A thermosetting polyimide and a method for preparing and using the same

Abstract

The application discloses a thermosetting polyimide and a preparation and application method thereof. The thermosetting polyimide resin has good performance, good heat resistance, high mechanical strength of a coating film and strong adhesion, and comprises the following steps: step 01, stirring and dissolving aromatic diamine into an organic solvent under the condition of nitrogen or argon and at 0 DEG C; step 02, adding aromatic dianhydride into the solution obtained in step 01, stirring for 2-4 hours at 30-35 DEG C, and mixing the solution; step 03, adding a blocking agent into the mixed solution obtained in step 02, and stirring for 16-18 hours; step 04, adding a dehydrating agent into the solution obtained in step 03, and refluxing for 4-6 hours at 150-200 DEG C to obtain a polyimide resin solution; step 05, mixing the polyimide resin solution obtained in step 04 with a cleaning agent to precipitate a solid; and step 06, heat-imidizing the solid obtained in step 05 to obtain the thermosetting polyimide resin.

Description

Technical Field

[0001] This invention relates to the field of special functional coating technology, and in particular to a thermosetting polyimide and its preparation and application methods. Background Technology

[0002] Thermosetting polyimide resins originated in the 1960s, addressing the urgent need for high-temperature resistant materials in the aerospace field. Thermosetting polyimides are a class of prepolymers containing repeating imide rings in their main molecular chain and active groups in the main chain or side chains. They react under heating or photo-initiated action to form a cross-linked three-dimensional network structure, exhibiting excellent heat resistance, mechanical properties, dielectric properties, and molding processability. In the 21st century, with the development of industries such as electronics and new energy, the synthesis process and performance of thermosetting polyimides have been continuously optimized, leading to the emergence of novel systems such as bismaleimide (BMI) and acetylene-terminated polyimides.

[0003] The rigid, conjugated molecular chain structure and strong intermolecular interactions of thermosetting polyimides typically give them high heat resistance. However, their linear network structure results in high resin rigidity, poor solubility, and difficult processing, limiting their applications. Meanwhile, next-generation aerospace composite parts place even higher demands on temperature resistance and molding processes. Introducing isomers or side groups through copolymerization of thermosetting polyimides can improve their processability to some extent.

[0004] Phenylacetylene-based polyimides exhibit good long-term thermal oxidation stability. Their imide prepolymers are dissolved in organic solvents such as N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF) and used as adhesives. After heating and cross-linking curing, a highly cross-linked three-dimensional structure is formed, exhibiting excellent heat resistance. This makes it suitable for short-term high-temperature bonding conditions. Furthermore, since no volatiles are released during curing, it is suitable for large-area bonding, meeting the material requirements of the aerospace industry. While using phenylacetylene-based polyimides allows for low processing viscosity, it also results in a small molecular weight and high brittleness after curing. Summary of the Invention

[0005] This invention provides a thermosetting polyimide and its preparation and application methods to overcome the shortcomings of the prior art, and obtains a thermosetting polyimide with good heat resistance, high mechanical strength of the coating film, and strong adhesion.

[0006] In order to achieve the objectives of this invention, the following technologies are proposed: The first aspect provides a thermosetting polyimide with the following chemical structural formula: ; Where n ranges from 3 to 26; R1 is , , One of them; R2 is , , , , , One of them; Furthermore, it exhibits excellent solubility in polar aprotic solvents, with a dissolved solid content ≥20wt%.

[0007] Furthermore, the polar aprotic solvent includes any one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0008] This thermosetting polyimide also incorporates aromatic dianhydride groups with rotatable angles or steric hindrance. On the one hand, it can improve the flexibility of the chain segments and control the molecular weight by adjusting the number of repeating units, thus giving it certain melt processing properties. On the other hand, by introducing C=O, CF and other groups that can form chemical bonds with the surface groups of heterogeneous materials, it can increase the interfacial adhesion, improve the bonding strength and toughness, and especially significantly improve the peel strength while improving the heat resistance.

