A method for preparing thermosetting polyimide resin prepolymer

Abstract

The invention discloses a method for preparing a thermosetting polyimide resin prepolymer, and belongs to the technical field of polymer materials. The preparation process of the preparation method is as follows: first, dianhydride monomer and end-capping agent are esterified into carboxylic acid ester in a low-boiling alcohol solvent, diamine monomer is added for dissolution, a polyimide monomer mixture solution is obtained, propylene glycol is added, the temperature is increased for polymerization reaction, and the solution is obtained by filtering, washing with water, and drying. The invention prepares a thermosetting polyimide resin by using propylene glycol as a solvent instead of a traditional organic non-protonic polar solvent, which not only avoids the use of highly corrosive non-protonic polar solvents and benzene dehydrating agents with carcinogenic risks, but also reduces production costs. At the same time, the obtained thermosetting polyimide prepolymer has good processing performance before curing and cross-linking, and has excellent thermal stability after curing and cross-linking.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a method for preparing a thermosetting polyimide resin prepolymer. Background Art

[0002] Polyimide resin refers to a class of polymers containing imide rings on the main chain of the molecule. Due to the special chemical structure of aromatic heterocyclic rings on the main chain, polyimide resin has excellent thermal stability, solvent resistance and dimensional stability. It can be used as a matrix resin for special engineering plastics, high temperature resistant adhesives, and high temperature resistant composite materials. Therefore, it is widely used in aerospace, rail transportation, weapons and equipment, automobiles and electronics industries. With the rapid development of science and technology, the functions of thermosetting polyimide resins have gradually diversified, and its application fields will be further broadened, bringing more convenience and benefits to people's production and life. However, at present, the polymerization of polyimide resins usually requires the use of non-protonic polar solvents and benzene dehydrating agents. Non-protonic polar solvents are extremely corrosive to ordinary plastics, rubbers and other materials, and have high requirements for sealing devices during the production process. In addition, benzene dehydrating agents have carcinogenic risks and are volatile, which has a great impact on the environment and human health.

[0003] Based on this, it is very necessary to develop a preparation method of thermosetting polyimide resin prepolymer that is green, environmentally friendly, has low production cost and is suitable for large-scale industrial production, so as to eliminate the dependence on non-protonic polar solvents and benzene dehydrating agents, thereby reducing the negative impact on the environment and human health. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing a thermosetting polyimide resin prepolymer. The preparation method uses propylene glycol as a solvent instead of a traditional organic aprotic polar solvent to prepare a thermosetting polyimide resin, which not only avoids the use of highly corrosive aprotic polar solvents and benzene dehydrating agents with carcinogenic risks, but also reduces production costs. At the same time, the prepared thermosetting polyimide prepolymer has good processing properties before curing and cross-linking, and has excellent thermal stability after curing and cross-linking.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a thermosetting polyimide resin prepolymer comprises the following steps: firstly, dianhydride monomer and end-capping agent are esterified into carboxylic acid ester in a low-boiling alcohol solvent, diamine monomer is added to dissolve to obtain a polyimide monomer mixture solution, propylene glycol is added, the temperature is raised to carry out polymerization reaction, and the prepolymer is obtained by filtering, washing with water and drying.

[0007] As a preferred embodiment of the present invention, the preparation method specifically comprises the following steps:

[0008] S1. Under the protection of inert gas, add the dianhydride monomer and the end-capping agent to a low-boiling alcohol solvent, heat it up and stir it thoroughly to esterify and generate a carboxylic acid ester;

[0009] S2, after cooling to room temperature, add diamine monomer and stir thoroughly until dissolved, add glycerol and dispersant after dissolution, continue stirring to react, and obtain polyimide suspension after the reaction is completed;

[0010] S3, filtering the polyimide suspension, washing the filtered polyimide with deionized water, vacuum drying to constant weight, and grinding to obtain a thermosetting polyimide resin prepolymer.

