A low dielectric constant polybenzoxazole aerogel and its preparation method and uses

Abstract

The present invention discloses a low dielectric constant polybenzoxazole aerogel and its preparation method and uses. The pore size distribution of the low dielectric constant polybenzoxazole aerogel is in the range of 10 to 100 nm, the specific surface area is 171 to 188 m 2 / g, the porosity is 78 to 88%, the thermal conductivity is 0.035 to 0.046 W / mK, the thermal stability is greater than 500 °C, and the dielectric constant is 1.45 to 1.58. The low dielectric constant polybenzoxazole aerogel of the present application has the advantages of low dielectric constant, high porosity, high specific surface area and low thermal conductivity. While meeting the low dielectric requirements, it also has good heat insulation effect, low sound velocity and light weight characteristics, overall extending the service life and cycle of the polybenzoxazole aerogel, reducing the maintenance cost, and can be widely used in the fields of microelectronics and heat insulation, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerogels, and particularly relates to a low dielectric constant polybenzoxazole aerogel and a preparation method thereof. Background Art

[0002] With the development and upgrading of material science and technology, higher requirements and standards have been put forward for insulating materials. In addition to meeting the normal requirements of heat preservation and insulation, they also need to have functional characteristics such as low dielectric, hydrophobicity, high temperature resistance, wave transmission, and mechanical strength. Traditional insulating materials mainly include two categories: inorganic materials and organic materials, and are widely used in fields such as aerospace, marine ships, chemical pipelines, and building insulation. However, inorganic materials mainly composed of mineral wool, asbestos, rock wool, and glass wool have problems such as serious water absorption, high density, and poor corrosion resistance, and are prone to slag dropping and dust generation during the construction process; while organic materials, such as rubber, polyurethane, polyimide, and styrene foams, have poor heat insulation effects, low high temperature resistance and mechanical strength, and high dielectric constants, making it difficult to meet the use requirements and difficult to repair and maintain. Therefore, it is of great significance to develop and find new heat-insulating and low-dielectric functional materials.

[0003] Aerogels are network interpenetrating porous materials composed of colloidal particles or polymer chains. Their unique nano-porous system and continuous three-dimensional network space endow aerogels with excellent properties such as ultra-low thermal conductivity, ultra-low dielectric constant, ultra-low density, high porosity, and high specific surface area, and are widely used in various fields. However, with the rapid development of aerogels, there are also many problems to be solved. For example, although silica aerogel has excellent heat insulation performance with a thermal conductivity as low as 0.017 W / mK, its structure is brittle and its mechanical strength is low, which is greatly limited in practical applications. Polymers such as polyimide, polyamide, and polyacrylonitrile have significant advantages in terms of mechanical strength due to their flexible molecular designability, and also have good solubility. For example, polyamide can be dissolved in many common polar solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). Therefore, aerogels can be directly prepared by the sol-gel method. However, these polymers themselves have poor heat resistance, and the long-term use temperature range mostly focuses between 100 and 200 °C.

[0004] Polybenzoxazole (PBO) is a rigid rod-like liquid crystal polymer with oxazole rings and benzene rings coplanar. It has good mechanical properties, low dielectric constant, thermal stability, chemical stability, fire resistance, and electron transport characteristics, etc. However, it has the disadvantage of poor solubility and is almost insoluble in organic solvents, only dissolving in strong proton acids such as methanesulfonic acid and polyphosphoric acid. Therefore, it is difficult to directly prepare it into an aerogel material. Currently, there are few articles reporting on polybenzoxazole aerogels. CN106221216 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 causes problems such as corrosion and pollution.

[0005] Therefore, there is an urgent need for a method that is simple to operate, convenient for production, and can prepare a high-rigidity polymer with poor solubility into an organic aerogel material with low dielectric constant, high temperature resistance, heat insulation, ultra-light weight, and good mechanical properties. 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 low dielectric constant polybenzoxazole aerogel and its preparation method and uses. In this application, first through structural design, a polyamide that can be converted into polybenzoxazole is determined, and then the polyamide is prepared into an aerogel, and further converted into a low dielectric constant polybenzoxazole aerogel. This strategy of converting polyamide aerogel to prepare polybenzoxazole aerogel avoids the problems of poor solubility of high-rigidity 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 low dielectric, heat insulation, high temperature resistance, and excellent mechanical properties.

