Thermosetting polyimide resin and preparation method thereof

Abstract

The invention discloses thermosetting polyimide resin as well as a preparation method and application thereof. The thermosetting polyimide resin comprises the following structural formula: # imgabs0 #, wherein Ar is a dibasic anhydride monomer residue; n is an integer, and 1 < = n < = 10; m is an integer, and m > = 0; transverse lines'-'connected to the benzene ring can be connected to any carbon atom of the benzene ring; the preparation method comprises the following steps: S1, adding a biphenyl diamine-containing monomer into a polar aprotic solvent under the protection of inert gas, stirring and dissolving, then adding a binary anhydride monomer for reaction, and then adding phenylacetylene phthalic anhydride for blocking to obtain a polyamide acid solution; s2, finally, carrying out gradient heating and curing treatment on the polyamide acid solution; compared with the prior art, the resin material with high efficiency and low melt viscosity provided by the invention has better processability and heat resistance, and is widely applied to the fields of aerospace, electronic equipment and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide resin synthesis, and more particularly, to a thermosetting polyimide resin and a preparation method thereof. Background Art

[0002] Thermosetting polyimide composites, as advanced materials with high heat resistance, high specific strength, and good chemical stability, are widely used in high-tech fields such as aerospace, electronics, and military. Especially for continuous fiber-filled thermosetting polyimide composites, their excellent mechanical and heat resistance properties make them ideal engineering materials. To meet the high-performance requirements of these applications, the prepolymer (i.e., the state before curing) of the thermosetting polyimide matrix resin should have low melt viscosity and good solubility for easy processing and handling. At the same time, after curing, the resin should have a high glass transition temperature (Tg) and good toughness to ensure its good mechanical properties under high temperature and harsh environments.

[0003] For a long time, the research and development of thermosetting polyimide resins have mainly focused on resolving the contradiction between the properties before and after curing. Traditionally, the end-capping agents have gradually evolved from norbornene and ethynyl to phenylethynyl. Among them, phenylacetylene phthalic anhydride, as the most commonly used end-capping agent in high-temperature thermosetting polyimide resins, is often applied to the molecular structure design of resins. However, in the prior art, although some thermosetting polyimide resins have low solubility and melt viscosity and a high glass transition temperature after curing, the processability of these materials is often limited. Especially in the thermosetting polyimide resin synthesized from 2-phenyl-4,4'-diaminodiphenyl ether designed in the Chinese patent application with the application number CN201280013680.X, although the asymmetry of the benzene side group arrangement reduces the viscosity of the resin, the glass transition temperature after curing is low, which limits its application in high-temperature environments.

[0004] To solve this problem, a new type of thermosetting polyimide resin was proposed in the Chinese patent application with the application number CN201480026647.X. This resin copolymerizes a diamine containing a fluorene group with 2-phenyl-4,4'-diaminodiphenyl ether, successfully increasing the glass transition temperature after curing. However, this method has too high a melt viscosity before curing, resulting in poor processability and limiting its application in industrial production.

[0005] In summary, how to design the molecular structure to balance the low melt viscosity and good solubility of the prepolymer of thermosetting polyimide resin while ensuring that the resin has a high glass transition temperature after curing is still the key challenge in the molecular structure design of thermosetting polyimide resins at present. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a thermosetting polyimide resin to solve the problems of high melt viscosity before curing, poor processability, low glass transition temperature after curing, and insufficient heat resistance in the prior art, and to provide a thermosetting polyimide resin with both a biphenyl structure and a benzene side group.

[0007] To overcome the above defects of the prior art, the present invention provides a thermosetting polyimide resin, and the thermosetting polyimide resin has the following structural formula:

[0008] Wherein, Ar is a residue of a dianhydride monomer; n is an integer, and 1 ≤ n ≤ 10; m is an integer, and m ≥ 0; the horizontal lines "-" connected to the benzene ring all represent that they can be connected to any carbon atom of the benzene ring.

[0009] In a possible implementation manner, the Ar is at least one of the following structural formulas:

[0010] Wherein, the horizontal lines "-" connected to the benzene ring on the outside of each monomer all represent the connection bond between the Ar group and the carbon atom in the repeating unit; the horizontal lines "-" connected to the benzene ring on the inside of the monomer all represent that they can be connected to any carbon atom of the benzene ring.

[0011] Compared with the prior art, the thermosetting polyimide resin of the present application has the following advantages: the resin of the present invention improves the thermal properties of the cured resin by introducing a biphenyl structure into the diamine monomer, introduces a benzene ring side group to increase the asymmetry and randomness of the chain segment, breaks the regular arrangement of the chain segment, significantly improves the solubility of the prepolymer and reduces the melt viscosity, improves the processability, and the biphenyl structure significantly improves the thermal stability and heat resistance after curing by increasing the rigidity of the resin. At the same time, the introduction of the benzene ring side group makes the resin have a low melt viscosity before curing, improves the processability, the glass transition temperature (Tg) of the resin is high, and its thermal properties are greatly improved. By optimizing the molecular structure of the thermosetting polyimide resin, a good balance is achieved between the processability of the resin and the thermal properties after curing, providing a feasible technical solution for the preparation of high-temperature resin matrix composites and having a wide application prospect, and is particularly suitable for fields with high performance requirements such as aerospace and electronic packaging.