[0011] As a preferred embodiment of the present invention, the dianhydride monomer in step S1 is a mixture of one or more of 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, hexafluorodianhydride, and 4,4'-phenylenedioxydiphthalic anhydride; the end-capping agent is 4-phenylethynylphthalic anhydride (4-PEPA); and the low-boiling alcohol solvent is a mixture of one or more of methanol, ethanol, and isopropanol.

[0012] As a preferred embodiment of the present invention, the temperature of the esterification reaction in step S1 is 60-100° C., and the stirring time is 2-12 h.

[0013] As a preferred embodiment of the present invention, the amount of the low-boiling point alcohol solvent added in step S1 is 40-60% of the total mass of the reaction system.

[0014] As a preferred embodiment of the present invention, the inert gas in step S1 is nitrogen or argon.

[0015] As a preferred embodiment of the present invention, the molar ratio of the diamine monomer to the dianhydride monomer and the end-capping agent in step S2 is dianhydride monomer:diamine monomer:end-capping agent=n:(n+1):2, wherein n=0-30.

[0016] As a preferred embodiment of the present invention, the amount of glycerol added in step S2 is 2 to 10 times the total mass of the dianhydride monomer, the diamine monomer and the end-capping agent; the amount of the dispersant added is 0.1 to 20% of the total mass of the dianhydride monomer, the diamine monomer and the end-capping agent.

[0017] As a preferred embodiment of the present invention, the diamine monomer in step S2 is one or a mixture of 3,3'-oxydianiline, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether (4,4'-ODA), 2,2'-bis(trifluoromethyl)diaminobiphenyl, 1,3-bis(4'-aminophenoxy)benzene and 1,3-bis(3-aminophenoxy)benzene; and the dispersant is polyvinyl pyrrolidone.

[0018] As a preferred embodiment of the present invention, in step S2, the dissolution temperature is 50-90° C., and the stirring time is 1-4 h; the reaction temperature is 140-250° C., and the reaction time is 2-24 h.

[0019] As a preferred embodiment of the present invention, the washing times of deionized water in step S3 is 3 to 10 times, and the vacuum drying conditions are: drying temperature is 60 to 200° C., vacuum degree is -0.05 to -0.1 MPa, and drying time is 1 to 12 hours.

[0020] The present invention also provides a thermosetting polyimide resin prepolymer prepared according to the above preparation method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Compared with the traditional method of using a non-protonic polar solvent and a benzene dehydrating agent to prepare a thermosetting polyimide prepolymer, the preparation method of the present invention uses propylene glycol as a polymerization solvent and utilizes its high boiling point characteristics to prepare the thermosetting polyimide prepolymer, and adds a dispersant in the preparation process to prevent solids precipitated during the polymerization process from agglomerating, so that polymerization can be completed directly in a solution. The prepared thermosetting polyimide prepolymer is a low molecular weight prepolymer before curing and cross-linking, and has good solubility and melt viscosity; the thermosetting polyimide prepolymer has high mechanical properties and temperature resistance after curing and cross-linking, and its performance is almost no different from that of a thermosetting polyimide resin prepared by a traditional method, and can be used as a matrix resin for engineering plastics, adhesives, and high-temperature resistant composite materials. Moreover, the production process does not require the use of highly corrosive organic non-protonic polar solvents and volatile and toxic benzene dehydrating agents, which is more environmentally friendly and can effectively reduce the negative impact on the environment and human health. At the same time, compared with non-protonic polar solvents and benzene dehydrating agents, propylene glycol has a high boiling point, is cheaper, is safer, is easy to handle, has low production costs, and is suitable for large-scale production. Therefore, it is of great significance to disperse and polymerize thermosetting polyimide resin prepolymers in propylene glycol. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The infrared characteristic peak spectra of the thermosetting polyimide resin prepolymer prepared in Example 1 and Comparative Example 1 of the present invention are shown.

[0024] Figure 2The rheological curves of the thermosetting polyimide resin prepolymers prepared in Example 1 and Comparative Example 1 of the present invention are shown.

[0025] Figure 3 The thermogravimetric curves of the thermosetting polyimide resin prepolymers prepared in Example 1 and Comparative Example 1 of the present invention are shown.

