CN114044903A - A kind of rigid polyimide foam and its preparation method and use - Google Patents

Abstract

The invention provides hard polyimide foam and a preparation method and application thereof, belonging to the field of high polymer materials. The rigid polyimide foam has a structure shown in formula I. The polyimide foam prepared by the invention has high compression strength, excellent comprehensive mechanical property, low apparent density, small self weight, convenient transportation and construction and can be used as a light material. Meanwhile, the polyimide foam has excellent thermal stability and thermal insulation performance and can be used at high temperature. The polyimide foam disclosed by the invention has the characteristics of good thermal stability, high compression strength, low density and small self weight, can be used as a structural material in various high-tech fields such as aerospace, military ships, energy sources and high-speed rail automobiles, and has a wide application prospect.

Description

A kind of rigid polyimide foam and its preparation method and use

technical field

The invention belongs to the field of polymer materials, and in particular relates to a rigid polyimide foam and a preparation method and application thereof.

Background technique

Polyimide (PI) foam material is a porous material formed by PI resin as the main component and containing open and closed cell structures of different scales. The segment of PI contains a large number of benzene rings and imide rings, which endow PI foam with excellent thermal stability, high and low temperature resistance, self-extinguishing flame retardant, chemical resistance and radiation resistance, making it widely used in aviation Aerospace, military ships, energy and high-speed rail vehicles and many other high-tech fields.

With the rapid development of aerospace and other technology industries, PI foams with higher mechanical strength and rigidity are urgently needed as structural materials, such as radome bushings, spherical frames, wings and airtight baffles of aircraft airtight cockpits, and composite wind turbines. Materials Rigid polymer foam in areas such as blades and submarine hulls and frame components. Currently, the rigid polymer foams used in this field are generally polymethacrylimide (PMI) foams. However, because of its weaker polyolefin polymer chain, the segment of PMI foam begins to decompose at 200°C, and its structure is damaged, so it cannot be used in an environment above 200°C. In addition, considering factors such as poor mechanical properties and limited high-temperature performance, isocyanate-based PI foams are not suitable for use as structural materials. Therefore, the preparation of rigid PI foams with excellent mechanical properties and lower density is of great significance for the development of high-tech fields.

The preparation technology of PI foam has been developed for decades. Using polyester ammonium salt (PEAS) as the precursor powder and thermal foaming method is an effective method to prepare PI foam. On this basis, the methods to improve the strength of PI foam mainly include the addition of reinforcing fillers and the modification of PI segments. The method of adding reinforcing fillers is often to add fibers, graphene, inorganic clay, honeycomb, etc. to PEAS to improve the mechanical properties of the foam. The reinforcing filler method has the problem of poor compatibility between the filler and the matrix, resulting in limited strength improvement of the prepared PI foam. The segment modification method is to introduce a cross-linked network structure or a rigid structure into the PI segment structure to strengthen the PI main chain and endow the foam with excellent compression resistance. However, adding fillers and building a cross-linked network or rigid structure will increase the viscosity during the foaming process, making it difficult to form, and at the same time, high viscosity will weaken the interaction between cells, resulting in a decrease in the mechanical strength of PI foams. Patent CN102964834A discloses a high temperature and high compression resistance cross-linked polyimide foam material, which is composed of organic tetraacid dianhydride or organic tetraacid diacid diester, norbornene monoacid monoester and aromatic Diamine is used as raw material to prepare polyimide foam. Although the polyimide foam has high temperature resistance, good toughness and small compression deformation at high temperature, it has the problems of high cost, low closed cell ratio, low compressive strength and complicated molding process.

At present, there is an urgent need to develop a PI foam with good comprehensive properties, low density, high strength, and good thermal stability.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a rigid polyimide foam and its preparation method and use.

The invention provides a kind of rigid polyimide foam, it has the structure shown in formula I:

in,

Ring A is selected from

R ₁ is selected from

R ₂ is selected from

n is an integer ≥1.

further,

n is an integer from 1 to 7;

Preferably, the n is 3.

