Amino-functionalized ZIF-8 modified polyimide composite film and preparation method thereof

Abstract

This invention discloses an amino-functionalized ZIF-8 modified polyimide composite film and its preparation method, belonging to the field of polyimide film technology. The process involves a binary copolymerization reaction of p-phenylenediamine (p-PDA) and biphenyl tetracarboxylic anhydride (BPDA) to obtain a polyamic acid (PAA) solution. Then, amino-functionalized ZIFs (ZIF-8-NH2) are ground and thoroughly mixed with a solvent. After ultrasonic extraction, the mixture is introduced into the aforementioned PAA solution to obtain a PAA / ZIF-8-NH2 composite liquid. After adjusting the molar ratio of the dianhydride and undergoing thermal imidization treatment, the amino-functionalized ZIF-8 modified polyimide composite film is obtained. This invention introduces ZIF-8, which possesses high porosity, large specific surface area, adjustable pore structure, excellent thermal stability, and low thermal conductivity, into the composite film preparation process. Based on this, the ZIF-8 is amino-functionalized, resulting in a composite film material with uniform filler dispersion, ultra-low dielectric constant, low dielectric loss, and excellent thermal insulation performance.

Description

Technical Field

[0001] This invention relates to the field of polyimide film material technology, specifically to an amino-functionalized ZIF-8 modified polyimide composite film and its preparation method. Background Technology

[0002] Polyimide (PI) refers to a class of polymers containing an imide ring (-CO-NR-CO-) in its main chain. It is one of the best-performing organic polymer materials, possessing excellent thermal stability, mechanical properties, dielectric properties, and chemical stability due to the highly rigid structure of its molecular chain and strong intermolecular association forces. It is widely used in aerospace, microelectronics, optoelectronic engineering, high-temperature insulation materials, gas separation, and other fields. Based on the different molecular chain structural units, PI is classified into aromatic, semi-aromatic, and aliphatic types.

[0003] Aromatic polyimide (PI) has been extensively studied due to its superior thermal and mechanical properties compared to aliphatic PI, thanks to its abundant benzene and imide ring structures. However, the rigidity of the aromatic PI molecular structure leads to limitations in its solubility and flexibility, despite its excellent heat resistance, thus restricting its processing. To address this issue, flexible structures are typically incorporated into the main chain. While this reduces some of the material's heat resistance, it significantly improves the solubility and processability of PI.

[0004] With the rapid development of 5G mobile communication technology, integrated circuits, and flexible electronic devices, increasingly higher requirements are being placed on the dielectric and thermal management performance of key packaging and substrate materials. Ideal materials need to possess both extremely low dielectric constant and dielectric loss to reduce signal transmission delay, crosstalk, and power consumption; and excellent thermal stability and low thermal conductivity to achieve effective thermal insulation and protection.

[0005] Currently, polyimide (PI) films are widely used in the thermal insulation field, with applications mainly including direct use, composite modification, and structural design optimization. Composite modification improves thermal insulation performance by introducing low thermal conductivity fillers or constructing porous structures to further reduce the thermal conductivity of the PI film. This includes filled composite materials: adding low thermal conductivity fillers (such as SiO2, Al2O3, BN, aerogel, etc.) to the PI matrix to reduce thermal conductivity. Some fillers (such as BN) can also enhance mechanical properties and electrical breakdown resistance. However, high filler content can severely compromise the film's mechanical flexibility, leading to brittleness and cracking. Furthermore, filler agglomeration is a significant problem, making uniform dispersion difficult, and some fillers (such as BN) are expensive, increasing manufacturing costs. Porous / foamed PI films are produced through chemical foaming (adding foaming agents), freeze-drying, or supercritical CO2 treatment. Porous PI films can achieve porosity of over 70%, resulting in lightweight construction. While achieving lower thermal conductivity, excessive porosity leads to a significant decrease in mechanical strength, making the film prone to compression deformation. Uneven pore structure distribution also results in poor batch-to-batch stability of thermal insulation performance. Furthermore, residual foaming agent may affect the film's heat resistance and electrical insulation properties. Multilayer composite structures involve alternating stacking of PI films with other low thermal conductivity materials (such as ceramic fibers, graphene, and PTFE). This method utilizes interface reflection and scattering effects to reduce heat conduction while maintaining flexibility and high strength. Structural optimization and surface treatment include biomimetic microstructure design: constructing micron / nanoscale trenches or honeycomb structures on the PI film surface using laser etching, nanoimprinting, and other techniques increases thermal reflection and scattering, reduces effective thermal conductivity, and improves surface hydrophobicity. Surface metallization / coating: depositing aluminum (Al), silver (Ag), or coating a high-reflectivity ceramic coating (such as ZrO2) on the PI film surface can reflect radiant heat (infrared reflectivity >90%), reducing heat radiation transfer.

