Organic dual-crosslinked rigid polymethacrylimide aerogel and preparation method and application thereof

Abstract

The present application relates to aerogel technical field, specifically to a kind of organic double crosslinking structure hard poly-methyl-acrylimide aerogel and preparation method and application.The structure of the hard poly-methyl-acrylimide aerogel includes imide crosslinking structure and methylene crosslinking structure shown in formula (I);The hard poly-methyl-acrylimide aerogel has nanoscale open-cell structure.This aerogel simultaneously exists specific organic double crosslinking structure in space structure, has excellent heat insulation and sound insulation performance, adsorption performance and mechanical property.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, specifically to an organic double cross-linked rigid polymethacrylimide aerogel, its preparation method, and its application. Background Technology

[0002] Aerogels, with their excellent properties such as ultra-low density, high porosity, low thermal conductivity, and high specific surface area, are widely used in thermal and sound insulation materials, catalyst carriers, and filtration devices. Aerogels can be classified into inorganic and organic aerogels according to their chemical composition. Inorganic aerogels have excellent thermal insulation properties but poor mechanical properties, while organic aerogels are diverse in type and have varying properties, exhibiting better mechanical properties and environmental stability. Among them, polyimide (PI) aerogel has the best performance. Polyimide (PI) refers to a class of polymers containing imide rings in their main chain, possessing good mechanical properties and thermal stability. Polyimide aerogel combines the advantages of both polyimide and aerogels, possessing the high specific surface area, high porosity, and low thermal conductivity of aerogels, as well as the high mechanical strength and high thermal stability of polyimide, making polyimide aerogel a three-dimensional porous material with excellent comprehensive performance. However, PI aerogels still suffer from shrinkage after high-temperature treatment and relatively low elasticity.

[0003] Polymethacrylimide (PMI) is also a type of polymer containing imide rings. The difference between PMI and PI is that PI contains imide rings in its main chain, while PMI contains imide rings in its side chains. Currently, the only commercially available PMI product is foam, which boasts a near 100% closed-cell structure. PMI's unique chemical structure endows it with unparalleled dimensional stability at high temperatures, making PMI foam widely used in structural components in aerospace, rail transportation, and other fields—a property lacking in PI materials. However, the closed-cell structure of PMI foam limits its applications in adsorption, thermal and sound insulation, and catalyst support.

[0004] To address the limitations of PMI foam applications, CN112358645A discloses a method for preparing polymethacrylimide aerogel, yielding a PMI open-cell aerogel with better thermal insulation and compression performance compared to PI aerogel. This PMI aerogel also exhibits dimensional stability at high temperatures. CN112521653A discloses a method for preparing polymethacrylimide hybrid aerogel, introducing nanoparticles into the PMI aerogel to improve its flame retardant properties. All of the above methods employ freeze-drying to prepare PMI aerogels, resulting in PMI aerogels with pore sizes not less than 20 μm (belonging to the category of giant pores), leading to lower thermal insulation, sound insulation, adsorption capacity, and mechanical properties. Summary of the Invention

[0005] This invention addresses the problems of existing polymethacrylimide aerogels, such as insufficient thermal and sound insulation performance, poor adsorption performance due to large pore size, and insufficient mechanical properties. It provides an organic double crosslinked rigid polymethacrylimide aerogel, its preparation method, and its application.

[0006] To achieve the above objectives, the first aspect of the present invention provides a rigid polymethacrylimide aerogel, wherein the rigid polymethacrylimide aerogel comprises an imide crosslinking structure and a methylene crosslinking structure as shown in formula (I);

[0007]

[0008] The rigid polymethacrylimide aerogel has a nanoscale open-pore structure.

[0009] A second aspect of this invention provides a method for preparing rigid polymethacrylimide aerogel, comprising:

[0010] (1) A reaction system containing an initiator, a first crosslinking agent, a second crosslinking agent, methacrylic acid, acrylonitrile and / or methacrylonitrile, and an organic solvent is subjected to a polymerization reaction to obtain a first gel;

[0011] (2) The first gel is subjected to aging treatment to obtain a second gel with a methylene crosslinking structure;

[0012] (3) The second gel is subjected to solvent replacement treatment to obtain a third gel;

[0013] (4) The third gel is dried in supercritical carbon dioxide to obtain the fourth gel;

[0014] (5) Heat treatment is performed on the fourth gel to obtain a rigid polymethacrylimide aerogel with a methylene crosslinking structure and an imide crosslinking structure.

