Preparation method of a polybenzoxazine wave-transparent heat-insulating aerogel material

Abstract

The application discloses a preparation method of a polybenzoxazine wave-transparent heat-insulating aerogel material. The method successfully prepares the polybenzoxazine wave-transparent heat-insulating aerogel material with a three-dimensional interconnected nano-porous structure by introducing alicyclic dianhydride into a benzoxazine system for synergistic regulation, combining an acid catalysis sol-gel and normal pressure drying process, so that the unification of low thermal conductivity, optimal dielectric property and formability is realized, and the application requirement of the wave-transparent heat-insulating integrated material is met. The process route of the method is "dissolution mixing-reaction to sol-gel-gel aging-solvent replacement-normal pressure drying", the preparation process is clear, and the operation is simple.

Description

Technical Field

[0001] This invention relates to the field of high-performance microwave-transparent thermal insulation materials, specifically a method for preparing polybenzoxazine microwave-transparent thermal insulation aerogel material. Background Technology

[0002] As aerospace vehicles, radar radomes, electronic packaging, and high-frequency communication components evolve towards higher frequencies, lighter weights, and greater environmental adaptability, related materials, while fulfilling their thermal protection functions, also need to minimize the impact of reflection, absorption, and scattering during electromagnetic wave propagation. Especially in applications such as radomes, hull housings, antenna windows, housing linings, and thermal insulation packaging for high-temperature electronic units, the integration of wave transmission and thermal insulation has become a crucial direction in material design. While the traditional layered design of "wave-transparent layer + thermal insulation layer" achieves functional division, it is prone to introducing problems such as interface mismatch, local delamination, and multiple reflections in practical applications. This hinders integrated structural design and can affect long-term service stability and component reliability.

[0003] Aerogel materials are a class of three-dimensional nanoporous materials characterized by high porosity, low density, and low thermal conductivity, and have broad application prospects in the field of microwave insulation. Existing microwave insulation aerogel materials mainly include SiO2 aerogel, polyimide aerogel, and their composite aerogels. Application No. 202211724807.0 discloses a silica aerogel and its preparation method, with a thermal conductivity of 0.038~0.052 W / (m·K). Application No. 201310233416.3 discloses a method for preparing a SiO2 aerogel / porous Si3N4 composite material, with a dielectric constant of 1.4~1.8 and a thermal conductivity of 0.03~0.08 W / (m·K). This demonstrates that SiO2 aerogel has certain advantages in terms of thermal insulation and low dielectric constant. However, existing SiO2 aerogels generally suffer from brittleness, fragility, and easy powder shedding. In the prior art, polyimide aerogels also exhibit low thermal conductivity and low dielectric properties. Application No. 202210117086.0 discloses a polyimide aerogel and its preparation method, with a thermal conductivity of 0.036~0.038 W / (m·K); application No. 201610708495.2 discloses a polyimide aerogel and its hybrid aerogel preparation method, wherein the dielectric constant of the polyimide aerogel is 1.2. Thus, polyimide aerogels possess low thermal conductivity and low dielectric properties, and generally exhibit better toughness and mechanical adaptability compared to inorganic aerogels. However, existing polyimide aerogel technologies still require complex processing steps, and suffer from high preparation costs and limited industrial applications. Therefore, developing a novel, low-cost aerogel-based wave-transparent thermal insulation material is particularly important.

[0004] Polybenzoxazine aerogels, as a type of organic polymer aerogel, combine the porous network thermal insulation characteristics of aerogel materials with the low dielectric properties of polybenzoxazine resin systems. Application No. 202210812165.3 discloses a water-based polybenzoxazine aerogel and its preparation method, showing a room-temperature thermal conductivity of 0.0249~0.0504 W / (m·K), indicating room for further improvement in thermal insulation performance. Furthermore, in existing polybenzoxazine aerogel technologies, achieving a proper balance between thermal insulation and dielectric properties remains challenging.

[0005] Therefore, how to achieve a synergistic match between low thermal conductivity and superior dielectric properties in polybenzoxazine aerogel systems remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing polybenzoxazine microwave-transparent thermal insulation aerogel material.

