High-impact-resistance polymethacrylimide foam as well as preparation method and application thereof

Abstract

The invention provides high-impact-resistance polymethacrylimide foam, a preparation method and application, and belongs to the technical field of foam materials, and the high-impact-resistance polymethacrylimide foam comprises the following raw materials: methacrylic acid, methacrylonitrile, an initiator, a composite foaming agent and an optional cross-linking agent, the polymethacrylimide foam can enhance energy dissipation and improve structural stability, has excellent impact resistance, and thus can be used in the fields of low-altitude aircrafts and the like.

Description

Technical Field

[0001] This application relates to the field of foam materials technology, and in particular to a high-impact polymethacrylimide foam, its preparation method, and its uses. Background Technology

[0002] Low-altitude aircraft face stringent technical standards in terms of range, load capacity, and operational safety. These standards constitute the research and development focus of the low-altitude economic supporting technology field and are also the core technical bottlenecks for the industry to overcome.

[0003] As the global low-altitude economy rapidly expands into scenarios such as passenger transport, logistics delivery, and emergency rescue, the complex environmental challenges faced by low-altitude aircraft are becoming increasingly prominent. The low-altitude domain is characterized by dense obstacles, diverse dynamic risk sources, and variable weather conditions, making aircraft susceptible to instantaneous impact loads during takeoff, landing, and cruise. If these impacts cannot be effectively mitigated, they may cause structural crack propagation, failure of critical components, or even loss of overall aircraft control, directly threatening personnel safety and mission reliability.

[0004] Polymethacrylimide (PMI foam) has significant advantages in terms of lightweight, high mechanical properties, and processability. However, PMI has low impact resistance. Therefore, improving the impact resistance of PMI foam is of great significance to the low-altitude economy. Summary of the Invention

[0005] Based on the technical problems existing in the prior art, this application provides a high-impact polymethacrylimide foam, its preparation method and its uses, and the obtained foam has excellent high impact resistance.

[0006] The specific technical solution of this application is as follows:

[0007] This application provides a polymethacrylimide foam comprising the following raw materials: methacrylic acid, methacrylonitrile, initiator, composite foaming agent, and optional crosslinking agent.

[0008] Preferably, for the polymethacrylimide foam described above, the composite blowing agent comprises a low-temperature blowing agent and a high-temperature blowing agent. Optionally, the low-temperature blowing agent is selected from one or more of isopropanol, isobutanol, tert-butanol, n-heptane, methyl ethyl ketone, and tert-butyl methyl ether; and / or

[0009] The high-temperature foaming agent is selected from one or more of azodicarbonamide, formamide, and glycerol.

[0010] Preferably, for the polymethacrylimide foam described above, the mass ratio of methacrylic acid, methacrylonitrile, initiator, low-temperature foaming agent, high-temperature foaming agent and optional crosslinking agent is 50-80:50-80:0.1-3:1-5:5-12:0-5.

[0011] Preferably, for any of the above-mentioned polymethacrylimide foams, the initiator is selected from one or more of azobisisobutyronitrile, azobisisopentanol, azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxypentanoate, tert-butyl peroxybenzoate, and tert-butyl peroxy-2-ethylhexanoate; and / or

[0012] The optional crosslinking agent is selected from one or more of calcium oxide, magnesium oxide, acrylamide, methacrylamide, triallyl cyanurate, allyl methacrylate, metal salt of methacrylate, metal salt of acrylate, allyl acrylate, allyl acrylamide, and allyl methacrylamide.

[0013] This application provides a method for making polymethacrylimide foam according to any one of the above claims, comprising:

[0014] Methacrylic acid, methacrylonitrile, an initiator, a composite foaming agent, and an optional crosslinking agent are mixed to obtain a mixture, and the mixture is subjected to a polymerization reaction and foaming to obtain polymethacrylimide foam.

[0015] Preferably, in the method described above, the polymerization reaction temperature is 30-50°C; and / or

[0016] The polymerization reaction takes 30-200 hours.

