A transition metal oxide-doped polyimide composite material and its preparation method

Abstract

The present invention relates to the technical field of polyimide composite materials, and discloses a transition metal oxide-doped polyimide composite material and a preparation method thereof. Calculated by mass parts, the preparation raw materials include: 5-7 parts of dianhydride monomer, 4-6 parts of diamine monomer, 0.1-0.3 part of modifier, 0.2-0.6 part of transition metal oxide, 2-4 parts of reinforcing agent, 0.08-0.1 part of catalyst and / or dehydrating agent, and the dianhydride monomer is a hydrophobic monomer. The present invention prepares a polyimide composite material network structure matrix with high-value properties by changing the hydrophobic network structure of the matrix and functionalizing the structure, and incorporates transition metal oxides such as oxides of iron, cobalt, nickel, copper, etc. into the matrix material, significantly changing the physical, chemical and mechanical properties of the material. It not only solves the problems of dimensional change and decline in electrical performance caused by hygroscopicity, but also can synergistically improve the change in thermal resistance caused by hygroscopicity by etherification modification to endow it with new functional groups.

Description

Technical Field

[0001] The invention relates to the technical field of polyimide composite materials, in particular to a transition metal oxide-doped polyimide composite material and a preparation method thereof. Background Art

[0002] With the advancement of technology, thermal conductive materials are also developing. Current research hotspots include developing materials with higher thermal conductivity, reducing thermal resistance, improving the durability and stability of materials, and developing new thermal conductive materials with intelligent response characteristics. In addition, with the application of nanotechnology, nanoscale fillers are used to enhance the thermal conductivity of materials, which has also become an important development direction.

[0003] At present, the preparation of large-sized thermally conductive microsheets is conducive to reducing high interfacial thermal resistance and can fundamentally improve in-plane heat conduction. Among them, polyimide is a type of three-dimensional material. This is because polyimide is composed of linear or branched polymer chains, which are interconnected by chemical bonds to form a continuous three-dimensional network structure, which can provide a large-sized interface for thermal conductive materials and thus reduce thermal resistance. However, it will absorb moisture in a humid environment, resulting in dimensional changes and a decrease in electrical properties. Especially under high humidity conditions, the dielectric constant and loss tangent of polyimide will increase, affecting its performance as an insulating material. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a transition metal oxide doped polyimide composite material and a preparation method thereof, which utilizes etherification modification doping technology to impart new functional groups to effectively improve the thermal resistance change caused by hygroscopicity of existing thermal conductive materials, so as to solve the above-mentioned technical problems.

[0005] A transition metal oxide doped polyimide composite material, wherein the raw materials for preparation include, by weight: 4-6 parts of dianhydride monomer, 5-7 parts of diamine monomer, 0.1-0.3 parts of modifier, 0.2-0.6 parts of transition metal oxide, 2-4 parts of reinforcing agent, 0.08-0.1 parts of catalyst and / or dehydrating agent;

[0006] Wherein, the dianhydride monomer is a hydrophobic monomer.

[0007] Optionally, the dianhydride monomer is one or more of perfluorohexyl dianhydride (PFDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-(hexafluoroisopropyl alcohol) diphthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroisopropyl alcohol) benzophenone tetracarboxylic dianhydride (6FBA), 3,3',4,4'-diphenylether tetracarboxylic dianhydride (BPADA), 3,3',4,4'-diphenylsulfide tetracarboxylic dianhydride (BTDA).

[0008] Optionally, the diamine monomer is one or more of 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (MDA), 3,3'-dimethyl-4,4'-diaminodiphenyl ether (OMDA), 4,4'-diaminodiphenyl sulfone (DDS), p-phenylenediamine (PDA), 4,4'-diaminodiphenyldimethylbiphenyl (BPDA), 3,3'-dimethyl-4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfone (DDS), 2,2-bis(4-aminophenoxy)hexafluoropropane (6FDA-DAM).

