properties of CPI materials has significant academic value and industrial implications.

[0003] Currently, the molecular design of CPIs mainly relies on introducing alicyclic structures to block conjugation, utilizing strongly electronegative fluorine groups, and using large-volume side groups to disrupt chain stacking to modulate photoelectric properties. However, while existing strategies improve optical transparency, they often fail to achieve a synergistic balance between thermal dimensional stability and a high glass transition temperature, leading to significant trade-offs in various material properties. For example, while introducing large-volume side groups or flexible segments effectively suppresses the formation of charge-transfer complexes (CTCs) by increasing free volume and significantly improves transmittance, this loose stacking structure weakens the intermolecular forces, causing a sharp increase in the coefficient of thermal expansion and a decrease in heat resistance, failing to meet the high-temperature dimensional matching requirements of precision manufacturing.

[0004] Based on this, developing new strategies that can eliminate color at the source through electronic effects and steric hindrance, and introduce specific intermolecular interactions to lock the molecular chains to maintain excellent dimensional stability, in order to achieve comprehensive synergy of CPI films in optical and thermal dimensions, is a problem that urgently needs to be solved in the field of high-performance polymer materials. Summary of the Invention

[0005] This application provides a novel aromatic heterocyclic diamine monomer, a colorless polyimide, and a preparation method thereof, aiming to solve the technical problem that existing colorless polyimides cannot simultaneously achieve high visible light transmittance, high thermal dimensional stability, and high heat resistance, thus failing to achieve comprehensive synergy in both optical and thermal dimensions.

[0006] To achieve the above objectives, the present application adopts the following technical solution.

[0007] In a first aspect, this application provides a novel aromatic heterocyclic diamine monomer, the chemical structure of which is shown in formula (1):

[0008] (1)

[0009] Where R is pyridine or pyrazine.

[0010] A second aspect of this application provides a method for preparing the aforementioned novel aromatic heterocyclic diamine monomer, comprising the following steps:

[0011] S1, under a nitrogen atmosphere, pyridine or pyrazine monomers containing amino groups and 4-nitro-2-(trifluoromethyl)benzoyl chloride are dissolved in an organic solvent and undergo an acylation condensation reaction under the action of a first catalyst; the reaction product is added to water, and then an inorganic salt is added to precipitate the product, which is then washed and dried to obtain a crude product; the crude product is purified to obtain a dinitro monomer;

[0012] S2, under a nitrogen atmosphere, the dinitro monomer and the second catalyst are dissolved in an alcohol solvent, heated to a predetermined temperature, and a reducing agent is slowly added to carry out a reduction reaction; the reaction product is added to water, and then an inorganic salt is added to precipitate the product. After washing and drying, a novel aromatic heterocyclic diamine monomer is obtained.

[0013] Preferably, the pyridine monomer is 2,5-diaminopyridine;

[0014] The pyrazine monomer is 2,5-diaminopyrazine;

[0015] The first catalyst is pyridine and 4-dimethylaminopyridine;

[0016] The organic solvent is N,N-dimethylacetamide;

[0017] The inorganic salt is sodium chloride;

[0018] And / or,

[0019] The second catalyst is a carbon-supported metal catalyst;

[0020] The alcohol solvent includes any one of methanol, ethanol, propanol, or butanol;

[0021] The reducing agent is hydrazine hydrate.

[0022] Preferably, in S1, the molar ratio of the amino-containing pyridine or pyrazine monomer and 4-nitro-2-(trifluoromethyl)benzoyl chloride is 1:2~3;

[0023] The molar ratio of the amino-containing pyridine or pyrazine monomer to the pyridine or 4-dimethylaminopyridine in the first catalyst is 1:3~4:0.05~0.15;

[0024] The purification was performed using silica gel column chromatography, with the eluent being a mixture of ethyl acetate and petroleum ether in a volume ratio of 1:1 to 20.

[0025] The feeding temperature for the acylation condensation reaction is 0~10 ℃, and the reaction temperature is 15~35 ℃;

[0026] Preferably, in S2, the ratio of dinitro monomer, second catalyst, and alcohol solvent is 1 g: 0.1~1 g: 10~50 mL;

[0027] The ratio of dinitro monomer to reducing agent is 1 g: 1~5 mL;

[0028] The reduction reaction is carried out at a temperature of 60~90℃;

[0029] The reducing agent is added at a rate of less than 1 drop per second.