[0017] Preferably, in the method described above, the foaming process includes low-temperature foaming, cooling, and high-temperature foaming.

[0018] Preferably, in the method described above, the low-temperature foaming temperature is 130-170°C; and / or

[0019] The low-temperature foaming time is 1-10 hours.

[0020] Preferably, in the method described above, the material that has undergone low-temperature foaming is cooled to 80-100°C to obtain cooled material; and / or

[0021] The cooled material is subjected to high-temperature foaming to obtain polymethacrylimide foam, optionally, the high-temperature foaming temperature is 170-250°C; and / or,

[0022] The high-temperature foaming time is 1-10 hours.

[0023] This application provides the use of any of the polymethacrylimide foams described in this application in the field of low-altitude aircraft materials.

[0024] The effects of the invention

[0025] The PMI foam described in this application has the following technical effects:

[0026] 1. Enhanced Energy Dissipation: The large pores in the layered homogeneous pore structure allow impact energy to rapidly penetrate the material's interior, while the small pores increase the internal interfaces and friction. When the material is impacted, the impact energy propagates through the large pores, undergoing multiple reflections, refractions, and scatterings at the small pores. This results in a more uniform energy distribution within the material, dissipating as heat or other forms of energy through friction and internal friction. The small pore structure also enhances damping during impact, effectively absorbing and dispersing the impact energy.

[0027] 2. Improved Structural Stability: The layered, homogeneous cellular structure enhances the material's structural stability, enabling it to maintain its structural integrity under impact. Large pores provide structural support, while small pores strengthen the material's toughness and resistance to deformation. Small pores can inhibit crack propagation; when a crack extends into the small pore region, the pores can disperse stress at the crack tip, altering or halting crack propagation, thereby improving the material's impact resistance.

[0028] 3. Due to their different decomposition temperatures, low-temperature blowing agents (such as isopropanol and tert-butanol) and high-temperature blowing agents (such as azodicarbonamide and glycerol) in composite blowing agents can release gases stepwise during polymerization. Low-temperature blowing agents first form initial cell nuclei at a lower temperature, while high-temperature blowing agents further expand the cells and form new bubble nuclei in the subsequent high-temperature stage, thus forming a homogeneous structure with a layered distribution of "large cells - small cells" inside the foam.

[0029] 4. Low-temperature foaming occurs after the polymerization reaction. During this stage, the low-temperature foaming agent decomposes slowly, forming a uniform initial cell core network at a higher viscosity stage, laying the foundation for subsequent structures. Cooling is used to cool the material after low-temperature foaming to a medium temperature range, temporarily solidifying the polymer chains and stabilizing the formed cell structure. High-temperature foaming occurs after cooling and setting, allowing the remaining foaming agent to fully decompose, promoting further cell expansion and the formation of a hierarchical structure. Detailed Implementation

[0030] The present application will now be described in detail with reference to the described embodiments. Although specific embodiments of the present application are shown, it should be understood that the present application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0031] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0032] This application provides a polymethacrylimide foam comprising the following raw materials: methacrylic acid, methacrylonitrile, initiator, composite foaming agent, and optional crosslinking agent.

[0033] In this application, optional representations may or may not exist; for example, optional crosslinking agent means that a crosslinking agent may or may not exist.

[0034] In some embodiments, the composite foaming agent comprises a low-temperature foaming agent and a high-temperature foaming agent. Optionally, the low-temperature foaming agent is selected from one or more of isopropanol, isobutanol, tert-butanol, n-heptane, methyl ethyl ketone, and tert-butyl methyl ether; and / or

[0035] The high-temperature foaming agent is selected from one or more of azodicarbonamide, formamide, and glycerol.

[0036] In this application, the low-temperature foaming agent can form initial cell nuclei at a lower temperature, while the high-temperature foaming agent will further expand the cells and form new bubble nuclei, thereby forming a homogeneous structure with a layered distribution of "large cells - small cells" inside the foam.

