Catalyst for synthesizing polyimide, method for preparing the same, and polyimide compound

Abstract

A catalyst for synthesizing polyimide, a preparation method thereof, and a polyimide compound are provided. The structural formula of the catalyst is represented by Formula (1), [Chemical Formula 1] JPEG2025518360000035.jpg5174In Formula (1), R 3 is selected from O or NH; R 4 is selected from O or NH; Ar 2 is a substituted aryl group, and the substituent of the substituted aryl group has a carboxyl group; R 5 is selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group; n is an integer in the range of 1 to 4.

Description

Technical Field

[0001] Cross - reference to Related Applications This disclosure claims the priority of Chinese Patent Application Publication No. 202210684716.2, titled "CATALYST FOR SYNTHESIZING POLYIMIDE, AND PREPARATION METHOD AND USE THEREFOR", filed on June 16, 2022, the entire content of which is incorporated herein by reference.

[0002] This disclosure relates to the technical field of polyimides, and in particular, to a catalyst for synthesizing polyimides, its preparation method, and polyimide compounds.

Background Art

[0003] Polyimide is a kind of polymer material having a molecular chain containing an imide ring, and has excellent properties such as high mechanical properties, high and low temperature resistance, flame retardancy, and irradiation resistance. Polyimide products include films, fibers, resins, foams, composites, etc., and are widely used in fields such as national defense and military industries, microelectronics, vehicles, and the chemical industry. Currently, as catalysts for synthesizing polyimides, amines, quinoline, pyridine, or other nitrogen - containing compounds are usually used. However, nitrogen - containing compounds are likely to react with uncyclized precursors to form salts, thereby making the removal of the catalyst difficult. Residual catalysts affect the film - forming property of polyimides and reduce the quality of products. Furthermore, existing catalysts have limited catalytic effects, and as a result, the manufacturing process further requires multiple heatings to promote the reaction, increasing the manufacturing cost.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In consideration of this, the present disclosure provides a novel catalyst for synthesizing polyimide. The catalyst has high reactivity to complete the reaction with a single heating, significantly reducing the manufacturing cost. Further, the catalyst can crosslink with the molecular chains of polyimide to form a part of the polymer, resulting in a reduction of free catalyst in the system, thereby ensuring good film-forming properties of the product.

Means for Solving the Problems

[0005] According to a first aspect of the present disclosure, a catalyst for synthesizing polyimide is provided. The catalyst has a structural formula represented by formula (1).

[0006]

Chemical Formula

[0007] In formula (1), R 3 is selected from O or NH; R 4 is selected from O or NH; Ar 2 is a substituted aryl group, and the substituent of the substituted aryl group contains a carboxyl group; R 5 is selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group, and n is an integer from 1 to 4.

[0008] Optionally, the catalyst has a structural formula represented by formula (1-1), formula (1-2), or formula (1-3).

[0009]

Chemical Formula

[0010] Optionally, the catalyst has a molecular structural formula represented by formulas (A) to (C).

[0011]

Chemical Formula

[0012] Optionally, R 5 is selected from an alkyl group or an alkoxy group; one or more of the n Rs 5 are

[0013]

Chemical formula

[0014]

Chemical formula

[0015] Optionally, the number of carbon atoms in the alkyl group ranges from 1 to 10; the number of carbon atoms in the haloalkyl group ranges from 1 to 10; the number of carbon atoms in the alkoxy group ranges from 1 to 10; and the number of carbon atoms in the ester group ranges from 1 to 10.

[0016] Optionally, the alkoxy group contains one or more of methoxy, ethoxy, propoxy, and butoxy; and the ester group contains one or more of methyl formate, methyl acetate, ethyl formate, or ethyl acetate.

[0017] According to a second aspect of the present disclosure, there is provided a method for preparing a catalyst for synthesizing polyimide, the method including the following steps: mixing a first raw material, a second raw material, and a first solvent to perform a first reaction to obtain an intermediate product; and hydrolyzing the intermediate product to obtain a catalyst for synthesizing polyimide. The chemical formula of the first raw material is Ar 1 2 PCl (wherein Ar 1 is a substituted aryl group, and the substituents of the substituted aryl group include one or more of cyano, 1,3-dioxolane, and methyl formate). The structural formula of the second raw material is shown in formula (2).

[0018] [Chemical] In formula (2), R 1 is selected from OH or NH 2 ; R 2 is selected from OH or NH 2 ; R 5 is selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group, and n is an integer from 1 to 4.

