Diamine containing intramolecular imide ring and fatty alkyl group, polyimide formed based on diamine, and preparation method and application thereof

Abstract

The invention discloses a diamine containing an intramolecular imide ring and a fatty alkyl group, a polyimide formed based on the diamine, and a preparation method and application thereof; the diamine monomer is prepared by introducing a fatty alkyl group and an imide ring structure through a condensation reaction between nitroanhydride and a diamine containing a fatty alkyl group, and then reducing the diamine monomer; when the monomer is polymerized into polyimide, the alkalinity of the amino group of the diamine monomer can be effectively weakened, and the phenomenon that precipitation is formed due to salt formation during the polymerization process, which makes the polymerization difficult, is avoided, thereby improving the degree of polymerization reaction, and helping to improve the molecular weight and mechanical properties of the polyimide; at the same time, the introduction of the fatty alkyl group can inhibit the formation of a complex of charge transfer between a diamine electron donor and a dianhydride electron acceptor, and improve the optical transparency of the polyimide film; after testing, the mechanical properties of the polyimide film of the present application are significantly better than those of a traditional polyimide film, and the film has high optical transparency, and has good prospects in the fields of electronic products such as flexible electronic display devices and flexible circuit board matrix materials.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a diamine containing an intramolecular imide ring and a fatty alkyl group, a polyimide formed based on the diamine, and a preparation method and application thereof. Background Art

[0002] Polyimide (PI) is a high-performance polymer with multiple imide five-membered heterocyclic rings. Due to its unique electrochemical properties, radiation resistance, chemical corrosion resistance, excellent mechanical properties and other properties, it is widely used in aerospace, electronics, gas separation, fuel cells, optics, biomedicine, sensors and other fields (Fuel, 2012, 96, 1: 15-28). Traditional fully aromatic polyimide has poor light transmittance due to the influence of intermolecular and intramolecular charge transfer complexes (CTC), usually appearing yellow, so it is not suitable for display fields with high light transmittance requirements. Aliphatic polyimide, especially fully alicyclic polyimide, usually has high light transmittance, and the color of the film material can be colorless, so aliphatic alkyl polyimide is more suitable for transparent display materials (Prog. Polym. Sci, 2008, 33, 6: 581-630).

[0003] Fatty alkyl polyimide refers to a polyimide containing a fatty alkyl structure in the polymer molecular chain. Fatty alkyl does not have π electrons, so it is difficult to form a CTC effect, which effectively improves the light transmittance of polyimide (Polymer, 2018, 151, 325-333). Fatty alkyl can significantly destroy the order of polymer molecular chains, reduce intermolecular forces, and make it easier for solvent molecules to penetrate between polymer chain segments, thereby improving the solubility of polyimide. Moreover, most fatty rings (five-membered fatty rings and six-membered fatty rings) have a certain rigidity, which can give polyimide good thermal and mechanical properties. In addition, some fatty alkyl groups have good hydrophobicity, which is beneficial to reduce the water absorption rate and dielectric constant of polymers. Therefore, polyimide containing fatty alkyl has the advantages of good thermal properties, mechanical strength, solubility and light transmittance (J. Photopolym. Sci. Tec, 2017, 30: 133-137).

[0004] Although fatty alkyl polyimides have broad application prospects, there are still few examples of their industrial applications. This is mainly because during the polymerization of polyimide, fatty amines easily form salts and produce precipitation, which hinders the polymerization and makes it difficult to obtain high molecular weight polymers, which greatly limits the application and development of fatty alkyl polyimides. Summary of the invention

[0005] The purpose of the present invention is to provide a diamine containing an intramolecular imide ring and a fatty alkyl group and a preparation method thereof.

[0006] Another object of the present invention is to provide a polyimide prepared by using the above-mentioned diamine containing intramolecular imide ring and fatty alkyl group and a preparation method thereof.

[0007] Another object of the present invention is to provide a polyimide film prepared from the above polyimide.

[0008] Another object of the present invention is to provide an application of the polyimide or polyimide film.

[0009] To this end, the technical solution of the present invention is as follows:

[0010] A diamine containing an intramolecular imide ring and a fatty alkyl group, the chemical structure of which is:

[0011]

[0012] In the formula, Ar is a benzene ring or a naphthalene ring; the R group is one of the formulas (1) to (10);

[0013] Formula (1): Wherein, m is an integer, and its value range is 2 to 7, preferably 2 to 5;

[0014] Formula (2): Wherein, m and n are integers; the value range of m is 1 to 4, preferably 1 to 2; the value range of n is 1 to 4, preferably 1 to 2;

[0015] Formula (3): Wherein, m is an integer, and its value range is 2 to 6, preferably 3 to 5;

[0016] Formula (4): Wherein, m is an integer, and its value range is 1 to 5, preferably 1 to 2;

[0017] Formula (5):

[0018] Formula (6): Wherein, m and n are integers; the value range of m is 1 to 3, preferably 2; the value range of n is 1 to 3, preferably 2;

[0019] Formula (7): Wherein, m and n are integers; the value range of m is 1 to 5, preferably 1 to 3; the value range of n is 1 to 5, preferably 1 to 3;

[0020] Formula (8): Wherein, m, n, and o are integers; the value range of m is 1 to 3; the value range of n is 2 to 3; the value range of o is 1 to 3, preferably 2;

[0021] Formula (9): Wherein, m, n, o, and p are integers; the value range of m is 1 to 3; the value range of n is 2 to 3, preferably 2; the value range of o is 2 to 3, preferably 2; the value range of p is 1 to 3;

[0022] Formula (10): Among them, m, n, o, p, and q are integers; the value range of m is 1 to 3; the value range of n is 2 to 3, preferably 2; the value range of o is 2 to 3, preferably 2; the value range of p is 2 to 3, preferably 2; and the value range of q is 1 to 3.

