Foam material with low water absorption rate and preparation method thereof

Abstract

The invention discloses a preparation method of a low-water-absorption PMI foam material, which comprises the following steps: proportionally mixing and stirring polymerization raw materials comprising a polymer monomer, a hydrophobic monomer, an initiator, a cross-linking agent and a foaming agent to obtain a raw material mixed solution; heating and polymerizing the raw material mixed solution to obtain a polymer; heating the polymer for polymerization reaction to obtain a foaming material; and soaking the foaming material in a hydrophobic solution, and drying to obtain the PMI foaming material with low water absorption rate. The PMI foam material with low moisture absorption performance provided by the invention can be applied to a long-term humid and hot environment to maintain the overall performance of the material.

Description

Technical Field

[0001] This application relates to the field of materials preparation technology, and in particular to a PMI foam material with low moisture absorption properties, its preparation method and application. Background Technology

[0002] Polymethacrylimide (PMI) foam, as a third-generation high-performance structural foam material, has become an irreplaceable core lightweight material in high-end equipment manufacturing fields such as aerospace, new energy, and rail transportation due to its unique closed-cell structure and excellent comprehensive performance. Traditional honeycomb sandwich structures widely used in the aerospace field consist of open or semi-open pores, which easily absorb moisture through the edges of the pores in humid and hot environments, leading to a significant increase in moisture absorption. The closed-cell structure of PMI material significantly reduces moisture absorption, solving the problem of humid and hot aging associated with traditional honeycomb structures and open-cell foams. However, in practical applications, the inherent hydrophilic groups such as NH and carboxyl groups in PMI foam molecules still give the material water absorption properties, and process defects in the preparation process also prevent the closed-cell ratio from reaching the theoretical value. In some harsh environments such as long-term humid and hot conditions, the material's moisture absorption rate remains significantly higher than ideal. High water absorption allows moisture to penetrate into the interior of the PMI foam, severely degrading the material's shear strength, flexural strength, and other mechanical properties. Long-term moisture absorption can also lead to dimensional deformation and other damage. Therefore, how to further reduce the water absorption rate of PMI materials is also an important research direction. Summary of the Invention

[0003] To address the aforementioned issues, the purpose of this application is to provide a PMI foam material with low water absorption rate, and the specific technical solution is as follows.

[0004] 1. A method for preparing a low water absorption PMI foam material, comprising the following steps:

[0005] The polymer raw materials, including polymer monomers, hydrophobic monomers, initiators, crosslinking agents, and foaming agents, are mixed and stirred in a certain proportion to obtain a raw material mixture.

[0006] The raw material mixture is heated and polymerized to obtain a polymer;

[0007] The polymer is heated to undergo a polymerization reaction to obtain a foamed material;

[0008] The foaming material is soaked in a hydrophobic aqueous solution and dried to obtain the low water absorption PMI foam material.

[0009] 2. The preparation method according to item 1, wherein the polymeric monomers are methacrylic acid and methacrylonitrile, and the hydrophobic monomers are selected from methyl methacrylate, styrene, trifluoroethyl methacrylate, and vinyltrimethylsilane.

[0010] 3. The preparation method according to item 1, wherein the crosslinking agent is a non-polar crosslinking agent, preferably a polyol polyacrylate crosslinking agent or divinylbenzene.

[0011] 4. The preparation method according to item 2, wherein, by weight, the ratio of methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent is 35-45:30-40:10-20:0.1-2:0.1-3:3-10.

[0012] 5. The preparation method according to item 1, wherein the hydrophobic aqueous solution is an ethanol solution containing a silane coupling agent.

[0013] 6. The preparation method according to item 1, wherein the initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol or azobisisoheptanol, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyoctanoate or diketal peroxide, hexadecyl percarbide, butyl percarbide, and pentyl percarbide, and the foaming agent is selected from isopropanol, n-butanol, isobutanol, tert-butanol, tert-pentanol, hexanol, urea, methylurea or dimethylurea.

[0014] 7. The preparation method according to item 1, wherein the raw material mixture is polymerized by heating at a temperature of 30 to 150°C for 100 to 300 hours.

[0015] 8. The preparation method according to item 1, wherein the polymer is heated to a temperature of 160-250°C and foamed for 2-7 hours to obtain the foamed material.

[0016] 9. The preparation method according to item 1, wherein the foaming material is soaked in a hydrophobic aqueous solution for 0.1-1 hours.

[0017] 10. A low water absorption PMI foam material prepared according to any one of items 1-9.

