A high-temperature resistant polybenzoxazole aerogel and its preparation method and uses

Abstract

The present invention discloses a high-temperature resistant polybenzoxazole aerogel, a preparation method and a use thereof. The preparation method prepares the high-temperature resistant polybenzoxazole aerogel through the conversion of a polyamide aerogel. The polymerization monomers forming the polyamide in the polyamide aerogel include 3,3-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride. The present invention avoids the problem of difficult dissolution during the preparation of a rigid polybenzoxazole aerogel through a conversion strategy. The preparation process is simple and convenient, and the obtained product has the characteristics of high thermal stability and can be widely applied in the fields of high-temperature resistance, heat preservation and heat insulation, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of aerogels, and in particular relates to a high temperature resistant polybenzoxazole aerogel and a preparation method thereof. Background Art

[0002] With the development and upgrading of materials science and technology, higher requirements and standards have been put forward for thermal insulation and high temperature resistant materials. Traditional insulation materials mainly include inorganic materials and organic materials, and are widely used in aerospace, marine ships, chemical pipelines and building insulation. However, inorganic materials such as mineral wool, asbestos, rock wool and glass wool have serious water absorption, high density and poor corrosion resistance, and are prone to slag and dust during construction. Organic insulation materials, such as rubber, polyurethane, polyimide and styrene foam, have poor insulation effect and low high temperature resistance and mechanical strength. It is difficult to meet long-term use requirements and difficult to repair and maintain. Therefore, it is of great significance to develop and find new high-efficiency insulation and high temperature resistant materials.

[0003] Aerogel is a network of interpenetrating porous materials composed of colloidal particles or polymer chains. Its unique nanoporous system and continuous three-dimensional network space give aerogel excellent properties such as ultra-low density, ultra-low thermal conductivity, high porosity and high specific surface area, so it is called a super thermal insulation material. However, while aerogel is developing rapidly, it is also accompanied by many problems that need to be solved. For example, although silica aerogel has excellent thermal insulation performance and a thermal conductivity as low as 0.017W / mK, its structure is brittle and its mechanical strength is low, which greatly limits its practical application. Polymers such as polyimide, polyamide and polyacrylonitrile have significant advantages in mechanical strength and other aspects due to their flexible molecular design, and have good solubility. For example, polyamide is soluble in many common polar solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO), so aerogel can be directly prepared by the sol-gel method. However, these polymers themselves have poor heat resistance, and the temperature range for long-term use is mostly concentrated between 100 and 200°C.

[0004] Polybenzoxazole (PBO) is a rigid rod-like liquid crystal polymer with coplanar oxazole rings and benzene rings, having good mechanical properties, thermal stability, chemical stability, fire resistance, low dielectric constant, and electron transport characteristics, etc. However, it has the disadvantage of poor solubility, being almost insoluble in organic solvents and only soluble in strong proton acids such as methanesulfonic acid and polyphosphoric acid. Therefore, it is difficult to directly prepare it into an aerogel material by the sol-gel method. Currently, there are few articles reported on polybenzoxazole aerogels. CN 106221216 A discloses a method for preparing polybenzoxazole nanoaerogels by dissolving PBO in a strong proton acid solution formed by methanesulfonic acid and trifluoroacetic acid. This method not only has a complex preparation process, but also the strong proton acid is corrosive to the mold, which will cause mold loss. In addition, the potential harm of strong proton acids to the human body is also great.

[0005] Therefore, there is an urgent need for a method that is simple to operate, convenient for production, and can prepare a highly rigid polymer with poor solubility into an ultra-light, heat-insulating, high-temperature-resistant, and good mechanical property organic aerogel material. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a high-temperature-resistant polybenzoxazole aerogel and its preparation method and use.

[0007] To achieve the above purpose and other related purposes, the present invention is obtained through the following technical solutions.

[0008] In the first aspect of the present invention, a preparation method of a high-temperature-resistant polybenzoxazole aerogel is provided. The preparation method first determines a polyamide that can be converted into the desired polybenzoxazole through structural design, then prepares the polyamide into a polyamide aerogel, and further converts it into a high-temperature-resistant polybenzoxazole aerogel. This strategy of converting a polyamide aerogel into a polybenzoxazole aerogel avoids the problems of poor solubility of highly rigid polybenzoxazole and difficulty in directly preparing aerogels in the prior art. At the same time, the polybenzoxazole aerogel prepared in this application has the characteristics of ultra-light, heat-insulating, high-temperature-resistant, and excellent mechanical properties.

[0009] According to the above-mentioned preparation method, the polymerization monomers forming the polyamide in the polyamide aerogel include 3,3-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride.

[0010] According to the above-mentioned preparation method, after 3,3-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride react to form a polyamide, the sol-gel method is used to form a polyamide aerogel, and then the polyamide aerogel is heat-treated to form the high-temperature-resistant polybenzoxazole aerogel.

