Crosslinked polyimide aerogel and normal-pressure drying preparation method thereof
Cross-linked polyimide aerogels were prepared by drying at normal pressure, using 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride as raw materials and 1,3,5-tris(4-aminophenoxy)benzene as a cross-linking agent. This solved the high cost and danger issues of traditional supercritical drying and achieved safe and low-cost large-scale production.
Patent Information
- Application Number
- CN202510683477.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-26
- Publication Date
- 2025-09-16
AI Technical Summary
The traditional preparation of cross-linked polyimide aerogels requires supercritical drying, which is expensive and dangerous, limiting their production and application.
Cross-linked polyimide aerogel was prepared using 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride as raw materials, through 1,3,5-tris(4-aminophenoxy)benzene cross-linking and atmospheric pressure drying, avoiding the supercritical drying process.
The difficulty and danger of preparation are reduced, large-scale production is achieved, and by strengthening the molecular skeleton to achieve volume shrinkage under normal pressure, the use of high-risk equipment is avoided.
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Figure CN120647939A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of polymer material synthesis, in particular to a cross-linked polyimide aerogel and a normal pressure drying preparation method thereof. Background Art
[0002] Cross-linked polyimide aerogels, a representative aromatic polyimide aerogel, possess superior high and low temperature resistance, hydrophobicity, and aging resistance, and have potential applications in high-tech fields such as aerospace, electronic information, and automotive manufacturing. However, the traditional preparation of cross-linked polyimide aerogels typically requires processes such as supercritical drying. Supercritical drying equipment is expensive and poses a high risk, limiting its production. Summary of the Invention
[0003] The present invention aims to provide a cross-linked polyimide aerogel and a method for preparing the same by drying at normal pressure, thereby reducing the difficulty of producing the cross-linked polyimide aerogel and providing a new approach for the preparation of the cross-linked polyimide aerogel.
[0004] In order to solve the above technical problems, the specific scheme adopted by the present invention is: a method for preparing a cross-linked polyimide aerogel by drying at normal pressure, using 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride as raw materials, cross-linking 1,3,5-tris(4-aminophenoxy)benzene to prepare a cross-linked polyimide, and then drying under normal pressure to obtain a cross-linked polyimide aerogel.
[0005] Preferably, the method comprises the following steps:
[0006] 1) dissolving 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride in N,N-dimethylformamide to obtain an N,N-dimethylformamide solution of anhydride group-terminated polyamic acid;
[0007] 2) Add 1,3,5-tris(4-aminophenoxy)benzene, acetic anhydride and pyridine to the N,N-dimethylformamide solution of the anhydride group-terminated polyamic acid, mix well and pour into a mold or lay a film on a stainless steel plate to obtain a wet gel;
[0008] 3) The wet gel is aged to remove N,N-dimethylformamide, and then dried at normal pressure to obtain a cross-linked polyimide aerogel.
[0009] Preferably, in step 1), N,N-dimethylformamide is first subjected to dehydration treatment, and the dehydration treatment method is: 4A type molecular sieve is heated at 10-15℃min -1The heating rates were maintained at 140-155° C. and 480-520° C. for 0.8-1.2 h and 2.8-3.2 h, respectively, and then N,N-dimethylformamide was filtered.
[0010] Preferably, in step 1), the molar ratio of 2,2'-dimethylbenzidine to 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10:(10.2-10.7); the total mass of 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride accounts for 9.5-10.5% of the mass of N,N-dimethylformamide.
[0011] Preferably, in step 1), 2,2'-dimethylbenzidine is first added to N,N-dimethylformamide, and mechanical stirring is used to ensure that 2,2'-dimethylbenzidine is fully dissolved, and then 3,3',4,4'-biphenyltetracarboxylic dianhydride is added in batches and stirred at 0°C for 5-7h to obtain an N,N-dimethylformamide solution of anhydride group-terminated polyamic acid.
[0012] Preferably, in step 2), the molar ratio of 1,3,5-tris(4-aminophenoxy)benzene to 2,2'-dimethylbenzidine is 10:(9.5-10.5); the amount of acetic anhydride added is 7.8-8 mL per 10 mmol of 2,2'-dimethylbenzidine, and the amount of pyridine added is 6.7-6.9 mL per 10 mmol of 2,2'-dimethylbenzidine.
[0013] Preferably, the aging time in step 3) is 22-25 hours.
[0014] Preferably, the method for removing N,N-dimethylformamide in step 3) is: performing multiple solvent replacements on the wet gel in n-hexane or ethanol to remove N,N-dimethylformamide.
[0015] Preferably, the temperature for drying under normal pressure in step 3) is 40-120° C., and the time for drying under normal pressure is 11-13 hours.
[0016] A cross-linked polyimide aerogel is prepared by adopting any of the above-mentioned normal pressure drying preparation methods for the cross-linked polyimide aerogel.
[0017] The TAB-crosslinked BPDA-DMBZ polyimide molecular structure prepared by the present invention presents a stronger molecular skeleton, thereby enabling volume shrinkage during normal pressure drying by strengthening the polyimide molecular skeleton, thereby eliminating the need for supercritical drying, reducing the difficulty of preparing the polyimide aerogel, lowering the risk factor of the preparation process, and enabling large-scale production.
