Method for preparing polybenzoxazine aerogel by base catalysis method

Abstract

The invention discloses a method for preparing polybenzoxazine aerogel by a base catalysis method, which comprises the following steps: dissolving a basic catalyst in a solvent to prepare a catalyst solution; uniformly mixing a formaldehyde solution and a catalyst solution to prepare a formaldehyde / catalyst mixed solution; the method comprises the following steps: dissolving a 3-aminophenol compound in an alcohol solvent to prepare a 3-aminophenol compound solution; uniformly mixing the 3-aminophenol compound solution and the formaldehyde / catalyst mixed solution to obtain sol; the sol is rapidly placed in a high-temperature closed environment for polycondensation and ring-opening polymerization reaction, and polybenzoxazine gel is obtained; carrying out solvent replacement on the polybenzoxazine gel to obtain polybenzoxazine final-state gel; and then carrying out CO2 supercritical drying on the polybenzoxazine final-state gel, so as to obtain the polybenzoxazine aerogel. The polybenzoxazine aerogel with a novel structure is obtained by taking a 3-aminophenol compound and formaldehyde as raw materials and an alkaline solution as a catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-performance thermal insulation materials, and particularly relates to a method for preparing polybenzoxazine aerogel by an alkali catalysis method. BACKGROUND

[0002] With the continuous growth of global energy demand, energy consumption has become a core challenge faced by various industries. In this context, advanced thermal insulation materials are seen as a key path to reducing energy waste, mitigating human environmental impact, and promoting infrastructure development in line with global sustainable development goals. Aerogel materials are one of the current high-performance thermal insulation materials, which have the characteristics of low density, high specific surface area, high porosity, and low thermal conductivity, and are one of the effective ways to solve the energy crisis.

[0003] Polybenzoxazine aerogel is a new type of polymer aerogel, which has attracted widespread attention from the scientific and industrial communities due to its advanced material performance combination. However, its synthesis relies on harmful solvents, which conflicts with the principles of green chemistry, limiting sustainable development.

[0004] Currently, the preparation of most polybenzoxazine aerogels requires the use of high-boiling, strongly polar non-environmentally friendly solvents such as DMF, NMP, DMSO, etc. In general, these solvent systems require the use of strong acid catalysts such as hydrochloric acid and benzene sulfonic acid to promote the ring-opening polymerization sol-gel of polybenzoxazine aerogel. The use of non-environmentally friendly solvents and strong acid catalysts violates the requirements of green and sustainable development. The preparation of polybenzoxazine aerogel with green solvents has become an important direction for the development of this field. Document No. 202210812165.3 discloses a polybenzoxazine aerogel prepared with water as a solvent and a method for preparing the same. The polybenzoxazine aerogel prepared has a relatively low thermal conductivity (0.0249~0.0504 W / (m·K)), effectively promoting the development of polybenzoxazine aerogel prepared with green solvent systems.

[0005] However, in the prior art, benzoxazine monomers used to prepare polybenzoxazine aerogel are mostly prepared from amine, phenol, and formaldehyde, and the monomer synthesis process is complex and toxic solvents such as toluene, xylene, and chloroform are commonly used. In addition, the thermal conductivity of polybenzoxazine aerogel prepared based on green solvents is relatively high, which cannot meet the performance requirements of high-efficiency thermal insulation materials, and further improvement is still needed.

[0006] Therefore, how to ensure that polybenzoxazine aerogel has excellent properties such as low thermal conductivity and low density while realizing the green and environmentally friendly raw materials and the simplification of the preparation process is a technical problem that technicians in the field are concerned about. SUMMARY

[0007] In view of the deficiencies of the prior art, the application provides a method for preparing polybenzoxazine aerogel by an alkali catalysis method.

[0008] The technical scheme for solving the technical problem of the application is to provide a method for preparing polybenzoxazine aerogel by an alkali catalysis method, which comprises the following steps: Step 1, dissolving an alkali catalyst in a solvent to prepare a catalyst solution; then mixing a formaldehyde solution and the catalyst solution uniformly to prepare a formaldehyde / catalyst mixed solution; Step 2, dissolving a 3-aminophenol compound in an alcohol solvent to prepare a 3-aminophenol compound solution; then mixing the 3-aminophenol compound solution and the formaldehyde / catalyst mixed solution of step 1 uniformly to obtain a sol; Step 3, placing the sol obtained in step 2 in a high-temperature sealed environment quickly to perform polycondensation and ring-opening polymerization to obtain a polybenzoxazine gel; Step 4, performing solvent replacement on the polybenzoxazine gel of step 3 to obtain a polybenzoxazine final-state gel; then performing CO2 supercritical drying on the polybenzoxazine final-state gel to obtain a polybenzoxazine aerogel.