[0026] Figure 4 The dynamic thermomechanical properties curves of the thermosetting polyimide resin prepolymers prepared in Example 1 and Comparative Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific implementation modes.

[0028] A method for preparing a thermosetting polyimide resin prepolymer comprises the following steps:

[0029] S1. Under the protection of inert gas nitrogen or argon, add dianhydride monomer and end-capping agent to low-boiling alcohol solvent, raise the temperature to 60-100° C. and fully stir for 2-12 hours to esterify to form carboxylic acid ester; wherein the amount of low-boiling alcohol solvent added is 40-60% of the total mass of the reaction system.

[0030] S2. After cooling to room temperature, add diamine monomer and stir thoroughly at 50-90° C. for 1-4 hours until dissolved. After dissolved, add propylene glycol and dispersant. Connect an external water separator and continue stirring to react at 140-250° C. for 2-24 hours. After the reaction is completed, a polyimide suspension is obtained; wherein the molar ratio of diamine monomer to dianhydride monomer and end-capping agent is dianhydride monomer: diamine monomer: end-capping agent=n:(n+1):2, wherein n=0-30; the amount of propylene glycol added is 2-10 times the total mass of dianhydride monomer, diamine monomer and end-capping agent; the amount of dispersant added is 0.1-20% of the total mass of dianhydride monomer, diamine monomer and end-capping agent.

[0031] S3. Filter the polyimide suspension, wash the filtered polyimide with deionized water for 3 to 10 times, and vacuum dry it to constant weight under the conditions of a drying temperature of 60 to 200° C., a vacuum degree of -0.05 to -0.1 MPa, and a drying time of 1 to 12 hours to ensure that the moisture is completely removed, and grind and pulverize the blocky polyimide resin prepolymer to obtain a thermosetting polyimide resin prepolymer powder.

[0032] In the above preparation method, the dianhydride monomer includes but is not limited to 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (a-BPDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-oxydiphthalic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic acid dianhydride, hexafluorodianhydride, 4,4'-phenylenedioxydiphthalic anhydride. The end-capping agent is preferably 4-phenylethynylphthalic anhydride (4-PEPA). Low-boiling alcohol solvents include but are not limited to methanol, ethanol, and isopropanol. Diamine monomers include but are not limited to 3,3'-oxydiphenylamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether (4,4'-ODA), 2,2'-bis(trifluoromethyl)diaminobiphenyl, 1,3-bis(4'-aminophenoxy)benzene and 1,3-bis(3-aminophenoxy)benzene. The dispersant is preferably polyvinylpyrrolidone.

[0033] The present invention will be further described below in conjunction with specific embodiments and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0034] Example 1

[0035] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0036] S1. Add 29.422 g of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (0.1 mol), 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 80 g of anhydrous ethanol into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a condenser and a nitrogen inlet and outlet. Stir the reaction at 85°C for 4 hours until the solution is completely clear and transparent.

[0037] S2. After cooling to room temperature, add 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and stir at 80°C for 2 h to form a polyimide monomer mixture solution. After the solution is cooled to room temperature, connect a water separator to the three-necked flask, then add 200 g of propylene glycol and 10 g of polyvinyl pyrrolidone, and react at 240°C for 12 h.

[0038] S3, after the polyimide suspension in the reactor is cooled to below 50°C, the solid is collected by filtration, the collected solid is poured into 500g of deionized water and stirred for 0.5h, then filtered, and the above operation is repeated 4 times. The solid is then vacuum dried at 180°C for 8h. Finally, the solid is ground into powder to obtain 71.22g of thermosetting polyimide resin prepolymer powder, with a yield of 91%.

[0039] Example 2

[0040] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0041] S1. Add 29.422 g of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (0.1 mol), 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 80 g of anhydrous ethanol into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a condenser and a nitrogen inlet and outlet. Stir the reaction at 85°C for 4 hours until the solution is completely clear and transparent.