[0019] Optionally, the first solvent contains one or more of tetrahydrofuran or ethyl ether.

[0020] Optionally, the second raw material contains one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, m-dihydroxybenzene, p-dihydroxybenzene, and o-dihydroxybenzene.

[0021] Optionally, the molar ratio of the first raw material, the second raw material, and the first solvent is (1.5 - 2.5):1:(10 - 300).

[0022] Optionally, the temperature of the first reaction is in the range of 0°C to 80°C, and the time of the first reaction is in the range of 2 hours to 48 hours.

[0023] Optionally, the reaction solution is obtained after the first reaction is completed. The extraction of the reaction solution is carried out using a mixture of a non-polar solvent and water, and the extracted organic phase is recrystallized to obtain an intermediate product. The non-polar solvent contains one or more of ethyl acetate, ethyl ether, and dichloromethane.

[0024] Optionally, the reaction solution is obtained after hydrolysis is completed. The reaction solution is extracted to obtain an aqueous phase solution, and an acid is added to the aqueous phase solution to obtain a catalyst.

[0025] Optionally, the extractant for extraction includes a nonpolar solvent and an aqueous alkali solution, and the nonpolar solvent includes one or more of ethyl acetate, ethyl ether, and dichloromethane.

[0026] Optionally, the alkali includes one or more of sodium hydroxide and potassium hydroxide.

[0027] According to a third aspect of the present disclosure, there is provided a method for preparing a polyimide, which includes mixing a catalyst obtained by using a method for preparing a catalyst for synthesizing a polyimide according to the first aspect or a method for preparing a catalyst for synthesizing a polyimide according to the second aspect, a diamine, a dianhydride, and a second solvent to perform a second reaction to obtain a polyimide.

[0028] Optionally, the molar ratio of the diamine, the dianhydride, the catalyst, and the second solvent is (0.95 to 1):(0.95 to 1):(0.0001 to 0.5):(25 to 200).

[0029] Optionally, the diamine includes one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1,3-diamino-2-methylpropane, N,N-bis(4-aminophenyl)-1,4-benzenediamine, and 9,9-bis(4-aminophenyl)fluorene.

[0030] Optionally, the dianhydride includes one or more of 2,3,3’,4’-diphenyl ether tetracarboxylic dianhydride, 3,3’,4,4’-tetracarboxybenzophenone dianhydride, 3,3’,4,4’-tetracarboxydiphenyl sulfone dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 4,4’-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4’-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4’-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride, and 4,4’-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride.

[0031] Optionally, the second solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0032] Optionally, the temperature of the second reaction ranges from 60°C to 180°C, and the time of the second reaction ranges from 1 hour to 48 hours.

[0033] Optionally, the reaction solution is obtained after the second reaction is completed. When a polar solvent is added to the reaction solution, the polyimide precipitates. The polar solvent includes one or more of methanol, ethanol, and water.

[0034] According to a fourth aspect of the present disclosure, a polyimide compound is provided. The polyimide compound is obtained by using the method for preparing polyimide according to the third aspect.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0036] The technical solution in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part, not all, of the embodiments of the present disclosure. All other embodiments obtained based on the embodiments of the present disclosure without creative efforts by those skilled in the art shall be included within the protection scope of the present disclosure.

[0037] Polyimide is usually obtained by polycondensing aromatic dianhydrides and aromatic diamines in an organic solution to produce polyamic acid or polyamide ester, and then imidizing (cyclizing) the polyamic acid or polyamide ester. Currently, nitrogen-containing compounds are usually used as catalysts for cyclizing polyimide. In the mass production process, the removal of the catalyst is abandoned because of the high cost. However, the remaining nitrogen-containing compounds interfere with the cross-linking of the molecular chains, and as a result, affect the film-forming property of the polyimide. Furthermore, the current catalyst has a limited catalytic effect, and in actual production, it is necessary to heat twice at a temperature exceeding 300 °C to promote cyclization. This increases the manufacturing cost and reduces the manufacturing efficiency. In order to improve the manufacturing efficiency of polyimide and ensure good film-forming property of the product, the present disclosure provides a novel catalyst. The catalyst has a structural formula shown in formula (1).

