Preparation method of silicon hybrid polybenzoxazine aerogel

Abstract

The invention discloses a preparation method of silicon hybrid polybenzoxazine aerogel, and belongs to the technical field of aerogel preparation. The method comprises the following steps: adding a phenol source, paraformaldehyde and an amine source into a solvent, reacting at 100 DEG C for 24 hours, then removing the solvent through reduced pressure distillation, redissolving with chloroform, then carrying out alkali washing and water washing until a water phase is neutral, drying overnight, and carrying out rotary evaporation to remove the solvent, so as to obtain a benzoxazine monomer; dissolving the chitosan and tannic acid in a solvent to obtain a composite solution; adding a hydrochloric acid catalyst, siloxane, deionized water and amino silane, uniformly mixing, and pouring into a prepared forming mold for gelation; and drying the wet gel at normal pressure. According to the preparation method of the silicon hybridized polybenzoxazine aerogel, gel can be formed at room temperature, the high polymerization activity of a benzoxazine monomer under the catalysis of acid is utilized, meanwhile, a two-step catalytic reaction method is adopted, a silicon precursor is promoted to be subjected to dehydration condensation through alkaline silane, and the silicon hybridized polybenzoxazine aerogel is obtained. The problem of incompatibility of benzoxazine and siloxane on the gel condition is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerogel preparation, and particularly relates to a preparation method of a novel silicon hybrid polybenzoxazine aerogel capable of gelling at room temperature. Background Art

[0002] Aerogel materials have a large number of pores. This special structural form endows aerogels with a low thermal conductivity. Therefore, the heat insulation of aerogels becomes the most important application scenario. In the aerospace field, the heat insulation and protection function of aerogels can ensure the safety of internal instruments, equipment and personnel during service. In the civilian field, the heat insulation function of building walls can reduce energy consumption, and even give people more evacuation time in case of fire.

[0003] Polybenzoxazine (PBz) aerogel is a new type of organic aerogel developed in recent years. It has the characteristics of low forming temperature, atmospheric pressure drying, excellent mechanical properties, flame retardancy, good heat resistance, etc. Its comprehensive performance is remarkable, and it is very suitable for practical application as a heat insulation and protection material. In order to further develop and improve the performance of polybenzoxazine aerogel, a second component - silicon can be introduced to prepare an organic-inorganic hybrid aerogel. The organic-inorganic hybrid strategy can combine the advantages of the two raw materials and further improve the heat resistance of the aerogel. The excellent mechanical properties of polybenzoxazine aerogel itself can just make up for the disadvantages of pure inorganic aerogel, such as brittleness and easy breakage. Polybenzoxazine aerogel can be prepared by acid catalysis or base catalysis. Acid catalysis can be carried out at low temperature with high efficiency and excellent mechanical properties of the product. Base catalysis requires heating under high temperature conditions, has high requirements for forming equipment, and the product is porous. However, for siloxane, it is more suitable for dehydration condensation under alkaline conditions. Therefore, there is a contradiction in the gelation conditions for preparing silicon hybrid polybenzoxazine aerogel at low temperature.

[0004] At present, researchers have carried out some research on organic-inorganic hybrid polybenzoxazine aerogels. First is the co-gel method. The inorganic silicon sources selected include silica sol, vinyl silane after free radical polymerization, partially polymerized silicone resin, etc. Second is to directly introduce a silicon skeleton and carry out a sol-gel reaction on the surface to form an interpenetrating network, such as carrying out the sol-gel process of benzoxazine again inside the SiO2 aerogel. Due to the polarity difference between Bz and polysiloxane, it is still a difficult problem to form a uniform network between the two, the uniformity of the product is poor, and the performance is adversely affected. At the same time, it is also important to simplify the process conveniently and reduce the gelation temperature. Whether cheap and easily available siloxane monomers can be directly used as raw materials without pre-polymerization and preparation of precursors is also a problem to be solved. Summary of the Invention

[0005] The object of the present invention is to solve the problems that benzoxazine and silane are prone to phase separation during the gelation process and the gelation conditions are contradictory, and to provide a preparation method of a novel silicon hybrid polybenzoxazine aerogel that can gel at room temperature. This method improves the comprehensive performance of the product and provides a simple and convenient new strategy for preparing silicon hybrid polybenzoxazine aerogel at room temperature.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a silicon hybrid polybenzoxazine aerogel, the method comprising:

[0008] Step 1: Synthesis of benzoxazine monomer: According to the stoichiometric ratio of phenolic hydroxyl group: formaldehyde: amino group of 1:2-2.1:1, a phenolic source, paraformaldehyde and an amine source are added to a solvent, and the reaction is carried out at 100 °C for 24 h. Then, the solvent is removed by vacuum distillation, redissolved with chloroform, washed with an aqueous NaOH solution, and then washed with distilled water until the aqueous phase is neutral. It is dried overnight with anhydrous sodium sulfate, and then the solvent is removed by a rotary evaporator to obtain the benzoxazine monomer; there is no clear concentration requirement for the initial dissolution and subsequent redissolution and alkali washing, and the concentration by mass fraction can be between about 20 wt.% and 40 wt.%.

