Diamine monomer based on benzoheteroaromatic structure, polyimide and preparation method

Abstract

The invention provides a diamine monomer based on a benzoaromatic heterocyclic structure, polyimide and a preparation method, and belongs to the technical field of polymer-based functional materials. The diamine monomer based on the benzoaromatic heterocyclic structure has a structure # imgabs0 # as shown in a formula I, R is-S-,-O-,-NH,-NPh or-N-iPr, and R1 is-H,-CF3 or-CH3. And polymerizing the diamine monomer and the dianhydride monomer to obtain polyimide. The heteroatoms are introduced into the prepared polyimide structure, so that stronger chemical bonds and intermolecular forces can be formed, the thermal stability, mechanical properties and solubility of the PI film are improved, meanwhile, the structure also has more chemical modification sites, and the properties of the PI film can be further improved by introducing different groups at different positions.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer-based functional materials, and particularly relates to a diamine monomer, a polyimide, and a preparation method based on a benzodiazole heterocyclic structure. Background Art

[0002] As one of the important special engineering plastics, polyimide (PI) has excellent mechanical properties, thermal properties, electrical properties, radiation resistance, and chemical resistance, and is widely used in the fields of aviation, aerospace, microelectronics, nuclear industry, automotive industry, separation membranes, etc. Traditional aromatic PI has poor solubility, low optical transparency, and poor processing performance, which limits the application of PI in many fields.

[0003] At present, many literatures have reported methods such as introducing flexible groups or large-volume side groups to improve the optical transparency and solubility of polyimide films, but the thermal stability and mechanical properties have decreased. Wu Bai et al. (RSC Advances, 2021, 11, 23802-23814) proposed a polyimide structure containing triphenylimidazole, but the synthesis steps of the diamine monomer involved in this structure are relatively complex, the glass transition temperature of the prepared polyimide film is relatively low, and most of them are dark films, which is not conducive to subsequent applications; Mihaela Homocianu et al. (Int. J. Mol. Sci. 2022, 23(21), 13174) proposed a series of polyimide structures containing large-volume phosphaphenanthrene units in the side chain, but the film-forming ability and mechanical properties have decreased, and due to the presence of more benzene ring structures in the structure, its solubility is also poor; Faqin Tong et al. (J. Mater. Chem. C, 2017, 5, 10375-10382) proposed an imide structure based on azobenzene pyrimidine diamine, but due to the presence of azo groups in the structure, the thermal stability of the polymer is poor, the glass transition temperature is low, and the use temperature is low. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a diamine monomer, a polyimide, and a preparation method based on a benzodiazole heterocyclic structure. In the present invention, the benzodiazole heterocyclic structure is introduced into the diamine monomer, and then polymerized with a dianhydride monomer to obtain PI. The introduction of the benzodiazole heterocyclic structure significantly improves the thermal stability, solubility, chemical stability, and processability of the polymer.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is a diamine monomer based on a benzodiazole heterocyclic structure, having the structure shown in Formula I:

[0007]

[0008] Among them, R = -S-, -O-, -NH, -NPh or -N-iPr, and R1 = -H, -CF3 or -CH3.

[0009] The second technical solution of the present invention is a preparation method of a diamine monomer based on the benzodiazole heterocyclic structure as described above, including the following steps:

[0010] Step 1. Mix a brominating agent, Compound 1 and Solvent 1 and carry out a bromination reaction to obtain Compound 2;

[0011] Step 2. Mix Compound 2, Compound 3, a palladium catalyst, an alkali metal salt and Solvent 2, and carry out a Suzuki reaction under an inert atmosphere. Monitor the reaction progress by TLC. After the reaction is completed, extract and purify to obtain the diamine monomer based on the benzodiazole heterocyclic structure;

[0012] The structural formula of Compound 1 is:

[0013] The structural formula of Compound 2 is:

[0014] The structural formula of Compound 3 is:

[0015] In Compound 1, Compound 2 and Compound 3, R is -S-, -O-, -NH, -NPh or -N-iPr, and R1 is -H, -CF3 or -CH3.

[0016] The third technical solution of the present invention is a polyimide having the structure shown in Formula II:

[0017]

[0018] Among them, R = -S-, -O-, -NH, -NPh or -N-iPr, R1 = -H, -CF3 or -CH3; 147 ≤ n ≤ 332.

[0019] The fourth technical solution of the present invention is a preparation method of the above polyimide, including the following steps:

[0020] Under the protection of an inert atmosphere, stir and react a dianhydride monomer, the above diamine monomer and Solvent 3 at room temperature to obtain a polyamic acid solution;

[0021] Carry out thermal imidization or chemical imidization on the polyamic acid solution to obtain the polyimide.

[0022] The present invention discloses the following technical effects:

[0023] In the present invention, the structure of benzodiazole heterocycle is introduced into diamine monomers, and a class of diamine monomers containing benzodiazole heterocycle structure is designed and synthesized. The synthesized diamine monomers have a large conjugated structure and different modification sites in their structures, and the synthesis steps are relatively simple. They are polymerized with commercially available dianhydrides with different structures to obtain corresponding polyimides. Due to the introduction of heteroatoms in the structure of the prepared polyimides, stronger chemical bonds and intermolecular forces can be formed, improving the thermal stability, mechanical properties and solubility of the PI film. At the same time, there are also many chemical modification sites in the structure, and the properties of the PI film can be further improved by introducing different groups at different positions. Description of the Drawings

[0024] Figure 1 1H NMR spectrum of diamine Diamine1 in Example 1; 1 1H NMR spectrum;

[0025] Figure 2 1H NMR spectrum of diamine Diamine2 in Example 2; 1 1H NMR spectrum;

[0026] Figure 3 1H NMR spectrum of diamine Diamine3 in Example 3; 1 1H NMR spectrum;

[0027] Figure 4 1H NMR spectrum of diamine Diamine4 in Example 4; 1 1H NMR spectrum;

[0028] Figure 5 1H NMR spectrum of diamine Diamine5 in Example 5; 1 1H NMR spectrum;

[0029] Figure 6 1H NMR spectrum of diamine Diamine6 in Example 6; 1 1H NMR spectrum;