[0009] Optionally, the modifier is one of 2-pyridyl ethylamine hydrochloride, cyclopentaneethylamine hydrochloride, 1-(4-iodophenyl)ethylamine hydrochloride, 2-fluoroethylamine hydrochloride, 2-(2-naphthyl)ethylamine hydrochloride, and hydroxyethylamine hydrochloride.

[0010] Optionally, the transition metal oxide is one or more of cobalt oxide, nickel oxide, molybdenum oxide, iron oxide, and copper oxide.

[0011] Optionally, the reinforcing agent is one or more of nano-ZnO, nano-SiO2, nano-BN flakes, and MXene nanosheets.

[0012] Optionally, the catalyst is one or more of hexafluoroisopropyl alcohol, trimethylchlorosilane, toluenesulfonic acid, pyridine, triethylamine, and acetic anhydride.

[0013] Optionally, the dehydrating agent is one or more of hexafluoroisopropyl alcohol, trimethylchlorosilane, toluenesulfonic acid, pyridine, triethylamine, and acetic anhydride.

[0014] A preparation method of a transition metal oxide-doped polyimide composite material is applied to prepare the above-mentioned transition metal oxide-doped polyimide composite material. The preparation method includes the following steps:

[0015] S1. Select 4 - 6 parts of dianhydride monomers and 5 - 7 parts of diamine monomers, ultrasonically disperse them in 20 mL of N,N - dimethylacetamide. Under an inert gas protection atmosphere, react at 35 - 50 °C for 0.5 - 1 h, then react at 0 °C for 3 - 5 h, and then let it stand at room temperature for 24 h to obtain a precursor solution;

[0016] Among them, the dianhydride monomer is a hydrophobic monomer;

[0017] S2. Select 0.1 - 0.3 parts of a modifier, dissolve it in 10 mL of N,N - dimethylformamide, and add it to the precursor solution. React at 50 - 80 °C for 3 - 5 h to obtain a polyimide composite network structure matrix;

[0018] S3. Add 0.2 - 0.6 parts of transition metal oxide, 2 - 4 parts of reinforcing agent, and 0.08 - 0.1 parts of catalyst and / or dehydrating agent to the polyimide composite network structure matrix. React at 80 °C for 24 h to obtain a preform;

[0019] S4. Pour the preform into a mold and obtain a transition metal oxide - doped polyimide composite through thermoforming.

[0020] Optionally, in the step S4, the thermoforming reaction conditions of the transition metal oxide - doped polyimide composite are as follows:

[0021] Place it in a flat vulcanizing machine, at a pressure of 20 - 70 MPa / cm 2 and react at 300 °C for 2 h.

[0022] The beneficial effects that the present invention can produce include:

[0023] A transition metal oxide - doped polyimide composite and a preparation method thereof provided by the present invention. When preparing the transition metal oxide - doped polyimide composite, the selected monomers are hydrophobic monomers, introducing hydrophobic functional groups from the structure. Through the reaction, a polyimide precursor solution with hydrophobic properties is obtained, and further etherification modification is carried out on the carboxyl groups in its structure to further enhance its hydrophobic properties and inhibit the change of its thermal resistance caused by moisture absorption. At the same time, by doping transition metal oxides, the transition metal oxide - doped polyimide composite is superior to traditional polyimide composites in terms of mechanical properties, thermal conductivity, expansion coefficient, and multifunctionality. Moreover, the nano - scale reinforcing agent can significantly improve the mechanical properties of the composite material. Due to the high specific surface area and strong interfacial interaction of the nano - particles, they can effectively transfer stress, thereby improving the overall mechanical properties of the transition metal oxide - doped polyimide composite, and synergistically improving the thermal conductivity and reducing the expansion coefficient. Description of the Drawings

[0024] Figure 1 Chemical reaction equation of the transition metal oxide-doped polyimide composite material in Example 1 of the present invention;

[0025] Figure 2 Schematic diagram of the surface water contact angle test of the transition metal oxide-doped polyimide composite material in Example 1 of the present invention;