[0030] A third aspect of this application provides a colorless polyimide, which is formed by the condensation polymerization of the above-mentioned diamine monomer and a tetracarboxylic acid dianhydride monomer, and its chemical structure is shown in formula (2):

[0031] (2)

[0032] Where R is pyridine or pyrazine.

[0033] n is an integer between 20 and 200.

[0034] A fourth aspect of this application provides a method for preparing the aforementioned colorless polyimide, comprising the following steps:

[0035] Step 1: Under nitrogen protection, dissolve the diamine monomer in an organic solvent, add the tetracarboxylic acid dianhydride monomer, stir until homogeneous, and then add the third catalyst to carry out the reaction.

[0036] Step 2: Add methanol to the reaction system to precipitate the product. Wash, dry and purify the precipitate to obtain colorless polyimide.

[0037] Preferably, the chemical structure of the tetracarboxylic acid dianhydride monomer is shown in formula (3):

[0038] (3)

[0039] The third catalyst includes pyridine and acetic anhydride.

[0040] Preferably, the feeding temperature of the reaction is 0~10 ℃, and the reaction temperature is 15~35 ℃;

[0041] The molar ratio of the tetracarboxylic acid dianhydride monomer to the diamine monomer is 1:0.5~2;

[0042] The molar ratio of diamine monomer, pyridine, and acetic anhydride is 1: 1.5~3.5: 2.0~4.5;

[0043] The purification process employed Soxhlet extraction.

[0044] A fifth aspect of this application provides a polyimide film prepared from the above-mentioned colorless polyimide, which is prepared by the following method:

[0045] The colorless polyimide was dissolved in an amide solvent to prepare a solution, and the solution was coated and dried to obtain a polyimide film.

[0046] The amide solvent is N,N-dimethylformamide or N,N-dimethylacetamide; the solid content of the colorless polyimide in the amide solvent is 5-30%.

[0047] Compared with the prior art, the beneficial effects of this application are as follows:

[0048] This application designs a diamine structure with pyridine or pyrazine as the core and connected by amide bonds containing trifluoromethylbenzene rings, and introduces it into the polyimide backbone. By utilizing the strong electron-withdrawing property and large steric hindrance of trifluoromethyl groups, the charge transfer effect of the polyimide chain is adjusted, effectively suppressing the formation of charge transfer complexes and giving the material high transparency. At the same time, pyridine / pyrazine groups are introduced into the polyimide backbone to increase coordination sites, and then hydrogen bonds are formed with heterocyclic nitrogen-containing groups through amide bonds to further restrict the movement of molecular chains and reduce the coefficient of thermal expansion.

[0049] The colorless polyimide prepared from the diamine monomer of this application has excellent thermal and optical properties, with an optical transmittance of 88.9% and the ability to withstand high temperatures of 325.7 °C, and has potential application value in the field of flexible displays. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 The 1H NMR spectrum of the dinitro monomer PAPdDN prepared in Example 1;

[0052] Figure 2 The carbon NMR spectrum of the dinitro monomer PAPdDN prepared in Example 1;

[0053] Figure 3 The 1H NMR spectrum of the diamine monomer PAPdDA prepared in Example 1;

[0054] Figure 4 The carbon NMR spectrum of the diamine monomer PAPdDA prepared in Example 1;

[0055] Figure 5 The 1H NMR spectrum of the dinitro monomer PAPzDN prepared in Example 2;

[0056] Figure 6 The carbon NMR spectrum of the dinitro monomer PAPzDN prepared in Example 2;

[0057] Figure 7 The 1H NMR spectrum of the diamine monomer PAPzDA prepared in Example 2;

[0058] Figure 8 The carbon NMR spectrum of the diamine monomer PAPzDA prepared in Example 2;

[0059] Figure 9 Infrared spectra of colorless polyimide 6FDA-PAPdDA prepared in Example 1 and colorless polyimide 6FDA-PAPzDA prepared in Example 2. Detailed Implementation

[0060] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0061] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0062] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0063] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0064] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0065] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. 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 this application.

