A modified polyamide acid aerogel, and a preparation method and application thereof

Abstract

The application belongs to the technical field of aerogel materials, and particularly relates to a modified polyamic acid aerogel and a preparation method and application thereof. The method comprises the following steps: preparing POSS modified polyamic acid by taking dianhydride, diamine and polyamino POSS monomer as raw materials; adding the POSS modified polyamic acid into deionized water to obtain POSS modified polyamic acid powder after sedimentation; adding the POSS modified polyamic acid powder and an organic alkaline compound into deionized water to obtain POSS modified polyamic acid hydrogel after sol-gel; and drying the POSS modified polyamic acid hydrogel, partially thermal imidizing, crushing to obtain the modified polyamic acid aerogel. The aerogel still retains a large number of active groups, improves the compatibility of the aerogel and the adhesive, and makes the aerogel adopt two ways of pore infiltration and active group connection to enhance the mechanical properties of the adhesive.

Description

Technical Field

[0001] This invention belongs to the field of aerogel materials technology, specifically relating to a modified polyamic acid aerogel, its preparation method, and its application. Background Technology

[0002] Adhesives are organic or inorganic, natural or synthetic substances that can bond two or more homogeneous or heterogeneous parts or materials together, achieving sufficient strength after curing. Adhesives bond to materials through surface adhesion, chemical bonding, diffusion, and physical adsorption. Compared to other bonding methods, they offer high strength and ease of use, and are widely used in the automotive, aerospace, home appliance, biomedical, and dental industries.

[0003] Currently, in the manufacturing industry, adhesives are widely used for bonding various materials due to their unique properties, such as curing time, bond strength, weather resistance, and moisture resistance. Research on adhesives focuses on enhancing their bond strength and tensile stress, improving corrosion resistance, reducing curing time, and reducing the thickness of adhesives used. These research advances have greatly met the diverse market demands for adhesive applications.

[0004] Adhesives used in the market mainly include inorganic adhesives and organic adhesives. Inorganic adhesives are primarily composed of inorganic salts, inorganic alkali metals, inorganic acids, metal oxides, and hydroxides. Based on the type of inorganic salt, they can be further classified into sulfate, phosphate, silicate, and borate adhesives. Due to the significant advantages of inorganic materials, inorganic adhesives possess excellent high and low temperature resistance, allowing use in a temperature range of -180℃ to 3000℃. They also exhibit low curing shrinkage, simple application processes, and low cost, making them widely used in machinery manufacturing and repair, architectural coatings, and other fields. However, inorganic adhesives suffer from poor acid and alkali resistance, water resistance, brittleness, poor impact resistance, and insufficient bonding strength, making performance improvement difficult and limiting their application.

[0005] Organic adhesives are a class of adhesives based on organic polymers, mainly including polyurethanes, epoxy resins, phenolic resins, silicone resins, and polyimides. They possess advantages such as high bonding strength, excellent acid and alkali resistance, and superior overall performance, making them widely used in the automotive, aerospace, and other fields. However, organic adhesives are mostly composed of high-molecular-weight polymers, which are prone to decomposition under high temperatures and have disadvantages such as poor oxidation resistance and low bonding strength, failing to meet current industry requirements for bonding strength. However, compared to inorganic adhesives, organic adhesives offer greater controllability, allowing for performance improvements through various means, and thus have significant development potential. Summary of the Invention

[0006] This invention provides a modified polyamic acid aerogel, its preparation method, and its application. The preparation process is simple, low-cost, and easy to operate, and the raw materials are readily available, which is conducive to industrial production. Furthermore, the adhesives modified by this modified polyamic acid aerogel have excellent mechanical properties and broad application prospects.

[0007] This objective of the invention is achieved through the following technical solution:

[0008] A method for preparing modified polyamic acid aerogel includes the following steps:

[0009] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the polyamino POSS monomer has 6-8 amino groups;

[0010] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3-5 hours, add the polyamino POSS monomer again and continue reacting for 3-6 hours to obtain POSS-modified polyamic acid. By adjusting the initial reaction time, the molecular weight can be fully increased, and premature cross-linking of the polyamic acid can be prevented from occurring due to excessive reaction time, thus improving the stability of the polymer. In particular, the reaction time is 3.2-4.5 hours or 3.5-4 hours;

[0011] (3) POSS-modified polyamic acid was added to deionized water and precipitated to obtain POSS-modified polyamic acid powder;

[0012] (4) POSS modified polyamic acid powder and organic alkaline compound were added to deionized water and sol-gelled to obtain POSS modified polyamic acid hydrogel.

