A method for preparing polybenzoxazine aerogel by base catalysis

Abstract

The application discloses a method for preparing polybenzoxazine aerogel by an alkali catalysis method, and comprises the following steps: dissolving an alkali catalyst in a solvent to prepare a catalyst solution; mixing formaldehyde solution and the catalyst solution uniformly to prepare a formaldehyde / catalyst mixed solution; dissolving 3-aminophenol compounds in an alcohol solvent to prepare a 3-aminophenol compound solution; mixing the 3-aminophenol compound solution and the formaldehyde / catalyst mixed solution uniformly to obtain a sol; placing the sol in a high-temperature closed environment quickly to perform polycondensation and ring-opening polymerization, and obtaining polybenzoxazine gel; performing solvent replacement on the polybenzoxazine gel to obtain polybenzoxazine final-state gel; and performing CO2 supercritical drying on the polybenzoxazine final-state gel to obtain polybenzoxazine aerogel. The method uses 3-aminophenol compounds and formaldehyde as raw materials, and uses an alkali solution as a catalyst, and polybenzoxazine aerogel with a novel structure is obtained.

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:

[0009] Step 1, dissolving an alkali catalyst in a solvent to prepare a catalyst solution; then mixing the formaldehyde solution and the catalyst solution uniformly to prepare a formaldehyde / catalyst mixed solution;

[0010] Step 2, dissolving 3-aminophenol compounds 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;

[0011] Step 3, quickly placing the sol obtained in step 2 in a high-temperature sealed environment to perform polycondensation and ring-opening polymerization to obtain a polybenzoxazine gel;

[0012] 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.

[0013] Compared with the prior art, the application has the following beneficial effects:

[0014] (1) The application uses 3-aminophenol compounds and formaldehyde as raw materials, uses an alkali solution as a catalyst, obtains a nanoparticle skeleton structure by a solvothermal method, and uses a supercritical drying method to maintain the nanoporous network structure, further reduces the thermal conductivity, enhances the heat insulation performance, and obtains a polybenzoxazine aerogel with a novel structure.

[0015] (2) The application uses a mixed solvent of water and an alcohol solvent as a green medium, which can effectively reduce the additional environmental hazards caused by solvent problems in the preparation process, and promote the development of green preparation of polybenzoxazine aerogel.

[0016] (3) The application uses an alkali solution as a catalyst, which not only effectively avoids the problem of complex preparation process existing in monomer synthesis when preparing benzoxazine by acid catalysis ring-closing polymerization, but also solves the environmental pollution problem of acid catalysts.

[0017] (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.

[0018] (5) The polybenzoxazine aerogel prepared by the method has a three-dimensional interconnected nanoporous network structure, and has the characteristics of low density and low thermal conductivity, the density is 0.106-0.225 g / cm 3 , the thermal conductivity is 0.0227-0.0431 W / (m·K), the polybenzoxazine aerogel with light weight and excellent heat insulation performance obtained in a green solvent is expected to realize large-scale production in an environmentally friendly manner. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The overall flowchart of the application is shown in the figure;

[0020] Figure 2 The macroscopic morphology diagram of the polybenzoxazine aerogel prepared in Example 1 of the application is shown in the figure;

[0021] Figure 3 The microstructure diagram of the polybenzoxazine aerogel prepared in Example 1 of the application is shown in the figure;

[0022] Figure 4 The macroscopic morphology diagram of the polybenzoxazine aerogel prepared in Example 9 of the application is shown in the figure;

[0023] Figure 5 The microstructure diagram of the polybenzoxazine aerogel prepared in Example 9 of the application is shown in the figure. DETAILED DESCRIPTION

[0024] The specific embodiments of the application are given below. The specific embodiments are only used to further illustrate the application, and do not limit the protection scope of the application.

[0025] The application provides a method for preparing polybenzoxazine aerogel by alkali catalysis (referred to as method, as shown in the figure), which comprises the following steps: Figure 1

[0026] 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;

[0027] Preferably, in step 1, the alkaline catalyst is at least one of NaHCO3, Na2CO3 and NaOH, and the compounding is in any ratio.