[0066] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0067] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0068] This application provides a novel aromatic heterocyclic diamine monomer with a diamine structure consisting of a pyridine or pyrazine core and a trifluoromethylbenzene ring linked by an amide bond. Introducing this novel aromatic heterocyclic diamine monomer into a polyimide backbone allows for the elimination of color at its source through electronic effects and steric hindrance, while also introducing specific intermolecular interactions to lock the molecular chains and maintain excellent dimensional stability—a novel strategy that achieves comprehensive synergy in both optical and thermal dimensions for CPI films.

[0069] The novel aromatic heterocyclic diamine monomer of this application has the chemical structure shown in formula (1):

[0070] (1)

[0071] Where R is pyridine or pyrazine.

[0072] In this application, when R is pyridine, the novel aromatic heterocyclic diamine monomer is designated as PAPdDA, and its structure is as follows:

[0073]

[0074] When R is pyrazine, the novel aromatic heterocyclic diamine monomer is designated PAPzDA, and its structure is as follows:

[0075]

[0076] The method for preparing the novel aromatic heterocyclic diamine monomer includes the following steps:

[0077] S1, under a nitrogen atmosphere, pyridine or pyrazine monomers containing amino groups and 4-nitro-2-(trifluoromethyl)benzoyl chloride are dissolved in an organic solvent and undergo an acylation condensation reaction under the action of a first catalyst; the reaction product is added to water, and then an inorganic salt is added to precipitate the product, which is then washed and dried to obtain a crude product; the crude product is purified to obtain a dinitro monomer;

[0078] In this application, the pyridine monomer is 2,5-diaminopyridine, and its chemical structural formula is as follows:

[0079]

[0080] The pyrazine monomer is 2,5-diaminopyrazine, and its chemical structural formula is as follows:

[0081]

[0082] The chemical structural formula of the 4-nitro-2-(trifluoromethyl)benzoyl chloride is:

[0083]

[0084] The molar ratio of pyridine or pyrazine monomer to 4-nitro-2-(trifluoromethyl)benzoyl chloride is 1:2~3, preferably 1:2~2.5.

[0085] The organic solvent is N,N-dimethylacetamide (DMAc).

[0086] The first catalyst is pyridine and 4-dimethylaminopyridine. The molar ratio of the above-mentioned amino-containing pyridine or pyrazine monomer to pyridine and 4-dimethylaminopyridine in the first catalyst is 1:3~4:0.05~0.15.

[0087] The inorganic salt is sodium chloride.

[0088] The purification is performed using silica gel column chromatography, with the eluent being a mixture of ethyl acetate and petroleum ether in a volume ratio of 1:1 to 20, more preferably in a volume ratio of ethyl acetate to petroleum ether of 1:4 to 12.

[0089] Specifically, under nitrogen conditions, pyridine or pyrazine monomers and 4-nitro-2-(trifluoromethyl)benzoyl chloride are added to an organic solvent at 0-10 °C, and then the mixture is stirred at 15-35 °C for 15-35 min.

[0090] In this application, when a pyridine monomer is used, the dinitro monomer is N,N'-[pyridine-2,5-diyl]bis[4-nitro-2-(trifluoromethyl)benzamide], denoted as PAPdDN, and its structural formula is:

[0091]

[0092] When a pyrazine monomer is used, the dinitro monomer is N,N'-[pyrazine-2,5-diyl]bis[4-nitro-2-(trifluoromethyl)benzamide], denoted as PAPzDN, with the following structural formula:

[0093]

[0094] S2, under a nitrogen atmosphere, the dinitro monomer and the second catalyst are dissolved in an alcohol solvent, heated to a predetermined temperature, and a reducing agent is slowly added to carry out a reduction reaction; the reaction product is added to water, and then an inorganic salt is added to precipitate the product. After washing and drying, a novel aromatic heterocyclic diamine monomer is obtained.

[0095] In this application, the second catalyst is a carbon-supported metal catalyst, such as a carbon-supported metal catalyst, preferably palladium on carbon (Pd / C).

[0096] The alcohol solvent is a lower alkanol, and can be any one of methanol, ethanol, propanol or butanol.

[0097] In this application, the ratio of dinitro monomer, second catalyst and alcohol solvent is 1 g: 0.1~1 g: 10~50 mL, preferably 1 g: 0.2~0.5 g: 20~35 mL, and more preferably 6 g: 1.36 g: 150 mL.

[0098] In this application, the reducing agent is hydrazine hydrate; the ratio of the dinitro monomer to the reducing agent is 1 g: 1~5 mL, preferably 1 g: 1.5~2.5 mL, and more preferably 6 g: 12.64 mL.