[0026] Figure 3 Schematic diagram of the tensile strength test results of the transition metal oxide-doped polyimide composite material, preform and commercially available product in the present invention;

[0027] Figure 4 Schematic diagram of the thermal conductivity test results of the transition metal oxide-doped polyimide composite material, preform and commercially available product in the present invention;

[0028] Figure 5 Schematic diagram of the expansion rate test results of the transition metal oxide-doped polyimide composite material, preform and commercially available product in the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] Existing thermal conductive materials will absorb moisture in a humid environment, resulting in dimensional changes and a decline in electrical properties. Especially under high humidity conditions, the dielectric constant and loss tangent of polyimide will increase, affecting its performance as an insulating material. Therefore, the present invention provides a transition metal oxide-doped polyimide composite material to improve the hygroscopicity defect of existing thermal conductive materials. Among them, by mass, the preparation raw materials include: 4-6 parts of dianhydride monomer, 5-7 parts of diamine monomer, 0.1-0.3 part of modifier, 0.2-0.6 part of transition metal oxide, 2-4 parts of reinforcing agent, 0.08-0.1 part of catalyst and / or dehydrating agent; among them, the dianhydride monomer is a hydrophobic monomer.

[0031] Further, the dianhydride monomer is one or more of perfluorohexyl dianhydride (PFDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroisopropylidene) benzophenone tetracarboxylic dianhydride (6FBA), 3,3',4,4'-diphenylether tetracarboxylic dianhydride (BPADA), 3,3',4,4'-diphenylsulfide tetracarboxylic dianhydride (BTDA).

[0032] Further, the diamine monomer is one or more of 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (MDA), 3,3'-dimethyl-4,4'-diaminodiphenyl ether (OMDA), 4,4'-diaminodiphenyl sulfone (DDS), p-phenylenediamine (PDA), 4,4'-diaminodiphenyldimethylbiphenyl (BPDA), 3,3'-dimethyl-4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfone (DDS), 2,2-bis(4-aminophenoxy)hexafluoropropane (6FDA-DAM).

[0033] Further, the modifier is one of 2-pyridyl ethylamine hydrochloride, cyclopentaneethylamine hydrochloride, 1-(4-iodophenyl)ethylamine hydrochloride, 2-fluoroethylamine hydrochloride, 2-(2-naphthyl)ethylamine hydrochloride, and hydroxyethylamine hydrochloride.

[0034] Further, the transition metal oxide is one or more of cobalt oxide (Co2O3), nickel oxide (NiO), molybdenum oxide (MoO3), iron oxide (Fe2O3), and copper oxide (CuO).

[0035] Further, the reinforcing agent is one or more of nano-ZnO, nano-SiO2, nano-BN sheets, and MXene nanosheets.

[0036] Further, the catalyst is one or more of hexafluoroisopropanol, trimethylchlorosilane, toluenesulfonic acid, pyridine, triethylamine, and acetic anhydride.

[0037] Further, the dehydrating agent is one or more of hexafluoroisopropanol, trimethylchlorosilane, toluenesulfonic acid, pyridine, triethylamine, and acetic anhydride.

[0038] Please refer to Figures 1 - 5 As shown, the present invention provides a method for preparing a transition metal oxide-doped polyimide composite material, which is applied to prepare the above-mentioned transition metal oxide-doped polyimide composite material. The preparation method includes the following steps:

[0039] Step 1: Select 4 - 6 parts of dianhydride monomer and 5 - 7 parts of diamine monomer, ultrasonically disperse them in 20 mL of N,N - dimethylacetamide, react for 0.5 - 1 h under an inert gas protection atmosphere, then react at 0 °C for 3 - 5 h, and then stand still at room temperature for 24 h to obtain a precursor solution; among them, the dianhydride monomer is a hydrophobic monomer;

[0040] Step 2: Select 0.1 - 0.3 part of modifier, dissolve it in 10 mL of N,N - dimethylformamide, and add it to the precursor solution, react at 50 - 80 °C for 3 - 5 h to obtain a polyimide composite material network structure matrix;