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

[0008] The first aspect of the present invention provides a low dielectric constant polybenzoxazole aerogel, the pore size distribution of the low dielectric constant polybenzoxazole aerogel is in the range of 10 - 100 nm, the specific surface area is 171 - 188 m 2 / g, and the porosity is 78 - 88%.

[0009] According to the above-mentioned low dielectric constant polybenzoxazole aerogel, the thermal conductivity of the low dielectric constant polybenzoxazole aerogel is 0.035 - 0.046 W / mK, the thermal stability is greater than 500 °C, and the dielectric constant is 1.45 - 1.58. Preferably, the thermal conductivity is 0.039 - 0.046 W / mK, and the dielectric constant is 1.5 - 1.58.

[0010] According to the above-mentioned low dielectric constant polybenzoxazole aerogel, the low dielectric constant polybenzoxazole has the following repeating structural unit:

[0011]

[0012] The second aspect of the present invention provides a method for preparing the low dielectric constant polybenzoxazole aerogel as described above, and the low dielectric constant polybenzoxazole aerogel is prepared by conversion of a polyamide aerogel.

[0013] According to the preparation method described above, the preparation method includes the following steps: a polyamide is formed into a polyamide aerogel by a sol-gel method, and then the polyamide aerogel is heat-treated to obtain the low dielectric constant polybenzoxazole aerogel.

[0014] According to the preparation method described above, the polymerization monomers used for forming the polyamide include 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride / isophthaloyl chloride.

[0015] Preferably, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane 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 be 0.01:(0.013-0.02). In certain specific embodiments, it is 0.01:0.015. The selection of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane introduces a fluorine-containing structure, and fluorine atoms can increase the free volume and reduce the polarizability. Thereby, it is beneficial to reduce the dielectric constant of polybenzoxazole.

[0016] 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.

[0017] 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.

[0018] According to the preparation method described above, when forming the polyamide, one or two of a co-solvent and an acid-binding agent are also used. During the reaction of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride / isophthaloyl chloride, hydrochloric acid is generated, which is not conducive to 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.

[0019] Preferably, the co-solvent is selected from lithium chloride.

[0020] Preferably, the acid-binding agent is selected from propylene oxide.

[0021] Preferably, the molar ratio of the acid-binding agent, 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, and terephthaloyl chloride / isophthaloyl chloride is (0.21 - 0.32):0.01:0.015.

[0022] 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).

[0023] According to the preparation method described above, the preparation reaction of the polyamide includes a first reaction stage and a second reaction stage.

[0024] 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. Terephthaloyl chloride / isophthaloyl chloride has strong activity. Conducting the reaction under high-temperature conditions not only leads to violent reactions but also low conversion rates. 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 certain specific embodiments, it is -6 °C, -8 °C, and -10 °C.

[0025] 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 certain specific embodiments, it is 1 h, 2 h, and 3 h.

[0026] 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 certain specific embodiments, it is 20 °C and 25 °C.

[0027] 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 certain specific embodiments, it is 12 h, 18 h, and 24 h.

[0028] According to the preparation method described above, the heat treatment temperature ≥ 200 °C. Preferably, the heat treatment temperature is 200 to 380 °C. More preferably, the heat treatment temperature can be 200 to 270 °C, can be 270 to 320 °C, or can be 320 to 380 °C. In certain specific embodiments, it is 380 °C.

[0029] According to the above-described preparation method, the heat treatment time is ≥240 min. Preferably, the heat treatment time is 240 - 330 min. More preferably, the heat treatment time can be 240 - 260 min, can be 260 - 290 min, or can also be 290 - 330 min. In certain specific embodiments, it is 240 min, 300 min, and 330 min.

[0030] According to the above-described preparation method, the heating rate during heat treatment is 2 - 5 °C / min. Preferably, the heating rate can be 2 - 3 °C / min, can be 3 - 4 °C / min, or can also be 4 - 5 °C / min. In certain specific embodiments, it is 2 °C / min, 4 °C / min, and 5 °C / min.

[0031] Preferably, the heat treatment method is staged heat treatment, and the program of the staged heat treatment is: treating at 200 - 220 °C for 20 - 40 min, 230 - 270 °C for 20 - 40 min, 270 - 290 °C for 20 - 40 min, 290 - 310 °C for 20 - 40 min, 310 - 330 °C for 20 - 40 min, 330 - 370 °C for 20 - 40 min, and 370 - 380 °C for 50 - 70 min.