[0018] The possible reasons why the TAB cross-linked BPDA-DMBZ type polyimide molecular structure prepared by the present invention exhibits a stronger molecular skeleton are as follows: 1) There is a flexible group ether bond in the ODA of the traditional TAB cross-linked BPDA-ODA type polyimide molecular structure, which weakens the rigidity of the molecular chain and thus exhibits a certain flexibility; 2) The methyl group of DMBZ in the TAB cross-linked BPDA-DMBZ type cross-linked polyimide has a certain steric effect, which can further strengthen its molecular skeleton. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 A synthetic route for preparing cross-linked polyimide aerogels using 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride;
[0020] Figure 2 This is the FTIR spectrum of the polyimide aerogel prepared at normal pressure of the present invention;
[0021] Figure 3 is a photograph of the polyimide aerogel prepared at normal pressure of the present invention;
[0022] Figure 4 This is a SEM electron microscope image of the polyimide aerogel prepared at normal pressure of the present invention;
[0023] Figure 5 These are photos of the polyimide aerogel (TAB cross-linked BPDA-DMBZ type polyimide) prepared by the normal pressure method based on 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride before and after drying (shrinkage rate is 31.2%).
[0024] Figure 6 The photos are of a polyimide aerogel (TAB cross-linked BPDA-ODA type polyimide) prepared based on 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride by the normal pressure method of the present invention before and after drying (shrinkage rate is 86.0%).
[0025] Figure 7 Schematic diagram of the repeating units of the molecular structure of the polyimide aerogel (TAB cross-linked BPDA-DMBZ type polyimide) prepared by the normal pressure method based on 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride of the present invention;
[0026] Figure 8 The diagram shows the molecular structure of a polyimide aerogel (TAB cross-linked BPDA-ODA type polyimide) prepared based on 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride by the normal pressure method of the present invention. DETAILED DESCRIPTION
[0027] like Figure 1 As shown, a method for preparing a cross-linked polyimide aerogel by drying at normal pressure of the present invention uses dianhydride 3,3',4,4'-biphenylcarboxylic dianhydride and diamine 2,2'-dimethylbenzidine as synthetic raw materials, and 1,3,5-triaminobenzene as a cross-linking agent, and obtains a cross-linked polyimide aerogel by drying at normal pressure. The technical solution of the present invention is described below through five embodiments:
[0028] Example 1
[0029] A method for preparing a cross-linked polyimide aerogel by drying at normal pressure in this embodiment includes the following steps:
[0030] 1) Dehydration of N,N-dimethylformamide using heat-treated 4A molecular sieve:
[0031] For 4A molecular sieve, the temperature was 10℃min -1 The heating rates were maintained at 150°C and 500°C for 1 h and 3 h, respectively, and then N,N-dimethylformamide was filtered using 4A molecular sieves.
[0032] 2) Add 10 mmol of 2,2'-dimethylbenzidine to N,N-dimethylformamide, and use mechanical stirring to ensure that 2,2'-dimethylbenzidine is fully dissolved. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride is added in batches and stirred at 0°C for 5-7h to obtain an N,N-dimethylformamide solution of anhydride group-terminated polyamic acid.
[0033] The molar amounts of 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride are 10.0 mmol and 10.5 mmol, respectively. The total mass of 2,2'-dimethylbenzidine and 3,3,4,4'-biphenyltetracarboxylic dianhydride accounts for 10 wt% of the total mass of N,N-dimethylformamide.
[0034] 3) After synthesizing the anhydride-terminated polyamic acid, 10.0 mmol of the cross-linking agent 1,3,5-tris(4-aminophenoxy)benzene was added and stirred for 2 min, followed by the addition of 7.9 mL of acetic anhydride and 6.8 mL of pyridine, which was stirred for 10 min. The mixture was poured into a mold or spread on a stainless steel plate to obtain a wet gel.
[0035] 4) After the wet gel was aged for 24 h, solvent replacement was performed in n-hexane or ethanol to remove N,N-dimethylformamide. The solvent replacement was repeated 10 times, each cycle lasting 12 h. The gel was then dried at 60° C. under normal pressure to obtain a cross-linked polyimide aerogel.
[0036] The FTIR spectrum, physical photograph, SEM electron microscope image, comparison photos before and after drying, and molecular structure diagram of the cross-linked polyimide aerogel prepared in this example are shown in Figures 2, 3, 4, 5, and 7, respectively.
[0037] Example 2
[0038] The preparation steps of this embodiment are basically the same as those of embodiment 1, except that in step 4) of this embodiment, drying is performed at 40° C. under normal pressure to obtain a cross-linked polyimide aerogel.
[0039] Example 3
[0040] The preparation steps of this embodiment are basically the same as those of embodiment 1, except that in step 4) of this embodiment, drying is performed at 80° C. under normal pressure to obtain a cross-linked polyimide aerogel.
