CN111925524B - Flexible high-temperature-resistant polyimide precursor gel, preparation method and application thereof, and polyimide flexible honeycomb structure - Google Patents

Flexible high-temperature-resistant polyimide precursor gel, preparation method and application thereof, and polyimide flexible honeycomb structure Download PDF

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CN111925524B
CN111925524B CN202010841950.2A CN202010841950A CN111925524B CN 111925524 B CN111925524 B CN 111925524B CN 202010841950 A CN202010841950 A CN 202010841950A CN 111925524 B CN111925524 B CN 111925524B
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polyimide precursor
precursor gel
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周宏伟
王成杨
童程霞
王大明
赵晓刚
陈春海
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Jilin University
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Abstract

The invention provides a flexible high-temperature-resistant polyimide precursor gel, a preparation method and application thereof, and a polyimide flexible honeycomb structure, and belongs to the technical field of 3D printing materials. In the invention, the polyimide precursor is polyamic acid which has a repeating unit with a structure of formula 1 or formula 2; the main chain of the molecule contains aromatic groups, and the polyimide precursor gel has a high-rigidity structure, so that the high-temperature resistance of the polyimide precursor gel is integrally improved; pendant group CF3The introduction of the structure or the sulfone group structure can reduce the regularity of the chain segment, so that the chain segment has certain melt processing performance at high temperature, and the effect of interlayer melting of the printing structure in the subsequent thermal curing process is met; the introduction of the siloxane chain segment fundamentally realizes the flexibility and resilience of the honeycomb structure. Meanwhile, the repeating unit of the invention contains multiple hydrogen bonds, pi-pi accumulation and coordination bonds, and the three components act together to realize the gelation of the polyimide precursor.

Description

Flexible high-temperature-resistant polyimide precursor gel, preparation method and application thereof, and polyimide flexible honeycomb structure
Technical Field
The invention relates to the technical field of 3D printing materials, in particular to a flexible high-temperature-resistant polyimide precursor gel, a preparation method and application thereof, and a polyimide flexible honeycomb structure.
Background
The honeycomb structure has the advantages of higher specific strength and specific modulus, good fatigue resistance and shock resistance and the like, and is favored by aviation and aerospace world since the past. With the development of aerospace craft towards high speed and high performance, the aerospace craft is required to have better mechanical property, lower density and thermal stability at high temperature (more than 300 ℃). Currently commercialized honeycomb products include: metallic aluminum honeycomb, Nomex paper honeycomb, Kevler paper honeycomb and the like, but the high temperature resistance is poor, and the use requirement of resisting more than 300 ℃ can not be met.
Polyimide is an aromatic heterocyclic polymer containing an imide ring in a repeating structural unit, is a high polymer material with highest heat-resistant grade and highest bulk strength applied in the industrial field so far, and a honeycomb structure made of polyimide is expected to meet the strong requirements of the fields of aerospace, rail transit, electronics and the like on high-temperature high-strength light structures.
The traditional polyimide forming methods include mould pressing, injection molding, casting film forming and the like, but the forming methods cannot manufacture the polyimide honeycomb with a complex structure. Emerging 3D printing technology of the polymer has high designability and high degree of freedom, and documents report that rigid high-temperature-resistant polyimide with different structures, strengths and temperature resistances can be obtained by adopting a 3D printing method of the polymer through methods such as photocuring and thermocuring. However, with the expansion of the exploration range and the field of aircrafts in the fields of aerospace and the like, the light honeycomb structure with the flexible characteristic and the high-temperature resistance has a new application prospect in aviation and space exploration, and for example, in parts such as low-temperature tank insulation, fan engine shells, antenna substrates, pneumatic aerodynamic speed reducers and the like, a flexible high-resilience high-temperature-resistant honeycomb structure needs to be adopted, but no report about a polyimide structure prepared into a flexible honeycomb structure by 3D printing is found in the current literature report.
Disclosure of Invention
In view of the above, the present invention aims to provide a flexible high temperature resistant polyimide precursor gel, and a preparation method and an application thereof. The polyimide precursor gel provided by the invention has good flexibility and high temperature resistance, and can be used as 3D printing gel ink to prepare a flexible and high temperature resistant polyimide honeycomb structure.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a flexible high-temperature-resistant polyimide precursor gel, wherein the polyimide precursor is polyamic acid which has a repeating unit with a structure shown in a formula 1 or a formula 2:
Figure BDA0002641748410000021
the ratio of k to t in formula 1 and formula 2 is independently 100: (1-10);
r in formula 1 and formula 21Independently is
Figure BDA0002641748410000022
Figure BDA0002641748410000023
One of (1);
R2independently is
Figure BDA0002641748410000024
Wherein m, n and p are independently 1-50;
the number average molecular weight of the polyamic acid is 5000-50000.
Preferably, the temperature of the flexible high-temperature-resistant polyimide precursor gel is-14 to-10 ℃.
The invention provides a preparation method of the flexible high-temperature-resistant polyimide precursor gel, which comprises the following steps:
(1) mixing aromatic diamine, first tertiary amine and a polar solvent, and carrying out a first condensation salt-forming reaction to obtain a first condensation salt-forming reaction product;
(2) mixing the first condensation salt-forming reaction product with siloxane-containing diamine and aromatic dianhydride to carry out condensation polymerization reaction to obtain a condensation polymerization reaction product;
(3) mixing the polycondensation reaction product with tertiary amine to perform a second polycondensation salt forming reaction to obtain a second polycondensation salt forming reaction product;
(4) adding a first metal coordination bond generator into the second condensation salt-forming reaction product, performing first standing, then adding a second metal coordination bond generator, and performing second standing to obtain a polyimide precursor;
(5) cooling the polyimide precursor to-14 to-10 ℃ at a cooling rate of 10-20 ℃/min to obtain flexible high-temperature-resistant polyimide precursor gel;
the aromatic diamine is 2- (4-aminophenyl) -5-aminobenzoxazole, 2, 5-bis (4-aminophenyl) pyrimidine or 2- (4-aminophenyl) -5-aminobenzimidazole;
the aromatic dianhydride is 4,4 ' - (hexafluoroisopropylidene) diphthalic anhydride or 3,3 ', 4,4 ' -diphenyl sulfone tetracarboxylic dianhydride;
the siloxane-containing diamine has a structure represented by formula 3:
Figure BDA0002641748410000031
in the formula 3, m, n and p are independently 1-50;
the first tertiary amine and the second tertiary amine are independently one or more of trimethylamine, tripropylamine, triisopropylamine, tri-N-butylamine, triethanolamine, tetramethylethylenediamine, diethylethanolamine, N-ethyldiethanolamine, N-methylazesopropane, N-methylazetidine, N-methylpiperidine, N dimethylcyclohexylamine, dimethylpiperazine and N, N-dimethylaniline.
