High-porosity fluorine-containing polyimide aerogel and preparation method thereof

Abstract

A preparation method of high-porosity fluorine-containing polyimide aerogel comprises the following steps: preparing a polyamide acid solution by taking a fluorine-containing diamine monomer TFMB, a fluorine-free aromatic diamine monomer ODA and a fluorine-containing dianhydride monomer 6FDA as raw materials, then adding triethylamine to prepare fluorine-containing polyamide acid salt, dissolving the fluorine-containing polyamide acid salt in a mixed solution of water and diphenyl ether, adding triethylamine and N, N-dimethylformamide, and stirring to obtain the high-porosity fluorine-containing polyimide aerogel. The preparation method comprises the following steps: preparing polyamide acid hydrogel from N, N-dimethyl cyclohexylamine, freeze-drying to obtain polyamide acid aerogel, and finally carrying out thermal imidization treatment to obtain the fluorine-containing polyimide aerogel. The aerogel is prepared from three monomers, is stable in structure, has a relatively high heat-resistant temperature, can maintain good performance at a high temperature, and has certain rigidity and strength, so that the aerogel is not easy to deform and structurally collapse under the action of external force. Under the process, the polyimide aerogel forms a high-porosity three-dimensional network structure, and has good heat insulation, sound insulation and other properties.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel materials, and in particular to a high-porosity fluorinated polyimide aerogel and a preparation method thereof. Background Art

[0002] Polyimides (PIs), a class of polymers containing a repeating imide ring (-CO-N-CO-) structure in their main molecular chain, are widely used in a wide range of fields, including aerospace, electronics, and automotive manufacturing, due to their excellent overall properties, including outstanding thermal stability, good mechanical properties, high chemical stability, and low dielectric constant. They are currently one of the most high-performance polymer materials. Traditionally, polyimides exist in the form of films, fibers, or molding compounds. With the advancement of materials science, new polyimide morphologies and aerogels have been explored.

[0003] With the growing demand for high-performance materials across various industries, the development of aerogels with specialized functions has become a research hotspot. For example, in the aerospace field, aerogel materials must not only be lightweight and thermally insulating, but also maintain stable performance in extreme environments. In the electronics field, aerogel materials are required to possess excellent electrical properties and thermal stability. Polyimide aerogel is a novel aerogel material with a polyimide backbone. It is formed by first preparing a wet polyimide gel via a sol-gel method, followed by supercritical drying to remove the liquid from the pores (retaining the air). Its structure is characterized by a nanoscale porous network with high porosity and low density. These properties give aerogels excellent thermal insulation, low sound propagation speed, and high specific surface area, demonstrating significant application potential in thermal insulation, sound absorption and noise reduction, and as catalyst supports.

[0004] Introducing fluorine atoms or fluorine-containing groups into the molecular structure of polyimide can significantly improve the performance of polyimide. Fluorine atoms have the characteristics of high electronegativity, small atomic radius, and large bond energy, which can give the material a lower dielectric constant, better chemical stability, thermal stability, and hydrophobicity. Combining the high porosity and low density characteristics of aerogels with the excellent performance of fluorinated polyimides, the high-porosity, low-density fluorinated polyimide aerogels developed have unique advantages in multiple fields. For example, in the aerospace field, its lightweight, heat-insulating and stable properties can be used in the thermal protection system of spacecraft; in electronic packaging, the low dielectric constant and good thermal stability help improve the performance and reliability of electronic devices.

[0005] However, the preparation of high-porosity, low-density fluorinated polyimide aerogels faces numerous technical challenges. For example, during the synthesis process, the polymerization reaction of the fluorinated monomer must be precisely controlled to avoid collapse of the aerogel structure due to an overly rapid or uneven reaction. Furthermore, during the aerogel molding process, maintaining high porosity and low density while ensuring a certain mechanical strength is also a major challenge. Summary of the Invention

[0006] The present invention aims to provide a high-porosity fluorinated polyimide aerogel having high porosity, low density, and excellent mechanical strength.

