A thermal insulation polybenzoxazole aerogel and its preparation method and use

Abstract

The invention discloses a thermal insulation polybenzoxazole aerogel and a preparation method and use thereof. The thermal insulation polybenzoxazole aerogel has a pore size distribution of 20 to 80 nm and a specific surface area of ​​160 to 190 m 2 / g, porosity is 83-92%, thermal conductivity is 0.030-0.039W / mK, and dielectric constant is 1.5-1.7. The thermal insulation polybenzoxazole aerogel of the present application has the advantages of high porosity, high specific surface area and low thermal conductivity. While meeting the thermal insulation requirements, it also has the characteristics of low dielectric, good mechanical properties, low sound velocity and light weight. Overall, it extends the service life and cycle of the material, reduces maintenance costs, and can be widely used in thermal insulation and other fields.

Description

Technical Field

[0001] The invention belongs to the technical field of aerogels, and in particular relates to a thermal insulation 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 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 problems such as severe water absorption, high density and poor corrosion resistance, and are prone to slag and dust during construction; while 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 the requirements of long-term use and difficult to maintain. Therefore, it is of great significance to develop and find new high-efficiency insulation 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. Therefore, it is called a super thermal insulation material and is widely used in various fields. 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 a variety of common polar solvents such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO). Therefore, aerogel can be directly prepared by the sol-gel method. However, these polymers themselves have poor heat resistance, and the long-term use temperature range is mostly concentrated between 100 and 200°C.

[0004] Polybenzoxazole (Polybenzoxazole, PBO) is a kind of rigid rod-shaped liquid crystal polymer with coplanar oxazole ring and benzene ring, with good mechanical properties, thermal stability, chemical stability, fire resistance, low dielectric constant and electron transport characteristics, but it has the disadvantage of poor solubility, is almost insoluble in organic solvents, and only dissolves in strong protonic acids such as methanesulfonic acid and polyphosphoric acid, so it is difficult to directly prepare aerogel materials. At present, there are fewer reports on polybenzoxazole aerogels, and CN106221216 A discloses that PBO is dissolved in a strong protonic acid solution formed by methanesulfonic acid and trifluoroacetic acid to prepare polybenzoxazole nano aerogels. This method not only has a complicated preparation process, but also produces corrosion and pollution.

[0005] Therefore, there is an urgent need for a method that is simple to operate, easy to produce, and can prepare high-rigidity polymers with poor solubility into ultra-light organic aerogel materials with good thermal insulation and mechanical properties. Summary of the invention

[0006] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a thermal insulation polybenzoxazole aerogel and its preparation method and use. The present application first determines the polyamide that can be converted into polybenzoxazole through structural design, and then prepares the polyamide into aerogel, and then converts it into a thermal insulation polybenzoxazole aerogel. This strategy of preparing polybenzoxazole aerogel by converting polyamide aerogel avoids the problem of poor solubility of high-rigidity polybenzoxazole in the prior art and difficulty in directly preparing aerogel. At the same time, the polybenzoxazole aerogel prepared by the present application has the characteristics of ultra-lightness, thermal insulation and excellent mechanical properties.

[0007] To achieve the above objectives and other related objectives, the present invention is achieved through the following technical solutions.

[0008] The first aspect of the present invention provides a thermal insulation polybenzoxazole aerogel. The thermal insulation polybenzoxazole aerogel has a pore size distribution of 20 to 80 nm and a specific surface area of ​​160 to 190 m 2 / g, and the porosity is 83-92%.

[0009] According to the thermal insulation polybenzoxazole aerogel described above, the thermal conductivity of the thermal insulation polybenzoxazole aerogel is 0.030-0.039 W / mK, and the dielectric constant is 1.5-1.7. Preferably, the thermal conductivity is 0.036-0.039 W / mK, and the dielectric constant is 1.61-1.7.

[0010] According to the thermal insulation polybenzoxazole aerogel described above, the thermal insulation polybenzoxazole has the following repeating structural units:

[0011]

[0012] A second aspect of the present invention provides a method for preparing a thermal insulation polybenzoxazole aerogel. The thermal insulation polybenzoxazole aerogel is prepared by converting a polyamide aerogel.

[0013] According to the preparation method described above, the preparation method comprises the following steps: forming polyamide aerogel from polyamide by a sol-gel method, and then heat-treating the polyamide aerogel to obtain the thermal insulation polybenzoxazole aerogel.