[0009] Compared with the prior art, the application has the following beneficial effects: (1) The application uses a 3-aminophenol compound and formaldehyde as raw materials, uses an alkali solution as a catalyst, obtains a nanoparticle skeleton structure by a solvothermal method, and maintains the nanoporous network structure by a supercritical drying method, further reduces the thermal conductivity, enhances the heat insulation performance, and obtains a polybenzoxazine aerogel with a novel structure.

[0010] (2) The application uses a mixed solvent of water and an alcohol solvent as a green medium, can effectively reduce the additional environmental hazards caused by solvent problems in the preparation process, and promotes the development of green preparation of the polybenzoxazine aerogel.

[0011] (3) The application uses an alkali solution as a catalyst, effectively avoids the problem of complex preparation process existing in monomer synthesis when an acid catalysis ring-closing polymerization is used to prepare benzoxazine, and solves the environmental pollution problem of the acid catalyst.

[0012] (4) The application uses a supercritical drying method, so that the material has a nanoporous network structure, thereby endowing the polybenzoxazine aerogel with the performance of light weight and high-efficiency heat insulation.

[0013] (5) The polybenzoxazine aerogel prepared by the application has a three-dimensional interconnected nanoporous network structure, has the characteristics of low density and low thermal conductivity, and the density is 0.106-0.225 g / cm 3The thermal conductivity is 0.0227-0.0431 W / (m*K), and the polybenzoxazine aerogel with light weight and excellent heat insulation performance obtained in a green solvent is expected to realize environment-friendly large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a whole flowchart of the present application; Figure 2 is a macroscopic morphology diagram of the polybenzoxazine aerogel prepared in Example 1 of the present application; Figure 3 is a microscopic structure diagram of the polybenzoxazine aerogel prepared in Example 1 of the present application; Figure 4 is a macroscopic morphology diagram of the polybenzoxazine aerogel prepared in Example 9 of the present application; Figure 5 is a microscopic structure diagram of the polybenzoxazine aerogel prepared in Example 9 of the present application. DETAILED DESCRIPTION

[0015] The specific embodiments of the present application are given below. The specific embodiments are only used to further illustrate the present application, and do not limit the protection scope of the present application.

[0016] The present application provides a method for preparing polybenzoxazine aerogel by alkali catalysis (referred to as method, as shown in Figure 1 The method comprises the following steps: Step 1, dissolving the alkaline catalyst in the solvent to prepare a catalyst solution; then mixing the formaldehyde solution and the catalyst solution uniformly to prepare a formaldehyde / catalyst mixed solution; Preferably, in step 1, the alkaline catalyst is at least one of NaHCO3, Na2CO3 and NaOH, and the compounding is in any ratio.

[0017] Preferably, in step 1, the solvent is a mixture of water and an alcohol solvent in any ratio; the alcohol solvent is ethanol, methanol or isopropanol.

[0018] Preferably, in step 1, the molar ratio of the alkaline catalyst to the solvent is 0.5-1.25:1.

[0019] Preferably, in step 1, the dissolving process is: using stirring to completely dissolve the alkaline catalyst in the solvent, the stirring speed is 200-400 rpm, the stirring time is 10-30 min, and the stirring temperature is room temperature (i.e. 20-30℃). Preferably, it is carried out in a magnetic stirrer.

[0020] Preferably, in step 1, the concentration of the formaldehyde solution is 0.05-0.15 mol / L; the mass ratio of the formaldehyde solution to the catalyst solution is 0.01-0.015:1.

[0021] Preferably, in step 1, 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.