Preferably, the polar solvent is one or more of N, N-dimethylformamide, N-dimethylacetamide, N-diethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, water, dimethyl sulfone, butyrolactone and caprolactone;
the first coordination metal bond generator and the second coordination metal bond generator are independently one or more of Mg salt, Ca salt and divalent Fe salt.
Preferably, the molar ratio of the sum of the aromatic diamine and the siloxane-containing diamine to the aromatic dianhydride is (0.9-1.2): 1;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1 (0.01-0.1).
Preferably, the mass ratio of the aromatic dianhydride to the polar solvent is 1 (2-10);
the molar ratio of the aromatic dianhydride to the first tertiary amine is 1: (0.03-1);
the molar ratio of the aromatic dianhydride to the second tertiary amine is 1: (0.02-1);
the molar ratio of the aromatic dianhydride to the first metal coordinate bond generator is 1: (0.0003 to 0.03);
the molar ratio of the aromatic dianhydride to the second metal coordinate bond generator is 1: (0.0002 to 0.02).
Preferably, the temperature of the first condensation salt forming reaction is 18-22 ℃, and the time is 1-5 h;
the temperature of the polycondensation reaction is 30-50 ℃, and the time is 0.5-2 h;
the temperature of the second condensation salt forming reaction is 5-10 ℃, and the time is 3-5 h.
Preferably, the first standing temperature is 0-2 ℃, and the time is 5-10 hours;
and the second standing temperature is 10-12 ℃, and the time is 4-6 h.
The invention provides application of the flexible high-temperature-resistant polyimide precursor gel as 3D printing gel ink.
The invention provides a polyimide flexible honeycomb structure which is prepared by a 3D printing method from the flexible high-temperature-resistant polyimide precursor gel;
the room temperature resilience of the polyimide flexible honeycomb structure is 20-90%, and the 300 ℃ resilience is 30-90%.
The invention provides a flexible high-temperature-resistant polyimide precursor gel, wherein the polyimide precursor is polyamic acid which has a repeating unit with a structure shown in a formula 1 or a formula 2; the molecular main chain of the invention contains bulky side group dianhydride, hydrogen bond and pi-pi stacking structure, the thickness between molecular chains and the thickness of a crystal region are adjusted by the combined action of the bulky side group dianhydride, the hydrogen bond and the pi-pi stacking structure, and the high elasticity and the flexibility of the honeycomb structure in the out-of-plane direction can be realized; the invention introduces the side-containing CF3Aromatic dianhydride structure of structure or sulfone group structure capable of reducing chain segmentThe regularity of the printing structure enables the printing structure to have certain melt processing performance at high temperature, thereby meeting the effect of interlayer melting of the printing structure in the subsequent thermocuring process; on the other hand, the large-volume side group ensures that the gel material has larger molecular chain movement capacity and chain rotation capacity, and establishes a foundation for realizing flexibility and resilience. The introduction of the siloxane chain segment fundamentally realizes the flexibility and resilience of the honeycomb structure.
Moreover, the main chain of the molecule of the polyimide precursor gel contains aromatic groups, and the polyimide precursor gel has a high-rigidity structure, so that the high-temperature resistance of the polyimide precursor gel is integrally improved; meanwhile, the repeating unit of the invention contains multiple hydrogen bonds, pi-pi accumulation and coordination bonds, the three components act together to realize the gelation of the polyimide precursor, and the obtained polyimide precursor gel has high and low temperature viscosity thixotropy (viscosity)RTViscosity60℃＞103). The example results show that the gel viscosity of the polyimide precursor provided by the inventionRTViscosity60℃＞103The temperature resistance can reach more than 300 ℃, and the printing precision is good when the ink is used as gel ink for 3D printing.
The invention provides a preparation method of flexible high-temperature-resistant polyimide precursor gel, which is simple to operate and can be used for large-scale and batch production.
The invention provides application of the flexible high-temperature-resistant polyimide precursor gel as 3D printing gel ink, and the flexible high-temperature-resistant polyimide precursor gel has good printing precision when being used as the 3D printing gel ink.
The invention provides a polyimide flexible honeycomb structure which is prepared from the flexible high-temperature-resistant polyimide precursor gel by a 3D printing method. The polyimide honeycomb structure provided by the invention has good flexibility and high temperature resistance, and the room temperature resilience can reach 90%, and the 300 ℃ resilience can reach 90%.
Drawings
FIG. 1 is an infrared spectrum of a flexible, high temperature resistant polyimide precursor gel prepared in examples 1-5;
FIG. 2 is a physical representation of a polyimide honeycomb prepared in example 1;
FIG. 3 is a compression test curve of the polyimide honeycomb prepared in example 1.
Detailed Description
The invention provides a flexible high-temperature-resistant polyimide precursor gel, wherein the polyimide precursor is polyamic acid which has a repeating unit with a structure shown in a formula 1 or a formula 2:
Figure BDA0002641748410000051
Figure BDA0002641748410000061
in the invention, the ratio of k to t in the formula 1 and the formula 2 is independently 100 (1-10); preferably 100 (3-7);
in the present invention, R in formula 1 and formula 21Independently is
Figure BDA0002641748410000062
Figure BDA0002641748410000063
One of (1);
R2independently is
Figure BDA0002641748410000064
Wherein m, n and p are independently 1-50, preferably 10-40;
in the invention, the molecular weight of the polyamic acid is 5000-50000, preferably 10000-30000.
In the present invention, the repeating unit is preferably of the following structure:
(1)
Figure BDA0002641748410000065
said R1Is composed of
Figure BDA0002641748410000071
R2Is composed of
Figure BDA0002641748410000072
The number average molecular weight of the polyamic acid is 5000-50000.
(2)
Figure BDA0002641748410000073
R1Is composed of
Figure BDA0002641748410000074
R2Is composed of
Figure BDA0002641748410000075
The number average molecular weight of the polyamic acid is 5000-50000.
(3)
Figure BDA0002641748410000076
Said R1Is composed of
Figure BDA0002641748410000077
Said R2Is composed of
Figure BDA0002641748410000078
The number average molecular weight of the polyamic acid is 5000-50000.
(4)
Figure BDA0002641748410000081
Said R1Is composed of
Figure BDA0002641748410000082
Said R2Is composed of
Figure BDA0002641748410000083
The number average molecular weight of the polyamic acid is 5000-50000.
