Carborane-containing polyimide aerogel as well as preparation method and application thereof

Abstract

The invention belongs to the field of thermal protection, and particularly relates to carborane-containing polyimide aerogel as well as a preparation method and application thereof. A diamine monomer containing a carborane structure is introduced into polyimide aerogel, and the modified polyimide aerogel is obtained. The modified polyimide aerogel prepared by the invention has the characteristics of low shrinkage rate, low density and light weight, has excellent dimensional stability and good thermal shrinkage resistance in a 200 DEG C high-temperature environment, has further improved heat resistance, can be applied to heat prevention and insulation in a 400 DEG C or above high-temperature environment, and has wide application prospects. The method has important application value in thermal protection or thermal insulation systems of aerospace, equipment, medical treatment, reactors and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of thermal protection, and particularly relates to a carbon-containing borane polyimide aerogel and a preparation method and use thereof. BACKGROUND

[0002] Aerogel is a kind of low-density bulk material with a nanometer-structured skeleton and open pores, and has excellent properties such as low thermal conductivity, low density and high specific surface area. Polyimide aerogel has inherent properties of aerogel and unique thermal stability and excellent mechanical properties of polyimide, and has been widely used in thermal protection and thermal insulation applications in extreme environments. However, polyimide aerogel is prone to thermal shrinkage due to volume reduction and skeleton structure collapse at medium-high temperatures (200℃) far below its thermal decomposition temperature, which has been a long-standing problem and limits its application at high temperatures (Liu, C., et al., Double-Phase-Networking Polyimide Hybrid Aerogel with Exceptional Dimensional Stability for Superior Thermal Protection System. SMALL, 2024. 20(44.)).

[0003] Carborane is a stable cage structure rich in boron elements, which is widely used in fields such as organometallic chemistry, medicinal chemistry, and luminescent materials. The icosahedral cage structure of carborane is a super-conjugated aromatic structure with a large volume and high symmetry. This special conjugation and aromaticity make it have unique potential in improving the heat-oxidation stability of polymers. Currently, it has been used to enhance the thermal performance of various polymer systems. For example, Cui et al. synthesized a carborane-containing curing agent, and then synthesized a new heat-resistant phenolic epoxy resin adhesive that can withstand 500℃ high temperature for a short time [Cui, M., Zhang, L., Lou, P., et al. Study on Thermal Degradation Mechanism of Heat-Resistant Epoxy Resin Modified with Carboranes [J]. Polymer Degradation and Stability, 2020, 176: 109143.]; Goyal et al. successfully synthesized a high-temperature-resistant cyanate ester composite containing carborane, and the carbon residue rate increased from 0% to 82% compared with the original resin [Goyal, S., Forrester, M. J., Coverdell, D., et al. High-Temperature-Performance Cyanate Ester Composites with Carboranes [J]. Macromolecules, 2021, 54(19): 9155-9164.].

[0004] The pore structure stability of polyimide aerogel is poor under high temperature environment. At 200-300℃, the microstructure of aerogel fibers will change, which will cause changes in the structure of polyimide aerogel, and the pore structure will collapse, shrink, even break and pulverize, which limits its practical application in space exploration, long-term high-temperature environment and other scenarios. Therefore, it is urgent to solve the problem of pore structure collapse and volume shrinkage of polyimide aerogel in the temperature range of 200℃, to ensure the performance of polyimide aerogel under harsh conditions, and effectively play its heat-proof role at high temperature. SUMMARY

[0005] The present application belongs to the field of thermal protection, and specifically relates to a carborane-containing polyimide aerogel and a preparation method and application thereof. The present application unexpectedly found that the introduction of carborane can effectively reduce the volume shrinkage of polyimide aerogel near 200℃.

[0006] A functionally modified polyimide aerogel is made from the following raw materials by weight:

[0007] from 1 to 10 parts of a diamine monomer,

[0008] from 1 to 10 parts of a dianhydride monomer,

[0009] from 0.01 to 1 part of a crosslinking agent,

[0010] from 1 to 20 parts of a dehydrating agent,

[0011] from 1 to 20 parts of a catalyst;

[0012] said diamine monomer includes from 0.1 to 4 parts of a carborane diamine.