[0011] According to the above-described preparation method, in the reaction for forming the polyamide, it is necessary to carry out the reaction under a protective atmosphere. The protective atmosphere is one of nitrogen and argon. Preferably, it is nitrogen.

[0012] According to the above-described preparation method, in the reaction for forming the polyamide, it is necessary to carry out the reaction in an organic solvent. The organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Preferably, the organic solvent is N,N-dimethylacetamide.

[0013] According to the above-described preparation method, in the reaction for forming the polyamide, the molar ratio of 3,3-dihydroxybenzidine to terephthaloyl chloride / isophthaloyl chloride is 0.01:(0.005 - 0.02). Preferably, the molar ratio can be 0.01:(0.005 - 0.008), can be 0.01:(0.008 - 0.013), or can also be 0.01:(0.013 - 0.02). In certain specific embodiments, it is 0.01:0.015. The selection of 3,3-dihydroxybenzidine introduces a biphenyl structure, which is beneficial to improving the thermal stability of polybenzoxazole.

[0014] According to the above-described preparation method, in the reaction for forming the polyamide, one or two of a cosolvent and an acid-binding agent are used. During the reaction between 3,3-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride, hydrochloric acid is generated, which is not conducive to the progress of the reaction. The addition of an acid-binding agent can neutralize hydrochloric acid, improve the reaction conversion rate, and ensure the formation of a polyamide with a stable structure.

[0015] Preferably, the cosolvent is selected from lithium chloride, and the acid-binding agent is selected from propylene oxide.

[0016] Preferably, the molar ratio of the acid-binding agent, 3,3-dihydroxybenzidine, and terephthaloyl chloride / isophthaloyl chloride is (0.21 - 0.32):0.01:(0.005 - 0.02), and more preferably, the molar ratio is (0.21 - 0.32):0.01:0.015.

[0017] Preferably, the molar ratio of lithium chloride, propylene oxide, and N,N-dimethylacetamide is (0.29 - 0.44):(0.21 - 0.32):(5.38 - 7.52).

[0018] According to the above-described preparation method, in the reaction for forming the polyamide, the reaction includes a first reaction stage and a second reaction stage.

[0019] Preferably, the temperature of the first reaction stage is -10 to -5 °C. Conducting the first reaction stage at a low temperature is beneficial to improving the conversion rate because the activity of terephthaloyl chloride / isophthaloyl chloride is strong. Conducting the reaction under high temperature conditions not only makes the reaction violent but also results in a low conversion rate. More preferably, the reaction temperature can be -10 to -8 °C, can be -8 to -6 °C, or can be -6 to -5 °C. In some specific embodiments, it is -6 °C, -8 °C, and -10 °C.

[0020] Preferably, the time of the first reaction stage is 1 to 3 h. More preferably, the reaction time can be 1 to 2 h, or can be 2 to 3 h. In some specific embodiments, it is 1 h, 2 h, and 3 h.

[0021] Preferably, the temperature of the second reaction stage is 15 to 25 °C. More preferably, the reaction temperature can be 15 to 18 °C, can be 18 to 23 °C, or can be 23 to 25 °C. In some specific embodiments, it is 20 °C and 25 °C.

[0022] Preferably, the time of the second reaction stage is 12 to 24 h. More preferably, the reaction time can be 12 to 18 h, can be 18 to 20 h, or can be 20 to 24 h. In some specific embodiments, it is 12 h, 18 h, and 24 h.

[0023] According to the preparation method described above, the heat treatment temperature ≥ 200 °C. Preferably, the heat treatment temperature is 200 to 450 °C. More preferably, the heat treatment temperature can be 200 to 270 °C, can be 270 to 360 °C, or can be 360 to 450 °C. In some specific embodiments, it is 450 °C.

[0024] According to the preparation method described above, the heat treatment time ≥ 300 min. Preferably, the heat treatment time is 300 to 360 min. More preferably, the heat treatment time can be 300 to 320 min, can be 320 to 340 min, or can be 340 to 360 min. In some specific embodiments, it is 300 min, 330 min, and 360 min.

[0025] According to the preparation method described above, the heating rate of the heat treatment is 2 to 5 °C / min. Preferably, the heating rate can be 2 to 3 °C / min, can be 3 to 4 °C / min, or can be 4 to 5 °C / min. In some specific embodiments, it is 2 °C / min, 4 °C / min, and 5 °C / min.

[0026] According to the preparation method described above, preferably, the heat treatment is carried out in stages, and the procedure of the staged heat treatment is as follows: treating at 200-220°C for 20-40 minutes, at 230-270°C for 20-40 minutes, at 280-320°C for 20-40 minutes, at 300-340°C for 50-70 minutes, at 330-370°C for 20-40 minutes, at 360-400°C for 30-60 minutes, at 380-420°C for 30-60 minutes, and at 430-450°C for 50-70 minutes.