[0032] According to the above-described preparation method, the preparation method of the polyamide aerogel is as follows:

[0033] 1) Aging polyamide in an organic solvent to obtain a gel;

[0034] 2) Performing solvent exchange on the gel and drying to obtain a polyamide aerogel.

[0035] According to the above-described preparation method, when preparing the 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-methylpyrrolidone.

[0036] According to the above-described preparation method, when preparing the polyamide aerogel, in 1), 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 also be 15 - 20 wt%. In certain specific embodiments, it is 6 wt%, 8 wt%, and 10 wt%.

[0037] According to the preparation method described above, when preparing polyamide aerogel, in 1), the aging time is 24 to 48 h. Preferably, the aging time can be 24 to 30 h, can be 30 to 40 h, or can be 40 to 48 h. In certain specific embodiments, it is 24 h, 36 h, and 48 h.

[0038] According to the preparation method described above, when preparing polyamide aerogel, in 2), the solvent for the exchange solvent is tert-butanol.

[0039] According to the preparation method described above, the synthetic route of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride / isophthaloyl chloride monomers to form polyamide and polybenzoxazole aerogels is as follows:

[0040]

[0041] In addition, in this application, a low-dielectric constant polybenzoxazole aerogel is obtained by converting polyamide aerogel. This method of preparing aerogel by converting the precursor aerogel well avoids the problem of dissolution and processing of rigid polybenzoxazole during the preparation of aerogel. At the same time, the polyamide in this application can be placed in a mold of any shape or complex structure, thereby forming a low-dielectric polybenzoxazole aerogel product with the corresponding shape or structure.

[0042] The third aspect of the present invention provides the use of the low-dielectric constant polybenzoxazole aerogel as described above as a low-dielectric material or a thermal insulation material in aerospace, ships, radar radomes, or buildings.

[0043] The low-dielectric constant polybenzoxazole aerogel prepared by converting polyamide aerogel in this application has better thermal stability, higher mechanical strength, and a lower dielectric constant. In addition, the low-dielectric constant polybenzoxazole aerogel of this application has the advantages of high porosity, high specific surface area, and low thermal conductivity.

[0044] As described above, the present invention provides a low-dielectric constant polybenzoxazole aerogel, its preparation method and use, and has the following beneficial effects:

[0045] 1) The low-dielectric constant polybenzoxazole aerogel prepared in the present invention is obtained by converting polyamide aerogel. This conversion strategy well avoids the problem of difficult dissolution of highly rigid polybenzoxazole during the direct preparation of aerogel. At the same time, by changing the shape and structure of the polyamide, a low-dielectric constant polybenzoxazole aerogel product with the corresponding arbitrary shape or complex structure can be formed, avoiding the problem of difficult processing of rigid polybenzoxazole.

[0046] 2) Compared with polyamide aerogel, the low dielectric constant polybenzoxazole aerogel of the present application has a lower dielectric constant, with the dielectric constant and dielectric loss as low as 1.45 and 0.0036. In addition, the aerogel has better thermal stability, a low thermal conductivity of 0.035 - 0.046 W / mK, a porosity of 78 - 88%, and a specific surface area of 171 - 188 m 2 / g. It is safe, non-toxic, meets the requirements of thermal insulation and low dielectric, and also has the characteristics of low sound velocity and light weight. Overall, it extends the service life and cycle of the material and reduces the maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The figure shows the thermal conductivity diagrams of the low dielectric constant polybenzoxazole aerogels obtained in Example 1, Example 2, and Example 3 of the present invention respectively.

[0048] Figure 2 The figure shows the dielectric constant diagrams of the low dielectric constant polybenzoxazole aerogels obtained in Example 1, Example 2, and Example 3 of the present invention respectively.

[0049] Figure 3 The figure shows the electron microscope image of the microstructure of the low dielectric constant polybenzoxazole aerogel obtained in Example 1 of the present invention.

[0050] Figure 4 The figure shows the infrared spectrum diagram of the conversion of the polyamide aerogel in Example 1 of the present invention into a low dielectric constant polybenzoxazole aerogel. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] 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.