[0099] In this application, the temperature of the reduction reaction is 60~90 ℃; the rate of addition of the reducing agent is less than 1 drop per second.

[0100] This application also provides a colorless polyimide, which is formed by the condensation polymerization of the above-mentioned diamine monomer and a tetracarboxylic acid dianhydride monomer, and its chemical structure is shown in formula (2):

[0101] (2)

[0102] Where R is pyridine or pyrazine.

[0103] n is an integer between 20 and 200.

[0104] This application designs a diamine structure with pyridine or pyrazine as the core and connected by amide bonds to a trifluoromethylbenzene ring, and introduces it into the polyimide backbone. Utilizing the strong electron-withdrawing property and large steric hindrance of the trifluoromethyl group, the charge transfer effect of the polyimide chain is adjusted, effectively suppressing the formation of charge-transfer complexes and imparting high transparency to the material. Simultaneously, pyridine / pyrazine groups are introduced into the polyimide backbone to increase coordination sites, and then hydrogen bonds are formed with heterocyclic nitrogen-containing groups via amide bonds, further restricting molecular chain movement and reducing the coefficient of thermal expansion. Based on the above synergistic effects, the colorless polyimide of this application possesses both excellent thermal properties and good optical properties.

[0105] The method for preparing the colorless polyimide includes the following steps:

[0106] Step 1: Under nitrogen protection, dissolve the diamine monomer in an organic solvent, add the tetracarboxylic acid dianhydride monomer, stir until homogeneous, and then add the third catalyst to carry out the reaction.

[0107] The tetracarboxylic acid dianhydride monomer is 6FDA, and its chemical structure is shown in formula (3):

[0108] (3)

[0109] The third catalyst includes pyridine and acetic anhydride.

[0110] Specifically, under nitrogen protection, the diamine monomers PAPdDA / PAPzDA are first dissolved in a dried and degassed DMAc solvent. After the solid is completely dissolved, 6FDA is added, and the system temperature is controlled at 0–15 °C for 0.5–3 h with continuous stirring, preferably at 2–10 °C for 2 h. Then, pyridine and acetic anhydride are added as catalysts, and a polycondensation reaction is carried out at 15–30 °C. During this process, small molecule byproducts (such as water molecules) generated in the reaction are removed in a timely manner by continuously purging nitrogen until complete imidization is achieved.

[0111] The molar ratio of the tetracarboxylic acid dianhydride monomer to the diamine monomer is 1:0.5~2, preferably 1:0.75~1.25, and more preferably 1:1.

[0112] The molar ratio of diamine monomer, pyridine and acetic anhydride is 1:1.5~3.5: 2.0~4.5, preferably 1:2~3: 2.5~3.5, and more preferably 2:4:6.

[0113] Step 2: Add methanol to the reaction system to precipitate the product. Wash, dry and purify the precipitate to obtain colorless polyimide.

[0114] Specifically, the system was cooled to room temperature and poured into methanol to precipitate the product. After collecting the solid product by filtration, it was washed three times with hot methanol and dried under vacuum at 60 °C for 24 h. Then, it was refluxed with methanol as solvent using a Soxhlet extraction apparatus for 72 h. After purification, it was dried under vacuum at 60 °C for 48 h. Finally, colorless polyimide was obtained by vacuum drying.

[0115] In this application, the colorless polyimide prepared using the diamine monomer PAPdDA is designated as 6FDA-PAPdDA; the colorless polyimide prepared using the diamine monomer PAPzDA is designated as 6FDA-PAPzDA.

[0116] The colorless polyimide of this application possesses both excellent thermal and optical properties, and can be used to prepare polyimide films. It is prepared by the following method:

[0117] The colorless polyimide was dissolved in an amide solvent to prepare a solution, and the solution was coated and dried to obtain a polyimide film.

[0118] The amide solvent is N,N-dimethylformamide or N,N-dimethylacetamide; the solid content of the colorless polyimide in the amide solvent is 5-30 wt%, preferably 10-20 wt%, and more preferably 20 wt%.

[0119] Specifically, the prepared polyimide solution is centrifuged to degas, then coated, and finally formed into a film at high temperature in a vacuum oven.