[0030] Figure 7 1H NMR spectrum of diamine Diamine7 in Example 7; 1 1H NMR spectrum;

[0031] Figure 8 1H NMR spectrum of diamine Diamine8 in Example 8; 1 1H NMR spectrum;

[0032] Figure 9 1H NMR spectrum of polyimide PI-1 in Example 9; 1 1H NMR spectrum;

[0033] Figure 10 1H NMR spectrum of polyimide PI-2 in Example 10; 1 1H NMR spectrum;

[0034] Figure 11 The HNMR spectrum of polyimide PI-3 in Example 11; 1 HNMR spectrum;

[0035] Figure 12 The HNMR spectrum of polyimide PI-4 in Example 12; 1 HNMR spectrum;

[0036] Figure 13 The HNMR spectrum of polyimide PI-5 in Example 13; 1 HNMR spectrum;

[0037] Figure 14 The FT-IR spectrum of polyimide PI-1 in Example 9;

[0038] Figure 15 The FT-IR spectrum of polyimide PI-2 in Example 10;

[0039] Figure 16 The FT-IR spectrum of polyimide PI-3 in Example 11;

[0040] Figure 17 The FT-IR spectrum of polyimide PI-4 in Example 12;

[0041] Figure 18 The FT-IR spectrum of polyimide PI-5 in Example 13. Detailed implementation manners

[0042] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the detailed implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0043] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0044] In the present invention, the room temperature means 20 ± 5°C.

[0045] Traditional aromatic PIs have poor solubility, low optical transparency, and poor processability, which limits their applications in many fields. Benzoaromatic heterocycles have a larger conjugated system and stronger molecular rigidity compared to ordinary benzene rings. Introducing benzoaromatic heterocyclic structures into PIs can significantly improve the thermal stability and mechanical strength of PIs, and the heteroatoms in benzoaromatic heterocycles can also improve solubility. Therefore, compared with ordinary aromatic ring structures, introducing benzoaromatic heterocyclic structures into PIs can significantly enhance the thermal stability, solubility, chemical stability, processability, etc. of the polymer.

[0046] In the first aspect of the present invention, a diamine monomer based on a benzoaromatic heterocyclic structure is provided, having the structure shown in Formula I:

[0047]

[0048] Wherein, R = -S-, -O-, -NH, -NPh or -N-iPr, and R1 = -H, -CF3 or -CH3.

[0049] In the second aspect of the present invention, a preparation method of the above diamine monomer based on a benzoaromatic heterocyclic structure is provided, including the following steps:

[0050] Step 1. Mix a brominating agent, Compound 1 (monosubstituted bromobenzoaromatic heterocycle) and Solvent 1, and carry out a bromination reaction to obtain Compound 2 (disubstituted bromobenzoaromatic heterocycle);

[0051] Step 2. Mix Compound 2, Compound 3 (substituted-4-aminophenylboronic acid pinacol ester), a palladium catalyst, an alkali metal salt and Solvent 2, and carry out a Suzuki reaction under an inert atmosphere. Monitor the reaction progress by TLC. After the reaction is completed, extract and purify to obtain the diamine monomer based on the benzoaromatic heterocyclic structure;

[0052] The structural formula of Compound 1 is:

[0053] The structural formula of Compound 2 is:

[0054] The structural formula of Compound 3 is:

[0055] In Compound 1, Compound 2 and Compound 3, R is -S-, -O-, -NH, -NPh or -N-iPr, and R1 is -H, -CF3 or -CH3.

[0056] The reaction general formula of the above reaction is:

[0057]

[0058] In the present invention, Compound 1 is known in the art and conforms to Compounds with the structure of R=-S-, -O-, -NH, -NPh or -N-iPr, or are obtained by using compounds with known structures as raw materials and selecting preparation methods well-known to those skilled in the art. The present invention lists the preparation methods of some Compound 1, which is not an exhaustive list.

[0059] For example:

[0060] (1) When Compound 1 is 1-phenyl-5-bromoindole, the preparation method of 1-phenyl-5-bromoindole is as follows:

[0061] Under the protection of an inert gas, 5-bromoindole, iodobenzene, CuI, Cs2CO3 and DMF are added to the reaction system, and the reaction is carried out at 120 °C for 10 - 12 h. After the reaction is completed, extraction and purification are carried out to obtain 1-phenyl-5-bromoindole.

[0062] The molar ratio of the 5-bromoindole, iodobenzene, CuI, and Cs2CO3 is 1.4:1:0.2:2.

[0063] (2) When Compound 1 is 1-isopropyl-6-bromoindole, the preparation method of 1-isopropyl-6-bromoindole is as follows:

[0064] Under an ice-water bath at 0 °C, 6-bromoindole and DMF are added to the reaction system. After all the raw materials are dissolved, NaH is added to the system, and the reaction is continued at 0 °C in an ice-water bath for 30 min. Then, 2-iodopropane is added and the reaction is carried out at room temperature for 8 - 10 h. After the reaction is completed, extraction and purification are carried out to obtain 1-isopropyl-6-bromoindole.

[0065] The molar ratio of the 6-bromoindole, NaH, and 2-iodopropane is 1:2:1.2.

[0066] In the present invention, the brominating agent is N-bromosuccinimide (NBS), 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) or pyridinium tribromide (PHBP); the molar ratio of Compound 1 and the brominating agent is 1:0.5 - 1.3.

[0067] When the brominating agent is N-bromosuccinimide, the molar ratio of Compound 1 and N-bromosuccinimide is 1:1.1 - 1.3, preferably 1:1.2;

[0068] When the brominating agent is 1,3-dibromo-5,5-dimethylhydantoin, the molar ratio of Compound 1 and 1,3-dibromo-5,5-dimethylhydantoin is 1:0.55 - 0.65, preferably 1:0.55;

[0069] When the brominating agent is pyridinium tribromide, the molar ratio of Compound 1 and pyridinium tribromide is 1:1.1 - 1.3, preferably 1:1.1.

