A thermosetting polyimide resin, a method for preparing the same, and a composite material

Abstract

The application provides a thermosetting polyimide resin, a preparation method thereof and a composite material. The structural formula of the thermosetting polyimide resin is shown in the description. The thermosetting polyimide resin has good heat resistance, processability and mechanical toughness, and solves the technical problems of poor processability and toughness of the existing thermosetting polyimide composite material.

Description

Technical Field

[0001] This invention belongs to the field of high-performance polymer material synthesis technology, specifically relating to a high-toughness, easy-to-process, high-temperature resistant thermosetting polyimide resin, its preparation method, and composite materials. Background Technology

[0002] Thermosetting polyimides are a class of polymeric materials whose prepolymer structure contains active end-capping groups. After cross-linking and curing, the resin has a three-dimensional network structure, exhibiting excellent heat resistance, mechanical properties, and dielectric properties. They are widely used in aerospace, machinery, chemical engineering, microelectronics, and many other fields. However, due to the rigid structure of polyimides, they possess strong intramolecular / intermolecular forces. These factors make the imidized polyimide resin insoluble and infusible, resulting in poor processability. Therefore, the preparation of its composites is mostly achieved by impregnating fibers with polyamic acid or PMR solution precursors, leading to relatively high porosity in the composites and requiring costly autoclave processes. Furthermore, the heat resistance and toughness of polyimide resins are contradictory and difficult to achieve simultaneously. Chinese patent applications CN116574259A and CN114369243A, as well as the article "High performance imide oligomers and thermosets derived from 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride" (Polymer2023,281,126086), have reported the synthesis of polyimides using non-coplanar tortuous rigid fluorene structures. This results in thermosetting polyimide resins exhibiting high solubility and high heat resistance after imidization. However, the rigid fluorene structure of the monomers used leads to high melt viscosity, poor processability, and insufficient toughness in the cured material due to the inherent rigidity of the monomer structure. Therefore, developing a high-temperature resistant, high-toughness, and easily processable soluble polyimide resin suitable for low-cost molding processes is a pressing technical challenge. To date, no research has been found on the preparation of thermosetting polyimide resins using ether-containing fluorene dianhydride monomers. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention provides a thermosetting polyimide resin, its preparation method, and composite materials, thereby overcoming a series of technical challenges such as the contradiction between heat resistance and toughness, poor processing performance, high melt viscosity, and insufficient toughness of the cured material in existing polyimide resins.

[0004] This invention is achieved through the following technical solution:

[0005] A thermosetting polyimide resin having a structure as shown in formula (I):

[0006]

[0007] Where n is any positive number from 1 to 10, and each Ar independently has the structure shown in any of the following formulas:

[0008]

[0009] R represents the structure shown in any of the following formulas:

[0010]

[0011] The dashed lines represent the sites where amino groups are introduced.

[0012] Preferably, the dissolved solids content of the thermosetting polyimide resin in a polar aprotic solvent is greater than 30%;

[0013] And / or, the minimum melt viscosity of the thermosetting polyimide resin is 3 to 1254 Pa·s;

[0014] And / or, the cured thermosetting polyimide resin has a glass transition temperature of 335–425°C;

[0015] And / or, the cured thermosetting polyimide resin has a 5% thermal weight loss temperature in air of more than 520°C and an elongation at break of more than 2%.

[0016] The method for preparing the thermosetting polyimide resin includes:

[0017] S1, under a protective atmosphere, an aromatic diamine monomer, an ether-fluorene dianhydride monomer and an organic solvent are mixed and reacted at 95-105°C for 6-8 hours;

[0018] S2, add the capping agent to the mixed reaction system obtained in step S1, and continue the reaction at 95-105℃ for 2-4 hours;

[0019] S3, heat the reaction mixture obtained in step S2 to 195-205°C and continue the reaction for 4-6 hours;

[0020] S4. The reaction mixture obtained in step S3 is mixed with a cleaning agent to precipitate a solid. The solid is then washed and dried to obtain a thermosetting polyimide resin.

[0021] Preferably, in step S1, the ether-containing fluorene dianhydride monomer has a structure as shown in formula (II):

[0022]

[0023] Preferably, in step S1, the aromatic diamine monomer is any one or a combination of two or more of 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline], 1,3-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 9,9-bis(4-aminophenyl)fluorene, [1,1':3',1”-terphenyl]-4,4”-diamine, [1,1':3',1”-terphenyl]-3,3”-diamine, and [1,1':4',1”-terphenyl]-3,3”-diamine.