Further, the aforementioned rigid polyimide foam is prepared from difunctional acid anhydrides, diamines and monofunctional acid anhydrides as raw materials;

The molar ratio of the difunctional acid anhydride, the diamine and the monofunctional acid anhydride is 1:(1-5):(0.1-1).

Further, the molar ratio of the difunctional acid anhydride, the diamine and the monofunctional acid anhydride is 1:(1.1-1.5):(0.25-1);

Preferably, the molar ratio of the difunctional acid anhydride, the diamine and the monofunctional acid anhydride is 1:1.25:0.5.

further,

The difunctional acid anhydride is selected from 3,3',4,4'-diphenyl ether tetraacid anhydride, 3,3',4,4'-biphenyl tetracarboxy dianhydride, pyromellitic dianhydride, 3 ,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenylsulfone tetracarboxylic dianhydride, 2,3,3',4'-biphenyl One or more of tetracarboxylic dianhydrides;

And/or, the diamine is selected from 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 3,3'-diphenylene Aminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 2,2'-dimethyldiaminobiphenyl, 2,6-diaminopyridine one or more of;

And/or, the acid anhydride of described monofunctionality is selected from one or more in norbornene dianhydride, 4-phenylethynyl phthalic anhydride, 4-ethynyl phthalic anhydride, maleic anhydride kind;

Preferably,

The difunctional acid anhydride is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride;

And/or, the diamine is selected from 4,4'-diaminodiphenylmethane;

And/or, the monofunctional acid anhydride is selected from norbornene dianhydride.

The present invention also provides a method for preparing the aforementioned rigid polyimide foam, which comprises the following steps:

(1) adding a ring-opening catalyst, an alcohol solvent and an ether solvent to the bifunctional acid anhydride, and after the reaction, a bifunctional polyamic acid precursor solution is obtained;

(2) adding a ring-opening catalyst, an alcohol solvent and an ether solvent to the monofunctional acid anhydride, and after the reaction, a monofunctional polyamic acid precursor solution is obtained;

(3) the solution obtained in step (1) and the solution obtained in step (2) are mixed and stirred to obtain a clear system;

(4) adding diamine, surfactant and imidization catalyst to the clarification system obtained in step (3), and purifying to obtain PEAS salt;

(5) The PEAS salt is foamed to obtain expanded microspheres and then imidized to obtain rigid polyimide foam.

further,

In step (1), the molar ratio of the bifunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:(0.001-0.1):(1-10):(1-10);

And/or, in step (2), the molar ratio of the monofunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:(0.001-0.1):(1-10):(1-10 );

And/or, in step (4), the molar ratio of the diamine to the imidization catalyst is 1:(0.01-0.1);

And/or, in step (4), the amount of the surfactant is 0.1-0.5wt% of the total mass of the bifunctional acid anhydride, the monofunctional acid anhydride and the diamine;

Preferably,

In step (1), the molar ratio of the bifunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:0.01:7:8;

And/or, in step (2), the molar ratio of the monofunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:0.01:3.5:4;

And/or, in step (4), the molar ratio of the diamine and the imidization catalyst is 1:0.04;

And/or, in step (4), the amount of the surfactant is 0.5 wt % of the total mass of the difunctional acid anhydride, the monofunctional acid anhydride and the diamine.

further,

In step (1), the ring-opening catalyst is dimethylimidazole;

And/or, in step (1), described alcoholic solvent is one or more in methyl alcohol, ethanol, propyl alcohol and Virahol;

And/or, in step (1), described ether solvent is tetrahydrofuran;

And/or, in step (2), the ring-opening catalyst is dimethylimidazole;

And/or, in step (2), described alcoholic solvent is one or more in methyl alcohol, ethanol, propyl alcohol and Virahol;

And/or, in step (2), the ether solvent is tetrahydrofuran;

And/or, in step (4), described surfactant is silicone oil;

And/or, in step (4), the imidization catalyst is isoquinoline.

further,

In step (1), described reaction is oil bath reflux reaction under nitrogen atmosphere;

And/or, in step (2), described reaction is stirring under nitrogen atmosphere condition;

And/or, in step (4), the reaction is 70°C～80°C for 1～5h;

And/or, in step (4), the purification is to remove the solvent, so that the solvent content in the obtained PEAS salt is 14-17%;

And/or, in step (5), the PAES salt is pulverized to a particle size of 0.1mm-0.3mm;

And/or, in step (5), the foaming condition is 150～200℃ for 30～60min;

And/or, in step (5), the imidization condition is 250-300° C. for 1-3 hours.