[0070] In the present invention, when the brominating agent is NBS, the solvent 1 is a mixed solvent of V CHCl3 :V HOAc = 1:1, and the addition amount of solvent 1 is: 1 - 3 mL of solvent 1 is added per 1 mmol of compound 1;

[0071] When the brominating agent is DBDMH, the solvent 1 is 1,4 - dioxane, and the addition amount of solvent 1 is: 10 - 11 mL of solvent 1 is added per 1 mmol of compound 1;

[0072] When the brominating agent is PHBP, the solvent 1 is DCM, and the addition amount of solvent 1 is: 10 - 11 mL of solvent 1 is added per 1 mmol of compound 1.

[0073] In the present invention, the temperature of the bromination reaction is from room temperature to 60 °C, and the reaction progress is monitored by TLC. When the brominating agent is NBS, the bromination reaction temperature is 50 - 60 °C; when the brominating agent is DBDMH or PHBP, the reaction temperature is from room temperature to 30 °C.

[0074] In the present invention, after the bromination reaction is completed, it further includes the steps of adding a quenching agent to the reaction system for quenching, and directly purifying by flash column chromatography after extraction with an organic solvent.

[0075] In the present invention, when the brominating agent is NBS, the quenching agent is a saturated Na2SO3 solution (3 - 5 mL of quenching agent is added per 1 mmol of compound 1); when the brominating agent is DBDMH, the quenching agent is a saturated NaHCO3 solution (3 - 5 mL of quenching agent is added per 1 mmol of compound 1); when the brominating agent is PHBP, the quenching agent is a saturated NaHSO4 solution (3 - 5 mL of quenching agent is added per 1 mmol of compound 1).

[0076] In the present invention, the extraction agent used for extraction with an organic solvent is ethyl acetate (EA), dichloromethane (DCM) or diethyl ether (Et2O); the dosage of the extraction agent is: 3 - 5 mL of extraction agent is added per 1 mmol of compound 1.

[0077] In the present invention, the alkali metal salt is an alkali metal carbonate or an alkali metal bicarbonate; the alkali metal carbonate is Na2CO3, K2CO3 or Cs2CO3; the alkali metal bicarbonate is NaHCO3 or KHCO3;

[0078] The palladium catalyst is Pd(PPh3)4, PdCl2(dppf), Pd(OAc)2 or PdCl2(PPh3)2;

[0079] The molar ratio of compound 2, compound 3, alkali metal salt, and palladium catalyst is 1:(2.2 - 2.4):(5 - 6):(0.1 - 0.15).

[0080] In the present invention, the compound 3 is a compound known in the art that conforms to the structure of R1 = -H, -CF3 or -CH3, or is obtained by using a compound with a known structure as a raw material and selecting a preparation method well-known to those skilled in the art. The present invention lists some preparation methods of the compound 3, but is not an exhaustive list.

[0081] For example, when the compound 3 is 3-trifluoromethyl-4-aminophenylboronic acid pinacol ester, the preparation method of 3-trifluoromethyl-4-aminophenylboronic acid pinacol ester is as follows:

[0082] Under an inert atmosphere, Togni reagent, 4-aminophenylboronic acid pinacol ester, K2CO3 and MeCN are added to the reaction system, and the reaction is carried out at 75 °C for 12 - 14 h. After the reaction is completed, extraction and purification are carried out to obtain the target product 3-trifluoromethyl-4-aminophenylboronic acid pinacol ester.

[0083] The molar ratio of the Togni reagent, 4-aminophenylboronic acid pinacol ester and K2CO3 is 1:3:1.5.

[0084] In the present invention, the solvent 2 is a mixed solvent with a volume ratio of V 甲苯 :V 乙醇 :V 水 = 1:1:1 (5 - 7 mL of the mixed solvent is added per 1 mmol of the reactant), a mixed solvent with a volume ratio of V 1,4-二氧六环 :V 水 = 1:1 (10 - 12 mL of the mixed solvent is added per 1 mmol of the reactant) or a mixed solvent with a volume ratio of V 四氢呋喃 :V 水 = 1:1 (10 - 12 mL of the mixed solvent is added per 1 mmol of the reactant).

[0085] In the present invention, the temperature of the Suzuki reaction is 80 °C - 95 °C.

[0086] The third aspect of the present invention provides a polyimide having the structure shown in Formula II:

[0087]

[0088] Wherein, R = -S-, -O-, -NH, -NPh or -N-iPr, R1 = -H, -CF3 or -CH3; 147 ≤ n ≤ 332.

[0089] The fourth aspect of the present invention provides a preparation method of the above polyimide, comprising the following steps:

[0090] Under the protection of an inert atmosphere, the dianhydride monomer, the diamine monomer as claimed in claim 1 and the solvent 3 are stirred and reacted at room temperature to obtain a polyamic acid solution;

[0091] The polyamic acid solution is subjected to thermal imidization or chemical imidization to obtain the polyimide.

[0092] The present invention does not make special limitations on the specific selection of the dianhydride monomer. It is only necessary to select a dianhydride monomer well-known to those skilled in the art to react with a diamine monomer. As an example, when the dianhydride monomer is selected from dianhydride monomers with the following structures, the general reaction formula for synthesizing polyimide is as follows:

[0093]

[0094] In the present invention, the molar ratio of the dianhydride monomer to the diamine monomer is 1:1; the stirring reaction time is 24 to 48 h.

[0095] The present invention does not make special limitations on the specific preparation steps and parameters of thermal imidization and chemical imidization. It is only necessary to select thermal imidization and chemical imidization methods well-known to those skilled in the art.

[0096] The technical solutions of the present invention are all conventional solutions in the art unless otherwise specified. The reagents or raw materials used are all purchased from commercial channels or have been made public unless otherwise specified.

[0097] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments.

[0098] Example 1

[0099] The diamine monomer containing a benzodiazole heterocyclic structure is shown in the following formula:

[0100]

[0101] (1) Bromination reaction: Add NBS (5.5 mmol, 0.98 g, 1.1 equiv), 5-bromobenzothiophene (5.0 mmol, 1.07 g, 1.0 equiv), and a mixed solution of CHCl3 and acetic acid (V:V = 1:1, 10 mL) to a 100 mL round-bottom flask equipped with a magnetic stirrer and a condenser. React at 50 °C for 18 h. After the reaction is completed, cool to room temperature. Add a saturated Na2SO3 solution (15 mL) to the reaction system. Extract the organic layer with DCM (15 mL), and wash the organic layer with a saturated Na2CO3 solution, H2O, and saturated brine. Purify by column chromatography (PE) to obtain the target product 3,5-dibromobenzothiophene, 1.09 g of white solid, with a yield of 75%.

