Catalytic method polyimide film preparation method

Abstract

The invention relates to the field of polyimide films, and discloses a catalytic polyimide film preparation method, which comprises: S1, preparing a prepolymer, dissolving a fluorine-containing diamine monomer in a polar solvent, placing in a reaction kettle, adding an aromatic dianhydride monomer at a low temperature of 0-10 DEG C, stirring, mixing, and reacting to generate a polyamide acid solution; s2, primary catalysis: adding an organic base catalyst into the polyamide acid solution prepared in the step S1; s3, second-stage catalysis: after the step S2 is completed, adding a coordination type organic basic catalyst into the first-stage catalyst; and S4, film formation and post-treatment. Amidation and ring-closure reactions are promoted in stages through the synergistic effect of the double catalysts, the reaction rate matching performance is remarkably improved, accurate control over molecular chains is achieved, a high-purity polymer matrix with uniform molecular weight distribution and complete ring closure is obtained, and the structural uniformity and mechanical strength of the film are fundamentally improved; the structure defect caused by incomplete reaction under a traditional single catalytic system is avoided.

Description

Technical Field

[0001] This invention relates to the field of polyimide film technology, specifically a catalytic method for preparing polyimide films. Background Technology

[0002] Polyimide films, as a high-performance engineering material, have a wide range of applications in electronics, aerospace and other fields. Traditional preparation methods generally rely on high-temperature thermal imidization processes (300-450℃), which leads to thermal degradation of molecular chains and affects the mechanical strength and thermal stability of the film.

[0003] Existing methods generally rely on high-temperature processing to achieve imidization ring closure. This process is not only energy-intensive but also prone to thermal degradation of polymer chains, leading to a significant deterioration in the mechanical properties and thermal stability of the film. In addition, conventional catalytic systems are not well-matched to amidation and ring-closure reactions, often resulting in a lack of effective control over the molecular chain growth stage, a wide molecular weight distribution of the product, and low efficiency in subsequent ring-closure reactions, leading to a large number of unclosed ring structure defects inside the film. While chemical imidization can lower the thermal processing temperature, the dehydrating agent system used can easily lead to byproduct residues, affecting the purity and dielectric properties of the film. This makes it difficult for traditional polyimide films to meet the stringent requirements for high-performance materials in advanced electronic devices, high-frequency communication equipment, and other fields. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a catalytic method for preparing polyimide films, which solves the problem that traditional polyimide films cannot meet the high-performance material requirements of advanced electronic devices, high-frequency communication equipment, and other fields.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a polyimide film, characterized in that it comprises the following raw materials in parts by weight:

[0006] 100 to 120 parts of aromatic dianhydride are used to participate in the formation of polyamic acid solution;

[0007] 100-110 parts of fluorinated diamine react with aromatic dianhydride monomers to form a prepolymer;

[0008] 0.5–2 parts of organic base catalyst and 0.3–1.5 parts of coordination-type organic base catalyst;

[0009] 1 to 5 parts of nano boron nitride filler are used to enhance the thermal conductivity of the film.

[0010] Preferably, the aromatic dianhydride includes one or more of biphenyl tetracarboxylic dianhydride, pyromellitic tetracarboxylic dianhydride, and diphenyl ether tetracarboxylic dianhydride, and the fluorinated diamine includes 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl or 4,4'-diaminooctafluorobiphenyl, which react with the aromatic dianhydride monomer to form a prepolymer.

[0011] Preferably, the aromatic dianhydride includes pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride, and the fluorinated diamine includes 4,4'-diaminooctafluorobiphenyl.

[0012] Preferably, the organic base catalyst comprises 1,8-diazabicycloundec-7-ene, the coordination-type organic base catalyst comprises isoquinoline, and the boron nitride nanofiller is boron nitride nanoparticles with a surface treated with a silane coupling agent, having a particle size range of 50-200 nm and a specific surface area ≥50 m². 2 / g, used to enhance the thermal conductivity and interfacial adhesion of the thin film.

[0013] Preferably, the molar ratio of the aromatic dianhydride to the fluorinated diamine is 1:0.9 to 1:1.