[0041] Step 3: Add 0.2 - 0.6 part of transition metal oxide, 2 - 4 parts of reinforcing agent, and 0.08 - 0.1 part of catalyst and / or dehydrating agent to the polyimide composite material network structure matrix, react at 80 °C for 24 h to obtain a preform;

[0042] Step 4: Pour the preform into a mold, and obtain a transition metal oxide - doped polyimide composite material through thermoforming. Among them, the thermoforming reaction conditions of the transition metal oxide - doped polyimide composite material are:

[0043] Place it in a flat vulcanizing machine, at 20 - 70 MPa / cm 2 Under pressure, react at 300 °C for 2 h.

[0044] Example 1: Select 5 parts of 3,3'-dimethyl - 4,4'-diaminodiphenylmethane (MDA) and 4 parts of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), ultrasonically disperse them in 20 mL of N,N - dimethylacetamide, and under an inert gas protection atmosphere, react at 35 °C for 0.5 h, then react at 0 °C for 3 h, and then stand still at room temperature for 24 h to obtain a precursor solution. Then, dissolve 0.1 part of 2-(2 - naphthyl)ethylamine hydrochloride in 10 mL of N,N - dimethylformamide, and add it to the precursor solution, react at 70 °C for 3 h to obtain a polyimide composite material network structure matrix; then add 0.2 part of cobalt oxide, 2 parts of nano - SiO2, and 0.08 part of a 1:1 mass ratio of hexafluoroisopropanol and pyridine to the polyimide composite material network structure matrix, react at 80 °C for 24 h to obtain a preform; pour the preform into a mold, and place the mold containing the preform in a flat vulcanizing machine, at 50 MPa / cm 2 Under pressure, react at 300 °C for 2 h to obtain a transition metal oxide - doped polyimide composite material (the first product).

[0045] Example 2: 6 parts of 4,4'-diaminodiphenyl ether (ODA) and 6 parts of 4,4'-(hexafluoroisopropyl alcohol) benzophenone tetracarboxylic dianhydride (6FBA) were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide, and under an inert gas protection atmosphere, reacted at 40 °C for 1 h, then reacted at 0 °C for 4 h, and then left standing at room temperature for 24 h to obtain a precursor solution; then, 0.2 part of 2-pyridylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide, and it was added to the precursor solution and reacted at 80 °C for 4 h to obtain a polyimide composite network structure matrix; then, 0.2 part of molybdenum oxide, 2 parts of nano BN sheets, and 0.1 part of triethylamine and pyridine with a mass ratio of 2:1 were added to the polyimide composite network structure matrix, and reacted at 80 °C for 24 h to obtain a preform; the preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer, and reacted at 300 °C for 2 h under a pressure of 50 MPa / cm 2 pressure to obtain a transition metal oxide-doped polyimide composite material (the second product).

[0046] Example 3: 6 parts of 3,3'-dimethyl-4,4'-diaminodiphenyl ether (OMDA) and 4,4'-diaminodiphenyl sulfone (DDS) with a mass ratio of 1:2 and 5 parts of pyromellitic dianhydride (PMDA) were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide, and under an inert gas protection atmosphere, reacted at 45 °C for 0.5 h, then reacted at 0 °C for 5 h, and then left standing at room temperature for 24 h to obtain a precursor solution; then, 0.1 part of 2-hydroxyethylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide, and it was added to the precursor solution and reacted at 80 °C for 4 h to obtain a polyimide composite network structure matrix; then, 0.4 part of nickel oxide, 3 parts of MXene nanosheets, and 0.1 part of acetic anhydride and pyridine with a mass ratio of 1:1 were added to the polyimide composite network structure matrix, and reacted at 80 °C for 24 h to obtain a preform; the preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer, and reacted at 300 °C for 2 h under a pressure of 50 MPa / cm 2 pressure to obtain a transition metal oxide-doped polyimide composite material (the third product).