[0027] According to the preparation method described above, the specific steps for forming the polyamide aerogel by the sol-gel method are as follows: polyamide is aged in an organic solvent to obtain a gel, and then solvent exchange is carried out, and after drying, a polyamide aerogel is formed.

[0028] According to the preparation method described above, in the specific steps of forming the polyamide aerogel, the organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Preferably, it is N,N-dimethylacetamide.

[0029] According to the preparation method described above, in the specific steps of forming the polyamide aerogel, based on the total mass of polyamide and the organic solvent, the mass fraction of the polyamide is 1-20 wt%. Preferably, the mass fraction can be 1-8 wt%, can be 8-15 wt%, or can be 15-20 wt%. In some specific embodiments, it is 3 wt%, 5 wt%, and 7 wt%.

[0030] According to the preparation method described above, in the specific steps of forming the polyamide aerogel, the aging time is 24-48 hours. Preferably, the aging time can be 24-30 hours, can be 30-40 hours, or can be 40-48 hours. In some specific embodiments, it is 24 hours, 36 hours, and 48 hours.

[0031] According to the preparation method described above, in the specific steps of forming the polyamide aerogel, the exchange solvent is tert-butanol.

[0032] According to the preparation method described above, in the specific steps of forming the polyamide aerogel, the drying method is freeze-drying.

[0033] According to the preparation method described above, the structural formulas and synthesis routes of 3,3'-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride monomers, polyamide, and polybenzoxazole aerogel are as follows:

[0034]

[0035] In addition, in this application, a high-temperature resistant polybenzoxazole aerogel is obtained through the transformation of polyamide aerogel. This method of preparing aerogel by transforming polymer aerogel well avoids the dissolution and processing problems of rigid polymers during the preparation of aerogel. At the same time, the polyamide in this application can be placed in molds of any shape or complex structure, so as to form high-temperature resistant polybenzoxazole aerogel products with corresponding shapes or structures.

[0036] The second aspect of the present invention provides a high-temperature resistant polybenzoxazole aerogel obtained by the preparation method as described above.

[0037] According to the high-temperature resistant polybenzoxazole aerogel as described above, the pore size distribution of the high-temperature resistant polybenzoxazole aerogel is in the range of 20-100 nm, the specific surface area is 60-140 m 2 / g, and the porosity is 78-89%.

[0038] According to the high-temperature resistant polybenzoxazole aerogel as described above, the thermal conductivity of the high-temperature resistant polybenzoxazole aerogel is 0.032-0.055 W / mK, the dielectric constant is 1.50-1.72, and the thermal stability is greater than 550 °C. Preferably, the thermal conductivity is 0.041-0.055 W / mK, the dielectric constant is 1.56-1.72, and the thermal stability is greater than 600 °C.

[0039] The third aspect of the present invention provides the use of the high-temperature resistant polybenzoxazole aerogel as described above as a high-temperature resistant thermal insulation material in aerospace, ships or buildings.

[0040] Compared with polyamide aerogel, the high-temperature resistant polybenzoxazole aerogel obtained by transforming polyamide aerogel in this application has better thermal stability and higher mechanical strength. In addition, the high-temperature resistant polybenzoxazole aerogel of this application has the advantages of high porosity, high specific surface area and low thermal conductivity.

[0041] As described above, the present invention provides a high-temperature resistant polybenzoxazole aerogel and its preparation method and use, which have the following beneficial effects:

[0042] 1) The high-temperature resistant polybenzoxazole aerogel prepared by the present invention is obtained by transforming polyamide aerogel. This transformation strategy well avoids the dissolution and processing problems of rigid polybenzoxazole during the direct preparation of aerogel. At the same time, corresponding high-temperature resistant polybenzoxazole aerogel products with any shape or complex structure can be formed by changing the shape and structure of polyamide.

[0043] 2) Compared with polyamide aerogels, the high-temperature resistant polybenzoxazole aerogels of the present application have better thermal stability, and the Td5 can reach 603 °C. In addition, the thermal conductivity of the aerogel is as low as 0.032 - 0.055 W / mK, the dielectric constant is 1.50 - 1.72, the porosity is 78 - 89%, and the specific surface area is 60 - 140 m 2 / g. They are safe and non-toxic. While meeting the requirements of heat insulation and high temperature resistance, they also have the characteristics of low sound velocity and light weight, which extends the service life and cycle of the material as a whole and reduces the maintenance cost. Description of the Drawings

[0044] Figure 1 It shows the thermogravimetric curve (TGA curve) of the high-temperature resistant polybenzoxazole aerogel obtained in Example 1 of the present invention.