[0042] S2. After cooling to room temperature, add 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and stir at 80°C for 2 h to form a polyimide monomer mixture solution. After the solution is cooled to room temperature, connect a water separator to the three-necked flask, then add 200 g of propylene glycol and 10 g of polyvinyl pyrrolidone, and react at 200°C for 12 h.

[0043] S3, after the polyimide suspension in the reactor is cooled to below 50°C, the solid is collected by filtration, the collected solid is poured into 500g of deionized water and stirred for 0.5h, then filtered, and the above operation is repeated 4 times. The solid is then vacuum dried at 150°C for 8h. Finally, the solid is ground into powder to obtain 68.09g of thermosetting polyimide resin prepolymer powder, with a yield of 87%.

[0044] Example 3

[0045] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0046] S1. Add 29.422 g of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (0.1 mol), 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 80 g of anhydrous ethanol into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a condenser and a nitrogen inlet and outlet. Stir the reaction at 85°C for 4 hours until the solution is completely clear and transparent.

[0047] S2. After cooling to room temperature, add 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and stir at 80°C for 2 h to form a polyimide monomer mixture solution. After the solution is cooled to room temperature, connect a water separator to the three-necked flask, then add 200 g of propylene glycol and 10 g of polyvinyl pyrrolidone, and react at 160°C for 12 h.

[0048] S3, after the polyimide suspension in the reactor is cooled to below 50°C, the solid is collected by filtration, the collected solid is poured into 500g of deionized water and stirred for 0.5h, then filtered, and the above operation is repeated 4 times. The solid is then vacuum dried at 150°C for 8h. Finally, the solid is ground into powder to obtain 66.52g of thermosetting polyimide resin prepolymer powder, with a yield of 85%.

[0049] Example 4

[0050] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0051] S1. Add 29.422 g of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (0.1 mol), 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 80 g of anhydrous ethanol into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a condenser and a nitrogen inlet and outlet. Stir the reaction at 85°C for 4 hours until the solution is completely clear and transparent.

[0052] S2. After cooling to room temperature, add 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and stir at 80°C for 2 h to form a polyimide monomer mixture solution. After the solution is cooled to room temperature, connect a water separator to the three-necked flask, then add 400 g of propylene glycol and 10 g of polyvinyl pyrrolidone, and react at 200°C for 6 h.

[0053] S3, after the polyimide suspension in the reactor is cooled to below 50°C, the solid is collected by filtration, the collected solid is poured into 500g of deionized water and stirred for 0.5h, then filtered, and the above operation is repeated 4 times. The solid is then vacuum dried at 180°C for 8h. Finally, the solid is ground into powder to obtain 65.72g of thermosetting polyimide resin prepolymer powder, with a yield of 84%.

[0054] Example 5

[0055] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0056] S1. Add 29.422 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (0.1 mol), 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 80 g of anhydrous ethanol into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a condenser and a nitrogen inlet and outlet. Stir the reaction at 85°C for 4 hours until the solution becomes completely clear and transparent.

[0057] S2. After cooling to room temperature, add 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and stir at 80°C for 2 h to form a polyimide monomer mixture solution. After the solution is cooled to room temperature, connect a water separator to the three-necked flask, then add 200 g of propylene glycol and 1 g of polyvinyl pyrrolidone, and react at 200°C for 12 h.

[0058] S3, after the polyimide suspension in the reactor is cooled to below 50°C, the solid is collected by filtration, the collected solid is poured into 500g of deionized water and stirred for 0.5h, then filtered, and the above operation is repeated 4 times. The solid is then vacuum dried at 150°C for 8h. Finally, the solid is ground into powder to obtain 66.52g of thermosetting polyimide resin prepolymer powder, with a yield of 85%.