[0007] The technical solution of the present invention to solve the aforementioned technical problem is to provide a method for preparing a polybenzoxazine microwave-transparent thermal insulation aerogel material, the method comprising the following steps: Step 1: Dissolve the benzoxazine monomer in a solvent to obtain a benzoxazine solution; Step 2: Mix the benzoxazine solution obtained in Step 1 with an alicyclic dianhydride to obtain a benzoxazine-alicyclic dianhydride solution; Step 3: Add the acid catalyst dropwise to the benzoxazine-alicyclic dianhydride solution obtained in Step 2, and after the reaction, polybenzoxazine sol is obtained; Step 4: Let the polybenzoxazine sol obtained in Step 3 stand, allowing it to gel first and then continue aging to obtain polybenzoxazine gel; Step 5: Solvent displacement is performed on the polybenzoxazine gel obtained in step 4 to obtain the final state polybenzoxazine gel; Step 6: Dry the polybenzoxazine final gel obtained in step 5 to obtain polybenzoxazine wave-transparent thermal insulation aerogel material.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention introduces alicyclic dianhydrides into the benzoxazine system for synergistic regulation, and combines acid-catalyzed sol-gel and atmospheric pressure drying processes to successfully prepare polybenzoxazine wave-transparent thermal insulation aerogel material with a three-dimensional interconnected nanoporous structure, thereby achieving a unity of low thermal conductivity, superior dielectric properties and formability, and meeting the application requirements of integrated wave-transparent thermal insulation materials.

[0009] (2) The present invention adopts the process route of "dissolution and mixing - reaction into sol - gel aging - solvent replacement - atmospheric pressure drying". The preparation process is clear and easy to operate. It avoids the dependence on complex equipment and harsh conditions such as supercritical drying in the preparation of some existing aerogel materials, reduces the difficulty of process implementation, and improves the operability and engineering scale-up potential of material preparation.

[0010] (3) The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this invention has a three-dimensional interconnected nanoporous network structure, and features low thermal conductivity and low dielectric constant, with a density of 0.326~0.431 g / cm³. 3 The thermal conductivity is 0.0254~0.0509 W / (m·K), the dielectric constant is 1.46~2.18, and the dielectric loss is 0.008~0.045.

[0011] (4) The present invention uses an atmospheric pressure drying process to prepare polybenzoxazine microwave-transparent thermal insulation aerogel material. Compared with the complex equipment, high energy consumption drying process and high preparation cost required in the preparation of some existing polyimide aerogels and inorganic aerogels, it has the advantages of mild process conditions, low equipment requirements and low overall cost. Attached Figure Description

[0012] Figure 1 This is a photograph of the polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in Example 1 of this invention; Figure 3 This is a photograph of the polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in Example 8 of the present invention; Figure 4 This is a SEM image of the polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in Example 8 of the present invention. Detailed Implementation

[0013] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0014] This invention provides a method for preparing polybenzoxazine microwave-transparent thermally insulating aerogel material (hereinafter referred to as the method), which includes the following steps: Step 1: Dissolve the benzoxazine monomer in a solvent to obtain a homogeneous benzoxazine solution; Preferably, in step 1, the benzoxazine monomer is a bisphenol A type benzoxazine monomer or a bisphenol F type benzoxazine monomer.

[0015] Preferably, in step 1, the concentration of the benzoxazine solution is 0.07~0.35 g / ml.

[0016] Preferably, in step 1, the solvent is one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), or dimethyl sulfoxide (DMSO).

[0017] Preferably, in step 1, the dissolution process is carried out by stirring at a speed of 200-400 rpm for 10-30 minutes at room temperature. Preferably, this is done using a magnetic stirrer.

[0018] Step 2: Mix the benzoxazine solution obtained in Step 1 with an alicyclic dianhydride to obtain a benzoxazine-alicyclic dianhydride solution; Preferably, in step 2, the alicyclic dianhydride is one of cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, dicyclooctene dianhydride, or maleic rosin dianhydride.

[0019] Preferably, in step 2, the mass ratio of alicyclic dianhydride to benzoxazine monomer is 0.05~0.2:1.

[0020] Preferably, in step 2, the process of achieving uniform mixing is as follows: stirring is used at a speed of 200-400 rpm for 10-30 minutes at room temperature. Preferably, this is done using a magnetic stirrer.

[0021] Step 3: Add the acid catalyst dropwise to the benzoxazine-alicyclic dianhydride solution obtained in Step 2, and after the reaction, polybenzoxazine sol is obtained; Preferably, in step 3, the acid catalyst is one of hydrochloric acid, oxalic acid, or p-benzenesulfonic acid.

[0022] Preferably, in step 3, the mass ratio of the acid catalyst to the benzoxazine monomer is 0.05~0.2:1.

[0023] Preferably, in step 3, the dropping rate is 0.5~1g / min, and stirring is performed while dropping; the stirring speed is 200~400rpm, and the stirring temperature is room temperature.