[0006] For example, patent publication number CN 119502504 A discloses a polyimide-based composite thermal insulation film laminate material structure and its preparation method. This polyimide-based composite thermal insulation film laminate material uses a PI thermal insulation base film as the mechanical support layer and airtight layer of the laminate structure, which can solve the problems of poor mechanical properties and insufficient thermal convection protection of PI fiber film. The introduction of porous PI fiber film into the laminate can significantly reduce thermal conductivity, while the design of the metal reflective layer can effectively block radiant heat. However, this technology directly deposits metal on the formed PI film (i.e., the "metal on PI" interface), and there is a lack of chemical bonding between the two. They are only bonded by physical action, and the initial adhesion is very weak. If the PI film surface has not undergone any treatment (such as plasma modification), its low surface energy and strong chemical inertness will further aggravate the problem of poor interfacial bonding. The thermal expansion coefficients of dense PI film, porous PI fiber film and metal layer are very different. When experiencing temperature changes, the expansion and contraction of each layer are inconsistent, which will generate periodic thermal stress at the interface and eventually cause microcracks. This may result in problems such as insufficient interlayer bonding, poor interfacial adhesion between the PI film and other functional layers (such as metal reflective layers and porous fiber layers), leading to delamination and peeling, and the formation of microcracks at the interface under high temperature or cyclic thermal stress, resulting in airtightness failure. Additionally, the porous structure may cause a decrease in mechanical properties and durability issues with the metal reflective layer. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides an amino-functionalized ZIF-8 modified polyimide composite film with uniform filler dispersion, ultra-low dielectric constant, low dielectric loss and excellent thermal insulation performance, and its preparation method.

[0008] This invention is achieved through the following technical solution:

[0009] An amino-functionalized ZIF-8 modified polyimide composite film is obtained by a binary copolymerization reaction of a highly heat-resistant aromatic diamine and an aromatic dianhydride to obtain polyamic acid, followed by grinding and adding the amino-functionalized zeolite imidazole ester skeleton material into the polyamic acid, and then obtaining a polyimide / zeolite imidazole ester skeleton material composite film after thermal imidization treatment.

[0010] A method for preparing an amino-functionalized ZIF-8 modified polyimide composite film includes the following steps: (1) P-phenylenediamine (PDA) was added to dimethylacetamide (DMAc) and stirred to dissolve. Then 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was added and reacted for 2-3 hours to obtain a polyamic acid solution. (2) Place 2-aminobenzimidazole and 2-methylimidazole in a container, add methanol as solvent, stir to dissolve, and then stir to react at 50-55℃ for 2-3h until a transparent and uniform solution is obtained, thus obtaining the linker solution; add the pre-prepared zinc nitrate solution to the linker solution under stirring, stir to react for 2-3h, and then obtain a milky white suspension, centrifuge, wash and dry to obtain ZIF-8-NH2 material; (3) Grind the ZIF-8-NH2 material obtained in step (2), add dimethylacetamide, and perform ultrasonic extraction. Then add it to the polyamic acid solution in step (1) and react for 5-6 hours to obtain PAA / ZIF-8-NH2 composite liquid. Then use an automatic coating machine to lay the film, and then perform programmed temperature rise to complete the thermal imidization treatment. After the treatment, cool naturally to room temperature and demold to obtain amino-functionalized ZIF-8 modified polyimide composite film, denoted as: PI / ZIF-8-NH2 composite film.

[0011] Further, in step (1), the molar ratio of p-phenylenediamine to 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is 1:0.97.

[0012] Further, in step (1), the solid content of the mixed solution of phenylenediamine, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and dimethylacetamide is 10%.

[0013] Further, in step (2), the molar ratio of 2-aminobenzimidazole to 2-methylimidazole is 1:4; the molar ratio of 2-aminobenzimidazole to zinc nitrate is 8:5.

[0014] Further, in step (2), the zinc nitrate solution is prepared by dissolving zinc nitrate hexahydrate in methanol. The centrifugation speed is 8500-9000 r / min, and the time is 10-15 min; washing is performed three times with methanol to remove any unreacted precursors and byproducts. Drying is performed under vacuum at 80°C for 10-12 h to eliminate residual solvent.

