Catalytic polyimide film with low thermal expansion coefficient and preparation method thereof

Abstract

The invention relates to the field of polyimide films, and discloses a catalytic polyimide film with a low thermal expansion coefficient and a preparation method thereof, the catalytic polyimide film comprises 43-47% of a rigid polyimide material, 28-32% of a flexible polyimide material, 4-6% of a dynamic cross-linking agent, 7-9% of a component agent, and the balance of a solvent; the dynamic cross-linking agent comprises maleimide terminated polyamide and a difuran compound, and the ratio of the maleimide terminated polyamide to the difuran compound is 3: 2. Through the synergistic effect of constructing a stable framework by a rigid polyimide material, buffering stress by a flexible polyimide material and uniformly dissipating heat by flaky boron nitride, a chemical regulation and control system of'rigid constraint-flexible buffering-heat conduction balance 'is formed, thermal expansion is inhibited from the molecular level, and compared with a traditional physical method which purely depends on external force or a single component, the thermal expansion coefficient is greatly improved. According to the system, through complementation of chemical mechanisms of all components, the dimensional stability under temperature fluctuation is improved to a new height, and the problem that the thermal expansion coefficient in a wide temperature range is difficult to control is solved.

Description

Technical Field

[0001] This invention relates to the field of polyimide film technology, specifically to a catalytically produced polyimide film with a low coefficient of thermal expansion and its preparation method. Background Technology

[0002] Polyimide films, due to their high-temperature resistance and excellent mechanical strength, have become key materials in high-end fields such as electronic packaging and aerospace. With the development of technologies such as 5G communication and flexible displays, devices place stringent requirements on the dimensional stability of materials—especially in environments with frequent temperature fluctuations, where the coefficient of thermal expansion (CTE) of the film must be controlled at extremely low levels; otherwise, thermal stress can easily lead to device failure. While traditional polyimide films possess basic properties, their dimensional stability over a wide temperature range (-50 to 200°C) still falls short of the demands of precision applications. The low CTE has become a core bottleneck restricting its breakthrough into high-end fields.

[0003] During use, existing polyimide films are subject to frequent temperature fluctuations, making it difficult to effectively control their coefficient of thermal expansion. This results in insufficient dimensional stability, especially in applications with stringent dimensional accuracy requirements, such as precision electronic devices and high-frequency communication modules. The accumulation of thermal stress can easily lead to film cracking or device failure, failing to meet the long-term stable operation requirements of high-end fields. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a polyimide film with a low coefficient of thermal expansion obtained by catalysis and its preparation method, which solves the problems of existing polyimide films being difficult to control in terms of coefficient of thermal expansion and having insufficient dimensional stability due to frequent temperature fluctuations, making them prone to failure in precision environments.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a polyimide film with low thermal expansion coefficient by catalytic method, comprising 43-47% rigid polyimide material, 28-32% flexible polyimide material, 4-6% dynamic crosslinking agent, 7-9% component agent, and solvent to make up the balance.

[0006] Preferably, the rigid polyimide material includes: homopolymer polyimide.

[0007] Preferably, the rigid polyimide material further includes: fluorinated biphenyl polyimide, wherein the ratio of pyromellitic polyimide to fluorinated biphenyl polyimide is 5:4.

[0008] Preferably, the flexible polyimide material includes: ether-oxygen chain polyimide.

[0009] Preferably, the dynamic crosslinking agent comprises: maleimide-terminated polyamide and a bisfuran compound, wherein the ratio of maleimide-terminated polyamide to bisfuran compound is 3:2; the component comprises: flake boron nitride and a silane coupling agent, wherein the ratio of flake boron nitride to silane coupling agent is 5:2; and the solvent comprises N-methylpyrrolidone and γ-butyrolactone, wherein the ratio of N-methylpyrrolidone to γ-butyrolactone is 4:1.

[0010] A method for preparing a polyimide film with a low coefficient of thermal expansion by catalysis includes the following steps:

[0011] S1. Raw material pretreatment: Weigh out the following in proportion: pyromellitic polyimide, fluorinated biphenyl polyimide, ether oxygen chain polyimide, maleimide-terminated polyamide, bisfuran compound, flake boron nitride, silane coupling agent, N-methylpyrrolidone and γ-butyrolactone.

[0012] S2. Mixing of rigid polyimide materials: Add the homopolymer polyimide and fluorinated biphenyl polyimide prepared in step S1 to a set of reaction vessels in a ratio of 5:4, and add the N-methylpyrrolidone prepared in step S1 at the same time, wherein the N-methylpyrrolidone accounts for 60% of the total amount; under nitrogen protection, stir and mix to fully dissolve the two rigid materials to form a rigid premixed liquid, which provides a preliminary skeleton structure for the overall material.

[0013] S3. Dissolving the flexible polyimide material: Add the ether-oxygen chain polyimide prepared in step S1 to another set of reaction vessels, add the remaining N-methylpyrrolidone and all of the γ-butyrolactone from step S2 until completely dissolved to obtain a flexible solution, so that it can be better integrated with the rigid premixed liquid in the future and play the role of absorbing expansion stress.