[0007] Another object of the present invention is to provide a method for preparing the polyimide aerogel, which effectively solves the problem of poor structural stability and easy collapse of the aerogel during the preparation process.

[0008] The purpose of the present invention is achieved through the following technical solutions: A high-porosity fluorinated polyimide aerogel is characterized by preparing a polyamic acid solution using a fluorinated diamine monomer 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB), a non-fluorinated aromatic diamine monomer bis(4-aminophenyl) ether (ODA), and a fluorinated dianhydride monomer 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) as raw materials, adding triethylamine to the polyamic acid solution to prepare a fluorinated polyamic acid salt, dissolving the fluorinated polyamic acid salt in a mixture of water and diphenyl ether, then adding triethylamine and N,N-dimethylcyclohexylamine to prepare a polyamic acid hydrogel, freeze-drying to obtain the polyamic acid aerogel, and finally performing a thermal imidization treatment to obtain the aerogel.

[0009] Furthermore, the molar ratio of TFMB, ODA and 6FDA is 0.5-0.8:0.5-0.2:1, and the solid content of the prepared polyamic acid solution is 12-20%.

[0010] Furthermore, the polar solvent is any one of DMF, DMAC, NMP, DMSO and THF.

[0011] Furthermore, the molar ratio of the sum of the fluorine-containing diamine monomer and the non-fluorine-containing aromatic diamine monomer to triethylamine used in the polyamic acid solution is 0.8-1.3:1.

[0012] Furthermore, in the process of preparing the polyamic acid hydrogel, the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether and fluorinated polyamic acid salt is 10:1: 0.4-0.7: 1-2: 0.8-1.2.

[0013] Furthermore, the freeze drying is performed at 5-10 Pa and -65 to -55° C. for 48 to 55 hours to obtain the polyamic acid aerogel.

[0014] Furthermore, thermal imidization is to heat the polyamic acid aerogel to 90~110℃ at 1~2℃ / min, keep it warm for 50~60min, then heat it to 180~220℃ at 3~5℃ / min, keep it warm for 50~60min, then heat it to 350~380℃ at 0.5~1℃ / min, keep it warm for 60~80min, so that the polyimide acid is dehydrated and condensed to form polyimide, and then cool it down to 25~40℃ at 2~4℃ / min.

[0015] A method for preparing a high-porosity fluorinated polyimide aerogel is characterized by: preparing a polyamic acid solution using a fluorinated diamine monomer TFMB, a non-fluorinated aromatic diamine monomer ODA, and a fluorinated dianhydride monomer 6FDA as raw materials; adding triethylamine TEA to the polyamic acid solution to prepare a fluorinated polyamic acid salt; dissolving the fluorinated polyamic acid salt in a mixture of water and diphenyl ether (DPE); adding triethylamine and N,N-dimethylcyclohexylamine (DMCHA) to prepare a polyamic acid hydrogel; freeze-drying to obtain the polyamic acid aerogel; and finally performing a thermal imidization treatment to obtain the fluorinated polyimide aerogel.

[0016] Furthermore, the molar ratio of TFMB, ODA and 6FDA is 0.5-0.8:0.5-0.2:1, and the solid content of the prepared polyamic acid solution is 12-20%.

[0017] Furthermore, the polar solvent is any one of DMF, DMAC, NMP, DMSO and THF.

[0018] Furthermore, the molar ratio of the sum of the fluorine-containing diamine monomer and the non-fluorine-containing aromatic diamine monomer used in the polyamic acid solution to triethylamine is 0.8-1.3:1.

[0019] Furthermore, in the process of preparing the polyamic acid hydrogel, the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether and fluorinated polyamic acid salt is 10:1: 0.4~0.7: 1~2: 0.8~1.2.

[0020] In the process of preparing fluorinated polyimide aerogel, due to the electron-withdrawing effect of fluorine and the steric hindrance of the fluorinated groups, the reaction rate fluctuates greatly, the cross-linking density of the gel grid is not high, the uniformity is poor, and the structural stability is low. In the subsequent thermal imidization process, stress distribution imbalance causes structural collapse, and the mechanical strength of the prepared aerogel is significantly reduced.