[0024] Preferably, in step S1, the molar ratio of the ether-fluorene dianhydride monomer, the aromatic diamine monomer, and the capping agent is n:(n+1):2, where n>0.

[0025] Preferably, in step S1, the organic solvent is any one or a combination of two or more of m-cresol and sulfolane.

[0026] Preferably, in step S2, the capping agent is any one of 4-phenylethynyl phthalic anhydride, ethynyl phthalic anhydride, and norbornene carboxylic anhydride;

[0027] And / or, in step S2, after adding the capping agent to the mixed reaction system obtained in step S1, the solid content in the obtained mixture is controlled at 20wt% to 40wt%, and the reaction continues for 2 to 4 hours.

[0028] Preferably, in step S4, the cleaning agent is one or more of methanol, ethanol, or deionized water;

[0029] And / or, in step S4, the drying temperature is 220–240°C.

[0030] The present invention also provides a polyimide resin-based composite material, comprising the thermosetting polyimide resin as described in any one of claims 1 to 2.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The thermosetting polyimide resin provided by this invention contains flexible ether bonds and a large-volume rigid non-coplanar fluorene group structure. The introduction of flexible ether bonds improves the segmental motion between molecular chains, thereby reducing the resin melt viscosity and improving the toughness of the cured resin. The large-volume fluorene group structure increases the inter-chain spacing, making it easier for solvent molecules to penetrate, while also possessing the characteristics of a rigid structure. Furthermore, since the flexible ether bonds and the rigid non-coplanar fluorene group structure reside on the same monomer, the high resin melt viscosity caused by monomer rigidity is avoided, resulting in a more robust polyimide resin. This thermosetting polyimide resin possesses high solubility and low viscosity, and its cured product exhibits high temperature resistance and high toughness. The dissolved solids content in polar aprotic solvents exceeds 30%, and the melt viscosity is adjustable within the range of 0–1500 Pa·s. The cured polyimide resin exhibits a 5% thermal weight loss temperature in air exceeding 520°C and an elongation at break greater than 2%. Therefore, this thermosetting polyimide resin combines excellent heat resistance, processability, and mechanical toughness, solving the technical challenges of difficult processing and poor toughness of the matrix resin in existing thermosetting polyimide composites. Composites based on this resin do not release small-molecule volatiles at high temperatures during molding, allowing for the production of low-porosity, large-thickness composite products using low-cost molding processes.

[0033] This invention innovatively uses ether-fluorene dianhydride monomers to prepare thermosetting polyimide resins. The introduction of flexible ether bonds improves chain segment movement between molecular chains, thereby reducing the resin melt viscosity and improving the toughness of the cured resin. The large-volume fluorene group structure increases the interchain spacing, making it easier for solvent molecules to penetrate, while also possessing the characteristics of a rigid structure. Furthermore, the flexible ether bonds and the rigid non-coplanar fluorene group structure reside on the same monomer, avoiding the problem of high resin melt viscosity caused by monomer rigidity. The resulting polyimide resin exhibits excellent heat resistance, processability, and mechanical toughness. This method employs a one-step process, directly preparing the polyimide resin in a reaction vessel without the need for any dehydrating agents or catalysts, making the process relatively simple. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is the FT-IR spectrum of the thermosetting polyimide resin prepared in Example 1 of this invention;

[0036] Figure 2 This is a DSC curve of the thermosetting polyimide resin prepared in Example 1 of the present invention;

[0037] Figure 3 This is a rheological curve of the thermosetting polyimide resin prepared in Example 1 of the present invention;

[0038] Figure 4 This is a DMA curve of the thermosetting polyimide resin prepared in Example 1 of the present invention;

[0039] Figure 5 This is a TGA curve of the cured thermosetting polyimide resin prepared in Example 1 of the present invention;

[0040] Figure 6 This is a diagram showing the mechanical properties of the thermosetting polyimide resin prepared in Example 1 of this invention;

[0041] Figure 7 This is a diagram showing the solubility of the thermosetting polyimide resin prepared in Example 1 of this invention in N-methylpyrrolidone, N,N-dimethylacetamide, tetrahydrofuran, and 1,4-dioxane. Detailed Implementation

[0042] In view of the deficiencies of the prior art, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention. The technical solution of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] This invention provides a thermosetting polyimide resin having a structure as shown in formula (I):

[0044]

[0045] Where n is any positive number from 1 to 10, and each Ar is independently structured as shown in any of the following formulas, that is, the Ar in each structural unit can be the same or different:

[0046]

[0047] R represents the structure shown in any of the following formulas:

[0048]

[0049] The dashed lines represent the sites where amino groups are introduced.