[0014] S4. Dynamic crosslinking agent premix: The maleimide-terminated polyamide and the bisfuran compound prepared in step S1 are placed in a high-speed mixer at a ratio of 3:2 and stirred at 0-20℃ for 0.8-1.2 hours to form a dynamic crosslinking premix, ensuring that the two can stably play a dynamic crosslinking role in subsequent steps.

[0015] S5. Mixing the main system: Slowly add the flexible solution prepared in step S3 to the rigid premixed liquid reactor obtained in step S2, and stir at 0-20℃ for 1.5-2.5 hours to fully mix the rigid and flexible materials. Then add the dynamic crosslinking premix prepared in step S4 and continue stirring for 1-2 hours to form a preliminary mixed system, allowing each material to initially exert a synergistic effect.

[0016] S6. Degassing treatment: Transfer the preliminary mixture obtained in step S5 into a vacuum degassing machine to remove air bubbles from the slurry and avoid pinhole defects after film forming.

[0017] S7. Addition of additives: Add the flake boron nitride treated in step S1 to the raw material after complete degassing treatment in step S6, and stir at 0-20℃ for 2.5-3.5 hours to ensure that the flake boron nitride is evenly dispersed in the system to form a thermally conductive network. At the same time, the effect of silane coupling agent is used to enhance its binding with the system.

[0018] S8. Casting film: After adding the boron nitride slurry in step S7, cast it evenly on a clean glass plate and use a film scraper to control the film thickness.

[0019] S9. Gradient temperature curing: The film cast in step S8, along with the glass plate, is placed in an oven. A heating scheme is used to form a stable structure in the film, achieving the characteristic of a low coefficient of thermal expansion. The heating scheme includes:

[0020] First, heat in an oven at 75-85℃ and dry for 1.5-2.5 hours to remove most of the solvent;

[0021] Then, the oven temperature is raised to 145-155℃ and maintained for 1.5-2.5 hours to promote the action of the dynamic crosslinking agent;

[0022] Next, the oven temperature is raised to 200-300℃ and maintained for 1-2 hours to further cure the film;

[0023] Finally, heat the oven to 400-500℃ and treat for 0.8-1.2 hours to complete the curing process;

[0024] S10. Peeling and Cutting: After the oven temperature in step S9 drops to room temperature, peel the film off the glass plate and cut it to the required size to obtain the finished polyimide film with low thermal expansion coefficient by catalytic method.

[0025] Preferably, in step S1, the sheet-like boron nitride needs to be processed separately, specifically: the sheet-like boron nitride is placed in an ethanol solution containing a silane coupling agent, ultrasonically dispersed for 25-35 minutes, refluxed at <70°C for 1.5-2.5 hours, filtered and dried for later use; the surface of the sheet-like boron nitride is modified by the silane coupling agent to enhance its bonding with other materials.

[0026] Preferably, in step S2, the parameters of the set of reaction vessels include: heating temperature <70℃, and stirring for 1.5-2.5 hours.

[0027] Preferably, in step S3, the parameters of the other set of reaction vessels include: heating temperature <70℃, stirring for 1-2 hours.

[0028] Preferably, in step S6, the parameters of the vacuum degassing machine include: vacuum degree 0.08-0.1MPa, and degassing for 25-35 minutes at <70℃.

[0029] This invention provides a polyimide film with a low coefficient of thermal expansion obtained by catalysis and its preparation method.

[0030] It has the following beneficial effects:

[0031] 1. This invention utilizes the synergistic effect of rigid polyimide material to construct a stable framework, flexible polyimide material to buffer stress, and sheet-like boron nitride to dissipate heat evenly, forming a chemical regulation system of "rigid constraint-flexible buffer-thermal balance". This system suppresses thermal expansion at the molecular level. Compared with traditional physical methods that rely solely on external forces or single components, this system improves dimensional stability under temperature fluctuations to a new level through the complementary chemical mechanisms of each component, solving the problem of difficult control of thermal expansion coefficient over a wide temperature range.

[0032] 2. This invention introduces a synergistic design of dynamic crosslinking agent and silane coupling agent. The reversible bonding of the dynamic crosslinking agent responds to temperature fluctuations to achieve self-repair, while the silane coupling agent strengthens the interfacial bonding of each component to avoid delamination. The combination of the two enables the film to resist thermal stress while having the ability to self-heal damage. This dual guarantee of "dynamic repair-interfacial strengthening" breaks through the limitations of poor compatibility and insufficient stability of existing dynamic crosslinking technology. It allows the film to maintain dimensional stability and autonomously repair micro-damage during long-term temperature cycling, significantly improving its durability in precision scenarios.