[0038]

Chemical formula

[0039] In formula (1), R 3 is selected from O or NH; R 4 is selected from O or NH; Ar 2 is a substituted aryl group, and the substituent of the substituted aryl group contains a carboxyl group; R 5is selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group, and n is an integer from 1 to 4. In some embodiments of the present disclosure, the number of carbon atoms in the alkyl group ranges from 1 to 10; the number of carbon atoms in the haloalkyl group ranges from 1 to 10; the number of carbon atoms in the alkoxy group ranges from 1 to 10; the number of carbon atoms in the ester group ranges from 1 to 10.

[0040] In some embodiments, the n R 5 are all selected from H, and the catalyst has a structural formula represented by formula (1-1), formula (1-2), or formula (1-3).

[0041]

Chemical formula

[0042] In formula (1-1), formula (1-2), and formula (1-3), R 3 is selected from O or NH; R 4 is selected from O or NH; Ar 2 is a substituted aryl group, and the substituent of the substituted aryl group contains a carboxyl group. In some embodiments of the present disclosure, Ar 2 may be any one of a substituted phenyl, a substituted naphthyl, and a substituted anthryl.

[0043] In some embodiments of the present disclosure, Ar 2 is a substituted phenyl group, and the substituent of the substituted phenyl group contains a carboxyl group. In some embodiments of the present disclosure, the structural formula of Ar 2 is represented by formula (1-4).

[0044]

Chemical formula

[0045] In formula (1-4), the wavy bond indicates the connection site.

[0046] Generally, existing polyimide catalysts, such as pyridine or quinoline catalysts, react mainly through the lone pair electrons of nitrogen atoms. Nitrogen is an element in the second period, and its orbitals are more restricted than those of other elements in the same main group. Therefore, the lone pair electrons of nitrogen are relatively less active in catalytic reactions. The catalyst provided in the present disclosure contains a phosphorus atom. The phosphorus atom has a larger orbital than the nitrogen atom, and thus it is easier to improve the reaction activity and lower the temperature required for the reaction, enabling the reaction to proceed under milder conditions, thereby reducing the manufacturing cost and improving the manufacturing efficiency. The structure of the catalyst has a carboxyl group at the end. The carboxyl group can crosslink with the amino group at the end of the polyimide molecule or form a hydrogen bond with the imide, resulting in the catalyst binding to the polymer chain to form part of the polymer chain and promoting strong linkage between polymer chains. This promotes the removal of the catalyst, thereby realizing stable film formation.

[0047] In some embodiments of the present disclosure, R 5 is selected from an alkyl group or an alkoxy group; one or more of the n R 5 are

[0048]

Chemical formula

[0049]

Chemical formula

[0050]

Chemical formula

[0051] [Chemistry] When in the ortho or para position of , it promotes further improvement in the activity of the catalyst. In some embodiments, the alkoxy group includes one or more of methoxy, ethoxy, propoxy, and butoxy. In some embodiments, the ester group includes one or more of methyl formate, methyl acetate, ethyl formate, or ethyl acetate.

[0052] In some specific embodiments of the present disclosure, the catalyst has a molecular structural formula represented by formulas (A) to (C).

[0053] [Chemistry]

[0054] The present disclosure further provides a method for preparing the aforementioned catalyst, which includes the following steps.

[0055] A first raw material, a second raw material, and a first solvent are mixed to carry out a first reaction to obtain an intermediate product. The intermediate product is hydrolyzed to obtain the catalyst.

[0056] In one embodiment of the present disclosure, the first raw material is phenylphosphonic acid chloride having a protecting group, and the chemical formula of the first raw material is Ar 1 2 PCl (wherein Ar 1 is a substituted aryl group, and the substituents of the substituted aryl group include one or more of cyano, 1,3 - dioxolane, and methyl formate). In some embodiments, the structural formula of Ar 1 is represented by formula (2 - 4), formula (2 - 5), or formula (2 - 6).

[0057] [Chemistry]

[0058] In one embodiment of the present disclosure, the structural formula of the second raw material is represented by formula (2).

[0059]

Chem.

[0060] In formula (2), R 1 and R 2 are, independently, selected from OH or NH 2 ; n R 5 are, independently, selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group, and n is an integer from 1 to 4. In some embodiments, all n R 5 are H, and the structural formula of the second raw material is shown in formula (2-1), formula (2-2), or formula (2-3).

[0061]

Chem.