[0012] In a possible implementation manner, the Ar is at least one of the following groups:

[0013] Wherein, the horizontal lines "-" connected to the benzene ring on the outside of each monomer all represent the connection bond between the Ar group and the carbon atom in the repeating unit; the horizontal lines "-" connected to the benzene ring on the inside of the monomer all represent that they can be connected to any carbon atom of the benzene ring.

[0014] Compared with the prior art, by adopting the above technical solution, the glass transition temperature (Tg) of the resin after curing can be significantly increased by introducing the residue Ar of the dianhydride monomer with higher rigidity, optimizing the structural rigidity of the resin, enhancing the thermal stability and heat resistance of the resin. The structure with higher rigidity can strengthen the interaction between polymer chains, resulting in the inhibition of the movement between chain segments, so as to maintain good stability at high temperatures. The polyimide resin with the above structure can maintain excellent mechanical properties and thermal stability under high temperature conditions.

[0015] In a possible implementation manner, the Ar is at least one of the following groups:

[0016] Among them, each horizontal line "-" connected to the benzene ring on the outside of each monomer represents the bonding bond between the Ar group and the carbon atom in the repeating unit.

[0017] Compared with the prior art, by adopting the above technical solution, the above structure has strong rigidity and presents a non-planar structure. The non-planar structure can increase the degree of twisting of the molecular chain. The introduction of the non-planar structure makes the arrangement of the molecular chain more disordered, thereby reducing the regularity between molecules, enhancing the fluidity and solubility of the resin, and at the same time improving the melt processability of the resin, thus effectively improving the solubility of the polymer and reducing the melt viscosity of the polymer. This design not only improves the processing performance of the resin prepolymer (before curing), but also increases the glass transition temperature (Tg) of the polymer after curing. The rigidity and non-planar characteristics of the above technical solution structure of the present invention enable the cured resin to exhibit better thermal stability and heat resistance at high temperatures.

[0018] Another technical problem to be solved by the present invention is to provide a preparation method of a thermosetting polyimide resin to solve the problems of poor processability, too high melt viscosity and relatively low glass transition temperature after curing existing in the prior art.

[0019] To overcome the defects of the above prior art, the present invention provides a preparation method of a thermosetting polyimide resin, including the following steps: S1: Under the protection of inert gas, add the biphenyl diamine monomer into a polar aprotic solvent and stir to dissolve, then add the dianhydride monomer to react, and then add phenylacetylene phthalic anhydride for end-capping to obtain a polyamic acid solution; S2: Finally, perform gradient heating and curing treatment on the polyamic acid solution; The phenylacetylene phthalic anhydride includes the following structure:

[0020] The alkynyl group in phenylacetylene phthalic anhydride can undergo a curing reaction under heating conditions to form a crosslinked network structure. The molar ratio of the dianhydride monomer, the biphenyl diamine monomer-containing monomer, and phenylacetylene phthalic anhydride is n:(n + 1):2, where n > 0.

[0021] Compared with the prior art, the preparation method of the thermosetting polyimide resin in this application has the following advantages: Compared with the prior art, the preparation method of the present invention can effectively solve the problems of too high resin melt viscosity and poor processing performance existing in the traditional technology. By reasonably selecting the reaction of the diamine monomer containing a biphenyl structure with the dianhydride and combining the phenylacetylene phthalic anhydride end-capping technology, a crosslinked network structure can be formed through chemical reactions during the resin preparation process, optimizing the molecular structure of the resin, reducing the melt viscosity of the resin, and significantly improving its processing performance. At the same time, the end-capping effect of phenylacetylene phthalic anhydride also makes the finally obtained resin have higher thermal stability and glass transition temperature, meeting the use requirements under high-temperature environments. The preparation method of the present invention realizes that while the resin maintains good solubility and processability, the glass transition temperature after curing is significantly increased through reasonable design of reaction conditions and reasonable molecular structure regulation, thus effectively solving the contradiction between processability and high-temperature performance in the prior art and providing an excellent performance basis for the wide application of the resin.

[0022] In a possible implementation manner, in the step S1, the structural formula of the biphenyl diamine monomer-containing monomer is as follows:

[0023] Among them, the horizontal line "-" connected to the benzene ring on the inner side of the monomer represents that it can be connected to any carbon atom of the benzene ring, and m is an integer, m ≥ 0.