Preferably,

In step (1), the reaction is a reflux reaction in an oil bath at 60°C to 65°C for 0.1 to 5 hours under a nitrogen atmosphere;

And/or, in step (2), the reaction is stirring for 0.1 to 5 h under a nitrogen atmosphere at 60°C to 65°C;

And/or, in step (4), the reaction is 70°C for 3h;

And/or, in step (4), the conditions for removing the solvent are a temperature of 60 to 65° C. and a pressure of -0.6 to -0.1 MPa;

And/or, in step (5), the condition of described foaming is 180 ℃ to keep 30min;

And/or, in step (5), the imidization condition is 300°C for 2h.

The present invention also provides the use of the aforementioned rigid polyimide foam in preparing a device used as a structural material in the fields of aerospace, military ships, energy, high-speed rail, and automobiles.

The polyimide foam prepared by the invention has high compressive strength, excellent comprehensive mechanical properties, low apparent density, low self-weight, convenient transportation and construction, and can be used as a light material. At the same time, the polyimide foam has excellent thermal stability and thermal insulation properties, and can be used at high temperatures. The polyimide foam of the invention also has the characteristics of good thermal stability, high compressive strength, low density and small self-weight, and can be used as a structural material in many high-tech fields such as aerospace, military ships, energy and high-speed rail vehicles. Broad application prospects.

Obviously, according to the above-mentioned content of the present invention, according to the common technical knowledge and conventional means in the field, without departing from the above-mentioned basic technical idea of the present invention, other various forms of modification, replacement or change can also be made.

The above content of the present invention will be further described in detail below through the specific implementation in the form of examples. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention.

Description of drawings

Figure 1 shows the apparent density and closed cell ratio of each rigid polyimide foam.

Figure 2 shows the compressive strength (10% strain) and compressive modulus of each rigid polyimide foam at room temperature.

Figure 3 shows the compressive strength (10% strain) and compressive modulus of each rigid polyimide foam at 200°C.

Figure 4 is the thermal degradation curve of each rigid polyimide foam in nitrogen and air atmosphere: a is in nitrogen, b is in air.

Figure 5 shows the storage modulus and tanδ curve of each rigid polyimide foam: a is the storage modulus, and b is the tanδ curve.

FIG. 6 is the thermal conductivity of each rigid polyimide foam.

Figure 7 shows the relationship between the renaturation viscosity and temperature of PEAS salts with different numbers of repeating units.

Figure 8 shows the internal cell structure of each rigid polyimide foam; a is PIF-2, b is PIF-4, c is PIF-6, d is PIF-8, and e is PIF-∞.

Detailed ways

The raw materials and equipment used in the specific embodiments of the present invention are all known products, which are obtained by purchasing commercially available products.

Embodiment 1, the preparation of rigid polyimide foam of the present invention

1. Preparation of polyester ammonium salt precursor

(1) Accurately weigh 0.1mol of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) into a 500ml three-necked flask, weigh 1mmol of dimethylimidazole (2-MI ), 0.7 mol of anhydrous methanol (CH ₃ OH), and 0.8 mol of tetrahydrofuran (THF) were added to the three-necked flask. Pour nitrogen into the above system to remove the air in the flask, and under nitrogen atmosphere, reflux reaction in an oil bath at 62 ° C for 1 hour, the color of the system solution gradually changes from a milky white liquid to a pale yellow clear solution to obtain BTDA diacid diester solution.