[0022] Step 2: Dissolve 3-aminophenol compounds in an alcohol solvent to prepare a 3-aminophenol compound solution; then mix the 3-aminophenol compound solution with the formaldehyde / catalyst mixed solution from Step 1 to obtain a sol. Preferably, in step 2, the 3-aminophenol compound is 3-aminophenol (molecular formula C6H7NO) or 3-amino-5-ethylphenol (molecular formula C8H7NO). 11 NO), 3-amino-6-methylphenol (molecular formula C7H9NO), 3-amino-5-methylphenol (molecular formula C7H9NO) or 3-amino-6-ethylphenol (molecular formula C8H9NO) 11 One of the NOs. The structural formula is as follows:

[0023] Preferably, in step 2, the alcohol solvent is ethanol, methanol, or isopropanol.

[0024] Preferably, in step 2, the molar ratio of 3-aminophenol compound to alcohol solvent is 1:1 to 2.5.

[0025] Preferably, in step 2, the dissolution process is as follows: the 3-aminophenol compound is completely dissolved in the alcohol solvent by stirring at a speed of 200-400 rpm for 10-30 minutes at room temperature. Preferably, this is carried out using a magnetic stirrer.

[0026] Preferably, in step 2, the mass ratio of the 3-aminophenol compound solution to the formaldehyde / catalyst mixed solution is 1:1~2.

[0027] 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.

[0028] Step 3: The sol obtained in Step 2 is rapidly placed in a high-temperature, sealed environment to carry out polycondensation and ring-opening polymerization reactions to obtain polybenzoxazine gel; Preferably, in step 3, the reaction temperature is 120~160℃ and the reaction time is 72~120h.

[0029] Preferably, step 3 specifically involves: rapidly placing the sol obtained in step 2 into a reaction vessel, then placing the reaction vessel in an oven to form a high-temperature sealed environment, raising the temperature to a reaction temperature of 120~160℃, and carrying out condensation and ring-opening polymerization reactions for 72~120 hours; after the reaction is completed and cooled to room temperature, the product is removed to obtain polybenzoxazine gel.

[0030] Step 4: Solvent displacement is performed on the polybenzoxazine gel obtained in Step 3 to obtain the final polybenzoxazine gel; then the final polybenzoxazine gel is subjected to supercritical CO2 drying to obtain polybenzoxazine aerogel.

[0031] Preferably, in step 4, the displacement process is as follows: at room temperature, the polybenzoxazine gel from step 3 is placed in a solvent with low supercritical temperature and pressure for solvent displacement, once every 9 to 18 hours, for a total of 4 to 6 times; the solvent with low supercritical temperature and pressure is acetone, ethanol, methanol or isopropanol.

[0032] Preferably, in step 4, the CO2 supercritical drying process is as follows: pressure is 8~16MPa, temperature is 40~60℃, drying time is 8~18h, and pressure is released at a rate of 80~190kPa / min after drying.

[0033] Example 1: (1) NaHCO3 and water with a molar ratio of 0.5:1 were stirred at 200 rpm for 15 min at room temperature to obtain a catalyst solution; then a formaldehyde solution with a concentration of 0.1 mol / L and the catalyst solution were mixed at a mass ratio of 0.01:1 and stirred at 200 rpm for 10 min at room temperature to prepare a formaldehyde / catalyst mixed solution. (2) Dissolve 3-aminophenol in ethanol at a molar ratio of 1:1 and stir at 200 rpm for 10 min at room temperature to prepare a 3-aminophenol solution; then stir the 3-aminophenol solution and the formaldehyde / catalyst mixed solution at 200 rpm for 10 min at room temperature in a mass ratio of 1:1 to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, and then the reaction vessel was placed in an oven and heated to 120°C for 72 hours. After the reaction was completed and cooled to room temperature, the sol was removed to obtain polybenzoxazine gel. (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 4 times, once every 9 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 8 MPa, a temperature of 40 °C, and a drying time of 8 hours. After drying, the pressure was released at a rate of 80 kPa / min to obtain polybenzoxazine aerogel.

[0034] The macroscopic morphology of the polybenzoxazine aerogel prepared in this embodiment is as follows: Figure 2 As shown, the sample exhibits good bulking properties and is lightweight. The microstructure is as follows: Figure 3 As shown, it exhibits a three-dimensional nanoporous network structure, which gives it a low thermal conductivity and a density of 0.106 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0227 W / (m·K).

[0035] Comparative Example 1: Comparative Example 1 is exactly the same as Example 1, except that the catalyst solution in step (1) is hydrochloric acid; after testing, a uniform gel was not obtained, and a precipitate or suspension was obtained instead.