[0009] Step 2: Preparation of benzoxazine aerogel: The benzoxazine monomer and tannic acid are dissolved in the solvent N,N-dimethylformamide (DMF) to obtain a composite solution; a hydrochloric acid catalyst is added to the composite solution, mixed evenly, and then a siloxane, deionized water and an amino silane are added, and mixed evenly again and then quickly poured into a pre-prepared molding mold, and gelation occurs slowly and evenly at room temperature; the wet gel is dried under normal pressure to obtain a silicon hybrid polybenzoxazine aerogel.

[0010] Further, in step 1, the phenolic source is one or more of bisphenol A, dihydroxybiphenyl, dihydroxydiphenylmethane or dihydroxydiphenylsulfone; the amine source is one or more of aniline, p-phenylenediamine, diaminodiphenyl ether or diaminodiphenylmethane; the solvent is one or more of dioxane, toluene or ethanol. The molecular structure of the obtained benzoxazine monomer is any one of the following structures:

[0011]

[0012] Further, in step 2, in the composite solution, the mass ratio of tannic acid to benzoxazine monomer is 1-8:100; too much tannic acid does not need to be added to play a role in uniform gelation; the mass ratio of benzoxazine monomer to solvent is 1:2-9. Too high a concentration will lead to a decrease in the porosity of the product and an increase in density, while too low a concentration will lead to serious mechanical degradation and loose and cracked structure.

[0013] Further, in Step 2, the siloxane is one or more of the following structures and serves as the main silicon source in the sol system.

[0014]

[0015] Further, in Step 2, the aminosilane is one or more of the following structures:

[0016]

[0017] Further, in Step 2, the mass ratio of the composite solution, hydrochloric acid catalyst, siloxane, deionized water, and aminosilane is 19.4 - 16.2:1:2 - 8:0.5 - 2:0.25.

[0018] Further, in Step 2, the gelation temperature is 25°C - 80°C, which can be room temperature (25°C), or the temperature can be appropriately increased, such as 50 - 80°C, to accelerate the reaction.

[0019] Further, in Step 2, the atmospheric drying is to perform solvent exchange of the wet gel in isopropanol, then leave it to dry at room temperature, and then put it into a 50°C forced-air oven until the mass remains unchanged.

[0020] A silicon hybrid polybenzoxazine aerogel prepared by the above preparation method.

[0021] The beneficial effects of the present invention compared with the prior art are as follows:

[0022] (1) In the preparation method of the silicon hybrid polybenzoxazine aerogel of the present invention, gelation can occur at room temperature. Utilizing the high polymerization activity of benzoxazine monomers under acid catalysis, and at the same time adopting a two-step catalytic reaction method, using basic silane to promote the dehydration condensation of silicon precursors, the incompatibility of benzoxazine and siloxane in gel conditions is ingeniously solved, and the problem that it is difficult to match and coordinate the gelation processes of siloxane and benzoxazine monomers in the prior art is solved.

[0023] (2) The present invention uses plant-derived tannic acid as a compatibilizer for benzoxazine and siloxane, effectively solving the problem of easy phase separation in the gel system of the two, and there is no need to pre-polymerize siloxane anymore.

[0024] (3) The benzoxazine monomers used in the present invention have rich structures, and at the same time, this method is also applicable to various structural silicon oxide precursors, and has good adaptability to both the organic phase and the inorganic phase, which is beneficial to the subsequent adjustment and improvement of product performance and the construction of structure-activity relationships.