[0062] In formula (2-1), formula (2-2), and formula (2-3), R 1 and R 2 are, independently, selected from OH or NH 2It is selected from. In some embodiments, the second raw material includes one or more of diphenol and diamine. The diamine may be one or more of o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine. The diphenol may be one or more of m-dihydroxybenzene, p-dihydroxybenzene, and o-dihydroxybenzene. In some embodiments of the present disclosure, the first solvent includes one or more of tetrahydrofuran or ethyl ether. In some embodiments of the present disclosure, the temperature of the first reaction ranges from 0°C to 80°C, and the time of the first reaction ranges from 2 hours to 48 hours. The temperature of the first reaction may specifically be 0°C, 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, 50°C, 60°C, or 80°C, but is not limited thereto. The time of the first reaction may specifically be 2 hours, 5 hours, 10 hours, 20 hours, 30 hours, or 48 hours, but is not limited thereto.

[0063] In some embodiments of the present disclosure, the method for preparing the catalyst includes the following steps.

[0064] Step 100: To react, a first raw material, a second raw material, and a first solvent are mixed. The molar ratio of the first raw material, the second raw material, and the first solvent is (1.5 - 2.5):1:(10 - 300), the reaction temperature ranges from 0°C to 80°C, and the reaction time ranges from 2 hours to 48 hours. In some embodiments, the molar ratio of the first raw material, the second raw material, and the first solvent is (1.8 - 2.1):1:(10 - 300). In some embodiments of the present disclosure, after the reaction is completed, for extraction, a mixture of a nonpolar solvent and water is added to the reaction solution, the upper organic phase is taken out and recrystallized to obtain an intermediate product. The nonpolar solvent includes one or more of ethyl acetate, ethyl ether, and dichloromethane. The solvent for recrystallization may be a mixture of dichloromethane and n - hexane, a mixture of ethanol and water, or a mixture of methanol and water. In some embodiments, a small amount of triethylamine is added to the mixture of the first raw material, the second raw material, and the first solvent to adjust the mixture to be weakly alkaline.

[0065] Step 200: The intermediate product is hydrolyzed under acidic or alkaline conditions. After the reaction is completed, for extraction, a nonpolar solvent and an aqueous alkali solution are added, an aqueous acid solution is added to the extracted aqueous phase solution, and the precipitate is filtered and washed to obtain a catalyst. The aqueous alkali solution may be an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 1 mol / L to 5 mol / L. The aqueous acid solution may be an aqueous solution of hydrogen chloride with a concentration of 1 mol / L to 5 mol / L.

[0066] Please refer to FIG. 1. FIG. 1 is a schematic diagram of a method for preparing a catalyst according to the present disclosure. (A) of FIG. 1 is a schematic diagram of a method for preparing the compound shown in formula (1 - 1). (B) of FIG. 1 is a schematic diagram of a method for preparing the compound shown in formula (1 - 2). (C) of FIG. 1 is a schematic diagram of a method for preparing the compound shown in formula (1 - 3).

[0067] The present disclosure further provides a method for preparing a polyimide, which includes the following steps. The catalyst provided in the present disclosure is mixed with a diamine, a dianhydride, and a second solvent to conduct a second reaction to obtain a polyimide. Please refer to FIG. 2. FIG. 2 is a schematic diagram of a method for preparing a polyimide according to an embodiment of the present disclosure. In some embodiments of the present disclosure, the molar ratio of the diamine, the dianhydride, the catalyst, and the solvent is (0.95 to 1):(0.95 to 1):(0.0001 to 0.5):(25 to 200). In some embodiments, the molar ratio of the diamine, the dianhydride, the catalyst, and the solvent is (0.95 to 1):(0.95 to 1):(0.01 to 0.1):(50 to 150). In some embodiments of the present disclosure, first, the diamine, the catalyst, and the second solvent are mixed, and then the dianhydride is slowly added. In some embodiments of the present disclosure, the compound represented by formula (1-2) is used as the catalyst for the reaction, where the molar ratio of the diamine, the dianhydride, the catalyst, and the solvent is (0.95 to 1):(0.95 to 1):(0.05 to 0.3):(25 to 200).

[0068] In some embodiments of the present disclosure, the diamine includes one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1,3-diamino-2-methylpropane, N,N-bis(4-aminophenyl)-1,4-benzenediamine, and 9,9-bis(4-aminophenyl)fluorene; the dianhydride includes one or more of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-tetracarboxybenzophenone dianhydride, 3,3',4,4'-tetracarboxydiphenyl sulfone dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride, and 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride; the second solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. In some embodiments of the present disclosure, the temperature of the second reaction ranges from 60°C to 180°C, and the time of the second reaction ranges from 1 hour to 48 hours. Specifically, the temperature of the second reaction may be 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, or 180°C, but is not limited thereto. Specifically, the time of the second reaction may be 1 hour, 2 hours, 5 hours, 10 hours, 20 hours, 30 hours, or 48 hours, but is not limited thereto.