[0036] Example 2: (1) Mix NaHCO3, Na2CO3 and water in a molar ratio of 1.5:1:2 at room temperature and stir for 15 min at 240 rpm to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.0105:1 and stir for 15 min at room temperature at 240 rpm to prepare formaldehyde / catalyst mixed solution; (2) Dissolve 3-amino-5-ethylphenol in ethanol at a molar ratio of 1:2 and stir at 240 rpm for 12 min at room temperature to prepare a 3-amino-5-ethylphenol solution; then stir the 3-amino-5-ethylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:1.1 at room temperature for 12 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 140°C, and kept for 78 hours; after the reaction was completed, it was cooled to room temperature and taken out to obtain polybenzoxazine gel. (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 5 times, once every 10 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 9 MPa, a temperature of 42 °C, and a drying time of 9 hours. After drying, the pressure was released at a rate of 90 kPa / min to obtain polybenzoxazine aerogel.

[0037] The polybenzoxazine aerogel prepared in this embodiment has good bulking properties and is lightweight, with a density of 0.119 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0249 W / (m·K).

[0038] Comparative Example 2: Comparative Example 2 is exactly the same as Example 2, except that in step (2), the molar ratio of 3-amino-5-ethylphenol to ethanol is 1:0.5, which makes it difficult to obtain a gel.

[0039] Example 3: (1) Mix NaHCO3, Na2CO3 and water in a molar ratio of 1:1:2 at room temperature at 270 rpm for 15 min to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.011:1 and stir at room temperature at 270 rpm for 20 min to prepare formaldehyde / catalyst mixed solution. (2) Dissolve 3-amino-6-methylphenol in ethanol at a molar ratio of 1:1.4 and stir at 270 rpm for 16 min at room temperature to prepare a 3-amino-6-methylphenol solution; then stir the 3-amino-6-methylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:1.2 at room temperature for 16 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 130°C, and kept for 84 hours; after the reaction was completed, it was cooled to room temperature and taken out to obtain polybenzoxazine gel; (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 6 times, once every 11 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 10 MPa, a temperature of 46 °C, and a drying time of 10 hours. After drying, the pressure was released at a rate of 100 kPa / min to obtain polybenzoxazine aerogel.

[0040] The density of the polybenzoxazine aerogel prepared in this embodiment is 0.124 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0263 W / (m·K).

[0041] Comparative Example 3: Comparative Example 3 was exactly the same as Example 3, except that in step (2), the molar ratio of 3-amino-6-methylphenol to ethanol was 1:3, and the density of the resulting polybenzoxazine aerogel was 0.335 g / cm³. 3 The thermal conductivity at room temperature and pressure is 0.0532 W / (m·K). The results indicate that aerogels with excessively high raw material concentrations have excessively high thermal conductivity, making them unsuitable for high-efficiency thermal insulation applications.

[0042] Example 4: (1) Mix NaHCO3, Na2CO3 and water in a molar ratio of 0.5:0.5:2 at room temperature and stir for 15 min at 300 rpm to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.0115:1 and stir for 18 min at room temperature at 300 rpm to prepare formaldehyde / catalyst mixed solution; (2) Dissolve 3-amino-5-methylphenol in ethanol at a molar ratio of 1:1.5 and stir at 300 rpm for 18 min at room temperature to prepare a 3-amino-5-methylphenol solution; then stir the 3-amino-5-methylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:1.3 at room temperature for 18 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 135°C, and kept for 90 h; after the reaction was completed, it was cooled to room temperature and taken out to obtain polybenzoxazine gel; (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 4 times, once every 12 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 11 MPa, a temperature of 48 °C, and a drying time of 11 hours. After drying, the pressure was released at a rate of 120 kPa / min to obtain polybenzoxazine aerogel.

[0043] The density of the polybenzoxazine aerogel prepared in this embodiment is 0.143 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0299 W / (m·K).