[0047] Example 4: 5 parts of 4,4'-diaminodiphenylmethane (MDA) and 4,4'-diaminodiphenyl sulfone (DDS) with a mass ratio of 2:3 and 6 parts of 3,3',4,4'-diphenylsulfide tetracarboxylic dianhydride (BTDA) were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide respectively. Under the protection of an inert gas atmosphere, the reaction was carried out at 50 °C for 0.5 h, then at 0 °C for 4 h, and then left standing at room temperature for 24 h to obtain a precursor solution; Next, 0.1 part of cyclopentylethylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide, and it was added to the precursor solution and reacted at 50 °C for 5 h to obtain a polyimide composite network structure matrix; Then, 0.4 part of cobalt oxide and iron oxide with a mass ratio of 3:1, 3 parts of nano-ZnO, and 0.08 part of trimethylchlorosilane and pyridine with a mass ratio of 5:3 were added to the polyimide composite network structure matrix, and the reaction was carried out at 80 °C for 24 h to obtain a preform; The preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer. At a pressure of 50 MPa / cm 2 pressure, the reaction was carried out at 300 °C for 2 h to obtain a transition metal oxide-doped polyimide composite material (the fourth product).

[0048] Example 5: 5 parts of 4,4'-diaminodiphenyldimethylbiphenyl (BPDA) and 4,4'-diaminodiphenyl sulfone (DDS) with a mass ratio of 2:3 and 6 parts of perfluorinated hexyl dianhydride (PFDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) with a mass ratio of 1:1 were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide. Under the protection of an inert gas atmosphere, the reaction was carried out at 40 °C for 0.5 h, then at 0 °C for 5 h, and then left standing at room temperature for 24 h to obtain a precursor solution; Next, 0.2 part of 1-(4-iodophenyl)ethylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide, and it was added to the precursor solution and reacted at 70 °C for 3 h to obtain a polyimide composite network structure matrix; Then, 0.3 part of nickel oxide and copper oxide with a mass ratio of 2:1, 3 parts of nano-ZnO and nano-SiO2 with a mass ratio of 5:1, and 0.1 part of triethylamine and acetic anhydride with a mass ratio of 1:2 were added to the polyimide composite network structure matrix, and the reaction was carried out at 80 °C for 24 h to obtain a preform; The preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer. At a pressure of 50 MPa / cm 2 pressure, the reaction was carried out at 300 °C for 2 h to obtain a transition metal oxide-doped polyimide composite material (the fifth product).

[0049] Example 6: 5 parts of 4,4'-diaminodiphenyl sulfone (DDS) and 2,2-bis(4-aminophenoxy)hexafluoropropane (6FDA-DAM) with a mass ratio of 1:3 and 6 parts of pyromellitic dianhydride (PMDA) and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) with a mass ratio of 1:2 were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide. Under an inert gas protection atmosphere, the reaction was carried out at 40 °C for 0.5 h, then at 0 °C for 5 h, and then left standing at room temperature for 24 h to obtain a precursor solution. Then, 0.1 part of 2-(2-naphthyl)ethylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide and added to the precursor solution, and the reaction was carried out at 70 °C for 4 h to obtain a polyimide composite network structure matrix. Then, 0.4 part of molybdenum oxide and copper oxide with a mass ratio of 3:1, 2 parts of MXene nanosheets, and 0.09 part of toluenesulfonic acid were added to the polyimide composite network structure matrix, and the reaction was carried out at 80 °C for 24 h to obtain a preform. The preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer. Under a pressure of 50 MPa / cm 2 pressure, the reaction was carried out at 300 °C for 2 h to obtain a transition metal oxide-doped polyimide composite material (the sixth product).