[0013] (5) The POSS-modified polyamic acid hydrogel was dried, partially thermally imidized, and pulverized to obtain the modified polyamic acid aerogel.

[0014] Polyimide typically cannot be directly fused with epoxy resin, while polyamic acid, the precursor of polyimide, is a liquid substance with a certain viscosity that can be uniformly mixed in epoxy resin, making the process extremely simple. The inventors previously used polyamic acid to modify adhesives. However, polyamic acid is mostly in a liquid state, exhibiting extremely poor stability and requiring immediate preparation, which limits its large-scale application. Aerogel materials, as lightweight materials with porous structures, are widely used as reinforcing stabilizers in bonding resin composites. Traditional inorganic aerogel materials have low strength, are brittle, and are difficult to process. Although common polymer aerogels are easier to process than inorganic aerogels, they still suffer from poor heat resistance. In contrast, polyimide-based aerogels retain the general properties of aerogel materials and, thanks to the excellent mechanical properties and high-temperature thermal stability of polyimide, overcome the shortcomings of traditional aerogels, such as low strength.

[0015] In particular, this invention involves partial imidization of the polyamic acid aerogel, which improves the stability of the POSS-modified polyamic acid aerogel, reduces the curing time of the adhesive, and improves the production process. Furthermore, because the partial thermal imidization of the polyamic acid is performed, a large number of active groups are retained on the aerogel, improving the compatibility between the aerogel and the adhesive. This allows the aerogel to enhance the mechanical properties of the adhesive through both pore wetting and active group bonding.

[0016] Preferably, the non-POSS diamine monomer in step (1) is selected from p-phenylenediamine, m-phenylenediamine, 2-trifluoromethyl-1,4-diaminobenzene, 5-methyl-1,3-diaminobenzene, 5-trifluoromethyl-1,3-diaminobenzene, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-bis(trifluoromethyl)diphenylmethane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, and 3,3'-diamino-4,4'-dichlorodiphenylmethane. One or more of benzophenone, 3,3'-diamino-4,4'-dimethoxybenzophenone, 4,4'-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)benzene, 4,4'-diaminodiphenyl sulfone, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethyl)biphenyl or 4,4'-bis(4-aminophenoxy)biphenyl.

[0017] Preferably, the polyamino POSS monomer in step (1) is selected from one or more of hexaaminopropyl silsesquioxane, hexaaminophenyl silsesquioxane, octaaminophenyl cage silsesquioxane, and octaaminopropyl cage silsesquioxane.

[0018] Preferably, the organic solvent in step (1) is one or more of N,N-dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; the stirring rate is 100-300 rpm. The amount of organic solvent used is not particularly limited, but the specific mass-to-volume ratio of the sum of the non-POSS diamine monomer, the two added polyamino POSS monomers, and the dianhydride monomer to the organic solvent is 1:(10-30) g / mL.

[0019] Preferably, the dianhydride monomer in step (2) is selected from pyromellitic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, 4,4'-hexafluoroisopropylphthalic anhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methyl One or more of the following: alkyl dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, and 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride; the dianhydride monomer is added to the diamine monomer mixed solution in 2-6 portions, with an interval of 2-6 minutes between each addition.

[0020] Preferably, the reaction temperature in step (2) is 25-35℃.

[0021] Preferably, the molar ratio of the dianhydride monomer in step (2) to the sum of all diamine monomers, including the non-POSS diamine monomer and the polyamino POSS monomer added twice, is (1-1.05):1.