[0024] Compared with the prior art, adopting the above technical solution can optimize the performance of the thermosetting resin by introducing the combination of a biphenyl structure and a benzene ring side group into the diamine monomer. The biphenyl structure helps to improve the heat resistance of the cured resin, but it usually causes an increase in the melt viscosity of the prepolymer, thereby reducing the processing performance of the polymer. To solve this problem, the present invention connects the biphenyl structure with a single benzene ring through an ether bond to form an asymmetric structure. The design of this asymmetric structure enables the molecular chain to have a larger free volume, which helps to promote the fluidity of the molecular chain, thereby improving the processing performance and reducing the melt viscosity. In addition, the benzene ring side groups in the diamine structure are located on one side of the monomer, and after reacting with the dianhydride, the adjacent benzene ring side groups on the molecular chain are arranged with a high degree of randomness. For example, the arrangement of adjacent benzene ring side groups can be different arrangements such as "tail-tail", "tail-head", "head-tail", or "head-head". This random arrangement significantly increases the free volume of the molecular chain, thereby reducing the melting viscosity and enhancing the fluidity and processability of the resin. At the same time, the asymmetric structure in the diamine monomer enables the resin to exhibit more excellent performance during the processing compared with the traditional structure. Especially while maintaining high heat resistance, the solubility of the prepolymer is improved, and the technical problem of too high melt viscosity is solved.

[0025] In a possible implementation manner, in the step S1, the structure formula of the biphenyl diamine monomer-containing is one of the following structures:

[0026] In a possible implementation manner, in the step S1, the structure formula of the biphenyl diamine monomer-containing is one of the following structures:

[0027] In a possible implementation manner, in the step S2, the conditions for the curing treatment are: the curing temperature is 350-380 °C, and the time is 1-4 h.

[0028] Compared with the prior art, adopting the above technical solution can significantly improve the processing performance and heat resistance of the thermosetting polyimide resin. The above technical solution uses a diamine monomer containing a biphenyl structure, in which the biphenyl structure not only increases the rigidity of the molecular chain but also forms a large steric hindrance through its unique arrangement of benzene side groups. The presence of the benzene side groups effectively increases the free volume between the molecular chains, reduces the intermolecular interaction, and thus promotes the fluidity of the molecular chain.

[0029] In a possible implementation manner, the present invention also provides a further solution. A long carbon chain structure is connected to the above benzene ring side group, and the structure formula of the biphenyl diamine monomer-containing is one of the following structures:

[0030] Where n is an integer and n > 0; Compared with the prior art, adopting the above technical solution, further introducing a long carbon chain on the side group of the benzene ring significantly weakens the regularity of the molecular chain. By introducing a longer carbon chain, the symmetry and regularity between the molecular chains are destroyed, further increasing the free volume between the molecular chains. This structural adjustment effectively reduces the close packing between the molecular chains, making the molecular chains more fluid, thereby reducing the melt viscosity of the resin. The introduction of the long carbon chain makes the structure of the molecular chain more flexible, weakens the intermolecular interaction, and promotes the resin to be more easily flowable and plastic during the processing; it not only improves the processing performance of the resin, but also effectively reduces the solubility and processing temperature requirements of the thermosetting polyimide resin, while maintaining high heat resistance because the long carbon chain does not overly affect the rigidity of the resin, thus ensuring its high glass transition temperature and good thermal stability.

[0031] The present invention also provides an application of the above thermosetting polyimide resin in the preparation of fiber composites, and the fiber composites include at least one of carbon fiber composites, glass fiber composites, and quartz fiber composites. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the arrangement of the side groups of the benzene ring. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of the present application and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments according to needs to adapt to specific application scenarios.

[0034] The present invention provides a thermosetting polyimide resin, and the thermosetting polyimide resin includes the following structural formula: ; where Ar is a residue of a dianhydride monomer; n is an integer and 1 ≤ n ≤ 10; m is an integer and m ≥ 0; the horizontal line "-" connected to the benzene ring represents that it can be connected to any carbon atom of the benzene ring.

[0035] As a preferred solution, the Ar is at least one of the following structural formulas: Wherein, the horizontal line "-" connected to the outside of each monomer to the benzene ring represents the connection bond between the Ar group and the carbon atom in the repeating unit; the horizontal line "-" connected to the inside of the monomer to the benzene ring represents that it can be connected to any carbon atom of the benzene ring.

[0036] Compared with the prior art, the present invention has the following beneficial effects: In the design of diamine monomers, a biphenyl structure and a benzene side group are both introduced into the monomer structure. A series of thermosetting polyimide resins are obtained by polymerizing it with dianhydride and using phenylacetylene phthalic anhydride for end-capping. The thermosetting polyimide resin prepolymer has a lower melt viscosity and better solubility, and has a higher glass transition temperature after curing. Moreover, the resin of the present invention can be compounded with carbon fiber, glass fiber, quartz fiber, etc. to prepare advanced composite materials, which can be used in the fields of aerospace, etc.

[0037] As a preferred embodiment, the Ar is at least one of the following groups: Among them, each horizontal line “-” connected to the benzene ring on the outside of the monomer represents the bonding bond between the Ar group and the carbon atom in the repeating unit; each horizontal line “-” connected to the benzene ring on the inside of the monomer represents that it can be connected to any carbon atom on the benzene ring.