(5)
Figure BDA0002641748410000084
Said R1Is composed of
Figure BDA0002641748410000085
Said R2Is composed of
Figure BDA0002641748410000086
The number average molecular weight of the polyamic acid is 5000-50000.
In the invention, the temperature of the flexible high-temperature-resistant polyimide precursor gel is preferably-14 to-10 ℃, and more preferably-12 ℃.
The main chain of the molecule of the invention contains aromatic groups, has a high-rigidity structure, and integrally improves the high-temperature resistance of the polyimide precursor gel. The invention introduces the side-containing CF3The aromatic dianhydride structure with the structure or the sulfone group structure can reduce the regularity of a chain segment and ensure that the chain segment has certain melt processing performance at high temperature, thereby meeting the effect of interlayer melting of a printing structure in the subsequent thermocuring process; on the other hand, the large-volume side group ensures that the gel material has larger molecular chain movement capacity and chain rotation capacity, and establishes a foundation for realizing flexibility and resilience.
Siloxane segments of the invention
Figure BDA0002641748410000091
The flexibility and resilience of the honeycomb structure are realized fundamentally. Because the siloxane chain segment is copolymerized and introduced in the polyimide main chain structure, the number average molecular weight of partial repeating units of the siloxane chain segment reaches 1000-5000, and the crosslinking points (benzimide ring) are greatly reduced) Thereby achieving high elongation of the material body. In the process of converting the performance of the polyimide precursor gel material body into the performance of the honeycomb structure, a nonlinear but exponential evolution law appears, namely the elongation of the polyimide and the flexibility/elasticity of the polyimide 3D printing honeycomb are in an exponential relationship. The ratio of k to t in the control repeat unit is 100: (1-10), the elasticity of the honeycomb structure can be greatly improved, so that the honeycomb structure has certain resilience; when the siloxane segment is incorporated in an excessively high amount, the heat resistance of the honeycomb as a whole is greatly affected. According to the invention, a small amount of polysiloxane is introduced to greatly improve the toughness of the honeycomb, because a large amount of hydrogen bonds in the polyimide precursor gel and the polysiloxane have synergistic effect, after the honeycomb is prepared into a three-dimensional structure, in an out-of-plane direction (namely Z-axis direction), the intermolecular strong force caused by the hydrogen bonds influences the chain segment spacing, and the introduction of the siloxane phase region not only improves the size and thickness of a crystal region, but also further increases the thickness of an amorphous region and reduces the orientation of the out-of-plane direction.
The repeating unit contains multiple hydrogen bonds among molecular chains, pi-pi accumulation among the benzimidazole rings and coordination bonds among polyamic acid carboxyl and coordination ions, and the three components act together to realize the gelation of the polyimide precursor; the polyimide precursor-polyamic acid contains intermolecular hydrogen bonds of N-H.O.C, so that the polyimide precursor-polyamic acid has high bonding energy (20-40 kJ/mol), and meanwhile, due to existence of a high-molecular-weight polyimide precursor repetitive structural unit, intermolecular multiple hydrogen bonds can be formed. In the invention, the benzimidazole, benzoxazole or benzopyrimidine structure in the aromatic diamine can form intermolecular hydrogen bond and has no space distortion structure. In the invention, intermolecular forces such as hydrogen bonds, pi-pi interaction, molecular steric hindrance and the like provide more possibility for self-organization behavior between molecules, so that molecular chains can be stacked and assembled at a higher level, and the gelation process can realize high controllability and high responsiveness along with external stimulation. Such as planar structures with smaller dihedral angles of the benzamides, are more favorable for hydrogen bonding. For polyimide precursor, under the action of rigid skeleton, pi-pi stacking mode and hydrogen bondResponse mode along with external stimulus. While utilizing-NH contained in the molecular chain2and-COOH polar groups, and the good gel thixotropy is obtained by adding metal ions, so that 3D printing is realized, photocuring is avoided, and a flexible and high-temperature-resistant polyimide honeycomb structure is prepared.
The invention provides a preparation method of the flexible high-temperature-resistant polyimide precursor gel, which comprises the following steps:
(1) mixing aromatic diamine, first tertiary amine and a polar solvent, and carrying out a first condensation salt-forming reaction to obtain a first condensation salt-forming reaction product;
(2) mixing the first condensation salt-forming reaction product with siloxane-containing diamine and aromatic dianhydride to carry out condensation polymerization reaction to obtain a condensation polymerization reaction product;
(3) mixing the polycondensation reaction product with tertiary amine to perform a second polycondensation salt forming reaction to obtain a second polycondensation salt forming reaction product;
(4) adding a first coordination bond generator into the second condensation salt-forming reaction product, performing first standing, then adding a second coordination bond generator, and performing second standing to obtain a polyimide precursor;
(5) and cooling the polyimide precursor to-14 to-10 ℃ at a cooling rate of 20 ℃/min to obtain the polyimide precursor gel.
Unless otherwise specified, the starting materials used in the present invention are commercially available. In the present invention, the molar ratio of the sum of the aromatic diamine and the siloxane-containing diamine to the aromatic dianhydride is preferably (0.9 to 1.2): 1, more preferably (1 to 1.1): 1;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is preferably 1 (0.01-0.1), more preferably 1: (0.04-0.08);
the mass ratio of the aromatic dianhydride to the polar solvent is preferably 1 (2-10), more preferably 1: (4-8);
the molar ratio of the aromatic dianhydride to the first tertiary amine is preferably 1: (0.03 to 1), more preferably 1: (0.1 to 0.5);
the molar ratio of the aromatic dianhydride to the second tertiary amine is preferably 1: (0.02 to 1), more preferably 1:0.05 to 0.5);
the molar ratio of the aromatic dianhydride to the first coordinate bond generator is preferably 1: (0.0003 to 0.03), more preferably 1: (0.001-0.02);
the molar ratio of the aromatic dianhydride to the second coordinate bond generator is preferably 1: (0.0002 to 0.02), more preferably 1: (0.001-0.01).