[0015] The second crosslinking agent is N-hydroxyalkylacrylamide.

[0016] The third aspect of the present invention provides a rigid polymethacrylimide aerogel prepared by the method described in the second aspect above.

[0017] The fourth aspect of this invention provides the application of the rigid polymethacrylamide aerogel described in the first or third aspect above in the fields of thermal insulation, sound insulation, and adsorption.

[0018] The rigid polymethacrylamide (PMI) aerogel provided by this invention possesses both specific methylene crosslinking and imide crosslinking structures in its spatial structure. Compared to PMI aerogels with a single imide ring crosslinking structure, it exhibits significantly improved mechanical properties, particularly high compressive strength. The aerogel also features a nanoscale open-pore structure, which, compared to PMI aerogels with a macroporous structure (pore size ≥ 20 μm), significantly enhances its thermal and acoustic insulation and adsorption properties. Furthermore, the aerogel requires no freeze-drying process during preparation, resulting in a short preparation process and low cost. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0020] Figure 1 This is a scanning electron microscope image of the rigid polymethacrylimide aerogel prepared in Example 1 of the present invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of the present invention provides a rigid polymethacrylimide aerogel, wherein the structure of the rigid polymethacrylimide aerogel includes an imide crosslinking structure and a methylene crosslinking structure as shown in formula (I);

[0023]

[0024] The rigid polymethacrylimide aerogel has a nanoscale open-pore structure.

[0025] According to the present invention, the rigid polymethacrylamide aerogel provided by the present invention has a "double crosslinking structure" in addition to the presence of an imide crosslinking structure, and also has a specific methylene crosslinking structure as shown in formula (I). The methylene crosslinking structure is formed by the self-crosslinking of N-hydroxyalkylacrylamide; the imide crosslinking structure is formed by thermal imidization crosslinking of amide groups in adjacent segments of the PMI prepolymer, or by thermal imidization crosslinking of amide groups in adjacent segments of the PMI prepolymer. The presence of these two crosslinking structures results in a significant improvement in mechanical properties, especially compressive strength, of the rigid polymethacrylamide aerogel provided by the present invention compared to PMI aerogels with a single imide ring crosslinking structure. Furthermore, the rigid polymethacrylamide aerogel provided by the present invention also possesses a nanoscale open-pore structure, which can significantly improve thermal and sound insulation performance and adsorption performance.

[0026] In this invention, the imide crosslinking structure is a characteristic structure of polymethacrylimide aerogel (PMI) known in the art, and its structure is shown in formula (II), wherein R1, R2, R3, and R4 are each independently methyl or hydrogen.

[0027]

[0028] According to the present invention, the rigid polymethacrylimide aerogel has a nanoscale open-pore structure, meaning that the pore size in the rigid polymethacrylimide aerogel is ≤100nm. In contrast, the pore size in prior art polymethacrylimide aerogels is typically not less than 20μm. The nanoscale open-pore structure endows the rigid polymethacrylimide aerogel of the present invention with better thermal insulation, sound insulation, and adsorption properties.

[0029] According to the present invention, preferably, the pore size of the rigid polymethacrylimide aerogel is 10-50 nm.

[0030] In this invention, the pore size of polymethacrylimide aerogel refers to the maximum straight-line distance between any two points on the spatial edge of the pore, which can be determined by field emission scanning electron microscopy.

[0031] According to the present invention, the rigid polymethacrylimide aerogel has good thermal insulation properties, exhibiting a low thermal conductivity. The thermal conductivity of the rigid polymethacrylimide aerogel is ≤0.025 W / (m·K), preferably 0.01-0.02 W / (m·K).