[0028] 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.

[0029] Preferably, in step 1, the molar ratio of the alkaline catalyst to the solvent is 0.5-1.25:1.

[0030] ​Preferably, in step 1, the dissolving process is: using stirring method until the basic catalyst is completely dissolved 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, the stirring is performed in a magnetic stirrer.

[0031] Preferably, in step 1, the concentration of the formaldehyde solution is 0.05-0.15 mol / L; and the mass ratio of the formaldehyde solution to the catalyst solution is 0.01-0.015:1.

[0032] Preferably, in step 1, the mixing process is: using stirring method, the stirring speed is 200-400 rpm, the stirring time is 10-30 min, and the stirring temperature is room temperature. Preferably, the stirring is performed in a magnetic stirrer.

[0033] Step 2, dissolving 3-aminophenol compound in alcohol solvent to prepare 3-aminophenol compound solution; then mixing the 3-aminophenol compound solution and the formaldehyde / catalyst mixed solution of step 1 uniformly to obtain sol;

[0034] Preferably, in step 2, the 3-aminophenol compound is one of 3-aminophenol (molecular formula is C6H7NO), 3-amino-5-ethylphenol (molecular formula is C8H 11 NO), 3-amino-6-methylphenol (molecular formula is C7H9NO), 3-amino-5-methylphenol (molecular formula is C7H9NO) or 3-amino-6-ethylphenol (molecular formula is C8H 11 NO). The structural formula is as follows:

[0035]

[0036] Preferably, in step 2, the alcohol solvent is ethanol, methanol or isopropanol.

[0037] Preferably, in step 2, the molar ratio of the 3-aminophenol compound to the alcohol solvent is 1:1-2.5.

[0038] Preferably, in step 2, the dissolving process is: using stirring method until the 3-aminophenol compound is completely dissolved in the alcohol solvent, the stirring speed is 200-400 rpm, the stirring time is 10-30 min, and the stirring temperature is room temperature. Preferably, the stirring is performed in a magnetic stirrer.

[0039] Preferably, in step 2, the mass ratio of the 3-aminophenol compound solution to the formaldehyde / catalyst mixed solution is 1:1-2.

[0040] Preferably, in step 2, the mixing uniformity process is: stirring at a stirring speed of 200-400 rpm for 10-30 min at room temperature. Preferably, the stirring is performed in a magnetic stirrer.

[0041] Step 3: rapidly placing the sol obtained in step 2 in a high-temperature sealed environment to perform polycondensation and ring-opening polymerization, thereby obtaining a polybenzoxazine gel;

[0042] Preferably, in step 3, the reaction temperature is 120-160°C, and the reaction time is 72-120 h.

[0043] Preferably, step 3 is specifically: rapidly placing the sol obtained in step 2 in a reaction kettle, then placing the reaction kettle in an oven to form a high-temperature sealed environment, and then performing polycondensation and ring-opening polymerization after the temperature is raised to a reaction temperature of 120-160°C for 72-120 h; after the reaction is completed and the temperature is cooled to room temperature, the polybenzoxazine gel is obtained.

[0044] Step 4: performing solvent replacement on the polybenzoxazine gel obtained in step 3 to obtain a polybenzoxazine final-state gel; and then performing CO2 supercritical drying on the polybenzoxazine final-state gel to obtain a polybenzoxazine aerogel.

[0045] Preferably, in step 4, the replacement process is: placing the polybenzoxazine gel obtained in step 3 in a solvent with low supercritical temperature and pressure at room temperature to perform solvent replacement, and replacing every 9-18 h for 4-6 times; the solvent with low supercritical temperature and pressure is acetone, ethanol, methanol or isopropanol.

[0046] Preferably, in step 4, the CO2 supercritical drying process is: the pressure is 8-16 MPa, the temperature is 40-60°C, the drying time is 8-18 h, and after the drying is completed, the pressure is released at a speed of 80-190 kPa / min.