[0021] In addition, triethylamine reacts with polyamic acid to form a salt. Triethylamine can also act as a catalyst for cyclization during the thermal imidization process, accelerating the dehydration of PAA. During the sol-gel process, triethylamine, as a linear aliphatic amine, is hindered in diffusion within the PAA sol, which can lead to differences in surface concentration (high) and internal concentration (low), causing PAA chain aggregation. This thermal imidization process can lead to poor uniformity in the gel network structure, easily causing stress concentration and reducing the mechanical strength of the aerogel. The present invention adds a composite catalyst of DMCHA and triethylamine. The composite catalyst contains a cyclohexyl ring structure, has stronger molecular rigidity, and a more stable diffusion rate. It can form a synergistic effect of "fast diffusion + uniform distribution" with triethylamine. Triethylamine quickly neutralizes the carboxyl groups on the surface of the sol, promotes the slow penetration of DMCHA into the interior for uniform neutralization, reduces local agglomeration, and makes the obtained gel network structure more uniform. A certain amount of diphenyl ether is also added in the sol-gel stage. The hydrophobic benzene ring of diphenyl ether can interact with the ethyl chain of triethylamine through van der Waals forces, reduce the local concentration gradient of triethylamine, and inhibit the uneven shrinkage of the gel caused by solvent volatilization. The low polarity of diphenyl ether can balance the interaction between the hydrophobic segments (such as fluorinated groups and aromatic rings) in polyamic acid salts and the polar solvent (water), weakening the excessive aggregation of the hydrophobic segments, promoting the uniform entanglement of the molecular chains, and forming a more regular gel network; during thermal imidization, under the regulation of diphenyl ether, the boiling point difference between triethylamine and DMCHA prolongs the catalytic cyclization reaction in the imidization process while not destroying the porous structure of the aerogel, thereby improving the uniformity of thermal stress distribution.

[0022] Furthermore, the freeze drying is performed at 5-10 Pa and -65 to -55° C. for 48 to 55 hours to obtain the polyamic acid aerogel.

[0023] Furthermore, thermal imidization is to heat the polyamic acid aerogel to 90~110℃ at 1~2℃ / min, keep it warm for 50~60min, then heat it to 180~220℃ at 3~5℃ / min, keep it warm for 50~60min, then heat it to 350~380℃ at 0.5~1℃ / min, keep it warm for 60~80min, so that the polyimide acid is dehydrated and condensed to form polyimide, and then cool it down to 25~40℃ at 2~4℃ / min.