[0032] In this invention, the thermal conductivity is determined by the method specified in ISO 22007-2-2022.

[0033] According to the present invention, the rigid polymethacrylimide aerogel has excellent mechanical properties, exhibiting high compressive strength. The compressive strength of the rigid polymethacrylimide aerogel is ≥0.25 MPa, preferably 0.3-0.5 MPa.

[0034] In this invention, the compressive strength is determined by the method specified in GB / T1041-2008.

[0035] According to the present invention, the rigid polymethacrylimide aerogel has good high-temperature dimensional stability, exhibiting a high heat distortion temperature. The heat distortion temperature of the rigid polymethacrylimide aerogel is ≥227℃, preferably 228-232℃.

[0036] In this invention, the heat distortion temperature is determined by the method specified in DIN 53424.

[0037] The rigid polymethacrylimide aerogel provided by this invention has excellent mechanical properties, thermal and sound insulation properties, adsorption properties and high-temperature dimensional stability, which can well meet the needs of use in the fields of thermal and sound insulation, adsorption, filter cartridges, catalyst carriers, etc., and is especially suitable for the fields of thermal and sound insulation and adsorption.

[0038] A second aspect of this invention provides a method for preparing rigid polymethacrylimide aerogel, comprising:

[0039] (1) A reaction system containing an initiator, a first crosslinking agent, a second crosslinking agent, methacrylic acid, acrylonitrile and / or methacrylonitrile, and an organic solvent is subjected to a polymerization reaction to obtain a first gel;

[0040] (2) The first gel is subjected to aging treatment to obtain a second gel with a methylene crosslinking structure;

[0041] (3) The second gel is subjected to solvent replacement treatment to obtain a third gel;

[0042] (4) The third gel is dried in supercritical carbon dioxide to obtain the fourth gel;

[0043] (5) Heat treatment is performed on the fourth gel to obtain a rigid polymethacrylimide aerogel with a methylene crosslinking structure and an imide crosslinking structure.

[0044] The second crosslinking agent is N-hydroxyalkylacrylamide.

[0045] According to the present invention, in the preparation method, in step (1), the polymerization reaction is carried out by free radical solution polymerization. In the polymerization reaction, methacrylic acid, acrylonitrile, the first crosslinking agent and the second crosslinking agent respectively open double bonds to form macromolecular chains. At the same time, the side alkyl group of N-hydroxyalkylacrylamide, which is the second crosslinking agent, undergoes a self-crosslinking reaction to remove formaldehyde and water, and initially forms a methylene crosslinking structure. After the reaction, a product in a gel state is obtained, namely the first gel.

[0046] According to the present invention, in the preparation method, in step (1), the weight ratio of methacrylic acid:acrylonitrile and / or methacrylonitrile can be 1:(0.8-1.8). Using the above monomer feeding ratio facilitates the generation of more imide six-membered rings during the subsequent heat treatment process, providing better mechanical properties of the PMI aerogel.

[0047] According to the present invention, preferably, the weight ratio of methacrylic acid:acrylonitrile and / or methacrylonitrile is 1:(1-1.6).

[0048] According to the present invention, in the preparation method, the initiator in step (1) is subject to a wide range of restrictions. Conventional initiators used in free radical solution polymerization reactions can be used, such as azo initiators, peroxide initiators, etc.

[0049] In this invention, the azo initiator may include, but is not limited to, at least one of the following: dimethyl azobisisobutyrate (AIBME), azodicarbonamide (ADC), azobisisopropylimidazoline hydrochloride (AIB1), azobiscyclohexylformonitrile (ACCN), azobiscyanopentanoic acid (ACVA), azobisisopropylimidazoline (AIP), azobisisobutyronitrile (AIBN), azobisisovalerate (AMBN), and azobisisoheptanenitrile (ABVN), preferably azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0050] In this invention, the peroxide initiator may include, but is not limited to, at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate and benzoyl peroxide, preferably dibenzoyl peroxide.

[0051] According to the present invention, preferably, the weight ratio of methacrylic acid to initiator is 1:(0.01-0.06).