[0009] The second aspect provides a method for preparing thermosetting polyimide, including the following steps: Step 01: In a nitrogen or argon atmosphere at 0°C, add an aromatic diamine to an organic solvent and stir to dissolve it, obtaining a solution with a solid content of 15wt% to 20wt%. Step 02: Add aromatic dianhydride to the solution obtained in Step 01, and stir at 30°C to 35°C for 2 to 4 hours to obtain a mixed solution with a solid content of 18 wt% to 28 wt%. Step 03: Add the capping agent to the mixed solution obtained in Step 02 and stir the reaction for 16 to 18 hours. Step 04: Add a dehydrating agent to the solution obtained in Step 03. The mass ratio of the dehydrating agent to the total mass of the aromatic dianhydride monomer, aromatic diamine monomer and capping agent is 1:1. Reflux the reaction at a temperature of 150°C to 200°C for 4 to 6 hours to obtain a polyimide resin solution. Step 05: Mix the polyimide resin solution obtained in step 04 with a cleaning agent, wherein the mass ratio of the cleaning agent to the obtained polyimide resin solution is (4 to 8): 1, to precipitate a solid, and then dry it at 200°C to 280°C. Step 06: The solid obtained in step 05 is thermally imidized at 200°C to 280°C for 8 to 12 hours to obtain a thermosetting polyimide resin.

[0010] Furthermore, the molar ratio of the aromatic dianhydride monomer, the aromatic diamine monomer, and the capping agent is n:(n+1):2, where 5≤n≤10.

[0011] The chemical structural formula of the aromatic dianhydride monomer is: , , One of them.

[0012] The chemical structural formula of the aromatic diamine monomer is: , , , , One of them.

[0013] The capping agent is 4-phenylethynyl phthalic anhydride, and its chemical structural formula is: .

[0014] Furthermore, the organic solvent is one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and N,N-dimethylpropionamide.

[0015] Furthermore, the total solid content of the aromatic dianhydride monomer, the aromatic diamine monomer, and the capping agent is 20wt% to 30wt%.

[0016] Furthermore, the dehydrating agent is xylene.

[0017] Furthermore, the cleaning agent is one or a combination of two or more of ethanol, methanol, or acetone.

[0018] Furthermore, the drying temperature is 200–280°C.

[0019] On the other hand, a method for applying thermosetting polyimide is provided, in which thermosetting polyimide resin is dissolved in a polar aprotic solvent to obtain a resin solution, which is then kept at 80~100 ℃ for 12~18 h to allow the solvent to gradually evaporate, and then the temperature is raised to 350~360 ℃ and kept for 1~2 hours to cure in order to form a coating layer. The solid content of the resin solution is 20 wt% to 40 wt%.

[0020] Furthermore, the polar aprotic solvents are polar aprotic solvents such as N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0021] The advantages of the above technical solution are: First, the thermosetting polyimide resin cured product obtained by the present invention has good properties, good heat resistance, high mechanical strength of the coating film, strong adhesion, and the resulting film has good flexibility.

[0022] Secondly, the present invention has excellent film-forming properties and simple film-forming conditions.

[0023] Finally, the present invention has excellent solubility and can be dissolved at room temperature in protic solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), as well as low-boiling-point solvents such as tetrahydrofuran (THF). Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0025] Figure 1 These are the FT-IR spectra of the thermosetting polyimide resins prepared in Examples 1-6 of this invention.

[0026] Figure 2 These are test images of the cured thermosetting polyimide resins prepared in Examples 1-6 of this invention, showing their flexibility.

[0027] Figure 3 This is a DSC glass transition temperature test curve of the thermosetting polyimide resin prepared in Examples 1-6 of this invention.

[0028] Figure 4 This is a TGA curve of the cured thermosetting polyimide resin prepared in Examples 1-6 of this invention. Detailed Implementation

[0029] Example 1 The method for preparing thermosetting polyimide resin provided in this embodiment specifically includes the following steps: Under nitrogen protection, 184 g of N,N-dimethylformamide was added to a three-necked flask at 0 °C. 2,2'-bis(trifluoromethyl)diaminobiphenyl (22.42 g, 0.07 mol) was dissolved by stirring. Then, 18.61 g of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (0.06 mol) was added to the three-necked flask. The mixture was heated to 30 °C and stirred for 3 h to obtain a mixed solution. 4-phenylethynyl phthalic anhydride (4.96 g, 0.02 mol) was added as a capping agent to the mixed solution, and the mixture was stirred for 18 h to form a polyimide solution with a solid content of 20 wt%. Then, 45 g of xylene was added, and the temperature was raised to 150 °C. The mixture was refluxed at 150 °C for 6 h. After the reaction system cooled to room temperature, it was poured into ethanol. The process was repeated three times by filtration and washing, and then dried at 200 °C for 12 h to obtain thermosetting polyimide resin.

[0030] The structural formula of the 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride is as follows: ; The structural formula of the 2,2'-bis(trifluoromethyl)diaminobiphenyl is as follows: ; The structural formula of the thermosetting polyimide is: ; R2 is .