[0024] A method for preparing a high-porosity fluorinated polyimide aerogel, characterized by comprising the following steps: (1) Preparation of fluorinated polyamic acid solution: The fluorine-containing diamine monomer TFMB and the non-fluorine-containing aromatic diamine monomer ODA are dissolved in a polar solvent under a nitrogen atmosphere to obtain a light yellow solution with a solid content of 12-20 wt%, and the fluorine-containing dianhydride monomer 6FDA is used as a raw material; the solution is continuously stirred for 2 h at a temperature of 0-10 °C under a nitrogen atmosphere, and then stirred for 6-8 h at a temperature of 10-25 °C to obtain a colorless and transparent polyamic acid solution, wherein the molar ratio of the TFBM, ODA and 6DA is 0.5-0.8:0.5-0.2:1, and the polar solvent is any one of DMF, DMAC, NMP, DMSO and THF; (ii) Preparation of fluorine-containing polyamic acid salt Triethylamine is added to the polyamic acid solution to react to form a fluorine-containing polyamic acid salt, and after the reaction is completed, the fluorine-containing polyamic acid salt is precipitated into deionized water and collected to obtain a filamentous or blocky solid, which is freeze-dried to obtain a fluorine-containing polyamic acid salt solid, the freeze-drying temperature is -65 to -56 °C, the pressure is 5-10 Pa, the freeze-drying time is 48-55 h, and the molar ratio of the total amount of the fluorine-containing diamine monomer and the non-fluorine-containing aromatic diamine monomer to triethylamine used in the polyamic acid solution is 0.8-1.3:1; (iii) Preparation of aerogel (a) The fluorine-containing polyamic acid salt prepared in step (ii) is added to a mixed solution of water and diphenyl ether, and then triethylamine and N,N-dimethylcyclohexylamine are added, and a polyamic acid hydrogel is obtained by sol-gel transformation through standing for 18-24 h, wherein the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether and fluorine-containing polyamic acid salt is 10:1:0.4-0.7:1-2:0.8-1.2; (b) The polyamic acid hydrogel is freeze-dried to obtain a polyamic acid aerogel, and finally a fluorine-containing polyimide aerogel is obtained by thermal imidization, wherein the freeze-drying is carried out at a pressure of 5-10 Pa and a temperature of -65 to -55 °C for 48-55 h to obtain a polyamic acid aerogel; (c) The thermal imidization is carried out by heating the polyamic acid aerogel to 90-110 °C at a rate of 1-2 °C / min, holding for 50-60 min, then heating to 180-220 °C at a rate of 3-5 °C / min, holding for 50-60 min, and then heating to 350-380 °C at a rate of 0.5-1 °C / min, holding for 60-80 min, to make the polyimide acid dehydrate and condense to form a polyimide, and then cooling to 25-40 °C at a rate of 2-4 °C / min.

[0025] The application slowly rises to the low-temperature section in the thermal imidization process, volatilizes the residual solvent and physically adsorbed water, and avoids the condensation skeleton from shrinking due to rapid weight loss. Then, the application rapidly rises to the medium-temperature section, and the PAA molecular chain is cyclized under the synergistic catalysis of triethylamine and DMCHA, the gel skeleton is gradually hardened, finally, the application slowly rises to the high-temperature section, the diphenyl ether effectively maintains the fluidity of the reaction system, further promotes the cyclization reaction, and forms a stable polyimide network structure, so that the mechanical properties of the aerogel are improved, and the residual stress in the aerogel is removed, in the process, the catalysis time of the cyclization reaction is effectively prolonged through the boiling point temperature difference between triethylamine and DMCHA and the specific imidization step regulation.

[0026] The application has the following technical effects: The aerogel prepared from the three monomers has stable structure, high heat resistance, good performance at high temperature, certain rigidity and strength, and is not easy to deform and collapse under external force. Under the process, the polyimide aerogel forms a three-dimensional network structure with high porosity, has good heat insulation and sound insulation properties, and has good resistance to acid, alkali, organic solvents and other chemicals, and can maintain stable performance in complex chemical environment. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Fig. 1 is a micro-morphology diagram of the aerogel prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0028] Figure 2 Fig. 3 is a thermogravimetric spectrum of the polyimide aerogel prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0029] Figure 3 Fig. 5 is a comparison of the density calculation results of the polyimide aerogel prepared in Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0030] The application will be specifically described below by examples, and it is necessary to point out here that the following examples are only used to further illustrate the application, and cannot be understood as limiting the protection scope of the application, and the person skilled in the art can make some non-essential improvements and adjustments to the application according to the above application content.