(2) At the same time, weigh 0.1 mol of norbornene dioic anhydride (NA), 0.35 mol of CH ₃ OH, 0.4 mol of THF and 1 mmol of 2-MI, and stir for 1 h under a nitrogen atmosphere at 62° C. The solution becomes clear to obtain Norbornene Diester Solution. Transfer the norbornene diacid diester solution to the BTDA diacid diester solution, mix and stir for 15 minutes, the solution changes from turbidity to clarity, and a clear system is obtained.

(3) 0.15mol 4,4'-diaminodiphenylmethane (MDA), 0.39g surfactant (silicon oil) and 5mmol isoquinoline were weighed and added to the above-mentioned clarifying system, the system temperature was raised to 70°C, and the reaction After 3h, a reddish-brown liquid with a certain viscosity was obtained. Part of the solvent was removed at 65°C and -0.6MPa to obtain PEAS salt. In this system, the solvent content in the PEAS salt is controlled to be 16-17%.

2. Preparation of polyimide foam

The PEAS salt with a solvent content of 16-17% is mechanically pulverized to obtain particles with a particle size of 0.1-0.3 mm. The particles are heated from room temperature to 180° C. and kept at 180° C. for 30 minutes to obtain micro-foamed PEAS microspheres. The micro-foamed PEAS microspheres were filled into the mold, the temperature was raised to 300° C. and kept for 2 h to complete foaming and imidization, and a rigid polyimide foam was obtained. This rigid polyimide foam has a chain segment number of 2 (n=2), and is named PIF-2.

Polyimide foams with different chain segments (n=4, 6, 8 or ∞) were prepared according to the preparation method described in Example 1, and the obtained polyimide foams were named PIF-4, PIF-6, PIF- 8 and PIF-∞. ∞ means that the number of links in the polyimide foam is infinite. The raw material formulation of each polyimide foam is shown in Table 1. CH ₃ OH, THF and 2-MI were added in two portions. In Table 1, the amount before "/" is the amount added to BTDA for the first time, and the amount after "/" is the amount added to norbornene for the second time. When the number of segments is ∞, the norbornene diacid diester solution is not added to the BTDA diacid diester solution.

Table 1. Raw material formulation of each polyimide foam

The beneficial effects of the present invention are demonstrated below through specific test examples.

Test Example 1. Performance characterization of the rigid polyimide foam of the present invention

1. Test method

(1) Apparent density

计算出表观密度，表观密度为多次测试结果取平均值。Refer to GB/T 6343-2009 "Determination of Apparent Density of Foamed Plastics and Rubber" for testing, select no less than 5 samples, PUF sample size is 30mm × 30mm × 20mm, weigh the quality of each foam sample ,use

Calculate the apparent density, and the apparent density is the average of the results of multiple tests.

(2) closed cell rate

The closed cell ratio test is to place a known mass of PI foam in water until its mass remains constant. The calculation method of open cell ratio is the ratio of the volume of displaced water to the sample volume, closed cell ratio=100%-open cell ratio.

(3) Mechanical properties

The compression performance test refers to GB/T 8813-2008 "Rigid Foam Compression Strength Test Method". The size of the PI foam sample is 30mm×30mm×20mm, and the number of tests is not less than 5. The test compression direction and cell growth direction Vertical, the compression rate is 2mm/min, and the test results are averaged for multiple measurements.

(4) Thermal properties

The thermal stability of PI foam was analyzed by thermogravimetric analyzer. The test atmosphere was nitrogen and air. The test temperature of the PI foam sample was 30-800 °C, and the heating rate was 10 °C/min. Dynamic mechanical thermal analysis was used to analyze the PI foam. The storage modulus and glass transition temperature of PI foam were tested, the test mode was compression mode, the test frequency was 1HZ, and the heating rate was 5°C/min; the thermal conductivity of PI foam was obtained by hot disk test. The hot plate sensor was placed between two prepared samples. The thermal conductivity of two samples is collected simultaneously and the reported value is the average of the two samples.

(5) Rheological properties

The PEAS rheological properties were analyzed using a torque rheometer, the strain was set to 0.5%, and the angular velocity was 10 rad s ^-1 . The temperature scanning range was 50-300°C, and the heating rate was 10°C min ^-1 .