[0038] As a preferred embodiment, the Ar is at least one of the following groups: Among them, each horizontal line “-” connected to the benzene ring on the outside of the monomer represents the bonding bond between the Ar group and the carbon atom in the repeating unit.

[0039] The present invention also provides a preparation method of the thermosetting polyimide resin, including the following steps: S1: Under the protection of an inert gas, add the biphenyl diamine monomer to a polar aprotic solvent and stir to dissolve it, then add the dianhydride monomer for reaction, and then add phenylacetylene phthalic anhydride for end-capping to obtain a polyamic acid solution; S2: Finally, perform gradient heating and curing treatment on the polyamic acid solution; The phenylacetylene phthalic anhydride includes the following structure: ; The molar ratio of the dianhydride monomer, the biphenyl diamine monomer and the phenylacetylene phthalic anhydride is n:(n + 1):2, where n > 0.

[0040] As a preferred embodiment, in the step S1, the structural formula of the biphenyl diamine monomer is as follows: Among them, each horizontal line “-” connected to the benzene ring on the inside of the monomer represents that it can be connected to any carbon atom on the benzene ring, m is an integer, and m ≥ 0; The above diamine monomer of the present invention contains both a biphenyl structure and a benzene ring side group. The biphenyl structure helps to improve the heat resistance of the cured thermosetting resin, but it increases the melt viscosity of the prepolymer and reduces the processing performance of the polymer. By connecting the biphenyl structure to another benzene ring through an ether bond, the diamine monomer forms an asymmetric structure. The presence of the benzene ring side group on the single benzene ring can increase the free volume between molecular chains, promote the flow of molecular chains, improve the processing performance, and make up for the deficiency of the biphenyl structure in terms of processing performance; in addition, there is a very crucial point, that is, the benzene ring side group in the diamine structure is located on one side of the monomer. After reacting with the dianhydride, the arrangement of adjacent benzene ring side groups on the molecular chain is irregular (the schematic diagram of the benzene ring side group arrangement is as shown in Figure 1 ), for example: benzene ring side groups 1 and 2 belong to the tail-tail structure, benzene ring side groups 2 and 3 belong to the tail-head structure, benzene ring side groups 3 and 4 belong to the head-tail structure, and there are other arrangements such as head-head. Moreover, the arrangement of all adjacent benzene ring side groups is completely random, making the degree of randomness of the molecular chain very high, increasing the free volume, and the melt viscosity will be lower. Patent CN201280013680.X introduced that the benzene side group in 2-phenyl-4,4'-diaminodiphenyl ether can play such a role. In the molecular structure of this diamine monomer, in addition to the asymmetry of the benzene side group, there is also another asymmetric structure (that is, the two ends of the ether bond are respectively linked to the biphenyl and single benzene ring structures). Therefore, the whole monomer has higher asymmetry and better effect compared with 2-phenyl-4,4'-diaminodiphenyl ether.

[0041] As a preferred solution, in the step S1, the biphenyl-containing diamine monomer structural formula is one of the following structures: As a preferred solution, in the step S1, the biphenyl-containing diamine monomer structural formula is one of the following structures: .

[0042] The present invention also provides a synthesis method of the above biphenyl-containing diamine monomer. Taking as an example, the specific synthesis steps are as follows:

[0043] (1) Step 1: Preparation of nitrobenzene: Benzene undergoes a nitration reaction with concentrated nitric acid under the catalysis of concentrated sulfuric acid. The nitro group is introduced into the benzene ring to generate nitrobenzene. Reaction mechanism: The hydrogen on the benzene ring is protonated by sulfuric acid to generate an activated intermediate. The intermediate reacts with nitric acid to introduce a nitro group and generate nitrobenzene. The product needs to be purified to ensure high-purity meta-substituted bromonitrobenzene.

[0044] (2)Step 2: Meta-bromination of nitrobenzene: Nitrobenzene, bromine, iron powder, in a polar solvent (such as DMF or DMSO), heated to an appropriate temperature, to form meta-substituted bromonitrobenzene. Reaction mechanism: The electron-withdrawing effect of the nitro group activates the meta-position of the benzene ring, making it more prone to electrophilic substitution reactions. Bromine generates an active bromine intermediate under the catalysis of iron powder, attacks the meta-position of the benzene ring, substitutes the hydrogen atom, and forms a C-Br bond.

[0045] (3)Step 3: Para-phenyl substitution of m-bromonitrobenzene: m-bromonitrobenzene and phenylsodium, in a polar solvent (such as DMF), heated to an appropriate temperature, to form the target product. Reaction mechanism: The nitro group, as a strong electron-withdrawing group, activates the para-position, making it prone to nucleophilic substitution reactions. The phenyl anion, as a nucleophile, attacks the hydrogen atom at the para-position, and a new C-C bond is formed after substitution.

[0046] (4)Step 4: Formation of an ether bond with biphenol: The above product, biphenol, and potassium carbonate in a polar solvent (such as DMF), heated to an appropriate temperature. Reaction mechanism: The bromine atom acts as a leaving group, and the phenoxide anion replaces it through a nucleophilic substitution reaction to form an ether bond.