According to the invention, aromatic diamine, first tertiary amine and a polar solvent are mixed to carry out a first condensation salt forming reaction to obtain a first condensation salt forming reaction product. In the present invention, the aromatic diamine is 2- (4-aminophenyl) -5-aminobenzoxazole, 2, 5-bis (4-aminophenyl) pyrimidine or 2- (4-aminophenyl) -5-aminobenzimidazole. The first tertiary amine is one or more of trimethylamine, tripropylamine, triisopropylamine, tri-N-butylamine, triethanolamine, tetramethylethylenediamine, diethylethanolamine, N-ethyldiethanolamine and the like, N-methylazaisopropane, N-methylazetidine, N-methylpiperidine, N dimethylcyclohexylamine, dimethylpiperazine and N, N-dimethylaniline. The polar solvent is preferably one or more of N, N-dimethylformamide, N-dimethylacetamide, N-diethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, water, dimethyl sulfone, butyrolactone and caprolactone.
The invention does not require any particular mixing means, such as stirring, known to the person skilled in the art. In the invention, the temperature of the first condensation salt forming reaction is preferably 18-22 ℃, and more preferably 20 ℃; the time is preferably 1 to 5 hours, and more preferably 2 to 4 hours. The first polycondensation salification reaction is preferably carried out in a nitrogen atmosphere; in the invention, the first polycondensation salt forming reaction is preferably carried out under the condition of stirring, and the stirring speed is preferably 100-500 rpm, and more preferably 200-400 rpm. In the invention, the first tertiary amine has a complexing effect, and in the first condensation salt forming process, the first tertiary amine and the aromatic diamine are completely salified.
After the first condensation salt forming reaction is finished, the first condensation salt forming reaction product is mixed with siloxane-containing diamine and aromatic dianhydride to carry out condensation polymerization reaction, and a condensation polymerization reaction product is obtained. In the invention, the aromatic dianhydride is 4,4 ' - (hexafluoroisopropylidene) diphthalic anhydride or 3,3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride; the siloxane-containing diamine has a structure represented by formula 3:
Figure BDA0002641748410000111
in the formula 3, m, n and p are independently 1-50, preferably 20-40, and more preferably 25-35. In the present invention, the siloxane-containing diamine is a both-terminal reactive polysiloxane diamine, and the number average molecular weight thereof is preferably > 1000, and more preferably 3000 to 5000. In the present invention, the siloxane-containing diamine is preferably one or more selected from DMS-A15, A21, A31 and A32 of Gelest corporation, and X-22-161B, X-22-161A, KF-8010 and KF-8008 of Japan shin-Etsu corporation.
According to the invention, preferably, siloxane-containing diamine is added into the first condensation salt-forming reaction product, and after stirring for 0.5-2 h, the aromatic dianhydride is added in three times uniformly. In the invention, the stirring speed is preferably 100-500 rpm, more preferably 200-400 rpm; in the invention, the interval time of adding the aromatic dianhydride each time is preferably 5-60 min.
The invention starts to heat to the polycondensation reaction temperature after the aromatic dianhydride is added completely. In the invention, the temperature of the polycondensation reaction is preferably 30-50 ℃, and more preferably 40 ℃; in the present invention, the heating rate of the heating to the polycondensation temperature is preferably 10 ℃/min, and the polycondensation reaction time is calculated from the time when the temperature reaches the polycondensation reaction temperature, and in the present invention, the polycondensation reaction time is preferably 0.5 to 2 hours, and more preferably 1 to 1.5 hours. The present invention preferably performs the polycondensation reaction under a nitrogen atmosphere; in the invention, the polycondensation reaction is preferably carried out under the condition of stirring, and the stirring speed is preferably 100-500 rpm, more preferably 200-400 rpm. In the invention, siloxane diamine, salified aromatic diamine and aromatic dianhydride are subjected to polycondensation reaction to obtain a polyamide acid structure polycondensed into salt.
After the polycondensation reaction is finished, the polycondensation reaction product is mixed with tertiary amine to carry out a second polycondensation salt-forming reaction, and a second polycondensation salt-forming reaction product is obtained. In the invention, the second tertiary amine is one or more of trimethylamine, tripropylamine, triisopropylamine, tri-N-butylamine, triethanolamine, tetramethylethylenediamine, diethylethanolamine, N-ethyldiethanolamine and the like, N-methylazesopropane, N-methylazetidine, N-methylpiperidine, N-dimethylcyclohexylamine, dimethylpiperazine and N, N-dimethylaniline.
The present invention does not require any particular mixing means, and mixing means known to those skilled in the art may be used. In the invention, the temperature of the second condensation salt forming reaction is preferably 5-10 ℃, and more preferably 6-8 ℃; in the present invention, the cooling rate from the polycondensation reaction temperature to the second polycondensation salt formation reaction is preferably 10 ℃/min; according to the invention, preferably, after the temperature is reduced to the second polycondensation salt-forming reaction temperature, the second tertiary amine is added to carry out the second polycondensation salt-forming reaction. In the invention, the time of the second condensation salt forming reaction is preferably 3-5 h, and more preferably 4 h. The second polycondensation salification reaction is preferably carried out in a nitrogen atmosphere; in the invention, the second polycondensation salt forming reaction is preferably carried out under the stirring condition, and the stirring speed is preferably 100-500 rpm, and more preferably 200-400 rpm. In the invention, the second tertiary amine plays a complexing role, more metal ions participate in the complexing role in the second condensation salt forming process, so that part of polyamic acid carboxyl and tertiary amine are formed into salt, and the solubility in a solvent and the gelation performance requirement under the intermolecular non-covalent bond action are regulated and controlled by regulating and controlling the types and the proportion of the introduced metal ions.
After the second condensation salt-forming reaction is completed, adding a first coordination bond generator to the second condensation salt-forming reaction product, performing first standing, then adding a second coordination bond generator, and performing second standing to obtain a polyimide precursor. In the present invention, the first and second coordinate bond generators are preferably one or more of Mg salt, Ca salt and divalent Fe salt, and particularly preferably one or more of magnesium chloride, calcium chloride and ferrous chloride.
In the invention, the first standing temperature is preferably 0-2 ℃, and more preferably 1 ℃; the time is preferably 5-10 h, more preferably 6-8 h; in the first standing process, the carboxyl group of the hydrolyzed aromatic dianhydride and the first coordination bond generator generate a coordination bond.
After the first coordination bond generation reaction is completed, the second coordination bond generator is preferably added under the conditions of nitrogen protection and stirring, and the stirring speed is preferably 100-500 rpm, more preferably 200-400 rpm. In the invention, the second standing temperature is preferably 10-12 ℃, and more preferably 11 ℃; the time is preferably 4-6 h, and more preferably 5 h. In the second standing process, the remaining unreacted carboxyl group forms a coordinate bond with the second coordinate bond generator.
After the polyimide precursor is obtained, the temperature of the polyimide precursor is reduced to-14 to-10 ℃ to obtain the polyimide precursor gel. In the present invention, the rate of cooling is 20 ℃/min. The polyimide precursor forms gel through the cooling.