[0052] According to the present invention, in the preparation method, in step (1), the first crosslinking agent is a thermal imidizing crosslinking agent, which promotes the formation of an imide crosslinking structure and an imide six-membered ring during the subsequent heat treatment process. In the present invention, the first crosslinking agent can be an acrylamide compound. For example, the first crosslinking agent can be acrylamide, methacrylamide, etc.

[0053] According to the present invention, preferably, the first crosslinking agent is acrylamide.

[0054] According to the present invention, preferably, the weight ratio of methacrylic acid to the first crosslinking agent is 1:(0.04-0.12), more preferably 1:(0.04-0.08).

[0055] According to the present invention, in the preparation method, in step (1), the second crosslinking agent promotes the formation of the methylene crosslinked structure in the polymerization reaction. Preferably, the second crosslinking agent may be selected from N-hydroxymethylacrylamide and / or N-hydroxyethylacrylamide.

[0056] According to the present invention, preferably, the weight ratio of methacrylic acid to the second crosslinking agent is 1:(0.08-0.2), more preferably 1:(0.08-0.18).

[0057] According to the present invention, in the preparation method, the organic solvent in step (1) is subject to a wide range of restrictions. Conventional solvents used in free radical solution polymerization reactions can be used, such as at least one of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0058] Preferably, the weight ratio of methacrylic acid to organic solvent is 1:(4-30).

[0059] According to the present invention, in the preparation method, step (1) does not have particular limitations on the operation process of the polymerization reaction, and conventional free radical solution polymerization can be used. Preferably, the conditions of the polymerization reaction include: a temperature of 55-75°C and a time of 96-240 h.

[0060] According to the present invention, in the preparation method, in step (2), the aging treatment can be performed by allowing the first gel to stand. Through the aging treatment, the cross-linking reaction continues to occur in the first gel, and the methylene cross-linking structure is further improved, resulting in a second gel with a methylene cross-linking structure.

[0061] According to the present invention, preferably, the aging treatment conditions include a temperature of 50-70°C and a time of 36-120 hours, which is more conducive to the formation of methylene cross-linked structures.

[0062] According to the present invention, in the preparation method, in step (3), the solvent replacement treatment can be carried out by immersing the second gel in a replacement solvent until the replacement solvent completely replaces the organic solvent in the second gel. Through the solvent replacement treatment, the organic solvent in the second gel is replaced with a replacement solvent that is easier to remove, thereby obtaining a third gel.

[0063] According to the present invention, the solvent used in the solvent replacement treatment (replacement solvent) can be selected from alcohol solvents and / or ketone solvents. Preferably, it is selected from at least one of methanol, ethanol and acetone, and more preferably methanol.

[0064] According to the present invention, in the preparation method, in step (4), the third gel is dried in supercritical carbon dioxide, so that the solvent in the third gel (i.e. the above-mentioned displacement solvent) is miscible with supercritical carbon dioxide, and is completely converted into gas during the depressurization drying process to obtain a fourth gel with a nano-sized open-pore structure.

[0065] According to the present invention, preferably, the drying conditions include: a temperature of 35-75°C, a pressure of 10-15 MPa, and a time of 8-12 h, which is more conducive to the miscibility of supercritical carbon dioxide and the solvent in the third gel, and the drying is more complete when the pressure is released.

[0066] In this invention, supercritical carbon dioxide refers to carbon dioxide existing above its critical temperature and critical pressure.

[0067] According to the present invention, in the preparation method, in step (5), a thermal imidization reaction occurs during the heat treatment process to form an imide crosslinking structure, and finally a rigid polymethacrylimide aerogel with a methylene crosslinking structure and an imide crosslinking structure is obtained.

[0068] In this invention, the heat treatment can employ conventional heating methods, and the invention does not impose any particular limitations on this. For example, the fourth gel can be placed in an oven for heating. Preferably, the heat treatment conditions include: a temperature of 140-200°C and a time of 6-10 hours.