[0069] In some embodiments of the present disclosure, the method for preparing the polyimide includes the following steps.

[0070] Step 100: The diamine, the catalyst, and the second solvent are sequentially added to the reactor and stirred and mixed uniformly at -20°C to 25°C.

[0071] Step 200: The dianhydride is slowly added to the reactor, heated to 60°C to 180°C, and reacted for 1 hour to 48 hours.

[0072] Step 300: The reaction solution is cooled to room temperature, then a polar solvent is added to the reaction system, filtered, and dried to obtain a polyimide.

[0073] In some embodiments, the polar solvent includes one or more of methanol, ethanol, and water. In some embodiments, the compound represented by formula (1-2) is used as a catalyst for the reaction, the temperature of the second reaction is in the range of 60°C to 100°C, and the time of the second reaction is in the range of 8 hours to 15 hours.

[0074] The method for preparing the polyimide provided by the present disclosure is simple, whereby the polyimide can be prepared by a one-step reaction. The operation is simple, the conditions are mild, and there is no need to remove impurities after the reaction. The product has good performance and good application prospects.

[0075] Hereinafter, the technical solution of the present disclosure will be further described using a plurality of examples.

Example

[0076] The method for preparing the catalyst included the following steps.

[0077] 18.2 g of bis(3-(1,3-bis(dioxolane)phenyl)phosphonic acid chloride, 20.2 g of triethylamine, and 11 g of m-dihydroxybenzene were dissolved in 250 mL of tetrahydrofuran under nitrogen protection and stirred at 25°C for 6 hours. After the reaction was completed, water and ethyl acetate were added for extraction. The upper organic phase was taken out, dried over anhydrous sodium sulfate, then concentrated using a rotary evaporator, and then recrystallized with dichloromethane and n-hexane to obtain a pale yellow solid, that is, intermediate product 1. The reaction formula of the above reaction was as follows.

[0078] [Chemical formula]

[0079] 10 g of intermediate product 1 was dissolved in 50 mL of acetone to obtain a solution. 5 g of p-toluenesulfonic acid was added dropwise to this solution, heated to 50 °C, and stirred for 3 hours. Then, 8 g of chromium trioxide was added and continuously stirred. After 18 hours of reaction, dichloromethane and 1 mol / L aqueous sodium hydroxide solution were added for extraction. The aqueous phase was taken out. 1 mol / L aqueous hydrochloric acid solution was slowly added dropwise to the extracted aqueous solution, and then filtered to obtain a filter residue. The filter residue was washed three times with distilled water and then dried to obtain a white solid. The white solid was Catalyst 1. The reaction formula for the above reaction was as follows.

[0080] [Chemical formula]

[0081] The method for preparing polyimide includes the following steps.

[0082] 4.810 g of 4,4'-diaminodiphenyl ether, 0.025 g of Catalyst 1, and 190 g of N-methylpyrrolidone were sequentially added to a reactor, stirred, and then cooled to 0 °C. The structure of Catalyst 1 was shown in formula (A).

[0083] [Chemical formula]

[0084] 3,3',4,4'-benzophenone tetracarboxylic dianhydride was slowly added to the reactor. The reactor was heated to 120 °C and then stirred for 36 hours. After the reaction system was cooled to room temperature, methanol was added, filtered, and dried to obtain a polyimide solid.

Example

[0085] The method for preparing the catalyst included the following steps.

[0086] 13.5 g of bis(4-(1,4-cyano)phenylphosphonic acid chloride, 20.2 g of triethylamine, and 10.8 g of p-phenylenediamine were dissolved in 250 mL of tetrahydrofuran under nitrogen protection and stirred at 80 °C for 12 hours. After the reaction was completed, water and ethyl acetate were added for extraction. The upper organic phase was taken out, dried over anhydrous sodium sulfate, then concentrated using a rotary evaporator, and then recrystallized from dichloromethane and n-hexane to obtain a pale yellow solid, i.e., intermediate product 2. The reaction formula for the aforementioned reaction was as follows.