[0024] Preferably, in step 3, the reaction process is as follows: stirring is used at a speed of 200-400 rpm for 10-30 minutes at room temperature. Preferably, the reaction is carried out in a magnetic stirrer.

[0025] Step 4: Let the polybenzoxazine sol obtained in Step 3 stand, allowing it to gel first and then continue aging to obtain polybenzoxazine gel; Preferably, in step 4, the settling process is carried out at a temperature of 10~30℃ for 48~96 hours. It is preferable to settling in a sealed environment.

[0026] Step 5: Solvent displacement is performed on the polybenzoxazine gel obtained in step 4 to obtain the final state polybenzoxazine gel; Preferably, in step 5, the solvent replacement process is as follows: at normal pressure and room temperature, the polybenzoxazine gel obtained in step 4 is placed in a solvent for solvent replacement, once every 9 to 18 hours, for a total of 4 to 6 times; the solvent is ethanol, methanol or isopropanol.

[0027] Step 6: Dry the polybenzoxazine final gel obtained in step 5 to obtain polybenzoxazine wave-transparent thermal insulation aerogel material.

[0028] Preferably, in step 6, the drying process is as follows: the pressure is normal, the temperature is 10~30℃, and the time is 24~72h.

[0029] Example 1: (1) The bisphenol A type benzoxazine monomer was completely dissolved in DMF by stirring at 400 rpm for 30 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.07 g / ml; (2) The benzoxazine solution and bicyclooctene dianhydride were stirred at 400 rpm for 20 min at room temperature until they were mixed evenly to obtain a benzoxazine-bicyclooctene dianhydride solution; wherein the mass ratio of bicyclooctene dianhydride to bisphenol A type benzoxazine monomer was 0.2:1; (3) At room temperature, hydrochloric acid was added dropwise as a catalyst to the benzoxazine-bicyclooctene dianhydride solution at a dropping rate of 0.5 g / min, while stirring at a stirring speed of 400 rpm. After the addition was completed, the reaction was continued to be stirred at 400 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of hydrochloric acid to bisphenol A type benzoxazine monomer was 0.15:1. (4) The polybenzoxazine sol was allowed to stand at 20°C to gel first and then continue to age for 48 hours to obtain polybenzoxazine gel; (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in ethanol for solvent replacement 5 times, once every 12 hours, to obtain the final state of polybenzoxazine gel. (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 20°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0030] The macroscopic morphology of the polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment is as follows: Figure 1 As shown, it exhibits good bulking properties and is lightweight. Its microstructure is as follows: Figure 2 As shown, it exhibits a three-dimensional nanoporous network structure, which gives it a low thermal conductivity.

[0031] The density of the polybenzoxazine microwave-transparent thermal insulation aerogel material was tested to be 0.326 g / cm³. 3 It has a thermal conductivity of 0.0254 W / (m·K) at room temperature and pressure, a dielectric constant of 1.46, and a dielectric loss of 0.008.

[0032] Comparative Example 1: Comparative Example 1 is exactly the same as Example 1, except that the catalyst solution in step (3) is acetic acid; as a result, a uniform gel is not obtained, but a precipitate or suspension is obtained.

[0033] Example 2: (1) The bisphenol F type benzoxazine monomer was completely dissolved in DMF by stirring at 400 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.1 g / ml; (2) The benzoxazine solution and cyclobutanetetracarboxylic dianhydride were stirred at 400 rpm for 20 min at room temperature until they were mixed evenly to obtain a benzoxazine-cyclobutanetetracarboxylic dianhydride solution; wherein the mass ratio of cyclobutanetetracarboxylic dianhydride to bisphenol F type benzoxazine monomer was 0.1:1; (3) At room temperature, hydrochloric acid was added dropwise as a catalyst to the benzoxazine-cyclobutanetetracarboxylic dianhydride solution at a dropping rate of 0.75 g / min, while stirring at a stirring speed of 400 rpm. After the addition was completed, the reaction was continued to be stirred at 400 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of hydrochloric acid to bisphenol F type benzoxazine monomer was 0.1:1. (4) The polybenzoxazine sol was allowed to stand at 20°C to gel first and then continue to age for 72 hours to obtain polybenzoxazine gel; (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in isopropanol for solvent replacement 5 times, once every 10 hours, to obtain the final state of polybenzoxazine gel. (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 20°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0034] The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment exhibits good bulking properties and is lightweight. Its density is 0.387 g / cm³. 3 It has a thermal conductivity of 0.0410 W / (m·K) at room temperature and pressure, a dielectric constant of 1.97, and a dielectric loss of 0.030.