[0015] Furthermore, in step (3), before grinding the ZIF-8-NH2 material, the material is activated by drying it at 120-150℃ for 1-2 hours to improve the stability of the ZIF-8-NH2 material.

[0016] Furthermore, in step (3), the amount of ZIF-8-NH2 powder added accounts for 1wt%-3wt% of the polyamic acid solution.

[0017] Further, in step (3), the mass ratio of ZIF-8-NH2 to dimethylacetamide is 1:200-220; ZIF-8-NH2 and dimethylacetamide are first stirred at a constant speed for 1-1.5h, and then ultrasonically extracted for 1-1.5h.

[0018] Further, in step (3), the programmed temperature rise is as follows: the room temperature is raised to 80°C and held for 30 min; then the temperature is raised to 150°C and held for 30 min; then the temperature is raised to 200°C and held for 30 min; then the temperature is raised to 250°C and held for 30 min; then the temperature is raised to 300°C and held for 30 min; then the temperature is raised to 350°C and held for 30 min; each temperature rise takes 30 min.

[0019] The amino-functionalized ZIF-8 modified polyimide composite film prepared by the method of this invention has a thermal conductivity of 0.0607-0.1603 W / m·K, a relative permittivity of 1.817-1.962 at an applied electric field frequency of 1 kHz, a dielectric loss of 0.0424-0.0511, a glass transition temperature of 342-348 °C, a coefficient of thermal expansion of 9.15-10.9 ppm / K, and a film thickness of 12-20 μm.

[0020] The p-phenylenediamine in this invention is a highly heat-resistant aromatic diamine; 3,3',4,4'-biphenyltetracarboxylic dianhydride is a highly heat-resistant aromatic dianhydride.

[0021] The preparation principle of this invention: (1) In this invention, polyamic acid is prepared by using highly heat-resistant aromatic dianhydride and aromatic diamine through a binary copolymerization reaction. That is, the carboxyl group of the dianhydride undergoes a nucleophilic addition-elimination reaction with the amino group of the diamine to form an amide bond. Then, through a thermal imidization process, the PAA film is heated, and the carboxyl group in the amic acid dehydrates and closes the ring with the adjacent amide group to form an imide five-membered ring, thereby obtaining polyimide.

[0022] (2) This invention modifies polyimide films by introducing zeolite imidazole ester framework material (ZIF-8). ZIF-8 has the characteristics of high porosity, large specific surface area, adjustable pore structure, low thermal conductivity, and good thermal stability. However, the original ZIF-8 is composed of Zn 2+The ZIF-8 matrix, coordinated with 2-methylimidazole, has an inert methyl group on its surface, resulting in poor interfacial compatibility and a tendency to aggregate. Therefore, amino functionalization of ZIF-8 (ZIF-8-NH2) was considered, whereby 2-aminoimidazole partially or completely replaces 2-methylimidazole as the ligand, introducing a reactive amino functional group into the ZIF-8 backbone. The -NH2 group on the ZIF-8-NH2 surface can react with the carboxyl group at the PAA chain terminus or the anhydride group generated during its dehydration cyclization to form amide or imide bonds. This covalent bonding is the strongest interfacial bonding mechanism, significantly improving interfacial stability. This means the composite material can maintain its structure at higher temperatures. Therefore, ZIF-8-NH2 can simultaneously and synergistically improve the thermal insulation and dielectric properties of the PI film, making this -NH2 group crucial for subsequent strong interfacial bonding with the PI matrix.

[0023] (3) The inherent cavities and windows inside ZIF-8-NH2 can be regarded as fixed "nanobubbles", in which the enclosed air has an extremely low dielectric constant (~1.0), effectively reducing the overall dielectric constant of the composite material. The strong interfacial bonding greatly reduces the interfacial defects caused by the mismatch between the modulus and polarity of the filler and the matrix. These defects are the main cause of harmful interfacial polarization, which will significantly increase dielectric loss. The strong interface effectively suppresses this polarization, thereby reducing the dielectric constant while maintaining low dielectric loss. The numerous and strongly bonded interfaces between the uniformly dispersed nanoparticles and the PI matrix constitute efficient phonon scattering centers (heat is mainly conducted in the form of lattice vibration waves (phonons) in non-metallic solids). The porous structure and strong interfaces work together to greatly increase the path resistance of heat conduction, thereby significantly reducing the thermal conductivity of the composite film and improving the thermal insulation performance.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. In the preparation of polyamic acid (PI), this invention introduces highly heat-resistant aromatic diamines and dianhydrides. The rigid biphenyl structure of the dianhydride and the linear rigid structure of the diamine endow PI with high thermal stability, excellent mechanical properties (high modulus and tensile strength), and a low coefficient of thermal expansion. Furthermore, an amino-functionalized zeolite imidazole ester framework material (ZIF-8-NH2) is introduced. The -NH2 groups on the surface of ZIF-8-NH2 can react with the carboxyl groups at the ends of the PAA chains or with the anhydride groups generated during its dehydration cyclization to form amide or imide bonds. This covalent bonding is the strongest interfacial bonding mechanism, significantly improving interfacial stability. This means the composite material can maintain its structure at higher temperatures. Therefore, ZIF-8-NH2 can simultaneously and synergistically enhance the thermal insulation and dielectric properties of PI films, making it an ideal candidate material for applications with extreme requirements for high-temperature thermal insulation and dimensional stability (such as aerospace flexible thermal protection and high-end electronic device packaging).