[0031] Example 1 A preparation method of a high-porosity fluorine-containing polyimide aerogel, comprising the following steps: (1) preparing a fluorine-containing polyamide acid solution: Under a nitrogen atmosphere, a fluorinated diamine monomer TFMB, a non-fluorinated aromatic diamine monomer ODA, and a fluorinated dianhydride monomer 6FDA were dissolved in a polar solvent DMAC to obtain a light yellow solution with a solid content of 16 wt%. The mixture was stirred at 5°C for 2 hours and then at 20°C for 7 hours under a nitrogen atmosphere to obtain a colorless and transparent polyamic acid solution. The molar ratio of TFBM, ODA, and 6FDA was 0.6:0.6:1. (2) Preparation of fluorinated polyamic acid salt Triethylamine TEA and N,N-dimethylcyclohexylamine DMCHA are added to a polyamic acid solution to react to generate a fluorinated polyamic acid salt. After the reaction is completed, the fluorinated polyamic acid salt is precipitated into deionized water and collected to obtain a filamentous or blocky solid, which is freeze-dried to obtain a fluorinated polyamic acid salt solid. The freeze-drying temperature is -60°C, the pressure is 8 Pa, and the freeze-drying time is 50 h. The molar ratio of the sum of the fluorinated diamine monomer and the non-fluorinated aromatic diamine monomer used in the polyamic acid solution to triethylamine is 1:1. (3) Preparation of aerogel (a) adding the fluorinated polyamic acid salt prepared in step (2) as a precursor to a mixture of water and diphenyl ether, then adding triethylamine and N,N-dimethylcyclohexylamine, and allowing to stand for 20 hours to undergo sol-gel conversion to obtain a polyamic acid hydrogel, wherein the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether, and fluorinated polyamic acid salt is 10:1:0.5:1.5:1; (b) The polyamic acid hydrogel is freeze-dried to obtain a polyamic acid aerogel, and finally thermally imidized to obtain a fluorinated polyimide aerogel, wherein the freeze-drying is performed at 6 Pa and -60°C for 48 to 55 hours to obtain the polyamic acid aerogel; (c) Thermal imidization is to heat the polyamic acid aerogel to 100°C at a rate of 1.5°C / min, keep it warm for 55 minutes, then heat it to 200°C at a rate of 2°C / min, keep it warm for 55 minutes, and then heat it to 360°C at a rate of 1°C / min, keep it warm for 70 minutes to dehydrate and condense the polyimide acid to form polyimide, and then cool it down to 30°C at a rate of 3°C / min.

[0032] CK group: Compared with Example 1, the difference is that in the sol-gel preparation process of step (iii), only triethylamine is added, and DPE and DMCHA are not added. The remaining steps are the same as those of Example 1.

[0033] Comparative Example 1 Compared with Example 1, the difference is that hexamethylenediamine is used instead of DMCHA in the sol-gel preparation process in step (iii), and the remaining steps are the same as those in Example 1.

[0034] Comparative Example 2 Compared with Example 1, the difference is that in the process of preparing the aerogel, NMP is used instead of diphenyl ether in step (a) to participate in the sol-gel conversion, and the remaining steps are the same as those in Example 1.

[0035] Figure 1 Figures 2 and 3 show the microstructures of aerogels prepared in Example 1 and various comparative examples. The aerogels prepared in the present invention exhibit a uniform, non-collapsed pore structure and a continuous skeleton. However, the aerogels in the CK group exhibited significant collapse, lacking a fully formed pore structure and a continuous skeleton. In Comparative Example 1, the use of hexamethylenediamine instead of DMCHA disrupted the catalytic equilibrium, leading to uncontrollable reaction rates and a collapsed aerogel structure. In Comparative Example 2, the substitution of diphenyl ether for NMP resulted in an inability to effectively control the reaction progress during thermal imidization, resulting in an unsatisfactory aerogel structure.

[0036] like Figure 2 As shown in the thermogravimetric spectra of each aerogel, it can be seen that the thermal decomposition temperature of the CK group aerogel is the lowest at 440°C, while the thermal decomposition temperature of Comparative Example 1 is 490°C, and the decomposition rate is the fastest. The thermal decomposition temperature of the aerogels prepared in Example 1 and Comparative Example 2 is the highest at 570°C, but as the temperature increases, the decomposition rate of Comparative Example 2 is faster, indicating that the aerogel prepared in Example 1 has excellent thermal stability and high temperature resistance.

[0037] The mechanical properties of the aerogels prepared in the CK group, Example 1, Comparative Example 1 and Comparative Example 2 were tested for compressive strength, Young's modulus and other mechanical properties, and the thermal conductivity and water adsorption rate of the aerogels were tested. The results are shown in Table 1.