[0023] A method for preparing a diamine containing an intramolecular imide ring and a fatty alkyl group, the preparation steps are as follows:

[0024] (1) Under the protection of inert gas, monomer I and monomer II are added to an organic solvent and mixed and stirred uniformly, and then placed at room temperature for reaction for 8h to 12h, and then heated to 150°C to 220°C for reflux for 12 to 24h; the reaction liquid is naturally cooled until a solid is precipitated, filtered, and the filtered precipitate is first washed with dilute hydrochloric acid and distilled water in sequence until neutral, and then washed with methanol for 2 to 5 times to obtain a crude product; the crude product is recrystallized using DMF, and the obtained solid is placed at 50°C to 100°C and vacuum dried to obtain a solid product;

[0025] (2) dissolving the solid product obtained in step (1) in an organic solvent, adding a catalyst, and then dripping hydrazine hydrate thereinto in an ice-water bath. After the dripping is completed, placing the mixed reaction liquid at 20° C. to 90° C. to continue the reaction for 5 h to 12 h to obtain a reaction product liquid; filtering the obtained reaction product liquid while hot, and concentrating the filtrate to precipitate a solid to obtain a crude product; recrystallizing the crude product using DMF, and vacuum drying the obtained solid at 0° C. to 50° C. to obtain a diamine monomer;

[0026] Preferably, in step (1), monomer I is Specifically, monomer I is ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diphenyl-2,5-hexanediamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, trans-1,4-diaminocyclohexane, 1,2-bis(2-aminoethyl)cyclohexane, 1,3-bis(2-aminoethyl)cyclohexane, 1,4-bis(2-aminoethyl)cyclohexane, bis(aminomethyl)ether, bis(2-aminoethyl)ether, bis(3-aminopropyl)ether, bis[(2-aminomethoxy)ethyl]ether , bis[2-(2-aminoethoxy)ethyl]ether, 1,2-bis(aminomethoxy)ethane, 1,2-bis(aminoethoxy)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane, 1,2-bis[2-(2-aminoethoxy)ethoxy]ethane, ethylene glycol bis(3-aminopropyl)ether, diethylene glycol bis(3-aminopropyl)ether, triethylene glycol bis(3-aminopropyl)ether, bis(4-aminocyclohexyl)methane, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, and at least one of 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane.

[0027] Preferably, monomer II is 4-nitrophthalic anhydride or 6-nitrophthalic anhydride.

[0028] Preferably, in step (1), the molar ratio of monomer I to monomer II is (1-5):1;

[0029] Preferably, in step (2), the molar ratio of the solid product obtained in step (1) to hydrazine hydrate is 1:(15-50).

[0030] Preferably, in step (1) and step (2), the organic solvent is one or two or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

[0031] Preferably, in step (2), the catalyst is Pd / C, Raney-Nickel / H2, SnCl2 / HCl or Fe / HCl; the amount of the catalyst used is: 20 mg to 80 mg of catalyst is added for every 1 mmol of the solid product obtained in step (1).

[0032] Preferably, in step (2), concentrating the filtrate is to concentrate the filtrate to 0.1 to 0.8 times the original volume.

[0033] A polyimide is obtained by polymerizing a diamine containing an imide ring and a fatty alkyl group in the molecule with a carboxylic acid anhydride to obtain a polyamic acid, and then undergoing thermal imidization or chemical imidization reaction; wherein the carboxylic acid anhydride is tetracarboxylic dianhydride or hexacarboxylic acid trianhydride.

[0034] Preferably, the carboxylic anhydride is 1,2,4,5-pyromellitic dianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, tetrahydronaphthalene dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, cis-1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,6,7,12-tetrachloro-3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 1,6,7,12-tetra-tert-butylphenoxyperylene-3,4,9,10-tetracarboxylic dianhydride, bicyclo(2.2.2)oct-7-ene-2 ,3,5,6-tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, 1,2,4-benzenetricarboxylic acid 1,2-anhydride ethylene ester, ethylenediaminetetraacetic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, p-phenylenedi(trimellitic acid) dianhydride, azophthalic anhydride, 4,4'-(4,4'-isopropyldiphenoxy)bis(phthalic anhydride), mellitic trianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, or 3,4,9,10-perylenetetracarboxylic anhydride.

[0035] A polyimide film is prepared from the above-mentioned polyimide.

[0036] The specific steps of a preparation method of the above-mentioned polyimide film (thermal imidization method) are:

[0037] 1) adding a diamine containing an intramolecular imide ring and a fatty alkyl group and a carboxylic anhydride in a molar ratio of (1 to 1.2):1 to an organic solvent, and preparing a polyamic acid solution with a solid content of 10 wt.% to 25 wt.% by polycondensation reaction; wherein the reaction temperature of the polycondensation reaction is -10°C to 100°C, and the reaction time is 4h to 24h;

[0038] 2) The polyamic acid solution is coated on a glass plate by a scraping method, and is placed at 80°C to 120°C for vacuum drying for 1h to 2h to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, and the temperature is gradually increased to 280°C to 350°C at a heating rate of 2°C / min to 5°C / min, and the reaction is continued at a constant temperature of 350°C for 1h to 1.5h; after natural cooling, the film is peeled off from the glass plate to obtain a thermally imidized polyimide film.

[0039] Another method for preparing the polyimide film (chemical imidization method) has the following specific steps:

[0040] 1) adding a diamine containing an imide ring and a fatty alkyl group in a molar ratio of (1 to 1.2):1 to an organic solvent, and preparing a polyamic acid solution having a solid content of 10 wt.% to 25 wt.% by polycondensation; wherein the reaction temperature of the polycondensation reaction is -10°C to 100°C, and the reaction time is 4h to 24h;

[0041] 2) 1 to 10 times the mole of acetic anhydride of the diamine containing intramolecular imide ring and fatty alkyl group and 1 to 12 times the mole of triethylamine of the diamine containing intramolecular imide ring and fatty alkyl group are mixed, and then slowly added dropwise to the polyamic acid solution, and stirred at 20°C for reaction for 12 hours; the reaction product is coated on a glass plate by a scraping method, and the solvent is removed by vacuum drying at 80°C for 2 hours; then placed in a muffle furnace in a nitrogen atmosphere, the temperature is gradually increased by 200°C at a heating rate of 5°C / min, and the reaction is continued at a constant temperature of 200°C for 1 hour; after natural cooling, the film is peeled off from the glass plate to obtain a chemically imidized polyimide film.