[0025] 2. The thermal conductivity of the polyimide film of the present invention before the introduction of ZIF-8-NH2 powder is 0.1896 W / m·K, the relative permittivity at an applied electric field frequency of 1 kHz is 3.447, and the glass transition temperature is 339 °C. The thermal conductivity of the PI / ZIF-8-NH2 composite film after the introduction of ZIF-8-NH2 powder is 0.0607 W / m·K, the relative permittivity at an applied electric field frequency of 1 kHz is 1.959, and the glass transition temperature is 348 °C. This indicates that the introduction of ZIF-8-NH2 into the polyimide of the present invention for modification can effectively improve the thermal insulation performance, dielectric properties, and thermal stability of the composite film.

[0026] 3. In the field of flexible thermal protection for aerospace, thin films are typically used as barrier films or base layers in flexible thermal insulation felts and multilayer thermal insulation components for thermal insulation of deployable structures, engine compartments, propellant lines, etc., in spacecraft. The thermal conductivity of these materials is typically required to be below 0.1 W / m·K, while the thermal conductivity of the polyimide composite film of this invention is 0.0607 W / m·K. In the field of high-end electronic device packaging materials, thin films are mainly used as interlayer dielectric layers in integrated circuits, substrates or cover layers in flexible circuit boards, requiring a dielectric constant below 3.0. The relative dielectric constant of the polyimide composite film of this invention is 1.959 at an applied electric field frequency of 1 kHz. Therefore, the composite polyimide film of this invention is expected to serve as an aerospace electronic packaging material. Attached Figure Description

[0027] Figure 1 This is a product image of the amino-functionalized ZIF-8 / polyimide composite film in Example 2.

[0028] Figure 2The image shows a comparison of the FI-IR infrared spectra of Example 1, Comparative Example 1, and Comparative Example 2.

[0029] Figure 3 SEM images of different films from Example 1, Comparative Example 1, and Comparative Example 2, where (a) is magnified at 450K. (a) SEM image of the PI surface at magnification of 450K; (b) SEM image of the PI / ZIF-8 surface at magnification of 450K; (c) SEM image of the PI / ZIF-8-NH2 surface at magnification of 450K. Detailed Implementation

[0030] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0031] Example 1 The preparation method of amino-functionalized ZIF-8 modified polyimide composite film includes the following steps: (1) Weigh 1.2937 g of p-phenylenediamine (PDA) and put it into a 100 ml beaker. Add 33.1973 g of dimethylacetamide (DMAC) solvent. After the p-phenylenediamine dissolves in the solvent, add 3.4042 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) into the solution in three portions, with an interval of 0.5 h each time. React at room temperature for 2 h to obtain a polyamic acid solution.

[0032] (2) Weigh 1.0985 g of 2-aminobenzimidazole and 2.6808 g of 2-methylimidazole and place them in a clean beaker. Add 100 ml of methanol as a solvent and stir until the compounds are completely dissolved. Then stir the solution vigorously at 50 °C for 2.5 h until a clear and homogeneous solution is obtained, ensuring that the linker components are completely dissolved, to obtain the linker solution.

[0033] In a separate container, 1.4874 g of zinc nitrate hexahydrate was dissolved in 100 mL of methanol to prepare a zinc nitrate solution. Once the binder solution cooled to room temperature, the zinc nitrate solution was slowly added under continuous stirring. After stirring for 2 h, a white milky suspension began to form. The product was centrifuged at 8500 r / min for 10 min, and then washed three times with fresh methanol to remove any unreacted precursors and byproducts. The washed material was then vacuum dried at 80 °C for 12 h to remove residual solvent, yielding the ZIF-8-NH2 material.