(6) Cell morphology

Cell structures were observed using a scanning electron microscope. All PI foam samples were sprayed with gold prior to observation.

2. Test results

The performance characterization results of each polyimide foam with different chain numbers are shown in Table 2, Table 3 and Figures 1-8.

Table 2. Characterization results of physical properties of each polyimide foam

Table 3. Thermal Properties Characterization Results of Each Polyimide Foam

For porous materials, high apparent density is beneficial to improve the mechanical strength, but high apparent density will increase the self-weight of the material, which is inconvenient for transportation and construction, and cannot be used as a lightweight material. Therefore, it is very important to study a low-density and high-strength polyimide foam for its application. It is found in the research of the present invention (Table 2 and Figures 1-3) that the polyimide foam prepared by the present invention has the beneficial effects of low density and high strength at the same time, especially PIF-4, which has a significantly lower apparent density. Improved compressive strength and compressive modulus. That is to say, under the condition of low apparent density, the polyimide foam has significantly improved comprehensive mechanical properties, excellent toughness and strength, and achieved better results, which is beneficial to the application of polyimide foam. At the same time, the polyimide foam prepared by the present invention still has a certain strength at high temperature, and can be used in a high temperature environment. In addition, the thermal properties results (Table 3 and Figures 4-6) also show that the polyimide foam prepared by the present invention has good thermal stability and excellent thermal insulation properties, which can be used at high temperatures.

Figure 7 shows the relationship between renaturation viscosity and temperature of PEAS salts with different numbers of repeating units. Combined with Figure 8, the viscosity results show that: with the decrease of the number of chain links, the viscosity of the system shows a downward trend, which helps to improve the interaction between cells (Figure 8b); when the number of chain links is ∞, the It has a higher viscosity and a wider temperature range, which makes the cells appear separated (Fig. 8e). When the number of chain links is 2, the viscosity of the system is low, resulting in insufficient cell wall strength to sustain the expansion process, resulting in the formation of a combined cell structure (Fig. 8a). It shows that the appropriate viscosity is beneficial to the formation of the internal cells of the polyimide foam, which makes it have good mechanical properties; the internal cells of PIF-4 are uniform and tightly connected, and it has good mechanical properties and significantly improved compressive strength.

To sum up, the polyimide foam prepared by the present invention has high compressive strength, excellent comprehensive mechanical properties, low apparent density, small self-weight, convenient transportation and construction, and can be used as a lightweight material. At the same time, the polyimide foam has excellent thermal stability and thermal insulation properties, and can be used at high temperatures. The polyimide foam of the invention also has the characteristics of good thermal stability, high compressive strength, low density and low self-weight, and can be used as a structural material in many high-tech fields such as aerospace, military ships, energy and high-speed rail vehicles. Broad application prospects.

Claims (10)

1. a rigid polyimide foam is characterized in that: it has the structure shown in formula I:

in, Ring A is selected from

R ₁ is selected from

R ₂ is selected from

n is an integer ≥1. 2. rigid polyimide foam according to claim 1 is characterized in that: n is an integer from 1 to 7; Preferably, the n is 3. 3. rigid polyimide foam according to claim 1 is characterized in that: it is prepared from bifunctional acid anhydride, diamine and monofunctional acid anhydride as raw materials; The molar ratio of the difunctional acid anhydride, the diamine and the monofunctional acid anhydride is 1:(1-5):(0.1-1). 4 . The rigid polyimide foam according to claim 3 , wherein the molar ratio of the difunctional acid anhydride, the diamine and the monofunctional acid anhydride is 1:(1.1～1.5):(0.25～ 1); Preferably, the molar ratio of the difunctional acid anhydride, the diamine and the monofunctional acid anhydride is 1:1.25:0.5. 5. The rigid polyimide foam according to claim 3 or 4, characterized in that: The difunctional acid anhydride is selected from 3,3',4,4'-diphenyl ether tetraacid anhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, 3 ,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenylsulfone tetracarboxylic dianhydride, 2,3,3',4'-biphenyl One or more of tetracarboxylic dianhydrides; And/or, the diamine is selected from 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 3,3'-diphenylene Aminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 2,2'-dimethyldiaminobiphenyl, 2,6-diaminopyridine one or more of; And/or, the acid anhydride of described monofunctionality is selected from one or more in norbornene dianhydride, 4-phenylethynyl phthalic anhydride, 4-ethynyl phthalic anhydride, maleic anhydride kind; Preferably, The difunctional acid anhydride is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride; And/or, the diamine is selected from 4,4'-diaminodiphenylmethane; And/or, the monofunctional acid anhydride is selected from norbornene dianhydride. 6. A method for preparing the rigid polyimide foam according to any one of claims 1 to 5, characterized in that: it comprises the following steps: (1) adding a ring-opening catalyst, an alcohol solvent and an ether solvent to the bifunctional acid anhydride, and after the reaction, a bifunctional polyamic acid precursor solution is obtained; (2) adding a ring-opening catalyst, an alcohol solvent and an ether solvent to the monofunctional acid anhydride, and after the reaction, a monofunctional polyamic acid precursor solution is obtained; (3) the solution obtained in step (1) and the solution obtained in step (2) are mixed and stirred to obtain a clear system; (4) adding diamine, surfactant and imidization catalyst to the clarification system obtained in step (3), and purifying to obtain PEAS salt; (5) The PEAS salt is foamed to obtain expanded microspheres and then imidized to obtain rigid polyimide foam. 7. The method according to claim 6, wherein: In step (1), the molar ratio of the bifunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:(0.001-0.1):(1-10):(1-10); And/or, in step (2), the molar ratio of the monofunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:(0.001-0.1):(1-10):(1-10 ); And/or, in step (4), the molar ratio of the diamine to the imidization catalyst is 1:(0.01-0.1); And/or, in step (4), the amount of the surfactant is 0.1-0.5wt% of the total mass of the bifunctional acid anhydride, the monofunctional acid anhydride and the diamine; Preferably, In step (1), the molar ratio of the bifunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:0.01:7:8; And/or, in step (2), the molar ratio of the monofunctional acid anhydride, the ring-opening catalyst, the alcohol solvent and the ether solvent is 1:0.01:3.5:4; And/or, in step (4), the molar ratio of the diamine and the imidization catalyst is 1:0.04; And/or, in step (4), the amount of the surfactant is 0.5 wt % of the total mass of the difunctional acid anhydride, the monofunctional acid anhydride and the diamine. 8. The method according to claim 6 or 7, wherein: In step (1), the ring-opening catalyst is dimethylimidazole; And/or, in step (1), described alcoholic solvent is one or more in methyl alcohol, ethanol, propyl alcohol and Virahol; And/or, in step (1), described ether solvent is tetrahydrofuran; And/or, in step (2), the ring-opening catalyst is dimethylimidazole; And/or, in step (2), described alcoholic solvent is one or more in methyl alcohol, ethanol, propyl alcohol and Virahol; And/or, in step (2), the ether solvent is tetrahydrofuran; And/or, in step (4), described surfactant is silicone oil; And/or, in step (4), the imidization catalyst is isoquinoline. 9. The method according to claim 6 or 7, wherein: In step (1), described reaction is oil bath reflux reaction under nitrogen atmosphere; And/or, in step (2), described reaction is stirring under nitrogen atmosphere condition; And/or, in step (4), the reaction is 70°C～80°C for 1～5h; And/or, in step (4), the purification is to remove the solvent, so that the solvent content in the obtained PEAS salt is 14-17%; And/or, in step (5), the PAES salt is pulverized to a particle size of 0.1mm-0.3mm; And/or, in step (5), the foaming condition is 150～200℃ for 30～60min; And/or, in step (5), the imidization condition is 250-300° C. for 1-3 hours. 10. Use of the rigid polyimide foam according to any one of claims 1 to 5 in the preparation of devices used as structural materials in the fields of aerospace, military ships, energy, high-speed rail, and automobiles.

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