[0038] Table 1:

[0039] The higher the porosity and density of the aerogel, the more serious the attenuation of the mechanical properties of the aerogel will be. Figure 3 As shown in the table above, the CK group has the highest density, which is 345.7 mg / cm 3 Although its density is high, due to the collapse of the microscopic pore structure of the gel and the discontinuous skeleton, there are a large number of defects inside it, and the mechanical strength is significantly reduced. Its compressive strength is only 1.8MPa, and its thermal conductivity is also relatively high. The density of the aerogels in Comparative Examples 1 and 2 is lower than that of the CK group, the porosity increases, and the thermal conductivity also decreases to a certain extent, but the mechanical properties also decrease accordingly. The density of the aerogel in Example 1 of the present invention is 61.2mg / cm 3, forming a high-porosity, low-density aerogel structure with a thermal conductivity as low as 0.022W / m·K. At the same time, due to maintaining a continuous skeleton, the structure and distribution of microscopic pores are effectively adjusted, which significantly improves the mechanical properties of the aerogel, with the compressive strength increased to 2.6MPa and the compressive Young's modulus reaching 50MPa.

[0040] Example 2 A method for preparing a high-porosity fluorinated polyimide aerogel comprises the following steps: (1) Preparation of fluorinated polyamic acid solution: Under a nitrogen atmosphere, a fluorinated diamine monomer TFMB, a non-fluorinated aromatic diamine monomer ODA, and a fluorinated dianhydride monomer 6FDA were dissolved in a polar solvent DMF to obtain a light yellow solution with a solid content of 12 wt%. The mixture was stirred at 10°C for 2 h and then at 10°C for 6 h under a nitrogen atmosphere to obtain a colorless and transparent polyamic acid solution, wherein the molar ratio of TFBM, ODA, and 6FDA was 0.5:0.5:1. (2) Preparation of fluorinated polyamic acid salt Triethylamine is added to a polyamic acid solution to react and generate a fluorinated polyamic acid salt. After the reaction is completed, the fluorinated polyamic acid salt is precipitated into deionized water and collected to obtain a filamentous or blocky solid, which is freeze-dried to obtain a fluorinated polyamic acid salt solid. The freeze-drying temperature is -65°C, the pressure is 10 Pa, and the freeze-drying time is 48 hours. The molar ratio of the sum of the fluorinated diamine monomer and the non-fluorinated aromatic diamine monomer used in the polyamic acid solution to the triethylamine is 0.8:1. (3) Preparation of aerogel (a) adding the fluorinated polyamic acid salt prepared in step (2) as a precursor to a mixture of water and diphenyl ether, then adding triethylamine and N,N-dimethylcyclohexylamine, and allowing to stand for 18 hours to undergo sol-gel conversion to obtain a polyamic acid hydrogel, wherein the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether, and fluorinated polyamic acid salt is 10:1:0.4:1:0.8; (b) freeze-drying the polyamic acid hydrogel to obtain a polyamic acid aerogel, and finally thermally imidizing the polyamic acid hydrogel to obtain a fluorinated polyimide aerogel, wherein the freeze-drying step is performed at 5 Pa and -55°C for 55 hours to obtain the polyamic acid aerogel; (c) Thermal imidization is to heat the polyamic acid aerogel to 110°C at a rate of 1°C / min, keep it warm for 50 minutes, then heat it to 220°C at a rate of 3°C / min, keep it warm for 50 minutes, and then heat it to 380°C at a rate of 1°C / min, keep it warm for 60 minutes to dehydrate and condense the polyimide acid to form polyimide, and then cool it down to 40°C at a rate of 2°C / min.

[0041] The density of the aerogel prepared in this example is 62.7 mg / cm 3 , thermal conductivity is 0.024W / m·K, its compressive strength is 2.5MPa, and the compression Young's modulus reaches 51MPa.