[0018] 11. Application of the low water absorption PMI foam material described in item 10 in aerospace and transportation materials.

[0019] The effects of the invention

[0020] The foam material preparation method provided in this application optimizes the raw materials for PMI foam material preparation, reduces the amount of hydrophilic raw materials added, and appropriately increases the participation of hydrophobic monomers in polymerization to reduce the proportion of hydrophilic groups in the polymer. Choosing a non-polar crosslinking agent reduces the number of water absorption sites after crosslinking. After foaming, a hydrophobic layer is constructed on the surface through impregnation with a hydrophobic solution, which reduces the surface energy of the material and enhances the hydrophobic effect. The PMI foam material prepared by this method achieves a lower water absorption rate, avoiding weight gain or structural defects due to moisture absorption in environments such as long-term humid and hot conditions. This low-water-absorption PMI foam material maintains good mechanical properties while reducing water absorption, and can be applied in the preparation of aerospace and transportation materials, such as those used in long-term humid and hot, freeze-thaw cycles, and other environments encountered by water transport vehicles like ships. Detailed Implementation

[0021] The present application will now be described in further detail with reference to specific embodiments. The embodiments given are intended to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0022] It should be noted that the terms "comprising" or "including" used throughout the specification and appendices are open-ended and should be interpreted as "comprising but not limited to". The subsequent 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 appendices.

[0023] This application addresses the water absorption problem of PMI foam materials in practical applications by providing a method for preparing low-water-absorption PMI foam materials, comprising the following steps:

[0024] The polymer raw materials, including polymeric monomers, hydrophobic monomers, initiators, crosslinking agents, and foaming agents, are mixed and stirred in a certain proportion to obtain a raw material mixture.

[0025] The raw material mixture is heated and polymerized to obtain a polymer;

[0026] The polymer is heated to undergo a polymerization reaction to obtain a foamed material;

[0027] The foaming material is soaked in a hydrophobic aqueous solution and dried to obtain the low water absorption PMI foam material.

[0028] In some specific embodiments of this application, the polymeric monomers are methacrylic acid and methacrylonitrile.

[0029] In some specific embodiments, the hydrophobic monomer is selected from methyl methacrylate, styrene, trifluoroethyl methacrylate, and vinyltrimethylsilane.

[0030] In the embodiments of this application, adding hydrophobic monomers to PMI foam raw materials mainly composed of methacrylic acid and methacrylonitrile can improve the overall hydrophobic properties of PMI materials.

[0031] In the embodiments of this application, the crosslinking agent is selected from non-polar crosslinking agents. Compared with polar crosslinking agents, non-polar crosslinking agents can reduce the water absorption sites of the crosslinked material to a certain extent and improve the overall crosslinking density of the material.

[0032] In some specific embodiments, the crosslinking agent is selected from polyol polyacrylate crosslinking agents or divinylbenzene.

[0033] In a specific embodiment, the proportions of methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent, and foaming agent in the polymer raw materials, by weight, are 35-45:30-40:10-20:0.1-2:0.1-3:3-10.

[0034] In some specific embodiments, the ratio of methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent by weight is 35-45:35:10-20:0.1-2:0.1-3:3-10.

[0035] In some preferred embodiments, the ratio of methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent, by weight, is 35-45:35:13:0.1-2:0.1-3:3-10.

[0036] Methacrylic acid in the polymerization raw materials has a certain degree of water absorption due to the presence of hydrophilic carboxyl groups. Therefore, the proportion of methacrylic acid should be appropriately reduced during polymerization to decrease water absorption.

[0037] In some specific embodiments, the initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol or azobisisoheptane, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyoctanoate or diketal peroxide, hexadecyl percarbonate, butyl percarbonate, and pentyl percarbonate.

[0038] In some specific embodiments, the foaming agent is selected from isopropanol, n-butanol, isobutanol, tert-butanol, tert-amyl alcohol, hexanol, urea, methylurea, or dimethylurea.

[0039] In a specific embodiment, the polymer raw materials are mixed and stirred according to the above proportion to obtain a raw material mixture, and the raw material mixture is heated to obtain a polymer.

[0040] In some specific embodiments, the heating temperature for obtaining the polymer is 30–50°C, and the reaction time is 100–300 hours. For example, the addition temperature is 30°C, 35°C, 40°C, 45°C, 50°C, or any range thereof; the reaction time is 100 hours, 120 hours, 140 hours, 160 hours, 180 hours, 200 hours, 220 hours, 240 hours, 260 hours, 280 hours, 300 hours, or any range thereof.