[0034] (3) In order to improve the stability of ZIF-8-NH2, ZIF-8-NH2 was first dried at 150℃ for 1h to activate it, and then ground for later use. Take 0.0469g of ground ZIF-8-NH2 and add it to a 50ml beaker containing 10.0535g of reserved DMAC solvent. Place the beaker on a magnetic stirrer and stir at a stirring speed of 300r / min for 1h. Then, extract the mixture by ultrasonication for 1h and add it to a polyamic acid solution. React for 6h to obtain PAA / ZIF-8-NH2 composite solution. Then, use an automatic coating machine to lay the film and perform a programmed temperature rise to complete the thermal imidization treatment. After the treatment, allow it to cool naturally to room temperature. The thermal imidization program is as follows: heat from room temperature to 80℃ and hold for 30 min; then heat to 150℃ and hold for 30 min; then heat to 200℃ and hold for 30 min; then heat to 250℃ and hold for 30 min; then heat to 300℃ and hold for 30 min; then heat to 350℃ and hold for 30 min. Each temperature rise time is 30 min. The resulting film was then placed in hot water at 100°C and allowed to stand. After demolding, an amino-functionalized ZIF-8 modified polyimide composite film was obtained, denoted as: PI / ZIF-8-NH2 composite film.

[0035] Example 2 The preparation method of amino-functionalized ZIF-8 modified polyimide composite film includes the following steps: (1) Weigh 1.2945 g of p-phenylenediamine (PDA) and put it into a 100 ml beaker. Add 34.0212 g of dimethylacetamide (DMAC) solvent. After the p-phenylenediamine dissolves in the solvent, add 3.4022 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) into the solution in three portions, with an interval of 0.5 h each time. React at room temperature for 2 h to obtain a polyamic acid solution.

[0036] (2) Weigh 1.0980 g of 2-aminobenzimidazole and 2.6805 g of 2-methylimidazole and place them in a clean beaker. Add 100 ml of methanol as a solvent and stir until the compounds are completely dissolved. Then stir the solution vigorously at 50 °C for 2.5 h until a clear and homogeneous solution is obtained, ensuring that the linker components are completely dissolved, to obtain the linker solution.

[0037] In a separate container, 1.4880 g of zinc nitrate hexahydrate was dissolved in 100 mL of methanol to prepare a zinc nitrate solution. Once the binder solution cooled to room temperature, the zinc nitrate solution was slowly added under continuous stirring. After stirring for 2 h, a white milky suspension began to form. The product was centrifuged at 8500 r / min for 10 min, and then washed three times with fresh methanol to remove any unreacted precursors and byproducts. The washed material was then vacuum dried at 80 °C for 12 h to remove residual solvent, yielding the ZIF-8-NH2 material.

[0038] (3) In order to improve the stability of ZIF-8-NH2, ZIF-8-NH2 was first dried at 150℃ for 1h to activate it, and then ground for later use. Take 0.0469g of ground ZIF-8-NH2 and add it to a 50ml beaker containing 10.0432g of reserved DMAC solvent. Place the beaker on a magnetic stirrer and stir at a stirring speed of 300r / min for 1h. Then, after ultrasonic extraction for 1h, add the mixture to a polyamic acid solution and react for 6h to obtain a PAA / ZIF-8-NH2 composite solution. Then, use an automatic coating machine to lay the film and perform a programmed temperature rise to complete the thermal imidization treatment. After the treatment, allow it to cool naturally to room temperature. The thermal imidization program is as follows: heat from room temperature to 80℃ and hold for 30 min; then heat to 150℃ and hold for 30 min; then heat to 200℃ and hold for 30 min; then heat to 250℃ and hold for 30 min; then heat to 300℃ and hold for 30 min; then heat to 350℃ and hold for 30 min. Each temperature rise time is 30 min. The resulting film was then placed in hot water at 100°C and allowed to stand. After demolding, an amino-functionalized ZIF-8 modified polyimide composite film was obtained, denoted as: PI / ZIF-8-NH2 composite film.

[0039] Example 3 The preparation method of amino-functionalized ZIF-8 modified polyimide composite film includes the following steps: (1) Weigh 1.2930 g of p-phenylenediamine (PDA) and put it into a 100 ml beaker. Add 33.9018 g of dimethylacetamide (DMAC) solvent. After the p-phenylenediamine dissolves in the solvent, add 3.4121 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) into the solution in three portions, with an interval of 0.5 h each time. React at room temperature for 2 h to obtain a polyamic acid solution.