[0050] In the thermosetting polyimide resin described above in this invention, R is preferably:

[0051]

[0052] The thermosetting polyimide resin of this invention has a minimum melt viscosity of 3–1254 Pa·s; the glass transition temperature of the cured thermosetting polyimide resin is 335–425 °C; the dissolved solids content of the thermosetting polyimide resin in a polar aprotic solvent is greater than 30%; the cured thermosetting polyimide resin has a 5% thermal weight loss temperature in air higher than 520 °C and an elongation at break greater than 2%. The polar aprotic solvent is N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), tetrahydrofuran (DMF), or 1,4-dioxane (1,4-Dioxance).

[0053] The method for preparing the thermosetting polyimide resin of the present invention includes:

[0054] S1, under a protective atmosphere, an aromatic diamine monomer, an ether-fluorene dianhydride monomer and an organic solvent are mixed and reacted at 95-105°C for 6-8 hours;

[0055] S2, add the capping agent to the mixed reaction system obtained in step S1, and continue the reaction at 95-105℃ for 2-4 hours;

[0056] S3, heat the reaction mixture obtained in step S2 to 195-205°C and continue the reaction for 4-6 hours;

[0057] S4. Pour the reaction mixture obtained in step S3 into the cleaning agent and stir thoroughly. After the solid precipitates, filter, wash and dry to obtain thermosetting polyimide resin.

[0058] In some more specific embodiments, in step S1, the ether-containing fluorene dianhydride monomer has a structure as shown in formula (II):

[0059]

[0060] In some more specific embodiments, in step S1, the aromatic diamine monomer is one or a combination of two or more of the following: 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline], 1,3-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 9,9-bis(4-aminophenyl)fluorene, [1,1':3',1”-terphenyl]-4,4”-diamine, [1,1':3',1”-terphenyl]-3,3”-diamine, and [1,1':4',1”-terphenyl]-3,3”-diamine, with the structural formulas shown in formulas (III) to (XI) respectively.

[0061]

[0062] In some more specific implementation schemes, the molar ratio of the ether-fluorene dianhydride monomer, the aromatic diamine monomer, and the capping agent is n:(n+1):2, where n>0.

[0063] In some more specific implementations, in step S1, the organic solvent is any one or a combination of two or more of m-cresol and sulfolane, but is not limited thereto.

[0064] In some more specific implementations, in step S1, the protective atmosphere is a nitrogen atmosphere and / or an inert gas atmosphere.

[0065] Furthermore, the inert gas atmosphere is an argon atmosphere and / or a helium atmosphere, but is not limited thereto.

[0066] In some more specific implementation schemes, step S2 specifically includes: after the reaction in step S1 is completed, adding a capping agent to the obtained mixed reaction system, while controlling the solid content in the obtained mixture to be 20wt% to 40wt%, and continuing the reaction for 2 to 4 hours.

[0067] In some more specific embodiments, in step S2, the capping agent is any one of 4-phenylethynyl phthalic anhydride (4-PEPA), ethynyl phthalic anhydride (4-EPA), and norbornenedicarboxylic anhydride (NA). The structural formulas of 4-phenylethynyl phthalic anhydride, ethynyl phthalic anhydride, and norbornenedicarboxylic anhydride are shown in formulas (XII) to (XIV), respectively.

[0068]

[0069] In some more specific implementations, the drying temperature in step S4 is 220–240°C.

[0070] In some more specific implementations, in step S4, the theoretical degree of polymerization of the obtained thermosetting polyimide resin is 1 to 10.

[0071] Furthermore, in step S4, the cleaning agent is one or more of methanol, ethanol, or deionized water, and the amount used is 5 to 10 times that of the organic solvent in step S1.