[0042] An optical material comprises the above-mentioned polyimide or polyimide film.

[0043] An image display device comprises the polyimide or polyimide film.

[0044] An electronic device comprises the polyimide or polyimide film.

[0045] Compared with the prior art, the diamine containing intramolecular imide ring and fatty alkyl group of the present application is a new monomer for synthesizing polyimide, which introduces fatty alkyl group and imide ring structure through condensation reaction of nitro anhydride and diamine containing fatty alkyl group, and then reduces the nitro groups at both ends of the molecule to prepare aromatic diamine containing imide ring and fatty alkyl group; when the monomer is polymerized into polyimide, the alkalinity of the amino group of the diamine monomer can be effectively weakened, and the phenomenon of precipitation formed due to salt formation during the polymerization process causing polymerization difficulty can be avoided, thereby improving the degree of polymerization reaction, helping to increase the molecular weight of polyimide, and improving the mechanical properties of polyimide film; in addition, the introduction of The introduction of the R group into the diamine monomer of the present application can interrupt the conjugated structure on the polyimide molecular chain, inhibit the formation of the charge transfer complex between the diamine electron donor and the dianhydride electron acceptor, thereby improving the optical transparency of the polyimide film; experimental verification shows that the glass transition temperature Tg and tensile strength Ts of the polyimide film prepared by the diamine containing intramolecular imide rings and fatty alkyl groups of the present application are significantly better than those of the traditional polyimide film, and have high optical transparency, and have good application and promotion prospects in the fields of electronic products such as flexible electronic display devices and flexible circuit board matrix materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1This is an infrared image of the polyimide film prepared in Example 9 of the present invention;

[0047] FIG2( a) is a physical picture of the polyimide film prepared in Example 9 of the present invention;

[0048] FIG2( b) is a physical picture of the polyimide film prepared in Comparative Example 1 of the present invention;

[0049] FIG2( c ) is a physical picture of the polyimide film prepared in Comparative Example 2 of the present invention;

[0050] FIG2( d ) is a physical picture of the polyimide film prepared in Comparative Example 3 of the present invention;

[0051] FIG3( a) is a scanning electron micrograph of a cross section of a polyimide film prepared in Example 9 of the present invention;

[0052] FIG3( b ) is a scanning electron micrograph of the surface of the polyimide film prepared in Example 9 of the present invention;

[0053] Figure 4 This is the XRD pattern of the polyimide thin film prepared in Example 9 of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0055] Example 1

[0056] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0057] S1, dissolving 3.86 g of 4-nitrophthalic anhydride in 30 mL of NMP solution to obtain a 4-nitrophthalic anhydride solution;

[0058] S2. Under nitrogen atmosphere protection and stirring conditions, 9.1 g of trans-1,4-cyclohexanediamine was added to 50 mL of NMP, and then the 4-nitrophthalic anhydride solution prepared in step S1 was slowly added dropwise thereto. The resulting mixed reaction solution was first placed at room temperature for 12 h, and then heated to 150 ° C for reflux reaction for 18 h, and the reaction was completed;

[0059] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing twice with methanol to obtain a crude product 1;

[0060] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 50° C. to obtain 3.6 g of solid product 1 with a yield of 78%;

[0061] S5, taking 0.93 g of solid product 1 and dissolving it in 15 mL of DMF, adding 85 mg of catalyst Pd / C, placing it in an ice water bath and adding dropwise 3.12 g of hydrazine hydrate, after the dropwise addition is completed, placing the mixed reaction liquid at 60° C. and continuing the reaction for 6 h to obtain a reaction product liquid;

[0062] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.2 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0063] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuum at 20° C. to finally obtain 0.79 g of a white solid powdery diamine monomer with a yield of 98%.

[0064] The chemical structural formula of the product obtained in Example 1 is:

[0065]

[0066] Example 2

[0067] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0068] S1, dissolving 3.86 g of 4-nitrophthalic anhydride in 30 mL of DMF solution to obtain a 4-nitrophthalic anhydride solution;

[0069] S2. Under nitrogen atmosphere protection and stirring conditions, 6 g of ethylenediamine was added to 50 mL of DMF, and then the 4-nitrophthalic anhydride solution prepared in step S1 was slowly added dropwise thereto. The resulting mixed reaction solution was first placed at room temperature for 11 hours, and then heated to 155° C. for reflux reaction for 12 hours. The reaction was completed;

[0070] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing twice with methanol to obtain a crude product 1;

[0071] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 80° C. to obtain 2.87 g of solid product 1 with a yield of 70%;

[0072] S5, taking 0.82 g of solid product 1 and dissolving it in 15 mL of DMF, adding 40 mg of catalyst Pd / C, placing it in an ice water bath and adding dropwise 1.87 g of hydrazine hydrate, after the dropwise addition is completed, placing the mixed reaction liquid at 20° C. and continuing the reaction for 5 h to obtain a reaction product liquid;

[0073] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.1 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0074] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuo at 30° C. to finally obtain 0.67 g of a white solid powdery diamine monomer with a yield of 95%.

[0075] The chemical structural formula of the product obtained in Example 2 is:

[0076]

[0077] Example 3

[0078] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0079] S1, dissolving 3.86 g of 4-nitrophthalic anhydride in 30 mL of DMAc solution to obtain a 4-nitrophthalic anhydride solution;

[0080] S2. Under nitrogen atmosphere protection and stirring conditions, 6.8 g of 1,3-bis(2-aminoethyl)cyclohexane was added to 50 mL of DMAc, and the 4-nitrophthalic anhydride solution prepared in step S1 was slowly added dropwise thereto. The resulting mixed reaction solution was first reacted at room temperature for 10 h, and then heated to 180° C. and refluxed for 16 h. The reaction was completed.