[0052] It should be noted that the process equipment or devices not specifically noted in the following examples 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 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. Moreover, unless otherwise stated, the numbering of each method step is only a convenient tool for identifying each method step, rather than limiting the arrangement order of each method step or the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present invention.

[0053] In the following specific embodiments of this application, a specific preparation method is adopted, including the following steps:

[0054] 1) Mix polyamide with an organic solvent and age it to obtain a gel;

[0055] 2) Perform solvent exchange on the gel and dry it to obtain a polyamide aerogel;

[0056] 3) Perform heat treatment on the polyamide aerogel to obtain the low dielectric constant polybenzoxazole aerogel.

[0057] Among them, the preparation method of polyamide includes the following steps:

[0058] 1-1) Under a protective atmosphere, 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride react in an organic solvent to obtain a reaction product;

[0059] 1-2) Mix the reaction product with water, perform solid-liquid separation, and dry it to obtain the polyamide.

[0060] According to the above-mentioned preparation method, in 1), a gelling agent is added during or after the mixing of the polyamide and the organic solvent, and the gelling agent is selected from one or more of acetonitrile, acetone, and deionized water. Preferably, the gelling agent is deionized water.

[0061] According to the above-mentioned preparation method, in 2), the solvent for solvent exchange is tert-butanol.

[0062] According to the above-mentioned preparation method, in 2), the number of solvent exchanges is 6 to 12 times. Preferably, the number of solvent exchanges can be 6 to 7 times, can be 7 to 10 times, or can be 10 to 12 times. In some specific embodiments, it is 6 times and 8 times. Each time of exchange, the retention time of the solvent is 8 to 12 h. Preferably, the retention time can be 8 to 9 h, can be 9 to 11 h, or can be 11 to 12 h. In some specific embodiments, it is 8 h and 12 h.

[0063] According to the above-mentioned preparation method, in 2), the drying method is freeze-drying.

[0064] According to the above-mentioned preparation method, 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.

[0065] 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, can be 10-15 Pa, or can be 15-20 Pa. In certain specific embodiments, it is 8 Pa, 10 Pa, and 15 Pa.

[0066] According to the preparation method described above, the freeze-drying time is 48-72 h. Preferably, the freeze-drying time can be 48-54 h, can be 54-64 h, or can be 64-72 h. In certain specific embodiments, it is 72 h.

[0067] 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, can be 70-85 °C, or can be 85-100 °C. In certain specific embodiments, it is 60 °C and 80 °C.

[0068] According to the preparation method described above, in 1-2), 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 certain specific embodiments, it is 8 h, 10 h, and 12 h.

[0069] In the following embodiments of the present application, the acid-binding agent is propylene oxide, and the co-solvent is selected from lithium chloride.

[0070] In the following embodiments of the present application, the polyamide has the following repeating structural units:

[0071]

[0072] Example 1

[0073] In this example, a low dielectric constant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0074] 1) Dissolve the polyamide in N-methylpyrrolidone to prepare a 6 wt% solution, pour it into a mold, add deionized water, let it stand for 12 h, and continue to age for 24 h to obtain a gel.

[0075] 2) Perform 6 solvent exchanges on the gel obtained in 1) with tert-butanol, each time maintaining for 8 h, and then perform freeze-drying for 72 h under the conditions of a pressure of 15 Pa and a temperature of -45 °C to obtain a polyamide aerogel.

[0076] 3) Place the polyamide aerogel obtained in 2) in a tube furnace under a nitrogen atmosphere, set the heating rate to 2 °C / min, and conduct the following segmented heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 280 °C for 30 min, 300 °C for 30 min, 320 °C for 30 min, 350 °C for 30 min, and 380 °C for 60 min to obtain a low dielectric constant polybenzoxazole aerogel. The mass percentage of the low dielectric constant polybenzoxazole aerogel obtained in this example is 6 wt%.

[0077] Among them, the preparation method of the polyamide is as follows:

[0078] 1-1) Take 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride and add them to a three-necked flask. Then add lithium chloride, propylene oxide, and N-methylpyrrolidone, and conduct the first reaction at -6 °C for 1 h in a nitrogen atmosphere, and then conduct the second reaction at 20 °C for 12 h to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 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)-hexafluoropropane is 3.66 g.

[0079] 1-2) Pour the reaction product obtained in 1-1) into deionized water to obtain a solid precipitate. After filtration, vacuum dry at 60 °C for 8 h to obtain polyamide.