[0047] (5)Step 5: Nitration of the phenolic hydroxyl group: The above product, sodium nitrite, concentrated hydrochloric acid (HCl), at low temperature (0 - 5 °C), stirred to form the diazonium salt of the phenol. The diazonium salt is heated under acidic conditions and undergoes a decomposition reaction to form nitrobenzene.

[0048] (6)Step 6: Reduction reaction of the nitro group: The above nitro product is added with iron powder (Fe) and hydrochloric acid (HCl), and refluxed and heated in ethanol (EtOH). Two nitro groups are simultaneously reduced to amino groups. Reaction mechanism: The nitro group is converted to a nitroso group under acidic conditions and then reduced to an amino group by iron powder.

[0049] Taking as an example, the specific synthesis steps are as follows:

[0050] (1)Step 1: Preparation of nitrobenzene: Benzene undergoes a nitration reaction with concentrated nitric acid under the catalysis of concentrated sulfuric acid. The nitro group is introduced onto the benzene ring to form nitrobenzene (C6H5NO2). Reaction mechanism: The hydrogen on the benzene ring is protonated by sulfuric acid to form an activated intermediate. The intermediate reacts with nitric acid to introduce the nitro group and form nitrobenzene.

[0051] (2)Step 2: Ortho-halogenation of nitrobenzene: Nitrobenzene reacts with HBr under the catalysis of AlBr3 to introduce a bromine atom to the ortho-position to form ortho-bromonitrobenzene. Reaction mechanism: The nitro group, as a strong electron-withdrawing group, activates the ortho-position, making it prone to electrophilic substitution reactions. AlBr3 helps generate Br⁺ for electrophilic attack and substitutes the hydrogen atom at the ortho-position.

[0052] (3) Step 3: p-Phenyl Substitution of o-Bromonitrobenzene o-Bromonitrobenzene and phenylsodium (C6H5Na) are heated to an appropriate temperature in a polar solvent (such as DMF). Reaction mechanism: The nitro group, as a strong electron-withdrawing group, activates the para position, making it prone to nucleophilic substitution reactions. The phenyl anion acts as a nucleophile, attacking the hydrogen atom at the para position, and a new C-C bond is formed after substitution.

[0053] (4) Step 4: Formation of an Ether Bond with Biphenol: The above product, biphenol, and potassium carbonate are heated to an appropriate temperature in a polar solvent (such as DMF). Reaction mechanism: The bromine atom acts as a leaving group, and the phenoxide anion replaces it through a nucleophilic substitution reaction to form an ether bond.

[0054] (5) Step 5: Nitration of the Phenolic Hydroxyl Group: The above product, sodium nitrite (NaNO2), and concentrated hydrochloric acid (HCl) are stirred at low temperature (0 - 5 °C) to generate the diazonium salt of the phenol. The diazonium salt is heated under acidic conditions and undergoes a decomposition reaction to form nitrobenzene.

[0055] (6) Step 6: Reduction Reaction of the Nitro Group: The above nitro product is added with iron powder (Fe) and hydrochloric acid (HCl), and refluxed and heated in ethanol (EtOH). The two nitro groups are simultaneously reduced to amino groups. Reaction mechanism: The nitro group is converted to a nitroso group under acidic conditions and then reduced to an amino group by iron powder.

[0056] As a preferred solution, in the step S2, the conditions for the curing treatment are: the curing temperature is 350 - 380 °C, and the time is 1 - 4 h.

[0057] The present invention also provides the application of the above thermosetting polyimide resin in the preparation of fiber composite materials, and the fiber composite materials include at least one of carbon fiber, glass fiber, and quartz fiber.

[0058] The following combines the above technical solutions of the present invention to provide specific examples and comparative examples of specific raw materials and product structures to further comprehensively expand the technical solutions of the present invention: In the following embodiments of the present invention, during the reaction of the diamine monomer and the dianhydride, the amino group and the acid anhydride randomly combine, and the arrangement of the positions of the adjacent benzene ring side groups on the molecular chain is irregular. The molecular structural formulas in the following embodiments only show one possible arrangement, and there are many other possible arrangements. This is hereby explained. Example 1

[0059] This example provides a thermosetting polyimide resin and its preparation method: The polyimide resin in this example has the following structure: Among them, n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a phenyl side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0060] The specific preparation method is as follows: S1. Under nitrogen protection, add 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 8.724 g (0.04 mol) of pyromellitic dianhydride (PMDA), react for 1 h, add 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride, and then add DMAc to adjust the solution concentration to 30%. Continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution.

[0061] S2. Then spread the polyamic acid prepolymer solution on a glass plate, bake it in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 150 °C for 2 h, and then heat-treat it at 250 °C in a vacuum oven for 2 h to obtain polyimide prepolymer powder.