[0022] Preferably, the molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer in step (1) is (0.01-1):100; and the molar ratio of the polyamino POSS monomer added again in step (2) to the non-POSS diamine monomer is (2-5):100. To improve the aerogel properties of polyamic acid and the dispersibility of polyamino POSS in the matrix, thereby improving the adhesive properties of the adhesive resin, this invention employs a stepwise feeding method to prepare POSS-modified polyamic acid. First, a small amount of polyamino POSS is added in the initial feeding portion. This portion of POSS is mainly used to introduce a cage-like structure into the polyamic acid backbone, which can improve the compatibility between polyimide and epoxy resin, and also improve the stability of polyamic acid. The amount of polyamino POSS used in the initial portion should not be excessive, otherwise it will affect the growth of the molecular chain and be detrimental to the improvement of mechanical properties. After a period of reaction, a larger amount of polyamino POSS monomer is added again. This monomer acts as both a chain extender and a crosslinking agent, forming a network structure of polyamic acid, promoting the formation of an interpenetrating network structure with the epoxy resin, and improving adhesion. Adding an appropriate amount of polyamino POSS monomer again can improve the performance of polyamic acid while avoiding excessive crosslinking that could increase the brittleness of the adhesive. Furthermore, the molar ratio of the added polyamino POSS monomer to the non-POSS diamine monomer is (2.5-4):100.

[0023] Preferably, the precipitation process in step (3) further includes subsequent washing and drying processes.

[0024] Preferably, the organic alkaline compound in step (4) is at least one of triethylamine, tripropylamine, diethylenetriamine, triethylenetetramine, and triethylenediamine; the mass ratio of the POSS modified polyamic acid powder to the organic alkaline compound is 1:(0.1-1).

[0025] Preferably, the drying in step (5) is freeze drying.

[0026] Preferably, the partial thermal imidization in step (5) is carried out at 100-160℃ for 1-3 hours. Specifically, it is carried out at 120-140℃ for 1.5-2.5 hours. In particular, the carboxyl groups on the partially imidized polyamic acid aerogel mainly react with the epoxy groups. Each unit has two active hydrogens at different positions, which may react simultaneously, thus forming a complex macromolecular ester graft copolymer and an interpenetrating network structure. When the temperature reaches 200-300℃, the carboxyl groups that have not reacted with the epoxy and the amino groups on the adjacent benzene ring will undergo a condensation reaction to form a five-membered ring group. The formation of this stable five-membered ring further improves the stability of the system, which is particularly beneficial to the improvement of heat resistance. Due to the presence of imide groups, the heat resistance of the system can be improved by modifying the epoxy resin adhesive with partially imidized polyamic acid aerogel, but the improvement in its mechanical properties is limited. In order to further improve its bonding strength, the present invention uses polyamino POSS to modify polyamic acid. The introduction of polyamino POSS groups can improve the wetting properties of adhesives with materials such as metals and increase the bonding strength.

[0027] On the other hand, the present invention also provides a modified polyamic acid aerogel and its application, wherein the modified polyamic acid aerogel is used in the field of adhesives, the adhesive comprising a bonding resin and the modified polyamic acid aerogel, which can greatly improve the mechanical properties of the resin adhesive.

[0028] Specifically, the adhesive may selectively include components such as a bonding resin, modified polyamic acid aerogel, a curing agent, and a small amount of diluent. The bonding resin may include polyurethane, epoxy, phenolic, silicone, and acrylic resins.