[0081] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing with methanol three times to obtain a crude product 1;

[0082] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 90° C. to obtain 3.54 g of solid product 1 with a yield of 68%;

[0083] S5, take 1.04g of solid product 1 and dissolve it in 15mL of NMP, add 60mg of catalyst Pd / C, place it in an ice water bath and drop 2.5g of hydrazine hydrate, after the dropwise addition is completed, place the mixed reaction liquid at 30°C and continue to react for 7h to obtain a reaction product liquid;

[0084] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.3 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0085] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuo at 30° C. to finally obtain 0.84 g of a white solid powdery diamine monomer with a yield of 92%.

[0086] The chemical structural formula of the product obtained in Example 3 is:

[0087]

[0088] Example 4

[0089] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0090] S1, 4.86g of 6-nitronaphthalene anhydride was dissolved in 30mL of NMP solution to obtain a 6-nitronaphthalene anhydride solution;

[0091] S2, under nitrogen atmosphere protection and stirring conditions, add 6.8 g of 1,3-diaminocyclohexane to 50 mL of NMP, and then slowly dropwise add the 6-nitronaphthalene anhydride solution prepared in step S1, and the resulting mixed reaction liquid is first placed at room temperature for 9 hours, and then heated to 220° C. and refluxed for 20 hours to complete the reaction;

[0092] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing with methanol three times to obtain a crude product 1;

[0093] S4, the crude product 1 was recrystallized using DMF, and the obtained solid was dried in vacuo at 100° C. to obtain 4.23 g of solid product 1, with a yield of 75%;

[0094] S5, take 1.13g of solid product 1 and dissolve it in 15mL of DMSO, add 80mg of catalyst Pd / C, place it in an ice water bath and drop 3.74g of hydrazine hydrate, after the dropwise addition is completed, place the mixed reaction liquid at 40°C and continue to react for 9h to obtain a reaction product liquid;

[0095] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.4 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0096] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuo at 50° C. to finally obtain 0.9 g of a white solid powdery diamine monomer with a yield of 90%.

[0097] The chemical structural formula of the product obtained in Example 4 is:

[0098]

[0099] Example 5

[0100] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0101] S1, dissolving 4.86 g of 6-nitronaphthenic anhydride in 30 mL of DMSO solution to obtain a 6-nitronaphthenic anhydride solution;

[0102] S2, under nitrogen atmosphere protection and stirring conditions, add 6.25g of bis(aminomethyl)ether to 50mL of DMSO, and then slowly dropwise add the 6-nitronaphthalene anhydride solution prepared in step S1, and the resulting mixed reaction solution is first placed at room temperature for 8h, and then heated to 200°C for reflux reaction for 22h, and the reaction is completed;

[0103] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing with methanol four times to obtain a crude product 1;

[0104] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 70° C. to obtain 4.27 g of solid product 1 with a yield of 77%;

[0105] S5, take 1.1 g of solid product 1 and dissolve it in 15 mL of DMAc, add 100 mg of catalyst Pd / C, place it in an ice water bath and drop 5 g of hydrazine hydrate, after the dropwise addition is completed, place the mixed reaction liquid at 50° C. and continue to react for 8 h to obtain a reaction product liquid;

[0106] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.5 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0107] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuum at 10° C. to finally obtain 0.87 g of a white solid powdery diamine monomer with a yield of 88%.

[0108] The chemical structural formula of the product obtained in Example 5 is:

[0109]

[0110] Example 6

[0111] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0112] S1, dissolving 3.86 g of 4-nitrophthalic anhydride in 30 mL of NMP solution to obtain a 4-nitrophthalic anhydride solution;

[0113] S2. Under nitrogen atmosphere protection and stirring conditions, 4.2 g of bis(4-aminocyclohexyl)methane was added to 50 mL of NMP, and the 4-nitrophthalic anhydride solution prepared in step S1 was slowly added dropwise thereto. The resulting mixed reaction solution was first reacted at room temperature for 9 h, and then heated to 220° C. and refluxed for 24 h. The reaction was completed;

[0114] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing with methanol four times to obtain a crude product 1;

[0115] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 100° C. to obtain 4.1 g of solid product 1 with a yield of 73%;

[0116] S5, take 1.12g of solid product 1 and dissolve it in 15mL of DMSO, add 120mg of catalyst Pd / C, place it in an ice water bath and drop 4.24g of hydrazine hydrate, after the dropwise addition is completed, place the mixed reaction liquid at 60°C and continue to react for 12h to obtain a reaction product liquid;

[0117] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.6 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0118] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuum at 0°C to finally obtain 0.84 g of a white solid powdery diamine monomer with a yield of 84%.

[0119] The chemical structural formula of the product obtained in Example 6 is:

[0120]

[0121] Example 7

[0122] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0123] S1, dissolving 3.86 g of 4-nitrophthalic anhydride in 30 mL of DMF solution to obtain a 4-nitrophthalic anhydride solution;

[0124] S2. Under nitrogen atmosphere protection and stirring conditions, 9.6 g of 1,2-bis(aminomethoxy)ethane was added to 50 mL of DMF, and the 4-nitrophthalic anhydride solution prepared in step S1 was slowly added dropwise thereto. The resulting mixed reaction solution was first reacted at room temperature for 10 h, and then heated to 160° C. and refluxed for 17 h. The reaction was completed;

[0125] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing with methanol five times to obtain a crude product 1;

[0126] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 60° C. to obtain 3.2 g of solid product 1 with a yield of 69%;

[0127] S5, taking 0.94 g of solid product 1 and dissolving it in 15 mL of NMP, adding 140 mg of catalyst Pd / C, placing it in an ice water bath and adding dropwise 4.4 g of hydrazine hydrate, after the dropwise addition is completed, placing the mixed reaction liquid at 70° C. and continuing the reaction for 10 h to obtain a reaction product liquid;

[0128] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.7 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0129] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuo at 25° C. to finally obtain 0.68 g of a white solid powdery diamine monomer with a yield of 83%.