[0044] Example 5: (1) Mix Na2CO3 and water in a molar ratio of 1:2 at room temperature at 320 rpm for 15 min to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.012:1 and stir at room temperature at 320 rpm for 20 min to prepare formaldehyde / catalyst mixed solution. (2) Dissolve 3-amino-6-ethylphenol in ethanol at a molar ratio of 1:1.8 and stir at 320 rpm for 20 min at room temperature to prepare a 3-amino-6-ethylphenol solution; then stir the 3-amino-6-ethylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:1.4 at room temperature for 20 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 140°C, and kept for 96 hours. After the reaction was completed and cooled to room temperature, the sol was removed to obtain polybenzoxazine gel. (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 5 times, once every 14 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 12 MPa, a temperature of 50 °C, and a drying time of 12 hours. After drying, the pressure was released at a rate of 140 kPa / min to obtain polybenzoxazine aerogel.

[0045] The density of the polybenzoxazine aerogel prepared in this embodiment is 0.156 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0324 W / (m·K).

[0046] Example 6: (1) Mix NaOH, Na2CO3 and water in a molar ratio of 0.5:1:2 at room temperature at 360 rpm for 15 min to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.0125:1 and stir at room temperature at 360 rpm for 22 min to prepare formaldehyde / catalyst mixed solution. (2) Dissolve 3-aminophenol in ethanol at a molar ratio of 1:2 and stir at 360 rpm for 22 min at room temperature to prepare a 3-aminophenol solution; then stir the 3-aminophenol solution and the formaldehyde / catalyst mixed solution at 360 rpm for 22 min at room temperature in a mass ratio of 1:1.5 to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 145°C, and kept for 102 h; after the reaction was completed, it was cooled to room temperature and taken out to obtain polybenzoxazine gel; (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 6 times, once every 15 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 13 MPa, a temperature of 52 °C, and a drying time of 14 hours. After drying, the pressure was released at a rate of 150 kPa / min to obtain polybenzoxazine aerogel.

[0047] The density of the polybenzoxazine aerogel prepared in this embodiment is 0.177 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0361 W / (m·K).

[0048] Example 7: (1) Mix NaOH, Na2CO3 and water in a molar ratio of 1:1:2 at room temperature and stir for 15 min at 370 rpm to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.013:1 and stir at room temperature for 24 min at 370 rpm to prepare formaldehyde / catalyst mixed solution. (2) Dissolve 3-amino-5-ethylphenol in ethanol at a molar ratio of 1:2.1 and stir at 370 rpm for 24 min at room temperature to prepare a 3-amino-5-ethylphenol solution; then stir the 3-amino-5-ethylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:1.6 at room temperature for 24 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 150°C, and kept for 108 h; after the reaction was completed and cooled to room temperature, it was taken out to obtain polybenzoxazine gel; (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 4 times, once every 16 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 14 MPa, a temperature of 54 °C, and a drying time of 15 hours. After drying, the pressure was released at a rate of 160 kPa / min to obtain polybenzoxazine aerogel.

[0049] The density of the polybenzoxazine aerogel prepared in this embodiment is 0.183 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0395 W / (m·K).

[0050] Example 8: (1) Mix NaOH, Na2CO3 and water in a molar ratio of 1.5:1:2 at room temperature and stir for 15 min at 380 rpm to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.014:1 and stir at room temperature for 24 min at 380 rpm to prepare formaldehyde / catalyst mixed solution. (2) Dissolve 3-amino-5-methylphenol in ethanol at a molar ratio of 1:2.4 and stir at 380 rpm for 28 min at room temperature to prepare a 3-amino-5-methylphenol solution; then stir the 3-amino-5-methylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:1.8 at room temperature for 28 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 155°C, and kept for 114 hours. After the reaction was completed and cooled to room temperature, the sol was removed to obtain polybenzoxazine gel. (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 5 times, once every 17 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 15 MPa, a temperature of 56 °C, and a drying time of 16 hours. After drying, the pressure was released at a rate of 180 kPa / min to obtain polybenzoxazine aerogel.

[0051] The density of the polybenzoxazine aerogel prepared in this embodiment is 0.212 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0420 W / (m·K).