[0045] Figure 2 It shows the thermal conductivity diagrams of the high-temperature resistant polybenzoxazole aerogels obtained in Example 1, Example 2, and Example 3 of the present invention respectively.

[0046] Figure 3 It shows the scanning electron microscope image of the high-temperature resistant polybenzoxazole aerogel obtained in Example 1 of the present invention.

[0047] Figure 4 It shows the infrared spectra of the conversion of polyamide aerogel to high-temperature resistant polybenzoxazole aerogel at different temperatures in Example 1 of the present invention. Detailed Description of the Invention

[0048] The following specific examples illustrate the embodiments of the present invention to verify the practical feasibility of the method of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0049] It should be noted that the process equipment or devices not specifically specified in the following examples are all conventional equipment or devices in the art. In addition, it should be understood that the protection scope of the present invention is not limited to the specific embodiments described below. One or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between these clearly mentioned steps, unless otherwise stated. It should also be understood that the terms used in the embodiments of the present invention are for the purpose of describing specific embodiments and not for limiting the protection scope of the present invention. The test methods without specific conditions mentioned in the following examples are usually carried out under conventional conditions or according to the conditions recommended by each manufacturer.

[0050] In the following specific embodiments of the present application, a specific preparation method is adopted, including the following steps:

[0051] 1) Under a protective atmosphere, 3,3-dihydroxybenzidine and terephthaloyl chloride react in an organic solvent to obtain a reaction product;

[0052] 2) The reaction product is mixed with water, separated by solid-liquid separation, and dried to obtain a polyamide;

[0053] 3) The polyamide is mixed with an organic solvent and aged to obtain a gel;

[0054] 4) The gel is subjected to solvent exchange and dried to obtain a polyamide aerogel;

[0055] 5) The polyamide aerogel is subjected to heat treatment to obtain the high-temperature resistant polybenzoxazole aerogel.

[0056] According to the above-mentioned preparation method, in step 2), the drying temperature is 60-100 °C. Preferably, the drying temperature can be 60-70 °C, can be 70-85 °C, or can be 85-100 °C. In some specific embodiments, it is 60 °C and 80 °C.

[0057] According to the above-mentioned preparation method, in step 2), the drying time is 8-12 h. Preferably, the drying time can be 8-9 h, can be 9-11 h, or can be 11-12 h. In some specific embodiments, it is 8 h, 10 h, and 12 h.

[0058] According to the above-mentioned preparation method, in step 4), the exchange solvent is tert-butanol. The number of exchanges is 6-12 times, and each time of exchange, the retention time of the solvent is 8-12 h.

[0059] Preferably, the number of exchanges can be 6-7 times, can be 7-10 times, or can be 10-12 times. In some specific embodiments, it is 6 times and 8 times.

[0060] Preferably, each time of exchange, the retention time can be 8-9 h, can be 9-11 h, or can be 11-12 h. In some specific embodiments, it is 8 h, 10 h, and 12 h.

[0061] According to the above-mentioned preparation method, in step 4), the drying method is freeze-drying.

[0062] The freeze-drying temperature is -50 to -40 °C. Preferably, the freeze-drying temperature can be -50 to -47 °C, can be -47 to -43 °C, or can be -43 to -40 °C. In some specific embodiments, it is -45 °C and -50 °C.

[0063] The freeze-drying pressure is 5 to 20 Pa. Preferably, the freeze-drying pressure can be 5 to 10 Pa, can be 10 to 15 Pa, or can be 15 to 20 Pa. In certain specific embodiments, it is 8 Pa, 15 Pa, and 10 Pa.

[0064] The freeze-drying time is 48 to 72 h. Preferably, the freeze-drying time can be 48 to 54 h, can be 54 to 64 h, or can be 64 to 72 h. In certain specific embodiments, it is 72 h.

[0065] In the following embodiments of the present application, the acid-binding agent is propylene oxide and the co-solvent is lithium chloride.

[0066] Example 1

[0067] In this embodiment, a high-temperature resistant polybenzoxazole aerogel and a preparation method thereof are provided, including the following steps:

[0068] 1) Take 3,3-dihydroxybenzidine and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide, and N,N-dimethylacetamide, and carry out the first reaction at -6°C for 1 h under nitrogen conditions, and then carry out the second reaction at 20°C for 12 h to obtain a reaction product. Among them, the molar ratio of 3,3-dihydroxybenzidine, terephthaloyl chloride, lithium chloride, propylene oxide, and N,N-dimethylacetamide is 0.01:0.015:0.29:0.21:5.38; the mass of 3,3-dihydroxybenzidine is 2.16 g.

[0069] 2) Pour the reaction product obtained in 1) into deionized water to obtain a solid precipitate, filter it, and then carry out vacuum drying at 60°C for 8 h to obtain polyamide.

