Pmi foams with toughening, methods of making and uses thereof

Abstract

The application relates to a PMI foam which comprises the following raw materials: methacrylonitrile, methacrylic acid, a toughening agent, a foaming agent, an initiator and a crosslinking agent. The PMI foam described in the application has excellent toughening performance by using modified nitrile rubber as the toughening agent, and the dissolution speed of the nitrile rubber can be greatly improved by using a mixture of ethyl-methoxyacetate and methyl-3-methoxypropionate to dissolve the modified nitrile rubber when the PMI foam is prepared.

Description

Technical Field

[0001] This application relates to the field of PMI foam technology, specifically to a toughened PMI foam, its preparation method, and its applications. Background Technology

[0002] Polymethacrylimide (PMI) foam, as a cross-linked rigid closed-cell material, has become a core material for high-performance sandwich structures due to its heat and compressive strength, high closed-cell ratio, high specific modulus, thermoforming capability, and resin compatibility. It supports lightweight breakthroughs in aerospace, rail transportation, wind power, and shipbuilding, demonstrating significant commercial value. However, the intrinsic properties of PMI—high modulus, high brittleness, and low elongation at break—limit its service stability. To ensure safe use in aviation and transportation equipment, continuously exploring toughening and modification pathways for PMI has become a core issue for overcoming material performance bottlenecks and expanding application boundaries.

[0003] There are several methods for toughening the PMI system. Among them, nitrile rubber has an excellent toughening effect on the PMI system. However, nitrile rubber has low solubility and slow dissolution in the system, which hinders its application in the PMI system. Invention Overview

[0004] Based on the problems of low solubility and slow dissolution of nitrile rubber in the existing technology, this application provides a PMI foam, a preparation method and its use. This application modifies nitrile rubber and dissolves the modified nitrile rubber by using a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate, which can greatly improve the solubility of the modified nitrile rubber, and the obtained PMI foam has excellent tensile properties.

[0005] Specifically, this application provides the following technical solutions.

[0006] 1. A PMI foam comprising the following raw materials:

[0007] Methacrylonitrile, methacrylic acid, toughening agents, foaming agents, initiators, and crosslinking agents.

[0008] 2. The PMI foam according to item 1, wherein, by weight, the methacrylonitrile is 40-60 parts.

[0009] The methacrylic acid content is 50-80 parts.

[0010] The toughening agent is in the form of 10-20 parts.

[0011] The foaming agent is 3-20 parts.

[0012] The first initiator is 0.1-3 parts.

[0013] The crosslinking agent is 0.5-2 parts.

[0014] 3. The PMI foam according to claim 1 or 2, wherein the foaming agent is selected from one or more of isopropanol, n-butanol, isobutanol, tert-butanol, tert-amyl alcohol, hexanol, urea, methylurea, and dimethylurea; and / or

[0015] The initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol, azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyoctanoate, diketal peroxide, butyl percarbonate, tert-butyl perpentanoate, tert-butyl perbenzoate, and tert-butyl per-2-ethylhexanoate; and / or

[0016] The crosslinking agent is selected from one or more of calcium oxide, magnesium oxide, acrylamide (AM), methacrylamide (MAM), triallyl cyanurate, allyl methacrylate, metal salts of methacrylate, metal salts of acrylate, allyl acrylate, allyl methacrylate, allyl acrylamide, and allyl methacrylamide; and / or

[0017] The toughening agent is modified nitrile rubber.

[0018] 4. The PMI foam according to item 3, wherein the modified nitrile rubber is obtained by modifying nitrile rubber with an organic acid or organic ester containing a double bond in the presence of a second initiator.

[0019] 5. The PMI foam according to item 4, wherein the second initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol, and azobisisoheptane.

[0020] 6. The PMI foam according to item 4 or 5, wherein the organic acid or organic ester containing a double bond is selected from one or more of methacrylic acid, acrylate, zinc methacrylate and maleic anhydride;

[0021] Optionally, the weight ratio of the nitrile rubber, the organic acid or organic ester containing double bonds, and the second initiator is 60-80:20-40:0.1-3.

[0022] 7. A method for preparing PMI foam according to any one of items 1-6, comprising:

[0023] Modified nitrile rubber was cut into small pieces and added to a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate to obtain a solution;

[0024] Methacrylic acid and methacrylonitrile are added to the solution to obtain a slurry, and a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate is removed to obtain a slurry of a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate removed.