[0014] A method for preparing polyimide films by catalysis includes the following steps:

[0015] S1. Preparation of prepolymer: Dissolve fluorinated diamine monomer in a polar solvent, place it in a reaction vessel, add aromatic dianhydride monomer under low temperature conditions of 0-10℃, stir and mix, and react to generate polyamic acid solution;

[0016] S2. Primary catalysis: An organic base catalyst is added to the polyamic acid solution prepared in step S1, and the reaction is stirred at room temperature to promote the extension of the amic acid chain and carry out primary catalysis to obtain the primary catalyst.

[0017] S3. Secondary catalysis: After step S2 is completed, a coordination-type organic basic catalyst is added to the primary catalyst, and the reaction vessel is heated to 60-80℃ for 1-3 hours to activate the closed-loop reaction and obtain the secondary catalyst;

[0018] S4. Film Formation and Post-treatment: The secondary catalyst is cast into a film using a casting machine, and then subjected to a gradient temperature increase in an oven from 80°C to 180°C to finally obtain the thin film.

[0019] Preferably, the primary catalytic time in S2 is controlled at 2-4 hours, and the molecular weight is controlled at 20,001-50,000. The organic base catalyst promotes the chain extension reaction by activating the carboxylic acid group of the amide acid chain, and the coordination-type organic base catalyst accelerates the dehydration and ring-closing reaction through Lewis acid sites.

[0020] Preferably, the gradient heating process in S4 includes the following stages: after maintaining a constant temperature of 80°C for 0.5 hours, the temperature is increased to 180°C at a rate of 120°C / h, and finally the temperature is maintained for 1 to 2 hours.

[0021] Preferably, step S1 further includes adding nano-boron nitride filler during the preparation process, and simultaneously dispersing it with the fluorinated diamine monomer in a polar solvent. The polar solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone. The mass ratio of the polar solvent to the total mass of the fluorinated diamine and aromatic dianhydride monomer is 3:1 to 5:1, ensuring that the viscosity of the prepolymer solution is controlled at 500-2000 mPa·s.

[0022] Preferably, the room temperature condition in S2 is 25±2℃, and the stirring rate is maintained at 200-400rpm to ensure uniform dispersion of the catalyst.

[0023] This invention provides a catalytic method for preparing polyimide films. It offers the following advantages:

[0024] 1. This invention promotes amidation and ring-closing reactions in stages through the synergistic effect of two catalysts, significantly improving the matching of reaction rates, achieving precise control of molecular chains, obtaining a high-purity polymer matrix with uniform molecular weight distribution and complete closed rings, improving the structural uniformity and mechanical strength of the film, and avoiding structural defects caused by incomplete reactions in traditional single-catalyst systems.

[0025] 2. This invention replaces the high-temperature thermal imidization process with a low-temperature stepwise reaction process, which effectively avoids the thermal degradation of polymer chains while ensuring high closed-loop efficiency. This not only significantly reduces energy consumption but also significantly improves the thermal stability and long-term reliability of the material, breaking through the bottleneck of high-temperature processes in improving film performance.

[0026] 3. This invention utilizes an in-situ composite strategy with functionalized nanofillers to enhance multiphase synergistic effects through interface optimization without damaging the polymer molecular structure, thereby simultaneously achieving a significant enhancement of the thermal conductivity and a balanced improvement in the mechanical properties of the thin film. This solves the problem of incompatibility between functional properties and matrix stability in traditional modification technologies. Attached Figure Description

[0027] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides a catalytically produced polyimide film, comprising the following raw materials:

[0030] Aromatic dianhydride: 100 to 120 parts, including biphenyl tetracarboxylic dianhydride in a specific embodiment, as an important monomer in the reaction, participating in the formation of the polyamic acid solution.

[0031] Fluorinated diamine: 100-110 parts, in one specific embodiment including 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, which reacts with biphenyltetracarboxylic dianhydride monomer to form a prepolymer, the fluorinated properties of which help improve the performance of the film.

[0032] The molar ratio of aromatic dianhydride monomers to fluorinated diamines is 1:0.9 to 1:1.

[0033] Organic base catalyst: 0.5 to 2 parts, in one specific embodiment including 1,8-diazabicycloundec-7-ene, which promotes ammonium acid chain elongation in primary catalysis.

[0034] Coordination-type organic basic catalyst: 0.3 to 1.5 parts, including isoquinoline in a specific embodiment, to activate the ring-closing reaction in secondary catalysis.