[0070] 3) Dissolve the polyamide obtained in 2) in N,N-dimethylacetamide to prepare a solution with a polyamide concentration of 3 wt%, pour it into a mold, let it stand for 12 h, and continue to age for 24 h to obtain a gel.

[0071] 4) Carry out 6 times of solvent exchange on the gel obtained in 3) with tert-butanol, each time maintaining for 8 h, and then carry out freeze-drying at a pressure of 15 Pa and a temperature of -45°C for 72 h to obtain a polyamide aerogel (labeled as polyamide precursor aerogel).

[0072] 5) Place the polyamide aerogel obtained in 4) in a tubular furnace under a nitrogen atmosphere, set the heating rate to 2 °C / min, and perform the following segmented heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 30 min, 380 °C for 30 min, 400 °C for 30 min, and 450 °C for 60 min to obtain a high-temperature resistant polybenzoxazole aerogel (labeled as DHB-type polybenzoxazole aerogel). The mass percentage of the high-temperature resistant polybenzoxazole aerogel is 3 wt%.

[0073] Samples were taken respectively after the treatment at 320 °C, 380 °C, and 450 °C and subjected to infrared detection. The results are shown in Figure 4 .

[0074] From Figure 4 it can be seen that the peak at 3409 cm -1 is attributed to the N-H stretching vibration. The characteristic peaks at 3400 - 3000 cm -1 indicate the presence of O-H. The peak at 1650 cm -1 is attributed to the C=O stretching vibration. The peak at 1501 cm -1 is attributed to the N-H bending vibration. The above structures correspond to polyamide. After heat treatment, the characteristic peaks of hydroxyl groups gradually disappear, and at the same time, new characteristic peaks appear. The peaks at 1623 and 1455 cm -1 are respectively attributed to the C=N stretching and bending vibrations. The peaks at 1260 and 1049 cm -1 are respectively attributed to the C-O stretching and bending vibrations, indicating the formation of an oxazole ring structure. Starting from the heat treatment at 320 °C, the molecular structure gradually begins to change. When the temperature reaches 450 °C, the polyamide is completely transformed into a polybenzoxazole structure.

[0075] Example 2

[0076] In this example, a high-temperature resistant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0077] 1) Take 3,3-dihydroxybenzidine and terephthaloyl chloride and add them to a three-necked flask. Then add lithium chloride, propylene oxide, and N,N-dimethylacetamide. React for the first time at -8 °C for 2 h under nitrogen conditions, and then react for the second time at 25 °C for 18 h to obtain a reaction product. Among them, the molar ratio of 3,3-dihydroxybenzidine, terephthaloyl chloride, lithium chloride, propylene oxide, and N,N-dimethylacetamide is 0.01:0.015:0.37:0.27:6.45; the mass of 3,3-dihydroxybenzidine is 2.16 g.

[0078] 2) Pour the reaction product obtained in 1) into deionized water to obtain a solid precipitate. After filtration, vacuum dry at 80 °C for 10 h to obtain polyamide.

[0079] 3) Dissolve the polyamide obtained in 2) in N,N-dimethylacetamide to prepare a solution with a polyamide concentration of 5 wt%. Pour it into a mold, let it stand for 18 h, and continue to age for 36 h to obtain a gel.

[0080] 4) Perform 8 solvent exchanges on the gel obtained in 3) with tert-butanol, each time for 10 h. Then, perform freeze-drying at a pressure of 10 Pa and a temperature of -45 °C for 72 h to obtain a polyamide aerogel.

[0081] 5) Place the polyamide aerogel obtained in 4) in a tube furnace under a nitrogen atmosphere. Set the heating rate to 4 °C / min and perform the following heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 30 min, 380 °C for 30 min, 400 °C for 60 min, and 450 °C for 60 min. Finally, obtain a high-temperature resistant polybenzoxazole aerogel, and the mass percentage of the high-temperature resistant polybenzoxazole aerogel is 5 wt%.

[0082] Example 3

[0083] In this example, a high-temperature resistant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0084] 1) Take 3,3-dihydroxybenzidine and terephthaloyl chloride and add them to a three-necked flask. Then add lithium chloride, propylene oxide, and N,N-dimethylacetamide. Perform the first reaction at -10 °C for 3 h under nitrogen conditions, and then perform the second reaction at 25 °C for 24 h to obtain a reaction product. Among them, the molar ratio of 3,3-dihydroxybenzidine, terephthaloyl chloride, lithium chloride, propylene oxide, and N,N-dimethylacetamide is 0.01:0.015:0.44:0.32:7.52; the mass of 3,3-dihydroxybenzidine is 2.16 g.

[0085] 2) Pour the reaction product obtained in 1) into deionized water to obtain a solid precipitate. After filtration, vacuum dry at 80 °C for 12 h to obtain polyamide.