[0031] The thermosetting polyimide resin obtained above was dissolved in N,N-dimethylacetamide at a solid content of 30 wt%, placed in a crucible, and subjected to a programmed temperature rise method. First, the temperature was maintained at 90 °C for 16 h to allow the solvent to gradually evaporate. Then, the temperature was increased to 350 °C and maintained for 1 h to finally obtain the cured thermosetting polyimide resin.

[0032] Example 2 The method for preparing thermosetting polyimide resin provided in this embodiment specifically includes the following steps: Under nitrogen protection, 377 g of N,N-dimethylacetamide was added to a three-necked flask at 0 °C. 57.03 g (0.11 mol) of 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane was dissolved by stirring. Then, 32.22 g (0.10 mol) of 2,3,3',4'-benzophenone tetracarboxylic dianhydride was added to the three-necked flask. The mixture was heated to 30°C and stirred for 4 hours to obtain a mixed solution. 4-Phenylacetyl phthalic anhydride (4.96 g, 0.02 mol) was added as a capping agent, and the mixture was stirred for 16 hours to form a polyimide solution with a solid content of 20 wt%. Then, 90 g of xylene was added, and the temperature was raised to 160°C. The mixture was refluxed at 160°C for 5 hours. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, and washed three times. Finally, it was dried at 220°C for 10 hours to obtain a thermosetting polyimide resin.

[0033] The structural formula of the 2,3,3',4'-benzophenone tetracarboxylic dianhydride is as follows: ; The structural formula of the 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane is as follows: ; The structural formula of the thermosetting polyimide is: ; R2 is .

[0034] The thermosetting polyimide resin obtained above was dissolved in N,N-dimethylformamide at a solid content of 20 wt%, placed in a crucible, and subjected to a programmed temperature rise method. First, the temperature was maintained at 80 °C for 16 h to allow the solvent to gradually evaporate, then the temperature was increased to 350 °C and maintained for 1.5 h to finally obtain the cured thermosetting polyimide resin.

[0035] Example 3 The method for preparing thermosetting polyimide resin provided in this embodiment specifically includes the following steps: Under nitrogen protection, 171 g of N,N-dimethylformamide was added to a three-necked flask at 0 °C. 1,3-bis(3-aminophenoxy)benzene (26.31 g, 0.09 mol) was dissolved by stirring. Then, 2,3,3',4'-benzophenone tetracarboxylic dianhydride (25.78 g, 0.08 mol) was added to the three-necked flask, and the mixture was stirred at 35 °C for 4 h to obtain a mixed solution. 4-phenylethynyl phthalic anhydride (4.96 g, 0.02 mol) was added as a capping agent to the mixed solution, and the mixture was stirred for 16 h to form a polyimide solution with a solid content of 25 wt%. Then, 55 g of xylene was added, and the temperature was raised to 150 °C. The mixture was refluxed at 150 °C for 6 h. After the reaction system cooled to room temperature, it was poured into methanol, filtered, and washed three times. The mixture was then dried at 200 °C for 12 h to obtain thermosetting polyimide resin.

[0036] The structural formula of the 2,3,3',4'-benzophenone tetracarboxylic dianhydride is as follows: ; The structural formula of the 1,3-bis(3-aminophenoxy)benzene is as follows: ; The structural formula of the thermosetting polyimide is: ; R2 is .

[0037] The thermosetting polyimide resin obtained above was dissolved in dimethyl sulfoxide at a solid content of 20 wt%, placed in a crucible, and subjected to a programmed temperature rise method. First, the temperature was maintained at 100 °C for 16 h to allow the solvent to gradually evaporate. Then, the temperature was increased to 350 °C and maintained for 1.5 h to finally obtain the cured thermosetting polyimide resin.

[0038] Example 4 The method for preparing thermosetting polyimide resin provided in this embodiment specifically includes the following steps: Under nitrogen protection, 103 g of N,N-dimethylacetamide was added to a three-necked flask at 0 °C. 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (24.63 g, 0.06 mol) was dissolved by stirring. Then, 14.71 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (0.05 mol) was added to the three-necked flask, and the mixture was stirred at 30 °C for 2 h to obtain a mixed solution. 4-phenylethynyl phthalic anhydride (4.96 g, 0.02 mol) was added as a capping agent to the mixed solution, and the mixture was stirred for 18 h to form a polyimide solution with a solid content of 30 wt%. Then, 44 g of xylene was added, and the temperature was raised to 180 °C. The mixture was refluxed at 180 °C for 4 h. After the reaction system cooled to room temperature, it was poured into acetone, filtered, and washed three times. The mixture was then dried at 210 °C for 12 h to obtain thermosetting polyimide resin.