[0069] The preparation method provided by this invention involves a self-crosslinking reaction of a specific crosslinking agent during the polymerization of methacrylic acid, acrylonitrile, and / or methacrylonitrile. After aging, the product achieves a one-step formation of a methylene crosslinked structure framework. Subsequently, drying is performed in supercritical carbon dioxide to form a nano-sized open-pore structure in the gel. Finally, a thermal imidization reaction is carried out to obtain a product with a specific methylene crosslinked structure. A rigid polymethacrylamide (PMI) aerogel with a "double crosslinked structure" and an imide crosslinking structure is presented, exhibiting a nanoscale open-pore structure. Preferably, the aerogel has a pore size ≤100 nm, a thermal conductivity ≤0.025 W / (m·K), a compressive strength ≥0.25 MPa, and a heat distortion temperature ≥227 °C. Compared to PMI aerogels with a single imide ring crosslinking structure, it shows significantly improved mechanical properties, especially compressive strength. Compared to PMI aerogels with a macroporous structure, it exhibits significantly improved thermal and sound insulation properties and adsorption properties. Furthermore, this method eliminates the need for freeze-drying and the preparation of quaternary ammonium salts, simplifying the preparation process and reducing costs.

[0070] The third aspect of the present invention provides a rigid polymethacrylimide aerogel prepared by the method described in the second aspect above.

[0071] In this invention, the rigid polymethacrylamide aerogel prepared by the method described in the second aspect above has the same chemical composition, structure and properties as the rigid polymethacrylamide aerogel described in the first aspect above, and will not be repeated here.

[0072] The fourth aspect of this invention provides the application of the rigid polymethacrylamide aerogel described in the first or third aspect above in the fields of thermal insulation, sound insulation, and adsorption.

[0073] The present invention will be described in detail below through examples. Unless otherwise specified, the following examples and comparative examples are all conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0074] Example 1

[0075] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The mixture was subjected to free radical solution polymerization at a constant temperature of 60°C for 120 h to obtain the first gel.

[0076] The weight ratio of methacrylic acid to acrylonitrile is 1:1; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.03; the weight ratio of methacrylic acid to acrylamide is 1:0.05; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.13; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:22.

[0077] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 50°C for 48 hours to obtain the second gel.

[0078] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0079] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 45°C and then the pressure was slowly increased to 12MPa. The gel was dried under heat and pressure for 9 hours to obtain the fourth gel.

[0080] (5) The above fourth gel was placed in a forced-air oven for heat treatment at 160°C for 8 hours to obtain rigid polymethacrylimide aerogel (denoted as P1).

[0081] Field emission scanning electron microscopy (FESEM) was performed on P1, and the results are as follows: Figure 1 As shown, Figure 1 As can be seen, the pore size in the P1 structure is less than 100 nm, exhibiting a nanoscale open-pore structure.

[0082] The test results of the pore size, thermal conductivity, compressive strength and heat distortion temperature of P1 are shown in Table 1.

[0083] Example 2

[0084] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The mixture was subjected to free radical solution polymerization at a constant temperature of 55°C for 240 h to obtain the first gel.

[0085] The weight ratio of methacrylic acid to acrylonitrile is 1:1.2; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.02; the weight ratio of methacrylic acid to acrylamide is 1:0.04; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.08; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:6.

[0086] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 60°C for 60 hours to obtain the second gel.

[0087] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0088] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 60°C and then the pressure was slowly increased to 13MPa. The gel was kept at the temperature and pressure for 10 hours to obtain the fourth gel.

[0089] (5) The above fourth gel was placed in a forced-air drying oven for heat treatment at 140°C for 10 hours to obtain rigid polymethacrylimide aerogel (denoted as P2).

[0090] The test results of P2's pore size, thermal conductivity, compressive strength, and heat distortion temperature are shown in Table 1.

[0091] Example 3

[0092] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The mixture was subjected to free radical solution polymerization at a constant temperature of 70°C for 96 h to obtain the first gel.

[0093] The weight ratio of methacrylic acid to acrylonitrile is 1:1.8; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.05; the weight ratio of methacrylic acid to acrylamide is 1:0.12; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.18; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:24.

[0094] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 70°C for 120 hours to obtain the second gel.