[0040] (2) Weigh 1.0979 g of 2-aminobenzimidazole and 2.6812 g of 2-methylimidazole and place them in a clean beaker. Add 100 ml of methanol as a solvent and stir until the compounds are completely dissolved. Then stir the solution vigorously at 50 °C for 2.5 h until a clear and homogeneous solution is obtained, ensuring that the linker components are completely dissolved, to obtain the linker solution.

[0041] In a separate container, 1.4877 g of zinc nitrate hexahydrate was dissolved in 100 mL of methanol to prepare a zinc nitrate solution. Once the binder solution cooled to room temperature, the zinc nitrate solution was slowly added under continuous stirring. After stirring for 2 h, a white milky suspension began to form. The product was centrifuged at 8500 r / min for 10 min, and then washed three times with fresh methanol to remove any unreacted precursors and byproducts. The washed material was then vacuum dried at 80 °C for 12 h to remove residual solvent, yielding the ZIF-8-NH2 material.

[0042] (3) In order to improve the stability of ZIF-8-NH2, ZIF-8-NH2 was first dried at 150℃ for 1h to activate it, and then ground for later use. Take 0.0469g of ground ZIF-8-NH2 and add it to a 50ml beaker containing 10.0226g of reserved DMAC solvent. Place the beaker on a magnetic stirrer and stir at a stirring speed of 300r / min for 1h. Then, after ultrasonic extraction for 1h, add the mixture to a polyamic acid solution and react for 6h to obtain a PAA / ZIF-8-NH2 composite solution. Then, use an automatic coating machine to lay the film and perform a programmed temperature rise to complete the thermal imidization treatment. After the treatment, allow it to cool naturally to room temperature. The thermal imidization program is as follows: heat from room temperature to 80℃ and hold for 30 min; then heat to 150℃ and hold for 30 min; then heat to 200℃ and hold for 30 min; then heat to 250℃ and hold for 30 min; then heat to 300℃ and hold for 30 min; then heat to 350℃ and hold for 30 min. Each temperature rise time is 30 min. The resulting film was then placed in hot water at 100°C and allowed to stand. After demolding, an amino-functionalized ZIF-8 modified polyimide composite film was obtained, denoted as: PI / ZIF-8-NH2 composite film.

[0043] Example 4 The preparation method of amino-functionalized ZIF-8 modified polyimide composite film includes the following steps: (1) Weigh 1.2957 g of p-phenylenediamine (PDA) and put it into a 100 ml beaker. Add 33.9256 g of dimethylacetamide (DMAC) solvent. After the p-phenylenediamine dissolves in the solvent, add 3.4004 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) into the solution in three portions, with an interval of 0.5 h each time. React at room temperature for 2 h to obtain a polyamic acid solution.

[0044] (2) Weigh 1.0986 g of 2-aminobenzimidazole and 2.6802 g of 2-methylimidazole and place them in a clean beaker. Add 100 ml of methanol as a solvent and stir until the compounds are completely dissolved. Then stir the solution vigorously at 50 °C for 2.5 h until a clear and homogeneous solution is obtained, ensuring that the linker components are completely dissolved, to obtain the linker solution.

[0045] In a separate container, 1.4885 g of zinc nitrate hexahydrate was dissolved in 100 mL of methanol to prepare a zinc nitrate solution. Once the binder solution cooled to room temperature, the zinc nitrate solution was slowly added under continuous stirring. After stirring for 2 h, a white milky suspension began to form. The product was centrifuged at 8500 r / min for 10 min, and then washed three times with fresh methanol to remove any unreacted precursors and byproducts. The washed material was then vacuum dried at 80 °C for 12 h to remove residual solvent, yielding the ZIF-8-NH2 material.

[0046] (3) In order to improve the stability of ZIF-8-NH2, ZIF-8-NH2 was first dried at 150℃ for 1h to activate it, and then ground for later use. Take 0.0469g of ground ZIF-8-NH2 and add it to a 50ml beaker containing 10.0332g of reserved DMAC solvent. Place the beaker on a magnetic stirrer and stir at a stirring speed of 300r / min for 1h. Then, after ultrasonic extraction for 1h, add the mixture to a polyamic acid solution and react for 6h to obtain a PAA / ZIF-8-NH2 composite solution. Subsequently, use an automatic coating machine to lay the obtained mixture into a film and then perform a programmed temperature rise to complete the thermal imidization treatment. After the treatment, allow it to cool naturally to room temperature. The thermal imidization program is as follows: heat from room temperature to 80℃ and hold for 30 min; then heat to 150℃ and hold for 30 min; then heat to 200℃ and hold for 30 min; then heat to 250℃ and hold for 30 min; then heat to 300℃ and hold for 30 min; then heat to 350℃ and hold for 30 min. Each temperature rise time is 30 min. The resulting film was then placed in hot water at 100°C and allowed to stand. After demolding, an amino-functionalized ZIF-8 modified polyimide composite film was obtained, denoted as: PI / ZIF-8-NH2 composite film.