[0072] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0073] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0074] Example 1

[0075] Under nitrogen protection, 5.6 g of [1,1':3',1”-terphenyl]-4,4”-diamine and 6.9116 g of ether-fluorene dianhydride monomer were added to a 100 ml reaction flask and placed in an oil bath. Then, 30 g of m-cresol was added, and the mixture was reacted at 95 °C for 6 h under mechanical stirring. Then, 5.3399 g of 4-PEPA and 10 g of m-cresol were added to adjust the solid content of the resulting solution to 30 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 190 °C and reacted for 6 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 240 °C for 2 h to obtain the thermosetting polyimide resin shown in formula (i).

[0076]

[0077] Structural characterization:

[0078] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 30% in the polar aprotic solvent N-methylpyrrolidone, a minimum melt viscosity of 3 Pa·s, a glass transition temperature of 385°C for the cured product, an elongation at break of 2.5%, and a 5% thermal weight loss temperature in air of 573°C.

[0079] Example 2

[0080] Under nitrogen protection, 8 g of 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] and 10.0018 g of ether-containing fluorene dianhydride monomer were added to a 100 ml reaction flask and placed in an oil bath. Then, 40 g of sulfolane was added, and the mixture was reacted at 100 °C for 6 h under mechanical stirring. Then, 1.5455 g of 4-PEPA and 10 g of m-cresol were added to adjust the solid content of the resulting solution to 28 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 195 °C and reacted for 5 h. After the reaction system was cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 220 °C for 3 h to obtain the thermosetting polyimide resin shown in formula (ii).

[0081]

[0082] Structural characterization:

[0083] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 33% in the polar aprotic solvent N,N-dimethylacetamide, a minimum melt viscosity of 205 Pa·s, a glass transition temperature of 342°C for the cured product, an elongation at break of 4.0%, and a 5% thermal weight loss temperature in air of 572°C.

[0084] Example 3

[0085] Under nitrogen protection, 3g of 1,3-phenylenediamine and 13.3704g of ether-fluorene dianhydride monomer were added to a 100ml reaction flask and placed in an oil bath. Then, 45g of m-cresol was added, and the mixture was reacted at 100℃ for 6h under mechanical stirring. Then, 3.4433g of 4-PEPA and 15g of m-cresol were added to adjust the solid content of the resulting solution to 30wt%. The reaction was continued for 4h. Then, under nitrogen protection, the reaction system was heated to 195℃ and reacted for 4h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 240℃ for 2h to obtain the thermosetting polyimide resin shown in formula (iii).

[0086]

[0087] Structural characterization:

[0088] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 35% in the polar aprotic solvent N-methylpyrrolidone, a minimum melt viscosity of 30 Pa·s, a glass transition temperature of 354°C for the cured product, an elongation at break of 3.4%, and a 5% thermal weight loss temperature in air of 568°C.

[0089] Example 4

[0090] Under nitrogen protection, 6 g of 2,2'-dimethyl-4,4'-diaminobiphenyl and 13.6217 g of ether-fluorene dianhydride monomer were added to a 250 ml reaction flask and placed in an oil bath. Then, 40 g of m-cresol was added, and the mixture was reacted at 105 °C for 6 h under mechanical stirring. Then, 3.5080 g of 4-PEPA and 20 g of m-cresol were added to adjust the solid content of the resulting solution to 30 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 195 °C and reacted for 6 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 220 °C for 4 h to obtain the thermosetting polyimide resin shown in formula (iv).

[0091]

[0092] Structural characterization:

[0093] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 36% in the polar aprotic solvent N-methylpyrrolidone, a minimum melt viscosity of 205 Pa·s, a glass transition temperature of 381°C for the cured product, an elongation at break of 3.5%, and a 5% thermal weight loss temperature in air of 563°C.

[0094] Example 5

[0095] Under nitrogen protection, 9 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether and 12.8996 g of ether-containing fluorene dianhydride monomer were added to a 250 ml reaction flask and placed in an oil bath. Then, 40 g of m-cresol was added, and the mixture was reacted at 95 °C for 4 h under mechanical stirring. Then, 3.3223 g of 4-PEPA and 18 g of m-cresol were added to adjust the solid content of the resulting solution to 30 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 195 °C and reacted for 5 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 230 °C for 2 h to obtain the thermosetting polyimide resin shown in formula (v).

[0096]

[0097] Structural characterization:

[0098] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 40% in the polar aprotic solvent N-methylpyrrolidone, a minimum melt viscosity of 102 Pa·s, a glass transition temperature of 346 °C for the cured product, an elongation at break of 3.8%, and a 5% thermal weight loss temperature in air of 564 °C.