[0087]

Chemical formula

[0088] 10 g of intermediate product 2 was dissolved in 50 mL of 0.5 mol / L dilute hydrochloric acid and heated under reflux for 18 hours. Then, the heating was stopped. After the solution was cooled to room temperature, dichloromethane and 1 mol / L aqueous sodium hydroxide solution were added for extraction. The aqueous phase was taken out. 1 mol / L aqueous hydrogen chloride solution was slowly dropped into the extracted aqueous phase solution, and then filtered to obtain a filter residue. The filter residue was washed three times with distilled water and then dried to obtain a white solid. The white solid was catalyst 2. The reaction formula for the aforementioned reaction was as follows.

[0089]

Chemical formula

[0090] The method for preparing the polyimide includes the following steps.

[0091] 4.810 g of 4,4'-diaminodiphenyl ether, 0.025 g of Catalyst 2, and 190 g of N-methylpyrrolidone were sequentially added to the reactor, stirred, and then cooled to 0°C. The structure of Catalyst 2 was shown in formula (B).

[0092]

Chemical formula

[0093] 3,3',4,4'-Benzophenone tetracarboxylic dianhydride was slowly added to the reactor. The reactor was heated to 80°C and then stirred for 12 hours. After the reaction system was cooled to room temperature, methanol was added, filtered, and dried to obtain a polyimide solid.

Example

[0094] The method for preparing the catalyst included the following steps.

[0095] 16.8 g of bis(2-(1,2-methyl ester)phenylphosphonic acid chloride, 20.2 g of triethylamine, and 10.8 g of o-dihydroxybenzene were dissolved in 350 mL of ethyl ether under nitrogen protection and stirred at 0°C for 6 hours. After the reaction was completed, water and ethyl acetate were added for extraction. The upper organic phase was taken out, dried over anhydrous sodium sulfate, then concentrated using a rotary evaporator, and then recrystallized with dichloromethane and n-hexane to obtain a pale yellow solid, that is, Intermediate 3. The reaction formula for the above reaction was as follows.

[0096]

Chemical formula

[0097] 10 g of the intermediate product 3 was dissolved in 50 mL of 0.5 mol / L dilute hydrochloric acid and heated under reflux for 18 hours. Subsequently, the heating was stopped. After the solution was cooled to room temperature, dichloromethane and 1 mol / L aqueous sodium hydroxide solution were added for extraction. The aqueous phase was taken out. 1 mol / L aqueous hydrochloric acid solution was slowly dropped into the extracted aqueous phase solution and then filtered to obtain a filter residue. The filter residue was washed three times with distilled water and then dried to obtain a white solid. The white solid was catalyst 3. The reaction formula for the aforementioned reaction was as follows.

[0098]

Chemical formula

[0099] The method for preparing polyimide includes the following steps.

[0100] 4.810 g of 4,4'-diaminodiphenyl ether, 0.025 g of catalyst 3, and 190 g of N-methylpyrrolidone were sequentially added to the reactor, stirred, and then cooled to 0 °C. The structure of catalyst 3 was shown in formula (C).

[0101]

Chemical formula

[0102] 3,3',4,4'-benzophenone tetracarboxylic dianhydride was slowly added to the reactor. The reactor was heated to 100 °C and then stirred for 48 hours. After the reaction system was cooled to room temperature, methanol was added, filtered, and dried to obtain a polyimide solid.

Example

[0103] The method for preparing polyimide includes the following steps.

[0104] The difference between Example 4 and Example 2 is that the amount of Catalyst 2 added in Example 4 was 0.5 g. The polyimide solid was prepared by using the same method as in Example 2.

[0105] Comparative Example 1 The method for preparing polyimide includes the following steps.

[0106] 4.810 g of 4,4'-diaminodiphenyl ether, 0.025 g of isoquinoline, and 190 g of N-methylpyrrolidone were sequentially added to a reactor, stirred, and then cooled to 0°C.

[0107] 3,3',4,4'-Benzophenone tetracarboxylic dianhydride was slowly added to the reactor. The reactor was heated to 60°C and then stirred for 12 hours. After the reaction system was cooled to room temperature, methanol was added, filtered, and dried to obtain a polyimide solid.

[0108] Effect Example To verify the properties of the catalyst and polyimide prepared in the present disclosure, the present disclosure further provides effect examples.

[0109] 1) The structures of the intermediate products and catalysts obtained in Examples 1 to 3 were characterized by nuclear magnetic resonance, and the following results of hydrogen NMR spectra were obtained.