[0120] The centrifugation speed is 1000-10000 r / min. -1 Preferably 8000 r min -1 The centrifugation time is 1~30 min, preferably 2~10 min, more preferably 5 min, then the coating is applied by scraping, and finally the film is formed at high temperature in a vacuum oven.

[0121] The high-temperature film formation temperature is 50~250 ℃, and a gradient heating process is adopted. The preferred gradient heating process is to heat at 80 ℃ for 1 h, raise the temperature to 150 ℃ for 2 h, and then raise the temperature to 200 ℃ for 2 h.

[0122] The present application will be further described below through specific embodiments.

[0123] Example 1

[0124] In this embodiment, the diamine monomer PAPdDA and colorless polyimide 6FDA-PAPdDA were synthesized using the following method:

[0125] 1. Preparation of the diamine monomer PAPdDA:

[0126] S1, under a nitrogen atmosphere, 4-nitro-2-(trifluoromethyl)benzoyl chloride (42 mmol) and 12 mL of N,N-dimethylacetamide (DMAc) were placed in a two-necked flask and stirred. Then, 2,5-diaminopyridine (18 mmol), pyridine (5.4 mL), and DMAc (12 mL) were ultrasonically mixed and added to the two-necked flask under an ice-water bath. Next, 6 mL of N,N-dimethylacetamide (DMAc) and 4-dimethylaminopyridine (1.8 mmol) were added, and the mixture was stirred and transferred to room temperature for 12 h. After the reaction was complete, the reaction product was poured into 300.0 mL of deionized water, and 3 g of sodium chloride was added and stirred to precipitate the product. The precipitate was filtered, dried, washed three times with deionized water, and then purified by column chromatography (PE-PE / EA = 2 / 1) to obtain 7.1 g of solid, namely the dinitro monomer PAPdDN, with a yield of 88.75%; its 1H NMR spectrum is shown below. Figure 1 As shown, the carbon NMR spectrum is as follows: Figure 2 As shown.

[0127] from Figure 1 It can be seen that the singlets at δ=11.42 ppm and δ=11.04 ppm clearly correspond to two amide bond protons, and the proton integral ratio in the aromatic region is completely consistent with the theoretical structure; Figure 2 Characteristic carbonyl carbon signals were observed at δ=164.9 ppm and δ=164.5 ppm, and typical carbon-fluorine coupling splitting peaks of trifluoromethyl were observed at 120–130 ppm. These spectral data collectively confirm that the target dinitro monomer has been successfully synthesized with high purity.

[0128] S2, 1.1 g of PAPdDN, 0.276 g of Pd / C (10 wt%), and 40.0 mL of ethanol were added to a two-necked flask and heated to 80 °C under nitrogen atmosphere. Then, 2.6 mL of hydrazine hydrate was slowly added dropwise to the mixture at a rate of one drop every two seconds. The reaction was then maintained at 80 °C and continuously stirred under nitrogen atmosphere for 12 h. After the reaction was complete, the mixture was immediately filtered while hot to remove the catalyst. The filtrate was then poured into 200.0 mL of ice-salt water and stirred continuously. The precipitate was filtered and dried under vacuum at room temperature for 24 h to obtain the crude product. The crude product was washed with a mixture of ethanol and water (1:1) and dried under vacuum to obtain 0.9426 g of white solid, namely the diamine monomer PAPdDA, with a yield of 96.34%. Its 1H NMR spectrum is shown below. Figure 3 As shown, the carbon NMR spectrum is as follows:Figure 4 As shown.

[0129] from Figure 3 It can be seen that the nitro signal of the reduced dinitro monomer completely disappeared, and a characteristic peak corresponding to the amino group and the ortho-aryl hydrogen that was shielded by it appeared at δ=5.92 ppm; at the same time, the amide bond proton signal appeared at δ=10.61 ppm and δ=10.35 ppm, respectively. Figure 4 It can be seen that the number of characteristic peaks corresponding to carbon atoms completely corresponds to the molecular configuration. Among them, δ=167.1 ppm and δ=166.8 ppm are the carbonyl carbon signals, respectively, and the trifluoromethyl carbon at δ=120~126 ppm exhibits a typical carbon-fluorine coupling splitting peak. The above results indicate that the dinitro monomer has been successfully and completely reduced to the target diamine monomer with high purity.