[0025] The foaming agent, initiator and crosslinking agent are added to the slurry of the mixture from which ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate have been removed, and the mixture is injected into a sealed mold to react and obtain the PMI prepolymer.

[0026] PMI foam is obtained by foaming PMI prepolymer.

[0027] 8. The method according to item 7, wherein the mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 3:7 to 7:3.

[0028] 9. The method according to item 7 or 8, wherein the reaction is carried out at a temperature of 30-130°C in a sealed mold, and / or

[0029] The reaction time is 30-200 h; and / or.

[0030] The foaming temperature is 150-250℃, and / or

[0031] The foaming time is 2-8 hours.

[0032] 10. Use of PMI foam in any one of items 1-6 in aerospace, rail transportation or wind power vessels.

[0033] Invention Effects

[0034] The PMI foam described in this application uses modified nitrile rubber as a toughening agent, which has excellent toughening properties. Furthermore, the use of a mixture of ethyl methoxyacetate and methyl 3-methoxypropionate to dissolve the modified nitrile rubber during the preparation of the PMI foam can greatly improve the dissolution rate of the nitrile rubber. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] This application provides a PMI foam comprising the following raw materials:

[0038] Methacrylonitrile, methacrylic acid, toughening agents, foaming agents, initiators, and crosslinking agents.

[0039] This application uses a toughening agent to prepare PMI foam, which can improve the toughness of PMI foam.

[0040] In some embodiments, the methacrylonitrile is 40-60 parts by weight.

[0041] The methacrylic acid content is 50-80 parts.

[0042] The toughening agent is in the form of 10-20 parts.

[0043] The foaming agent is 3-20 parts.

[0044] The first initiator is 0.1-3 parts.

[0045] The crosslinking agent is 0.5-2 parts.

[0046] For example, by weight, the methacrylonitrile can be 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, etc.

[0047] The methacrylic acid can be in quantities of 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, etc.

[0048] The toughening agent can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, etc.

[0049] The foaming agent can be 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, etc.

[0050] The first initiator can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, 3 parts, etc.

[0051] The crosslinking agent is present in amounts of 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2 parts, etc.

[0052] In some embodiments, the foaming agent is selected from one or more of isopropanol, n-butanol, isobutanol, tert-butanol, tert-amyl alcohol, hexanol, urea, methylurea, and dimethylurea; and / or

[0053] The initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol, azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyoctanoate, diketal peroxide, butyl percarbonate, tert-butyl perpentanoate, tert-butyl perbenzoate, and tert-butyl per-2-ethylhexanoate; and / or

[0054] The crosslinking agent is selected from one or more of calcium oxide, magnesium oxide, acrylamide (AM), methacrylamide (MAM), triallyl cyanurate, allyl methacrylate, metal salts of methacrylate, metal salts of acrylate, allyl acrylate, allyl methacrylate, allyl acrylamide, and allyl methacrylamide; and / or

[0055] The toughening agent is modified nitrile rubber.

[0056] This application addresses the issues of high brittleness and low elongation at break in PMI foam materials by providing a PMI foam with excellent toughening properties. It utilizes modified nitrile rubber as the elastomer, forming an "island structure" within the PMI. Under stress, the rubber phase induces crazing and shear banding, undergoing elastic deformation and effectively absorbing impact energy, significantly improving the elongation at break of PMI while maintaining high specific strength and modulus. Furthermore, the heat resistance of the modified nitrile rubber matches the high-temperature resistance of PMI, enabling structural stability to be maintained in demanding processes such as composite co-curing.

[0057] Furthermore, modified nitrile rubber is produced by modifying nitrile rubber by grafting carboxyl groups, which improves the compatibility of nitrile rubber in PMI. After dissolving nitrile rubber in a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate, the nitrile rubber solution is better dispersed in the PMI monomer. The solvent is then removed by desolventizing, which does not hinder subsequent polymerization.

[0058] In this application, the modification of nitrile rubber can be carried out using conventional methods in the art. For example, in some embodiments, the modified nitrile rubber is obtained by modifying nitrile rubber with an organic acid or organic ester containing a double bond in the presence of a second initiator.