[0110] Intermediate Product 1: 1H NMR (500 MHz, chloroform-d) δ 7.58 (ddt, J = 7.6, 2.3, 1.2 Hz, 1H), 7.49 - 7.41 (m, 2H), 7.43 - 7.33 (m, 2H), 6.84 - 6.78 (m, 1H), 5.68 (d, J = 0.7 Hz, 1H), 4.08 - 3.95 (m, 6H).

[0111] Catalyst 1: 1H NMR (500 MHz, chloroform-d) δ 7.99 (td, J = 2.1, 1.2 Hz, 1H), 7.91 (ddd, J = 7.5, 2.1, 1.2 Hz, 1H), 7.64 (ddt, J = 7.8, 2.3, 1.2 Hz, 1H), 7.50 - 7.43 (m, 1H), 6.84 - 6.78 (m, 1H).

[0112] Intermediate Product 2: 1H NMR (500 MHz, chloroform-d) δ 7.70 - 7.62 (m, 2H), 7.57 - 7.51 (m, 2H), 6.89 (s, 1H).

[0113] Catalyst 2: 1H NMR (500 MHz, chloroform-d) δ 9.85 (s, 1H), 8.04 - 7.97 (m, 3H), 7.54 - 7.48 (m, 3H), 6.89 (s, 1H), 5.85 (s, 1H).

[0114] Intermediate Product 3: 1H NMR (500 MHz, chloroform-d) δ 7.91 - 7.85 (m, 1H), 7.55 - 7.45 (m, 2H), 7.36 - 7.29 (m, 1H), 7.08 - 6.95 (m, 1H), 3.89 (s, 2H).

[0115] Catalyst 3: 1H NMR (500 MHz, chloroform-d) δ 7.84 (ddd, J = 7.7, 4.0, 1.6 Hz, 1H), 7.57 - 7.49 (m, 1H), 7.43 (dt, J = 7.9, 1.3 Hz, 1H), 7.29 (td, J = 7.5, 1.5 Hz, 1H), 7.08 - 6.95 (m, 1H).

[0116] Polyimide of Comparative Example 1: 1H NMR (500 MHz, THF-d8) δ 8.48 (d, J = 1.7 Hz, 1H), 8.39 (d, 2H), 8.26 (d, 1H), 8.15 (ddd, 3H), 8.04 (d, 2H), 7.45 - 7.39 (m, 4H), 7.15 - 7.09 (m, 4H).

[0117] The degree of cyclization of the products obtained in Examples 1 to 4 and Comparative Example 1 was tested by hydrogen NMR spectrum (500 MHz, DMSO-d6). The non-cyclized chemical shift was 7.94 ppm and the cyclized chemical shift was 8.24 ppm. The degree of cyclization = integral value of cyclized chemical shift / (integral value of non-cyclized chemical shift + integral value of cyclized chemical shift). The test results are shown in Table 1.

[0118] 2) The film-forming properties of the polyimides obtained in Examples 1 to 4 and Comparative Example 1 were characterized using the following specific evaluation criteria and process. The wet film of the corresponding solution was prepared on a clean glass plate by coating and casting. The wet film was transferred to an oven and heated according to the following heating procedure for imidization: 80 °C / 2 hours, 120 °C / 1 hour, 160 °C / 1 hour, 180 °C / 1 hour, 240 °C / 1 hour, 280 °C / 1 hour, and 350 °C / 1 hour at a heating rate of 2 °C / minute. After the glass plate was cooled to room temperature, the glass plate coated with the polyimide film was immersed in deionized water, and the polyimide film was peeled off to obtain the corresponding self-supporting PI film. The evaluation of the film-forming properties is specifically as follows: When the film is formed as an integral film material on the glass, there are no cracks on the surface, and it remains intact after peeling, the film-forming property is very good. When the film is formed as an integral film material on the glass, there are no cracks on the surface, but it cannot maintain its intact state after peeling, the film-forming property is average. When the film is formed in fragments on the glass, the film cannot be formed. The test results are shown in Table 1.