[0080] Perform infrared detection on the polyamide and the low dielectric constant polybenzoxazole aerogel. The results are shown in Figure 4 .

[0081] 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 hydroxyl groups, the peak at 1650 cm -1 is attributed to the C=O stretching vibration, the peak at 1511 cm -1 is attributed to the N-H bending vibration, and the above structures correspond to polyamide. After heat treatment of the polyamide, the hydroxyl characteristic peak disappears, and at the same time, new characteristic peaks appear. The peaks at 1621 and 1479 cm -1 are respectively attributed to the C=N stretching and bending vibrations, and the peaks at 1262 and 1049 cm -1 are respectively attributed to the C-O stretching and bending vibrations, indicating that after heat treatment, the molecular structure has changed, that is, the amide structure dehydrates to form an oxazole structure, and a low dielectric polybenzoxazole aerogel is successfully obtained.

[0082] The polyamide aerogel obtained in step 2) of Example 1 and the low-dielectric-constant polybenzoxazole aerogel obtained in step 3) were subjected to thermogravimetric detection. The specific operation steps were as follows:

[0083] a) Select the sample to be tested, weigh 3 - 5 mg, and record the accurate mass value.

[0084] b) Turn on the thermogravimetric analyzer, place the sample in the sample chamber of the thermogravimetric analyzer, and seal the chamber door to avoid external interference.

[0085] c) Conduct the test under nitrogen conditions. Set the heating rate to: 10 °C / min, and the temperature range to: 25 - 800 °C.

[0086] d) Start the thermogravimetric analyzer, start the heating program, and record the curve of mass change with temperature.

[0087] e) 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.

[0088] The analysis results of the thermogravimetric detection are shown in Table 1.

[0089] Table 1

[0090]

[0091] As can be seen from Table 1, the thermal stability of the low-dielectric-constant 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 529 °C, which is more than twice that of the polyamide aerogel; the temperature at which the material weight loss reaches 10% is 543 °C, which is more than one time that of the polyamide aerogel. In addition, the char residue rate of the low-dielectric-constant polybenzoxazole aerogel of this application is also significantly higher than that of the polyamide aerogel.

[0092] Taken together, it shows that the low-dielectric-constant polybenzoxazole aerogel of this application has excellent thermal stability.

[0093] Example 2

[0094] In this example, a low-dielectric-constant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0095] 1) Dissolve polyamide in N-methylpyrrolidone to prepare an 8 wt% solution, pour it into a mold, add deionized water, let it stand for 18 h, and continue to age for 36 h to obtain a gel.

[0096] 2) The gel obtained in 1) was subjected to 8 solvent exchanges with tert-butanol, each time for 10 h, and then freeze-dried for 72 h under the conditions of a pressure of 10 Pa and a temperature of -45 °C to obtain a polyamide aerogel.

[0097] 3) Place the polyamide aerogel obtained in 2) 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, 280 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 60 min, and 380 °C for 60 min to obtain a low dielectric constant polybenzoxazole aerogel. The mass percentage of the low dielectric constant polybenzoxazole aerogel obtained in this example is 8 wt%.

[0098] Among them, the preparation method of the polyamide is as follows:

[0099] 1-1) Take 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide, and N-methylpyrrolidone, and conduct the first reaction at -6 °C for 2 h under a nitrogen atmosphere, and then conduct the second reaction at 25 °C for 18 h to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 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)-hexafluoropropane is 3.66 g.

[0100] 1-2) Pour the reaction product obtained in 1-1) into deionized water to obtain a solid precipitate, filter it, and vacuum dry it at 80 °C for 10 h to obtain polyamide.

[0101] Example 3

[0102] In this example, a low dielectric constant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0103] 1) Dissolve the polyamide in N-methylpyrrolidone to prepare a 10 wt% solution, pour it into a mold, add deionized water, and let it stand for 24 h, and continue to age for 48 h to obtain a gel.

[0104] 2) Perform 8 solvent exchanges on the gel obtained in 1) with tert-butanol, each time maintaining for 12 h, and then conduct freeze-drying at a pressure of 8 Pa and a temperature of -50 °C for 72 h to obtain a polyamide aerogel.