[0062] S3. Press and cure the polyimide prepolymer powder at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0063] The lowest melt viscosity of the polyimide prepolymer powder is about 453 Pa·s, and the concentration in the NMP solution is <20%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 363 °C. Example 2

[0064] This example provides a thermosetting polyimide resin and its preparation method: The thermosetting polyimide resin in this example has the following structure: Among them, n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a phenyl side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0065] The specific preparation method is as follows: S1. Under nitrogen protection, add 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 11.92 g (0.04 mol) of biphenyltetracarboxylic dianhydride (s-BPDA), react for 1 h, add 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride, and then add DMAc to adjust the solution concentration to 30%. Continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution.

[0066] S2. Then, spread the polyamic acid prepolymer solution on a glass plate, dry it in a common oven at 60°C for 2 h, 80°C for 2 h, 100°C for 2 h, 120°C for 2 h, 150°C for 2 h, and then heat-treat it at 250°C for 4 h in a vacuum oven to obtain polyimide prepolymer powder.

[0067] S3. Press and cure the polyimide prepolymer powder at 370°C for 2 h to obtain a thermosetting polyimide resin film.

[0068] The lowest melt viscosity of the polyimide prepolymer powder is about 302 Pa·s, and its concentration in the NMP solution is <10%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 335°C. Example 3

[0069] This example provides a thermosetting polyimide resin and its preparation method: The polyimide resin in this example has the following structure: where n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a benzene side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0070] The specific preparation method is as follows: Under nitrogen protection, add 17.6 g (0.05 mol) of benzidine diamine and 200 mL of N,N-dimethylacetamide (DMAc) to a 500 mL reaction flask, stir at room temperature, and after the benzidine diamine is completely dissolved, add 12.4 g (0.04 mol) of 4,4'-biphenyl ether dianhydride (ODPA), react for 1 h, add 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride, and then add DMAc to adjust the solution concentration to 30%, and continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution.

[0071] S2. Then, spread the polyamic acid prepolymer solution on a glass plate, dry it in a common oven at 60°C for 2 h, 80°C for 2 h, 100°C for 2 h, 120°C for 2 h, 150°C for 2 h, and then heat-treat it at 250°C for 4 h in a vacuum oven to obtain polyimide prepolymer powder.

[0072] S3. Press and cure the polyimide prepolymer powder at 370°C for 2 h to obtain a thermosetting polyimide resin film.

[0073] The lowest melt viscosity of the polyimide prepolymer powder is about 200 Pa·s, and its concentration in the NMP solution is <20%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 318°C. Example 4

[0074] This embodiment provides a thermosetting polyimide resin and a preparation method thereof: The polyimide resin in this embodiment has the following structure: Where n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a benzene side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0075] The specific preparation method is as follows: S1. Under nitrogen protection, 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 8.724 g (0.04 mol) of pyromellitic dianhydride (PMDA) is added, and the reaction is carried out for 1 h. Then 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride is added, and then DMAc is added to adjust the solution concentration to 30%. Stir at room temperature for another 24 hours to obtain a viscous polyamic acid solution.

[0076] S2. Then the polyamic acid prepolymer solution is spread on a glass plate and dried in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 150 °C for 2 h, and then heat-treated at 250 °C in a vacuum oven for 2 h to obtain polyimide prepolymer powder.

[0077] S3. The polyimide prepolymer powder is pressure-cured at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0078] The minimum melt viscosity of the polyimide prepolymer powder is about 374 Pa·s, and the concentration in the NMP solution is <30%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 357 °C. Example 5

[0079] This embodiment provides a thermosetting polyimide resin and a preparation method thereof: The polyimide resin in this embodiment has the following structure: Where n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a benzene side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0080] The specific preparation method is as follows: S1. Under nitrogen protection, add 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 11.92 g (0.04 mol) of biphenyl tetracarboxylic dianhydride (s-BPDA), react for 1 h, add 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride, and then add DMAc to adjust the solution concentration to 30%. Continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution.

[0081] S2. Then spread the polyamic acid prepolymer solution on a glass plate, bake it in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 150 °C for 2 h, and then heat-treat it in a vacuum oven at 250 °C for 4 h to obtain polyimide prepolymer powder.

[0082] S3. Press and cure the polyimide prepolymer powder at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0083] The minimum melt viscosity of the polyimide prepolymer powder is about 254 Pa·s, and the concentration in the NMP solution is <20%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 328 °C. Example 6

[0084] This example provides a thermosetting polyimide resin and its preparation method: The polyimide resin in this example has the following structure: Where n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a benzene side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0085] The specific preparation method is as follows: S1. Under nitrogen protection, add 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) into a 500 mL reaction flask, stir at room temperature. After the biphenyl diamine is completely dissolved, add 12.4 g (0.04 mol) of isomeric 4,4'-biphenyl ether dianhydride (ODPA), react for 1 h, add 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride, and then add DMAc to adjust the solution concentration to 30%. Continue to stir at room temperature for 24 hours to obtain a viscous polyamic acid solution.

[0086] S2. Then spread the polyamic acid prepolymer solution on a glass plate, bake it in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 150 °C for 2 h, and then heat-treat it in a vacuum oven at 250 °C for 4 h to obtain polyimide prepolymer powder.