[0014] According to the preparation method described above, the polymerization monomers used in the preparation of the polyamide include 2,2-bis(3-amino-4-hydroxyphenyl)-propane and p-phthaloyl chloride. Preferably, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane to p-phthaloyl chloride is 0.01:(0.005-0.02). More preferably, the molar ratio can be 0.01:(0.005-0.008), 0.01:(0.008-0.013), or 0.01:(0.013-0.02). In some specific embodiments, it is 0.01:0.015.

[0015] According to the preparation method described above, the polyamide is formed under a protective atmosphere. Preferably, the protective atmosphere is selected from one of nitrogen and argon. More preferably, it is nitrogen.

[0016] According to the preparation method described above, the polyamide is formed in an organic solvent. Preferably, the organic solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide. More preferably, the organic solvent is N-methylpyrrolidone.

[0017] According to the above-mentioned preparation method, when forming the polyamide, one or both of a cosolvent and an acid binding agent are also used. In the reaction process of 2,2-bis(3-amino-4-hydroxyphenyl)-propane and p-phthaloyl chloride, hydrochloric acid will be produced, which is not conducive to the reaction. The addition of the acid binding agent can neutralize the hydrochloric acid, improve the reaction conversion rate, and ensure that the polyamide with stable structure is obtained.

[0018] Preferably, the co-solvent is selected from lithium chloride.

[0019] Preferably, the acid binding agent is selected from propylene oxide.

[0020] Preferably, the molar ratio of the acid binding agent, 2,2-bis(3-amino-4-hydroxyphenyl)-propane and p- / 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.

[0021] Preferably, the molar ratio of lithium chloride, propylene oxide and N-methylpyrrolidone is (0.29-0.44): (0.21-0.32): (5.2-7.26).

[0022] According to the preparation method described above, the preparation reaction of polyamide includes a first reaction stage and a second reaction stage.

[0023] Preferably, the temperature of the first reaction stage is -10 to -5°C. Carrying out the first reaction stage at a low temperature is conducive to improving the conversion rate. The activity of isophthaloyl chloride is strong. The reaction under high temperature conditions is not only violent but also has a low conversion rate. More preferably, the reaction temperature can be -10 to -8°C, -8 to -6°C, or -6 to -5°C. In some specific embodiments, it is -6°C, -8°C, and -10°C.

[0024] Preferably, the first reaction stage lasts for 1 to 3 hours, more preferably, the reaction time can be 1 to 2 hours, or 2 to 3 hours. In some specific embodiments, the reaction time is 1 hour, 2 hours, and 3 hours.

[0025] Preferably, the temperature of the second reaction stage is 15-25°C, more preferably, the reaction temperature can be 15-18°C, 18-23°C, or 23-25°C. In some specific embodiments, it is 20°C and 25°C.

[0026] Preferably, the second reaction stage lasts for 12 to 24 hours. More preferably, the reaction time can be 12 to 18 hours, 18 to 20 hours, or 20 to 24 hours. In some specific embodiments, the reaction time is 12 hours, 18 hours, or 24 hours.

[0027] According to the preparation method described above, the heat treatment temperature is ≥ 200°C, preferably, the heat treatment temperature is 200-380°C, more preferably, the heat treatment temperature can be 200-270°C, can be 270-320°C, or can be 320-380°C. In some specific embodiments, it is 380°C.

[0028] According to the preparation method described above, the heat treatment time is ≥ 210 min, preferably, the heat treatment time is 210-270 min, more preferably, the heat treatment time can be 210-230 min, 230-250 min, or 250-270 min. In some specific embodiments, the heat treatment time is 210 min, 240 min, and 270 min.

[0029] According to the preparation method described above, the heating rate of the heat treatment is: 2-5°C / min. Preferably, the heating rate can be 2-3°C / min, 3-4°C / min, or 4-5°C / min. In some specific embodiments, it is 2°C / min, 4°C / min, and 5°C / min.

[0030] Preferably, the heat treatment is performed in stages, and the procedure of the staged heat treatment is: treatment at 200-220°C for 20-40 min, treatment at 230-270°C for 20-40 min, treatment at 290-310°C for 20-40 min, treatment at 310-330°C for 30-60 min, treatment at 330-370°C for 50-70 min, and treatment at 370-380°C for 50-70 min.