[0105] 3) Place the polyamide aerogel obtained in 2) in a tubular furnace under a nitrogen atmosphere, set the heating rate at 5 °C / min, and conduct the following heat treatment: treat at 200 °C for 30 min, 250 °C for 30 min, 280 °C for 30 min, 300 °C for 60 min, 320 °C for 60 min, 350 °C for 60 min, and 380 °C for 60 min to obtain a low dielectric constant polybenzoxazole aerogel. In this example, the mass percentage of the obtained low dielectric constant polybenzoxazole aerogel is 10 wt%.

[0106] Among them, the preparation method of the polyamide is as follows:

[0107] 1-1) Take 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide, and N-methylpyrrolidone, and conduct the first reaction at -10 °C for 3 h in a nitrogen atmosphere, and then conduct the second reaction at 25 °C for 24 h to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 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)-hexafluoropropane is 3.66 g.

[0108] 1-2) Pour the reaction product obtained in 1-1) into deionized water to obtain a solid precipitate, filter it, and then dry it in vacuo at 80 °C for 12 h to obtain polyamide.

[0109] Example 4

[0110] The difference between this comparative example and Example 1 is that in step 3), no segmented heat treatment is carried out, but only the polyamide aerogel is directly heat-treated at 380 °C for 240 min, and the rest is the same as in Example 1.

[0111] Example 5

[0112] In this example, a low dielectric constant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0113] 1) Dissolve the polyamide in N-methylpyrrolidone to prepare a 6 wt% solution, pour it into a mold, add deionized water, let it stand for 12 h, and continue to age for 24 h to obtain a gel.

[0114] 2) Perform 6 solvent exchanges on the gel obtained in 1) with tert-butanol, each time maintaining for 8 h, and then conduct freeze-drying at a pressure of 15 Pa and a temperature of -45 °C for 72 h to obtain a polyamide aerogel.

[0115] 3) Place the polyamide aerogel obtained in 2) in a tube 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, 280 °C for 30 min, 300 °C for 30 min, 320 °C for 30 min, 350 °C for 30 min, and 380 °C for 60 min to obtain a low dielectric constant polybenzoxazole aerogel. In this example, the mass percentage of the obtained low dielectric constant polybenzoxazole aerogel is 6 wt%.

[0116] Among them, the preparation method of the polyamide is as follows:

[0117] 1-1) Take 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide, and N-methylpyrrolidone, and conduct the first reaction at -6 °C for 1 h in a nitrogen atmosphere, and then conduct the second reaction at 20 °C for 12 h to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 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)-hexafluoropropane is 3.66 g.

[0118] 1-2) Pour the reaction product obtained in 1-1) into deionized water to obtain a solid precipitate, filter it, and vacuum dry it at 60 °C for 8 h to obtain polyamide.

[0119] Example 6

[0120] In this example, a low dielectric constant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0121] 1) Dissolve the polyamide in N-methylpyrrolidone to prepare an 8 wt% solution, pour it into a mold, add deionized water, and let it stand for 18 h, and continue to age for 36 h to obtain a gel.

[0122] 2) Perform 8 solvent exchanges on the gel obtained in 1) with tert-butanol, each time maintaining for 10 h, and then conduct freeze-drying at a pressure of 10 Pa and a temperature of -45 °C for 72 h to obtain a polyamide aerogel.

[0123] 3) Place the polyamide aerogel obtained in 2) in a tubular 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, 280 °C for 30 min, 300 °C for 30 min, 320 °C for 60 min, 350 °C for 60 min, 380 °C for 60 min to obtain a low dielectric constant polybenzoxazole aerogel. In this example, the mass percentage of the obtained low dielectric constant polybenzoxazole aerogel is 8 wt%.

[0124] Among them, the preparation method of the polyamide is as follows:

[0125] 1-1) Take 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide and N-methylpyrrolidone, and carry out the first reaction at -6 °C for 2 h in a nitrogen atmosphere, and then carry out the second reaction at 25 °C for 18 h to obtain a reaction product. Among them, the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 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)-hexafluoropropane is 3.66 g.

[0126] 1-2) Pour the reaction product obtained in 1-1) into deionized water to obtain a solid precipitate, filter it and dry it in vacuo at 80 °C for 10 h to obtain polyamide.