[0037] In this application, the term "large pore" refers to a pore with a diameter of 100-350 μm, and the term "small pore" refers to a pore with a diameter of 1-50 μm.

[0038] In this application, no restrictions are placed on the methods for determining large and small pores. Those skilled in the art can use conventional methods in the field to perform the determination. For example, a sharp blade can be used to prepare sections, the thickness of which should not be too thick to avoid overlapping of multiple pores. After sectioning, staining is performed, and then the pore size is observed using an optical microscope, or the pore size can be obtained through further analysis using ImageJ.

[0039] The foam described in this application has a homogeneous structure with a layered distribution of "large pores - small pores". The large pores allow impact energy to enter the interior of the material quickly, while the small pores increase the interfaces and friction inside the material. Therefore, when the foam material is impacted, the impact energy will be reflected, refracted and scattered multiple times at the small pores during the propagation of the impact energy in the large pores, so that the energy is more evenly distributed inside the material and dissipated into heat energy and other forms of energy through friction and internal friction.

[0040] In some embodiments, the mass ratio of the methacrylic acid, methacrylonitrile, initiator, low-temperature foaming agent, high-temperature foaming agent, and optional crosslinking agent is 50-80:50-80:0.1-3:1-5:5-12:0-5.

[0041] When no crosslinking agent is present, the mass ratio of the methacrylic acid, methacrylonitrile, initiator, low-temperature foaming agent, and high-temperature foaming agent is 50-80:50-80:0.1-3:1-5:5-12, for example, the mass ratio of the five substances (m 甲基丙烯酸 :m 甲基丙烯腈 :m 引发剂 :m 低温发泡剂 :m 高温发泡剂The possible values ​​are 50:50:0.1:1:5, 50:55:0.1:1:5, 50:60:0.1:1:5, 50:65:0.1:1:5, 50:70:0.1:1:5, 50:75:0.1:1:5, 50:80:0.1:1:5, 50:55:0.5:1:5, 50:55:1:1:5, 50:55:1.5:1:5, and 50:55:2: 1:5, 50:55:2.5:1:5, 50:55:3:1:5, 50:55:0.5:1.5:5, 50:55:0.5:2:5, 50:55:0.5:2.5:5, 50:55:0.5:3:5, 50:55:0.5:3.5:5, 50:55:0.5:4:5, 50:55:0.5:4.5:5, 50:55:0.5:5:5 50:55:0.5:2:5.5, 50:55:0.5:2:6, 50:55:0.5:2:6.5, 50:55:0.5:2:7, 50:55:0.5:2:7.5, 50:55:0.5:2:8, 50:55:0.5:2:8.5, 50:55:0.5:2:9, 50:55:0.5:2:9.5, 50:55:0.5:2:10 50:55:0.5:2:10.5, 50:55:0.5:2:11, 50:55:0.5:2:11.5, 50:55:0.5:2:12, 55:55:0.5:2:8, 60:55:0.5:2:8, 65:55:0.5:2:8, 70:55:0.5:2:8, 75:55:0.5:2:8, 80:55:0.5:2:8, etc.