[0047] Example 1:

[0048] (1) mixing NaHCO3 and water in a mass ratio of 0.5:1 at room temperature and stirring at 200 rpm for 15 min to obtain a catalyst solution; then mixing a formaldehyde solution with a concentration of 0.1 mol / L and the catalyst solution in a mass ratio of 0.01:1, stirring at 200 rpm for 10 min at room temperature, and preparing a formaldehyde / catalyst mixed solution;

[0049] (2) dissolving 3-aminophenol in ethanol, the mass ratio of 3-aminophenol to ethanol being 1:1, stirring at 200 rpm for 10 min at room temperature, and preparing a 3-aminophenol solution; then mixing the 3-aminophenol solution and the formaldehyde / catalyst mixed solution in a mass ratio of 1:1, stirring at 200 rpm for 10 min at room temperature, and obtaining a sol.

[0050] (3) quickly transfer the sol into a reactor, then put the reactor into an oven, and heat to 120℃ and keep for 72h; after the reaction is completed, cool to room temperature, and take out, to obtain a polybenzoxazine gel;

[0051] (4) solvent exchange the polybenzoxazine gel in ethanol at room temperature, exchange 4 times, exchange once every 9h, to obtain a polybenzoxazine final gel; then perform CO2 supercritical drying on the polybenzoxazine final gel, the pressure of CO2 supercritical drying is 8MPa, the temperature is 40℃, the drying time is 8h, after the drying is completed, release the pressure at a speed of 80kPa / min, to obtain a polybenzoxazine aerogel.

[0052] The macroscopic morphology of the polybenzoxazine aerogel prepared in this example is shown in Figure 2 , the sample has good blockiness, light weight and other characteristics. The microstructure is shown in Figure 3 , which presents a three-dimensional nano-porous network structure, which makes it have a low thermal conductivity, the density is 0.106g / cm 3 , and the thermal conductivity at room temperature and normal pressure is 0.0227W / (m·K).

[0053] Comparative Example 1:

[0054] Comparative Example 1 is exactly the same as Example 1, the only difference is that the catalyst solution in step (1) is hydrochloric acid; after testing, no uniform gel is obtained, and a precipitate or suspension is obtained.

[0055] Example 2:

[0056] (1) mix NaHCO3, Na2CO3 and water in a mass ratio of 1.5:1:2 at room temperature and 240rpm for 15min, to obtain a catalyst solution; then mix the formaldehyde solution with a concentration of 0.1mol / L and the catalyst solution in a mass ratio of 0.0105:1, stir at room temperature and 240rpm for 15min, to prepare a formaldehyde / catalyst mixed solution;

[0057] (2) dissolve 3-amino-5-ethylphenol in ethanol, the mass ratio of the two is 1:2, stir at room temperature and 240rpm for 12min to prepare a 3-amino-5-ethylphenol solution; then mix the 3-amino-5-ethylphenol solution and the formaldehyde / catalyst mixed solution in a mass ratio of 1:1.1, stir at room temperature and 240rpm for 12min, to obtain a sol;

[0058] (3) quickly transfer the sol into a reactor, put the reactor into an oven, heat to 140℃ and keep for 78h; after the reaction is completed, cool to room temperature, and take out, to obtain a polybenzoxazine gel;

[0059] (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent exchange, and the exchange was performed 5 times at an interval of 10 h to obtain a polybenzoxazine final gel; and the polybenzoxazine final gel was subjected to CO2 supercritical drying at a pressure of 9 MPa and a temperature of 42 °C for 9 h, and after the drying was completed, the pressure was released at a speed of 90 kPa / min to obtain a polybenzoxazine aerogel.

[0060] The polybenzoxazine aerogel prepared in this example has good blockability, light weight and other characteristics, and the density thereof is 0.119 g / cm3. 3 The thermal conductivity thereof at room temperature and normal pressure is 0.0249 W / (m·K).

[0061] Comparative Example 2:

[0062] Comparative Example 2 is completely identical to Example 2, and the only difference is that in step (2), the molar ratio of 3-amino-5-ethylphenol to ethanol is 1:0.5, and as a result, it is difficult to obtain a gel.