[0095] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0096] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 75°C and then the pressure was slowly increased to 15MPa. The gel was dried under heat and pressure for 8 hours to obtain the fourth gel.

[0097] (5) The above fourth gel was placed in a forced-air oven for heat treatment at 200°C for 7 hours to obtain rigid polymethacrylimide aerogel (denoted as P3).

[0098] The test results of P3's pore size, thermal conductivity, compressive strength, and heat distortion temperature are shown in Table 1.

[0099] Example 4

[0100] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The mixture was subjected to free radical solution polymerization at a constant temperature of 55°C for 240 h to obtain the first gel.

[0101] The weight ratio of methacrylic acid to acrylonitrile is 1:0.8; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.01; the weight ratio of methacrylic acid to acrylamide is 1:0.04; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.08; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:4.

[0102] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 50°C for 120 hours to obtain the second gel.

[0103] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0104] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 35°C and then the pressure was slowly increased to 15MPa. The gel was dried under heat and pressure for 8 hours to obtain the fourth gel.

[0105] (5) The above fourth gel was placed in a forced-air oven for heat treatment at 140°C for 10 hours to obtain rigid polymethacrylimide aerogel (denoted as P4).

[0106] The test results of the pore size, thermal conductivity, compressive strength, and heat distortion temperature of P4 are shown in Table 1.

[0107] Example 5

[0108] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The free radical solution polymerization reaction was carried out at a constant temperature water bath of 75°C for 96 h to obtain the first gel.

[0109] The weight ratio of methacrylic acid to acrylonitrile is 1:1.8; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.06; the weight ratio of methacrylic acid to acrylamide is 1:0.12; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.2; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:30.

[0110] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 70°C for 36 hours to obtain the second gel.

[0111] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0112] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 75°C and then the pressure was slowly increased to 10 MPa. The gel was dried under heat and pressure for 8 hours to obtain the fourth gel.

[0113] (5) The above fourth gel was placed in a forced-air oven for heat treatment at 200°C for 6 hours to obtain rigid polymethacrylimide aerogel (denoted as P5).

[0114] The test results of the pore size, thermal conductivity, compressive strength, and heat distortion temperature of P5 are shown in Table 1.

[0115] Example 6

[0116] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The free radical solution polymerization reaction was carried out at a constant temperature water bath of 65°C for 168 h to obtain the first gel.

[0117] The weight ratio of methacrylic acid to acrylonitrile is 1:1.3; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.04; the weight ratio of methacrylic acid to acrylamide is 1:0.08; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.14; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:17.

[0118] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 60°C for 78 hours to obtain the second gel.

[0119] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0120] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 60°C and then the pressure was slowly increased to 13MPa. The gel was kept at the temperature and pressure for 10 hours to obtain the fourth gel.

[0121] (5) The above fourth gel was placed in a forced-air drying oven for heat treatment at 170°C for 8 hours to obtain rigid polymethacrylimide aerogel (denoted as P6).

[0122] The test results of pore size, thermal conductivity, compressive strength and heat distortion temperature of P6 are shown in Table 1.

[0123] Example 7

[0124] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), N-hydroxymethylacrylamide (NMA), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The free radical solution polymerization reaction was carried out at a constant temperature water bath of 65°C for 168 h to obtain the first gel.

[0125] The weight ratio of methacrylic acid to acrylonitrile is 1:1.3; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.04; the weight ratio of methacrylic acid to acrylamide is 1:0.08; the weight ratio of methacrylic acid to N-hydroxymethylacrylamide is 1:0.18; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:17.

[0126] (2) The first sol was placed in a mold and allowed to stand for aging at a temperature of 60°C for 78 hours to obtain the second gel.

[0127] (3) Place the second gel above into a container, pour in methanol, and perform solvent replacement at room temperature to completely replace the original solvent N-methylpyrrolidone. The replacement time is 24h to obtain the third gel.

[0128] (4) The third gel was placed in a supercritical carbon dioxide drying instrument, and the temperature was slowly increased to 60°C and then the pressure was slowly increased to 13MPa. The gel was kept at the temperature and pressure for 10 hours to obtain the fourth gel.