[0029] Beneficial Effects: This invention employs a step-by-step feeding method to prepare POSS-modified polyamic acid. First, a small amount of polyamino POSS is added in the initial feeding stage. This POSS primarily introduces a cage-like structure into the polyamic acid backbone, improving both the compatibility of polyimide and epoxy resin, and enhancing the stability of the polyamic acid. After a period of reaction, a larger amount of polyamino POSS monomer is added. This monomer acts as both a chain extender and a crosslinking agent, forming a network structure in the polyamic acid and promoting the formation of an interpenetrating network with the epoxy resin, thus improving adhesion. Adding a suitable amount of polyamino POSS monomer further enhances the performance of the polyamic acid while preventing excessive crosslinking that could increase adhesive brittleness. Partial imidization of the polyamic acid aerogel improves its stability, reduces adhesive curing time, and improves the production process. In addition, due to the partial thermal imidization treatment of polyamic acid, a large number of active groups are still retained on the aerogel, which improves the compatibility between the aerogel and the adhesive. This allows the aerogel to enhance the mechanical properties of the adhesive through both pore wetting and active group bonding. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] Unless otherwise specified, the raw material types and specific process parameters of the following examples and comparative examples are consistent. The product performance testing method is as follows: under the same conditions, the effect of the modified polyamic acid aerogel prepared in Examples 1-10 and Comparative Examples 1-2 on the performance of the epoxy resin adhesive is tested. The epoxy resin adhesive comprises: 100 parts of E-51 epoxy resin, 3.5 parts of modified polyamic acid aerogel, 20 parts of 4,4'-diaminodiphenyl sulfone, etc. After uniformly mixing the epoxy resin and modified polyamic acid aerogel, the curing agent 4,4'-diaminodiphenyl sulfone is added, and the mixture is stirred at 95°C for 0.6 hours to obtain the epoxy resin adhesive. The epoxy resin adhesive is uniformly coated on the treated aluminum alloy surface and cured at 120°C for 0.5 hours, 150°C for 0.5 hours, 170°C for 1.5 hours, 210°C for 1.5 hours, and 250°C for 1.5 hours; the curing pressure is 0.2 MPa. Specifically, refer to GB7124-86 to test its shear strength.

[0032] Example 1

[0033] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0034] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a diamine monomer mixed solution; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.3:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminobenzophenone and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0035] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3 hours, add the polyamino POSS monomer again and continue reacting for 6 hours to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 2.5:100. The dianhydride monomer is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The dianhydride monomer is added to the diamine monomer mixture in 3 batches, with an interval of 5 minutes between each batch. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28℃. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.01:1.

[0036] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0037] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.4.

[0038] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 120°C for 3 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0039] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 29.5 MPa.

[0040] Example 2

[0041] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0042] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 1:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N-methylpyrrolidone; the stirring speed is 200 rpm;

[0043] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 4 hours, add the polyamino POSS monomer again and continue reacting for 3 hours to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 4:100. The dianhydride monomer is selected from a mixture of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 2,3,3',4'-benzophenone tetracarboxylic dianhydride with a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture in 3 batches, with an interval of 5 minutes between each batch. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28℃. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.05:1.

[0044] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0045] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.7.

[0046] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 140°C for 1 hour for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0047] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 32.5 MPa.

[0048] Example 3

[0049] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0050] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.6:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0051] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3.5 h, add the polyamino POSS monomer again and continue reacting for 4.5 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 2:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0052] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0053] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0054] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 130°C for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0055] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 28.8 MPa.

[0056] Example 4

[0057] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0058] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.3:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0059] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 3.1 h, add the polyamino POSS monomer again and continue reacting for 5.5 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 3.7:100. The dianhydride monomer is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.04:1.

[0060] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0061] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.7.

[0062] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 136℃ for 2.3h for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0063] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 32.6 MPa.

[0064] Example 5

[0065] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0066] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.6:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0067] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 3.5 h, add the polyamino POSS monomer again and continue reacting for 4.5 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 5:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0068] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0069] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0070] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 130°C for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0071] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 30.0 MPa.

[0072] Example 6

[0073] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0074] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.4:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenylmethane and 4,4'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N-methylpyrrolidone; the stirring speed is 200 rpm;

[0075] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3.2 h, add the polyamino POSS monomer again and continue reacting for 5.4 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 2.8:100. The dianhydride monomer is selected from 2,3,3',4'-benzophenone tetracarboxylic dianhydride. The dianhydride monomer is added to the diamine monomer mixture in 3 batches, with an interval of 5 minutes between each batch. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.02:1.

[0076] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0077] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.5.

[0078] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, kept at 125℃ for 2.4h for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0079] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 31.1 MPa.

[0080] Example 7

[0081] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0082] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.6:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0083] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 3.5 h, add the polyamino POSS monomer again and continue reacting for 4.5 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 3.2:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0084] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0085] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0086] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 100°C for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0087] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 29.9 MPa.