[0042] When a crosslinking agent is present, the mass ratio of the methacrylic acid, methacrylonitrile, initiator, low-temperature foaming agent, high-temperature foaming agent, and optional crosslinking agent is 50-80:50-80:0.1-3:1-5:5-12:0.1-5, for example, the mass ratio of the six substances (m 甲基丙烯酸 :m 甲基丙烯腈 :m 引发剂 :m 低温发泡剂 :m 高温发泡剂 :m 交联剂The possible values ​​are 50:50:0.1:1:5:0.1, 50:55:0.1:1:5:0.1, 50:60:0.1:1:5:0.1, 50:65:0.1:1:5:0.1, 50:70:0.1:1:5:0.1, 50:75:0.1:1:5:0.1, 50:80:0.1:1:5:0.1, 50:55:0.5:1:5:0.1, 50:55:1:1:5:0.1, 50:55:1.5:1:5:0.1, 50:55:2:1:5:0.1, 50:55:2.5:1:5:0.1, 50:55:3:1:5:0.1, 50:55: 0.5:1.5:5:0.1, 50:55:0.5:2:5:0.1, 50:55:0.5:2:5:0.1, 50:55:0.5:2.5:5:0.1, 50:55:0.5:3:5:0.1, 50:55:0.5:3.5:5:0.1, 50:55:0.5:4:5:0.1, 50:55:0.5:4.5:5:0.1, 50:55:0.5:5:5:0.1, 50:55:0.5:2:5.5:0.1, 50:55:0.5:2:6:0.1, 50:55:0.5:2:6.5:0.1, 50:55:0.5:2:7:0. 1. 50:55:0.5:2:7.5:0.1, 50:55:0.5:2:8:0.1, 50:55:0.5:2:8.5:0.1, 50:55:0.5:2:9:0.1, 50:55:0.5:2:9.5:0.1, 50:55:0.5:2:10:0.1, 50:55:0.5:2:10.5:0.1, 50:55:0.5:2:11:0.1, 50:55:0.5:2:11.5:0.1, 50:55:0.5:2:12:0.1, 50:55:0.5:2:8:0.5, 50:55:0.5:2:8:1, 50:55:0 .5:2:8:1.5, 50:55:0.5:2:8:2, 50:55:0.5:2:8:2.5, 50:55:0.5:2:8:3, 50:55:0.5:2:8:3.5, 50:55:0.5:2:8:4, 50:55:0.5:2:8:4.5, 50:55:0.5:2:8:5, 55:55:0.5:2:8:0.5, 60:55:0.5:2:8:0.5, 65:55:0.5:2:8:0.5, 70:55:0.5:2:8:0.5, 75:55:0.5:2:8:0.5, 80:55:0.5:2:8:0.5, etc.

[0043] In some embodiments, the initiator is selected from one or more of azobisisobutyronitrile, azobisisopentanol, azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxypentanoate, tert-butyl peroxybenzoate, and tert-butyl peroxy-2-ethylhexanoate; and / or

[0044] The optional crosslinking agent is selected from one or more of calcium oxide, magnesium oxide, acrylamide, methacrylamide, triallyl cyanurate, allyl methacrylate, metal salt of methacrylate, metal salt of acrylate, allyl acrylate, allyl methacrylate, allyl acrylamide, and allyl methacrylamide.

[0045] The metal salts of methacrylate include sodium salt, zinc salt, calcium salt, copper salt, and silver salt of methacrylate.

[0046] Metal salts of acrylate include sodium salt, potassium salt, calcium salt, magnesium salt, zinc salt, copper salt, and aluminum salt.

[0047] The foam described in this application has a moderate apparent density and excellent failure impact energy.

[0048] This application provides a method for preparing the polymethacrylimide foam according to any one of the above claims, comprising:

[0049] A mixture of methacrylic acid, methacrylonitrile, an initiator, a composite foaming agent, and optionally a crosslinking agent is prepared, and the mixture is subjected to a polymerization reaction and foaming to obtain polymethacrylimide foam. In some embodiments, the polymerization reaction is carried out at a temperature of 30-50°C; and / or

[0050] The polymerization reaction takes 30-200 hours.

[0051] For example, the polymerization temperature can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, etc.

[0052] The polymerization reaction time can be 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, 120h, 130h, 140h, 150h, 160h, 170h, 180h, 190h, 200h, etc.

[0053] In some embodiments, the foaming includes low-temperature foaming, cooling, and high-temperature foaming.

[0054] In this application, the low-temperature foaming is performed using a low-temperature foaming agent, and the high-temperature foaming is performed using a high-temperature foaming agent.

[0055] In this application, the low-temperature foaming temperature is 130-170℃, for example, the low-temperature foaming temperature can be 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, etc.

[0056] The low-temperature foaming time is 1-10 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0057] In some embodiments, the material that has undergone low-temperature foaming is cooled to 80-100°C to obtain cooled material; and / or

[0058] The cooled material is subjected to high-temperature foaming to obtain polymethacrylimide foam, optionally, the high-temperature foaming temperature is 170-250°C; and / or,

[0059] The high-temperature foaming time is 1-10 hours.