[0127] Example 7

[0128] In this example, a low dielectric constant polybenzoxazole aerogel and its preparation method are provided, including the following steps:

[0129] 1) Dissolve the polyamide in N-methylpyrrolidone to prepare a 10 wt% solution, pour it into a mold, add deionized water and let it stand for 24 h, and continue to age for 48 h to obtain a gel.

[0130] 2) Perform 8 solvent exchanges on the gel obtained in 1) with tert-butanol, each time 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.

[0131] 3) Place the polyamide aerogel obtained in 2) in a tubular 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, 280 °C for 30 min, 300 °C for 60 min, 320 °C for 60 min, 350 °C for 60 min, and 380 °C for 60 min to obtain a low dielectric constant polybenzoxazole aerogel. In this example, the mass percentage of the obtained low dielectric constant polybenzoxazole aerogel is 10 wt%.

[0132] Among them, the preparation method of the polyamide is as follows:

[0133] 1-1) Take 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and terephthaloyl chloride and add them to a three-necked flask, then add lithium chloride, propylene oxide, and N-methylpyrrolidone, and carry out the first reaction at -10 °C for 3 h in 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 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, 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)-hexafluoropropane is 3.66 g.

[0134] 1-2) Pour the reaction product obtained in 1-1) into deionized water to obtain a solid precipitate, filter it, and dry it in vacuum at 80 °C for 12 h to obtain polyamide.

[0135] Comparative Example 1

[0136] The difference between this comparative example and Example 1 is that in step 3), segmented heat treatment is not carried out, but only the polyamide aerogel is directly heat-treated at 170 °C for 240 min, and the rest is the same as in Example 1. Finally, due to the extremely slow or non-closed-loop reaction, a low dielectric constant polybenzoxazole aerogel cannot be obtained.

[0137] Perform thermal conductivity detection, dielectric constant detection, specific surface area and porosity detection on the low dielectric constant polybenzoxazole aerogels obtained in Examples 1, 2, 3, 4 and Comparative Example 1.

[0138] 1) The specific operation steps for thermal conductivity detection are as follows:

[0139] a) Prepare an aerogel sample of a certain size (40 mm long and 20 mm wide);

[0140] b) Place the sample in a TC 3000 thermal conductivity measuring instrument to ensure that the test piece is completely covered;

[0141] c) Set the temperature parameter, conduct a thermal conductivity test on the sample, and obtain the thermal conductivity coefficient of the sample.

[0142] 2) The specific operation for dielectric constant detection is as follows:

[0143] a) Place the sample (diameter 20 mm, thickness 1 mm) into a Concept 40 type broadband dielectric spectrometer.

[0144] b) Set the test range to 10 - 10 7 Hz, conduct the test, and obtain the dielectric constant of the sample.

[0145] 3) Specific surface area detection and calculation of the shrinkage rate

[0146] Use a TriStar II 3flex type analyzer to detect the specific surface area of the low dielectric constant polybenzoxazole aerogels obtained in Examples 1, 2, 3, 4 and Comparative Example 1, and obtain the specific surface area of the sample.

[0147] Measure the dimensions of the aerogel sample before and after heat treatment, using the following formula:

[0148] Shrinkage rate = (dimension before heat treatment - dimension after heat treatment) / dimension before heat treatment

[0149] Calculate the shrinkage rate of the sample.

[0150] The specific results of the thermal conductivity coefficient, dielectric constant, specific surface area, porosity and shrinkage rate of Examples 1, 2, 3, 4 and Comparative Example 1 are shown in Table 2.

[0151] Table 2

[0152]

[0153] As can be seen from Table 2, the dielectric constant and thermal conductivity coefficient of the low dielectric constant polybenzoxazole aerogel obtained in this application are relatively low, the specific surface area is high, ranging from 171 to 188 m 2 / g, the porosity is high, ranging from 78% to 88%, and at the same time the shrinkage rate is low; while the comparative example cannot obtain a low dielectric constant polybenzoxazole aerogel. Therefore, the preparation method of this application can not only obtain polybenzoxazole aerogel, but also this polybenzoxazole aerogel has a relatively low dielectric constant and good heat insulation performance.