[0013] Preferably, it is made from the following parts by weight of raw materials:

[0014] from 1.8 to 3.3 parts of a diamine monomer,

[0015] from 3 to 4 parts of a dianhydride monomer,

[0016] from 0.08 to 0.1 part of a crosslinking agent,

[0017] from 8 to 9 parts of a dehydrating agent,

[0018] from 5 to 8 parts of a catalyst;

[0019] said diamine monomer includes from 0.2 to 1.1 parts of a carborane diamine.

[0020] Preferably, it is made from the following parts by weight of raw materials:

[0021] 2.59 parts of a diamine monomer,

[0022] 3.04 parts of a dianhydride monomer,

[0023] 0.1 part of a crosslinking agent,

[0024] 8.44 parts of a dehydrating agent,

[0025] 6.54 parts of a catalyst;

[0026] said diamine monomer includes 0.79 parts of a carborane diamine.

[0027] Preferably, said diamine monomer further includes at least one of 4,4'-diamino-2,2'-dimethyl-1,1 '-biphenyl, 4,4'-diaminodiphenyl ether;

[0028] and / or, said dianhydride monomer is selected from at least one of 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride;

[0029] and / or, said crosslinking agent is selected from 1,3,5-tris(4-aminophenoxy)benzene;

[0030] and / or, the dehydrating agent is selected from acetic anhydride;

[0031] and / or, the catalyst is selected from pyridine.

[0032] Preferably, the molar percentage of the carborane diamine in the diamine monomer is 10-15%.

[0033] Preferably, the molar percentage of the carborane diamine in the diamine monomer is 15%.

[0034] The present application also provides a preparation method of the functional modified polyimide aerogel described above, comprising the following steps:

[0035] Step 1, reacting the diamine monomer and the dianhydride monomer to obtain a carborane unit-containing polyamide acid solution;

[0036] Step 2, reacting the carborane unit-containing polyamide acid solution with a crosslinking agent, a dehydrating agent and a catalyst to obtain solution A;

[0037] Step 3, aging and freeze-drying solution A to obtain the functional modified polyimide aerogel.

[0038] Preferably, the solid content of the carborane unit-containing polyamide acid solution is 5wt%-7wt%; and the polymerization degree of the carborane unit-containing polyamide acid in the carborane unit-containing polyamide acid solution is 20-30.

[0039] Preferably, the solid content of the carborane unit-containing polyamide acid solution is 7wt%; and the polymerization degree of the carborane unit-containing polyamide acid in the carborane unit-containing polyamide acid solution is 30.

[0040] The present application also provides the use of the functional modified polyimide aerogel described above in the preparation and / or as a thermal protection material.

[0041] The present application introduces a diamine monomer containing a carborane structure to prepare a modified polyimide aerogel, which has the characteristics of low shrinkage, low density and light weight, and can improve the heat resistance of the polyimide aerogel, effectively solving the shrinkage problem of the polyimide aerogel at 200℃ high temperature, exhibiting excellent size stability and good heat shrinkage resistance in high temperature environment, and expanding the practical application prospect of the polyimide aerogel under harsh conditions.

[0042] Obviously, according to the above content of the present application, according to the ordinary technical knowledge and common means in the art, other various forms of modifications, replacements or changes can be made without departing from the above basic technical idea of the present application.

[0043] The above mentioned subject matter of the present application will be further explained in details by way of specific embodiments in the form of examples. However, it should not be construed that the scope of the above mentioned subject matter of the present application is limited to the following examples. Any technology realized based on the above mentioned subject matter of the present application falls within the scope of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 SEM image of Example 2.

[0045] Figure 2 SEM image of Example 4. DETAILED DESCRIPTION

[0046] In the following examples and experimental examples, the reagents and materials not specifically mentioned are commercially available.

[0047] Preparation of modified polyimide aerogel of Example 1

[0048] Step 1: Synthesis of aromatic carborane diamine (DNCB)

[0049] (1) Synthesis of decaborane-acetonitrile complex (B 10 H 12 (CH3CN)2)

[0050] The decaborane-acetonitrile complex was prepared by the following method: 50 g of decaborane was dissolved in excess anhydrous acetonitrile, and reacted at 80°C for 12 h. The reaction system was filtered to obtain white crystals, which were dried to obtain the decaborane-acetonitrile complex.