[0130] 2. Preparation of colorless polyimide 6FDA-PAPdDA:

[0131] Under a nitrogen atmosphere, 1.5 mmol of PAPdDA was placed in a two-necked flask, and 6.9 mL of N,N-dimethylacetamide (DMAc) was added. After stirring until dissolved, 1.5 mmol of 6FDA was added in an ice-water bath, and the mixture was stirred for 2 h. Then, the mixture was transferred to room temperature and stirred for 22 h. Next, a mixed solution of 0.426 mL of acetic anhydride and 0.2418 mL of pyridine was added dropwise every two seconds, and the reaction was carried out at room temperature for 24 h. After the reaction was complete, the mixture was poured into 100 mL of methanol to precipitate a solid. The solid was filtered off and washed with hot methanol. After vacuum drying, 0.57 g of colorless polyimide 6FDA-PAPdDA was obtained.

[0132] Dissolve 0.5 g of 6FDA-PAPdDA in 2 g of DMAc, then centrifuge to degas (8000 r min). -1 (5 min) Then coat the film and heat it in a vacuum oven at 80 ℃ for 1 h, then heat it at 150 ℃ for 2 h, and then heat it at 200 ℃ for 2 h to obtain a colorless polyimide film.

[0133] Example 2

[0134] In this embodiment, the diamine monomer PAPzDA and colorless polyimide 6FDA-PAPzDA were synthesized, and the preparation method is as follows:

[0135] 1. Preparation of the diamine monomer PAPzDA:

[0136] S1, under a nitrogen atmosphere, 4-nitro-2-(trifluoromethyl)benzoyl chloride (42 mmol) and 12 mL of N,N-dimethylacetamide (DMAc) were placed in a two-necked flask and stirred. Then, 2,5-diaminopyrazine (18 mmol), pyridine (5.4 mL), and DMAc (12 mL) were ultrasonically mixed and added to the two-necked flask under an ice-water bath. Next, 6 mL of N,N-dimethylacetamide (DMAc) and 4-dimethylaminopyridine (1.8 mmol) were added, and the mixture was stirred and transferred to room temperature for 12 h. After the reaction was complete, the reaction product was poured into 300.0 mL of deionized water, and 3 g of sodium chloride was added and stirred to precipitate the product. The precipitate was filtered, dried, washed three times with deionized water, and then purified by column chromatography (PE-PE / EA = 2 / 1) to obtain 7.2 g of solid, namely the dinitro monomer PAPzDN, with a yield of 81%. Its 1H NMR spectrum is shown below. Figure 5 As shown, the carbon NMR spectrum is as follows: Figure 6 As shown.

[0137] from Figure 5 It can be seen that, due to the high central symmetry of the molecule, its 1H NMR spectrum has only a singlet corresponding to two equivalent amide bond protons at δ=11.79 ppm, and a characteristic singlet of the pyrazine ring proton is observed at δ=9.18 ppm. The integrated area of ​​each aromatic hydrogen perfectly matches the molecular configuration. Figure 6 The carbon NMR spectrum shown exhibits a single strong carbonyl carbon signal at δ=165.1 ppm, and clearly displays the characteristic carbon-fluorine coupling splitting peak of trifluoromethyl carbon in the δ=120~128 ppm region. These spectral data jointly confirm the successful preparation of the target dinitro intermediate with high molecular symmetry and excellent purity.

[0138] S2, 1.6 g of PAPzDN, 0.29 g of Pd / C (10 wt%), and 40.0 mL of ethanol were added to a two-necked flask and heated to 80 °C under nitrogen atmosphere. Then, 2.6 mL of hydrazine hydrate was slowly added dropwise to the mixture at a rate of one drop every two seconds. The reaction was then maintained at 80 °C and continuously stirred under nitrogen atmosphere for 12 h. After the reaction was complete, the mixture was immediately filtered while hot to remove the catalyst. The filtrate was then poured into 200.0 mL of ice-salt water and stirred continuously. The precipitate was filtered and dried under vacuum at room temperature for 24 h to obtain the crude product. The crude product was washed with a mixture of ethanol and water (1:1) and dried under vacuum to obtain 1.27 g of white solid, namely the diamine monomer PAPzDA, with a yield of 90.17%. Its 1H NMR spectrum is shown below. Figure 7 As shown, the carbon NMR spectrum is as follows: Figure 8 As shown.