The invention provides application of the flexible high-temperature-resistant polyimide precursor gel as 3D printing gel ink. When the polyimide precursor gel is used as 3D printing gel ink, due to the fact that the polyimide precursor gel has multiple dynamic intermolecular forces, especially under the conjugation effect of rigid coplanar benzimide, thixotropy (viscosity) with high and low temperature viscosity (viscosity) which other 3D printing inks do not have can be realizedRTViscosity60℃＞103) Thereby avoiding the introduction of photocuring groups to reduce the temperature resistance and strength of the system. When the flexible high-temperature-resistant polyimide precursor gel is used as gel ink for 3D printing, the printing precision is good.
When the flexible high-temperature-resistant polyimide precursor gel is used as the 3D printing gel ink, the polyimide precursor gel 3D cooled to-14 to-10 ℃ is preferably immediately put into a printer for later use, so that the printing effect of the gel ink is ensured.
The invention provides a polyimide flexible honeycomb structure which is prepared from the flexible high-temperature-resistant polyimide precursor gel by a 3D printing method. In the invention, the honeycomb structure has good flexibility and rebound resilience and can resist the high temperature of 300 ℃.
In the present invention, the method for preparing a polyimide flexible honeycomb structure by 3D printing preferably comprises the steps of:
(1) using flexible high-temperature-resistant polyimide precursor gel as 3D printing gel ink for 3D printing to obtain a printed product;
(2) and carrying out staged heat treatment on the printed product to obtain the polyimide flexible honeycomb structure.
In the present invention, the parameters of the 3D printing preferably include:
the needle head for 3D printing is a 50-300 mu m needle head;
the extrusion air pressure during 3D printing is 0.1-0.3 MPa; the moving speed of the spray head is 1-20 mm/s; the temperature of the needle cylinder for 3D printing is 60-75 ℃.
In the present invention, the staged heat treatment preferably includes the following steps performed in order:
keeping the temperature at 60 ℃ for 20 h;
keeping the temperature at 100 ℃ for 2 h;
keeping the temperature at 150 ℃ for 1 h;
keeping the temperature at 200 ℃ for 1 h;
keeping the temperature at 250 ℃ for 1 h;
preserving heat for 1h at 250 ℃ under a vacuum condition;
drying at 350 deg.C under vacuum for 1 hr.
In the present invention, the temperature increase rate of the staged heat treatment is preferably 10 ℃/min, and the solvent can be volatilized by the staged heat treatment to gradually imidize the polyimide precursor gel.
According to the invention, the thickness among molecular chains and the thickness of a crystal region are adjusted by combined action of bulky side-group dianhydride, hydrogen bonds, pi-pi accumulation and polysiloxane in the flexible high-temperature-resistant polyimide precursor gel, and the flexible polyimide honeycomb structure is prepared by using the flexible high-temperature-resistant polyimide precursor gel as 3D printing gel ink, so that high elasticity and flexibility of the honeycomb structure in the out-of-plane direction can be realized.
The flexible high temperature resistant polyimide precursor gel, the preparation method and the application thereof, and the polyimide flexible honeycomb structure provided by the present invention will be described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) Mixing 2- (4-aminophenyl) -5-aminobenzimidazole, diethylethanolamine and water, and carrying out a first condensation salt-forming reaction for 1h under the stirring conditions of a nitrogen atmosphere, 20 ℃ and 200rpm to obtain a first condensation salt-forming reaction product;
(2) heating the reaction temperature to 30 ℃, adding siloxane-containing diamine (DMS-A15 of Gelest company, molecular weight 3000), stirring for 2h, uniformly dividing 4, 4' - (hexafluoroisopropylidene) diphthalic anhydride for three times, adding into a three-necked bottle, and stirring for carrying out polycondensation reaction for 1h to obtain a polycondensation reaction product;
(3) reducing the reaction temperature from 30 ℃ to 10 ℃, adding diethylethanolamine, stirring for carrying out a second condensation salt-forming reaction for 3 hours to obtain a second condensation salt-forming reaction product;
(4) adding ferrous chloride into the second condensation salt-forming reaction product, standing for 10 hours at the temperature of 2 ℃, then adding the ferrous chloride, and standing for 5 hours at the temperature of 10 ℃ to obtain a polyimide precursor;
(5) and cooling the polyimide precursor to-10 ℃ at the speed of 20 ℃/min to obtain polyimide precursor gel PI-1.
Wherein the molar ratio of the aromatic dianhydride to the sum of the aromatic diamine and the siloxane-containing diamine is 1: 1.02;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1: 0.05;
the mass ratio of the aromatic dianhydride to the polar solvent is 1: 5;
the molar ratio of aromatic dianhydride to first portion of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the second part of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the first part of the coordination bond generator is 1: 0.005;
the molar ratio of the aromatic dianhydride to the second part of the coordination bond generator is 1: 0.005.
the repeat unit of the obtained polyamic acid is
Figure BDA0002641748410000151
Said R1Is composed of
Figure BDA0002641748410000152
R2Is composed of
Figure BDA0002641748410000161
The number average molecular weight of the polyamic acid was found to be 43500.
Performing structural characterization on the obtained polyimide precursor gel PI-1, wherein the obtained spectrogram is shown in figure 1: as can be seen from FIG. 1, 1773cm-1，1712cm-1，1362cm-1Is a characteristic peak of a polyimide five-membered imine ring. Wherein, 1773cm-1And 1712cm-1Caused by stretching vibration of carbonyl group, 1362cm-1And 804cm-1Is caused by stretching vibrations of the-C-N-C-group. 1253cm-1Where is a Si-C group, 1061cm-1At position of 1002cm-1At 792cm-1There is a Si-O bond vibration peak, indicating the presence of siloxane groups in the product.
Example 2
A polyimide precursor gel was prepared according to the method of example 1, except that:
the aromatic dianhydride is 3,3 ', 4, 4' -diphenyl sulfone tetracarboxylic dianhydride;
the siloxane-containing diamine is DMS-A31 from Gelest corporation, molecular weight 25000.
Wherein the molar ratio of the aromatic dianhydride to the sum of the aromatic diamine and the siloxane-containing diamine is 1: 1;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1: 0.05;
the mass ratio of the aromatic dianhydride to the polar solvent is 1: 3;
the molar ratio of aromatic dianhydride to first portion of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the second part of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the first part of the coordination bond generator is 1: 0.005;
the molar ratio of the aromatic dianhydride to the second part of the coordination bond generator is 1: 0.005.
the repeat unit of the polyamic acid obtained was:
Figure BDA0002641748410000162
R1is composed of
Figure BDA0002641748410000163
R2Is composed of
Figure BDA0002641748410000171
The polyamic acid was found to have a number average molecular weight of 49320.