[0059] In this application, no restrictions are placed on the organic acids or organic esters containing double bonds, as long as the organic acid or organic ester contains a double bond. For example, the organic acid or organic ester containing a double bond may be selected from one or more of methacrylic acid, acrylate, zinc methacrylate and maleic anhydride.

[0060] In some embodiments, the second initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol, and azobisisoheptane.

[0061] In this application, no restrictions are placed on the method for preparing modified nitrile rubber. Conventional methods in the art can be used, such as adding organic acids or organic esters containing double bonds to nitrile rubber under the influence of a second initiator to react and obtain modified nitrile rubber.

[0062] In this application, no restrictions are placed on the reaction temperature and reaction time. Those skilled in the art can make conventional selections based on actual needs, such as a reaction temperature of 40-70°C and a reaction time of 3-8 hours.

[0063] For example, the reaction temperature can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, etc.

[0064] The reaction time can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, etc.

[0065] In some embodiments, the weight ratio (m) of the nitrile rubber, the organic acid or organic ester containing a double bond, and the second initiator is... 丁腈橡胶 :m 含有双键的有机酸或有机酯 :m 第二引发剂 The ratio is 60-80:20-40:0.1-3.

[0066] For example, the weight ratio (m) of the nitrile rubber, the organic acid or organic ester containing double bonds, and the second initiator. 丁腈橡胶 :m 含有双键的有机酸或有机酯 :m 第二引发剂 The values ​​can be 60:20:0.1, 60:20:0.5, 60:20:1, 60:20:1.5, 60:20:2, 60:20:2.5, 60:20:3, 60:25:0.5, 60:30:0.5, 60:35:0.5, 60:40:0.5, 65:30:0.5, 70:30:0.5, 75:30:0.5, 80:30:0.5, etc.

[0067] In this application, the nitrile rubber referred to is nitrile rubber conventionally used in the art, and can be nitrile rubber from any source, such as Lanxess-Taiwan Rubber (Nantong) Chemical Industry Co., Ltd.

[0068] As mentioned above, due to the presence of toughening agents in the raw materials, the prepared PMI foam has good tensile strength and elongation at break, thus it can be used in aerospace, rail transportation or wind power ships.

[0069] This application provides a method for preparing the above-mentioned PMI foam, which includes:

[0070] Modified nitrile rubber was cut into small pieces and added to a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate to obtain a solution;

[0071] Methacrylic acid and methacrylonitrile are added to the solution to obtain a slurry, and a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate is removed to obtain a slurry of a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate removed.

[0072] The foaming agent, initiator and crosslinking agent are added to the slurry of the mixture from which ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate have been removed, and the mixture is injected into a sealed mold to react and obtain the PMI prepolymer.

[0073] PMI foam is obtained by foaming PMI prepolymer.

[0074] This application uses a mixture containing ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate to dissolve modified nitrile rubber, which can greatly improve the dissolution rate of modified nitrile rubber. After adding methacrylic acid and methacrylonitrile, the mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate is removed, and the resulting PMI foam has excellent toughening properties.

[0075] In some embodiments, the mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 3:7 to 7:3.

[0076] For example, the mass ratio of ethyl 2-methoxyethyl acetate to methyl 3-methoxypropionate (m) 2-甲氧基乙酸乙酯 :m 3-甲氧基丙酸甲酯 The ratios can be 3:7, 4:6, 5:5, 6:4, 7:3, etc.

[0077] In some embodiments, the reaction is carried out at a temperature of 30-130°C in a sealed mold, and / or

[0078] The reaction time is 30-200 hours.

[0079] For example, the reaction temperatures are 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, etc.

[0080] The reaction times are 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, 75h, 80h, 85h, 90h, 95h, 100h, 105h, 110h, 115h, 120h, 125h, 130h, 135h, 140h, 145h, 150h, 155h, 160h, 165h, 170h, 175h, 180h, 185h, 190h, 195h, and 200h.

[0081] In some embodiments, the foaming temperature is 150-250°C, and / or

[0082] The foaming time is 2-8 hours.

[0083] For example, foaming temperatures are 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc.

[0084] The foaming time is 2-8 hours.

[0085] The foaming time is 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, etc.