[0130] The chemical structural formula of the product obtained in Example 7 is:

[0131]

[0132] Example 8

[0133] A diamine containing an intramolecular imide ring and a fatty alkyl group is prepared by the following method:

[0134] S1, dissolving 3.86 g of 4-nitrophthalic anhydride in 30 mL of DMF solution to obtain a 4-nitrophthalic anhydride solution;

[0135] S2, under nitrogen atmosphere protection and stirring conditions, add 6.2 g of 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane to 50 mL of DMF, and then slowly dropwise add the 4-nitrophthalic anhydride solution prepared in step S1, and the resulting mixed reaction solution is first placed at room temperature for 12 hours, and then heated to 180° C. and refluxed for 19 hours to complete the reaction;

[0136] S3, naturally cooling the reaction solution obtained in step S2 until solids are precipitated, filtering, and washing the filtered precipitate with dilute hydrochloric acid and distilled water in sequence until neutral, and then washing with methanol five times to obtain a crude product 1;

[0137] S4. The crude product 1 was recrystallized using DMF, and the obtained solid was dried under vacuum at 70° C. to obtain 3.63 g of solid product 1 with a yield of 72%;

[0138] S5, taking 1.09 g of solid product 1 and dissolving it in 15 mL of DMAc, adding 160 mg of catalyst Pd / C, placing it in an ice water bath and adding dropwise 3.12 g of hydrazine hydrate, after the dropwise addition is completed, placing the mixed reaction liquid at 90° C. and continuing the reaction for 11 h to obtain a reaction product liquid;

[0139] S6, filtering the reaction solution obtained in step S5 while hot, and concentrating the filtrate to 0.8 times of the original volume, and precipitating a solid from the obtained concentrated solution, i.e., crude product 2;

[0140] S7. The crude product 2 was recrystallized using DMF, and the obtained solid was dried in vacuo at 35° C. to finally obtain 0.68 g of a white solid powdery diamine monomer with a yield of 77%.

[0141] The chemical structural formula of the product obtained in Example 8 is:

[0142]

[0143] Example 9

[0144] 4 g of the diamine monomer prepared in Example 1 was dissolved in 19.6 mL of DMF, and 2.2 g of pyromellitic dianhydride was added thereto at 0° C. to allow the diamine monomer and pyromellitic dianhydride to undergo a polycondensation reaction under stirring for 20 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0145] The polyamic acid solution was coated on a glass plate by a scraping method and placed at 80°C for vacuum drying for 2 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, gradually heated to 280°C at a heating rate of 5°C / min, and continued to react at a constant temperature of 280°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0146] The chemical structure of the polyimide film is:

[0147]

[0148] Example 10

[0149] 3.5 g of the diamine monomer prepared in Example 2 was dissolved in 47.8 mL of NMP, and 1.96 g of cyclobutane tetracarboxylic dianhydride was added thereto at -10°C to allow the diamine monomer and cyclobutane tetracarboxylic dianhydride to undergo polycondensation reaction under stirring for 24 h to obtain a polyamic acid solution with a solid content of 10 wt.%;

[0150] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 100°C for 1 hour to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, gradually heated to 290°C at a heating rate of 4°C / min, and continued to react at a constant temperature of 290°C for 1.5 hours; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0151] The chemical structure of the polyimide film is:

[0152]

[0153] Embodiment 11

[0154] 4.6 g of the diamine monomer prepared in Example 3 was dissolved in 33.5 mL of DMSO, and 1.98 g of 1,2,3,4-butanetetracarboxylic acid-1,2,3,4-dianhydride was added thereto at 20° C., and the diamine monomer and 1,2,3,4-butanetetracarboxylic acid-1,2,3,4-dianhydride were subjected to polycondensation reaction under stirring for 4 hours to obtain a polyamic acid solution with a solid content of 15 wt.%;

[0155] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 120°C for 1.5 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, gradually heated to 300°C at a heating rate of 3°C / min, and continued to react at a constant temperature of 300°C for 2 hours; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0156] The chemical structure of the polyimide film is:

[0157]

[0158] Example 12

[0159] 5.04 g of the diamine monomer prepared in Example 4 was dissolved in 30.8 mL of DMAc, and 2.2 g of pyromellitic anhydride was added thereto at 30° C. to allow the diamine monomer and pyromellitic anhydride to undergo a condensation reaction under stirring for 8 hours to obtain a polyamic acid solution with a solid content of 20 wt.%;

[0160] The polyamic acid solution was coated on a glass plate by a scraping method and placed at 100°C for vacuum drying for 2 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, gradually heated to 310°C at a heating rate of 2°C / min, and continued to react at a constant temperature of 310°C for 2.5 hours; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0161] The chemical structure of the polyimide film is:

[0162]

[0163] Example 13

[0164] 4.94 g of the diamine monomer prepared in Example 5 was dissolved in 66.8 mL of DMF, and 2.1 g of 1,2,3,4-cyclopentanetetracarboxylic dianhydride was added thereto at 50° C. to allow the diamine monomer and 1,2,3,4-cyclopentanetetracarboxylic dianhydride to undergo polycondensation reaction under stirring for 12 h to obtain a polyamic acid solution with a solid content of 10 wt.%;

[0165] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 120°C for 1 hour to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, gradually heated to 320°C at a heating rate of 1°C / min, and continued to react at a constant temperature of 320°C for 2 hours; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0166] The chemical structure of the polyimide film is:

[0167]

[0168] Embodiment 14

[0169] 5 g of the diamine monomer prepared in Example 6 was dissolved in 31.5 mL of NMP, and 3.1 g of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride was added thereto at 80° C., and the diamine monomer and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride were subjected to polycondensation reaction under stirring for 14 h to obtain a polyamic acid solution with a solid content of 20 wt.%;

[0170] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 110°C for 2.5 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, the temperature was gradually increased to 330°C at a heating rate of 2°C / min, and the reaction was continued at a constant temperature of 330°C for 1.5 hours; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0171] The chemical structure of the polyimide film is:

[0172]

[0173] Embodiment 15

[0174] 4.1 g of the diamine monomer prepared in Example 7 was dissolved in 17.2 mL of DMSO, and 2.2 g of pyromellitic dianhydride was added thereto at 70° C. to allow the diamine monomer and pyromellitic dianhydride to undergo a condensation reaction under stirring for 16 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0175] The polyamic acid solution was coated on a glass plate by a scraping method and placed at 90°C for vacuum drying for 2.5 hours to remove the solvent; then placed in a muffle furnace with a nitrogen atmosphere, the temperature was gradually increased to 340°C at a heating rate of 3°C / min, and the reaction was continued at a constant temperature of 340°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0176] The chemical structure of the polyimide film is:

[0177]

[0178] Example 16

[0179] 4.45 g of the diamine monomer prepared in Example 8 was dissolved in 25.7 mL of DMAc, and 3.58 g of 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride was added thereto at 100° C. to allow the diamine monomer and 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride to undergo polycondensation reaction under stirring for 20 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0180] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 85°C for 1.5 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, the temperature was gradually increased to 350°C at a heating rate of 5°C / min, and the reaction was continued at a constant temperature of 350°C for 1.5 hours; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0181] The chemical structure of the polyimide film is:

[0182]

[0183] Embodiment 17

[0184] 4.1 g of the diamine monomer prepared in Example 7 was dissolved in 26.6 mL of DMF, and 2.24 g of 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride was added thereto at 0° C. to allow the diamine monomer and 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride to undergo a polycondensation reaction under stirring for 20 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0185] 9.4 mL of acetic anhydride and 13.9 mL of triethylamine were slowly added dropwise to the polyamic acid solution, and the mixture was stirred at 20°C for reaction for 12 hours; the reaction product was coated on a glass plate by a scraping method, and the solvent was removed by vacuum drying at 80°C for 2 hours; then the mixture was placed in a muffle furnace in a nitrogen atmosphere, and the temperature was gradually increased by 200°C at a heating rate of 5°C / min, and the reaction was continued at a constant temperature of 200°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a chemically imidized polyimide film.

[0186] The chemical structure of the polyimide film is:

[0187]

[0188] Embodiment 18

[0189] 4.04 g of the diamine monomer prepared in Example 1 was dissolved in 69.7 mL of NMP, and 3.92 g of 3,4,9,10-perylenetetracarboxylic anhydride was added thereto at 20° C., and the diamine monomer and 3,4,9,10-perylenetetracarboxylic anhydride were subjected to polycondensation reaction under stirring for 18 h to obtain a polyamic acid solution with a solid content of 10 wt.%;

[0190] 9.4 mL of acetic anhydride and 13.9 mL of triethylamine were slowly added dropwise to the polyamic acid solution, and the mixture was stirred at 20°C for reaction for 12 hours; the reaction product was coated on a glass plate by a scraping method, and the solvent was removed by vacuum drying at 80°C for 2 hours; then the mixture was placed in a muffle furnace in a nitrogen atmosphere, and the temperature was gradually increased by 200°C at a heating rate of 5°C / min, and the reaction was continued at a constant temperature of 200°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a chemically imidized polyimide film.

[0191] The chemical structure of the polyimide film is:

[0192]

[0193] Embodiment 19

[0194] 3.5 g of the diamine monomer prepared in Example 2 was dissolved in 28.7 mL of DMAc, and 3.22 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added thereto at 50° C., and the diamine monomer and 3,3',4,4'-benzophenonetetracarboxylic dianhydride were subjected to polycondensation reaction under stirring for 14 h to obtain a polyamic acid solution with a solid content of 20 wt.%;

[0195] 9.4 mL of acetic anhydride and 13.9 mL of triethylamine were slowly added dropwise to the polyamic acid solution, and the mixture was stirred at 20°C for reaction for 12 hours; the reaction product was coated on a glass plate by a scraping method, and the solvent was removed by vacuum drying at 80°C for 2 hours; then the mixture was placed in a muffle furnace in a nitrogen atmosphere, and the temperature was gradually increased by 200°C at a heating rate of 5°C / min, and the reaction was continued at a constant temperature of 200°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a chemically imidized polyimide film.

[0196] The chemical structure of the polyimide film is:

[0197]

[0198] Embodiment 20

[0199] 4.6 g of the diamine monomer prepared in Example 3 was dissolved in 20.6 mL of DMSO, and 2.94 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added thereto at 20° C., and the diamine monomer and 3,3',4,4'-biphenyltetracarboxylic dianhydride were subjected to polycondensation reaction under stirring for 10 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0200] 9.4 mL of acetic anhydride and 13.9 mL of triethylamine were slowly added dropwise to the polyamic acid solution, and the mixture was stirred at 20°C for reaction for 12 hours; the reaction product was coated on a glass plate by a scraping method, and the solvent was removed by vacuum drying at 80°C for 2 hours; then the mixture was placed in a muffle furnace in a nitrogen atmosphere, and the temperature was gradually increased by 200°C at a heating rate of 5°C / min, and the reaction was continued at a constant temperature of 200°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a chemically imidized polyimide film.

