An oriented long fiber reinforced polyimide foam material and its preparation method

Abstract

This invention discloses a method for preparing oriented long fiber reinforced polyimide foam material, comprising: adding fatty alcohol, aromatic dianhydride and end-capping agent to a solvent for esterification reaction; adding diamine to continue the reaction; drying to remove solvent and obtain RTM-type foamable precursor; mixing and extruding linear thermoplastic polyimide resin with RTM-type foamable precursor, uniformly distributing long fibers on the inner wall of a custom die head, achieving tight encapsulation of oriented long fibers during extrusion; cutting the material to a fixed length and completing volumetric foaming in a foaming mold. This invention also discloses an oriented long fiber reinforced polyimide foam material, using long fibers as reinforcement and a mixed extrudate of linear thermoplastic polyimide resin and RTM-type foamable precursor as the matrix, which improves the flexural strength, compressive strength and toughness of the polyimide foam material, and can be applied to foam sandwich materials in the aerospace field, radar dome sandwich materials, etc.

Description

Technical Field

[0001] This invention relates to an oriented long fiber reinforced polyimide foam material and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Rigid polyimide foam is a novel type of high-performance polymer foam material. Currently, polymethacrylamide foam (PMI), as a side-chain polyimide, has been widely used in various fields such as aerospace, high-end instruments, and wind power generation due to its excellent comprehensive properties. However, it is prone to softening at temperatures above 200°C, making it difficult to meet the temperature resistance requirements of next-generation equipment. Compared to PMI, main-chain polyimide foam has better temperature resistance and can operate in high-temperature environments above 200°C, with some types reaching temperatures above 250°C.

[0003] There are several methods for preparing main-chain polyimide foam materials, including: preparing microspheres using aromatic dianhydrides and aromatic diamines as the main raw materials, and then hot-pressing the microspheres; or, preparing them using aromatic dianhydrides and isocyanates as raw materials. This type of foam material has good performance and can be used at temperatures up to 200–250°C. In addition, rigid polyimide foam can also be prepared based on RTM process resins, using norbornene adiene anhydride as the end-capping agent and α-isomeric biphenyl anhydride as the main dianhydride. The prepared foam has a high closed-cell rate, which can reach over 90%.

[0004] However, the compressive strength and flexural strength of the main-chain polyimide foam material prepared by the above system are lower than those of PMI of the same density, and it exhibits brittle fracture. In view of the above, it is necessary to explore a method for preparing main-chain polyimide foam materials with high compressive strength and high flexural strength. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the inventors conducted intensive research and provided an oriented long fiber reinforced polyimide foam material and its preparation method, solving the problem that main-chain polyimide foam materials are difficult to guarantee compressive and flexural strength under high-temperature environments. The oriented long fiber reinforced polyimide foam material obtained by this invention possesses high compressive strength and high flexural strength, and can be used at high temperatures.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for preparing an oriented long fiber reinforced polyimide foam material, characterized by comprising the following steps:

[0008] (1) Add aromatic dianhydride, end-capping agent and fatty alcohol to the solvent until the esterification reaction is complete;

[0009] (2) Add diamine to the product from the previous step and react for 0.5 to 3 hours;

[0010] (3) The product from the previous step is dried and then pulverized to obtain an RTM-type foamable precursor.

[0011] (4) The linear thermoplastic polyimide resin is mixed with the product from the previous step and extruded. The long fibers are evenly oriented and distributed along the inner wall of the mold cavity, and the long fibers are coated during the mixing and extrusion process.

[0012] (5) Cut the product from the previous step into a fixed length, fill it into the mold in the same direction, and perform fixed-volume foaming to obtain polyimide foam material reinforced with oriented long fibers.

[0013] Further, in step (1), the aromatic dianhydride comprises at least one of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride;

[0014] Further, in step (1), the solvent contains at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone;

[0015] Furthermore, in step (1), the fatty alcohol includes methanol or ethanol;

[0016] Furthermore, in step (1), the capping agent comprises at least one of 5-norbornene-2,3-dianhydride or 4-phenylacetylene phthalic anhydride.

[0017] Further, in step (1), the molar ratio of both fatty alcohol and capping agent to aromatic dianhydride is (6-2):1, wherein the molar ratio of anhydride group in capping agent to anhydride group in aromatic dianhydride is 1:(1-5).

[0018] Further, in step (2), the diamine comprises at least one of p-phenylenediamine, m-phenylenediamine, 1,3-bis(4'-aminophenoxy)benzene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, or 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

[0019] Furthermore, in step (2), the molar ratio of the anhydride groups in the aromatic dianhydride and the capping agent to the amino groups in the diamine is 1:(1 to 1.1).