[0059] Comparative Example 1

[0060] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0061] Into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a water separator, a condenser, and a nitrogen inlet and outlet, 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and 175 g of N-methylpyrrolidone (NMP) were added, and stirred under nitrogen protection until completely dissolved to obtain a homogeneous solution. Then, a slurry mixed with 29.422 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (0.1 mol) and 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 20 g of NMP was added to the above homogeneous solution, and the reaction was continued to stir at room temperature for 8 hours to obtain a polyamic acid resin solution with a solid content of 30%. 55 g of xylene was added to the above-mentioned polyamic acid resin solution, the reaction system was heated to 180°C, and after reflux reaction for 8 hours, the xylene was evaporated, the heating was stopped, the reaction solution was cooled to about 100°C and poured into a mixed solution of deionized water and ethanol to obtain a crude resin product, the crude resin product was repeatedly washed with a mixed solution of deionized water and ethanol and then filtered, and vacuum dried at 150°C for 8 hours to obtain 70.48 g of thermosetting polyimide resin prepolymer powder with a yield of 90%.

[0062] Figure 1 Display, wave number 2210cm -1 The characteristic absorption peak of phenylethynyl is 1780cm -1 and 1720cm -1 is the carbonyl absorption peak of the imide group, 1370 cm -1 The CN stretching peak of the imide ring is 745 cm -1 It is the C=O bending vibration absorption peak on the imide ring, which indicates that the thermosetting polyimide resin prepolymer prepared by the present invention has the same structure as the thermosetting polyimide resin prepolymer prepared by the traditional method. Figure 2 The rheological curve diagram shows that the melt viscosity change of the thermosetting polyimide resin prepolymer prepared by the present invention is the same as that of the thermosetting polyimide resin prepolymer prepared by the traditional method, proving that the processing performance is similar. Figure 3 The thermogravimetric curve diagram shows that the thermosetting polyimide resin prepolymer prepared by the present invention has the same thermogravimetric change as the thermosetting polyimide resin prepolymer prepared by the traditional method, and has similar thermal stability. Figure 4 The dynamic thermal mechanical performance curve diagram shows that the final cured product of the polyimide resin prepolymer prepared by the present invention has the same dynamic thermal stability as the final cured product of the polyimide resin prepolymer prepared by the traditional method, and has good heat resistance.

[0063] It can be seen that the thermosetting polyimide resin prepolymer prepared by the present invention has almost no difference in performance from the thermosetting polyimide resin prepared by the traditional method. The preparation method of the present invention does not need to use highly corrosive organic non-protonic polar solvents and volatile and toxic benzene dehydrating agents during the production process, has more environmental benefits, and can well reduce the negative impact on the environment and human health. At the same time, compared with non-protonic polar solvents and benzene dehydrating agents, propylene glycol has a high boiling point, is cheaper, has high safety, is easy to handle, has low production cost, and is suitable for large-scale production.

[0064] Comparative Example 2

[0065] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0066] Into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a water separator, a condenser, and a nitrogen inlet and outlet, 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and 175 g of NN dimethylacetamide (DMAc) were added, and stirred under nitrogen protection until completely dissolved to obtain a homogeneous solution. Then, a slurry mixed with 29.422 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (0.1 mol) and 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 20 g of DMAc was added to the above homogeneous solution, and the reaction was continued to be stirred at room temperature for 8 hours to obtain a polyamic acid resin solution with a solid content of 30%. 55 g of xylene was added to the above polyamic acid resin solution, the reaction system was heated to 180° C., and after reflux reaction for 8 hours, the xylene was evaporated, the heating was stopped, the reaction solution was cooled to about 100° C. and poured into a mixed solution of deionized water and ethanol to obtain a crude resin product. The crude resin product was repeatedly washed with a mixed solution of deionized water and ethanol and then filtered, and vacuum dried at 150° C. for 8 hours to obtain 68.91 g of thermosetting polyimide resin prepolymer powder with a yield of 88%.