[0035] Nano-boron nitride filler: 1-5 parts, used to enhance the thermal conductivity of the film. It is added to the polar solvent along with the diamine monomer during the prepolymer preparation stage. The nano-boron nitride filler consists of boron nitride nanoparticles with a surface treated with a silane coupling agent, a particle size range of 50-200 nm, and a specific surface area ≥50 m². 2 / g, used to enhance the thermal conductivity and interfacial adhesion of the thin film.

[0036] In a specific embodiment, in addition to biphenyl dianhydride, aromatic dianhydride substitutes can also be pyromellitic dianhydride, diphenyl ether dianhydride, etc. Pyromellitic dianhydride has high reactivity and can accelerate the formation of prepolymer, but the film produced has relatively poor flexibility; the film produced by diphenyl ether dianhydride has better flexibility, but slightly lower reactivity. In practical applications, a suitable aromatic dianhydride substitute can be selected according to different requirements for film performance, and its dosage remains at 100 parts.

[0037] In a specific embodiment, in addition to 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminooctafluorobiphenyl is also a feasible alternative for fluorinated diamines. 4,4'-diaminooctafluorobiphenyl has a higher fluorine content, which can further improve the corrosion resistance and dielectric properties of the film, but the price is relatively high. Its dosage can be adjusted in the range of 90 to 110 parts according to the specific reaction conditions.

[0038] A method for preparing a catalytically synthesized polyimide film includes the following steps:

[0039] Please see Figure 1

[0040] S1. Prepolymer preparation: Nano-boron nitride filler and diamine monomer are dissolved in a polar solvent and placed in a reaction vessel. Aromatic dianhydride monomer is added and stirred under low-temperature conditions of 0-10℃ to generate a polyamic acid solution. Low-temperature conditions are chosen to suppress side reactions and ensure the purity and structural integrity of the prepolymer. Polar solvents include N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone. The mass ratio of the polar solvent to the total mass of the fluorinated diamine and aromatic dianhydride monomer is 3:1 to 5:1 to ensure the viscosity of the prepolymer solution is controlled at 500-2000 mPa·s.

[0041] Prepolymer preparation experiments were conducted at temperatures of -5℃, 0℃, 5℃, 10℃, and 15℃. The results showed that within the range of 0-10℃, the molecular weight of the prepolymer gradually increased with increasing temperature. However, when the temperature exceeded 10℃, side reactions increased significantly, and the purity of the prepolymer decreased. Therefore, 0-10℃ was selected as the prepolymerization temperature.

[0042] S2. Primary catalysis: An organic base catalyst is added to the polyamic acid solution prepared above to promote the extension of the amic acid chain. The primary catalysis time is controlled at 2-4 hours to keep the molecular weight at 20,001-50,000, thus obtaining the primary catalyst. The organic base catalyst can effectively promote the growth of the amic acid chain and increase the molecular weight of the prepolymer.

[0043] In one specific embodiment, experiments were conducted with primary catalytic times of 1 h, 2 h, 3 h, 4 h, and 5 h. When the catalytic time was 2–4 h, the molecular weight could be controlled within the range of 20,000–50,000, and the molecular weight distribution was relatively narrow. When the time was less than 2 h, the molecular weight was lower. When the time exceeded 4 h, the molecular weight distribution became wider. Therefore, the primary catalytic time was determined to be 2–4 h. The organic base catalyst promotes chain extension reaction by activating the carboxylic acid groups of the amide acid chain, and the coordination-type organic base catalyst accelerates the dehydration and ring-closing reaction through Lewis acid sites.

[0044] S3. Secondary catalysis: After the primary catalysis is completed, a coordination-type organic basic catalyst is added to the primary catalyst and reacted at 60-80℃ for 1-3 hours with the stirring rate controlled at 200-400 rpm to activate the ring-closure reaction and obtain the secondary catalyst. The coordination-type organic basic catalyst can efficiently catalyze the ring-closure reaction at this temperature, so that the ring-closure efficiency reaches more than 95%.

[0045] S4. Film Formation and Post-treatment: After the secondary catalyst is cast into a film using a casting machine, it is subjected to a gradient temperature treatment in an oven from 80℃ to 180℃. The gradient temperature treatment can make the reaction more complete and uniform, avoid film defects caused by sudden temperature rise, and further improve the film performance.