[0031] According to the preparation method described above, the preparation method of the polyamide aerogel is:

[0032] 1) Aging of polyamide in an organic solvent to obtain a gel;

[0033] 2) Solvent exchange and drying of the gel to obtain a polyamide aerogel.

[0034] According to the above-mentioned preparation method, when preparing polyamide aerogel, the organic solvent is one or more selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide. Preferably, the organic solvent is N,N-dimethylformamide.

[0035] According to the preparation method described above, when preparing polyamide aerogel, in 1), based on the total mass of polyamide and organic solvent, the mass fraction of polyamide is 1-20wt%. Preferably, the mass fraction can be 1-8wt%, 8-15wt%, or 15-20wt%. In some specific embodiments, it is 6wt%, 8wt% and 10wt%.

[0036] According to the preparation method described above, when preparing polyamide aerogel, in 1), the aging time is 24 to 48 hours. Preferably, the aging time can be 24 to 30 hours, 30 to 40 hours, or 40 to 48 hours. In some specific embodiments, it is 24 hours, 36 hours, and 48 hours.

[0037] According to the preparation method described above, when preparing polyamide aerogel, in 2), the solvent for exchanging solvents is tert-butanol.

[0038] According to the preparation method described above, the synthesis route of the polyamide and polybenzoxazole aerogel synthesized from 2,2-bis(3-amino-4-hydroxyphenyl)-propane and p- / isophthaloyl chloride monomers is as follows:

[0039]

[0040] In addition, the present application obtains thermal insulation polybenzoxazole aerogel by converting polyamide aerogel. This method of preparing polybenzoxazole aerogel by converting polyamide aerogel avoids the dissolution and processing problem of rigid polybenzoxazole in the process of preparing aerogel. At the same time, the polyamide of the present application can be placed in a mold of any shape or complex structure, thereby forming a thermal insulation polybenzoxazole aerogel product of the corresponding shape or structure.

[0041] The third aspect of the present invention provides use of the thermal insulation polybenzoxazole aerogel as described above as a thermal insulation material in aerospace, shipbuilding, construction or pipelines.

[0042] The thermal insulation polybenzoxazole aerogel obtained by converting polyamide aerogel in the present application has a lower thermal conductivity and good thermal insulation performance. It also has the advantages of high thermal stability, excellent mechanical strength and low dielectric constant.

[0043] As described above, the present invention provides a thermal insulation polybenzoxazole aerogel and a preparation method and use thereof, which have the following beneficial effects:

[0044] 1) The thermal insulation polybenzoxazole aerogel prepared by the present invention is obtained by converting polyamide aerogel. This conversion strategy effectively avoids the dissolution processing problem of high-rigidity polybenzoxazole in the direct preparation of aerogel. At the same time, the macroscopic shape structure of the polyamide aerogel can be changed to form a corresponding thermal insulation polybenzoxazole aerogel product of arbitrary shape or complex structure.

[0045] 2) Compared with polyamide aerogel, the thermal insulation polybenzoxazole aerogel of the present application has high porosity and high specific surface area. The porosity of the aerogel is as high as 92%, and the specific surface area is as high as 190m 2 / g, and at the same time, it has low thermal conductivity, low dielectric constant, is safe and non-toxic, and meets the needs of thermal insulation. It also has the characteristics of low sound velocity and lightweight, which overall extends the service life and cycle of the material and reduces maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1Shown are graphs of thermal conductivity of thermal insulating polybenzoxazole aerogels obtained in Example 1, Example 2 and Example 3 of the present invention, respectively.

[0047] Figure 2 The scanning electron microscope image shows the microscopic morphology of the thermal insulation polybenzoxazole aerogel obtained in Example 1 of the present invention.

[0048] Figure 3 It shows the infrared spectrum of the polyamide aerogel in Example 1 of the present invention converted into thermal insulation polybenzoxazole aerogel. DETAILED DESCRIPTION

[0049] The following is an explanation of the embodiments of the present invention by specific examples 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 contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0050] It should be noted that the process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0051] A specific preparation method is adopted in the following specific embodiments of the present application, comprising the following steps:

[0052] 1) mixing polyamide with an organic solvent and aging to obtain a gel;

[0053] 2) exchanging solvents of the gel and drying the gel to obtain a polyamide aerogel;

[0054] 3) heat-treating the polyamide aerogel to obtain the thermal insulation polybenzoxazole aerogel.