[0051] (2) Synthesis of 1,2-di(4-bromophenyl)-carborane (DPCB)

[0052] A 500 mL three-necked flask was equipped with a magnetic stirrer, a spherical condenser and a three-way adapter. 6.72 g (0.02 mol) of di(4-bromophenyl)acetylene, 2.02 g (0.01 mol) of B 10 H 12 (CH3CN)2 and 100 mL of toluene were added to the three-necked flask. After the addition was completed, the reaction system was vacuumed and back-flushed with nitrogen three times, and then reacted at 100°C under a magnetic stirring for 12 h. After the reaction was completed, the reaction system was filtered, and the filtrate was washed with saturated brine and methanol. After the solvent was removed by rotary evaporation under reduced pressure at 80 rpm, the product 1,2-di(4-bromophenyl)-carborane (DPCB) was obtained by recrystallization and vacuum drying at 80°C for 12 h.

[0053]

[0054] (3) Synthesis of aromatic carborane diamine (DNCB)

[0055] Into a three-necked flask was added 2.0 g (4.5 mmol) of 1,2-di(4-bromophenyl)- carborane, 1.1 g (9.4 mmol) of p-ethynylaniline, and 40 mg (2.1 mmol) of CuI. Vacuum was applied and purged with nitrogen three times. Then 50 mL of tetrahydrofuran and 50 mL of triethylamine were added under nitrogen protection, followed by 0.26 g (0.22 mmol) of Pd(PPh3)4, then sealed and stirred at 45 °C for 48 h. The resulting brown suspension was filtered, washed with saturated brine to remove impurities, and then rotary evaporated at 80 rpm to dryness, to obtain a black-brown product, which was an internal alkyne-containing aromatic carborane diamine (DNCB).

[0056]

[0057] Step 2: Preparation of modified polyimide aerogel

[0058] DNCB (0.5 g, 1.0 mmol), 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl (DMBZ) (1.9 g, 9.0 mmol) and DMAc (55 g) were placed in a three-necked flask equipped with electric stirring and nitrogen protection, and stirred at room temperature until the diamine was completely dissolved. After 20 min, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (3.0 g, 10.3 mmol) and 10 g of DMAc were added at 20 °C, and the mixture was stirred overnight under nitrogen atmosphere to obtain a polyamic acid (PAA) solution with a solid content of 7 wt% and a degree of polymerization of the polyamic acid of 30. Then 0.1 g of TAB (1,3,5-tris(4-aminophenoxy)benzene) was dissolved in DMAc solvent (7 g), which was added to the polyamic acid (PAA) solution. After stirring for 20 min for sufficient crosslinking, acetic anhydride (8.44 g) and pyridine (6.54 g) were added for chemical imidization reaction. Finally, the imidized PAA was stirred uniformly and poured into a φ 30 mm cylindrical silica gel mold, aged for 24 h, and then solvent exchanged. Tert-butyl alcohol was used as the exchange solvent, and DMAc was exchanged in the order of tert-butyl alcohol volume ratio of 25%, 75%, and 100%. The wet gel was exchanged every 12 h according to the order, and after the exchange was completed, the wet gel was placed in a freeze dryer for 48 h to obtain a modified polyimide aerogel with a DNCB to DMBZ molar ratio of 10:90, denoted as 10DNCB / PIA-D.

[0059]

[0060] Example 2 Preparation of modified polyimide aerogel

[0061] The modified polyimide aerogel 15DNCB / PIA-D was prepared according to the preparation method of Example 1, except that the molar ratio of DNCB to DMBZ was 15:85, and the specific amounts of raw materials DNCB and DMBZ were as shown in Table 1.

[0062] Preparation of modified polyimide aerogel of Example 3

[0063] The modified polyimide aerogel 10DNCB / PIA-N was prepared according to the preparation method of Example 1, except that NMP was used as the solvent in the synthesis of the PAA solution containing carborane units.

[0064] Preparation of modified polyimide aerogel of Example 4

[0065] The modified polyimide aerogel 15DNCB / PIA-N was prepared according to the preparation method of Example 3, except that the molar ratio of DNCB to DMBZ was 15:85, and the specific amounts of raw materials DNCB and DMBZ were as shown in Table 1.

[0066] The following is the preparation method of the control sample.

[0067] Preparation of polyimide aerogel of Comparative Example 1 (PIA-D)

[0068] The polyimide aerogel PIA-D was prepared according to the preparation method of Example 1, except that no DNCB was added.

[0069] Preparation of polyimide aerogel of Comparative Example 2 (PIA-N)

[0070] The polyimide aerogel PIA-N was prepared according to the preparation method of Example 3, except that no DNCB was added.