[0154] In addition, the dielectric constant of the low-dielectric-constant polybenzoxazole aerogel obtained in this application is 1.45 to 1.58, which is lower than that of the polyamide aerogel and also lower than that of the polybenzoxazole (PBO) film. Literature 1 (He Shuaijie. Preparation and Properties of Melamine-based Polyamide Aerogels [D]. Southwest University of Science and Technology, 2015.) discloses that the dielectric constant of the polyamide aerogel prepared from melamine and isophthaloyl chloride is 2.48; Literature 2 (Song Wan. Preparation and Properties of Low-dielectric-constant Polybenzoxazole [D]. Donghua University.) discloses that the dielectric constants of polybenzoxazole (PBO) films with different contents of branched structures are 2.27 to 2.59. These evidences indicate that the dielectric constant of the polybenzoxazole aerogel obtained in this application is not only much lower than that of the polyamide aerogel commonly used in the current prior art, but also lower than that of the low-dielectric-constant polybenzoxazole film containing branched structures.

[0155] Overall, the low-dielectric-constant polybenzoxazole aerogel of this application endows the aerogel material with the characteristics of low dielectric, heat insulation, high temperature resistance, ultra-light weight and excellent mechanical properties.

[0156] In summary, the low-dielectric-constant polybenzoxazole aerogel prepared in this application has a lower dielectric constant and better thermal stability. At the same time, the lowest thermal conductivity is 0.035 W / mK, showing good heat insulation performance. The pore size distribution of the low-dielectric-constant polybenzoxazole aerogel of this application is in the range of 10 to 100 nm, the specific surface area is 171 to 188 m 2 / g, the porosity is 78 to 88%, the thermal conductivity is 0.035 to 0.046 W / mK, the thermal stability is greater than 529 °C, and the dielectric constant is only 1.45 to 1.58. This aerogel material simultaneously has the characteristics of low dielectric, high temperature resistance, heat insulation, ultra-light weight and excellent mechanical properties.

[0157] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended 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 made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A low dielectric constant polybenzoxazole aerogel, characterized in that, The pore size distribution of the low dielectric constant polybenzoxazole aerogel is in the range of 10 to 100 nm, the specific surface area is 171 to 188 m 2 / g, the porosity is 78 to 88%, the dielectric constant is 1.45 to 1.58, and the low dielectric constant polybenzoxazole aerogel has the following repeating structural units: or; ; The low dielectric constant polybenzoxazole aerogel is prepared by converting a polyamide aerogel; The polyamide forms a polyamide aerogel by the sol-gel method, and then the polyamide aerogel is heat-treated to obtain the low dielectric constant polybenzoxazole aerogel; The reaction for forming the polyamide includes a first reaction stage and a second reaction stage; The temperature of the first reaction stage is -10 to -5 °C; The temperature of the second reaction stage is 15 to 25 °C; The heat treatment temperature is ≥ 200 °C; The time of the heat treatment is ≥ 240 min; The heating rate of the heat treatment is 2 to 5 °C / min.

2. The low dielectric constant polybenzoxazole aerogel according to claim 1, characterized in that, The thermal conductivity of the aerogel is 0.035 to 0.046 W / mK, and the thermal stability is greater than 500 °C.

3. The low dielectric constant polybenzoxazole aerogel according to claim 1, characterized in that, It includes one or more of the following characteristics: The polymerization monomers used to form the polyamide include 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and p / m-phthaloyl chloride; The polyamide is formed under a protective atmosphere; The polyamide is formed in an organic solvent; One or two of a co-solvent and an acid-binding agent are also used to form the polyamide.

4. The low dielectric constant polybenzoxazole aerogel according to claim 3, wherein The molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane to p / m-phthaloyl chloride is 0.01:(0.005 - 0.02); And / or, 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, 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane to p / m-phthaloyl chloride is (0.21 - 0.32):0.01:(0.005 - 0.02).

5. The low dielectric constant polybenzoxazole aerogel according to claim 1, characterized in that, The preparation method of the polyamide aerogel is: 1) The polyamide is aged in an organic solvent to obtain a gel; 2) The gel is subjected to solvent exchange and drying to obtain the polyamide aerogel.

6. The low dielectric constant polybenzoxazole aerogel according to claim 5, characterized in that, In 1), the organic solvent is selected from one or more of 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 h; And / or, in 2), the solvent for the solvent exchange is tert-butanol.

7. Use of the low dielectric constant polybenzoxazole aerogel according to any one of claims 1 to 6 as a low dielectric material or a thermal insulation material in aerospace or ships or radar radomes or buildings.

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