[0129] (5) The above fourth gel was placed in a forced-air oven for heat treatment at 170°C for 8 hours to obtain rigid polymethacrylimide aerogel (denoted as P7).

[0130] The test results of the pore size, thermal conductivity, compressive strength, and heat distortion temperature of P7 are shown in Table 1.

[0131] Comparative Example 1

[0132] (1) Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), azobisisobutyronitrile (AIBN), and solvent N-methylpyrrolidone (NMP) were placed in a reaction flask and mixed evenly. The free radical solution polymerization reaction was carried out under constant temperature water bath conditions of 60℃ for 96h to obtain PMI prepolymer solution.

[0133] The weight ratio of methacrylic acid to acrylonitrile is 1:1; the weight ratio of methacrylic acid to azobisisobutyronitrile is 1:0.02; the weight ratio of methacrylic acid to acrylamide is 1:0.05; and the weight ratio of methacrylic acid to N-methylpyrrolidone is 1:5.

[0134] (2) Add triethylamine (the molar ratio of methacrylic acid to triethylamine is 1:3) to the PMI prepolymer solution obtained in step (1), stir thoroughly until a uniform liquid phase is formed, and then let it stand at 20°C for 6 hours to obtain a viscous liquid phase containing PMI prepolymer quaternary ammonium salt.

[0135] (3) Place the above viscous liquid phase containing PMI prepolymer quaternary ammonium salt into a container, and wash the above viscous liquid phase repeatedly with acetone until the white lumpy solid phase is completely precipitated. Then place the precipitated solid phase in an oven at 40°C for 48 hours to evaporate and remove the acetone, and obtain PMI prepolymer quaternary ammonium salt.

[0136] (4) Prepare an aqueous solution of the above PMI prepolymer quaternary ammonium salt and freeze solidify it at -20℃; then freeze dry the solidified PMI prepolymer quaternary ammonium salt to obtain PMI prepolymer quaternary ammonium salt aerogel after drying.

[0137] (5) The above PMI prepolymer quaternary ammonium salt aerogel was sent into a forced-air drying oven for heat treatment at a temperature of 170°C for 8 hours to obtain rigid polymethacrylimide aerogel (denoted as DP1).

[0138] The test results of DP1's pore size, thermal conductivity, compressive strength, and heat distortion temperature are shown in Table 1.

[0139] Comparative Example 2

[0140] The method of Example 6 was followed, except that in step (4), the drying was not carried out in a supercritical carbon dioxide drying apparatus, but at 25°C and atmospheric pressure. All other steps and conditions were the same as in Example 6. After drying in step (4), the gel volume shrank and the skeleton collapsed, and a rigid polymethacrylamide aerogel was not obtained.

[0141] Comparative Example 3

[0142] Methacrylic acid (MAA), acrylonitrile (AN), acrylamide (AM), azobisisobutyronitrile (AIBN), and N-methylpyrrolidone (NMP) were mixed evenly in a reaction flask (wherein the weight ratio of methacrylic acid to acrylonitrile was 1:1.3; the weight ratio of methacrylic acid to azobisisobutyronitrile was 1:0.04; the weight ratio of methacrylic acid to acrylamide was 1:0.08; and the weight ratio of methacrylic acid to N-methylpyrrolidone was 1:17). The mixture was subjected to free radical solution polymerization at a constant temperature water bath of 65°C for 168 h. The resulting product was a viscous liquid that could not maintain a stable shape and could not be dried in supercritical carbon dioxide. Therefore, rigid polymethacrylimide aerogel could not be obtained.