[0042] Example 3 A method for preparing a high-porosity fluorinated polyimide aerogel comprises the following steps: (1) Preparation of fluorinated polyamic acid solution: Under a nitrogen atmosphere, a fluorinated diamine monomer TFMB, a non-fluorinated aromatic diamine monomer ODA, and a fluorinated dianhydride monomer 6FDA were dissolved in a polar solvent DMAC to obtain a pale yellow solution with a solid content of 12-20 wt%. The mixture was stirred at 0°C for 2 hours and then at 25°C for 8 hours under a nitrogen atmosphere to obtain a colorless and transparent polyamic acid solution. The molar ratio of TFBM, ODA, and 6FDA was 0.8:0.2:1. (2) Preparation of fluorinated polyamic acid salt Triethylamine is added to a polyamic acid solution to react and generate a fluorinated polyamic acid salt. After the reaction is completed, the fluorinated polyamic acid salt is precipitated into deionized water and collected to obtain a filamentous or blocky solid, which is freeze-dried to obtain a fluorinated polyamic acid salt solid. The freeze-drying temperature is -56°C, the pressure is 5 Pa, and the freeze-drying time is 55 hours. The molar ratio of the sum of the fluorinated diamine monomer and the non-fluorinated aromatic diamine monomer used in the polyamic acid solution to the triethylamine is 1.3:1. (3) Preparation of aerogel (a) adding the fluorinated polyamic acid salt prepared in step (2) as a precursor to a mixture of water and diphenyl ether, then adding triethylamine and N,N-dimethylcyclohexylamine, and allowing to stand for 24 hours to undergo sol-gel conversion to obtain a polyamic acid hydrogel, wherein the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether, and fluorinated polyamic acid salt is 10:1:0.7:2:1.2; (b) freeze-drying the polyamic acid hydrogel to obtain a polyamic acid aerogel, and finally thermally imidizing the polyamic acid hydrogel to obtain a fluorinated polyimide aerogel, wherein the freeze-drying step is performed at 10 Pa and -65°C for 48 hours to obtain the polyamic acid aerogel; (c) Thermal imidization is to heat the polyamic acid aerogel to 90°C at a rate of 2°C / min, keep it warm for 60 minutes, then heat it to 180°C at a rate of 5°C / min, keep it warm for 60 minutes, and then heat it to 350°C at a rate of 0.5°C / min, keep it warm for 80 minutes to dehydrate and condense the polyimide acid to form polyimide, and then cool it down to 25°C at a rate of 4°C / min.

[0043] The density of the aerogel prepared in this example is 63.6 mg / cm 3, thermal conductivity is 0.025W / m·K, its compressive strength is 2.8MPa, and the compression Young's modulus reaches 47MPa.

Claims

1. A high-porosity fluorinated polyimide aerogel, characterized by: A polyamic acid solution was prepared using the fluorinated diamine monomer 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB), the non-fluorinated aromatic diamine monomer bis(4-aminophenyl) ether (ODA), and the fluorinated dianhydride monomer 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) as raw materials. Triethylamine was added to the polyamic acid solution to prepare a fluorinated polyamic acid salt. The fluorinated polyamic acid salt was dissolved in a mixture of water and diphenyl ether, and triethylamine and N,N-dimethylcyclohexylamine were added to prepare a polyamic acid hydrogel. The polyamic acid aerogel was obtained by freeze-drying and finally subjected to thermal imidization treatment.

2. The method for preparing a high-porosity fluorinated polyimide aerogel according to claim 1, wherein: The molar ratio of TFMB, ODA and 6FDA is 0.5-0.8:0.5-0.2:1, and the solid content of the prepared polyamic acid solution is 12-20%.

3. The method for preparing a high-porosity fluorinated polyimide aerogel according to claim 1 or 2, wherein: The molar ratio of the sum of the fluorine-containing diamine monomer and the non-fluorine-containing aromatic diamine monomer used in the polyamic acid solution to triethylamine is 0.8-1.3:

1.