[0050] Example 7: 5 parts of 3,3'-dimethyl-4,4'-diaminodiphenyl ether (OMDA) and 2,2-bis(4-aminophenoxy)hexafluoropropane (6FDA-DAM) with a mass ratio of 1:4 and 5 parts of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 3,3',4,4'-diphenylsulfide tetracarboxylic dianhydride (BTDA) with a mass ratio of 2:3 were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide. Under an inert gas protection atmosphere, the reaction was carried out at 45 °C for 1 h, then at 0 °C for 4 h, and then left standing at room temperature for 24 h to obtain a precursor solution. Then, 0.2 part of 1-(4-iodophenyl)ethylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide and added to the precursor solution, and the reaction was carried out at 50 °C for 5 h to obtain a polyimide composite network structure matrix. Then, 0.6 part of cobalt oxide and nickel oxide with a mass ratio of 1:5, 2 parts of ZnO and nano BN sheets with a mass ratio of 3:1, and 0.1 part of pyridine were added to the polyimide composite network structure matrix, and the temperature was raised to 80 °C and the reaction was carried out for 24 h to obtain a preform. The preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer. Under a pressure of 50 MPa / cm 2 pressure, the reaction was carried out at 300 °C for 2 h to obtain a transition metal oxide-doped polyimide composite material (the seventh product).

[0051] Example 8: 7 parts of p-phenylenediamine and 4,4'-diaminodiphenyl sulfone (DDS) with a mass ratio of 5:1 and 6 parts of 4,4'-(hexafluoroisopropanol) diphthalic anhydride (6FDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), and 4,4'-(hexafluoroisopropanol) benzophenone tetracarboxylic dianhydride (6FBA) with a mass ratio of 2:2:3 were ultrasonically dispersed in 20 mL of N,N-dimethylacetamide. Under an inert gas protection atmosphere, the reaction was carried out at 50 °C for 0.5 h, then at 0 °C for 5 h, and then left standing at room temperature for 24 h to obtain a precursor solution; Next, 0.3 parts of 1-(4-iodophenyl)ethylamine hydrochloride was dissolved in 10 mL of N,N-dimethylformamide and added to the precursor solution, and the reaction was carried out at 70 °C for 3 h to obtain a polyimide composite network structure matrix; Then, 0.5 parts of cobalt oxide, iron oxide, and copper oxide with a mass ratio of 1:1:3, 3 parts of ZnO, nano-SiO2, and nano-BN sheets with a mass ratio of 1:1:1, and 0.08 parts of hexafluoroisopropanol, toluenesulfonic acid, and triethylamine with a mass ratio of 4:2:3 were added to the polyimide composite network structure matrix, and the reaction was carried out at 80 °C for 24 h to obtain a preform; The preform was poured into a mold, and the mold containing the preform was placed in a flat vulcanizer, and at a pressure of 50 MPa / cm 2 pressure, the reaction was carried out at 300 °C for 2 h to obtain a transition metal oxide-doped polyimide composite material (the eighth product).

[0052] In the present invention, the above-prepared transition metal oxide-doped polyimide composite material can be applied to the production of a heat-conducting layer. When preparing the transition metal oxide-doped polyimide composite material, the selected monomers are hydrophobic monomers, hydrophobic functional groups are introduced into the structure, a polyimide precursor solution with hydrophobic properties is obtained through reaction, and the carboxyl groups in its structure are further etherified to further enhance its hydrophobic properties and inhibit the change of thermal resistance caused by moisture absorption; At the same time, by doping transition metal oxides, the transition metal oxide-doped polyimide composite material is superior to traditional polyimide composite materials in terms of mechanical properties, thermal conductivity, coefficient of expansion, and multifunctionality; Moreover, the nano-scale reinforcing agent can significantly improve the mechanical properties of the composite material. Due to the high specific surface area and strong interfacial interaction of the nanoparticles, they can effectively transfer stress, thereby improving the overall mechanical properties of the transition metal oxide-doped polyimide composite material and synergistically improving the thermal conductivity and reducing the coefficient of expansion.