[0020] Furthermore, in steps (1) and (2), the reaction temperature is 50–70°C.

[0021] Furthermore, in step (4), the long fibers include at least one of carbon fiber, aramid fiber, poly(p-phenylenebenzodioxazole) fiber, glass fiber, or quartz fiber.

[0022] Furthermore, in step (4), the processing temperature is 250–270°C;

[0023] Furthermore, in step (4), the long fiber distribution direction is along the extrusion direction of the mixture of linear thermoplastic polyimide resin and RTM-type foamable precursor.

[0024] Furthermore, in step (4), the mass ratio of linear thermoplastic polyimide resin to RTM-type foamable precursor is 1:(1-10).

[0025] Furthermore, in step (5), the foaming temperature is 280–320°C.

[0026] An oriented long fiber reinforced polyimide foam material is obtained according to the above-mentioned preparation method of oriented long fiber reinforced polyimide foam material, with long fibers as reinforcement and a mixed extrusion of linear thermoplastic polyimide resin and RTM type foamable precursor as matrix.

[0027] The density of the oriented long fiber reinforced polyimide foam material is 100-600 kg / m³. 3 The compressive strength is 1.5–2.5 MPa, and the flexural strength is 1.9–5.1 MPa.

[0028] The method for preparing oriented long fiber reinforced polyimide foam material provided by the present invention has the following beneficial effects:

[0029] (1) In the process of adding long fiber reinforcement, the long fibers are oriented and distributed along a specific direction of the mixed extrudate matrix, and the stiffness of the long fibers is fully utilized, effectively improving the flexural strength and compressive strength of the polyimide foam material. The oriented long fiber reinforced polyimide foam material of the present invention has outstanding mechanical properties. Compared with the existing technology, the compressive strength of the foam material of the same density is increased by 20% to 50%, and the flexural strength is increased by 80% to 200%. It improves the poor compressive strength and flexural strength of the main chain polyimide foam and approaches the mechanical properties of PMI of the same density.

[0030] (2) In the process of preparing the mixed extrusion matrix, the present invention adds linear thermoplastic polyimide resin, which effectively improves the toughness of polyimide foam material.

[0031] (3) The oriented long fiber reinforced polyimide foam material prepared in this invention can operate at temperatures above 200°C, broadening the application temperature range of rigid polyimide foam materials. It can replace foam materials such as PMI in high-temperature scenarios. It is suitable as a foam core material in sandwich materials, such as foam sandwich materials in the aerospace field and radar dome sandwich materials.

[0032] (4) In the process of coating the long fiber reinforcement, the long fibers are evenly distributed along the inner wall of a customized mold, and the mold size is adapted to the die head size of the screw extruder. The tight orientation coating of the long fibers is completed at the same time as the mixture matrix is ​​extruded, which is convenient to operate. Detailed Implementation

[0033] The present invention will become clearer and more apparent from the following detailed description. However, this should not be construed as limiting the scope of the invention. Unless otherwise specified, all raw materials / materials described in this invention are derived from commercially available products.

[0034] This invention proposes an oriented long fiber reinforced polyimide foam material. This material uses long fibers as reinforcement and a mixed extrudate of linear thermoplastic polyimide resin and RTM-type foamable precursor as the matrix. The uniform orientation of the reinforcement over the matrix improves the flexural strength, compressive strength, and toughness of the main-chain polyimide foam material under high-temperature conditions. First, fatty alcohol, aromatic dianhydride, and an end-capping agent are added to a solvent until esterification is complete. Then, diamine is added, and the reaction is carried out for 0.5–3 hours. The solvent is removed by drying, and the resulting material is pulverized to obtain the RTM-type foamable precursor. A custom die is used in the die head of a screw extruder to uniformly distribute the long fibers along the inner wall of the die. The RTM-type foamable precursor and linear thermoplastic polyimide resin are mixed and extruded using a screw extruder, achieving uniform orientation of the long fibers during extrusion. The extrudate is cut to a fixed length according to the size of the foaming die, then filled into the die, and foamed to a fixed volume to obtain the oriented long fiber reinforced polyimide foam material. The density of the oriented long fiber reinforced polyimide foam material is 100-600 kg / m³. 3 The preferred value is 100-200 kg / m³. 3 The compressive strength can reach 1.5 to 2.5 MPa, and the flexural strength can reach 1.9 to 5.1 MPa.