[0201] The chemical structure of the polyimide film is:

[0202]

[0203] Comparative Example 1

[0204] 2 g of 4,4'-diaminodiphenyl ether was dissolved in 11.45 mL of DMSO, and 2.2 g of pyromellitic anhydride was added thereto at 20°C to allow the diamine monomer and pyromellitic anhydride to undergo polycondensation reaction under stirring for 20 hours to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0205] The polyamic acid solution was coated on a glass plate by a scraping method and placed at 90°C for vacuum drying for 2.5 hours to remove the solvent; then placed in a muffle furnace with a nitrogen atmosphere, the temperature was gradually increased to 300°C at a heating rate of 3°C / min, and the reaction was continued at a constant temperature of 300°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0206] The chemical structure of the polyimide film is:

[0207]

[0208] Comparative Example 2

[0209] 2 g of 4,4'-diaminodiphenyl ether was dissolved in 11.8 mL of DMSO, and 2.24 g of 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride was added thereto at 25°C to allow the diamine monomer and 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride to undergo polycondensation reaction under stirring for 18 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0210] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 120°C for 2 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, the temperature was gradually increased to 300°C at a heating rate of 3°C / min, and the reaction was continued at a constant temperature of 300°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0211] The chemical structure of the polyimide film is:

[0212]

[0213] Comparative Example 3

[0214] 2.92 g of 1,4-di(4-aminophenoxy)benzene was dissolved in 11.8 mL of DMSO, and 2.94 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added thereto at 20° C., and the diamine monomer and 3,3',4,4'-biphenyltetracarboxylic dianhydride were subjected to polycondensation reaction under stirring for 16 h to obtain a polyamic acid solution with a solid content of 25 wt.%;

[0215] The polyamic acid solution was coated on a glass plate by a scraping method and placed under vacuum drying at 80°C for 2 hours to remove the solvent; then placed in a muffle furnace in a nitrogen atmosphere, the temperature was gradually increased by 200°C at a heating rate of 5°C / min, and the reaction was continued at a constant temperature of 200°C for 1 hour; after natural cooling, the film was peeled off the glass plate to obtain a thermally imidized polyimide film.

[0216] The chemical structure of the polyimide film is:

[0217]

[0218] Performance Test:

[0219] (I) Molecular weight test of polyimide film:

[0220] In the above embodiments, Embodiments 1 to 8 are examples of preparing diamines containing intramolecular imide rings and fatty alkyl groups; Embodiments 9 to 16 are examples of preparing the polyimide film of the present application by using a thermal imidization method; Embodiments 17 to 20 are examples of preparing the polyimide film of the present application by using a chemical imidization method; Comparative Examples 1 to 3 are examples of preparing traditional polyimide films by using a thermal imidization method. The weight average molecular weight of the polyimide films prepared in the above embodiments 9 to 20 and Comparative Examples 1 to 3 and the phenomena occurring during the preparation process are shown in Table 1 below.

[0221] Table 1:

[0222]

[0223] Based on the analysis of the results in Table 1, it can be seen that in Comparative Examples 1 to 3, due to the strong alkalinity of the diamine in the polycondensation reaction, partial salt formation occurs during the polymerization process, which hinders the polymerization reaction. Therefore, the molecular weight of the polyimide synthesized by the polycondensation is lower than that of the polyimide prepared using the diamine monomer of the present application.

[0224] (II) Infrared structural characterization of polyimide film:

[0225] like Figure 1 The infrared image of the polyimide film prepared in Example 9 is shown; it can be seen from the figure that the characteristic absorption peaks of the amide at wavelengths of 3300-3500cm-1 (NH) and 1660cm-1 (C=O) disappear. The characteristic absorption peaks of the imide ring appear at 1780cm-1 (C=O asymmetric stretching), 1720cm-1 (C=O symmetric stretching), 1360cm-1 (CN stretching) and 720cm-1 (C=O), proving that the polyimide polymer is successfully synthesized. Correspondingly, the infrared spectra of the polyimide films prepared in Examples 10 to 20 have the same functional group characterization characteristics as Example 9.

[0226] (III) Macroscopic and microscopic characterization of polyimide films:

[0227] As shown in Figure 2(a), this is a physical picture of the polyimide film prepared in Example 9; it can be seen from the figure that Example 9 successfully prepared a polyimide film, and the obtained film is a dense, defect-free, transparent film material; accordingly, the physical appearance of the polyimide films prepared in Examples 10 to 20 are the same as the film prepared in Example 9, and are all dense, defect-free, transparent films.

[0228] As shown in Figures 2(b), 2(c) and 2(d), they are actual pictures of the polyimide films prepared in Comparative Examples 1 to 3, respectively. It can be seen from the figures that the color of the polyimide film prepared in Comparative Example 1 is dark brown, the color of the polyimide film prepared in Comparative Example 2 is yellow, and the color of the polyimide film prepared in Comparative Example 3 is dark yellow, and its transparency is worse than that of the polyimide films of Comparative Examples 1 and 2. Compared with the polyimide films prepared in Comparative Examples 1 to 3, the polyimide film prepared in the embodiment of the present application is significantly lighter in color than the traditional polyimide film.

[0229] FIG3(a) shows a cross-sectional SEM image of the polyimide film prepared in Example 9; FIG3(b) shows a surface SEM image of the polyimide film prepared in Example 9; it can be seen from the figure that the cross-sectional and surface of the obtained polyimide film have no defects, proving that the polyimide dense film is successfully prepared. Correspondingly, the SEM images of the polyimide films prepared in Examples 10 to 20 also have the same microstructural characteristics as those in Example 9.

[0230] like Figure 4 The XRD pattern of the polyimide film prepared in Example 9 is shown; there is only one large broad peak characteristic of the polymer in the XRD pattern, which proves that the polyimide polymer is successfully synthesized. Correspondingly, the XRD patterns of the polyimide films prepared in Examples 10 to 20 are also the same as the characterization results of Example 9, that is, there is only one large broad peak characteristic of the polymer.

[0231] (IV) Mechanical and optical characterization of polyimide films:

[0232] The mechanical properties and optical properties of the imide films prepared in Examples 9 to 20 and Comparative Examples 1 to 3 were tested, and the specific test results are shown in Table 2 below.

[0233] Table 2:

[0234]

[0235] It can be clearly seen from the mechanical test results in Table 2 that, based on the above analysis of the molecular weight test results of the polyimide film, the polyimide films of Comparative Examples 1 to 3 do exhibit corresponding mechanical properties (glass transition temperature Tg and tensile strength Ts) that are significantly lower than the tensile strength of the polyimide films prepared in Examples 9 to 20; specifically, the glass transition temperature of the polyimide film ranges from 332 to 367°C, and the tensile strength can reach up to 180 MPa. Its excellent glass transition temperature and tensile strength enable it to become the preferred polymer material for improving the reliability of flexible circuits. Therefore, the polyimide film prepared from the diamine monomer containing an imide ring and a fatty alkyl structure in the present application has great potential for use in flexible electronic display devices.