[0102] (2) Suzuki reaction: Under a nitrogen atmosphere, in a 100 mL dry round-bottom flask, add 3,5-dibromobenzothiophene (2.0 mmol, 0.58 g, 1.0 equiv), 4-aminophenylboronic acid pinacol ester (4.8 mmol, 1.05 g, 2.4 equiv), Na2CO3 (10.0 mmol, 1.06 g, 5.0 equiv), Pd(PPh3)4 (0.2 mmol, 0.23 g, 0.1 equiv), V 甲苯 : V 乙醇 : V 水 = 1:1:1 (12 mL) mixed solution. React at 80 °C for 18 h. After the reaction is completed, cool to room temperature. Add water (4 mL) to the reaction system, extract the organic layer with EA (4 mL), wash the organic layer with saturated brine, and purify by column chromatography (DCM:MeOH = 200 - 100:1) to obtain the target product Diamine1, 0.36 g of yellow solid, with a yield of 57%.

[0103] Example 2

[0104] The diamine monomer containing a benzoheterocyclic structure is shown in the following formula:

[0105]

[0106] (1) Bromination reaction: The method is the same as the "bromination reaction" step in Example 1, except that only the amount of NBS is adjusted to 1.16 g (6.5 mmol, 1.3 equiv) to obtain the target product 3,5-dibromobenzothiophene, 1.13 g of white solid, with a yield of 78%.

[0107] (2) Nucleophilic substitution reaction

[0108] Under a nitrogen atmosphere, in a 100 mL dry round-bottom flask, add Togni reagent (3.0 mmol, 0.95 g, 1.0 equiv), 4-aminophenylboronic acid pinacol ester (9.0 mmol, 1.97 g, 3.0 equiv), K2CO3 (4.5 mmol, 0.62 g, 1.5 equiv), MeCN (18 mL). React at 75 °C for 14 h. After the reaction is completed, cool to room temperature. Add water (12 mL) to the reaction system to dilute the reaction system, extract the organic layer with EA (12 mL), wash the organic layer with saturated brine, and purify by column chromatography (PE:EA = 30 - 15:1) to obtain the target product 3-trifluoromethyl-4-aminophenylboronic acid pinacol ester, 0.65 g of bright yellow solid, with a yield of 76%.

[0109] (3) Suzuki reaction: The procedure was the same as the "Suzuki reaction" step in Example 1, except that Na2CO3 was adjusted to Cs2CO3, 4-aminophenylboronic acid pinacol ester was replaced by 3-trifluoromethyl-4-aminophenylboronic acid pinacol ester, and the amount used was adjusted to 1.26 g (4.4 mmol, 2.2 equiv). Purification was carried out by column chromatography (PE:DCM:Et3N = 3 - 1:1:0.1) to obtain the target product Diamine2, 0.68 g of white solid, with a yield of 63%.

[0110] Example 3

[0111] The diamine monomer containing a benzoaromatic heterocyclic structure is shown in the following formula:

[0112]

[0113] (1) Bromination reaction: The procedure was the same as the "bromination reaction" step in Example 1, except that the amount of NBS was only adjusted to 1.07 g (6.0 mmol, 1.2 equiv) to obtain the target product 3,6-dibromobenzothiophene, 1.16 g of white solid, with a yield of 80%.

[0114] (2) Suzuki reaction: The procedure was the same as the "Suzuki reaction" step in Example 1, except that 4-aminophenylboronic acid pinacol ester was replaced by 2-methyl-4-aminophenylboronic acid pinacol ester, the amount of Na2CO3 was adjusted to 1.27 g (12 mmol, 6.0 equiv), and the amount of Pd(PPh3)4 was adjusted to 0.35 g (0.3 mmol, 0.15 equiv). Purification was carried out by column chromatography (PE:DCM:Et3N = 5 - 1:1:0.1) to obtain the target product Diamine3, 0.71 g of light yellow solid, with a yield of 69%.

[0115] Example 4

[0116] The diamine monomer containing a benzoaromatic heterocyclic structure is shown in the following formula:

[0117]

[0118] (1) Bromination reaction: Add DBDMH (5.5 mmol, 1.57 g, 0.55 equiv), 5-bromobenzofuran (10.0 mmol, 1.97 g, 1.0 equiv), and 1,4-dioxane (100 mL) to a 250 mL round-bottom flask equipped with a magnetic stir bar and a condenser. React at room temperature for 60 min. Add saturated NaHCO3 solution (30 mL) to the reaction system. Extract the organic layer with EA (30 mL), and wash the organic layer with saturated brine. Purify by column chromatography (PE) to obtain the target product 3,5-dibromobenzofuran, 0.99 g of white solid, with a yield of 65%.

[0119] (2) Suzuki reaction: Under a nitrogen atmosphere, add 3,5-dibromobenzofuran (2.0 mmol, 0.55 g, 1.0 equiv), 4-aminophenylboronic acid pinacol ester (4.8 mmol, 1.05 g, 2.4 equiv), K2CO3 (10.0 mmol, 1.38 g, 5.0 equiv), PdCl2(dppf) (0.3 mmol, 0.22 g, 0.15 equiv), V 1,4-二氧六环 :V 水 = 1:1 (20 mL) mixed solution. React at 95 °C for 18 h. After the reaction is completed, cool to room temperature. Add water (8 mL) to the reaction system. Extract the organic layer with EA (8 mL), and wash the organic layer with saturated brine. Purify by column chromatography (DCM~DCM:MeOH = 200:1) to obtain the target product Diamine4, 0.29 g of yellow solid, with a yield of 48%.

[0120] Example 5

[0121] The diamine monomer containing a benzofused heterocyclic structure is shown in the following formula:

[0122]

[0123] (1) Bromination reaction: The method is the same as the "Bromination reaction" step in Example 4, except that the amount of DBDMH is adjusted to 1.86 g (6.5 mmol, 0.65 equiv) to obtain the target product 3,7-dibromobenzofuran, 1.07 g of white solid, with a yield of 70%.