[0039] The structural formula of the 2,3,3',4'-biphenyltetracarboxylic dianhydride is as follows: ; The structural formula of the 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is as follows: ; The structural formula of the thermosetting polyimide is: ; R2 is .

[0040] The thermosetting polyimide resin obtained above was dissolved in N,N-dimethylformamide at a solid content of 40 wt%, placed in a crucible, and subjected to a programmed temperature rise method. First, the temperature was maintained at 100 °C for 12 h to allow the solvent to gradually evaporate. Then, the temperature was increased to 350 °C and maintained for 1 h to finally obtain the cured thermosetting polyimide resin.

[0041] Example 5 The method for preparing thermosetting polyimide resin provided in this embodiment specifically includes the following steps: Under nitrogen protection, 166 g of N,N-dimethylacetamide was added to a three-necked flask at 0 °C. 3,4'-diaminodiphenyl ether (16.02 g, 0.08 mol) was dissolved by stirring. Then, 2,3,3',4'-biphenyltetracarboxylic dianhydride (20.59 g, 0.07 mol) was added to the three-necked flask, and the mixture was stirred at 30 °C for 2 h to obtain a mixed solution. 4-phenylethynyl phthalic anhydride (4.96 g, 0.02 mol) was added as a capping agent to the mixed solution, and the mixture was stirred for 18 h to form a polyimide solution with a solid content of 20 wt%. Then, 40 g of xylene was added, and the temperature was raised to 180 °C. The mixture was refluxed at 180 °C for 4 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, and washed three times. The mixture was then dried at 230 °C for 10 h to obtain thermosetting polyimide resin.

[0042] The structural formula of the 2,3,3',4'-biphenyltetracarboxylic dianhydride is as follows: ; The structural formula of the 3,4'-diaminodiphenyl ether is as follows: ; The structural formula of the thermosetting polyimide is: ; R2 is .

[0043] The thermosetting polyimide resin obtained above was dissolved in N,N-dimethylpyrrolidone at a solid content of 40 wt%, placed in a crucible, and subjected to a programmed temperature rise method. First, the temperature was maintained at 100 °C for 14 h to allow the solvent to gradually evaporate. Then, the temperature was increased to 360 °C and maintained for 1 h to finally obtain the cured thermosetting polyimide resin.

[0044] Example 6 The method for preparing thermosetting polyimide resin provided in this embodiment specifically includes the following steps: Under nitrogen protection, 260 g of N,N-dimethylpyrrolidone was added to a three-necked flask at 0 °C. 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (33.62 g, 0.10 mol) was dissolved by stirring. Then, 2,3,3',4'-biphenyltetracarboxylic dianhydride (26.48 g, 0.09 mol) was added to the three-necked flask. The mixture was stirred at 30°C for 4 hours to obtain a mixed solution. 4-Phenylacetyl phthalic anhydride (4.96 g, 0.02 mol) was added to the mixed solution as a capping agent. The mixture was stirred for 16 hours to form a polyimide solution with a solid content of 20 wt%. Then, 65 g of xylene was added, and the temperature was raised to 200°C. The mixture was refluxed at 200°C for 5 hours. After the reaction system cooled to room temperature, it was poured into ethanol. The process was repeated three times by filtration and washing. The mixture was then dried at 280°C for 8 hours to obtain a thermosetting polyimide resin.

[0045] The structural formula of the 2,3,3',4'-biphenyltetracarboxylic dianhydride is as follows: ; The structural formula of the 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether is as follows: ; The structural formula of the thermosetting polyimide is: ; R2 is .

[0046] The thermosetting polyimide resin obtained above was dissolved in N,N-dimethylpyrrolidone at a solid content of 30 wt%, placed in a crucible, and subjected to a programmed temperature rise method. First, the temperature was maintained at 90 °C for 16 h to allow the solvent to gradually evaporate. Then, the temperature was increased to 350 °C and maintained for 1 h to finally obtain the cured thermosetting polyimide resin.

[0047] The thermosetting polyimide resins prepared in Examples 1 to 6 were subjected to FT-IR spectroscopy and glass transition temperature tests. The cured products were also tested for flexibility, thermal stability, shear strength, adhesion, and peel strength, as shown in the table below. Figures 1-4 As shown. The test conditions for each performance item are in accordance with the following standards (methods): 1. Infrared spectroscopy was performed using a Fourier transform infrared spectrometer with potassium bromide as the background and 32 scans.