[0088] Example 8

[0089] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0090] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.9:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diamino-3,3'-dimethyldiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0091] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 3.8 h, add the polyamino POSS monomer again and continue reacting for 4.3 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 3.1:100. The dianhydride monomer is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes between each batch. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.04:1.

[0092] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0093] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0094] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 136℃ for 1.3h for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0095] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 31.6 MPa.

[0096] Example 9

[0097] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0098] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.6:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0099] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 3.5 h, add the polyamino POSS monomer again and continue reacting for 4.5 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 3.2:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0100] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0101] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0102] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 160℃ for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0103] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 27.3 MPa.

[0104] Example 10

[0105] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0106] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.5:100; the non-POSS diamine monomer is selected from 4,4'-diaminodiphenyl ether; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N-methylpyrrolidone; the stirring speed is 200 rpm;

[0107] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3.4 h, add the polyamino POSS monomer again and continue reacting for 5.2 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 3.6:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture in 3 batches, with an interval of 5 minutes between each batch. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0108] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0109] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.4.

[0110] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, kept at 128℃ for 2.2h for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0111] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 31.5 MPa.

[0112] Example 11

[0113] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0114] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 0.6:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0115] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 3.5 h, add the polyamino POSS monomer again and continue reacting for 4.5 h to obtain POSS-modified polyamic acid. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer added again is 3.2:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0116] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0117] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0118] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 130°C for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0119] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 33.6 MPa.

[0120] Comparative Example 1

[0121] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0122] (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the molar ratio of polyamino POSS monomer to non-POSS diamine monomer is 3.8:100; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0123] (2) Continue stirring and add the dianhydride monomer in batches to the diamine monomer mixture solution. After reacting for 8 hours, POSS-modified polyamic acid is obtained. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture solution in 3 batches, with an interval of 5 minutes between each batch. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28℃. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0124] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0125] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0126] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 130°C for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0127] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 14.3 MPa.

[0128] Comparative Example 2

[0129] A method for preparing modified polyamic acid aerogel, characterized by comprising the following steps:

[0130] (1) Add the non-POSS diamine monomer to an organic solvent and stir to disperse it evenly to obtain a mixed solution of diamine monomers; the non-POSS diamine monomer is selected from a mixture of 4,4'-diaminodiphenyl ether and 3,3'-diaminobenzophenone in a molar ratio of 1:1; the organic solvent is N,N-dimethylacetamide; the stirring speed is 200 rpm;

[0131] (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3.5 h, add the polyamino POSS monomer again and continue reacting for 4.5 h to obtain POSS-modified polyamic acid. The polyamino POSS monomer is selected from octaaminophenyl cage-type silsesquioxane. The molar ratio of the polyamino POSS monomer added again to the non-POSS diamine monomer is 3.8:100. The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 1:1. The dianhydride monomer is added to the diamine monomer mixture in 3 batches, with an interval of 5 minutes each time. The mass-volume ratio of the sum of the non-POSS diamine monomer, the polyamino POSS monomer, and the dianhydride monomer to the organic solvent is 1:15 g / mL. The reaction temperature is 28 °C. The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer is 1.03:1.

[0132] (3) POSS modified polyamic acid was added to deionized water, and after precipitation, washing and drying, POSS modified polyamic acid powder was obtained.

[0133] (4) POSS modified polyamic acid powder and organic alkaline compound triethylamine are added to deionized water, and POSS modified polyamic acid hydrogel is obtained after sol-gelation; the mass ratio of POSS modified polyamic acid powder to organic alkaline compound is 1:0.6.

[0134] (5) The POSS-modified polyamic acid hydrogel was freeze-dried, heated at 130°C for 2 hours for thermal imidization, and then pulverized to obtain the modified polyamic acid aerogel.

[0135] The modified polyamic acid aerogel adhesive was tested and found to have a shear strength of 17.1 MPa.