[0035] This invention discloses a method for preparing a polyimide foam material reinforced with oriented long fibers, comprising the following steps:

[0036] (1) Add aromatic dianhydride, end-capping agent and fatty alcohol to the solvent until the esterification reaction is complete;

[0037] (2) Add diamine to the product from the previous step and react for 0.5 to 3 hours.

[0038] (3) The solvent in the product from the previous step is removed by drying, and the product is pulverized to obtain an RTM type foamable precursor.

[0039] (4) The linear thermoplastic polyimide resin is mixed with the product from the previous step and extruded. A custom mold is made at the die head of the screw extruder, and the long fibers are evenly oriented and distributed along the inner wall of the mold. The long fibers are coated during the mixing and extrusion process.

[0040] (5) Cut the product from the previous step to a fixed length according to the size of the foaming mold, fill it into the mold in the same direction, and perform fixed-volume foaming to obtain polyimide foam material reinforced with oriented long fibers.

[0041] Furthermore, in step (1), the aromatic dianhydride comprises at least one of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, or 3,3',4,4'-biphenyltetracarboxylic dianhydride;

[0042] Furthermore, in step (1), the solvent contains at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.

[0043] Furthermore, in step (1), the fatty alcohol includes methanol or ethanol.

[0044] Furthermore, in step (1), the capping agent comprises at least one of 5-norbornene-2,3-dianhydride or 4-phenylacetylene phthalic anhydride.

[0045] Furthermore, in step (1), the molar ratio of both fatty alcohol and capping agent to aromatic dianhydride is (6-2):1, wherein the molar ratio of anhydride groups in the capping agent to anhydride groups in the aromatic dianhydride is 1:(1-5).

[0046] Furthermore, in step (2), the diamine comprises at least one of p-phenylenediamine, m-phenylenediamine, 1,3-bis(4'-aminophenoxy)benzene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, or 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

[0047] Furthermore, in step (2), the molar ratio of the anhydride groups in the aromatic dianhydride and the capping agent to the amino groups in the diamine is 1:(1 to 1.1).

[0048] Furthermore, in steps (1) and (2), the reaction temperature is 50–70°C.

[0049] Furthermore, in step (4), the long fibers include one or more of the following: carbon fiber, aramid fiber, poly(p-phenylenebenzodioxazole) fiber, glass fiber, quartz fiber, etc.

[0050] Furthermore, in step (4), the processing temperature is 250–270°C.

[0051] Furthermore, in step (4), the long fiber distribution direction is along the extrusion direction of the mixture of linear thermoplastic polyimide resin and RTM-type foamable precursor.

[0052] Furthermore, in step (4), the mass ratio of linear thermoplastic polyimide resin to RTM-type foamable precursor is 1:(1-10).

[0053] Furthermore, in step (5), the foaming temperature is 280–320°C.

[0054] Example

[0055] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention will now be described in detail with examples, but these examples should not be construed as limiting the scope of implementation of the present invention.

[0056] (1) RTM type foamable precursor

[0057] In a three-necked flask equipped with a stirrer and a condenser, add 1.3 kg of tetrahydrofuran and 0.55 kg of ethanol, then add 0.728 kg of 2,3,3',4'-biphenyltetracarboxylic dianhydride and 0.338 kg of 5-norbornene-2,3-dianhydride. Heat to 60°C and continue the reaction for 3 hours. Then add 0.4 kg of 1,3-m-phenylenediamine, mix for 2 hours, remove the solvent, and then dry in a 240°C oven for 1 hour. Finally, use a high-speed pulverizer to break down the mixture for later use.

[0058] (2) Linear thermoplastic polyimide resin

[0059] In a three-necked flask equipped with a stirrer and a condenser, 160 kg of N,N-dimethylacetamide and 16.4 kg of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane were added. After complete dissolution, the mixture was cooled to 0°C, and then 12.4 kg of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride was added. The mixture was reacted at this temperature for 24 h, and then 20 kg of toluene was added. The mixture was dehydrated in an oil bath at 110°C for 4 h. After removing the toluene, the mixture was filtered, washed three times with water, and dried in an oven at 100°C. Then, the temperature was raised to 210°C and dried for 4 h to obtain linear polyimide resin.

[0060] Example 1

[0061] Take 400g of RTM-type foamable precursor, add 80g of linear polyimide resin, mix evenly, and then use an SHJ-20 twin-screw extruder to extrude the untwisted quartz fiber (brand name SJ114 from Henan Shenjiu Tianhang New Material Co., Ltd.) evenly along the inner wall of the die-customized mold that matches the extruder. After stretching and drawing into strips, air-cool (composite resin strip diameter 2mm), cut to a fixed length to obtain a 15cm fiber-wrapped composite resin strip. Then take 65g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm, place it in an environment of 280℃ for 1 hour, in an environment of 320℃ for 2 hours, and cool it to below 250℃ to demold, obtaining the final foam / fiber composite material.