[0041] In specific embodiments, the polymer is further heated to 160–250°C for foaming for 2–7 hours. In some specific embodiments, the foaming temperature is 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or any range thereof; the foaming time is 2 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 7 hours or any range thereof.

[0042] In a specific implementation, the foamed material obtained after foaming is soaked in a hydrophobic aqueous solution to form a hydrophobic outer layer on the surface of the material.

[0043] In some specific embodiments, the hydrophobic aqueous solution is an ethanol solution containing a silane coupling agent.

[0044] In some specific embodiments, the foaming material is soaked in a hydrophobic aqueous solution for 0.1 to 1 hour to form the hydrophobic outer layer.

[0045] In some specific embodiments, the soaking time is 0.1 hours, 0.2 hours, 0.3 hours, 0.4 hours, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1.0 hours or any other time.

[0046] In some preferred embodiments, the soaking time is less than 0.5 hours.

[0047] This application also provides a low water absorption PMI foam material prepared by the above preparation method.

[0048] This application also provides the application of the aforementioned low water absorption PMI foam material in aerospace and transportation materials.

[0049] In some specific embodiments, the transportation materials are manufacturing materials for ships and other water vehicles, waterproof materials, thermal insulation materials, repair materials, or other functional materials.

[0050] Example

[0051] 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, % means wt%, i.e., weight percentage. The reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products or conventional laboratory instruments.

[0052] Example 1: Preparation of Low Water Absorption Foam Material

[0053] Prepare PMI foam material according to the following steps:

[0054] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0055] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0056] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0057] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0058] (4) The foaming material is soaked in an ethanol solution of phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0059] Example 2: Preparation of Low Water Absorption Foam Material

[0060] Prepare PMI foam material according to the following steps:

[0061] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 45:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0062] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0063] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0064] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0065] (4) The foaming material is soaked in an ethanol solution of phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0066] Example 3: Preparation of Low Water Absorption Foam Material

[0067] Prepare PMI foam material according to the following steps:

[0068] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 35:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0069] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0070] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0071] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0072] (4) The foaming material is soaked in an ethanol solution of a hydrophobic phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0073] Example 4: Preparation of Low Water Absorption Foam Material

[0074] Prepare PMI foam material according to the following steps:

[0075] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0076] The hydrophobic monomer is methyl methacrylate, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0077] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0078] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0079] (4) The foaming material is soaked in an ethanol solution of a hydrophobic phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0080] Example 5: Preparation of Low Water Absorption Foam Material

[0081] Prepare PMI foam material according to the following steps:

[0082] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0083] The hydrophobic monomer is styrene, the crosslinking agent is ethylene glycol diacrylate, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0084] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0085] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0086] (4) The foaming material is soaked in an ethanol solution of a hydrophobic phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0087] Example 6: Preparation of Low Water Absorption Foam Material

[0088] Prepare PMI foam material according to the following steps:

[0089] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0090] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0091] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0092] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0093] (4) The foaming material is soaked in an ethanol solution of a hydrophobic aqueous solution of methyltrimethoxysilane for (0.4) hours and then dried to obtain the low water absorption rate PMI foam material.

[0094] Comparative Example 1: Preparation of PMI Foam Material

[0095] Prepare PMI foam material according to the following steps:

[0096] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 50:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0097] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0098] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0099] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0100] (4) The foaming material is soaked in an ethanol solution of phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0101] Preparation of PMI foam material (Comparative Example 2)

[0102] Prepare PMI foam material according to the following steps:

[0103] (1) The polymer raw materials containing methacrylic acid, methacrylonitrile, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:0.6:1.4:6 to obtain a raw material mixture;

[0104] The crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0105] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0106] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0107] (4) The foaming material is soaked in an ethanol solution of phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0108] Preparation of Comparative Example 3PMI Foam Material

[0109] Prepare PMI foam material according to the following steps:

[0110] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0111] The hydrophobic monomer is styrene, the crosslinking agent is acrylamide, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0112] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0113] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0114] (4) The foaming material is soaked in an ethanol solution of phenyltrimethoxysilane for 0.4 hours and then dried to obtain the low water absorption rate PMI foam material.

[0115] Preparation of Comparative Example 4 PMI Foam Material

[0116] Prepare PMI foam material according to the following steps:

[0117] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0118] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0119] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0120] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain PMI foam material.