[0099] Example 6

[0100] Under nitrogen protection, 4 g of 9,9-bis(4-aminophenyl)fluorene and 3.6885 g of ether-fluorene dianhydride monomer were added to a 100 ml reaction flask and placed in an oil bath. Then, 15 g of m-cresol was added, and the mixture was reacted at 100 °C for 6 h under mechanical stirring. Then, 2.8497 g of 4-PEPA and 8 g of m-cresol were added to adjust the solid content of the resulting solution to 30 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 200 °C and reacted for 4 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 240 °C for 2 h to obtain the thermosetting polyimide resin shown in formula (vi).

[0101]

[0102] Structural characterization:

[0103] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 30% in the polar aprotic solvent 1,4-dioxane, a minimum melt viscosity of 485 Pa·s, a glass transition temperature of 425°C for the cured product, an elongation at break of 2.8%, and a 5% thermal weight loss temperature in air of 568°C.

[0104] Example 7

[0105] Under nitrogen protection, 6 g of [1,1':3',1”-terphenyl]-3,3”-diamine and 13.1650 g of ether-fluorene dianhydride monomer were added to a 100 ml reaction flask and placed in an oil bath. Then, 40 g of sulfolane was added, and the mixture was reacted at 95 °C for 4 h under mechanical stirring. Then, 1.2714 g of 4-PEPA and 10 g of sulfolane were added to adjust the solid content of the resulting solution to 30 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 200 °C and reacted for 4 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 240 °C for 2 h to obtain the thermosetting polyimide resin shown in formula (vii).

[0106]

[0107] Structural characterization:

[0108] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 35% in the polar aprotic solvent N-methylpyrrolidone, a minimum melt viscosity of 1254 Pa·s, a glass transition temperature of 362°C for the cured product, an elongation at break of 3.6%, and a 5% thermal weight loss temperature in air of 570°C.

[0109] Example 8

[0110] Under nitrogen protection, 8 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 8.0268 g of ether-fluorene dianhydride monomer were added to a 250 ml reaction flask and placed in an oil bath. Then, 40 g of m-cresol was added, and the mixture was reacted at 100 °C for 4 h under mechanical stirring. Then, 4.3004 g of EPA and 8 g of m-cresol were added to adjust the solid content of the solution to 30 wt%. The reaction was continued for 4 h. Then, under nitrogen protection, the reaction system was heated to 195 °C and reacted for 6 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was dried at 230 °C for 2 h to obtain the thermosetting polyimide resin shown in formula (viii).

[0111]

[0112] Structural characterization:

[0113] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 32% in the polar aprotic solvent 1,4-dioxane, a minimum melt viscosity of 57 Pa·s, a glass transition temperature of 342°C for the cured product, an elongation at break of 2.6%, and a 5% thermal weight loss temperature in air of 535°C.

[0114] Example 9

[0115] Under nitrogen protection, 1.0097 g of 2,2'-dimethyl-4,4'-diaminobiphenyl, 2.9732 g of 1,3-phenylenediamine, and 12 g of ether-fluorene dianhydride monomer were added to a 100 ml reaction flask and placed in an oil bath. Then, 32 g of sulfolane was added, and the mixture was reacted at 95 °C for 4 h with mechanical stirring. Next, 2.3178 g of 4-PEPA and 10 g of sulfolane were added to adjust the solid content of the solution to 35 wt%, and the reaction was continued for another 4 h. Then, under nitrogen protection, the reaction system was heated to 195 °C and reacted for 5 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 2 h to obtain the thermally heated product shown in formula (ix).

[0116]

[0117] Structural characterization:

[0118] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 40% in the polar aprotic solvent N,N-dimethylacetamide, a minimum melt viscosity of 16 Pa·s, a glass transition temperature of 387°C for the cured product, an elongation at break of 3.2%, and a 5% thermal weight loss temperature in air of 555°C.