[0055] Wherein, the preparation method of polyamide comprises the following steps:

[0056] 1-1) Under a protective atmosphere, 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride react in an organic solvent to obtain a reaction product;

[0057] 1-2) The reaction product is mixed with water, separated into solid and liquid, and dried to obtain polyamide.

[0058] According to the preparation method described above, in 1), a gelling agent is added during or after the polyamide is mixed with the organic solvent. The gelling agent is selected from one or more of acetonitrile, acetone and deionized water. Preferably, the gelling agent is acetonitrile.

[0059] According to the preparation method described above, in 2), the solvent for solvent exchange is tert-butanol.

[0060] According to the preparation method described above, in 2), the number of solvent exchanges is 6 to 12 times. Preferably, the number of exchanges can be 6 to 7 times, 7 to 10 times, or 10 to 12 times. In some specific embodiments, it is 6 times and 8 times; during each exchange, the solvent retention time is 8 to 12 hours. Preferably, the retention time can be 8 to 9 hours, 9 to 11 hours, or 11 to 12 hours. In some specific embodiments, it is 8 hours, 10 hours, and 12 hours.

[0061] According to the preparation method described above, in 2), the drying method is freeze-drying.

[0062] According to the preparation method described above, the freeze-drying temperature is -50 to -40°C, preferably, the freeze-drying temperature can be -50 to -47°C, -47 to -43°C, or -43 to -40°C. In some specific embodiments, it is -45°C and -50°C.

[0063] According to the preparation method described above, the freeze-drying pressure is 5-20 Pa. Preferably, the freeze-drying pressure can be 5-10 Pa, 10-15 Pa, or 15-20 Pa. In some specific embodiments, it is 8 Pa, 10 Pa, and 15 Pa.

[0064] According to the preparation method described above, the freeze-drying time is 48 to 72 hours. Preferably, the freeze-drying time can be 48 to 54 hours, 54 to 64 hours, or 64 to 72 hours. In some specific embodiments, it is 72 hours.

[0065] According to the preparation method described above, in 1-2), the drying temperature is 60-100° C. Preferably, the drying temperature can be 60-70° C., 70-85° C., or 85-100° C. In some specific embodiments, it is 60° C. and 80° C.

[0066] According to the preparation method described above, in 1-2), the drying time is 8 to 12 hours. Preferably, the drying time can be 8 to 9 hours, 9 to 11 hours, or 11 to 12 hours. In some specific embodiments, the drying time is 8 hours, 10 hours, and 12 hours.

[0067] In the following embodiments of the present application, the acid binding agent is propylene oxide and the co-solvent is selected from lithium chloride.

[0068] In the following embodiments of the present application, the polyamide has the following repeating structural units:

[0069]

[0070] Example 1

[0071] In this embodiment, a thermal insulation polybenzoxazole aerogel and a preparation method thereof are provided, comprising the following steps:

[0072] 1) Dissolve polyamide in N,N-dimethylformamide to prepare a 6 wt % solution, pour it into a mold, add acetonitrile solvent, let it stand for 12 hours, and continue to age for 24 hours to obtain a gel.

[0073] 2) The gel obtained in 1) was subjected to 6 solvent exchanges with tert-butyl alcohol, each time for 8 hours, and then freeze-dried for 72 hours at a pressure of 15 Pa and a temperature of -45°C to obtain a polyamide aerogel.

[0074] 3) The polyamide aerogel obtained in 2) is placed in a tubular furnace in a nitrogen atmosphere, the heating rate is set to 2°C / min, and the following staged heat treatment is performed: 200°C for 30min, 250°C for 30min, 300°C for 30min, 320°C for 30min, 350°C for 30min and 380°C for 60min to obtain a thermal insulation polybenzoxazole aerogel. The mass percentage of the thermal insulation polybenzoxazole aerogel obtained in this embodiment is 6wt%.

[0075] Wherein, the preparation method of polyamide is as follows:

[0076] 1-1) Weigh 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride and add them into a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out a first reaction at -6°C for 1 hour under nitrogen, and then carry out a second reaction at 20°C for 12 hours to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane, terephthaloyl chloride, lithium chloride, propylene oxide and N-methylpyrrolidone is 0.01:0.015:0.29:0.21:5.2; the mass of 2,2-bis(3-amino-4-hydroxyphenyl)-propane is 2.58g.