[0063] Example 3:

[0064] (1) NaHCO3, Na2CO3 and water in a molar ratio of 1:1:2 were mixed and stirred at room temperature at 270 rpm for 15 min to obtain a catalyst solution; and a formaldehyde solution with a concentration of 0.1 mol / L and the catalyst solution were mixed in a mass ratio of 0.011:1, and stirred at room temperature at 270 rpm for 20 min to prepare a formaldehyde / catalyst mixed solution;

[0065] (2) 3-amino-6-methylphenol was dissolved in ethanol, and the molar ratio of the two was 1:1.4, and the solution was prepared by stirring at room temperature at 270 rpm for 16 min; and the 3-amino-6-methylphenol solution and the formaldehyde / catalyst mixed solution were mixed in a mass ratio of 1:1.2, and stirred at room temperature at 270 rpm for 16 min to obtain a sol;

[0066] (3) The sol was quickly transferred to a reaction kettle, and placed in an oven, and heated to 130 °C and kept for 84 h; and after the reaction was completed and the temperature was cooled to room temperature, the polybenzoxazine gel was taken out;

[0067] (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent exchange, and the exchange was performed 6 times at an interval of 11 h to obtain a polybenzoxazine final gel; and the polybenzoxazine final gel was subjected to CO2 supercritical drying at a pressure of 10 MPa and a temperature of 46 °C for 10 h, and after the drying was completed, the pressure was released at a speed of 100 kPa / min to obtain a polybenzoxazine aerogel.

[0068] The density of the polybenzoxazine aerogel prepared in this example was 0.124 g / cm 3 , and the thermal conductivity at room temperature and normal pressure was 0.0263 W / (m·K).

[0069] Comparative Example 3:

[0070] 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 polybenzoxazine aerogel obtained was 0.335 g / cm 3 , and the thermal conductivity at room temperature and normal pressure was 0.0532 W / (m·K). The results showed that the thermal conductivity of the aerogel obtained by too high a concentration ratio of raw materials was too high, which was not suitable for the field of high-efficiency thermal insulation.

[0071] Example 4:

[0072] (1) NaHCO3, Na2CO3 and water with a molar ratio of 0.5:0.5:2 were mixed and stirred at room temperature at 300 rpm for 15 min to obtain a catalyst solution; then a formaldehyde solution with a concentration of 0.1 mol / L and the catalyst solution were mixed in a mass ratio of 0.0115:1, and stirred at room temperature at 300 rpm for 18 min to prepare a formaldehyde / catalyst mixed solution;

[0073] (2) 3-amino-5-methylphenol was dissolved in ethanol, and the molar ratio of the two was 1:1.5. The mixture was stirred at room temperature at 300 rpm for 18 min to prepare a 3-amino-5-methylphenol solution; then the 3-amino-5-methylphenol solution and the formaldehyde / catalyst mixed solution were mixed in a mass ratio of 1:1.3 and stirred at room temperature at 300 rpm for 18 min to obtain a sol;

[0074] (3) The sol was quickly transferred to a reaction kettle, which was placed in an oven and heated to 135°C for 90 h; after cooling to room temperature, the polybenzoxazine gel was taken out;

[0075] (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement, and the replacement was performed 4 times, once every 12 h, to obtain a polybenzoxazine final-state gel; then the polybenzoxazine final-state gel was subjected to CO2 supercritical drying, the pressure of CO2 supercritical drying was 11 MPa, the temperature was 48°C, and the drying time was 11 h; after drying, the pressure was released at a speed of 120 kPa / min to obtain a polybenzoxazine aerogel.

[0076] The density of the polybenzoxazine aerogel prepared in this example was 0.143 g / cm 3 , and the thermal conductivity at room temperature and normal pressure was 0.0299 W / (m·K).