[0086] This application provides for the use of the foam described above in aerospace, rail transportation, or wind-powered vessels.

[0087] Example

[0088] The following embodiments and exemplary implementations are intended to be purely illustrative of this application and should not be construed as limiting the application in any way. The following embodiments and detailed descriptions are provided by way of illustration rather than limitation.

[0089] Example 1

[0090] (1) Using 0.5 g of azobisisobutyronitrile (AIBN) as the second initiator, 30 g of methacrylic acid was added to 70 g of nitrile butadiene rubber (purchased from Lanxess-Taiwan Rubber (Nantong) Chemical Industry Co., Ltd.) at 65 °C and reacted for 5 h to obtain modified AIBN. The modified AIBN was identified by infrared spectroscopy, and the modified AIBN was obtained at 2985 cm⁻¹. -1 A strong peak appeared at 3462cm. -1 A small peak appears at the position, which should be the carboxyl absorption peak, indicating that the nitrile rubber has been successfully modified to obtain nitrile rubber.

[0091] (2) Cut 17g of modified nitrile rubber into small pieces and dissolve it in a mixture of 100g of ethyl 2-methoxyacetate and methyl 3-methoxypropionate to obtain a solution, wherein the mass ratio of ethyl 2-methoxyacetate and methyl 3-methoxypropionate is 1:1.

[0092] (3) Add 70g of methacrylic acid and 50g of methacrylonitrile to the solution in step (2) and mix them evenly to obtain a slurry;

[0093] (4) The mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate was removed to obtain a slurry of the mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate removed;

[0094] (5) Add 0.5g azobisisobutyronitrile, 7g isopropanol and 1.3g acrylamide to the slurry of the mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate removed in step (4), mix evenly, and pour into a sealed mold. React at 55°C for 240h to obtain PMI prepolymer.

[0095] (6) The PMI prepolymer was foamed at 220°C for 3 hours to obtain PMI foam.

[0096] Example 2

[0097] The difference between Example 2 and Example 1 is that the mass ratio of ethyl 2-methoxyacetate and methyl 3-methoxypropionate used is 3:7.

[0098] Example 3

[0099] The difference between Example 3 and Example 1 is that the mass ratio of ethyl 2-methoxyacetate and methyl 3-methoxypropionate used is 7:3.

[0100] Example 4

[0101] The difference between Example 4 and Example 1 is that the mass ratio of ethyl 2-methoxyacetate and methyl 3-methoxypropionate used is 1:9.

[0102] Example 5

[0103] The difference between Example 5 and Example 1 is that the mass ratio of ethyl 2-methoxyacetate and methyl 3-methoxypropionate used is 9:1.

[0104] Example 6

[0105] The difference between Example 6 and Example 1 is that in Example 6, the modified nitrile rubber was cut into small pieces and added to toluene to obtain a solution.

[0106] Example 7

[0107] The difference between Example 7 and Example 1 is that the toughening agent is nitrile rubber.

[0108] Example 8

[0109] The difference between Example 8 and Example 1 is that the amount of modified nitrile rubber used is 10g.

[0110] Example 9

[0111] The difference between Example 9 and Example 1 is that the amount of modified nitrile rubber used is 20g.

[0112] Example 10

[0113] The difference between Example 10 and Example 1 is that the amount of modified nitrile rubber used is 23g.

[0114] Example 11

[0115] The difference between Example 11 and Example 1 is that the amount of modified nitrile rubber used is 7g.

[0116] Example 12

[0117] The difference between Example 12 and Example 1 is that the modified nitrile rubber is directly dissolved in the polymerization solution.

[0118] Table 1

[0119] Example 2 17g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 3:7. Example 3 17g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 7:3. Example 4 17g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 1:9. Example 5 17g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 9:1. Example 6 17g modified nitrile rubber Toluene Example 7 17g Nitrile Rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 1:1. Example 8 10g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 1:1. Example 9 20g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 1:1. Example 10 23g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 1:1. Example 11 7g modified nitrile rubber The mass ratio of ethyl 2-methoxyacetate to methyl 3-methoxypropionate is 1:1. Example 12 17g modified nitrile rubber Polymerization solution

[0120] Test case

[0121] The apparent density and tensile properties of the foams obtained in Examples 1-12 were determined, and the results are shown in Table 2. The apparent density was determined according to GB / T6343-2009 Determination of Apparent Density of Foamed Plastics and Rubber; the tensile properties were determined according to ASTM-D638-2010 Tensile Testing of Plastics.