[0048] 2. Glass transition temperature was determined using differential scanning calorimetry (DSC). Test temperature range: from room temperature to 350℃; heating rate: 10℃ / min; test atmosphere: nitrogen.

[0049] 3. Thermal stability: The test was conducted using a thermogravimetric analyzer (TGA). Heating rate: 20℃ / min; Test atmosphere: air.

[0050] 4. Flexibility: GB / T 1731-2020 Test method for flexibility of paint film and putty film; Material: tinplate sheet.

[0051] 5. Shear strength: GB / T 7124-2008 Determination of tensile shear strength of adhesives; Material: Stainless steel.

[0052] 6. Adhesion: GB / T 5210-2006 Paint and Varnish Pull-Off Test; Material: Copper Alloy.

[0053] 7. Peel strength: GB / T 7122-2025 Determination of peel strength of high-strength adhesives (floating roller method); Material: Stainless steel.

[0054] Table 1 Test Standards and Results The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A thermosetting polyimide, characterized by, Its chemical structural formula is: Where n ranges from 3 to 26; R1 is , , One of them; R2 is , , , , , One of them.

2. The thermosetting polyimide according to claim 1, characterized in that, The dissolved solids content in polar aprotic solvents is ≥20wt%.

3. The thermosetting polyimide according to claim 2, characterized in that, Polar aprotic solvents include any one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

4. A method for preparing a thermosetting polyimide as described in any one of claims 1 to 3, characterized in that, Including the following steps: Step 01: In a nitrogen or argon atmosphere at 0°C, add an aromatic diamine to an organic solvent and stir to dissolve it, obtaining a solution with a solid content of 15wt% to 20wt%. Step 02: Add aromatic dianhydride to the solution obtained in Step 01, and stir at 30°C to 35°C for 2 to 4 hours to obtain a mixed solution with a solid content of 18 wt% to 28 wt%. Step 03: Add the capping agent to the mixed solution obtained in Step 02 and stir the reaction for 16 to 18 hours. Step 04: Add a dehydrating agent to the solution obtained in Step 03, and reflux the reaction at a temperature of 150°C to 200°C for 4 to 6 hours to obtain a polyimide resin solution. Step 05: Mix the polyimide resin solution obtained in step 04 with the cleaning agent to precipitate the solid, and dry it at 200°C to 280°C. Step 06: The solid obtained in step 05 is thermally imidized at 200°C to 280°C for 8 to 12 hours to obtain a thermosetting polyimide resin.

5. The method for preparing thermosetting polyimide according to claim 4, characterized in that, The molar ratio of aromatic dianhydride monomer, aromatic diamine monomer and capping agent is n:(n+1):2, where 5≤n≤10.

6. The method for preparing thermosetting polyimide according to claim 4, characterized in that, The chemical structural formula of the aromatic dianhydride monomer is: , , One of them; The chemical structural formula of the aromatic diamine monomer is: , , , , One of them; The capping agent is 4-phenylethynyl phthalic anhydride, and its chemical structural formula is: ; Furthermore, the total solid content of the aromatic dianhydride monomer, aromatic diamine monomer, and capping agent is 20wt% to 30wt%.

7. The method for preparing thermosetting polyimide according to claim 4, characterized in that, The organic solvent is one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-diethylacetamide, and N,N-dimethylpropionamide.

8. The method for preparing thermosetting polyimide according to claim 4, characterized in that, The dehydrating agent is xylene, and the mass ratio of the dehydrating agent to the total mass of the aromatic dianhydride monomer, aromatic diamine monomer, and capping agent is 1:

1.

9. The method for preparing thermosetting polyimide according to claim 4, characterized in that, The cleaning agent is one or a combination of two or more of ethanol, methanol or acetone, and the mass ratio of the cleaning agent to the obtained polyimide resin solution is (4 to 8):

1.

10. A method for applying the thermosetting polyimide as described in any one of claims 1 to 3, characterized in that, Thermosetting polyimide resin is dissolved in a polar aprotic solvent to obtain a resin solution, which is then kept at 80~100 ℃ for 12~18 h to allow the solvent to gradually evaporate. Then, the temperature is raised to 350~360 ℃ and kept for 1~2 hours to cure the coating. The solid content of the resin solution is 20 wt% to 40 wt%.

Images