The structure of the obtained polyimide precursor gel PI-2 is characterized, the obtained spectrogram is shown in figure 1, and the spectrogram is similar to that of the polyimide precursor gel obtained in example 1.
Example 3
A polyimide precursor gel was prepared according to the method of example 1, except that:
the siloxane-containing diamine is X-22-161A of shin-Etsu corporation, and has a molecular weight of 1600;
wherein the molar ratio of the aromatic dianhydride to the sum of the aromatic diamine and the siloxane-containing diamine is 1: 1.02;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1: 0.05;
the mass ratio of the aromatic dianhydride to the polar solvent is 1: 5;
the molar ratio of aromatic dianhydride to first portion of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the second part of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the first part of the coordination bond generator is 1: 0.005;
the molar ratio of the aromatic dianhydride to the second part of the coordination bond generator is 1: 0.005.
the repeat unit of the obtained polyamic acid is
Figure BDA0002641748410000172
Said R1Is composed of
Figure BDA0002641748410000173
R2Is composed of
Figure BDA0002641748410000181
The number average molecular weight of the polyamic acid was detected to be 41020.
The obtained polyimide precursor gel PI-3 is subjected to structural characterization, the obtained spectrogram is shown in figure 1, and the spectrogram is similar to that of the polyimide precursor gel obtained in example 1.
Example 4
A polyimide precursor gel was prepared according to the method of example 1, except that:
the tertiary amine is N-methylazetidine;
the coordination bond generator is calcium chloride;
the polar solvent is a mixture of water and dimethyl sulfoxide, wherein the weight ratio of water: the mass ratio of dimethyl sulfoxide is 1: 1;
in the preparation process, the temperature of the first condensation salt forming reaction is 18 ℃, and the time is 3 hours;
the temperature of the polycondensation reaction is 40 ℃, and the time is 1.5 h;
the temperature of the second condensation salt forming reaction is 5 ℃, and the time is 3 hours;
the first standing temperature is 1 ℃, and the time is 8 hours;
the temperature of the second standing is 12 ℃, and the time is 5 hours.
Wherein the molar ratio of the aromatic dianhydride to the sum of the aromatic diamine and the siloxane-containing diamine is 1: 1.01;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1: 0.1;
the mass ratio of the aromatic dianhydride to the solvent is 1: 5;
the molar ratio of aromatic dianhydride to first portion of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the second part of tertiary amine is 1: 0.1;
the molar ratio of the aromatic dianhydride to the first part of the coordination bond generator is 1: 0.005;
the molar ratio of the aromatic dianhydride to the second part of the coordination bond generator is 1: 0.005.
the repeat unit of the obtained polyamic acid is
Figure BDA0002641748410000191
Said R1Is composed of
Figure BDA0002641748410000192
R2Is composed of
Figure BDA0002641748410000193
The number average molecular weight of the polyamic acid is 43020.
The obtained polyimide precursor gel PI-4 is subjected to structural characterization, the obtained spectrogram is shown in figure 1, and the spectrogram is similar to that of the polyimide precursor gel obtained in example 1.
Example 5
A polyimide precursor gel was prepared according to the method of example 1, except that:
the aromatic diamine is 2- (4-aminophenyl) -5-aminobenzoxazole.
Wherein the molar ratio of the aromatic dianhydride to the sum of the aromatic diamine and the siloxane-containing diamine is 1: 1.02;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1: 0.05;
the mass ratio of the aromatic dianhydride to the solvent is 1: 5;
the molar ratio of aromatic dianhydride to first portion of tertiary amine is 1: 0.015;
the molar ratio of the aromatic dianhydride to the second part of tertiary amine is 1: 0.015;
the molar ratio of the aromatic dianhydride to the first part of the coordination bond generator is 1: 0.005;
the molar ratio of the aromatic dianhydride to the second part of the coordination bond generator is 1: 0.005.
the repeat unit of the obtained polyamic acid is
Figure BDA0002641748410000194
Said R1Is composed of
Figure BDA0002641748410000201
R2Is composed of
Figure BDA0002641748410000202
The polyamic acid was found to have a number average molecular weight of 45300.
The structure of the obtained polyimide precursor gel PI-5 is characterized, the obtained spectrogram is shown in figure 1, and the spectrogram is similar to that of the polyimide precursor gel obtained in example 1.
Example 6
A polyimide precursor gel was prepared according to the method of example 1, except that:
the aromatic diamine is 2, 5-bis (4-aminophenyl) pyrimidine.
Wherein the molar ratio of the aromatic dianhydride to the sum of the aromatic diamine and the siloxane-containing diamine is 1: 1.02;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1: 0.08;
the mass ratio of the aromatic dianhydride to the polar solvent is 1: 4;
the molar ratio of aromatic dianhydride to first portion of tertiary amine is 1: 0.2;
the molar ratio of the aromatic dianhydride to the second part of tertiary amine is 1: 0.2;
the molar ratio of the aromatic dianhydride to the first part of the coordination bond generator is 1: 0.005;
the molar ratio of the aromatic dianhydride to the second part of the coordination bond generator is 1: 0.005.
the repeat unit of the obtained polyamic acid is
Figure BDA0002641748410000203
Said R1Is composed of
Figure BDA0002641748410000204
R2Is composed of
Figure BDA0002641748410000211
The number average molecular weight of the polyamic acid was determined to be 32020.
Comparative example 1
Comparative example 1 differs from example 1 in that the tertiary amine used is triethylamine.
The preparation method of comparative example 1 is the same as that of example 1, except that in comparative example 1, when the polyimide precursor is cooled to-10 ℃ in the step (5), the polyimide precursor is subjected to phase separation to form two components, namely a clear yellow solution and a black gel, and cannot be used as gel ink for 3D printing.
Comparative example 2
Comparative example 2 differs from example 5 in that no silicone-containing diamine is added.
The repeat unit of the polyamic acid in the polyimide precursor is as follows:
Figure BDA0002641748410000212
said R1Is composed of
Figure BDA0002641748410000213
The molecular weight of the polyimide precursor is 39200.
Comparative example 3
The comparative example 3 is different from the example 5 in that the temperature of the second standing is 30 ℃, and after the completion of the standing, the temperature is reduced from 30 ℃ to 5 ℃ at a natural cooling rate, and the result shows that the polyimide precursor still maintains the solution state and cannot form gel.