[0087] S3. The polyimide prepolymer powder is pressure-cured at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0088] The lowest melt viscosity of the polyimide prepolymer powder is about 164 Pa·s, and the concentration in the NMP solution is > 20%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 275 °C. Example 7

[0089] This example provides a thermosetting polyimide resin and its preparation method: The polyimide resin in this example has the following structure: where n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a benzene side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0090] The specific preparation method is as follows: S1. Under nitrogen protection, 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 8.724 g (0.04 mol) of isomeric pyromellitic dianhydride (MPDA) is added, and the reaction is carried out for 1 h. Then 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride is added, and then DMAc is added to adjust the solution concentration to 30%, and stirring is continued at room temperature for 24 hours to obtain a viscous polyamic acid solution.

[0091] S2. Then the polyamic acid prepolymer solution is spread on a glass plate and dried in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 150 °C for 2 h, and then heat-treated at 250 °C in a vacuum oven for 4 h to obtain a polyimide prepolymer powder.

[0092] S3. The polyimide prepolymer powder is pressure-cured at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0093] The lowest melt viscosity of the polyimide prepolymer powder is about 235 Pa·s, and the concentration in the NMP solution is > 30%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 376 °C. Example 8

[0094] This example provides a thermosetting polyimide resin and its preparation method: The polyimide resin in this example has the following structure: Among them, n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a phenyl side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0095] The specific preparation method is as follows: S1. Under nitrogen protection, 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 11.92 g (0.04 mol) of isomeric biphenyltetracarboxylic dianhydride (a-BPDA) is added, and the reaction is carried out for 1 h. Then 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride is added, and then DMAc is added to adjust the solution concentration to 30%. Stir at room temperature for another 24 hours to obtain a viscous polyamic acid solution.

[0096] S2. Then the polyamic acid prepolymer solution is spread on a glass plate and dried in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, 150 °C for 2 h, and then heat-treated at 250 °C in a vacuum oven for 4 h to obtain polyimide prepolymer powder.

[0097] S3. The polyimide prepolymer powder is pressure-cured at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0098] The lowest melt viscosity of the polyimide prepolymer powder is about 187 Pa·s, and the concentration in the NMP solution is > 30%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 355 °C. Example 9

[0099] This example provides a thermosetting polyimide resin and its preparation method: The polyimide resin in this example has the following structure: Among them, n = 4. The molar ratio of the dianhydride monomer, the diamine monomer containing a biphenyl structure and a phenyl side group, and phenylacetylene phthalic anhydride is 4:5:2.

[0100] The specific preparation method is as follows: S1. Under nitrogen protection, 17.6 g (0.05 mol) of biphenyl diamine and 200 mL of N,N-dimethylacetamide (DMAc) are added to a 500 mL reaction flask, stirred at room temperature. After the biphenyl diamine is completely dissolved, 8.724 g (0.04 mol) of isomeric pyromellitic dianhydride (MPDA) is added, and the reaction is carried out for 1 h. Then 4.96 g (0.02 mol) of phenylacetylene phthalic anhydride is added, and then DMAc is added to adjust the solution concentration to 30%. Stir at room temperature for another 24 hours to obtain a viscous polyamic acid solution.

[0101] S2. Then, spread the polyamic acid prepolymer solution on a glass plate, dry it in a common oven at 60 °C for 2 h, 80 °C for 2 h, 100 °C for 2 h, 120 °C for 2 h, and 150 °C for 2 h, and then heat-treat it at 250 °C for 4 h in a vacuum oven to obtain polyimide prepolymer powder.

[0102] S3. Press and cure the polyimide prepolymer powder at 370 °C for 2 h to obtain a thermosetting polyimide resin film.

[0103] The lowest melt viscosity of the polyimide prepolymer powder is about 239 Pa·s, and its concentration in the NMP solution is > 30%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 392 °C.

[0104] Comparative Example 1 In this comparative example, the thermosetting polyimide resin is the resin reported in the literature "High Performance Polymers 2012 24: 180", and its molecular structure is as follows: Among them, n = 4, and the molar ratio of the dianhydride monomer, the diamine monomer with a benzene side group (p-TPEQ), and phenylacetylene phthalic anhydride is 4:5:2.

[0105] The lowest melt viscosity of the polyimide prepolymer powder is about 43 Pa·s, and its concentration in the NMP solution is < 30%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 270 °C.

[0106] Comparative Example 2 In this comparative example, the thermosetting polyimide resin is the resin in Patent CN201280013680.X, and its molecular structure is as follows: Among them, n = 4, and the molar ratio of the dianhydride monomer, the diamine monomer with a benzene side group (p-ODA), and phenylacetylene phthalic anhydride is 4:5:2.

[0107] The lowest melt viscosity of the polyimide prepolymer powder is about 208 Pa·s, and its concentration in the NMP solution is > 30%; the glass transition temperature of the obtained thermosetting polyimide resin measured by DSC is 354 °C.