[0077] 1-2) The reaction product obtained in 1-1) was poured into deionized water to obtain a solid precipitate, which was filtered and vacuum dried at 60° C. for 8 h to obtain a polyamide.

[0078] The polyamide and thermal insulation polybenzoxazole aerogel were subjected to infrared detection. The results are shown in Figure 3 .

[0079] from Figure 3 It can be seen that 3409cm -1 The peak at 3400-3000cm is attributed to NH stretching vibration. -1 The characteristic peak at 1650cm -1 The peak at 1540 cm is attributed to C=O stretching vibration. -1 The peak at 1622 cm-1 and 1473 cm-1 are attributed to NH bending vibration, and the above structure corresponds to polyamide. After heat treatment, the characteristic peak of hydroxyl group disappears, and new characteristic peaks appear at 1622 cm-1 and 1473 cm-1. -1 The peaks at 1251 and 1050 cm-1 are attributed to C=N stretching and bending vibrations, respectively. -1 The peaks at are attributed to CO stretching and bending vibrations, respectively. The results show that after heat treatment, the molecular structure changes, that is, the amide structure is dehydrated to form an oxazole structure, and finally a thermal insulating polybenzoxazole aerogel is obtained.

[0080] Example 2

[0081] In this embodiment, a thermal insulation polybenzoxazole aerogel and a preparation method thereof are provided, comprising the following steps:

[0082] 1) Dissolve polyamide in N,N-dimethylformamide to prepare an 8 wt % solution, pour it into a mold, add acetonitrile solvent, let it stand for 18 hours, and continue to age for 36 hours to obtain a gel.

[0083] 2) The gel obtained in 1) was subjected to 8 solvent exchanges with tert-butyl alcohol, each time for 10 hours, and then freeze-dried for 72 hours at a pressure of 10 Pa and a temperature of -45°C to obtain a polyamide aerogel.

[0084] 3) The polyamide aerogel obtained in 2) is placed in a tubular furnace in a nitrogen atmosphere, the heating rate is set to 4°C / min, and the following heat treatment is performed: 200°C for 30min, 250°C for 30min, 300°C for 30min, 320°C for 30min, 350°C for 60min and 380°C for 60min to obtain a thermal insulation polybenzoxazole aerogel. The mass percentage of the thermal insulation polybenzoxazole aerogel obtained in this embodiment is 8wt%.

[0085] Wherein, the preparation method of polyamide is as follows:

[0086] 1-1) Weigh 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride and add them into a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out a first reaction at -8°C for 2 hours under nitrogen, and then carry out a second reaction at 25°C for 18 hours to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane, terephthaloyl chloride, lithium chloride, propylene oxide and N-methylpyrrolidone is 0.01:0.015:0.37:0.27:6.2; the mass of 2,2-bis(3-amino-4-hydroxyphenyl)-propane is 2.58g.

[0087] 1-2) The reaction product obtained in 1-1) was poured into deionized water to obtain a solid precipitate, which was filtered and vacuum dried at 80° C. for 10 h to obtain a polyamide.

[0088] Example 3

[0089] 1) Dissolve polyamide in N,N-dimethylformamide to prepare a 10 wt% solution, pour it into a mold, add acetonitrile solvent, let it stand for 24 hours, and continue to age for 48 hours to obtain a gel.

[0090] 2) The gel obtained in 1) was subjected to 8 solvent exchanges with tert-butyl alcohol, each time for 12 hours, and then freeze-dried for 72 hours at a pressure of 8 Pa and a temperature of -50°C to obtain a polyamide aerogel.

[0091] 3) The polyamide aerogel obtained in 2) is placed in a tubular furnace in a nitrogen atmosphere, the heating rate is set to 5°C / min, and the following heat treatment is performed: 200°C for 30min, 250°C for 30min, 300°C for 30min, 320°C for 60min, 350°C for 60min and 380°C for 60min to obtain a thermal insulation polybenzoxazole aerogel. The mass percentage of the thermal insulation polybenzoxazole aerogel obtained in this embodiment is 10wt%.