[0025] (4) The introduction of Si in the present invention can improve the ablation resistance of the polybenzoxazine aerogel, while taking into account the excellent mechanical properties of the polybenzoxazine aerogel, broadening its application fields, and improving its service safety as a thermal protection matrix. Description of the Drawings

[0026] Figure 1 It is the microstructural diagram of the silicon hybrid polybenzoxazine aerogel at the scale of 1 micron;

[0027] Figure 2 It is the microstructural diagram of the silicon hybrid polybenzoxazine aerogel at the scale of 500 nm;

[0028] Figure 3 It is the XPS spectrum of the silicon hybrid polybenzoxazine aerogel;

[0029] Figure 4 It is the pore size distribution diagram of the silicon hybrid polybenzoxazine aerogel;

[0030] Figure 5 It is the thermogravimetric curve (10 °C / min) diagram of the silicon hybrid polybenzoxazine aerogel. Detailed Embodiments

[0031] The technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments, but are not limited thereto. Any modifications or equivalent replacements of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered within the protection scope of the present invention.

[0032] Example 1

[0033] Using dioxane as a solvent, 22.8 g of bisphenol A, 12 g of paraformaldehyde, and 18.6 g of aniline were added to a three-necked flask, 200 mL of dioxane was added, and the reaction was carried out at 100 °C for 24 h. Then, the solvent was removed by vacuum distillation, redissolved with chloroform, washed with 0.2 M aqueous NaOH solution, and then washed with distilled water until the aqueous phase was neutral, dried overnight with anhydrous sodium sulfate, and then the solvent was removed with a rotary evaporator to obtain the benzoxazine resin monomer.

[0034] 6 g of the benzoxazine monomer and 0.12 g of tannic acid were dissolved in 24 g of N,N-dimethylformamide (DMF) to obtain a composite solution. Then, 1 g of hydrochloric acid was added to the composite solution, mixed evenly, and then 6 g of methyltriethoxysilane, 1 mL of deionized water, and 0.6 g of 3-(2-aminoethylamino)propyltrimethoxysilane were added, mixed evenly again, and then quickly poured into a pre-prepared molding mold, and gelation occurred slowly and evenly at room temperature. The wet gel was dried under normal pressure to obtain the silicon hybrid polybenzoxazine aerogel.

[0035] Example 2

[0036] Using toluene as the solvent, 19.8 g of 4,4'-diaminodiphenylmethane, 12 g of paraformaldehyde, and 18.8 g of phenol were added to a three-necked flask. 180 mL of toluene was added, and the reaction was carried out at 100 °C for 24 h. Then, the solvent was removed by vacuum distillation, redissolved with chloroform, washed with 1 M aqueous NaOH solution, and then washed with distilled water until the aqueous phase was neutral. It was dried overnight with anhydrous sodium sulfate, and then the solvent was removed using a rotary evaporator to obtain the benzoxazine resin monomer.

[0037] 4.8 g of benzoxazine monomer and 0.24 g of tannic acid were dissolved in 15 g of N,N-dimethylformamide (DMF) to obtain a composite solution. Then, 1 g of hydrochloric acid was added to the composite solution and mixed evenly. Then, 6 g of methyltrimethoxysilane, 1.2 g of phenyltrimethoxysilane, 1 mL of deionized water, and 0.8 g of aminopropyltriethoxysilane were added, and mixed evenly again. Then, it was quickly poured into a pre-prepared molding mold, and gelation occurred slowly and evenly at room temperature. The wet gel was dried under normal pressure to obtain a silicon hybrid polybenzoxazine aerogel. The Si 2p signal could be detected by XPS, indicating the successful binding of Si element ( Figure 3 ). The microstructure of the aerogel is shown in Figure 1 and 2 . It is formed by particle packing and has a large number of pores. From the pore size distribution, it can be seen that the pore volume is mainly concentrated at 30 - 40 nm ( Figure 4 ). The introduction of Si element effectively improved the heat resistance, and the residual mass reached 60% at 1000 °C in a nitrogen atmosphere ( Figure 5 ), while the residual mass of pure polybenzoxazine aerogel is usually less than 40%.

[0038] When the addition amount of tannic acid TA reaches 5 wt.% of the total solute, it can play a role in increasing the solubility, and at the same time, the product is uniform and has higher strength. The compressive strength can be increased by 308% compared with the sample without TA addition.

[0039] Example 3

[0040] Using toluene / ethanol as the solvent, 20 g of 4,4-dihydroxydiphenylmethane, 12 g of paraformaldehyde, and 18.6 g of aniline were added to a three-necked flask. 140 mL of toluene and 70 mL of ethanol were added, and the reaction was carried out at 100 °C for 24 h. Then, the solvent was removed by vacuum distillation, redissolved with chloroform, washed with 0.5 M aqueous NaOH solution, and then washed with distilled water until the aqueous phase was neutral. It was dried overnight with anhydrous sodium sulfate, and then the solvent was removed using a rotary evaporator to obtain the benzoxazine resin monomer.