[0077] Example 5:

[0078] (1) Na2CO3 and water with a molar ratio of 1:2 were mixed and stirred at room temperature at 320 rpm for 15 min 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 0.012:1, and stirred at room temperature at 320 rpm for 20 min to prepare a formaldehyde / catalyst mixed solution;

[0079] (2) 3-amino-6-ethylphenol was dissolved in ethanol at a molar ratio of 1:1.8, and stirred at room temperature at 320 rpm for 20 min to prepare a 3-amino-6-ethylphenol solution; then the 3-amino-6-ethylphenol solution and the formaldehyde / catalyst mixed solution were mixed at a mass ratio of 1:1.4, and stirred at room temperature at 320 rpm for 20 min to obtain a sol;

[0080] (3) The sol was quickly transferred to a reaction kettle, placed in an oven, and heated to 140℃ and kept for 96 h; after cooling to room temperature, the reaction was completed and the product was taken out to obtain a polybenzoxazine gel;

[0081] (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement, and the replacement was performed 5 times, once every 14 h, to obtain a polybenzoxazine final-state gel; then the polybenzoxazine final-state gel was subjected to CO2 supercritical drying, the pressure of CO2 supercritical drying was 12 MPa, the temperature was 50℃, and the drying time was 12 h; after drying, the pressure was released at a speed of 140 kPa / min to obtain a polybenzoxazine aerogel.

[0082] The density of the polybenzoxazine aerogel prepared in this example was 0.156 g / cm 3 , and the thermal conductivity at room temperature and normal pressure was 0.0324 W / (m·K).

[0083] Example 6:

[0084] (1) NaOH, Na2CO3 and water with a molar ratio of 0.5:1:2 were mixed and stirred at room temperature at 360 rpm for 15 min 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 0.0125:1, and stirred at room temperature at 360 rpm for 22 min to prepare a formaldehyde / catalyst mixed solution;

[0085] (2) 3-aminophenol was dissolved in ethanol at a molar ratio of 1:2, and stirred at room temperature at 360 rpm for 22 min to prepare a 3-aminophenol solution; then the 3-aminophenol solution and the formaldehyde / catalyst mixed solution were mixed at a mass ratio of 1:1.5, and stirred at room temperature at 360 rpm for 22 min to obtain a sol;

[0086] (3) quickly transfer the sol into a reactor, place it in an oven, and heat it to 145℃ and keep it for 102h; after the reaction is completed and the temperature is cooled to room temperature, the polybenzoxazine gel is obtained;

[0087] (4) place the polybenzoxazine gel in ethanol at room temperature to perform solvent replacement, replace it for 6 times, replace it once every 15h, and obtain a polybenzoxazine final gel; then perform CO2 supercritical drying on the polybenzoxazine final gel, the pressure of the CO2 supercritical drying is 13MPa, the temperature is 52℃, the drying time is 14h, after the drying is completed, release the pressure at a speed of 150kPa / min, and obtain a polybenzoxazine aerogel.

[0088] The density of the polybenzoxazine aerogel prepared in this example is 0.177g / cm3. 3 The thermal conductivity at room temperature and normal pressure is 0.0361W / (m·K).

[0089] Example 7:

[0090] (1) mix NaOH, Na2CO3 and water in a mass ratio of 1:1:2 at room temperature and 370rpm for 15min to obtain a catalyst solution; then mix a formaldehyde solution with a concentration of 0.1mol / L and the catalyst solution in a mass ratio of 0.013:1, stir them at room temperature and 370rpm for 24min, and prepare a formaldehyde / catalyst mixed solution;

[0091] (2) dissolve 3-amino-5-ethylphenol in ethanol, the mass ratio of the two is 1:2.1, and stir them at room temperature and 370rpm for 24min to prepare a 3-amino-5-ethylphenol solution; then mix the 3-amino-5-ethylphenol solution and the formaldehyde / catalyst mixed solution in a mass ratio of 1:1.6, stir them at room temperature and 370rpm for 24min, and obtain a sol;

[0092] (3) quickly transfer the sol into a reactor, place it in an oven, and heat it to 150℃ and keep it for 108h; after the reaction is completed and the temperature is cooled to room temperature, the polybenzoxazine gel is obtained;

[0093] (4) place the polybenzoxazine gel in ethanol at room temperature to perform solvent replacement, replace it for 4 times, replace it once every 16h, and obtain a polybenzoxazine final gel; then perform CO2 supercritical drying on the polybenzoxazine final gel, the pressure of the CO2 supercritical drying is 14MPa, the temperature is 54℃, the drying time is 15h, after the drying is completed, release the pressure at a speed of 160kPa / min, and obtain a polybenzoxazine aerogel.