[0086] 3) Dissolve the polyamide obtained in 2) in N,N-dimethylacetamide to prepare a solution with a polyamide concentration of 7 wt%. Pour it into a mold, let it stand for 24 h, and continue to age for 48 h to obtain a gel.

[0087] 4) The gel obtained in 3) was subjected to 8 solvent exchanges with tert-butanol, each time maintaining for 12 h, and then freeze-dried for 72 h under the conditions of a pressure of 8 Pa and a temperature of -50 °C to obtain a polyamide aerogel.

[0088] 5) The polyamide aerogel obtained in 4) was placed in a tube furnace under a nitrogen atmosphere, the heating rate was set at 5 °C / min, and the following heat treatment was carried out: treated at 200 °C for 30 min, 250 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 30 min, 380 °C for 60 min, 400 °C for 60 min, and 450 °C for 60 min. Finally, a high-temperature resistant polybenzoxazole aerogel was obtained, and the mass percentage of the high-temperature resistant polybenzoxazole aerogel was 7 wt%.

[0089] Example 4

[0090] The difference between this example and Example 1 is that in step 5), segmented heat treatment was not carried out, but only the polyamide aerogel was directly heat-treated at 450 °C for 300 min, and the rest was the same as in Example 1.

[0091] Example 5

[0092] In this example, a high-temperature resistant polybenzoxazole aerogel and a preparation method thereof are provided, including the following steps:

[0093] 1) 3,3-Dihydroxybenzidine and terephthaloyl chloride were taken and added to a three-necked flask, and then lithium chloride, propylene oxide, and N,N-dimethylacetamide were added. The first reaction was carried out at -6 °C for 1 h under nitrogen conditions, and the second reaction was carried out at 20 °C for 12 h to obtain a reaction product. Among them, the molar ratio of 3,3-dihydroxybenzidine, terephthaloyl chloride, lithium chloride, propylene oxide, and N,N-dimethylacetamide was 0.01:0.005:0.29:0.21:5.38; the mass of 3,3-dihydroxybenzidine was 2.16 g.

[0094] 2) The reaction product obtained in 1) was poured into deionized water to obtain a solid precipitate, which was filtered and then vacuum-dried at 60 °C for 8 h to obtain polyamide.

[0095] 3) The polyamide obtained in 2) was dissolved in N,N-dimethylacetamide to prepare a solution with a polyamide concentration of 3 wt%, poured into a mold, allowed to stand for 12 h, and further aged for 24 h to obtain a gel.

[0096] 4) The gel obtained in 3) was subjected to 6 solvent exchanges with tert-butanol, each time maintaining for 8 h, and then freeze-dried for 72 h under the conditions of a pressure of 15 Pa and a temperature of -45 °C to obtain a polyamide aerogel.

[0097] 5) Place the polyamide aerogel obtained in 4) in a tubular furnace under a nitrogen atmosphere, set the heating rate to 2 °C / min, and conduct the following heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 30 min, 380 °C for 30 min, 400 °C for 30 min, and 450 °C for 60 min to obtain a high-temperature resistant polybenzoxazole aerogel. The mass percentage of the high-temperature resistant polybenzoxazole aerogel is 3 wt%.

[0098] Example 6

[0099] In this example, a high-temperature resistant polybenzoxazole aerogel and a preparation method thereof are provided, including the following steps:

[0100] 1) Take 3,3-dihydroxybenzidine and terephthaloyl chloride and add them to a three-necked flask. Then add lithium chloride, propylene oxide, and N,N-dimethylacetamide. Conduct the first reaction at -8 °C for 2 h under nitrogen conditions, and then conduct the second reaction at 25 °C for 18 h to obtain a reaction product. Among them, the molar ratio of 3,3-dihydroxybenzidine, terephthaloyl chloride, lithium chloride, propylene oxide, and N,N-dimethylacetamide is 0.01:0.013:0.37:0.27:6.45; the mass of 3,3-dihydroxybenzidine is 2.16 g.

[0101] 2) Pour the reaction product obtained in 1) into deionized water to obtain a solid precipitate. After filtration, vacuum dry at 80 °C for 10 h to obtain polyamide.

[0102] 3) Dissolve the polyamide obtained in 2) in N,N-dimethylacetamide to prepare a solution with a polyamide concentration of 5 wt%. Pour it into a mold, let it stand for 18 h, and continue to age for 36 h to obtain a gel.

[0103] 4) Perform 8 solvent exchanges on the gel obtained in 3) with tert-butanol, each time maintaining for 10 h. Then conduct freeze-drying at a pressure of 10 Pa and a temperature of -45 °C for 72 h to obtain a polyamide aerogel.

[0104] 5) Place the polyamide aerogel obtained in 4) in a tubular furnace under a nitrogen atmosphere, set the heating rate to 4 °C / min, and conduct the following heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 30 min, 380 °C for 30 min, 400 °C for 60 min, and 450 °C for 60 min to finally obtain a high-temperature resistant polybenzoxazole aerogel. The mass percentage of the high-temperature resistant polybenzoxazole aerogel is 5 wt%.