[0119] Example 10

[0120] Under nitrogen protection, 4.7571 g of 2,2'-dimethyl-4,4'-diaminobiphenyl and 12 g of ether-fluorene dianhydride monomer were added to a 100 ml reaction flask and placed in an oil bath. Then, 38 g of m-cresol was added, and the mixture was reacted at 100 °C for 4 h under mechanical stirring. Next, 1.8542 g of 4-PEPA and 5 g of m-cresol were added to adjust the solid content of the solution to 29 wt%. The reaction was continued for another 4 h. Then, under nitrogen protection, the reaction system was heated to 195 °C and reacted for 6 h. After the reaction system cooled to room temperature, it was poured into ethanol, filtered, washed, and repeated three times. The mixture was then dried at 240 °C for 2 h to obtain the thermosetting polyimide resin shown in formula (x).

[0121]

[0122] Structural characterization:

[0123] The thermosetting polyimide resin prepared in this embodiment has a dissolved solids content of 30% in the polar aprotic solvent N-methylpyrrolidone, a minimum melt viscosity of 963 Pa·s, a glass transition temperature of 335°C for the cured product, an elongation at break of 3.4%, and a 5% thermal weight loss temperature in air of 520°C.

[0124] Figure 1 This is the FT-IR spectrum of the thermosetting polyimide resin prepared in Example 1 of this invention, with a wavenumber of 2211 cm⁻¹. -1 The peak at this point corresponds to the C≡C stretching vibration of the phenylacetylene group, with a wavenumber of 1776 cm⁻¹. -1 and 1720cm -1 The peaks at 1370 cm⁻¹ represent the asymmetric and symmetric stretching vibrations of the carbonyl C=O group on the imide ring, respectively. -1 The peak represents the CN stretching vibration on the imide ring. This indicates that the thermosetting polyimide resin with the structure described in formula (I) has been successfully prepared by this invention.

[0125] Figure 2 This is a DSC curve of the thermosetting polyimide resin prepared in Example 1 of the present invention. The endothermic peak at 200-240°C represents the resin melting endothermic process, and the exothermic peak between 330°C and 430°C is attributed to the exothermic reaction of the crosslinking reaction of phenylacetylene phthalic anhydride end cap. The temperature range of the melting peak and the exothermic peak is >100°C, indicating that this type of resin has a wide processing window.

[0126] Figure 3 This is the rheological curve of the thermosetting polyimide resin prepared in Example 1 of the present invention. The lowest melt viscosity is 3 Pa·s at a temperature of about 330°C, indicating good processability and suitability for molding and autoclave processes.

[0127] Figure 4 This is the DMA curve of the thermosetting polyimide resin prepared in Example 1 of the present invention. The temperature at 385°C corresponds to the glass transition temperature of the cured resin.

[0128] Figure 5 This is a TGA curve of the cured thermosetting polyimide resin prepared in Example 1 of the present invention. It can be seen that the cured polyimide resin has a thermal decomposition temperature of up to 573°C at 5wt%, which shows that it has excellent heat resistance.

[0129] Figure 6 This is a mechanical property diagram of the thermosetting polyimide resin prepared in Example 1 of the present invention. It can be seen that the elongation at break of the cured polyimide resin is 2.5%, which indicates that it has relatively good mechanical properties.

[0130] Figure 7This is a solubility graph of the thermosetting polyimide resin prepared in Example 1 of the present invention in NMP, DMAC, DMF, and 1,4-dioxane. The solid content of each of them reaches 30%, indicating that the thermosetting polyimide resin of the present invention has the characteristic of high solubility and is a soluble thermosetting polyimide resin.

[0131] Performance discussion:

[0132] Table 1 lists the solubility, rheological properties, thermogravimetric temperature and elongation at break of typical examples 3-5 of the present invention and the previously reported thermosetting polyimides synthesized from fluorene dihydride (BPAF) and flexible diamine (4,4'-ODA). As can be seen from the table, the solubility, rheological properties, thermogravimetric temperature and elongation at break of examples 3-5 are all superior to those of the BPAF-4,4'-ODA (n=3) polyimide resin in the literature (Reference: Polymer 2023, 281, 126086).

[0133] Table 1. Data on the solubility, rheology, thermal weight loss, and elongation at break of polyimide resins

[0134]

[0135] The experimental results above show that the thermosetting polyimide resin of the present invention has the characteristics of high solubility and low viscosity, and good processability; furthermore, the cured thermosetting polyimide resin of the present invention has both good high temperature resistance and high toughness.

[0136] In addition, the present invention has also conducted experiments with other raw materials, process operations and process conditions described in this specification, with reference to the foregoing embodiments, and has obtained relatively ideal results in all cases.