[0139] from Figure 7It can be seen that the nitro group of the reduced dinitro intermediate completely disappears, and a characteristic broad single peak corresponding to the amino group is clearly observed at δ = 6.00 ppm. Due to the strong electron-donating effect of the amino group, the protons C, D, and E of the benzene ring are significantly shifted to higher fields to δ = 7.39, 6.94, and 6.75 ppm, and the single peak at δ = 10.99 ppm confirms the preservation of the amide skeleton. Figure 8 The C NMR spectrum shows a single amide carbonyl carbon signal at δ=167.3 ppm, an aromatic carbon signal at δ=151.4 ppm, and a clear carbon-carbon coupling splitting peak of trifluoromethyl carbon in the δ=120~126 ppm range. These data collectively confirm that the target diamine monomer has been successfully prepared with excellent purity.

[0140] 2. Preparation of colorless polyimide 6FDA-PAPzDA,

[0141] Under a nitrogen atmosphere, 1.5 mmol of PAPzDA was placed in a two-necked flask, and 6.9 mL of N,N-dimethylacetamide (DMAc) was added. After stirring until dissolved, 1.5 mmol of 6FDA was added in an ice-water bath, and the mixture was stirred for 2 h. Then, the mixture was transferred to room temperature and stirred for 22 h. Next, a mixed solution of 0.426 mL of acetic anhydride and 0.2418 mL of pyridine was added dropwise every two seconds, and the reaction was carried out at room temperature for 24 h. After the reaction was complete, the mixture was poured into 100 mL of methanol to precipitate a solid. The solid was filtered off and washed with hot methanol. After vacuum drying, 0.61 g of colorless polyimide 6FDA-PAPzDA was obtained.

[0142] Dissolve 0.5 g of 6FDA-PAPzDA in 2 g of DMAc, then centrifuge to degas (8000 r min). -1 After 5 min, the film is coated again and heated in a vacuum oven at 80 °C for 1 h, then heated to 150 °C for 2 h, and then heated to 200 °C for 2 h to obtain a colorless polyimide film.

[0143] The infrared spectra of colorless polyimide 6FDA-PAPdDA prepared in Example 1 and colorless polyimide 6FDA-PAPzDA prepared in Example 2 are shown below. Figure 9 As shown. Between 3100 and 3400 cm. -1 In the region, neither group of films showed a broad absorption band belonging to the hydroxyl groups or unreacted amino groups in the polyamic acid intermediate, indicating that the imidization reaction proceeded very thoroughly. At 1780 cm⁻¹ -1 and 1720 cm -1 Near the cyclocarbonyl group of the imide ring, both asymmetric and symmetric stretching vibration peaks can be observed; simultaneously, at 1690–1685 cm⁻¹... -1The characteristic peaks of the carbonyl stretching vibration of the amide bond are clearly visible. Additionally, they are located at 1620–1615 cm⁻¹. -1 and 1430~1425 cm -1 The absorption peaks at these locations are attributed to skeletal vibrations of the aromatic heterocycles (pyridine / pyrazine) in the main chain. Infrared spectroscopy results confirm that the target thin film has been successfully prepared and possesses the expected molecular structure.

[0144] The polyimide films prepared in Examples 1 and 2 were subjected to performance tests. The glass transition temperature (T0) of the polyimide films was measured. g The temperature was measured by DMA, and the characterization instrument was a DMA Q800, with a heating rate of 5 °C / min. -1 Air atmosphere; coefficient of linear expansion (CTE) was measured by TMA, characterization instrument was TMA Q400, heating rate 5 ℃ min. -1 The optical transparency of the polyimide film was measured under a nitrogen atmosphere. The characterization instrument was a UV9000s spectrophotometer, with a range of 200–800 nm. The test results are shown in Table 1.

[0145] Table 1 Performance test data of colorless polyimide films in the examples

[0146]

[0147] As shown in Table 1, both colorless polyimide films prepared in this invention exhibit excellent properties. Among them, the 6FDA-PAPdDA film has a high glass transition temperature of 325.7 °C and a low linear thermal expansion coefficient of 33.3 ppm K. -1 Furthermore, the transmittance at 500 nm reaches 88.9%. Test results show that, through reasonable molecular structure design, the film of the present invention maintains excellent optical transparency while possessing excellent thermal stability and dimensional stability.