[0062] The density of the resulting foam is 120 kg / m³ 3 The compressive strength is 1.6 MPa and the flexural strength is 2.4 MPa.

[0063] Example 2

[0064] Take 400g of RTM-type foamable precursor, add 120g of linear polyimide resin, mix evenly, and then use an SHJ-20 twin-screw extruder to extrude the untwisted quartz fiber (brand name SJ114 from Henan Shenjiu Tianhang New Material Co., Ltd.) evenly along the inner wall of the die-customized mold that matches the extruder. After stretching and drawing into strips, air-cool (resin strip diameter 1.2mm), cut to a fixed length to obtain a 15cm fiber-encapsulated composite resin strip. Then take 65g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm, place it in an environment of 280℃ for 1 hour, in an environment of 320℃ for 2 hours, and cool it to below 250℃ to demold, obtaining the final foam / fiber composite material.

[0065] The density of the resulting foam is 160 kg / m³ 3 The compressive strength is 2.2 MPa and the flexural strength is 3.9 MPa.

[0066] Example 3

[0067] Take 400g of RTM-type foamable precursor, add 80g of linear polyimide resin, mix evenly, and then use an SHJ-20 twin-screw extruder to extrude the carbon fiber (Weihai Guangwei Composite Materials Co., Ltd. TZ800S) evenly along the inner wall of the die-customized mold that matches the extruder. After stretching and drawing into strips, air-cool (the diameter of the composite resin strip is 1.8mm), cut to a fixed length to obtain a 15cm long fiber-encapsulated composite resin strip. Then take 62g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm. Place it in an environment of 280℃ for 1 hour, in an environment of 320℃ for 2 hours, and cool it to below 250℃ to demold, thus obtaining the final foam / fiber composite material.

[0068] The density of the resulting foam is 108 kg / m³ 3 The compressive strength is 1.5 MPa and the flexural strength is 3.0 MPa.

[0069] Example 4

[0070] Take 400g of RTM-type foamable precursor, add 120g of linear polyimide resin, mix evenly, and then use an SHJ-20 twin-screw extruder to extrude the carbon fiber (Weihai Guangwei Composite Materials Co., Ltd. TZ800S) evenly along the inner wall of the die-customized mold that matches the extruder. After stretching and drawing into strips, air-cool (the diameter of the composite resin strip is 1.8mm), cut to a fixed length to obtain a 15cm long fiber-encapsulated composite resin strip. Then take 110g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm. Place it in an environment of 280℃ for 1 hour, in an environment of 320℃ for 2 hours, and cool it to below 250℃ to demold, thus obtaining the final foam / fiber composite material.

[0071] The density of the resulting foam is 170 kg / m³ 3 The compressive strength is 2.5 MPa, and the flexural strength is 5.1 MPa.

[0072] Example 5

[0073] Take 400g of RTM foamable precursor, add 80g of linear polyimide resin, mix evenly, and then use an SHJ-20 twin-screw extruder to extrude the glass fiber (T984T2 from Taishan Glass Fiber Co., Ltd.) evenly along the inner wall of the die-customized mold that matches the extruder. After stretching and drawing into strips, air-cool (the diameter of the composite resin strip is 1.8mm), cut to a fixed length to obtain a 15cm long fiber-wrapped composite resin strip. Then take 70g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm. Place it in an environment of 280℃ for 1 hour, in an environment of 320℃ for 2 hours, and cool it to below 250℃ to demold, thus obtaining the final foam / fiber composite material.

[0074] The density of the resulting foam is 120 kg / m³ 3 The compressive strength is 1.5 MPa and the flexural strength is 1.9 MPa.

[0075] Example 6

[0076] Take 400g of RTM foamable precursor, add 160g of linear polyimide resin, mix evenly, and then use an SHJ-20 twin-screw extruder to extrude the glass fiber (T984T2 from Taishan Glass Fiber Co., Ltd.) evenly along the inner wall of the die-customized mold that matches the extruder. After stretching and drawing into strips, air-cool (the diameter of the composite resin strip is 1.1mm), cut to a fixed length to obtain a 15cm long fiber-wrapped composite resin strip. Then take 120g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm. Place it in an environment of 280℃ for 1 hour, in an environment of 320℃ for 2 hours, and cool it to below 250℃ to demold, thus obtaining the final foam / fiber composite material.