[0122] In addition, the dissolution of modified nitrile rubber was also studied during the foam preparation process, and the dissolution time is shown in Table 2.

[0123] Table 2

[0124]

[0125] As can be seen from Table 2, directly dissolving the modified nitrile rubber in the polymerization solution results in a long dissolution time and incomplete dissolution (see Example 2). Dissolving the modified nitrile rubber in toluene also results in a relatively long dissolution time (see Example 6). However, using a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate to dissolve the modified nitrile rubber not only results in a fast dissolution rate but also improves the toughening properties of the PMI foam.

[0126] 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 PMI foam comprising the following raw materials: Methacrylonitrile, methacrylic acid, toughening agent, foaming agent, primary initiator, and crosslinking agent; The methacrylonitrile is 40-60 parts by weight. The methacrylic acid content is 50-80 parts. The toughening agent is in the form of 10-20 parts. The foaming agent is 3-20 parts. The first initiator is 0.1-3 parts. The crosslinking agent is 0.5-2 parts; The toughening agent is modified nitrile rubber; The modified nitrile rubber is obtained by modifying nitrile rubber with organic acids or organic esters containing double bonds in the presence of a second initiator. The modified nitrile rubber was dissolved using a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate to obtain a solution; The mass ratio of ethyl 2-methoxyethyl acetate to methyl 3-methoxypropionate is 3:7 to 7:3; The PMI foam is prepared by a method comprising the following steps: Methacrylic acid and methacrylonitrile are added to the solution to obtain a slurry, and a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate is removed to obtain a slurry of a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate removed. The foaming agent, the first initiator and the crosslinking agent are added to the slurry of the mixture from which ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate have been removed, and the mixture is injected into a sealed mold to react and obtain the PMI prepolymer. PMI foam is obtained by foaming PMI prepolymer.

2. The PMI foam according to claim 1, wherein, The foaming agent is selected from one or more of isopropanol, n-butanol, isobutanol, tert-butanol, tert-amyl alcohol, hexanol, urea, methylurea, and dimethylurea; and / or The first initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol, azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyoctanoate, diketal peroxide, butyl percarbonate, tert-butyl perpentanoate, tert-butyl perbenzoate, and tert-butyl per-2-ethylhexanoate; and / or The crosslinking agent is selected from one or more of calcium oxide, magnesium oxide, acrylamide (AM), methacrylamide (MAM), triallyl cyanurate, allyl methacrylate, metal salt of methacrylate, metal salt of acrylate, allyl acrylate, allyl methacrylate, allyl acrylamide, and allyl methacrylamide.

3. The PMI foam according to claim 1, wherein the second initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol, and azobisisoheptane.

4. The PMI foam according to any one of claims 1-3, wherein the organic acid or organic ester containing a double bond is selected from one or both of methacrylic acid and acrylate; Optionally, the weight ratio of the nitrile rubber, the organic acid or organic ester containing double bonds, and the second initiator is 60-80:20-40:0.1-3.

5. A method for preparing PMI foam according to any one of claims 1-4, comprising: Modified nitrile rubber was cut into small pieces and added to a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate to obtain a solution; Methacrylic acid and methacrylonitrile are added to the solution to obtain a slurry, and a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate is removed to obtain a slurry of a mixture of ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate removed. The foaming agent, the first initiator and the crosslinking agent are added to the slurry of the mixture from which ethyl 2-methoxyethyl acetate and methyl 3-methoxypropionate have been removed, and the mixture is injected into a sealed mold to react and obtain the PMI prepolymer. PMI prepolymer is foamed to obtain PMI foam; The mass ratio of ethyl 2-methoxyethyl acetate to methyl 3-methoxypropionate is 3:7 to 7:

3.

6. The method according to claim 5, wherein the reaction is carried out at a temperature of 30-130°C in a sealed mold, and / or The reaction time is 30-200 hours; and / or The foaming temperature is 150-250℃, and / or The foaming time is 2-8 hours.

7. Use of PMI foam according to any one of claims 1-4 in aerospace, rail transportation or wind power vessels.

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