[0094] The density of the polybenzoxazine aerogel prepared in this example is 0.183g / cm3. 3, the thermal conductivity at room temperature and normal pressure is 0.0395 W / (m·K).

[0095] Example 8:

[0096] (1) NaOH, Na2CO3 and water with a molar ratio of 1.5:1:2 were mixed and stirred at room temperature at 380 rpm for 15 min 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 0.014:1, and stirred at room temperature at 380 rpm for 24 min to prepare a formaldehyde / catalyst mixed solution;

[0097] (2) 3-amino-5-methylphenol was dissolved in ethanol, and the molar ratio of the two was 1:2.4, and the solution was prepared by stirring at room temperature at 380 rpm for 28 min; then the 3-amino-5-methylphenol solution and the formaldehyde / catalyst mixed solution were mixed at a mass ratio of 1:1.8, and stirred at room temperature at 380 rpm for 28 min to obtain a sol;

[0098] (3) The sol was quickly transferred to a reaction kettle and placed in an oven, and heated to 155℃ and kept for 114 h; after cooling to room temperature, the polybenzoxazine gel was obtained;

[0099] (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement, and replaced for 5 times, once every 17 h, to obtain a polybenzoxazine final gel; then the polybenzoxazine final gel was subjected to CO2 supercritical drying, the pressure of CO2 supercritical drying was 15 MPa, the temperature was 56℃, and the drying time was 16 h; after drying, the pressure was released at a speed of 180 kPa / min to obtain a polybenzoxazine aerogel.

[0100] The density of the polybenzoxazine aerogel prepared in this example was 0.212 g / cm 3 , and the thermal conductivity at room temperature and normal pressure was 0.0420 W / (m·K).

[0101] Example 9:

[0102] (1) NaOH and water with a molar ratio of 1:2 were mixed and stirred at room temperature at 400 rpm for 15 min 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 0.015:1, and stirred at room temperature at 400 rpm for 30 min to prepare a formaldehyde / catalyst mixed solution;

[0103] (2) 3-amino-6-methylphenol solution was prepared by dissolving 3-amino-6-methylphenol in ethanol at a molar ratio of 1:2.5, stirring at 400 rpm for 30 min at room temperature; then 3-amino-6-methylphenol solution and formaldehyde / catalyst mixed solution were mixed at a mass ratio of 1:2, stirring at 400 rpm for 30 min at room temperature to obtain a sol;

[0104] (3) The sol was quickly transferred to a reaction kettle and placed in an oven, and heated to 160℃ and kept for 120 h; after cooling to room temperature, the polybenzoxazine gel was obtained;

[0105] (4) The polybenzoxazine gel was placed in ethanol at room temperature for solvent replacement, and the replacement was performed 6 times, once every 18 h, to obtain a polybenzoxazine final-state gel; then the polybenzoxazine final-state gel was subjected to CO2 supercritical drying, the pressure of CO2 supercritical drying was 16 MPa, the temperature was 60℃, and the drying time was 18 h; after drying, the pressure was released at a speed of 190 kPa / min to obtain a polybenzoxazine aerogel.

[0106] The macroscopic morphology of the polybenzoxazine aerogel prepared in the embodiment is shown in Figure 4 , the sample has good blockiness and light weight, etc. The microstructure is shown in Figure 5 , which presents a three-dimensional nano-porous network structure, and the density is 0.225 g / cm 3 , and the thermal conductivity at room temperature and normal pressure is 0.0431 W / (m·K).

[0107] The unmentioned parts of the present application are applicable to the prior art.

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. The molar ratio of 3-aminophenol compounds to alcohol solvents is 1:1 to 2.5; Step 3: The sol obtained in Step 2 is quickly placed in a high-temperature sealed environment and subjected to polycondensation and ring-opening polymerization at a reaction temperature of 120~160℃ 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 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 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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