[0035] Comparative Example 2: Comparative Example 2 is exactly the same as Example 2, except that in step (3), the mass ratio of hydrochloric acid to bisphenol F benzoxazine monomer is 0.04:1, which makes it difficult to obtain a gel.

[0036] Example 3: (1) The bisphenol A type benzoxazine monomer was completely dissolved in NMP by stirring at 400 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.1 g / ml; (2) The benzoxazine solution and maleic rosin dianhydride were stirred at 400 rpm for 20 min at room temperature until they were mixed evenly to obtain a benzoxazine-maleic rosin dianhydride solution; wherein the mass ratio of maleic rosin dianhydride to bisphenol A type benzoxazine monomer was 0.2:1; (3) At room temperature, p-benzenesulfonic acid was added dropwise as a catalyst to the benzoxazine-maleic rosin dianhydride solution at a dropping rate of 1 g / min, while stirring at a stirring speed of 300 rpm. After the addition was completed, the reaction was stirred at 300 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of p-benzenesulfonic acid to bisphenol A type benzoxazine monomer was 0.15:1. (4) The polybenzoxazine sol was allowed to stand at 30°C to gel first and then continue to age for 60 hours to obtain polybenzoxazine gel. (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in methanol for solvent replacement 5 times, once every 12 hours, to obtain the final state of polybenzoxazine gel; (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 30°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0037] The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment exhibits good bulking properties and is lightweight. Its density is 0.389 g / cm³. 3 It has a thermal conductivity of 0.0405 W / (m·K) at room temperature and pressure, a dielectric constant of 1.90, and a dielectric loss of 0.024.

[0038] Comparative Example 3: Comparative Example 3 was exactly the same as Example 3, except that the concentration of the benzoxazine solution in step (1) was 0.4 g / ml, and the thermal conductivity of the resulting polybenzoxazine microwave-transparent thermal insulation aerogel material at room temperature and pressure was 0.0606 W / (m·K). The results show that the thermal conductivity of the aerogel obtained by the raw material concentration is too high, which is not suitable for the field of high-efficiency thermal insulation.

[0039] Example 4: (1) The bisphenol F type benzoxazine monomer was completely dissolved in DMSO solvent by stirring at 300 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.30 g / ml; (2) The benzoxazine solution and 1,2,4,5-cyclohexanetetracarboxylic dianhydride were stirred at 300 rpm for 30 min at room temperature until they were mixed evenly to obtain a benzoxazine-1,2,4,5-cyclohexanetetracarboxylic dianhydride solution; wherein the mass ratio of 1,2,4,5-cyclohexanetetracarboxylic dianhydride to bisphenol F type benzoxazine monomer was 0.2:1; (3) At room temperature, p-benzenesulfonic acid was added dropwise as a catalyst to a benzoxazine-1,2,4,5-cyclohexanetetracarboxylic acid dianhydride solution at a dropping rate of 1 g / min, while stirring at a stirring speed of 300 rpm. After the addition was completed, the reaction was continued to be stirred at 300 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of p-benzenesulfonic acid to bisphenol F type benzoxazine monomer was 0.2:1. (4) The polybenzoxazine sol was allowed to stand at 30°C to gel first and then continue to age for 48 hours to obtain polybenzoxazine gel; (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in isopropanol for solvent replacement 4 times, once every 12 hours, to obtain the final state of polybenzoxazine gel. (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 30°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0040] The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment exhibits good bulking properties and is lightweight. Its density is 0.425 g / cm³. 3 It has a thermal conductivity of 0.0487 W / (m·K) at room temperature and pressure, a dielectric constant of 2.14, and a dielectric loss of 0.039.