[0071] Table 1

[0072]

[0073] The technical solutions of the present application are further illustrated by experiments.

[0074] Experimental Example 1 Microscopic morphology of modified polyimide aerogel

[0075] I. Experimental method

[0076] The modified polyimide aerogels prepared in Example 2 (15DNCB / PIA-D) and Example 4 (15DNCB / PIA-N) were observed for their microscopic morphology using scanning electron microscopy (SEM).

[0077] II. Experimental results

[0078] Figure 1 、 Figure 2 Shown are SEM images of the modified PI aerogels prepared in Examples 2 and 4, respectively. The sample prepared using NMP as the solvent (Example 4) is composed of fiber bundles connected by small spheres, with nanometer-scale pores, exhibiting a typical three-dimensional nanoporous aerogel structure. Compared to the sample prepared using NMP as the solvent, the sample prepared using DMAc as the solvent (Example 2) exhibits larger pores overall, exhibiting a coral-like network structure with interlaced, coarse skeletons.

[0079] Experimental Example 2 Physical properties of modified polyimide aerogel

[0080] 1. Experimental Methods

[0081] The apparent density of the sample was calculated using the following formula:

[0082]

[0083] Where ρ is the apparent density of the sample in g / cm 3 ; The sample mass m is obtained by analytical balance test, the unit is g; a, b, c are the length, width and height of the sample, respectively, which are obtained by vernier caliper test, the unit is mm.

[0084] The sample will shrink to varying degrees during gel aging, solvent replacement, and drying, which will have a significant impact on the performance of the sample. The overall linear shrinkage of the sample is calculated using the following formula:

[0085]

[0086] Where S is the shrinkage rate of the sample, in %; L0 is the diameter of the mold, and L is the diameter of the sample, measured by a vernier caliper, in mm.

[0087] 2. Experimental Results

[0088] Table 2 shows the changes in linear shrinkage and apparent density during the preparation of modified polyimide aerogels prepared with two solvents. From the perspective of overall linear shrinkage, the shrinkage of samples prepared with both solvents showed a decreasing trend with the addition of DNCB. Among them, the overall shrinkage of samples prepared with NMP solvent gradually decreased from 22.55% to 13.86%, and the shrinkage of samples prepared with DMAc solvent decreased from 20.41% to 9.6% with the addition of DNCB. The density change was consistent with the shrinkage change trend. Combined with the SEM results, the introduction of the rigid cage structure of carborane caused the PI aerogel skeleton network to become thicker, the rigidity of the PI molecular chain increased, and the ability of the PI aerogel to resist shrinkage during the preparation stage was synergistically enhanced.

[0089] Overall, the shrinkage of the two solvent-prepared samples during the drying process remained a regular change closely related to the internal microstructure with the addition of carborane units. The shrinkage of Example 2 (15DNCB / PIA-D) was reduced by 50% compared to the comparative sample, with low shrinkage (9.6%), low density (0.083 g / cm 3 ), and light weight characteristics.

[0090] Table 2

[0091]

[0092]

[0093] Heat resistance of modified polyimide aerogels

[0094] I. Experimental method

[0095] The thermal decomposition temperature of the sample was tested by a TG209 thermal gravimetric analyzer. The initial mass of the sample was 3-8 mg, the test atmosphere was nitrogen, the test temperature was 35-800°C, and the heating rate was 10°C / min.

[0096] The thermal conductivity of the sample was characterized by a Hot Disk 2500S thermal constant analyzer, and the test temperature was 23°C.

[0097] The medium-high temperature resistance of the sample was tested in a 200°C oven, and the linear shrinkage of the test sample before and after 8h heat treatment at 200°C was tested.

[0098] II. Experimental results

[0099] Table 3 lists the comprehensive thermal properties of the modified polyimide aerogels. Among them, compared with the respective polyimide aerogel comparative sample, the initial decomposition temperature and the carbon residue mass fraction of each sample increase with the increase of DNCB content, which shows that the introduction of carborane structure has a significant positive effect on the improvement of the thermal stability of PI aerogel.

[0100] The room temperature thermal conductivity of the modified samples prepared by different solvents was tested, and it was found that the thermal conductivity of the NMP solvent sample decreased to 0.038 W / m.K with the increase of DNCB content, which was the same as the apparent density change trend. The DMAc solvent sample, due to the sacrifice of the heat insulation performance of the large-pore coral-like network structure, obtained the compensation of the introduction of DNCB, and maintained similar level of heat insulation performance with the pure sample.