[0046] The specific mechanism is as follows: In the primary catalytic stage, the organic base catalyst interacts with the carboxyl groups in polyamic acid, neutralizing part of the acidity and reducing the intermolecular repulsion, thereby promoting the extension of the amic acid chain. In the secondary catalytic stage, the coordination-type organic base catalyst, including isoquinoline, can activate the carboxylic anhydride sites on the amic acid molecular chain, reduce the activation energy of the ring-closing reaction, and thus accelerate the ring-closing reaction.

[0047] Meanwhile, a synergistic effect exists between the organic-base catalyst and the coordination-type organic-base catalyst. The organic-base catalyst promotes the elongation of the amide acid chain, forming a longer molecular chain, which provides more reaction sites for the ring-closure reaction catalyzed by the coordination-type organic-base catalyst. Conversely, the efficient ring-closure reaction of the coordination-type organic-base catalyst promptly converts the elongated amide acid chain into an imide ring, preventing excessively long amide acid chains from becoming entangled and hindering further reaction progress. This synergistic effect allows the rates of amidation and ring-closure reactions to be well matched, ensuring the efficient conduct of the reaction.

[0048] Through the synergistic effect and staged catalysis of dual catalysts, polyimide preparation was achieved at a maximum temperature of 180℃ under low-temperature conditions, significantly reducing energy consumption and avoiding the adverse effects of high temperatures on film performance. The staged synergistic catalysis of dual catalysts can exert highly efficient catalytic effects on amidation and ring-closing reactions respectively, solving the problem of low efficiency of single catalysts and making the reaction more thorough and efficient. Due to the reasonable matching of reaction rates, imidization is thorough and molecular chain degradation caused by high-temperature post-processing is avoided. The prepared polyimide film has a more uniform molecular weight distribution and a more complete molecular structure. Therefore, the uniformity and various properties of the film are significantly improved. At the same time, the addition of functional monomer modification and nano-boron nitride filler further optimizes the film performance, such as improving the mechanical strength and thermal conductivity of the film, making it better able to meet the application requirements of different fields.

[0049] Example 1:

[0050] In one specific embodiment, the preparation of the above-mentioned catalytic polyimide film includes the following steps:

[0051] S1. Preparation of prepolymer: 5 parts by weight of boron nitride nanofiller and 100 parts by weight of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl are dissolved in N,N-dimethylformamide. The solid content of the resulting polyamic acid solution is controlled at 10-25 wt%. The stirring speed is not less than 300 rpm and the reaction time is 3-5 hours. 100 parts by weight of biphenyltetracarboxylic dianhydride are added at 0℃ and the reaction is stirred to generate a polyamic acid solution.

[0052] S2. Primary catalysis: Add 0.5 parts by weight of organic base catalyst to the above prepolymer, stir and react at room temperature for 2 hours to make the molecular weight reach 20,000. The room temperature is 25±2℃, and the stirring rate is maintained at 200-400 rpm to ensure uniform dispersion of the catalyst.

[0053] S3. Secondary catalysis: Add 0.3 parts by weight of isoquinoline, heat to 60°C, react for 3 hours, and the ring-closing efficiency is 95%;

[0054] S4. Film Formation and Post-treatment: The reaction solution is cast into a film, and then subjected to a gradient heating treatment, gradually increasing from 80℃ to 180℃ to obtain a polyimide film.

[0055] Example 2:

[0056] In one specific embodiment, the preparation of a catalytically synthesized polyimide film includes the following steps:

[0057] S1. Preparation of prepolymer: 5 parts by weight of boron nitride nanofiller and 100 parts by weight of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl are dissolved in N,N-dimethylformamide, and 100 parts by weight of biphenyltetracarboxylic dianhydride are added at 0°C. The mixture is stirred to generate a polyamic acid solution.

[0058] S2. Primary catalysis: Add 0.5 parts by weight of organic base catalyst to the above prepolymer and stir the reaction at room temperature for 2 hours to achieve a molecular weight of 20,000.

[0059] S3. Secondary catalysis: Without adding a coordination-type organic basic catalyst, directly heat to 60℃ and react for 3 hours.

[0060] S4. Film Formation and Post-treatment: The reaction solution is cast into a film, and then subjected to a gradient heating treatment, gradually increasing from 80℃ to 180℃ to obtain a polyimide film.

[0061] The difference between this embodiment and Embodiment 1 is that no coordination-type organic basic catalyst is added during the secondary catalysis in step S3. This embodiment simplifies the process by eliminating the coordination-type organic basic catalyst.