[0041] Example 5: (1) The bisphenol A type benzoxazine monomer was completely dissolved in DMSO solvent by stirring at 400 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.2 g / ml; (2) The benzoxazine solution and cyclobutanetetracarboxylic dianhydride were stirred at 400 rpm for 20 min at room temperature until they were mixed evenly to obtain a benzoxazine-cyclobutanetetracarboxylic dianhydride solution; wherein the mass ratio of cyclobutanetetracarboxylic dianhydride to bisphenol A type benzoxazine monomer was 0.05:1. (3) At room temperature, hydrochloric acid was added dropwise as a catalyst to the benzoxazine-cyclobutanetetracarboxylic dianhydride solution at a dropping rate of 0.75 g / min, while stirring at a stirring speed of 400 rpm. After the addition was completed, the reaction was continued to be stirred at 400 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of hydrochloric acid to bisphenol A type benzoxazine monomer was 0.1:1. (4) The polybenzoxazine sol was allowed to stand at 10°C to gel first and then continue to age for 48 hours to obtain polybenzoxazine gel. (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in ethanol for solvent replacement 4 times, once every 18 hours, to obtain the final state of polybenzoxazine gel. (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 10°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0042] The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment exhibits good bulking properties and is lightweight. Its density is 0.422 g / cm³. 3 It has a thermal conductivity of 0.0424 W / (m·K) at room temperature and pressure, a dielectric constant of 2.05, and a dielectric loss of 0.030.

[0043] Example 6: (1) The bisphenol F type benzoxazine monomer was completely dissolved in NMP by stirring at 300 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.15 g / ml; (2) The benzoxazine solution and bicyclooctene dianhydride were stirred at 300 rpm for 20 min at room temperature until they were mixed evenly to obtain a benzoxazine-bicyclooctene dianhydride solution; wherein the mass ratio of bicyclooctene dianhydride to bisphenol F type benzoxazine monomer was 0.05:1; (3) At room temperature, hydrochloric acid was added dropwise as a catalyst to the benzoxazine-bicyclooctene dianhydride solution at a dropping rate of 0.5 g / min, while stirring at a stirring speed of 300 rpm. After the addition was completed, the reaction was continued to be stirred at 300 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of hydrochloric acid to bisphenol F type benzoxazine monomer was 0.05:1. (4) The polybenzoxazine sol was sealed and allowed to stand at 10°C to gel first and then continue to age. After 48 hours, the polybenzoxazine gel was obtained. (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in methanol for solvent replacement 5 times, once every 12 hours, to obtain the final state of polybenzoxazine gel; (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 10°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0044] The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment exhibits good bulking properties and is lightweight. Its density is 0.388 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0410 W / (m·K), its dielectric constant is 1.99, and its dielectric loss is 0.031.

[0045] Example 7: (1) The bisphenol A type benzoxazine monomer was completely dissolved in DMF by stirring at 300 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.25 g / ml; (2) The benzoxazine solution and 1,2,4,5-cyclohexanetetracarboxylic dianhydride were stirred at 300 rpm for 30 min at room temperature until they were mixed evenly to obtain a benzoxazine-1,2,4,5-cyclohexanetetracarboxylic dianhydride solution; wherein the mass ratio of 1,2,4,5-cyclohexanetetracarboxylic dianhydride to bisphenol A type benzoxazine monomer was 0.2:1; (3) At room temperature, p-benzenesulfonic acid was added dropwise as a catalyst to a benzoxazine-1,2,4,5-cyclohexanetetracarboxylic acid dianhydride solution at a dropping rate of 1 g / min, while stirring at a stirring speed of 300 rpm. After the addition was completed, the reaction was continued to be stirred at 300 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of p-benzenesulfonic acid to bisphenol A type benzoxazine monomer was 0.1:1. (4) The polybenzoxazine sol was sealed and allowed to stand at 20°C to gel first and then continue to age. After 72 hours, the polybenzoxazine gel was obtained. (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in ethanol for solvent replacement 4 times, once every 12 hours, to obtain the final state of polybenzoxazine gel. (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 20°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0046] The polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment exhibits good bulking properties and is lightweight. Its density is 0.425 g / cm³. 3 It has a thermal conductivity of 0.0445 W / (m·K) at room temperature and pressure, a dielectric constant of 2.09, and a dielectric loss of 0.035.

[0047] Example 8: (1) The bisphenol A type benzoxazine monomer was completely dissolved in NMP by stirring at 200 rpm for 20 min at room temperature to obtain a clear and transparent benzoxazine solution with a concentration of 0.35 g / ml; (2) The benzoxazine solution and maleic rosin dianhydride were stirred at 200 rpm for 20 min at room temperature until they were mixed evenly to obtain a benzoxazine-maleic rosin dianhydride solution; wherein the mass ratio of maleic rosin dianhydride to bisphenol A type benzoxazine monomer was 0.2:1; (3) At room temperature, p-benzenesulfonic acid was added dropwise as a catalyst to the benzoxazine-maleic rosin dianhydride solution at a dropping rate of 0.5 g / min, while stirring at a stirring speed of 200 rpm. After the addition was completed, the reaction was continued to be stirred at 200 rpm for 20 min to obtain polybenzoxazine sol. The mass ratio of p-benzenesulfonic acid to bisphenol A type benzoxazine monomer was 0.1:1. (4) The polybenzoxazine sol was sealed and allowed to stand at 10°C to gel first and then continue to age. After 60 h, the polybenzoxazine gel was obtained. (5) At normal pressure and room temperature, the polybenzoxazine gel was placed in methanol for solvent replacement 4 times, once every 18 hours, to obtain the final state of polybenzoxazine gel. (6) The polybenzoxazine final state gel was dried at normal pressure at a temperature of 10°C for 48 hours. After drying, polybenzoxazine wave-transparent heat-insulating aerogel material was obtained.