[0041] Example 4
[0042] The preparation steps of this embodiment are basically the same as those of embodiment 1, except that in step 4) of this embodiment, drying is performed at 100° C. under normal pressure to obtain a cross-linked polyimide aerogel.
[0043] Example 5
[0044] The preparation steps of this embodiment are basically the same as those of embodiment 1, except that in step 4) of this embodiment, drying is performed at 120° C. under normal pressure to obtain a cross-linked polyimide aerogel.
[0045] Comparative Example
[0046] The preparation method of the comparative example is the same as that of Example 1, except that the raw materials used in the comparative example are 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride. The molecular structure diagram of the cross-linked polyimide aerogel prepared by the comparative example is shown in FIG. Figure 8 As shown, the comparison photos before and after drying are as follows Figure 6 shown.
[0047] In addition, the cross-linked polyimide aerogels prepared by drying at normal pressure at different temperatures in Examples 2-5 of the present invention have shrinkage rates of 48.0%, 42.2%, 52.3%, and 45.3% before and after drying, respectively, which are similar to the shrinkage rate of Example 1 and significantly lower than the shrinkage rate of 86.0% in the comparative example.
[0048] By comparing the molecular structures of two different cross-linked polyimide aerogels, it can be found that compared with the molecular structure of the traditional TAB cross-linked BPDA-ODA polyimide in the comparative example (such as Figure 8 As shown), the TAB cross-linked BPDA-DMBZ type polyimide molecular structure of Example 1 of the present invention (as shown Figure 7The results (shown in Figure 2) suggest a stronger molecular backbone, likely due to the following reasons: 1) The flexible ether bonds in the ODA molecular structure of TAB-crosslinked BPDA-ODA polyimide weaken the molecular chain rigidity, thereby exhibiting a certain degree of flexibility; 2) The methyl groups of DMBZ in TAB-crosslinked BPDA-DMBZ polyimide have a certain steric effect, further strengthening its molecular backbone. Based on this, the BPDA-DMBZ polyimide selected in this invention aims to achieve volume shrinkage during atmospheric pressure drying by strengthening the polyimide molecular backbone.
Claims
1. A method for preparing a cross-linked polyimide aerogel by drying at normal pressure, characterized in that: Cross-linked polyimide was prepared by cross-linking 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride with 1,3,5-tris(4-aminophenoxy)benzene, and then dried under normal pressure to obtain cross-linked polyimide aerogel.
2. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 1, wherein: The following steps are involved: 1) dissolving 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride in N,N-dimethylformamide to obtain an N,N-dimethylformamide solution of anhydride group-terminated polyamic acid; 2) Add 1,3,5-tris(4-aminophenoxy)benzene, acetic anhydride and pyridine to the N,N-dimethylformamide solution of the anhydride group-terminated polyamic acid, mix well and pour into a mold or lay a film on a stainless steel plate to obtain a wet gel; 3) The wet gel is aged to remove N,N-dimethylformamide, and then dried at normal pressure to obtain a cross-linked polyimide aerogel.
3. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: In step 1), N,N-dimethylformamide is first dehydrated by: treating 4A molecular sieve at 10-15℃min -1 The heating rates were maintained at 140-155° C. and 480-520° C. for 0.8-1.2 h and 2.8-3.2 h, respectively, and then N,N-dimethylformamide was filtered.
4. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: In step 1), the molar ratio of 2,2'-dimethylbenzidine to 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10:(10.2-10.7); the total mass of 2,2'-dimethylbenzidine and 3,3',4,4'-biphenyltetracarboxylic dianhydride accounts for 9.5-10.5% of the mass of N,N-dimethylformamide.
5. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: In step 1), 2,2'-dimethylbenzidine is first added to N,N-dimethylformamide, and mechanical stirring is used to ensure that 2,2'-dimethylbenzidine is fully dissolved. Subsequently, 3,3',4,4'-biphenyltetracarboxylic dianhydride is added in batches and stirred at 0°C for 5-7h to obtain an N,N-dimethylformamide solution of anhydride group-terminated polyamic acid.
6. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: In step 2), the molar ratio of 1,3,5-tris(4-aminophenoxy)benzene to 2,2'-dimethylbenzidine is 10:(9.5-10.5); the amount of acetic anhydride added is 7.8-8 mL per 10 mmol of 2,2'-dimethylbenzidine, and the amount of pyridine added is 6.7-6.9 mL per 10 mmol of 2,2'-dimethylbenzidine.
7. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: The aging time in step 3) is 22-25h.
8. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: The method for removing N,N-dimethylformamide in step 3) is: performing multiple solvent replacements on the wet gel in n-hexane or ethanol to remove N,N-dimethylformamide.
9. The method for preparing a cross-linked polyimide aerogel by drying at normal pressure according to claim 2, wherein: In step 3), the temperature for normal pressure drying is 40-120° C., and the time for normal pressure drying is 11-13 hours.
10. A cross-linked polyimide aerogel, characterized in that: The cross-linked polyimide aerogel is prepared by the normal pressure drying preparation method according to any one of claims 1 to 9.