[0092] Wherein, the preparation method of polyamide is as follows:

[0093] 1-1) Weigh 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride and add them into a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out a first reaction at -10°C for 3 hours under nitrogen, and then carry out a second reaction at 25°C for 24 hours to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane, terephthaloyl chloride, lithium chloride, propylene oxide and N-methylpyrrolidone is 0.01:0.015:0.44:0.32:7.26; the mass of 2,2-bis(3-amino-4-hydroxyphenyl)-propane is 2.58g.

[0094] 1-2) The reaction product obtained in 1-1) was poured into deionized water to obtain a solid precipitate, which was filtered and vacuum dried at 80° C. for 12 h to obtain a polyamide.

[0095] Example 4

[0096] The difference between this embodiment and embodiment 1 is that in step 3), no segmented heat treatment is performed, but the polyamide aerogel is directly heat treated at 380° C. for 210 min. The rest is the same as in embodiment 1.

[0097] Example 5

[0098] In this embodiment, a thermal insulation polybenzoxazole aerogel and a preparation method thereof are provided, comprising the following steps:

[0099] 1) Dissolve polyamide in N,N-dimethylformamide to prepare a 6 wt % solution, pour it into a mold, add acetonitrile solvent, let it stand for 12 hours, and continue to age for 24 hours to obtain a gel.

[0100] 2) The gel obtained in 1) was subjected to 6 solvent exchanges with tert-butyl alcohol, each time for 8 hours, and then freeze-dried for 72 hours at a pressure of 15 Pa and a temperature of -45°C to obtain a polyamide aerogel.

[0101] 3) The polyamide aerogel obtained in 2) is placed in a tubular furnace in a nitrogen atmosphere, the heating rate is set to 2°C / min, and the following heat treatment is performed: 200°C for 30min, 250°C for 30min, 300°C for 30min, 320°C for 30min, 350°C for 60min and 380°C for 60min to obtain a thermal insulation polybenzoxazole aerogel. The mass percentage of the thermal insulation polybenzoxazole aerogel obtained in this embodiment is 6wt%.

[0102] Wherein, the preparation method of polyamide is as follows:

[0103] 1-1) Weigh 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride and add them into a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out a first reaction at -6°C for 1 hour under nitrogen, and then carry out a second reaction at 20°C for 12 hours to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane, terephthaloyl chloride, lithium chloride, propylene oxide and N-methylpyrrolidone is 0.01:0.005:0.29:0.21:5.2; the mass of 2,2-bis(3-amino-4-hydroxyphenyl)-propane is 2.58g.

[0104] 1-2) The reaction product obtained in 1-1) was poured into deionized water to obtain a solid precipitate, which was filtered and vacuum dried at 60° C. for 8 h to obtain a polyamide.

[0105] Example 6

[0106] In this embodiment, a thermal insulation polybenzoxazole aerogel and a preparation method thereof are provided, comprising the following steps:

[0107] 1) Dissolve polyamide in N,N-dimethylformamide to prepare an 8 wt % solution, pour it into a mold, add acetonitrile solvent, let it stand for 18 hours, and continue to age for 36 hours to obtain a gel.

[0108] 2) The gel obtained in 1) was subjected to 8 solvent exchanges with tert-butyl alcohol, each time for 10 hours, and then freeze-dried for 72 hours at a pressure of 10 Pa and a temperature of -45°C to obtain a polyamide aerogel.

[0109] 3) The polyamide aerogel obtained in 2) is placed in a tubular furnace in a nitrogen atmosphere, the heating rate is set to 4°C / min, and the following heat treatment is performed: 200°C for 30min, 250°C for 30min, 300°C for 30min, 320°C for 60min, 350°C for 60min and 380°C for 60min to obtain a thermal insulation polybenzoxazole aerogel. The mass percentage of the thermal insulation polybenzoxazole aerogel obtained in this embodiment is 8wt%.

[0110] Wherein, the preparation method of polyamide is as follows:

[0111] 1-1) Weigh 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride and add them into a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out a first reaction at -8°C for 2 hours under nitrogen, and then carry out a second reaction at 25°C for 18 hours to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane, terephthaloyl chloride, lithium chloride, propylene oxide and N-methylpyrrolidone is 0.01:0.013:0.37:0.27:6.2; the mass of 2,2-bis(3-amino-4-hydroxyphenyl)-propane is 2.58g.