[0060] For example, materials that have undergone low-temperature foaming are cooled to 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, or 100°C to obtain cooled materials.

[0061] In the process of preparing foam, this application cools the material after low-temperature foaming, which makes the pore core of the material more stable, and performs high-temperature foaming, which expands the pore core and further forms new pores, thereby obtaining a foam with a homogeneous structure with layered distribution.

[0062] The high-temperature foaming temperature can be, for example, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, etc.

[0063] The high-temperature foaming time can be, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0064] The foam prepared in this application has a homogeneous structure with a layered distribution and excellent impact resistance, thus it can be used in low-altitude aircraft, etc.

[0065] This application provides the use of the aforementioned foam in the field of low-altitude aircraft materials.

[0066] As described above, the foam described in this application has excellent failure impact energy, that is, excellent impact resistance, and can be used in the field of low-altitude aircraft materials.

[0067] Example

[0068] This application provides a general and / or specific description of the materials and test methods used in the experiments. In the following examples, unless otherwise specified, % represents wt%, i.e., weight percentage. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0069] Example 1: Preparation of PMI Foam

[0070] (1) 70g of methacrylic acid, methacrylonitrile, initiator (azobisisobutyronitrile), low-temperature foaming agent isopropanol, high-temperature foaming agent formamide and crosslinking agent magnesium oxide are added to the reaction vessel and mechanically stirred to obtain a mixture. Then the obtained mixture is injected into a mold for polymerization reaction to obtain the polymerization reaction material. The polymerization reaction temperature is 45℃ and the polymerization reaction time is 180h.

[0071] (2) The polymer reaction material is foamed at a low temperature of 165℃ for 3 hours to obtain a low-temperature foamed material.

[0072] (3) Cool the low-temperature foamed material to 90°C to obtain cooled material, and then foam the cooled material at 220°C for 2.5 hours to obtain polymethacrylimide foam.

[0073] Examples 2-5

[0074] The difference between Examples 2-5 and Example 1 lies in the amount of low-temperature foaming agent used to obtain polymethacrylimide foam.

[0075] Examples 6-9

[0076] The difference between Examples 6-9 and Example 1 lies in the amount of high-temperature foaming agent used to obtain polymethacrylimide foam.

[0077] Example 10

[0078] The difference between Example 10 and Example 1 is that a low-temperature foaming agent is not used to obtain polymethacrylimide foam.

[0079] Example 11

[0080] The difference between Example 11 and Example 1 is that polymethacrylimide foam is obtained without using a high-temperature foaming agent.

[0081] Example 12

[0082] The difference between Example 12 and Example 1 is that polymethacrylimide foam was obtained by cooling to a temperature of 80°C.

[0083] Example 13

[0084] The difference between Example 13 and Example 1 is that polymethacrylimide foam was obtained by cooling to a temperature of 100°C.

[0085] Example 14

[0086] The difference between Example 14 and Example 1 is that polymethacrylimide foam was obtained by cooling to a temperature of 50°C.

[0087] Example 15

[0088] The difference between Example 15 and Example 1 is that polymethacrylimide foam was obtained by cooling to a temperature of 120°C.

[0089] Example 16

[0090] The difference between Example 16 and Example 1 is that polymethacrylimide foam is obtained by high-temperature foaming without cooling.

[0091] Example 17

[0092] The difference between Example 17 and Example 1 is that the polymethacrylamide foam is obtained by using methyl ethyl ketone (MEK) as a low-temperature foaming agent for low-temperature foaming.

[0093] Example 18

[0094] The difference between Example 18 and Example 1 is that glycerol, a high-temperature foaming agent, is used for high-temperature foaming to obtain polymethacrylimide foam.