[0077] The density of the resulting foam is 180 kg / m³ 3 The compressive strength is 2.2 MPa and the flexural strength is 4.9 MPa.

[0078] Comparative Example 7

[0079] Take 400g of RTM foamable precursor, add 160g of linear polyimide resin, mix evenly, and then extrude using an SHJ-20 twin-screw extruder. Use a custom die head to stretch the resin strip, then air-cool it (resin strip diameter 1.8mm), and cut it to a fixed length to obtain a 15cm resin strip. Then take 66g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm. Place it in an environment of 280℃ for 1 hour, then in an environment of 320℃ for 2 hours, and then cool it to below 250℃ to demold, obtaining the final foam material.

[0080] The density of the resulting foam is 110 kg / m³ 3The compressive strength is 1.4 MPa and the flexural strength is 1.2 MPa.

[0081] Comparative Example 8

[0082] Take 400g of RTM foamable precursor, add 160g of linear polyimide resin, mix evenly, and then extrude using an SHJ-20 twin-screw extruder. Use a custom die head to stretch the resin strip, then air-cool it (resin strip diameter 1.1mm), and cut it to a fixed length to obtain a 15cm resin strip. Then take 105g and put it into a foaming mold with an inner cavity size of 15cm x 15cm x 2.5cm. Place it in an environment of 280℃ for 1 hour, then in an environment of 320℃ for 2 hours, and then cool it to below 250℃ to demold, obtaining the final foam material.

[0083] The density of the resulting foam is 180 kg / m³ 3 The compressive strength is 2.1 MPa and the flexural strength is 2.2 MPa.

[0084] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0085] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for preparing an oriented long fiber reinforced polyimide foam material, characterized by comprising the following steps: (1) Add aromatic dianhydride, end-capping agent and fatty alcohol to the solvent until the esterification reaction is complete; (2) Add diamine to the product from the previous step and react for 0.5 to 3 hours; (3) The product from the previous step is dried and then pulverized to obtain an RTM-type foamable precursor. (4) The linear thermoplastic polyimide resin is mixed and extruded with the product from the previous step. The long fibers are evenly oriented and distributed along the inner wall of the die head. The long fibers are coated during the mixing and extrusion process. (5) Cut the product from the previous step into a fixed length and fill it into a foaming mold in the same direction. Perform fixed-volume foaming to obtain polyimide foam material reinforced with oriented long fibers. In step (4), the long fibers include at least one of carbon fiber, aramid fiber, poly(p-phenylenebenzodioxazole) fiber, glass fiber or quartz fiber. In step (4), the processing temperature is 250~270℃; In step (4), the long fiber distribution direction is along the extrusion direction of the mixture of linear thermoplastic polyimide resin and RTM foamable precursor. The density of polyimide foam material is 100~600 kg / m³. 3 The compressive strength is 1.5~2.5MPa, and the flexural strength is 1.9~5.1MPa.

2. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In step (1), the aromatic dianhydride includes at least one of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride; In step (1), the solvent contains at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone; In step (1), the fatty alcohol includes methanol or ethanol; In step (1), the capping agent contains at least one of 5-norbornene-2,3-dianhydride or 4-phenylacetylene phthalic anhydride.

3. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In step (1), the molar ratio of fatty alcohol and capping agent to aromatic dianhydride is 6~2:1, wherein the molar ratio of anhydride group in capping agent to anhydride group in aromatic dianhydride is 1:1~5.

4. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In step (2), the diamine comprises at least one of p-phenylenediamine, m-phenylenediamine, 1,3-bis(4'-aminophenoxy)benzene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, or 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

5. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In step (2), the sum of the amounts of the aromatic dianhydride and the anhydride groups in the capping agent is in a ratio of 1:1 to 1.1 to the amount of the amino groups in the diamine.

6. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In steps (1) and (2), the reaction temperature is 50~70℃.

7. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In step (4), the mass ratio of linear thermoplastic polyimide resin to RTM foamable precursor is 1:1~10.

8. The method for preparing an oriented long fiber reinforced polyimide foam material according to claim 1, characterized in that: In step (5), the foaming temperature is 280~320℃.

9. A polyimide foam material reinforced with oriented long fibers, characterized in that, The polyimide foam material is prepared by the method of any one of claims 1 to 8, wherein the long fibers are used as the reinforcement and the mixed extrusion of linear thermoplastic polyimide resin and RTM-type foamable precursor is used as the matrix.

10. The oriented long fiber reinforced polyimide foam material according to claim 9, wherein the density is 100~600 kg / m³. 3 The compressive strength is 1.5~2.5MPa, and the flexural strength is 1.9~5.1MPa.