[0112] 1-2) The reaction product obtained in 1-1) was poured into deionized water to obtain a solid precipitate, which was filtered and vacuum dried at 80° C. for 10 h to obtain a polyamide.

[0113] Example 7

[0114] 1) Dissolve polyamide in N,N-dimethylformamide to prepare a 10 wt% solution, pour it into a mold, add acetonitrile solvent, let it stand for 24 hours, and continue to age for 48 hours to obtain a gel.

[0115] 2) The gel obtained in 1) was subjected to 8 solvent exchanges with tert-butyl alcohol, each time for 12 hours, and then freeze-dried for 72 hours at a pressure of 8 Pa and a temperature of -50°C to obtain a polyamide aerogel.

[0116] 3) The polyamide aerogel obtained in 2) is placed in a tubular furnace in a nitrogen atmosphere, the heating rate is set to 5°C / min, and the following heat treatment is performed: 200°C for 30min, 250°C for 30min, 300°C for 60min, 320°C for 60min, 350°C for 60min and 380°C for 60min to obtain a thermal insulation polybenzoxazole aerogel. The mass percentage of the thermal insulation polybenzoxazole aerogel obtained in this embodiment is 10wt%.

[0117] Wherein, the preparation method of polyamide is as follows:

[0118] 1-1) Weigh 2,2-bis(3-amino-4-hydroxyphenyl)-propane and terephthaloyl chloride and add them into a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out a first reaction at -10°C for 3 hours under nitrogen, and then carry out a second reaction at 25°C for 24 hours to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-propane, terephthaloyl chloride, lithium chloride, propylene oxide and N-methylpyrrolidone is 0.01:0.02:0.44:0.32:7.26; the mass of 2,2-bis(3-amino-4-hydroxyphenyl)-propane is 2.58g.

[0119] 1-2) The reaction product obtained in 1-1) was poured into deionized water to obtain a solid precipitate, which was filtered and vacuum dried at 80° C. for 12 h to obtain a polyamide.

[0120] Comparative Example 1

[0121] The difference between this comparative example and Example 1 is that in step 3), no segmented heat treatment is performed, but the polyamide aerogel is directly heat treated at 170° C. for 210 min, and the rest is the same as Example 1. Finally, the thermal insulation polybenzoxazole aerogel cannot be obtained because the ring closing reaction is extremely slow or cannot be closed.

[0122] The thermal insulation polybenzoxazole aerogels of Examples 1, 2, 3, 4 and Comparative Example 1 were tested for thermal conductivity, dielectric constant, specific surface area and porosity, and the shrinkage was calculated.

[0123] 1) The specific steps for thermal conductivity testing are:

[0124] a) Prepare an aerogel sample of a certain size (40 mm in length and 20 mm in width);

[0125] b) Place the sample into the TC 3000 thermal conductivity measuring instrument, making sure the test piece is completely covered;

[0126] c) Setting temperature parameters, conducting thermal conductivity test on the sample, and obtaining the thermal conductivity coefficient of the sample.

[0127] 2) The specific operation of dielectric constant detection is:

[0128] a) Place the sample (20 mm in diameter, 1 mm in thickness) into the Concept 40 broadband dielectric tester;

[0129] b) Set the test interval to 10~10 7 Hz, test and obtain the dielectric constant of the sample.

[0130] 3) Specific surface area detection and calculation of shrinkage rate

[0131] The specific surface area of ​​the thermal insulation polybenzoxazole aerogel obtained in Examples 1, 2, 3, 4 and Comparative Example 1 was measured using a TriStar II 3flex analyzer to obtain the specific surface area of ​​the sample. The size of the aerogel sample before and after heat treatment was measured using the following formula:

[0132] Shrinkage rate = (size before heat treatment - size after heat treatment) / size before heat treatment

[0133] The shrinkage of the sample was calculated.

[0134] The specific results of thermal conductivity, dielectric constant, specific surface area, porosity and shrinkage of Examples 1, 2, 3, 4 and Comparative Example 1 are shown in Table 1.

[0135] Table 1

[0136]

[0137] As shown in Table 1, in the present application, the thermal insulation polybenzoxazole aerogel obtained in the embodiment has a thermal conductivity as low as 0.0361 W / mK, a low dielectric constant, and a high specific surface area of ​​175 to 190 m 2 / g, a high porosity of 81-89%, and a low shrinkage rate; while the comparative example cannot obtain a thermal insulation polybenzoxazole aerogel. Therefore, the preparation method of the present application can not only obtain a polybenzoxazole aerogel, but also the polybenzoxazole aerogel has good thermal insulation performance.