Comparative example 4
Comparative example 4 differs from example 1 in that the aromatic diamine used is p-phenylenediamine.
The preparation method of comparative example 4 is the same as that of example 1 except that in comparative example 1, when the polyimide precursor is cooled to-10 ℃ at a rate of 20 ℃/min in step (5), the polyimide precursor is subjected to phase separation, and no gel is formed.
Test example 1
The gels obtained in the examples 1 to 6 and the comparative example 2 were coated on a glass plate, and were kept at a constant temperature of 50 ℃ for 5 hours, then placed in a normal oven, kept at a constant temperature of 100 ℃ for 2 hours, then kept at a constant temperature of 150 ℃ for 1 hour, then kept at a constant temperature of 200 ℃ for 1 hour, and finally kept at a constant temperature of 250 ℃ for 1 hour, and after the temperature rise was completed, taken out after being cooled to room temperature, then placed in a vacuum oven, kept at a constant temperature of 250 ℃ for 1 hour, and then kept at a constant temperature of 350 ℃ for 1 hour, thereby obtaining a film.
The 5% thermogravimetric temperature, 800 ℃ carbon residue rate and glass transition temperature of the film were measured, respectively, and the obtained results are shown in table 1. The test method is as follows.
5% thermogravimetric temperature: the test was conducted using a thermogravimetric analyzer (TGA). The heating rate is as follows: 10 ℃/min; testing atmosphere: air.
Carbon residue rate at 800 ℃: the test was conducted using a thermogravimetric analyzer (TGA). The heating rate is as follows: 10 ℃/min; testing atmosphere: nitrogen gas.
Glass transition temperature: the test employed a dynamic thermomechanical analyzer (DMA). The heating rate is as follows: 5 ℃/min; testing atmosphere: air.
TABLE 1 high temperature resistance of the gels obtained in examples 1-6 and comparative example 2
Performance of Unit of Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative example 2
Glass transition temperature ℃ 330 310 340 327 386 390 350
5% thermal weight loss temperature ℃ 570 560 574 540 560 580 584
Carbon residue rate at 800 DEG C ％ 42 45 44 45 43 43 37
Elongation of film ％ 40 80 25 70 30 20 5
As can be seen from Table 1, the glass transition temperatures of the gels obtained in the inventive examples 1-6, i.e., the comparative example 2, are all more than 300 ℃, and the gels have good high temperature resistance, but the elongation of the gel film obtained in the comparative example 2 is low, which indicates that the flexibility is poor.
Test example 2
The viscosity values and shear rate changes (10) of the products obtained in examples 1 to 6 and comparative examples 1 to 4 at different temperatures were measured using a rotational rheometer3～10-3rad/s) time to recover the viscosity to 104pa.s, and the results are shown in table 2.
TABLE 2 rheological Properties of the products obtained in examples 1 to 6 and comparative examples 1 to 4
Figure BDA0002641748410000231
As is clear from Table 2, the viscosities of the gels obtained in examples 1 to 6 of the present inventionRTViscosity60℃＞103The thixotropic property of high and low temperature viscosity is shown, and the time for recovering viscosity after high-speed shearing is short; without the use of a specific type of tertiary amine (as in comparative example 1), or without the use of a preparation process that forms at a rapidly reduced temperature (as in comparative example 2), or without the use of a siloxane in combination with a diamine having multiple hydrogen bonding capabilities (as in comparative example 4), all resulted in solutions that formed that were difficult to gel, either failed to yield a polyimide precursor gel or split phase, and were not useful for 3D printing.
Test example 3
The polyimide precursor gels prepared in examples 1 to 6 and comparative example 2 were tested using a RegenHU bio 3D printer-3D Discovery in switzerland:
(1) testing printing accuracy
The printing mode is single-wire printing, and the printing conditions and parameters are as follows:
the extrusion pressure is 0.2MPa, the moving speed of a spray head is 5mm/s, and the temperature of a needle cylinder is 70 ℃;
the printing heads were 3D printed at 100, 200, 500, 1000 and 50 μm respectively, and the highest precision with which printing could be performed was tested, and the results are listed in table 3.
(2) Testing for print defectiveness
A100-micron needle head is selected to print a 5-layer structure, and the printing conditions and parameters are as follows:
the extrusion pressure is 0.2MPa, the moving speed of a spray head is 5mm/s, and the temperature of a needle cylinder is 70 ℃;
carrying out heat treatment on the printed product for 20h at the temperature of 60 ℃ in an oven to obtain a xerogel product; placing the dried gel product in a common oven, keeping the temperature constant for 2h at the temperature of 100 ℃, keeping the temperature constant for 1h at the temperature of 150 ℃, keeping the temperature constant for 1h at the temperature of 200 ℃, keeping the temperature constant for 1h at the temperature of 250 ℃, cooling to room temperature after the temperature is raised, taking out the dried gel product, placing the dried gel product in a vacuum oven, keeping the temperature constant for 1h at the temperature of 250 ℃, and keeping the temperature constant for 1h at the temperature of 350 ℃ to obtain a heat-treated product, namely a flexible and high-temperature-resistant polyimide honeycomb structure; and respectively observing the surface and interface conditions of the printed product, the xerogel product and the heat-treated product, including the existence of fine bubbles, defects and delamination. The results obtained are shown in Table 3.
(3) Testing printed honeycomb structure effects
A100-micron needle head is selected to print a 200-layer structure, and the printing conditions and parameters are as follows:
extruding the mixture under the pressure of 0.2MPa, moving the nozzle at the speed of 5mm/s and the temperature of the needle cylinder at 70 ℃ to obtain a printed product; carrying out heat treatment on the printed product for 20h at the temperature of 60 ℃ in an oven to obtain a xerogel product; placing the dried gel product in a common oven, keeping the temperature constant for 2h at 100 ℃, then keeping the temperature constant for 1h at 150 ℃, then keeping the temperature constant for 1h at 200 ℃, finally keeping the temperature constant for 1h at 250 ℃, taking out the dried gel product after the temperature is raised to room temperature, then placing the dried gel product in a vacuum oven, keeping the temperature constant for 1h at 250 ℃, and then keeping the temperature constant for 1h at 350 ℃ to obtain the product with the density of 0.25g/cm3The heat-treated product of (a), i.e., a polyimide honeycomb structure. A physical diagram of a polyimide honeycomb structure obtained by 3D printing of the polyimide precursor gel in example 1 is shown in fig. 2.