[0124] (2) Suzuki reaction: The procedure was the same as the "Suzuki reaction" step in Example 4, except that 4-aminophenylboronic acid pinacol ester was replaced by 2-methyl-4-aminophenylboronic acid pinacol ester, the amount of K2CO3 was adjusted to 1.66 g (12 mmol, 6.0 equiv), PdCl2(dppf) was adjusted to PdCl2(PPh3)2, and purification was carried out by column chromatography (DCM~DCM:MeOH = 200:1) to obtain the target product Diamine5, 0.36 g of pale yellow solid, with a yield of 55%.

[0125] Example 6

[0126] The diamine monomer containing a benzoheterocyclic structure is shown in the following formula:

[0127]

[0128] (1) Bromination reaction: 6-Bromoindole (2.0 mmol, 0.39 g, 1.0 equiv) and PHBP (2.2 mmol, 0.72 g, 1.1 equiv) were mixed in DCM (20 mL) and reacted overnight at room temperature. After the reaction, the system was diluted with DCM (6 mL), and the organic phase was washed successively with 10% sodium bisulfate solution (5 mL), saturated sodium bicarbonate solution, and saturated brine, and purified by column chromatography (PE:EA = 15~10:1) to obtain the target product 3,6-dibromoindole, 1.21 g of white solid, with a yield of 80%.

[0129] (2) Suzuki reaction: The procedure was the same as the "Suzuki reaction" step in Example 4, except that K2CO3 was adjusted to KHCO3, 4-aminophenylboronic acid pinacol ester (4.8 mmol, 1.05 g, 2.4 equiv) was adjusted to 3-methyl-4-aminophenylboronic acid pinacol 1.07 g (4.6 mmol, 2.3 equiv), and purification was carried out by column chromatography (DCM:EA = 10~3:1) to obtain the target product Diamine6, 0.7 g of pale yellow solid, with a yield of 43%.

[0130] Example 7

[0131] The diamine monomer containing a benzoheterocyclic structure is shown in the following formula:

[0132]

[0133] (1) Nucleophilic substitution reaction: Under a nitrogen atmosphere, 5-bromoindole (7.0 mmol, 1.38 g, 1.4 equiv), iodobenzene (5.0 mmol, 1.02 g, 1.0 equiv), CuI (1.0 mmol, 0.19 g, 0.2 equiv), Cs2CO3 (10.0 mmol, 3.26 g, 2.0 equiv), and DMF (10 mL) were added to a dry 100 mL round-bottom flask. The reaction was carried out at 120 °C for 12 h. After the reaction was completed, it was cooled to room temperature. Water (10 mL) was added to the reaction system, and the organic layer was extracted with EA (10 mL). The organic layer was washed with saturated brine and purified by column chromatography (PE) to obtain the target product 1-phenyl-5-bromoindole, a white solid of 1.25 g, with a yield of 92%.

[0134] (2) Bromination reaction: The method was the same as the "bromination reaction" step in Example 6, except that the amount of PHBP was adjusted to 0.79 g (2.4 mmol, 1.2 equiv), and 6-bromoindole was replaced with 1-phenyl-5-bromoindole to obtain the target product 1-phenyl-3,5-dibromoindole, a white solid of 1.68 g, with a yield of 87%.

[0135] (3) Suzuki reaction: The method was the same as the "Suzuki reaction" step in Example 1, except that Na2CO3 was adjusted to NaHCO3, and purification was carried out by column chromatography (DCM:EA:Et3N = 10~3:1:0.1). The obtained yellow solid was then rinsed with dichloromethane to obtain the target product Diamine7, a pale yellow solid of 1.13 g, with a yield of 60%.

[0136] Example 8

[0137] The diamine monomer containing a benzofused heterocyclic structure is shown in the following formula:

[0138]

[0139] (1) Nucleophilic substitution reaction: Under an ice-water bath at 0 °C, 6-bromoindole (30.0 mmol, 5.88 g, 1.0 equiv) and DMF (120 mL) were added to a dry 250 mL round-bottom flask. After all the raw materials were dissolved, NaH (60% in oil) (60 mmol, 2.4 g, 2.0 equiv) was added to the system in batches. After reacting for 30 min at this temperature, 2-iodopropane (36 mmol, 6.12 g, 1.2 equiv) was added dropwise with a syringe. The reaction was carried out at room temperature for 10 h. Water (200 mL) was added to the reaction system, and the organic layer was extracted with EA (200 mL). The organic layer was washed with saturated brine and purified by column chromatography (PE) to obtain the target product 1-isopropyl-6-bromoindole, a colorless liquid of 6.43 g, with a yield of 90%.

[0140] (2) Bromination reaction: The method is the same as the "bromination reaction" step in Example 6, except that the amount of PHBP is adjusted to 0.85 g (2.6 mmol, 1.3 equiv), 6-bromoindole is adjusted to 1-isopropyl-6-bromoindole, and purification is carried out by column chromatography (PE) to obtain the target product 1-isopropyl-3,6-dibromoindole, a colorless liquid of 1.68 g, with a yield of 87%.

[0141] (3) Suzuki reaction: The method is the same as the "Suzuki reaction" step in Example 1, except that Na2CO3 is adjusted to NaHCO3, Pd(PPh3)4 is adjusted to Pd(OAc)2, 3,5-dibromobenzofuran is adjusted to 1-isopropyl-3,6-dibromoindole, and purification is carried out by column chromatography (DCM:EA:Et3N = 10~3:1:0.1). Then the obtained yellow solid is rinsed with dichloromethane to obtain the target product Diamine8, a pale yellow solid of 1.24 g, with a yield of 52%.

[0142] Example 9

[0143] The diamine with the structure of and the dianhydride with the structure of are polymerized by the thermal imidization method.