[0052] Example 9: (1) Mix NaOH and water in a molar ratio of 1:2 at room temperature at 400 rpm for 15 min to obtain a catalyst solution; then mix formaldehyde solution with a concentration of 0.1 mol / L and catalyst solution in a mass ratio of 0.015:1 and stir at room temperature at 400 rpm for 30 min to prepare a formaldehyde / catalyst mixed solution. (2) Dissolve 3-amino-6-methylphenol in ethanol at a molar ratio of 1:2.5 and stir at 400 rpm for 30 min at room temperature to prepare a 3-amino-6-methylphenol solution; then stir the 3-amino-6-methylphenol solution and the formaldehyde / catalyst mixed solution at a mass ratio of 1:2 at room temperature for 30 min to obtain a sol. (3) The sol was quickly transferred to the reaction vessel, placed in an oven, heated to 160°C, and kept for 120 h; after the reaction was completed, it was cooled to room temperature and taken out to obtain polybenzoxazine gel; (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement 6 times, once every 18 hours, to obtain the final state of polybenzoxazine gel; the final state of polybenzoxazine gel was then subjected to supercritical CO2 drying at a pressure of 16 MPa, a temperature of 60 °C, and a drying time of 18 hours. After drying, the pressure was released at a rate of 190 kPa / min to obtain polybenzoxazine aerogel.

[0053] The macroscopic morphology of the polybenzoxazine aerogel prepared in this embodiment is as follows: Figure 4 As shown, the sample exhibits good bulking properties and is lightweight. The microstructure is as follows: Figure 5 As shown, it exhibits a three-dimensional nanoporous network structure with a density of 0.225 g / cm³. 3 Its thermal conductivity at room temperature and pressure is 0.0431 W / (m·K).

[0054] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing polybenzoxazine aerogel by an alkaline catalysis method, characterized in that, The method includes the following steps: Step 1: Dissolve the alkaline catalyst in a solvent to prepare a catalyst solution; then mix the formaldehyde solution and the catalyst solution evenly to prepare a formaldehyde / catalyst mixed solution. Step 2: Dissolve 3-aminophenol compounds in an alcohol solvent to prepare a 3-aminophenol compound solution; then mix the 3-aminophenol compound solution with the formaldehyde / catalyst mixed solution from Step 1 to obtain a sol. Step 3: The sol obtained in Step 2 is rapidly placed in a high-temperature, sealed environment to carry out polycondensation and ring-opening polymerization reactions to obtain polybenzoxazine gel; Step 4: Solvent displacement is performed on the polybenzoxazine gel obtained in Step 3 to obtain the final polybenzoxazine gel; then the final polybenzoxazine gel is subjected to supercritical CO2 drying to obtain polybenzoxazine aerogel.

2. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 1, the alkaline catalyst is at least one of NaHCO3, Na2CO3 and NaOH, and the ratio can be arbitrary when they are combined. In step 1, the solvent is a mixture of water and an alcohol solvent in any proportion; the alcohol solvent is ethanol, methanol, or isopropanol.

3. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 1, the molar ratio of the alkaline catalyst to the solvent is 0.5~1.25:1; 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.

4. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 1, the concentration of the formaldehyde solution is 0.05~0.15 mol / L; the mass ratio of formaldehyde solution to catalyst solution is 0.01~0.015:1; In step 1, 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 polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 2, the 3-aminophenol compound is one of 3-aminophenol, 3-amino-5-ethylphenol, 3-amino-6-methylphenol, 3-amino-5-methylphenol, or 3-amino-6-ethylphenol; In step 2, the alcohol solvent is ethanol, methanol, or isopropanol.

6. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 2, the molar ratio of 3-aminophenol compounds to alcohol solvents is 1:1 to 2.5; In step 2, the dissolution process is as follows: the 3-aminophenol compound is completely dissolved in the alcohol solvent by stirring at a speed of 200-400 rpm for 10-30 min at room temperature.

7. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 2, the mass ratio of the 3-aminophenol compound solution to the formaldehyde / catalyst mixed solution is 1:1~2; 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.

8. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 3, the reaction temperature is 120~160℃ and the reaction time is 72~120h.

9. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 4, the displacement process is as follows: at room temperature, the polybenzoxazine gel from step 3 is placed in a solvent with low supercritical temperature and pressure for solvent displacement, once every 9 to 18 hours, for a total of 4 to 6 times; the solvent with low supercritical temperature and pressure is acetone, ethanol, methanol or isopropanol.

10. The method for preparing polybenzoxazine aerogel by alkaline catalysis according to claim 1, characterized in that, In step 4, the CO2 supercritical drying process is as follows: pressure is 8~16MPa, temperature is 40~60℃, drying time is 8~18h, and pressure is released at a rate of 80~190kPa / min after drying.

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