[0143] Table 1

[0144]

[0145]

[0146] As shown in Table 1, the rigid polymethacrylamide aerogels prepared in Examples 1-7 have nanoscale open-pore structures, a thermal conductivity of less than 0.025 W / (m·K), a heat distortion temperature of not less than 227℃, and a compressive strength higher than 0.25 MPa due to the specific organic double cross-linked structure in the aerogel. Therefore, P1-P7 possess excellent thermal and sound insulation properties, adsorption properties, and mechanical properties. Comparative Example 1, prepared by freeze-drying, has an aerogel with only a single imide ring cross-linked structure and a large pore size. Its comprehensive performance in terms of thermal and sound insulation, adsorption, and mechanical properties is inferior to that of P1-P7. Comparative Example 2 did not undergo drying treatment in supercritical carbon dioxide in step (4), and Comparative Example 3 did not use the cross-linking agent N-hydroxyalkylacrylamide in step (1), so neither could obtain the rigid polymethacrylamide aerogel of the present invention.

[0147] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A rigid polymethacrylimide aerogel, characterized in that, The rigid polymethacrylimide aerogel includes an imide crosslinking structure and a methylene crosslinking structure as shown in formula (I); The rigid polymethacrylimide aerogel has a nanoscale open-pore structure.

2. The rigid polymethacrylimide aerogel according to claim 1, wherein, The rigid polymethacrylimide aerogel has a pore size ≤100nm, preferably 10-50nm.

3. The rigid polymethacrylimide aerogel according to claim 1 or 2, wherein, The thermal conductivity of the rigid polymethacrylimide aerogel is ≤0.025 W / (m·K), preferably 0.01-0.02 W / (m·K); And / or, the rigid polymethacrylimide aerogel has a compressive strength ≥0.25MPa, preferably 0.3-0.5MPa; And / or, the heat distortion temperature of the rigid polymethacrylimide aerogel is ≥227℃, preferably 228-232℃.

4. A method for preparing rigid polymethacrylimide aerogel, characterized in that, include: (1) A reaction system containing an initiator, a first crosslinking agent, a second crosslinking agent, methacrylic acid, acrylonitrile and / or methacrylonitrile, and an organic solvent is subjected to a polymerization reaction to obtain a first gel; (2) The first gel is subjected to aging treatment to obtain a second gel with a methylene crosslinking structure; (3) The second gel is subjected to solvent replacement treatment to obtain a third gel; (4) The third gel is dried in supercritical carbon dioxide to obtain the fourth gel; (5) Heat treatment is performed on the fourth gel to obtain a rigid polymethacrylimide aerogel with a methylene crosslinking structure and an imide crosslinking structure. The second crosslinking agent is N-hydroxyalkylacrylamide.

5. The method according to claim 4, wherein, In step (1), the weight ratio of methacrylic acid:acrylonitrile and / or methacrylonitrile is 1:(0.8-1.8), preferably 1:(1-1.6); And / or, the weight ratio of methacrylic acid to initiator is 1:(0.01-0.06); And / or, the weight ratio of methacrylic acid to the first crosslinking agent is 1:(0.04-0.12), preferably 1:(0.04-0.08); And / or, the weight ratio of methacrylic acid to the second crosslinking agent is 1:(0.08-0.2), preferably 1:(0.08-0.18); And / or, the weight ratio of methacrylic acid to organic solvent is 1:(4-30); And / or, the conditions for the polymerization reaction include: a temperature of 55-75°C and a time of 96-240 h.

6. The method according to claim 4 or 5, wherein, In step (1), the first crosslinking agent is a thermal imidization crosslinking agent, preferably an acrylamide compound; And / or, the second crosslinking agent is selected from N-hydroxymethylacrylamide and / or N-hydroxyethylacrylamide.

7. The method according to any one of claims 4-6, wherein, In step (2), the aging treatment conditions include: a temperature of 50-70℃ and a time of 36-120h; And / or, in step (3), the solvent used in the solvent replacement treatment is selected from alcohol solvents and / or ketone solvents.

8. The method according to any one of claims 4-7, wherein, In step (4), the drying conditions include: a temperature of 35-75℃, a pressure of 10-15MPa, and a time of 8-12h; And / or, in step (5), the conditions for the heat treatment include: a temperature of 140-200℃ and a time of 6-10h.

9. The rigid polymethacrylimide aerogel prepared by the method according to any one of claims 4-8.

10. The application of the rigid polymethacrylamide aerogel according to any one of claims 1-3 and 9 in the fields of thermal insulation, sound insulation and adsorption.

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