[0236] It can be clearly seen from the optical test results in Table 1 that due to the strong conjugation of the traditional imide molecular chain, the charge transfer complex between the diamine and the dianhydride is significantly increased. Therefore, compared with the polyimide film prepared by the diamine monomer containing an imide ring and a fatty alkyl structure in the present application in Examples 9 to 20, the color of the polyimide film prepared in Comparative Examples 1 to 3 is obviously too dark and the optical transparency is very low. Specifically, the transmittance of the polyimide film prepared in Examples 9 to 20 at 450nm ultraviolet wavelength is higher than 82%, and the maximum transmittance of the polyimide film at 500nm ultraviolet wavelength is 95.9%; at the same time, the chromaticity index of the polyimide film in terms of brightness parameter L*, red-green parameter a*, and yellow-blue parameter b* is significantly better than the chromaticity index of the polyimide film prepared in Examples 9 to 20, which further illustrates that the film has a high optical transparency, that is, the use of the diamine monomer containing an imide ring and a fatty alkyl structure in the present application can significantly improve the optical properties of the polyimide film. The excellent optical transparency of polyimide film will become an alternative matrix material for flexible circuit boards. With the advent of new electronic products such as foldable mobile phones and the increasing demand for high-quality flexible circuit boards, higher requirements are also placed on the light transmittance of polyimide as a matrix material. It can be seen that the polyimide film with excellent optical properties prepared from diamine monomers containing imide rings and fatty alkyl structures in this application has good prospects in the field of electronic products such as flexible circuit boards.

Claims

1. A diamine containing an intramolecular imide ring and a fatty alkyl group, It is characterized in that Its chemical structure is: In the formula, Ar is a benzene ring or a naphthalene ring; the R group is one of formulas (1) to (4); Formula (1): Wherein, m and n are integers, the value range of m is 1 to 4, and the value range of n is 1 to 4; Formula (2): Wherein, m is an integer, and its value range is 1 to 5; Formula (3): Formula (4): Wherein, m and n are integers, the value range of m is 1 to 3, and the value range of n is 1 to 3.

2. A method for preparing a diamine containing an intramolecular imide ring and a fatty alkyl group according to claim 1, It is characterized in that The preparation steps are as follows: (1) Under the protection of inert gas, monomer I and monomer II are added to an organic solvent and mixed and stirred evenly, and then placed at room temperature for reaction for 8h to 12h, and then heated to 150°C to 220°C for reflux for 12 to 24h; the reaction liquid is naturally cooled until a solid is precipitated, filtered, and the filtered precipitate is first washed with dilute hydrochloric acid and distilled water in sequence until neutral, and then washed with methanol for 2 to 5 times to obtain a crude product; the crude product is recrystallized using DMF, and the obtained solid is placed at 50°C to 100°C for vacuum drying to obtain a solid product; wherein monomer I is Monomer II is 4-nitrophthalic anhydride or 6-nitrophthalic anhydride, and the molar ratio of the two is (1-5):1; (2) dissolving the solid product obtained in step (1) in an organic solvent, adding a catalyst, and then dripping hydrazine hydrate thereinto in an ice-water bath. After the dripping is completed, placing the mixed reaction liquid at 20° C. to 90° C. to continue the reaction for 5 h to 12 h to obtain a reaction product liquid; filtering the obtained reaction product liquid while hot, and concentrating the filtrate to precipitate a solid to obtain a crude product; recrystallizing the crude product using DMF, and vacuum drying the obtained solid at 0° C. to 50° C. to obtain a diamine monomer; wherein the molar ratio of the solid product obtained in step (1) to hydrazine hydrate is 1:(15 to 50).

3. The method for preparing a diamine containing an intramolecular imide ring and a fatty alkyl group according to claim 2, It is characterized in that In step (1) and step (2), the organic solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP).

4. The method for preparing a diamine containing an intramolecular imide ring and a fatty alkyl group according to claim 2, It is characterized in that In step (2), the catalyst is Pd / C, Raney-Nickel / H 2 SnCl 2 / HCl or Fe / HCl; the amount of catalyst used is: 20mg-80mg of catalyst is added for every 1mmol of the solid product obtained in step (1).

5. A polyimide, which is obtained by polymerizing the diamine containing an imide ring and a fatty alkyl group in the molecule as claimed in claim 1 with a polyamic acid obtained by carboxylic anhydride, and then undergoing thermal imidization or chemical imidization reaction; in, The carboxylic anhydride is tetracarboxylic dianhydride or hexacarboxylic dianhydride.

6. The polyimide according to claim 5, It is characterized in that The carboxylic anhydride is 1,2,4,5-pyromellitic dianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, tetrahydronaphthalene dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, cis-1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,6,7,12-tetrachloro-3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 1,6,7,12-tetra-tert-butylphenoxyperylene-3,4,9,10-tetracarboxylic dianhydride, bicyclo(2.2.2)oct-7-ene-2,3 ,5,6-tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, 1,2,4-benzenetricarboxylic acid 1,2-anhydride ethylene ester, ethylenediaminetetraacetic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, p-phenylenedi(trimellitic acid) dianhydride, azophthalic anhydride, 4,4'-(4,4'-isopropyldiphenoxy)bis(phthalic anhydride), mellitic trianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, or 3,4,9,10-perylenetetracarboxylic anhydride.

7. A polyimide film, prepared from the polyimide according to claim 5 or 6. 8 . An optical material comprising the polyimide according to claim 5 or 6 , or the polyimide film according to claim 7 . 9 . An image display device comprising the polyimide according to claim 5 or 6 , or the polyimide film according to claim 7 . 10 . An electronic device comprising the polyimide according to claim 5 or 6 , or the polyimide film according to claim 7 .

Images