[0062] Example 3:

[0063] In one specific embodiment, the preparation of a catalytically synthesized polyimide film includes the following steps:

[0064] S1. Preparation of prepolymer: 100 parts by weight of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl are dissolved in N,N-dimethylformamide, and 100 parts by weight of biphenyltetracarboxylic dianhydride are added at 0°C. The mixture is stirred to generate a polyamic acid solution.

[0065] S2. Primary catalysis: Add 0.5 parts by weight of organic base catalyst to the above prepolymer and stir the reaction at room temperature for 2 hours to achieve a molecular weight of 20,000.

[0066] S3. Secondary catalysis: Add 0.3 parts by weight of isoquinoline, heat to 60°C, react for 3 hours, and the ring-closing efficiency is 95%.

[0067] S4. Film Formation and Post-treatment: The reaction solution is cast into a film, and then subjected to a gradient heating treatment, gradually increasing from 80℃ to 180℃ to obtain a polyimide film.

[0068] The difference from Example 1 is that no nano boron nitride filler is added, which simplifies the preparation process and reduces raw material costs, but loses the reinforcing function of the filler.

[0069] Example 4:

[0070] In one specific embodiment, the preparation of a catalytically synthesized polyimide film includes the following steps:

[0071] S1. Preparation of prepolymer: 5 parts by weight of boron nitride nanofiller and 180 parts by weight of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl are dissolved in N,N-dimethylformamide, and 100 parts by weight of biphenyltetracarboxylic dianhydride are added at 0°C. The mixture is stirred to generate a polyamic acid solution.

[0072] S2. Primary catalysis: Add 0.5 parts by weight of organic base catalyst to the above prepolymer and stir the reaction at room temperature for 1 hour to achieve a molecular weight of 15,000.

[0073] S3. Secondary catalysis: Add 0.3 parts by weight of isoquinoline, heat to 60°C, react for 3 hours, and the ring-closing efficiency is 95%.

[0074] S4. Film Formation and Post-treatment: The reaction solution is cast into a film, and then subjected to a gradient heating treatment, gradually increasing from 80℃ to 180℃ to obtain a polyimide film.

[0075] The difference between this embodiment and Embodiment 1 is that the primary catalytic time is shortened from 2 hours to 1 hour, thereby reducing the molecular weight of the prepolymer and aiming to optimize the reaction efficiency.

[0076] Example 5:

[0077] In one specific embodiment, the preparation of a catalytically synthesized polyimide film includes the following steps:

[0078] S1. Preparation of prepolymer: 5 parts by weight of boron nitride nanofiller and 180 parts by weight of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl are dissolved in N,N-dimethylformamide, and 100 parts by weight of biphenyltetracarboxylic dianhydride are added at 0°C. The mixture is stirred to generate a polyamic acid solution.

[0079] S2. Primary catalysis: Add 0.5 parts by weight of organic base catalyst to the above prepolymer and stir the reaction at room temperature for 2 hours to achieve a molecular weight of 20,000.

[0080] S3. Secondary catalysis: Add 0.3 parts by weight of isoquinoline, heat to 60°C, react for 3 hours, and the ring-closing efficiency is 95%.

[0081] S4. Film formation: After casting, bake directly at 180℃ for 1 hour to obtain a polyimide film.

[0082] The difference between this embodiment and Embodiment 1 is that the gradient heating is replaced with direct baking at 180°C for 1 hour, which significantly shortens the process time.

[0083] To verify the catalytic polyimide film provided in this application, the following experiments were prepared:

[0084] Experimental subjects:

[0085] The experimental group included the polyimide films prepared in Examples 1 to 5.

[0086] The control group consisted of polyimide films prepared using conventional methods, one of which involved dissolving aromatic dianhydrides and fluorinated diamines in a polar solvent and stirring to obtain a polyamic acid solution, followed by casting and curing at 300°C to obtain the film.

[0087] Test methods: Based on standards such as ASTM and ISO, key performance parameters were compared.

[0088] Performance testing equipment and standards:

[0089] Closed-loop efficiency: Using a Nicoleti S50 FTIR spectrometer, through a 1370 cm⁻¹... -1 The imide ring and 1510 cm -1 Calculation of the area ratio of characteristic peaks of the benzene ring.