[0144] The specific experimental steps are as follows: Under an N2 atmosphere, weigh the dried diamine Diamine1 (1 mmol, 0.3274 g, 1.0 equiv) into a 50 mL dry round-bottom flask, add anhydrous DMAc solvent through a syringe. After the diamine is completely dissolved, then dropwise add the anhydrous DMAc solution of dianhydride HPMDA (1 mmol, 0.2242 g, 1.0 equiv) through a syringe, control the solid content at 15% (a total of 4.6442 g of anhydrous DMAc solvent is added to the system), react at room temperature for 24 h to obtain the polyamic acid solution PAA-1. Then pour the polyamic acid solution onto a clean glass plate, scrape the film with a spatula, control the film thickness at 50 μm, and carry out thermal imidization by vacuum removing the solvent in a programmed temperature rise in an imidization furnace (programmed temperature rise process: 60 °C / h, 80 °C / h, 100 °C / h, 130 °C / h, 150 °C / h, 200 °C / h, 230 °C / h, 260 °C / h). After the thermal imidization is completed, wait for the temperature of the tubular furnace to drop to room temperature, take out the glass plate, and immerse the obtained polyimide film into deionized water. Wait for it to fall off naturally or peel it off with a blade. Put the obtained polyimide film into an oven at 100 °C to dry the residual solvent and moisture to obtain the polyimide film PI-1.

[0145] Example 10

[0146] The diamine with the structure of and the structure of The dianhydride is polymerized by a thermal imidization method.

[0147] The specific experimental procedure is as follows: The method is the same as in Example 9, except that the dianhydride HPMDA is adjusted to 6FDA to obtain the polyimide film PI-2.

[0148] Example 11

[0149] The diamine with the structure of and the dianhydride with the structure of are polymerized by a chemical imidization method.

[0150] The specific experimental procedure is as follows: Under an N2 atmosphere, weigh the dried diamine Diamine7 (1 mmol, 0.3755 g, 1.0 equiv) into a 50 mL dry round-bottom flask, add anhydrous DMAc solvent through a syringe. After the diamine is completely dissolved, add a solution of dianhydride 6FDA (1.01 mmol, 0.4487 g, 1.01 equiv) in anhydrous DMAc (a total of 2.6286 g of anhydrous DMAc solvent is added to the system) dropwise through a syringe. React at room temperature for 24 h, then add a mixed solution of acetic anhydride and pyridine (10 equiv) with a molar ratio of 1:1 through a syringe, and continue to react at room temperature for 24 h to obtain the polyimide solution PI-3. Dilute with DMAc, pour the reaction solution into deionized water to obtain the polyimide solid PI-3. Filter and dry to remove residual moisture and solvent. Then dissolve the polyimide solid in DCM, control the solid content at 15%, pour the polyimide solution evenly onto a clean glass plate, and place it in an oven to dry the solvent to obtain the corresponding polyimide film PI-3.

[0151] Example 12

[0152] The diamine with the structure of and the dianhydride with the structure of are polymerized by a chemical imidization method.

[0153] The specific experimental procedure is as follows: The method is the same as in Example 11, except that the dianhydride 6FDA is adjusted to PMDA and the amount of PMDA is adjusted to 0.2225 g (1.02 mmol, 1.02 equiv) to obtain the corresponding polyimide film PI-4.

[0154] Example 13

[0155] The diamine with the structure of and the dianhydride with the structure of are polymerized by a chemical imidization method.

[0156] The specific experimental steps are as follows: The method is the same as that in Example 11, except that the dianhydride 6FDA is adjusted to ODPA and the amount of ODPA is adjusted to 0.3102 g (1.0 mmol, 1.0 equiv) to obtain the corresponding polyimide film PI-5.

[0157] Characterization:

[0158] Figure 1 It is the 1 1H NMR spectrum of diamine Diamine1 in Example 1;

[0159] From Figure 1 it can be seen that 1 1H NMR (400 MHz, DMSO-d6) δ 7.99 (d, J = 9.3 Hz, 2H), 7.58 (d, J = 8.4 Hz, 1H), 7.53 (s, 1H), 7.40 (d, J = 8.3 Hz, 2H), 7.35 (d, J = 8.2 Hz, 2H), 6.76 (d, J = 8.2 Hz, 2H), 6.71 (d, J = 8.3 Hz, 2H), 5.35 - 5.19 (m, 4H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine1.

[0160] Figure 2 It is the 1 1H NMR spectrum of diamine Diamine2 in Example 2;

[0161] From Figure 2 it can be seen that 1 1H NMR (400 MHz, CDCl3) δ 7.95 - 7.89 (m, 2H), 7.67 (s, 2H), 7.57 - 7.51 (m, 3H), 7.36 (s, 1H), 6.87 (d, J = 8.3 Hz, 1H), 6.82 (d, J = 8.4 Hz, 1H), 4.29 (s, 2H), 4.22 (s, 2H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine2.

[0162] Figure 3 It is the 1 1H NMR spectrum of diamine Diamine3 in Example 3;

[0163] From Figure 3 it can be seen that 11H NMR (400 MHz, CDCl3) δ 8.18 (s, 1H), 7.93 (d, J = 7.5 Hz, 1H), 7.85 (d, J = 8.8 Hz, 1H), 7.58 (s, 1H), 7.34 (d, J = 7.5 Hz, 1H), 7.24 (d, J = 7.5 Hz, 1H), 6.71 - 6.57 (m, 4H), 4.18 (s, 4H), 2.50 (s, 3H), 2.34 (s, 3H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine3.

[0164] Figure 4 1H NMR spectrum of diamine Diamine4 in Example 4; 1 HNMR spectrum;

[0165] From Figure 4 it can be seen that 1 1H NMR (400 MHz, CDCl3) δ 8.03 (d, J = 1.4 Hz, 1H), 7.75 (s, 1H), 7.71 - 7.65 (m, 2H), 7.34 - 7.27 (m, 4H), 6.77 (t, J = 7.3 Hz, 4H), 4.47 (s, 2H), 4.46 (s, 2H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine4.

[0166] Figure 5 1H NMR spectrum of diamine Diamine5 in Example 5; 1 HNMR spectrum;

[0167] From Figure 5 it can be seen that 1 1H NMR (400 MHz, CDCl3) δ 7.73 - 7.67 (m, 2H), 7.62 (s, 1H), 7.53 (d, J = 7.5 Hz, 1H), 7.28 (d, J = 7.5 Hz, 1H), 7.24 (d, J = 7.5 Hz, 1H), 6.68 (d, J = 7.7 Hz, 2H), 6.66 - 6.61 (m, 2H), 4.18 (s, 4H), 2.44 (s, 3H), 2.33 (s, 3H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine5.