[0047] (In Example 4, there was a large amount of ZIF-8-NH2, and the resulting composite film was not easy to demold and was brittle and easily broken, so it was not considered.)

[0048] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that ZIF-8-NH2 material was not added in Comparative Example 1, while the rest of the preparation process and conditions were the same as in Example 1, and a polyimide film (PI film) was obtained.

[0049] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that ZIF-8-NH2 was replaced with ZIF-8 in Comparative Example 2, that is, the ZIF-8 nanoparticles were not amino-functionalized. The rest of the preparation process and conditions were the same as in Example 1, and a PI / ZIF-8 composite film was obtained.

[0050] Material characterization analysis The functional groups of the thin film materials in Example 1, Comparative Example 1, and Comparative Example 2 were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR). The analysis results are as follows: Figure 2 As shown. Field emission scanning electron microscopy (SEM) was used to examine Example 1 and Example 2. The microstructure of the thin film surfaces in Example 1 and Comparative Example 2 was observed, and the results are as follows: Figure 3 As shown.

[0051] Figure 2 Middle, 730cm -1 The absorption peak near 1772 cm⁻¹ represents the characteristic peak of the CNC bending vibration of the polyimide ring. -1 1710cm -1 The existence of the PI structure was proven by the asymmetric and symmetric stretching vibrations of C=O in the five-membered imine ring structure, respectively. (1510 cm⁻¹) -1 It is the imidazole C=N stretching vibration and 3475cm -1 The stretching vibrations of the amino group proved that ZIF-8 and ZIF-8-NH2 were complexed into PI.

[0052] Figure 3 In the image, (a) is a SEM image of the PI surface at a magnification of 450K; (b) is a PI / ZIF-8 image at a magnification of 450K. (C) is a SEM image of the surface; (D) is a SEM image of the PI / ZIF-8-NH2 surface at 450K magnification. The comparison shows that both the PI substrate film and the PI / ZIF-8-NH2 composite film exhibit smooth and flat surfaces, proving that ZIF-8-NH2... Both were effectively embedded in the thin film, while the PI / ZIF-8 composite film surface had fewer protruding particles, which should be due to the presence of ZIF-8 nanoparticles. Since the particles were not completely bound to PI, comparing (b) and (c), it can be seen that the surface of (c) is smoother, which proves that after amino functionalization, ZIF-8-NH2 can be more uniformly dispersed in PI.

[0053] Material property testing The glass transition temperature, coefficient of thermal expansion, dielectric constant, and thermal conductivity of the thin film materials in Example 1, Comparative Example 1, and Comparative Example 2 were tested. The performance testing methods were as follows: (1) The coefficient of thermal expansion was tested using a static thermomechanical analyzer (TMA) under the following conditions: initial temperature 25℃, final temperature 250℃, load 0.05 N, heating rate 10℃ / min, and nitrogen protection 50 mL / min. (2) The glass transition temperature Tg was determined by differential scanning calorimetry (DSC). Pretreatment conditions: 30 s in 200℃ environment followed by 5 min cooling. Test conditions: initial temperature 25℃, final temperature 250℃, load 0.05 N, heating rate 10℃ / min, nitrogen protection 50 mL / min.

[0054] (3) Dielectric test: Dielectric performance test is performed using a precision impedance analyzer. Cut circles of the same diameter from a film of uniform thickness, attach aluminum sheets to both sides, and perform dielectric performance test in a dry environment. The initial frequency of the dielectric test is set to 1KHz and the termination frequency is set to 110MHz.

[0055] (4) Thermal conductivity test, measured by a transient planar heat source thermal conductivity meter (Hot Disk). Before the test, the thin film sample was cut into a circle with a diameter ≥20 mm, and two samples of the same thickness were stacked together to ensure complete coverage of the sensor's detection area.

[0056] The results of the thin film material properties measured by the above test methods are shown in Table 1.

[0057] Table 1. Performance test results of different thin film materials

[0058] As can be seen from the data in Table 1: (1) Compared with Comparative Example 1, the thermal conductivity and relative permittivity of the composite films obtained by adding ZIF-8-NH2 nanoparticles in Examples 1, 2 and 3 of the present invention are reduced. The thermal conductivity is reduced by 1.485-1.63; the thermal conductivity is reduced by 0.0293-0.1289 W / mk. Among them, the thermal conductivity of Example 2 is reduced most significantly, as low as 0.0607 W / m·k, which is 68% lower than that of Comparative Example 1. This shows that the addition of ZIF-8-NH2 nanoparticles has a good promoting effect on the thermal insulation and dielectric properties of the composite film.