[0041] 6 g of benzoxazine monomer and 0.36 g of tannic acid were dissolved in 12 g of N,N-dimethylformamide (DMF) to obtain a composite solution. Then, 1 g of hydrochloric acid was added to the composite solution and mixed evenly. Subsequently, 3 g of tetraethyl orthosilicate, 3 g of dimethyldiethoxysilane, 1 mL of deionized water, and 0.5 g of 3-aminopropylmethyldimethoxysilane were added, and the mixture was homogenized again and then quickly poured into a pre-prepared molding mold, where gelation occurred slowly and evenly at room temperature. The wet gel was dried under atmospheric pressure to obtain a silica-hybridized polybenzoxazine aerogel.

[0042] The thermal insulation performance, mechanical properties, and heat resistance of the aerogel were tested, and the results are summarized in Table 1. The thermal conductivity was measured using a thermal conductivity tester. Two flat aerogel samples were clamped on both sides of the sensor, and the thermal conductivity was measured after thermal equilibrium was reached. The mechanical properties were characterized by a constant-rate compression test with a compression plate advancement rate of 5 mm / min. The heat resistance was characterized by thermogravimetric analysis and was tested separately under nitrogen and air atmospheres with a heating rate of 10 °C / min.

[0043] Table 1

[0044]

[0045]

Claims

1. A preparation method of a silicon hybrid polybenzoxazine aerogel, characterized in that: The method is as follows: Step 1: Synthesis of benzoxazine monomer: According to the stoichiometric ratio of phenolic hydroxyl group: formaldehyde: amino group being 1: 2-2.1: 1, add a phenolic source, paraformaldehyde and an amine source to a solvent, react at 100 °C for 24 h, then remove the solvent by vacuum distillation, redissolve with chloroform, wash with an aqueous NaOH solution, and then wash with distilled water until the aqueous phase is neutral. Dry overnight with anhydrous sodium sulfate, and then remove the solvent with a rotary evaporator to obtain the benzoxazine monomer. Step 2: Preparation of benzoxazine aerogel: Dissolve the benzoxazine monomer and tannic acid in the solvent N, N-dimethylformamide (DMF) to obtain a composite solution; add a hydrochloric acid catalyst to the composite solution, mix evenly, then add siloxane, deionized water and aminosilane, mix evenly again and then quickly pour it into a pre-prepared molding mold, and slowly and evenly undergo gelation; subject the wet gel to atmospheric drying to obtain a silicon hybrid polybenzoxazine aerogel.

2. The preparation method of a novel silicon hybrid polybenzoxazine aerogel of room temperature gel according to claim 1, characterized in that: In Step 1, the phenolic source is one or more of bisphenol A, dihydroxybiphenyl, dihydroxydiphenylmethane or dihydroxydiphenylsulfone; the amine source is one or more of aniline, p-phenylenediamine, diaminodiphenyl ether or diaminodiphenylmethane; the solvent is one or more of dioxane, toluene or ethanol.

3. The preparation method of a novel silicon hybrid polybenzoxazine aerogel of room temperature gel according to claim 1, characterized in that: In Step 2, in the composite solution, the mass ratio of tannic acid to benzoxazine monomer is 1-8: 100; the mass ratio of benzoxazine monomer to the solvent is 1: 2-9.

4. The preparation method of a novel silicon hybrid polybenzoxazine aerogel of room temperature gel according to claim 1, characterized in that: In Step 2, the siloxane is one or more of the structures shown below 5. A method for preparing a novel silicon hybrid polybenzoxazine aerogel of room temperature gel, characterized in that: In Step 2, the aminosilane is one or more of the structures shown below:

6. The preparation method of a novel silicon hybrid polybenzoxazine aerogel of room temperature gel according to claim 1, characterized in that: In Step 2, the mass ratio of the composite solution, hydrochloric acid catalyst, siloxane, deionized water and aminosilane is 19.4-16.2: 1: 2-8: 0.5-2: 0.

25.

7. The preparation method of a novel silicon hybrid polybenzoxazine aerogel of room temperature gel according to claim 1, characterized in that: In Step 2, the temperature of the gelation is 25 °C - 80 °C.

8. A preparation method of a novel silicon hybrid polybenzoxazine aerogel of room temperature gel, characterized in that: In Step 2, the atmospheric drying is to perform solvent exchange of the wet gel in isopropanol, then leave it to dry at room temperature, and then put it into a 50 °C forced-air oven until the mass remains unchanged.

9. A silicon hybrid polybenzoxazine aerogel prepared by the preparation method according to any one of claims 1-8.

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