[0090] Molecular weight and distribution: A Waters 1515 GPC system with three detectors in series (RI / UV / LS) was used. The mobile phase was DMF containing 0.05 M LiBr, and the flow rate was 1.0 mL / min.

[0091] Thermal conductivity: LFA467 laser flare analyzer (Netzsch), sample size Φ12.7mm, test temperature 25℃.

[0092] Mechanical properties: The tensile rate was 10 mm / min using an Instron 5967 universal testing machine, and the sample was a dumbbell type according to ASTM D882 standard.

[0093] Thermal stability: The TGAQ50 thermogravimetric analyzer (TAInstruments) was used under a nitrogen atmosphere, with a heating rate of 10℃ / min to 800℃.

[0094] Surface morphology: The sample was sputtered with gold using a FEINovaNanoSEM450 field emission microscope with an accelerating voltage of 5kV.

[0095] Experimental performance test results:

[0096] Chemical structure and reaction efficiency:

[0097] Group Closed-loop efficiency (%) Weight-average molecular weight (Mw) Molecular weight distribution (PDI) Example 1 95.2±0.5 68,000 1.25 Example 2 72.3±1.2 35,000 2.48 Example 3 94.8±0.7 65,500 1.30 Example 4 88.1±1.5 28,000 3.05 Example 5 90.6±0.9 59,000 1.72 control group 84.7±2.0 45,000 2.15

[0098] Example 1, through stepwise catalysis with a dual catalyst, significantly improved the ring-closing efficiency to 95.2%, with a high weight-average molecular weight of 68,000 and a narrow molecular weight distribution of only 1.25. This indicates that the method can effectively promote the reaction and yield a product with a high molecular weight and uniform distribution. Example 2, lacking a coordinating organic basic catalyst, saw a sharp drop in ring-closing efficiency to 72.3%, a drastic decrease in molecular weight, and a widening of the PDI to 2.48. This fully demonstrates the crucial role of the coordinating organic basic catalyst in the directional induction of the ring-closing reaction. Example 3, without the addition of nano-boron nitride filler, showed relatively low ring-closing efficiency and low molecular weight distribution. The molecular weight and other parameters are similar to those in Example 1, indicating that the nano-boron nitride filler has little impact on the chemical structure and reaction efficiency. In Example 4, the molecular weight is low and the distribution is wide due to insufficient first-stage catalysis time, indicating that the first-stage catalysis time needs to be controlled within an appropriate range to ensure product quality. In Example 5, the ring-closing efficiency and molecular weight are lower than those in Example 1 because the film was baked at high temperature directly without gradient heating after film formation, which reflects the importance of gradient heating for the full reaction. The control group used the traditional method, and all indicators were not as good as those in Example 1, showing the advantages of the method of the present invention in improving chemical structure and reaction efficiency.

[0099] Comparison of thermal and mechanical properties

[0100]

[0101] Example 1, with the addition of nano-boron nitride filler, achieved a thermal conductivity of 4.02 W / m·K, a 130% improvement compared to Example 3 without the filler. This demonstrates that nano-boron nitride filler significantly enhances the thermal conductivity of the film. In terms of mechanical properties and thermal stability, Example 1 exhibited a tensile strength of 152 MPa, an elongation at break of 12.5%, and a 5% thermal decomposition temperature of 532 °C, all superior to Example 3 and the control group. Example 3, without the addition of nano-boron nitride filler, showed slightly lower mechanical properties and thermal stability than Example 1, but still superior to the control group. The control group, due to severe molecular chain degradation, had a mechanical strength of only 54% of Example 1 and poor thermal stability. This further highlights the effectiveness of the present invention in improving the thermal and mechanical properties of the film, particularly the positive effects of adding nano-boron nitride filler and employing dual-catalyst synergistic catalysis.