[0136] As can be seen from the above examples and comparative examples, the present invention prepares modified polyamic acid aerogel using a stepwise feeding method. First, a small amount of polyamino POSS is added in the initial feeding stage. This POSS is mainly used to introduce a cage-like structure into the polyamic acid backbone, which improves both the compatibility of polyimide and epoxy resin and the stability of polyamic acid. After a period of reaction, a larger amount of polyamino POSS monomer is added. This monomer acts as both a chain extender and a crosslinking agent, forming a network structure of polyamic acid, promoting the formation of an interpenetrating network structure with the epoxy resin, and improving adhesion. Adding an appropriate amount of polyamino POSS monomer further improves the performance of polyamic acid while preventing excessive crosslinking that could increase the brittleness of the adhesive. Compared with Example 11, Comparative Example 1 and Comparative Example 2 added polyamino POSS only in step (1) or step (2), respectively. Adding polyamino POSS only in step (1) would affect the growth of the molecular chain, and adding polyamino POSS only in step (2) would lead to excessive cross-linking of polyamic acid. The modified polyamic acid aerogel prepared had poor performance, which affected the wetting and reaction of the bonding resin and could not effectively improve the bonding strength of epoxy resin.

[0137] The above description is merely a preferred embodiment of the invention and is not intended to limit the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should be considered within the technical scope of this invention.

Claims

1. A method for preparing modified polyamic acid aerogel, characterized in that, Includes the following steps: (1) Add non-POSS diamine monomer and polyamino POSS monomer to an organic solvent and stir to disperse evenly to obtain a mixed solution of diamine monomer; the polyamino POSS monomer has 6-8 amino groups; (2) Continue stirring and add the dianhydride monomer to the diamine monomer mixture in batches. After reacting for 3-5 hours, add the polyamino POSS monomer again and continue reacting for 3-6 hours to obtain POSS modified polyamic acid. (3) POSS-modified polyamic acid was added to deionized water and precipitated to obtain POSS-modified polyamic acid powder; (4) POSS modified polyamic acid powder and organic alkaline compound were added to deionized water and sol-gelled to obtain POSS modified polyamic acid hydrogel. (5) The POSS-modified polyamic acid hydrogel was dried, partially thermally imidized, and pulverized to obtain the modified polyamic acid aerogel. The molar ratio of the polyamino POSS monomer to the non-POSS diamine monomer in step (1) is (0.01-1):100; the molar ratio of the polyamino POSS monomer added again in step (2) to the non-POSS diamine monomer is (2-5):

100.

2. The method for preparing a modified polyamic acid aerogel as described in claim 1, characterized in that, The polyamino POSS monomer mentioned in step (1) is selected from one or more of hexaaminopropyl silsesquioxane, hexaaminophenyl silsesquioxane, octaaminophenyl cage silsesquioxane, and octaaminopropyl cage silsesquioxane.

3. The method for preparing a modified polyamic acid aerogel as described in claim 1, characterized in that, The molar ratio of the dianhydride monomer to the sum of the non-POSS diamine monomer and the polyamino POSS monomer in step (2) is (1-1.05):

1.

4. The method for preparing a modified polyamic acid aerogel as described in claim 1, characterized in that, The precipitation process described in step (3) also includes subsequent washing and drying processes.

5. The method for preparing a modified polyamic acid aerogel as described in claim 1, characterized in that, The organic alkaline compound mentioned in step (4) is at least one of triethylamine, tripropylamine, diethylenetriamine, triethylenetetramine, and triethylenediamine; the mass ratio of the POSS modified polyamic acid powder to the organic alkaline compound is 1:(0.1-1).

6. The method for preparing a modified polyamic acid aerogel as described in claim 1, characterized in that, The drying process described in step (5) is freeze drying.

7. The method for preparing a modified polyamic acid aerogel as described in claim 1, characterized in that, The partial thermal imidization described in step (5) is carried out at 100-160℃ for 1-3 hours.

8. A modified polyamic acid aerogel, characterized in that, It is prepared by any one of the methods for preparing a modified polyamic acid aerogel according to claims 1-7.

9. An application of the modified polyamic acid aerogel as described in claim 8, characterized in that, Modified polyamic acid aerogels are used in the field of adhesives.

10. An adhesive, characterized in that, It comprises a bonding resin and a modified polyamic acid aerogel, wherein the modified polyamic acid aerogel is the modified polyamic acid aerogel according to claim 8.