[0148] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A novel aromatic heterocyclic diamine monomer, characterized in that, Its chemical structure is shown in formula (1): (1) Where R is pyridine or pyrazine.

2. The method for preparing the novel aromatic heterocyclic diamine monomer according to claim 1, characterized in that, Includes the following steps: S1, under a nitrogen atmosphere, pyridine or pyrazine monomers containing amino groups and 4-nitro-2-(trifluoromethyl)benzoyl chloride are dissolved in an organic solvent and undergo an acylation condensation reaction under the action of a first catalyst; the reaction product is added to water, and then an inorganic salt is added to precipitate the product, which is then washed and dried to obtain a crude product; the crude product is purified to obtain a dinitro monomer; S2, under a nitrogen atmosphere, the dinitro monomer and the second catalyst are dissolved in an alcohol solvent, heated to a predetermined temperature, and a reducing agent is slowly added to carry out a reduction reaction; the reaction product is added to water, and then an inorganic salt is added to precipitate the product. After washing and drying, a novel aromatic heterocyclic diamine monomer is obtained.

3. The preparation method according to claim 2, characterized in that, The pyridine monomer is 2,5-diaminopyridine; The pyrazine monomer is 2,5-diaminopyrazine; The first catalyst is pyridine and 4-dimethylaminopyridine; The organic solvent is N,N-dimethylacetamide; The inorganic salt is sodium chloride; And / or, The second catalyst is a carbon-supported metal catalyst; The alcohol solvent includes any one of methanol, ethanol, propanol, or butanol; The reducing agent is hydrazine hydrate.

4. The preparation method according to claim 2, characterized in that, In S1, the molar ratio of the amino-containing pyridine or pyrazine monomer to 4-nitro-2-(trifluoromethyl)benzoyl chloride is 1:2~3; The molar ratio of the amino-containing pyridine or pyrazine monomer to the pyridine or 4-dimethylaminopyridine in the first catalyst is 1:3~4:0.05~0.15; The purification was performed using silica gel column chromatography, with the eluent being a mixture of ethyl acetate and petroleum ether in a volume ratio of 1:1 to 20. The feeding temperature for the acylation condensation reaction is 0~10 ℃, and the reaction temperature is 15~35 ℃.

5. The preparation method according to claim 2, characterized in that, In S2, the ratio of dinitro monomer, second catalyst, and alcohol solvent is 1 g: 0.1~1 g: 10~50 mL; The ratio of dinitro monomer to reducing agent is 1 g: 1~5 mL; The reduction reaction is carried out at a temperature of 60~90℃; The reducing agent is added at a rate of less than 1 drop per second.

6. A colorless polyimide, characterized in that, It is formed by the condensation polymerization of the diamine monomer described in claim 1 and a tetracarboxylic acid dianhydride monomer, and its chemical structure is shown in formula (2): (2) Where R is pyridine or pyrazine. n is an integer between 20 and 200.

7. The method for preparing the colorless polyimide according to claim 6, characterized in that, Includes the following steps: Step 1: Under nitrogen protection, dissolve the diamine monomer in an organic solvent, add the tetracarboxylic acid dianhydride monomer, stir until homogeneous, and then add the third catalyst to carry out the reaction. Step 2: Add methanol to the reaction system to precipitate the product. Wash, dry and purify the precipitate to obtain colorless polyimide.

8. The preparation method according to claim 7, characterized in that, The chemical structure of the tetracarboxylic acid dianhydride monomer is shown in formula (3): (3) The third catalyst includes pyridine and acetic anhydride.

9. The preparation method according to claim 7, characterized in that, The feeding temperature for the reaction is 0~10 ℃, and the reaction temperature is 15~35 ℃; The molar ratio of the tetracarboxylic acid dianhydride monomer to the diamine monomer is 1:0.5~2; The molar ratio of diamine monomer, pyridine, and acetic anhydride is 1: 1.5~3.5: 2.0~4.5; The purification process employed Soxhlet extraction.

10. The polyimide film prepared from the colorless polyimide according to claim 6, characterized in that, It is prepared by the following method: The colorless polyimide was dissolved in an amide solvent to prepare a solution, and the solution was coated and dried to obtain a polyimide film. The amide solvent is N,N-dimethylformamide or N,N-dimethylacetamide; the solid content of the colorless polyimide in the amide solvent is 5-30%.

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