[0102] Energy consumption and economic assessment

[0103]

[0104] The highest process temperature in Example 1 was 180℃, far lower than the 300℃ of the control group, and the overall energy consumption was only 24.5 kW·h / kg, a reduction of 60.7% compared to the control group, significantly reducing energy costs. Although the raw material cost of Example 1 increased slightly to 85 USD / kg due to the use of dual catalysts, about 9% higher than the control group, the overall economic efficiency was better due to the significant reduction in processing energy consumption, demonstrating the advantages of the method in terms of energy consumption and economy. Furthermore, due to the reasonable matching of reaction rates, thorough imidization, and avoidance of molecular chain degradation caused by high-temperature post-treatment, the prepared polyimide film has a more uniform molecular weight distribution and a more complete molecular structure, thus significantly improving the uniformity and various properties of the film.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A polyimide film, characterized in that: Including the following parts by weight of raw materials: 100 to 120 parts of aromatic dianhydride are used to participate in the formation of polyamic acid solution; 100-110 parts of fluorinated diamine react with aromatic dianhydride monomers to form a prepolymer; 0.5–2 parts of organic base catalyst and 0.3–1.5 parts of coordination-type organic base catalyst; 1 to 5 parts of nano boron nitride filler are used to enhance the thermal conductivity of the film.

2. The polyimide film according to claim 1, characterized in that: The aromatic dianhydride includes one or more of biphenyl tetracarboxylic dianhydride, pyromellitic tetracarboxylic dianhydride, and diphenyl ether tetracarboxylic dianhydride, and the fluorinated diamine includes 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl or 4,4'-diaminooctafluorobiphenyl, which react with the aromatic dianhydride monomer to form a prepolymer.

3. The polyimide film according to claim 1, characterized in that: The aromatic dianhydride includes pyromellitic dianhydride or diphenyl ether tetracarboxylic dianhydride, and the fluorinated diamine includes 4,4'-diaminooctafluorobiphenyl.

4. The polyimide film according to claim 1, characterized in that: The organic base catalyst comprises 1,8-diazabicycloundec-7-ene, the coordination-type organic base catalyst comprises isoquinoline, and the boron nitride nanofiller consists of boron nitride nanoparticles with a surface treated with a silane coupling agent, having a particle size range of 50-200 nm and a specific surface area ≥50 m². 2 / g, used to enhance the thermal conductivity and interfacial adhesion of the thin film.

5. A polyimide film according to claim 1, characterized in that: The molar ratio of the aromatic dianhydride to the fluorinated diamine is 1:0.9 to 1:

1.

6. A method for preparing polyimide films by catalysis according to any one of claims 1-5, characterized in that: Includes the following steps: S1. Preparation of prepolymer: Dissolve fluorinated diamine monomer in a polar solvent, place it in a reaction vessel, add aromatic dianhydride monomer under low temperature conditions of 0-10℃, stir and mix, and react to generate polyamic acid solution; S2. Primary catalysis: An organic base catalyst is added to the polyamic acid solution prepared in step S1, and the reaction is stirred at room temperature to promote the extension of the amic acid chain and carry out primary catalysis to obtain the primary catalyst. S3. Secondary catalysis: After step S2 is completed, a coordination-type organic basic catalyst is added to the primary catalyst, and the reaction vessel is heated to 60-80℃ for 1-3 hours with the stirring rate controlled at 200-400 rpm to activate the closed-loop reaction and obtain the secondary catalyst. S4. Film Formation and Post-treatment: The secondary catalyst is cast into a film using a casting machine, and then subjected to a gradient temperature increase in an oven from 80°C to 180°C to finally obtain the thin film.

7. The method for preparing polyimide films by catalysis according to claim 6, characterized in that: The primary catalytic time in S2 is controlled at 2-4 hours, and the molecular weight is controlled at 20,001-50,000. The organic base catalyst promotes chain extension reaction by activating the carboxylic acid group of the amide acid chain, and the coordination type organic base catalyst accelerates the dehydration and ring-closing reaction through Lewis acid sites.

8. The method for preparing polyimide films by catalysis according to claim 6, characterized in that: The gradient heating process in S4 includes the following stages: after maintaining a constant temperature of 80°C for 0.5 hours, the temperature is increased to 180°C at a rate of 120°C / h, and finally maintained at the temperature for 1 to 2 hours.

9. The method for preparing polyimide films by catalysis according to claim 6, characterized in that: The S1 further includes adding nano-boron nitride filler during the preparation process, and simultaneously dispersing it with the fluorinated diamine monomer in a polar solvent. The polar solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone. The mass ratio of the polar solvent to the total mass of the fluorinated diamine and aromatic dianhydride monomer is 3:1 to 5:

1.

10. The method for preparing a catalytic polyimide film according to claim 6, characterized in that: In S2, the room temperature condition is 25±2℃, and the stirring rate is maintained at 200-400rpm to ensure uniform dispersion of the catalyst.

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