[0059] (2) Compared with Comparative Examples 1 and 2, the glass transition temperature Tg of the composite films of Examples 1, 2 and 3 of the present invention is also significantly improved, by 3-9℃ and 7-13℃ respectively, which also shows that the addition of ZIF-8-NH2 nanoparticles has a good effect on improving the thermal stability of the composite films.

[0060] (3) Compared with Comparative Examples 1 and 2, although the composite films of Examples 1, 2 and 3 of the present invention have a slight increase in thermal expansion coefficient and dielectric loss, the CTE is still below 10ppm / K and the dielectric loss is only 0.0424-0.0511, which all meet the material performance requirements.

[0061] The above description illustrates that the present invention provides an amino-functionalized ZIF-8 modified polyimide composite film with good interfacial compatibility, uniform filler dispersion, ultra-low dielectric constant, low dielectric loss and excellent thermal insulation performance.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an amino-functionalized ZIF-8 modified polyimide composite film, characterized in that, Includes the following steps: (1) Add p-phenylenediamine to dimethylacetamide and stir to dissolve. Then add 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and react for 2-3 hours to obtain a polyamic acid solution. (2) Place 2-aminobenzimidazole and 2-methylimidazole in a container, add methanol as solvent, stir to dissolve, and then stir to react at 50-55℃ for 2-3h until a transparent and uniform solution is obtained, thus obtaining the linker solution; add the pre-prepared zinc nitrate solution to the linker solution under stirring, stir to react for 2-3h, and then obtain a milky white suspension, centrifuge, wash and dry to obtain ZIF-8-NH2 material; (3) Grind the ZIF-8-NH2 material obtained in step (2), add dimethylacetamide, and perform ultrasonic extraction. Then add it to the polyamic acid solution in step (1) and react for 5-6 hours to obtain PAA / ZIF-8-NH2 composite liquid. Then use an automatic coating machine to lay the film, and then perform programmed temperature rise to complete the thermal imidization treatment. After the treatment, cool naturally to room temperature and demold to obtain amino-functionalized ZIF-8 modified polyimide composite film.

2. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 1, characterized in that, In step (1), the molar ratio of p-phenylenediamine to 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is 1:0.

97.

3. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 4, characterized in that, In step (1), the solid content of the mixed solution of phenylenediamine, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and dimethylacetamide is 10%.

4. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 1, characterized in that, In step (2), the molar ratio of 2-aminobenzimidazole to 2-methylimidazole is 1:4; the molar ratio of 2-aminobenzimidazole to zinc nitrate is 8:

5.

5. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 1, characterized in that, In step (3), before grinding the ZIF-8-NH2 material, the material is activated by drying it at 120-150℃ for 1-2 hours.

6. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 1, characterized in that, In step (3), the amount of ZIF-8-NH2 powder added accounts for 1wt%-3wt% of the polyamic acid solution.

7. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 1, characterized in that, In step (3), the mass ratio of ZIF-8-NH2 to dimethylacetamide is 1:200-220; ZIF-8-NH2 and dimethylacetamide are first stirred at a constant speed for 1-1.5h, and then ultrasonically extracted for 1-1.5h.

8. The method for preparing the amino-functionalized ZIF-8 modified polyimide composite film according to claim 1, characterized in that, In step (3), the programmed temperature increase is as follows: the room temperature is raised to 80°C and held for 30 min; then the temperature is raised to 150°C and held for 30 min; then the temperature is raised to 200°C and held for 30 min; then the temperature is raised to 250°C and held for 30 min; then the temperature is raised to 300°C and held for 30 min; then the temperature is raised to 350°C and held for 30 min; each temperature increase takes 30 min.

9. An amino-functionalized ZIF-8 modified polyimide composite film obtained by the preparation method according to any one of claims 1-8, characterized in that, The amino-functionalized ZIF-8 modified polyimide composite film has a thermal conductivity of 0.0607-0.1603 W / m·K, a relative permittivity of 1.817-1.962 at an applied electric field frequency of 1 kHz, a dielectric loss of 0.0424-0.0511, a glass transition temperature of 342-348 °C, a coefficient of thermal expansion of 9.15-10.9 ppm / K, and a film thickness of 12-20 μm.

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