The compression resilience of the polyimide honeycomb structure at room temperature and 300 ℃ is respectively tested by adopting an instron universal tester, the comparison between the first compression strength and the 100 th compression strength is used as a judgment basis for the resilience ratio, if the compression strength of the 100 th compression is more than or equal to 90 percent of the compression strength of the first compression, the resilience of the polyimide honeycomb structure at the compression ratio is obtained, and the obtained results are listed in Table 3. The change curve of the multi-time compression strength of the polyimide honeycomb structure obtained by 3D printing of the polyimide precursor gel in example 1 is shown in fig. 3, and as can be seen from fig. 2, the compression strength of the honeycomb structure is not changed after 100 times of compression, which indicates that the flexibility and recovery effect are good.
TABLE 3 Properties of printed products obtained in examples 1 to 6 and comparative example 2
Item Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative example 2
Printable precision (mum) 50 50 50 50 50 50 50
Defective property of printing Is free of Is free of Is free of Is free of Is free of Is free of Is provided with
Room temperature rebound resilience (%) 50 90 20 66 30 30 0
Rebound resilience at 300 ℃ (%) 65 90 30 75 40 30 0
As can be seen from Table 3, the polyimide honeycomb structures obtained in the embodiments 1 to 6 of the present invention have good resilience at room temperature and 300 ℃, which indicates that the polyimide honeycomb structures have good flexibility and high temperature resistance; the honeycomb structure obtained in comparative example 2 had no resilience at room temperature and 300 c, indicating that it was not flexible.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (10)

1. A flexible high-temperature-resistant polyimide precursor gel is prepared by using a polyamic acid, wherein the polyamic acid has a repeating unit with a structure shown in a formula 1 or a formula 2:
Figure FDA0003013734660000011
the ratio of k to t in formula 1 and formula 2 is independently 100: (1-10);
r in formula 1 and formula 21Independently is
Figure FDA0003013734660000012
Figure FDA0003013734660000013
One of (1);
R2independently is
Figure FDA0003013734660000014
Wherein m, n and p are independently 1-50;
the number average molecular weight of the polyamic acid is 5000-50000.
2. The flexible high temperature resistant polyimide precursor gel according to claim 1, wherein the temperature of the flexible high temperature resistant polyimide precursor gel is-14 to-10 ℃.
3. The method for preparing the flexible high-temperature-resistant polyimide precursor gel as claimed in claim 1 or 2, which is characterized by comprising the following steps:
(1) mixing aromatic diamine, first tertiary amine and a polar solvent to obtain a first reaction product;
(2) mixing the first reaction product with siloxane-containing diamine and aromatic dianhydride to carry out polycondensation reaction to obtain a polycondensation reaction product;
(3) mixing the polycondensation reaction product with tertiary amine to perform a second polycondensation salt forming reaction to obtain a second polycondensation salt forming reaction product;
(4) adding a first metal coordination bond generator into the second condensation salt-forming reaction product, performing first standing, then adding a second metal coordination bond generator, and performing second standing to obtain a polyimide precursor;
(5) cooling the polyimide precursor to-14 to-10 ℃ at a cooling rate of 10-20 ℃/min to obtain flexible high-temperature-resistant polyimide precursor gel;
the aromatic diamine is 2- (4-aminophenyl) -5-aminobenzoxazole, 2, 5-bis (4-aminophenyl) pyrimidine or 2- (4-aminophenyl) -5-aminobenzimidazole;
the aromatic dianhydride is 4,4 ' - (hexafluoroisopropylidene) diphthalic anhydride or 3,3 ', 4,4 ' -diphenyl sulfone tetracarboxylic dianhydride;
the siloxane-containing diamine has a structure represented by formula 3:
Figure FDA0003013734660000021
in the formula 3, m, n and p are independently 1-50;
the first tertiary amine and the second tertiary amine are independently one or more of trimethylamine, tripropylamine, triisopropylamine, tri-N-butylamine, triethanolamine, tetramethylethylenediamine, diethylethanolamine, N-ethyldiethanolamine, N-methylazesopropane, N-methylazetidine, N-methylpiperidine, N dimethylcyclohexylamine, dimethylpiperazine and N, N-dimethylaniline.
4. The preparation method according to claim 3, wherein the polar solvent is one or more of N, N-dimethylformamide, N-dimethylacetamide, N-diethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, water, dimethyl sulfone, butyrolactone and caprolactone;
the first metal coordination bond generator and the second metal coordination bond generator are independently one or more of Mg salt, Ca salt and divalent Fe salt.
5. The method according to claim 3, wherein the molar ratio of the sum of the aromatic diamine and the siloxane-containing diamine to the aromatic dianhydride is (0.9-1.2): 1;
the molar ratio of the aromatic diamine to the siloxane-containing diamine is 1 (0.01-0.1).
6. The preparation method according to claim 3 or 5, wherein the mass ratio of the aromatic dianhydride to the polar solvent is 1 (2-10);
the molar ratio of the aromatic dianhydride to the first tertiary amine is 1: (0.03-1);
the molar ratio of the aromatic dianhydride to the second tertiary amine is 1: (0.02-1);
the molar ratio of the aromatic dianhydride to the first metal coordinate bond generator is 1: (0.0003 to 0.03);
the molar ratio of the aromatic dianhydride to the second metal coordinate bond generator is 1: (0.0002 to 0.02).
7. The preparation method according to claim 3, wherein the aromatic diamine, the first tertiary amine and the polar solvent are mixed at a temperature of 18 to 22 ℃ for 1 to 5 hours;
the temperature of the polycondensation reaction is 30-50 ℃, and the time is 0.5-2 h;
the temperature of the second condensation salt forming reaction is 5-10 ℃, and the time is 3-5 h.
8. The preparation method according to claim 3, wherein the first standing temperature is 0-2 ℃ and the time is 5-10 h;
and the second standing temperature is 10-12 ℃, and the time is 4-6 h.
9. The flexible high-temperature-resistant polyimide precursor gel as defined in claim 1 or 2 or the flexible high-temperature-resistant polyimide precursor gel prepared by the preparation method as defined in any one of claims 3 to 8 is applied as a 3D printing gel ink.
10. A polyimide flexible honeycomb structure is characterized in that the flexible high-temperature-resistant polyimide precursor gel of claim 1 or 2 or the flexible high-temperature-resistant polyimide precursor gel prepared by the preparation method of any one of claims 3 to 8 is prepared by a 3D printing method;
the room temperature resilience of the polyimide flexible honeycomb structure is 20-90%, and the 300 ℃ resilience is 30-90%.
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