[0053] In the above, referring to Figures 2 - 5 as shown, the present invention respectively carried out water contact angle tests, mechanical property tests, and thermal property tests on the transition metal oxide-doped polyimide composite materials prepared in Examples 1-8. Specifically, Figure 2Schematic diagram of the surface water contact angle test of the transition metal oxide-doped polyimide composite in Example 1. Among them, Figures a, b, c, and d are schematic diagrams of the process of dropping the liquid to be tested onto the surface of the transition metal oxide-doped polyimide composite in sequence. As can be seen from Figure d, the water contact angle of the transition metal oxide-doped polyimide composite can reach 159.8°, which is much larger than 90°. It can be shown that by doping transition metal oxides, the polyimide composite belongs to the hydrophobic category. It should be noted that generally, when the water contact angle is within 90°, it indicates that the liquid tends to spread on the material surface, and this surface is called a hydrophilic surface; when the water contact angle is 90 - 150°, it indicates that the liquid tends to form beads and roll on the material surface without easy spreading, and this surface is called a hydrophobic surface; while when the water contact angle is greater than 150°, the material surface is considered superhydrophobic. Among them, Figure 3 、 Figure 4 and Figure 5 respectively correspond to the schematic diagrams of the tensile strength, thermal conductivity, and expansion rate test results of the transition metal oxide-doped polyimide composites prepared in Examples 1 - 8, as well as the pre-products and commercially available products prepared from the network structure matrix of the polyimide composite without doping transition metal oxides; from Figure 3 it can be seen that the first to eighth products adopted chemical modification to prepare cross-linked network structure polyimide composites and used transition metal doping to further improve their tensile strength (compared with commercially available products). The tensile strength of the transition metal oxide-doped polyimide composite can reach 2000 MPa, showing strong mechanical properties; from Figure 4 it can be seen that compared with commercially available products, the first to eighth products are the cross-linked network structures prepared in the present invention, and the thermal conductivity can reach 2 W·m -1 ·K -1 , effectively improving their thermal conductivity. Among them, the content of the transition metal oxides used in the third and fourth products is relatively high, and their thermal conductivity is higher than that of other products. It can be obtained that the cross-linked network structure and the doping of transition metal oxides synergistically improve their thermal conductivity; from Figure 5 it can be obtained that by performing water absorption expansion tests on the first to eighth products, the anti-expansion effect can be achieved.

[0054] In the above, the test methods for the water contact angle test, mechanical property test, and thermal property test of the transition metal oxide-doped polyimide composite are as follows:

[0055] 1) Water contact angle test: Cut the transition metal oxide-doped polyimide composite in Example 1 into specimens of 10×30 mm, paste them onto a glass plate, drop a drop of deionized water on its surface and then read the value. Each specimen is tested at 3 points, and the results are averaged.

[0056] 2) Tensile property test: According to GB / T1040.3—2006, dumbbells with a length of 110 mm were respectively made from the transition metal oxide-doped polyimide composites prepared in Examples 1-8, the pre-products mentioned above, and commercially available products, and were respectively clamped on the fixture for tensile test; among them, the distance between the fixtures was 80 mm, the sensor test pressure was 500 N, and the tensile rate was 10 mm / min; for each group of experiments, 3 samples with the same performance were selected for parallel test, and the test results were averaged to obtain the test results.

[0057] 3) Thermal conductivity test: The thermal diffusivity of the transition metal oxide-doped polyimide composites prepared in Examples 1-8, the pre-products mentioned above, and commercially available products was measured by a German NETZSCH LFA467 type laser thermal conductivity meter, and its thermal conductivity was calculated by the following formula: Thermal conductivity = density × specific heat capacity × thermal diffusivity.

[0058] 4) Swelling rate test: 0.5 g of the transition metal oxide-doped polyimide composites prepared in Examples 1-8, the pre-products mentioned above, and commercially available products were respectively selected, and were respectively soaked in 30,000 mL of water and left standing for 24 h, taken out, dried the surface moisture and weighed, and its swelling rate was: (absorbed water mass - mass before water absorption) / mass before water absorption × 100%.