[0137] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0138] The use of titles and sections in this invention is not intended to limit the invention; each section can be applied to any aspect, embodiment or feature of the invention.

[0139] Throughout this invention, wherever a composition is described as having, containing, or including specific components, or wherever a process is described as having, containing, or including specific process steps, it is contemplated that the compositions taught in this invention are also substantially composed of or consisting of the described components, and that the processes taught in this invention are also substantially composed of or consisting of the described process steps.

[0140] It should be understood that the order of the steps or the order in which specific actions are performed is not particularly important, as long as the teachings of this invention remain operable. Furthermore, two or more steps or actions can be performed simultaneously.

[0141] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.

Claims

1. A thermosetting polyimide resin, characterized in that, The thermosetting polyimide resin has a structure as shown in formula (I): （I） Where n is any positive number from 1 to 10, and Ar independently has the structure shown in any of the following formulas: R represents the structure shown in any of the following formulas: The dashed lines represent the sites where amino groups are introduced; The cured thermosetting polyimide resin has a 5% thermal weight loss temperature in air of higher than 520°C and an elongation at break of greater than 2%; the cured thermosetting polyimide resin has a glass transition temperature of 335~425°C. The method for preparing the thermosetting polyimide resin includes: S1, under a protective atmosphere, an aromatic diamine monomer, an ether-fluorene dianhydride monomer and an organic solvent are mixed and reacted at 95~105℃ for 6~8h; S2, add the capping agent to the mixed reaction system obtained in step S1, and continue the reaction at 95~105℃ for 2~4h; S3, heat the reaction mixture obtained in step S2 to 195~205℃ and continue the reaction for 4~6h; S4. The reaction mixture obtained in step S3 is mixed with a cleaning agent to precipitate a solid. The solid is then washed and dried to obtain a thermosetting polyimide resin.

2. The thermosetting polyimide resin according to claim 1, characterized in that, The thermosetting polyimide resin has a dissolved solids content of greater than 30% in a polar aprotic solvent; And / or, the minimum melt viscosity of the thermosetting polyimide resin is 3~1254 Pa•s.

3. The method for preparing the thermosetting polyimide resin according to any one of claims 1 to 2, characterized in that, include: S1, under a protective atmosphere, an aromatic diamine monomer, an ether-fluorene dianhydride monomer and an organic solvent are mixed and reacted at 95~105℃ for 6~8h; S2, add the capping agent to the mixed reaction system obtained in step S1, and continue the reaction at 95~105℃ for 2~4h; S3, heat the reaction mixture obtained in step S2 to 195~205℃ and continue the reaction for 4~6h; S4. The reaction mixture obtained in step S3 is mixed with a cleaning agent to precipitate a solid. The solid is then washed and dried to obtain a thermosetting polyimide resin.

4. The method for preparing the thermosetting polyimide resin according to claim 3, characterized in that, In step S1, the ether-containing fluorene dianhydride monomer has the structure shown in formula (II): (II).

5. The method for preparing the thermosetting polyimide resin according to claim 3, characterized in that, In step S1, the aromatic diamine monomer is any one or a combination of two or more of the following: 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline], 1,3-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 9,9-bis(4-aminophenyl)fluorene, [1,1':3',1''-terphenyl]-4,4''-diamine, [1,1':3',1''-terphenyl]-3,3''-diamine, and [1,1':4',1''-terphenyl]-3,3''-diamine.

6. The method for preparing the thermosetting polyimide resin according to claim 3, characterized in that, In step S1, the organic solvent is any one or a combination of two of m-cresol and sulfolane.

7. The method for preparing the thermosetting polyimide resin according to claim 3, characterized in that, In step S2, the capping agent is any one of 4-phenylethynyl phthalic anhydride, ethynyl phthalic anhydride, and norbornene carboxylic anhydride; And / or, in step S2, after adding the capping agent to the mixed reaction system obtained in step S1, the solid content in the obtained mixture is controlled at 20wt%~40wt%, and the reaction continues for 2~4h.

8. The method for preparing the thermosetting polyimide resin according to claim 3, characterized in that, In step S4, the cleaning agent is one or more of methanol, ethanol, or deionized water; And / or, in step S4, the drying temperature is 220~240℃.

9. A polyimide resin-based composite material, characterized in that, Includes the thermosetting polyimide resin according to any one of claims 1 to 2.

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