[0105] Example 7

[0106] In this embodiment, a high-temperature resistant polybenzoxazole aerogel and a preparation method thereof are provided, including the following steps:

[0107] 1) Take 3,3-dihydroxybenzidine and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide, and N,N-dimethylacetamide. Carry out the first reaction at -10 °C for 3 h under a nitrogen atmosphere, and then carry out the second reaction at 25 °C for 24 h to obtain a reaction product. Among them, the molar ratio of 3,3-dihydroxybenzidine, terephthaloyl chloride, lithium chloride, propylene oxide, and N,N-dimethylacetamide is 0.01:0.02:0.44:0.32:7.52; the mass of 3,3-dihydroxybenzidine is 2.16 g.

[0108] 2) Pour the reaction product obtained in 1) into deionized water to obtain a solid precipitate. After filtration, vacuum dry at 80 °C for 12 h to obtain polyamide.

[0109] 3) Dissolve the polyamide obtained in 2) in N,N-dimethylacetamide to prepare a solution with a polyamide concentration of 7 wt%, pour it into a mold, let it stand for 24 h, and continue to age for 48 h to obtain a gel.

[0110] 4) Perform 8 solvent exchanges on the gel obtained in 3) with tert-butanol, each time maintaining for 12 h, and then carry out freeze-drying at a pressure of 8 Pa and a temperature of -50 °C for 72 h to obtain a polyamide aerogel.

[0111] 5) Place the polyamide aerogel obtained in 4) in a tube furnace under a nitrogen atmosphere, set the heating rate to 5 °C / min, and perform the following heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 30 min, 380 °C for 60 min, 400 °C for 60 min, and 450 °C for 60 min. Finally, obtain a high-temperature resistant polybenzoxazole aerogel, and the mass percentage of the high-temperature resistant polybenzoxazole aerogel is 7 wt%.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 1 is that in step 5), segmented heat treatment is not carried out, but only the polyamide aerogel is directly heat-treated at 170 °C for 300 min, and the rest is the same as in Example 1. Finally, due to the extremely slow or non-closed-loop reaction, a high-temperature resistant polybenzoxazole aerogel cannot be obtained.

[0114] Perform thermogravimetric detection on the polyamide aerogel (marked as polyamide precursor aerogel) obtained in step 4) of Example 1 and the high-temperature resistant polybenzoxazole aerogel (marked as DHB-type polybenzoxazole aerogel) obtained in step 5). The specific operation steps are as follows:

[0115] 1) Select the sample to be tested, weigh 3 - 5 mg, and record the accurate mass value.

[0116] 2) Turn on the thermogravimetric analyzer, place the sample in the sample chamber of the thermogravimetric analyzer, and seal the chamber door to avoid interference from external air.

[0117] 3) Conduct the test under a nitrogen atmosphere. Set the heating rate to: 10 °C / min, and the temperature range to: 25 - 800 °C.

[0118] 4) Start the thermogravimetric analyzer, initiate the heating program, and record the curve of mass change with temperature.

[0119] 5) Based on the mass change curve, information such as the thermogravimetric curve of the sample can be obtained, and data processing and analysis are carried out.

[0120] The analysis results of the thermogravimetric detection data are shown in Table 1.

[0121] Table 1

[0122]

[0123] As can be seen from Table 1, the thermal stability of the high-temperature resistant polybenzoxazole aerogel of this application is much higher than that of the polyamide aerogel. The temperature at which the material weight loss reaches 5% is 602 °C, which is about 3 times that of the polyamide aerogel; the temperature at which the material weight loss reaches 10% is 634 °C, which is more than twice that of the polyamide aerogel. In addition, the char residue rate of the high-temperature resistant polybenzoxazole aerogel of this application is also significantly higher than that of the polyamide aerogel.

[0124] Generally speaking, the DHB-type high-temperature resistant polybenzoxazole aerogel of this application has excellent thermal stability.

[0125] Perform performance tests such as thermal conductivity, dielectric constant, specific surface area, and porosity on the polybenzoxazole aerogels obtained in Examples 1, 2, 3, 4, and Comparative Example 1. The results are shown in Table 2.

[0126] Table 2

[0127]

[0128] As can be seen from Table 2, the high-temperature resistant polybenzoxazole aerogel of this application has a low thermal conductivity, excellent heat insulation performance, and a low dielectric constant not higher than 1.72. In addition, the high-temperature resistant polybenzoxazole aerogel of this application has a high specific surface area of 70 - 107 m 2 / g, with a high porosity of 73-89% and a low shrinkage rate. In contrast, the comparative example could not form a high-temperature resistant polybenzoxazole aerogel. Therefore, the conversion strategy adopted in this application can obtain a high-temperature resistant polybenzoxazole aerogel, and this aerogel material simultaneously has the characteristics of being ultra-light, heat-insulating, high-temperature resistant, and excellent mechanical properties.