Claims

1. A transition metal oxide doped polyimide composite material, characterized in that: The raw materials for preparation include, by weight: 4-6 parts of dianhydride monomer, 5-7 parts of diamine monomer, 0.1-0.3 parts of modifier, 0.2-0.6 parts of transition metal oxide, 2-4 parts of reinforcing agent, 0.08-0.1 parts of catalyst and / or dehydrating agent; Wherein, the dianhydride monomer is a hydrophobic monomer; The modifier is one of 2-pyridylethylamine hydrochloride, cyclopentaneethylamine hydrochloride, 1-(4-iodophenyl)ethylamine hydrochloride, 2-fluoroethylamine hydrochloride, 2-(2-naphthyl)ethylamine hydrochloride and hydroxyethylamine hydrochloride.

2. The transition metal oxide-doped polyimide composite material according to claim 1, characterized in that: The dianhydride monomer is one or more of perfluorohexyl dianhydride (PFDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-(hexafluoroisopropanol) diphthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroisopropanol) benzophenonetetracarboxylic dianhydride (6FBA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (BPADA), and 3,3',4,4'-diphenyl sulfide tetracarboxylic dianhydride.

3. The transition metal oxide-doped polyimide composite material according to claim 1, characterized in that: The diamine monomer is one or more of 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (MDA), 3,3'-dimethyl-4,4'-diaminodiphenyl ether (OMDA), 4,4'-diaminodiphenyl sulfone (DDS), p-phenylenediamine (PDA), 4,4'-diaminodiphenyl dimethyl biphenyl (BPDA), 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 2,2-bis(4-aminophenoxy)hexafluoropropane (6FDA-DAM).

4. The transition metal oxide-doped polyimide composite material according to claim 1, characterized in that: The transition metal oxide is one or more of cobalt oxide, nickel oxide, molybdenum oxide, iron oxide and copper oxide.

5. The transition metal oxide-doped polyimide composite material according to claim 1, characterized in that: The reinforcing agent is one or more of nano ZnO, nano SiO2, nano BN sheet, and MXene nano sheet.

6. The transition metal oxide-doped polyimide composite material according to claim 1, characterized in that: The catalyst is one or more of hexafluoroisopropanol, trimethylchlorosilane, toluenesulfonic acid, pyridine, triethylamine and acetic anhydride.

7. The transition metal oxide-doped polyimide composite material according to claim 1, characterized in that: The dehydrating agent is one or more of hexafluoroisopropanol, trimethylsilyl chloride, toluenesulfonic acid, pyridine, triethylamine, and acetic anhydride.

8. A method for preparing a transition metal oxide-doped polyimide composite material, characterized in that: The method is applied to prepare the transition metal oxide-doped polyimide composite material according to any one of claims 1 to 7, and the preparation method comprises the following steps: S1, select 4-6 parts of dianhydride monomer and 5-7 parts of diamine monomer, ultrasonically disperse them in 20mL N, N-dimethylacetamide, react at 35-50°C for 0.5-1h under an inert gas atmosphere, then react at 0°C for 3-5h, and then stand at room temperature for 24h to obtain a precursor solution; Wherein, the dianhydride monomer is a hydrophobic monomer; S2, selecting 0.1-0.3 parts of a modifier and dissolving it in 10 mL of N,N-dimethylformamide, and adding it to the precursor solution and reacting it at 50-80° C. for 3-5 hours to obtain a polyimide composite material network structure matrix; S3, adding 0.2-0.6 parts of transition metal oxide, 2-4 parts of reinforcing agent and 0.08-0.1 parts of catalyst and / or dehydrating agent to the polyimide composite material network structure matrix, reacting at 80° C. for 24 hours to obtain a preform; S4, pouring the preform into a mold, and obtaining a transition metal oxide-doped polyimide composite material through thermal forming.

9. The method for preparing a transition metal oxide-doped polyimide composite material according to claim 8, characterized in that: In S4, the thermal forming reaction conditions of the transition metal oxide-doped polyimide composite material are: Place it in a flat vulcanizer and react at 300℃ for 2h under a pressure of 20-70MPa.

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