[0101] The heat resistance of the modified samples at medium high temperature of 200 DEG C was tested, and the size shrinkage of the samples after heat treatment at 200 DEG C for 8h was measured to analyze the high temperature size stability. From the shrinkage monitoring, the heat shrinkage resistance of the modified samples was significantly improved. Among them, the sample prepared with DMAc as the solvent showed a significant downward trend in shrinkage rate with the addition of DNCB at medium high temperature of 200 DEG C. The shrinkage rate of 15DNCB / PIA-D(3.72%) was reduced by nearly 60% compared with PIA-D(9.32%). The sample prepared with NMP as the solvent was affected by the pore network structure at 200 DEG C, and the heat shrinkage resistance was lower than that of the sample prepared with DMAc as the solvent. Similarly, the high temperature size shrinkage rate was reduced with the introduction of carborane.

[0102] The above results show that the modified polyimide aerogel effectively improves the thermal performance of the polyimide aerogel. In the heat resistance test at medium high temperature of 200 DEG C, the modified polyimide aerogel has good heat shrinkage resistance.

[0103] Table 3

[0104]

[0105] In summary, by introducing the diamine monomer DNCB containing carborane structure, the modified polyimide aerogel has the characteristics of low shrinkage rate, low density and light weight, and can improve the heat resistance of the polyimide aerogel. The pore structure is stable at high temperature of 200 DEG C, has good heat shrinkage resistance and high temperature size stability, and can be widely used in the thermal protection system or heat insulation structure of aerospace vehicles, solar power stations, medical treatment and nuclear power fields.

Claims

1. A functionally modified polyimide aerogel, characterized in that: It is made from the following raw materials in parts by weight: 1-10 parts of diamine monomer, 1-10 parts of dianhydride monomer, Cross-linking agent 0.01-1 part, 1-20 parts of dehydrating agent, 1-20 parts of catalyst; The diamine monomer includes 0.1-4 parts of carborane diamine.

2. The functionally modified polyimide aerogel according to claim 1, characterized in that: It is made from the following raw materials in parts by weight: 1.8-3.3 parts of diamine monomer, 3-4 parts of dianhydride monomer, Cross-linking agent 0.08-0.1 parts, 8-9 parts of dehydrating agent, 5-8 parts of catalyst; The diamine monomer includes 0.2-1.1 parts of carborane diamine.

3. The functionally modified polyimide aerogel according to claim 1, characterized in that: The diamine monomer further comprises at least one of 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl and 4,4'-diaminodiphenyl ether; and / or, the dianhydride monomer is at least one selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and pyromellitic dianhydride; and / or, the cross-linking agent is selected from 1,3,5-tris(4-aminophenoxy)benzene; and / or, the dehydrating agent is selected from acetic anhydride; And / or, the catalyst is selected from pyridine.

4. The functionally modified polyimide aerogel according to claim 1 or 2, characterized in that: The mole percentage of the carborane diamine in the diamine monomer is 10-15%.

5. The functionally modified polyimide aerogel according to claim 4, characterized in that: The mole percentage of the carborane diamine in the diamine monomer is 15%.

6. The method for preparing the functionally modified polyimide aerogel according to any one of claims 1 to 5, characterized in that: The steps include: Step 1, reacting a diamine monomer and a dianhydride monomer to obtain a polyamic acid solution containing a carborane unit; Step 2, reacting a polyamic acid solution containing carborane units with a crosslinking agent, a dehydrating agent, and a catalyst to obtain a solution A; Step 3: aging and freeze-drying the solution A to obtain the functionally modified polyimide aerogel.

7. The preparation method according to claim 6, characterized in that: The solid content of the polyamic acid solution containing carborane units is 5wt% to 7wt%; the polymerization degree of the polyamic acid containing carborane units in the polyamic acid solution containing carborane units is 20 to 30.

8. The preparation method according to claim 7, characterized in that: The solid content of the polyamic acid solution containing carborane units is 7 wt %; the polymerization degree of the polyamic acid containing carborane units in the polyamic acid solution containing carborane units is 30.

9. Use of the functionally modified polyimide aerogel according to any one of claims 1 to 5 in the preparation and / or as a thermal protection material.

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