[0138] Overall, it is shown that the thermal insulation polybenzoxazole aerogel of the present application enables aerogel materials to achieve the characteristics of ultra-lightness, thermal insulation, low dielectric and excellent mechanical properties.

[0139] In summary, the thermal insulation polybenzoxazole aerogel prepared in the present application has a low thermal conductivity, a high specific surface area and porosity, and has good thermal insulation performance. The thermal insulation polybenzoxazole aerogel of the present application has a three-dimensional network structure formed by nanofibers, with a pore size distribution of 20 to 80 nm and a specific surface area of ​​160 to 190 m 2 / g, the porosity is 83-92%, the thermal conductivity is 0.030-0.039W / mK, and the dielectric constant is 1.5-1.7. The aerogel material has the characteristics of ultra-lightness, heat insulation, low dielectric and excellent mechanical properties.

[0140] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A thermal insulation polybenzoxazole aerogel, characterized in that: The thermal insulation polybenzoxazole aerogel has a pore size distribution of 20 to 80 nm and a specific surface area of ​​160 to 190 m 2 / g, the porosity is 83-92%, and the thermal insulation polybenzoxazole aerogel has the following repeating structural units:

2. The thermal insulation polybenzoxazole aerogel according to claim 1, characterized in that: The thermal conductivity of aerogel is 0.030-0.039 W / mK, and the dielectric constant is 1.5-1.

7.

3. A method for preparing the thermal insulation polybenzoxazole aerogel according to claim 1 or 2, characterized in that: The thermal insulation polybenzoxazole aerogel is prepared by converting polyamide aerogel; The polyamide is formed into a polyamide aerogel by a sol-gel method, and the polyamide aerogel is heat-treated to obtain the thermal insulation polybenzoxazole aerogel; The heat treatment method is staged heat treatment, and the procedure of the staged heat treatment is: treatment at 200-220°C for 20-40min, treatment at 230-270°C for 20-40min, treatment at 290-310°C for 20-40min, treatment at 310-330°C for 30-60min, treatment at 330-370°C for 50-70min, and treatment at 370-380°C for 50-70min.

4. The method for preparing the thermal insulation polybenzoxazole aerogel according to claim 3, characterized in that: Includes one or more of the following features: The polymerization monomers used to form the polyamide include 2,2-bis(3-amino-4-hydroxyphenyl)-propane and p- / isophthaloyl chloride; Forming polyamide under protective atmosphere; Formation of polyamides in organic solvents; The formation of polyamide also uses one or both of a cosolvent and an acid-binding agent; The reaction to form the polyamide includes a first reaction stage and a second reaction stage.

5. The method for preparing the thermal insulation polybenzoxazole aerogel according to claim 4, characterized in that: The molar ratio of the 2,2-bis(3-amino-4-hydroxyphenyl)-propane to p- / isophthaloyl chloride is 0.01: (0.005～0.02)； And / or, the protective atmosphere is selected from one or both 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, 2,2-bis(3-amino-4-hydroxyphenyl)-propane and p- / isophthaloyl chloride is (0.21-0.32):0.01:(0.005-0.02); And / or, the temperature of the first reaction stage is -10 to -5°C; And / or, the temperature of the second reaction stage is 15-25°C.

6. The method for preparing the thermal insulation polybenzoxazole aerogel according to claim 3, characterized in that: The preparation method of polyamide aerogel is as follows: 1) Aging of polyamide in an organic solvent to obtain a gel; 2) Solvent exchange and drying of the gel to obtain a polyamide aerogel.

7. The method for preparing the thermal insulation polybenzoxazole aerogel according to claim 6, characterized in that: 1), the aging organic solvent is one or more selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide; And / or, in 1), based on the total mass of the polyamide and the organic solvent, the mass fraction of the polyamide is 1 to 20 wt%; And / or, in 1), the aging time is 24 to 48 hours; And / or, in 2), the solvent for the exchange solvent is tert-butanol.

8. Use of the thermal insulation polybenzoxazole aerogel according to claim 1 or 2 as a thermal insulation material in aerospace, shipbuilding, construction or pipelines.

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