[0119]

Table 1

[0120] As can be seen from Table 1, the polyimide prepared with the catalyst of the present disclosure has a higher degree of cyclization compared to the polyimide prepared with the catalyst of Comparative Example 1. The catalyst with the structure in Example 2 has more remarkable catalytic performance due to the electrical properties of the catalyst, and as a result, the polyimide has a higher degree of cyclization. The degree of cyclization of the polyimide in Example 3 is lower due to the steric hindrance effect of the catalyst. Regarding film formation, the catalyst as a small molecule in Comparative Example 1 hinders the cross-linking of the polyimide and thus affects the film formation effect, while the catalyst with a specific structure in the examples of the present disclosure can cross-link with the polyimide, promoting the film formation of the product and improving the film-forming property of the product. In Example 4, since the amount of the added catalyst is extremely large, under the same conditions, although the catalyst showed a cross-linking effect, the film material prepared due to the increase in polar groups is prone to water absorption, and the hardening of the film material becomes difficult due to the increase in small molecules in the solution. As a result, the film-forming property of the product decreases slightly.

[0121] The foregoing description is an exemplary embodiment of the present disclosure, but it should not be construed as limiting the scope of the present disclosure. Those skilled in the art should note that some improvements and modifications can be further made without departing from the principles of the present disclosure. These improvements and modifications shall be within the protection scope of the present disclosure.

Claims

1. A catalyst for synthesizing a polyimide, having a structural formula represented by formula (1): 【Chemical 1】 (In formula (1), R ３ is selected from O or NH; R ４ is selected from O or NH; Ar ２ is a substituted aryl group, and the substituent of the substituted aryl group has a carboxyl group; R ５ is selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group, and n is an integer from 1 to 4) A catalyst having the structural formula shown.

2. A catalyst for synthesizing the polyimide according to claim 1, having a structural formula represented by formula (1-1), formula (1-2), or formula (1-3): 【Chemical 2】

3. A catalyst for synthesizing the polyimide according to claim 2, having a molecular structural formula represented by formulas (A) to (C): [Chemical 3]

4. R ５ is selected from an alkyl group or an alkoxy group; one or more of the n Rs ５ among them are 【Chemical Formula 4】 is in the ortho or para position and / or one or more of the n Rs ５ is / are 【Chemical Formula 5】 A catalyst for synthesizing the polyimide according to claim 1, which is in the ortho position or para position of

5. The number of carbon atoms of the alkyl group is in the range of 1 to 10; the number of carbon atoms of the haloalkyl group is in the range of 1 to 10; the number of carbon atoms of the alkoxy group is in the range of 1 to 10; the number of carbon atoms of the ester group is in the range of 1 to 10. A catalyst for synthesizing the polyimide according to claim 1 or 4.

6. A method for preparing a catalyst for synthesizing a polyimide, comprising: Mixing a first raw material, a second raw material, and a first solvent to carry out a first reaction to obtain an intermediate product; Hydrolyzing the intermediate product to obtain the catalyst for synthesizing a polyimide, wherein the structural formula of the second raw material is represented by formula (2): The chemical formula of the first raw material is Ar １ ２ PCl (wherein Ar １ is a substituted aryl group, and the substituent of the substituted aryl group comprises one or more of cyano, 1,3-dioxolane, and methyl formate); [Chemical Formula 6] (In formula (2), R １ is selected from OH or NH ２ ; R ２ is selected from OH or NH ２ ; R ５ is selected from a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, an ester group, an alkyl group, an alkoxy group, or a haloalkyl group, and n is an integer from 1 to 4) A method as described.

7. A method for preparing a catalyst for synthesizing a polyimide according to claim 6, wherein the temperature of the first reaction is in the range of 0°C to 80°C, and the time of the first reaction is in the range of 2 hours to 48 hours.

8. A method for preparing a catalyst for synthesizing a polyimide according to claim 6 or 7, wherein the molar ratio of the first raw material, the second raw material, and the first solvent is (1.5 to 2.5):1:(10 to 300).

9. The second raw material comprises one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, m-dihydroxybenzene, p-dihydroxybenzene, and o-dihydroxybenzene. A method for preparing a catalyst for synthesizing a polyimide according to any one of claims 6 to 8.

10. A polyimide compound obtained by mixing a catalyst obtained by using the method for preparing a catalyst for synthesizing a polyimide according to any one of claims 1 to 5 or a catalyst for synthesizing a polyimide according to any one of claims 6 to 9, a diamine, a dianhydride, and a second solvent to carry out a second reaction.

11. The polyimide compound according to claim 10, wherein the molar ratio of the diamine, the dianhydride, the catalyst, and the second solvent is (0.95 to 1):(0.95 to 1):(0.0001 to 0.5):(25 to 200).

12. The polyimide compound according to claim 10 or 11, wherein the temperature of the second reaction is in the range of 60°C to 180°C, and the time of the second reaction is in the range of 1 hour to 48 hours.

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