[0095] Table 1

[0096]

[0097] Experimental Example

[0098] The apparent density, failure impact energy, size of large and small pores, and area of ​​large and small pores of the PMI foam obtained in Examples 1 to 16 were measured. The results are shown in Table 2. The apparent density was determined according to GB / T 6343-2009 Determination of Apparent Density of Foamed Plastics and Rubber.

[0099] Failure impact energy test method: 1) Fix the sample (100*100*10mm) on a square fixture, ensuring that the sample does not shake and the bottom center position is 0.5cm away from the marker pen.

[0100] 2) Select one sample of each type for pre-testing. Adjust the ball mass and drop height, starting from a low height (0.5m) and gradually increasing it (0.2m each time) until the sample shows obvious damage (cracks or dents deeper than 0.5cm, etc.), which indicates that the sample has reached the upper limit of its impact resistance performance. Record the ball mass (m) and drop height (h). This data is not included in the final result.

[0101] 3) Test the mass and drop height of the ball obtained in 2) once for each sample. Test 5 samples in each group and record h1 five times. Measure the depth of the indentation (if any) and record the direction of crack propagation.

[0102] Failure impact energy: Ea = mgh.

[0103] Methods for determining the size and area of ​​large and small pores: Prepare sections using a sharp blade, ensuring the sections are not too thick to avoid overlapping of multiple pores. After sectioning, stain the sections, typically with red. Then, observe the pore size and area using an optical microscope, or perform further analysis using ImageJ to obtain the size and area of ​​large and small pores.

[0104] Table 2

[0105]

[0106] The above description is merely a preferred embodiment of this application and is not intended to limit the application in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the protection scope of this application.

Claims

1. A polymethacrylimide foam comprising the following raw materials: methacrylic acid, methacrylonitrile, initiator, composite blowing agent and optional crosslinking agent; The composite foaming agent comprises a low-temperature foaming agent and a high-temperature foaming agent. Optionally, the low-temperature foaming agent is selected from one or more of isopropanol, isobutanol, tert-butanol, n-heptane, methyl ethyl ketone, and tert-butyl methyl ether; and / or The high-temperature foaming agent is selected from one or more of azodicarbonamide, formamide and glycerol; The mass ratio of the methacrylic acid, methacrylonitrile, initiator, low-temperature foaming agent, high-temperature foaming agent, and optional crosslinking agent is 50-80:50-80:0.1-3:1-5:5-12:0-5.

2. The polymethacrylimide foam according to claim 1, wherein, The initiator is selected from one or more of azobisisobutyronitrile, azobisisopentanol, azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxypentanoate, tert-butyl peroxybenzoate, and tert-butyl peroxy-2-ethylhexanoate; and / or The optional crosslinking agent is selected from one or more of calcium oxide, magnesium oxide, acrylamide, methacrylamide, triallyl cyanurate, allyl methacrylate, metal salt of methacrylate, metal salt of acrylate, allyl acrylate, allyl acrylamide, and allyl methacrylamide.

3. A method for preparing the polymethacrylimide foam according to claim 1 or 2, comprising: Methacrylic acid, methacrylonitrile, an initiator, a composite foaming agent, and an optional crosslinking agent are mixed to obtain a mixture, and the mixture is subjected to a polymerization reaction and foaming to obtain polymethacrylimide foam.

4. The method according to claim 3, wherein the polymerization reaction temperature is 30-50°C; and / or The polymerization reaction takes 30-200 hours.

5. The method according to claim 3 or 4, wherein the foaming includes low-temperature foaming, cooling, and high-temperature foaming.

6. The method according to claim 5, wherein the low-temperature foaming temperature is 130-170°C; and / or The low-temperature foaming time is 1-10 hours.

7. The method of claim 5, wherein the material that has undergone low-temperature foaming is cooled to 80-100°C to obtain the cooled material; and / or The cooled material is subjected to high-temperature foaming to obtain polymethacrylimide foam, optionally, the high-temperature foaming temperature is 170-250°C; and / or, The high-temperature foaming time is 1-10 hours.

8. Use of the polymethacrylimide foam according to claim 1 or 2 in the field of low-altitude aircraft materials.

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