[0067] Comparative Example 3

[0068] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0069] Into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a water separator, a condenser, and a nitrogen inlet and outlet, 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and 175 g of N-methylpyrrolidone (NMP) were added, and stirred under nitrogen protection until completely dissolved to obtain a homogeneous solution. Then, a slurry mixed with 29.422 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (0.1 mol) and 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 20 g of NMP was added to the above homogeneous solution, and the reaction was continued to stir at room temperature for 8 hours to obtain a polyamic acid resin solution with a solid content of 30%. 55 g of toluene was added to the above polyamic acid resin solution, the reaction system was heated to 180° C., and after reflux reaction for 8 hours, the toluene was evaporated, the heating was stopped, the reaction solution was cooled to about 100° C. and poured into a mixed solution of deionized water and ethanol to obtain a crude resin product. The crude resin product was repeatedly washed with a mixed solution of deionized water and ethanol and then filtered, and vacuum dried at 150° C. for 8 hours to obtain 66.50 g of thermosetting polyimide resin prepolymer powder with a yield of 85%.

[0070] Comparative Example 4

[0071] A method for preparing a thermosetting polyimide resin prepolymer, the preparation process of which is as follows:

[0072] S1. Add 29.422 g of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (0.1 mol), 24.823 g of 4-phenylethynylphthalic anhydride (0.1 mol) and 80 g of anhydrous ethanol into a three-necked round-bottom flask equipped with a mechanical stirring paddle, a condenser and a nitrogen inlet and outlet. Stir the reaction at 85°C for 4 hours until the solution is completely clear and transparent.

[0073] S2. After cooling to room temperature, add 30.036 g of 4,4-diaminodiphenyl ether (0.15 mol) and stir at 80°C for 2 h to form a polyimide monomer mixture solution. After the solution is cooled to room temperature, connect a water separator to the three-necked flask, then add 200 g of propylene glycol and 10 g of sodium dodecylbenzene sulfonate, and react at 240°C for 12 h.

[0074] S3, after the polyimide suspension in the reactor is cooled to below 50°C, the solid is collected by filtration, the collected solid is poured into 500g of deionized water and stirred for 0.5h, then filtered, and the above operation is repeated 4 times. The solid is then vacuum dried at 180°C for 8h. Finally, the solid is ground into powder to obtain 40.70g of thermosetting polyimide resin prepolymer powder, with a yield of 52%.

[0075] Thermosetting polyimide resin performance test

[0076] The performance of the thermosetting polyimide resins prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was tested. The test results are shown in Table 1.

[0077] Table 1 Performance data of thermosetting polyimide resin

[0078] project <![CDATA[η min a (Pa.s)]]> <![CDATA[T 5％ b (℃)]]> <![CDATA[T g c (℃)]]> Example 1 4.2 557 397 Example 2 4.3 555 396 Example 3 4.1 556 396 Example 4 4.2 555 395 Example 5 4.1 555 395 Comparative Example 1 4.3 555 395 Comparative Example 2 4.2 553 391 Comparative Example 3 4.5 550 390 Comparative Example 4 4.2 545 390

[0079] In the above table, a:η min is the minimum melt viscosity of the resin, and the test conditions are: strain 1%, angular frequency 10rad / s, and heating rate 4℃ / min. b:T 5％ The temperature at which the resin loses 5% of its weight by thermal decomposition in air atmosphere. The test conditions are: air flow rate of 25 ml / min, heating rate of 10°C / min, and test temperature of 100-800°C. c:T g is the glass transition temperature of the resin, T g The reading temperature is the peak temperature of the loss factor (tanδ), and the test conditions are: heating rate of 5°C / min, amplitude of 25μm, and frequency of 1Hz.