[0168] Figure 6 1H NMR spectrum of diamine Diamine6 in Example 6; 1 HNMR spectrum;

[0169] From Figure 6 it can be seen that 11H NMR (400 MHz, CDCl3) δ 8.05 (s, 1H), 7.94 (d, J = 9.4 Hz, 2H), 7.79 (d, J = 7.5 Hz, 1H), 7.67 (s, 1H), 7.33 (d, J = 9.9 Hz, 2H), 7.21 - 7.14 (m, 2H), 6.72 (d, J = 4.5 Hz, 1H), 6.70 (d, J = 4.5 Hz, 1H), 4.74 (s, 4H), 2.14 (s, 3H), 2.13 (s, 3H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine6.

[0170] Figure 7 1H NMR spectrum of diamine Diamine7 in Example 7 1 1H NMR spectrum;

[0171] From Figure 7 it can be seen that 1 1H NMR (400 MHz, DMSO-d6) δ 7.91 (s, 1H), 7.72 (s, 1H), 7.66 (d, J = 7.6 Hz, 2H), 7.60 (t, J = 8.1 Hz, 3H), 7.47 - 7.41 (m, 3H), 7.40 - 7.35 (m, 3H), 6.71 (d, J = 8.4 Hz, 2H), 6.66 (d, J = 8.4 Hz, 2H), 5.12 (d, J = 6.2 Hz, 4H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine7.

[0172] Figure 8 1H NMR spectrum of diamine Diamine8 in Example 8 1 1H NMR spectrum;

[0173] From Figure 8 it can be seen that 1 1H NMR (400 MHz, CDCl3) δ 7.82 (d, J = 7.5 Hz, 1H), 7.70 (d, J = 7.5 Hz, 1H), 7.57 (s, 1H), 7.31 - 7.23 (m, 2H), 7.08 (t, J = 8.0 Hz, 2H), 7.00 (s, 1H), 6.77 - 6.71 (m, 2H), 4.70 (p, J = 6.8 Hz, 1H), 4.39 (d, J = 6.3 Hz, 4H), 1.37 (d, J = 6.9 Hz, 6H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of diamine Diamine8.

[0174] Figure 9 1H NMR spectrum of polyimide PI-1 in Example 9 1 1H NMR spectrum;

[0175] As can be seen from Figure 9 that 1 1H NMR (400 MHz, DMSO-d6) δ 8.11 (s, 2H), 7.97 - 7.60 (m, 6H), 7.40 (d, J = 31.2 Hz, 4H), 2.36 (s, 2H), 2.05 (s, 2H). The peak positions and integral peak areas are consistent with the structure, indicating the successful synthesis of polyimide PI-1.

[0176] Figure 10 is the 1 1H NMR spectrum of polyimide PI-2 in Example 10;

[0177] As can be seen from Figure 10 that 1 1H NMR (400 MHz, CDCl3) δ 8.05 (m, 6H), 7.94 (d, J = 21.6 Hz, 4H), 7.83 (d, J = 11.7 Hz, 1H), 7.76 - 7.56 (m, 2H), 7.56 - 7.40 (m, 2H). The peak positions and integral peak areas are consistent with the polyimide fragment structure, indicating the successful synthesis of polyimide PI-2.

[0178] Figure 11 is the 1 1H NMR spectrum of polyimide PI-3 in Example 11;

[0179] As can be seen from Figure 11 that 1 1H NMR (400 MHz, DMSO-d6) δ 8.22 (d, J = 35.6 Hz, 4H), 7.93 (d, J = 39.7 Hz, 6H), 7.73 (d, J = 30.6 Hz, 5H), 7.66 - 7.36 (m, 8H). The peak positions and integral peak areas are consistent with the polyimide fragment structure, indicating the successful synthesis of polyimide PI-3.

[0180] Figure 12 is the 1 1H NMR spectrum of polyimide PI-4 in Example 12;

[0181] As can be seen from Figure 12 that 11H NMR (400 MHz, CDCl3) δ 8.46 (d, J = 2.7 Hz, 3H), 8.20 (s, 1H), 7.80 (s, 1H), 7.71 (d, J = 9.2 Hz, 2H), 7.61 - 7.55 (m, 2H), 7.49 (d, J = 7.5 Hz, 1H), 7.39 (s, 1H), 7.29 (d, J = 7.5 Hz, 1H), 2.45 (d, J = 0.9 Hz, 3H), 2.39 (d, J = 0.9 Hz, 3H). The peak positions and integral peak areas are consistent with the polyimide fragment structure, indicating the successful synthesis of polyimide PI-4.

[0182] Figure 13 1H NMR spectrum of polyimide PI-5 in Example 13 1 ;

[0183] From Figure 13 it can be seen that 1 1H NMR (400 MHz, CDCl3) δ 8.37 - 8.31 (m, 1H), 8.08 - 8.03 (m, 1H), 7.98 (d, J = 7.5 Hz, 1H), 7.87 (d, J = 7.5 Hz, 1H), 7.74 - 7.66 (m, 2H), 7.66 - 7.61 (m, 2H), 7.57 (m, 3H), 7.52 (d, J = 8.9 Hz, 1H), 7.42 (d, J = 7.5 Hz, 1H), 7.34 (m 2H), 7.07 (s, 1H), 4.72 (p, J = 6.8 Hz, 1H), 1.38 (m, 6H). The peak positions and integral peak areas are consistent with the polyimide fragment structure, indicating the successful synthesis of polyimide PI-5.

[0184] Figure 14 , Figure 15 , Figure 16 , Figure 17 , Figure 18 FT-IR spectra of polyimides PI-1 - 5 in Examples 9 - 13;

[0185] From the FT-IR spectra, the disappearance of 3220 - 3450 cm -1 (N-H stretching vibration) and 1580 - 1620 cm -1 (N-H bending vibration) and the appearance of 1781 cm -1 (C=O asymmetric stretching vibration), 1715 cm -1 (C=O symmetric stretching vibration), 1379 cm -1 (C-N stretching vibration) prove that the synthesized polyimides PI-1 - 5 are completely imidized. Combining with the previous NMR spectra, it proves that the target polyimide structure is obtained.