[0048] The macroscopic morphology of the polybenzoxazine microwave-transparent thermal insulation aerogel material prepared in this embodiment is as follows: Figure 3 As shown, it exhibits good bulking properties and is lightweight. Its microstructure is as follows: Figure 4 As shown, it exhibits a three-dimensional nanoporous network structure with a density of 0.431 g / cm³. 3 It has a thermal conductivity of 0.0509 W / (m·K) at room temperature and pressure, a dielectric constant of 2.18, and a dielectric loss of 0.045.

[0049] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing a polybenzoxazine wave-transparent thermal insulation aerogel material, characterized in that, The method includes the following steps: Step 1: Dissolve the benzoxazine monomer in a solvent to obtain a benzoxazine solution; Step 2: Mix the benzoxazine solution obtained in Step 1 with an alicyclic dianhydride to obtain a benzoxazine-alicyclic dianhydride solution; Step 3: Add the acid catalyst dropwise to the benzoxazine-alicyclic dianhydride solution obtained in Step 2, and after the reaction, polybenzoxazine sol is obtained; Step 4: Let the polybenzoxazine sol obtained in Step 3 stand, allowing it to gel first and then continue aging to obtain polybenzoxazine gel; Step 5: Solvent displacement is performed on the polybenzoxazine gel obtained in step 4 to obtain the final state polybenzoxazine gel; Step 6: Dry the polybenzoxazine final gel obtained in step 5 to obtain polybenzoxazine wave-transparent thermal insulation aerogel material.

2. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1, characterized in that, In step 1, the benzoxazine monomer is either a bisphenol A type benzoxazine monomer or a bisphenol F type benzoxazine monomer; In step 1, the solvent is one of NMP, DMF, or DMSO; In step 1, the dissolution process is as follows: stirring is used, with a stirring speed of 200~400 rpm, a stirring time of 10~30 min, and a stirring temperature of room temperature.

3. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1 or 2, characterized in that, In step 1, the concentration of the benzoxazine solution is 0.07~0.35 g / ml.

4. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1, characterized in that, In step 2, the alicyclic dianhydride is one of cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, dicyclooctene dianhydride, or maleic rosin dianhydride. In step 2, the process of achieving uniform mixing is as follows: stirring is used, with a stirring speed of 200~400 rpm, a stirring time of 10~30 min, and a stirring temperature of room temperature.

5. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1 or 4, characterized in that, In step 2, the mass ratio of alicyclic dianhydride to benzoxazine monomer is 0.05~0.2:

1.

6. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1, characterized in that, In step 3, the acid catalyst is one of hydrochloric acid, oxalic acid, or p-benzenesulfonic acid; In step 3, the dropping rate is 0.5~1g / min, and stirring is performed while adding the solution; the stirring speed is 200~400rpm, and the stirring temperature is room temperature; In step 3, the reaction process is as follows: stirring is used, the stirring speed is 200~400 rpm, the stirring time is 10~30 min, and the stirring temperature is room temperature.

7. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1 or 6, characterized in that, In step 3, the mass ratio of acid catalyst to benzoxazine monomer is 0.05~0.2:

1.

8. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1, characterized in that, In step 4, the settling process is as follows: temperature is 10~30℃, and time is 48~96h.

9. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1, characterized in that, In step 5, the solvent replacement process is as follows: at normal pressure and room temperature, the polybenzoxazine gel obtained in step 4 is placed in a solvent for solvent replacement, once every 9 to 18 hours, for a total of 4 to 6 times; the solvent is ethanol, methanol or isopropanol.

10. The method for preparing the polybenzoxazine microwave-transparent thermal insulation aerogel material according to claim 1, characterized in that, In step 6, the drying process is as follows: the pressure is normal, the temperature is 10~30℃, and the time is 24~72h.

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