[0080] As shown in Table 1, the data of the minimum melt viscosity show that the melt viscosity change of the thermosetting polyimide resin prepolymer prepared by the present invention is the same as that of the thermosetting polyimide resin prepolymer prepared by the traditional method, proving that the processing performance is similar. The temperature of 5% weight loss by thermal decomposition in Table 1 shows that the thermosetting polyimide resin prepolymer prepared by the present invention and the thermosetting polyimide resin prepolymer prepared by the traditional method have the same thermal weight loss change and similar thermal stability. The glass transition temperature in Table 1 shows that the final cured product of the polyimide resin prepolymer prepared by the present invention has the same dynamic thermal stability as that of the final cured product of the polyimide resin prepolymer prepared by the traditional method, and has good heat resistance. By comparing Comparative Example 4 with Example 1, the thermal weight loss temperature of Comparative Example 4 has decreased and the yield has decreased significantly. This is because sodium dodecylbenzene sulfonate is used as a dispersant, and the poor dispersion effect leads to polymer agglomeration during the reaction, incomplete product reaction, reduced thermal weight loss temperature, and also affected the product yield.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Any non-substantial changes and replacements made by those skilled in the art on the basis of the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a thermosetting polyimide resin prepolymer, characterized in that: The preparation process is as follows: first, the dianhydride monomer and the end-capping agent are esterified into carboxylic acid ester in a low-boiling alcohol solvent, and the diamine monomer is added to dissolve to obtain a polyimide monomer mixture solution, and then propylene glycol is added, the temperature is increased to carry out polymerization reaction, and the product is obtained by filtering, washing with water, and drying.

2. The method for preparing a thermosetting polyimide resin prepolymer according to claim 1, characterized in that: The specific steps include: S1. Under the protection of inert gas, add the dianhydride monomer and the end-capping agent to a low-boiling alcohol solvent, heat it up and stir it thoroughly to esterify and generate a carboxylic acid ester; S2, after cooling to room temperature, add diamine monomer and stir thoroughly until dissolved, add glycerol and dispersant after dissolution, continue stirring to react, and obtain polyimide suspension after the reaction is completed; S3, filtering the polyimide suspension, washing the filtered polyimide with deionized water, vacuum drying to constant weight, and grinding to obtain a thermosetting polyimide resin prepolymer.

3. The method for preparing a thermosetting polyimide resin prepolymer according to claim 2, characterized in that: In step S1, the dianhydride monomer is a mixture of one or more of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, hexafluorodianhydride, and 4,4'-phenylenedioxydiphthalic anhydride; the end-capping agent is 4-phenylethynylphthalic anhydride; and the low-boiling point alcohol solvent is a mixture of one or more of methanol, ethanol, and isopropanol.

4. The method for preparing a thermosetting polyimide resin prepolymer according to claim 2, wherein: The temperature of the esterification reaction in step S1 is 60-100° C., and the stirring time is 2-12 hours.

5. The method for preparing a thermosetting polyimide resin prepolymer according to claim 2, wherein: The amount of the low boiling point alcohol solvent added in step S1 is 40-60% of the total mass of the reaction system.

6. The method for preparing a thermosetting polyimide resin prepolymer according to claim 1, wherein: The molar ratio of the diamine monomer to the dianhydride monomer and the end-capping agent in step S2 is dianhydride monomer: diamine monomer: end-capping agent = n: (n+1): 2, wherein n = 0-30.

7. The method for preparing a thermosetting polyimide resin prepolymer according to claim 1, characterized in that: In step S2, the amount of glycerol added is 2 to 10 times the total mass of the dianhydride monomer, the diamine monomer and the end-capping agent; the amount of the dispersant added is 0.1 to 20% of the total mass of the dianhydride monomer, the diamine monomer and the end-capping agent.

8. The method for preparing a thermosetting polyimide resin prepolymer according to claim 1, wherein: The diamine monomer in step S2 is one or a mixture of 3,3'-oxydiphenylamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 1,3-bis(4'-aminophenoxy)benzene and 1,3-bis(3-aminophenoxy)benzene; and the dispersant is polyvinyl pyrrolidone.

9. The method for preparing a thermosetting polyimide resin prepolymer according to claim 1, wherein: In step S2, the dissolution temperature is 50-90° C. and the stirring time is 1-4 h; the reaction temperature is 140-250° C. and the reaction time is 2-24 h.

10. The method for preparing a thermosetting polyimide resin prepolymer according to claim 1, characterized in that: In step S3, the washing times of deionized water are 3 to 10 times, and the vacuum drying conditions are: drying temperature is 60 to 200° C., vacuum degree is -0.05 to -0.1 MPa, and drying time is 1 to 12 hours.

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