[0108] Through the further comparison of the above-mentioned embodiments and comparative examples, it can be seen that the thermosetting polyimide resin provided by the present invention has obvious advantages. Compared with the resin in the comparative examples, the resin prepared by the present invention has a lower melt viscosity and better solubility, and at the same time exhibits a higher glass transition temperature after curing. These improvements have significantly enhanced the processing performance and heat resistance of the resin, especially the use stability at high temperatures. By introducing the design of biphenyl structure and benzene side groups, the present invention effectively solves the problems of too high melt viscosity, difficult processing and relatively low glass transition temperature after curing of thermosetting polyimide resins in the prior art. This resin not only has excellent thermal stability, but also can be used in combination with fiber composite materials, further expanding its application prospects in high-end fields such as aerospace. Therefore, the thermosetting polyimide resin and its preparation method of the present invention have great technological breakthroughs and commercial potential in terms of performance and application.

[0109] For the points not fully exhausted in the technical scope claimed by the present invention in the embodiments herein, as well as the new technical solutions formed by the equivalent replacement of single or multiple technical features in the technical solutions of the embodiments, they are also within the scope claimed by the present invention; at the same time, in all the exemplified or unexemplified embodiments of the present invention, each parameter in the same embodiment only represents an example (i.e., a feasible solution) of its technical solution, and there is no strict cooperation and limitation relationship between the parameters. Among them, the parameters can be replaced with each other without violating the axioms and the requirements of the present invention, unless otherwise specifically stated.

[0110] The technical means disclosed in the present invention is not limited to the technical means disclosed by the above technical means, but also includes the technical solutions composed of any combination of the above technical features. The above is the specific implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches are also regarded as the protection scope of the present invention.

[0111] The specific embodiments described herein are only illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements or use similar means to replace the described specific embodiments, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A thermosetting polyimide resin, characterized in that, The thermosetting polyimide resin includes the following structural formula: ; wherein, Ar is a residue of a dianhydride monomer; n is an integer, and 1 ≤ n ≤ 10; m is an integer, and m ≥ 0; the horizontal lines "-" connected to the benzene ring each represent that they can be connected to any one of the carbon atoms of the benzene ring.

2. The thermosetting polyimide resin according to claim 1, characterized in that The Ar is at least one of the following structural formulas: Among them, each horizontal line "-" connecting the outside of each monomer to the benzene ring represents the bonding bond between the Ar group and the carbon atom in the repeating unit; each horizontal line "-" connecting the inside of the monomer to the benzene ring represents that it can be connected to any carbon atom on the benzene ring.

3. A thermosetting polyimide resin according to claim 2, characterized in that, The Ar is at least one of the following groups: Among them, each horizontal line "-" connecting the outside of each monomer to the benzene ring represents the bonding link between the Ar group and the carbon atom in the repeating unit; each horizontal line "-" connecting the inside of the monomer to the benzene ring represents that it can be connected to any carbon atom on the benzene ring.

4. A thermosetting polyimide resin according to claim 3, wherein, The Ar is at least one of the following groups: Among them, each horizontal line "-" connecting the outside of each monomer to the benzene ring represents the bonding connection between the Ar group and the carbon atom in the repeating unit.

5. A method for preparing the thermosetting polyimide resin according to any one of claims 1-4, characterized in that, It includes the following steps: S1: Under the protection of inert gas, add the diamine monomer containing biphenyl to a polar aprotic solvent, stir and dissolve it, then add the dianhydride monomer to react, and then add phenylacetylene phthalic anhydride for end-capping to obtain a polyamic acid solution; S2: Finally, perform gradient heating and curing treatment on the polyamic acid solution; The phenylacetylene phthalic anhydride includes the following structure: ; The molar ratio of the dianhydride monomer, the biphenyl diamine monomer and the phenylacetylene phthalic anhydride is n:(n + 1):2, where n >

0.

6. The preparation method of the thermosetting polyimide resin according to claim 5, wherein, In the step S1, the structural formula of the diamine monomer containing biphenyl is as follows: Among them, the horizontal lines "-" connecting the inside of the monomer to the benzene ring all indicate that they can be connected to any carbon atom of the benzene ring, m is an integer, and m ≥ 0.

7. The preparation method of the thermosetting polyimide resin according to claim 6, characterized in that, In the step S1, the structural formula of the diamine monomer containing biphenyl is one of the following structures: 。 8. The preparation method of the thermosetting polyimide resin according to claim 7, characterized in that, In the step S1, the structural formula of the diamine monomer containing biphenyl is one of the following structures: 。 9. The preparation method of the thermosetting polyimide resin according to claim 8, characterized in that, In the step S1, the structural formula of the diamine monomer containing biphenyl is one of the following structures: Wherein, n is an integer and n >

0.

10. The preparation method of the thermosetting polyimide resin according to claim 7, characterized in that, In the step S2, the conditions for the curing treatment are: the curing temperature is 350 - 380 °C, and the time is 1 - 4 h.

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