[0121] Preparation of Comparative Example 5 PMI Foam Material

[0122] Prepare PMI foam material according to the following steps:

[0123] (1) The polymerization raw materials containing methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent are mixed and stirred in a ratio of 40:35:13:0.6:1.4:6 to obtain the raw material mixture;

[0124] The hydrophobic monomer is styrene, the crosslinking agent is divinylbenzene, the initiator is azobisisobutyronitrile, and the foaming agent is tert-butanol;

[0125] (2) The above raw material mixture was heated at 50°C for 240 hours to polymerize, thereby obtaining the polymer;

[0126] (3) The polymer is heated to 220°C and foamed for 4.5 hours to obtain a foamed material;

[0127] (4) The foaming material is soaked in an ethanol solution of a hydrophobic phenyltrimethoxysilane for 1.5 hours and then dried to obtain the low water absorption rate PMI foam material.

[0128] Experimental Example 1

[0129] The materials obtained in the above embodiments and comparative examples were subjected to performance tests. The results are shown in Table 1.

[0130] The testing standards and methods include: apparent density according to GB / T 6343-2009 Determination of Apparent Density of Foamed Plastics and Rubber; tensile properties according to ASTM-D638-2010 Tensile Strength of Plastics; compressive properties according to GB / T 8813-2008 Determination of Compressive Properties of Rigid Foamed Plastics; and water absorption (or other water absorption-related indicators) according to GB / T 8810 Determination of Water Absorption of Rigid Foamed Plastics.

[0131] Table 1. Test results of material mechanical properties and water absorption.

[0132]

[0133] The experimental results show that the technical solution of this application, through optimization of the polymerization raw materials, including reducing the proportion of hydrophilic raw materials, increasing the proportion of hydrophobic monomers, and selecting non-polar crosslinking agents, can improve the overall hydrophobicity of the material. Furthermore, adding a hydrophobic outer layer formed by a hydrophobic aqueous solution to the material surface can further reduce the material's water absorption rate. However, an excessively thick hydrophobic outer layer can negatively impact the material's mechanical properties, requiring careful control during the preparation process.

[0134] 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 method for preparing a low water absorption PMI foam material, comprising the following steps: The polymer raw materials, including polymer monomers, hydrophobic monomers, initiators, crosslinking agents, and foaming agents, are mixed and stirred in a certain proportion to obtain a raw material mixture. The raw material mixture is heated and polymerized to obtain a polymer; The polymer is heated to undergo a polymerization reaction to obtain a foamed material; The foaming material is soaked in a hydrophobic aqueous solution and dried to obtain the low water absorption PMI foam material.

2. The preparation method according to claim 1, wherein, The polymer monomers are methacrylic acid and methacrylonitrile, and the hydrophobic monomers are selected from methyl methacrylate, styrene, trifluoroethyl methacrylate, and vinyltrimethylsilane.

3. The preparation method according to claim 1, wherein, The crosslinking agent is a non-polar crosslinking agent, preferably a polyol polyacrylate crosslinking agent or divinylbenzene.

4. The preparation method according to claim 2, wherein, The proportions of the methacrylic acid, methacrylonitrile, hydrophobic monomer, initiator, crosslinking agent and foaming agent, by weight, are 35-45:30-40:10-20:0.1-2:0.1-3:3-10.

5. The preparation method according to claim 1, wherein, The hydrophobic aqueous solution is an ethanol solution containing a silane coupling agent.

6. The preparation method according to claim 1, wherein, The initiator is selected from one or more of azobisisobutyronitrile (AIBN), azobisisopentanol or azobisisoheptanol, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxyoctanoate or diketal peroxide, hexadecyl percarbonate, butyl percarbonate, and pentyl percarbonate; the foaming agent is selected from isopropanol, n-butanol, isobutanol, tert-butanol, tert-pentanol, hexanol, urea, methylurea or dimethylurea.

7. The preparation method according to claim 1, wherein, The raw material mixture is polymerized by heating at 30–150°C for 100–300 hours.

8. The preparation method according to claim 1, wherein, The polymer is heated to 160-250°C and foamed for 2-7 hours to obtain the foamed material.

9. The preparation method according to claim 1, wherein, The foaming material is soaked in a hydrophobic aqueous solution for 0.1-1 hours.

10. The low water absorption PMI foam material prepared by the preparation method according to any one of claims 1-9.

11. The application of the low water absorption PMI foam material of claim 10 in aerospace and transportation materials.

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