[0129] In summary, the high-temperature resistant polybenzoxazole aerogel prepared in this application has better thermal stability and better mechanical strength, and at the same time has a low thermal conductivity and good heat-insulating performance. The pore size of the high-temperature resistant polybenzoxazole aerogel of this application is distributed in 20-100 nm, the specific surface area is 60-140 m 2 / g, the porosity is 78-89%, the thermal conductivity is 0.032-0.055 W / mK, the dielectric constant is 1.50-1.72, the thermal stability is greater than 550 °C, and this aerogel material simultaneously has the characteristics of being ultra-light, heat-insulating, high-temperature resistant, and having excellent mechanical properties.

[0130] The above embodiments only illustrate the principles and effects of the present invention by way of example, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of a high-temperature resistant polybenzoxazole aerogel, characterized in that, A high-temperature resistant polybenzoxazole aerogel is prepared by converting a polyamide aerogel. The polymerization monomers forming the polyamide in the polyamide aerogel include 3,3-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride; The preparation method comprises the following steps: after 3,3-dihydroxybenzidine and terephthaloyl chloride / isophthaloyl chloride react to form a polyamide, a sol-gel method is adopted to form a polyamide aerogel, and then the polyamide aerogel is heat-treated to form the high-temperature resistant polybenzoxazole aerogel; The heat treatment is ≥ 200 °C; The heat treatment time is ≥ 300 min; The way of the heat treatment is staged heat treatment, and the program of the staged heat treatment is: treating at 200 - 220 °C for 20 - 40 min, treating at 230 - 270 °C for 20 - 40 min, treating at 280 - 320 °C for 20 - 40 min, treating at 300 - 340 °C for 50 - 70 min, treating at 330 - 370 °C for 20 - 40 min, treating at 360 - 400 °C for 30 - 60 min, treating at 380 - 420 °C for 30 - 60 min, treating at 430 - 450 °C for 50 - 70 min.

2. The preparation method according to claim 1, wherein In the reaction for forming the polyamide, one or more of the following characteristics are included: It is carried out under a protective atmosphere; It is carried out in an organic solvent; The molar ratio of 3,3-dihydroxybenzidine to terephthaloyl chloride / isophthaloyl chloride is 0.01:(0.005 - 0.02); One or two of a co-solvent and an acid-binding agent are adopted; The reaction includes a first reaction stage and a second reaction stage; And / or, the heating rate of the heat treatment is 2 - 5 °C / min.

3. The preparation method according to claim 2, characterized in that, The protective atmosphere is selected from one or two of nitrogen and argon; And / or, the organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide; And / or, the co-solvent is selected from lithium chloride; And / or, the acid-binding agent is selected from propylene oxide; And / or, the molar ratio of the acid-binding agent, 3,3-dihydroxybenzidine to terephthaloyl chloride / isophthaloyl chloride is (0.21 - 0.32):0.01:(0.005 - 0.02); And / or, the temperature of the first reaction stage is -10 - -5 °C; And / or, the time of the first reaction stage is 1 - 3 h; And / or, the temperature of the second reaction stage is 15 - 25 °C; And / or, the time of the second reaction stage is 12 - 24 h.

4. The preparation method according to claim 1, characterized in that, The specific steps for forming the polyamide aerogel by the sol-gel method are: the polyamide is aged in an organic solvent to obtain a gel, and then solvent exchange is carried out, and after drying, a polyamide aerogel is formed.

5. The preparation method according to claim 4, characterized in that, The organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide; And / or, based on the total mass of the polyamide and the organic solvent, the mass fraction of the polyamide is 1 - 20 wt%; And / or, the aging time is 24 to 48 h; And / or, the solvent for solvent exchange is tert-butanol.

6. A high-temperature resistant polybenzoxazole aerogel obtained by the preparation method according to any one of claims 1 to 5.

7. The high-temperature resistant polybenzoxazole aerogel according to claim 6, wherein The pore size distribution of the high-temperature resistant polybenzoxazole aerogel is in the range of 20 to 100 nm, the specific surface area is 60 to 140 m 2 / g, and the porosity is 78 to 89%.

8. The high-temperature resistant polybenzoxazole aerogel according to claim 7, wherein The thermal conductivity of the aerogel is 0.032 to 0.055 W / mK, the dielectric constant is 1.50 to 1.72, and the thermal stability > 550 °C.

9. Use of the high-temperature resistant polybenzoxazole aerogel according to any one of claims 6 to 8 as a high-temperature resistant thermal insulation material in aerospace or ships or buildings.

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