[0186] Performance Test:

[0187] Thermal property (DSC) test procedure for polyimide films PI-1 to 5: Weigh 3 to 5 mg of polyimide films PI-1 to 5 into a peeled solid crucible. Under a nitrogen atmosphere, with a heating rate of 20 °C / min, measure the glass transition temperature of polymers PI-1 to 5 in the temperature range of 40 - 400 °C. This glass transition temperature is obtained from the second test curve after sample annealing. The test results are shown in Table 1.

[0188] Thermal stability (TGA) test procedure for polyimides PI-1 to 5: Weigh 5 to 10 mg of solid polyimides PI-1 to 5 into a clean peeled solid crucible. Under an air or nitrogen atmosphere, with a heating rate of 20 °C / min, in the temperature range of 100 - 820 °C, detect the thermal stability of polyimides PI-1 to 5 under an air or nitrogen atmosphere. The test results are shown in Table 1.

[0189] Mechanical property test procedure for polyimides PI-1 to 5: Test the film (thickness about 45 μm, width 6 mm, length 25 mm) at room temperature, with a tensile rate of 5 mm / min. The test results are the average of 5 test samples. The test results are shown in Table 3.

[0190] Dissolution property test for polyimides PI-1 to 5: Take a certain amount of polyimide, dissolve it in different solvents to prepare a solution with a concentration of 10 mg / mL, and conduct corresponding tests on its solubility. The test results are shown in Table 2.

[0191] Table 1 DSC and TGA test data of polyimides prepared in Examples 9 - 13

[0192]

[0193] Table 2 Solubility of polyimides prepared in Examples 9 - 13 in six common solvents

[0194]

[0195] (Note: -: Insoluble upon heating, +-: Partially soluble, +: Soluble upon heating, ++: Readily soluble at room temperature)

[0196] Table 3 Tensile strength, tensile modulus, and elongation at break of polyimides prepared in Examples 9 - 13

[0197]

[0198]

[0199] As can be seen from Table 1, the Tg of the five synthesized polyimides is between 304 - 379 °C, all having relatively high glass transition temperatures; from the TGA curves and the table, it can be known that the 5% thermal weight loss ranges of the polyimide in air atmosphere and nitrogen atmosphere are 420 - 526 °C and 444 - 540 °C respectively, indicating that the polyimide has good thermal stability in both air atmosphere and nitrogen atmosphere.

[0200] As can be seen from Table 2, the solution concentrations of polyimides with different structures formed in different solvents are all 10 mg / mL. From the results, it can be known that Examples 9 - 13 all have good solubility in some common polar aprotic solvents.

[0201] As can be seen from Table 3, the tensile strength, tensile modulus, and elongation at break of the polyimide are 174 - 208 MPa, 3.3 - 5.2 GPa, and 16.8 - 22.5% respectively. The introduction of benzodiazole heterocycle improves the tensile strength of the polymer, making the polyimide have good mechanical properties.

[0202] The present invention also uses diamine to prepare polyimides with different dianhydrides respectively, and conducts DSC and TGA tests, solubility tests, and mechanical property tests on the obtained polyimides. The test results show that the polyimide provided by the present invention has a relatively high glass transition temperature, good thermal stability, and good solubility in common organic solvents.

[0203] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A diamine monomer based on a benzoaromatic heterocyclic structure, characterized in that: It has the structure shown in formula I: Wherein, R=-S-, -O-, -NH, -NPh or -N-iPr, R1=-H, -CF3 or -CH3.

2. A method for preparing a diamine monomer based on a benzoaromatic heterocyclic structure according to claim 1, characterized in that: The following steps are involved: Step 1. Mix a brominating agent, compound 1 and solvent 1 and perform a bromination reaction to obtain compound 2; Step 2. Compound 2, compound 3, palladium catalyst, alkali metal salt and solvent 2 are mixed, and Suzuki reaction is carried out under an inert atmosphere. The progress of the reaction is monitored by TLC. After the reaction is completed, extraction and purification are performed to obtain the diamine monomer based on the benzoaromatic heterocyclic structure; The structural formula of the compound 1 is: The structural formula of the compound 2 is: The structural formula of the compound 3 is: In Compound 1, Compound 2 and Compound 3, R is -S-, -O-, -NH, -NPh or -N-iPr, and R1 is -H, -CF3 or -CH3.

3. The preparation method according to claim 2, characterized in that: The brominating agent is N-bromosuccinimide, dibromohydantoin or pyridinium tribromide; the molar ratio of the compound 1 to the brominating agent is 1:0.5-1.

3.

4. The preparation method according to claim 2, characterized in that: The temperature of the bromination reaction is room temperature to 60° C., and the reaction progress is monitored by TLC.

5. The preparation method according to claim 2, characterized in that: The alkali metal salt is an alkali metal carbonate or an alkali metal bicarbonate; the alkali metal carbonate is Na2CO3, K2CO3 or Cs2CO3; the alkali metal bicarbonate is NaHCO3 or KHCO3; The palladium catalyst is Pd(PPh3)4, PdCl2(dppf), Pd(OAc)2 or PdCl2(PPh3)2; The molar ratio of the compound 2, the compound 3, the alkali metal salt and the palladium catalyst is 1:(2.2-2.4):(5-6):(0.1-0.15).

6. The preparation method according to claim 2, characterized in that: The temperature of the Suzuki reaction is 80-95°C.

7. A polyimide, characterized in that: It has the structure shown in formula II: Wherein, R=-S-, -O-, -NH, -NPh or -N-iPr, R1=-H, -CF3 or -CH3; 147≤n≤332.

8. A method for preparing the polyimide according to claim 7, characterized in that: The following steps are involved: Under the protection of an inert atmosphere, the dianhydride monomer, the diamine monomer according to claim 1 and the solvent 3 are stirred and reacted at room temperature to obtain a polyamic acid solution; The polyamic acid solution is subjected to thermal imidization or chemical imidization to obtain the polyimide.

9. The preparation method according to claim 8, characterized in that: The molar ratio of the dianhydride monomer to the diamine monomer is 1:1; and the stirring reaction time is 24 to 48 hours.

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