4. The method for preparing a high-porosity fluorinated polyimide aerogel according to any one of claims 1 to 3, wherein: In the process of preparing the polyamic acid hydrogel, the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether and fluorine-containing polyamic acid salt is 10:1:0.4-0.7:0.1-0.2:0.8-1.

2.

5. The method for preparing a high-porosity fluorinated polyimide aerogel according to any one of claims 1 to 4, characterized in that: The freeze drying is carried out at 5-10 Pa and -65--55° C. for 48-55 hours to obtain the polyamic acid aerogel.

6. The method for preparing a high-porosity fluorinated polyimide aerogel according to claim 5, wherein: Thermal imidization is to heat the polyamic acid aerogel to 90~110℃ at 1~2℃ / min, keep it warm for 50~60min, then heat it to 180~220℃ at 3~5℃ / min, keep it warm for 50~60min, then heat it to 350~380℃ at 0.5~1℃ / min, keep it warm for 60~80min, so that the polyimide acid is dehydrated and condensed to form polyimide, and then cool it down to 25~40℃ at 2~4℃ / min.

7. A method for preparing a high-porosity fluorinated polyimide aerogel, characterized in that: The steps include: (1) Preparation of fluorinated polyamic acid solution: Under a nitrogen atmosphere, a fluorinated diamine monomer TFMB, a non-fluorinated aromatic diamine monomer ODA, and a fluorinated dianhydride monomer 6FDA are dissolved in a polar solvent as raw materials to obtain a light yellow solution with a solid content of 12-20 wt%; under a nitrogen atmosphere, stirring is continued at a temperature of 0-10°C for 2 hours, and then at a temperature of 10-25°C for 6-8 hours to obtain a colorless and transparent polyamic acid solution, wherein the molar ratio of the TFBM, ODA, and 6DA is 0.5-0.8:0.5-0.2:1, and the polar solvent is any one of DMF, DMAC, NMP, DMSO, and THF; (2) Preparation of fluorinated polyamic acid salt Triethylamine is added to a polyamic acid solution to react and generate a fluorinated polyamic acid salt. After the reaction is completed, the fluorinated polyamic acid salt is precipitated into deionized water and collected to obtain a filamentous or blocky solid, which is freeze-dried to obtain a fluorinated polyamic acid salt solid. The freeze-drying temperature is -65 to -56°C, the pressure is 5 to 10 Pa, and the freeze-drying time is 48 to 55 hours. The molar ratio of the sum of the fluorinated diamine monomer and the non-fluorinated aromatic diamine monomer used in the polyamic acid solution to triethylamine is 0.8 to 1.3:

1. (3) Preparation of aerogel (a) adding the fluorinated polyamic acid salt prepared in step (2) as a precursor to a mixture of water and diphenyl ether, then adding triethylamine and N,N-dimethylcyclohexylamine, and allowing to stand for 18 to 24 hours to undergo sol-gel conversion to obtain a polyamic acid hydrogel, wherein the mass ratio of water, triethylamine, N,N-dimethylcyclohexylamine, diphenyl ether, and fluorinated polyamic acid salt is 10:1:0.4-0.7:0.1-0.2:0.8-1.2; (b) freeze-drying the polyamic acid hydrogel to obtain a polyamic acid aerogel, and finally thermally imidizing the polyamic acid hydrogel to obtain a fluorinated polyimide aerogel, wherein the freeze-drying step is performed at 5-10 Pa and -65 to -55° C. for 48 to 55 hours to obtain the polyamic acid aerogel; (c) Thermal imidization is to heat the polyamic acid aerogel to 90~110℃ at a rate of 1~2℃ / min, keep it warm for 50~60min, then heat it to 180~220℃ at a rate of 3~5℃ / min, keep it warm for 50~60min, then heat it to 350~380℃ at a rate of 0.5~1℃ / min, keep it warm for 60~80min, so that the polyimide acid is dehydrated and condensed to form polyimide, and then cool it down to 25~40℃ at a rate of 2~4℃ / min.

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