[0033] 3. This invention adds flake-shaped boron nitride and a silane coupling agent. The flake-shaped boron nitride constructs a thermally conductive pathway for uniform heat dissipation, while the silane coupling agent enhances its bonding with the matrix through chemical modification, and the solvent ensures uniform material dispersion. This material and formulation design allows the components to both help reduce thermal expansion and enhance the stability of the dynamic crosslinking agent, forming a "three-in-one" chemical synergistic effect with rigid and flexible materials. The overall performance improvement far exceeds the sum of the individual effects of each component. Attached Figure Description

[0034] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0035] 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.

[0036] Please see the appendix Figure 1This invention provides a polyimide film with a low coefficient of thermal expansion obtained by catalysis, comprising 43-47% rigid polyimide material, 28-32% flexible polyimide material, 4-6% dynamic crosslinking agent, 7-9% component agent, and solvent to make up the balance.

[0037] The rigid polyimide material comprises: pyromellitic polyimide and fluorinated biphenyl polyimide, wherein the ratio of pyromellitic polyimide to fluorinated biphenyl polyimide is 5:4;

[0038] The homopolymer polyimide provides a skeletal support effect for the overall material;

[0039] The fluorinated biphenyl polyimide-assisted homophenyl polyimide further improves the strength of rigid polyimide materials;

[0040] The flexible polyimide material includes: etheroxy chain polyimide;

[0041] The ether-oxygen chain polyimide is used to absorb the expansion stress impact of the material during thermal cycling and prevent the film from cracking.

[0042] The dynamic crosslinking agent comprises: maleimide-terminated polyamide and a bisfuran compound, wherein the ratio of maleimide-terminated polyamide to bisfuran compound is 3:2;

[0043] The maleimide-terminated polyamide serves as a crosslinking anchor point for the dynamic network, maintaining network stability at room temperature and achieving molecular bridging through long-chain flexibility after high-temperature dissociation.

[0044] The bisfuran compound is a dynamic crosslinking agent that enhances temperature responsiveness, undergoes reversible ring-opening at 120°C, and drives the flow of healing molecules.

[0045] The formulation comprises: flake boron nitride and silane coupling agent, wherein the ratio of flake boron nitride to silane coupling agent is 5:2;

[0046] The sheet-like boron nitride provides a thermally conductive network for the thin film material, enabling uniform heat dissipation, reducing local thermal stress, and further suppressing overall thermal expansion.

[0047] The silane coupling agent strengthens boron nitride, further improving the bonding effect of plate boron nitride, preventing material delamination, and at the same time isolating water and oxygen to prevent water and oxygen from eroding the dynamic crosslinking agent.

[0048] The solvent comprises N-methylpyrrolidone and γ-butyrolactone, wherein the ratio of N-methylpyrrolidone to γ-butyrolactone is 4:1.

[0049] The N-methylpyrrolidone completely dissolves both rigid and flexible polyimide materials, ensuring that the solvent evaporates slowly during film formation and avoiding pinhole defects.

[0050] The γ-butyrolactone reduces the roughness of the finished film and improves the surface smoothness. A method for preparing a polyimide film with a low coefficient of thermal expansion via catalytic method includes the following steps:

[0051] S1. Raw material pretreatment: Weigh out the following components according to the specified proportions: pyromellitic polyimide, fluorinated biphenyl polyimide, ether oxide chain polyimide, maleimide-terminated polyamide, bisfuran compound, flake boron nitride, silane coupling agent, N-methylpyrrolidone, and γ-butyrolactone. The flake boron nitride requires separate treatment, specifically:

[0052] Flake boron nitride was placed in an ethanol solution containing a silane coupling agent, ultrasonically dispersed for 30 minutes, refluxed at <70°C for 2 hours, filtered and dried for later use; the surface of the flake boron nitride was modified by the silane coupling agent to enhance its bonding with other materials.

[0053] S2. Mixing of rigid polyimide materials: Add the homopolymer polyimide and fluorinated biphenyl polyimide prepared in step S1 to a set of reaction vessels in a ratio of 5:4, and add the N-methylpyrrolidone prepared in step S1 at the same time, wherein the N-methylpyrrolidone accounts for 60% of the total amount.

[0054] Under nitrogen protection, stir at <70℃ for 2 hours to fully dissolve and mix the two rigid materials to form a rigid premixed liquid, which provides a preliminary framework for the overall material structure.

[0055] S3. Dissolving the flexible polyimide material: Add the ether-oxygen chain polyimide prepared in step S1 to another set of reaction vessels, add the remaining N-methylpyrrolidone and all of the γ-butyrolactone from step S2, stir at <70℃ for 1.5 hours until completely dissolved to obtain a flexible solution, so that it can be better integrated with the rigid premixed liquid in the future and play the role of absorbing expansion stress.

[0056] S4. Dynamic crosslinking agent premix: The maleimide-terminated polyamide and the bisfuran compound prepared in step S1 are placed in a high-speed mixer at a ratio of 3:2 and stirred at 0-20°C for 1 hour to form a dynamic crosslinking premix, ensuring that the two can stably play a dynamic crosslinking role in subsequent steps.

[0057] S5. Mixing the main system: Slowly add the flexible solution prepared in step S3 to the rigid premixed liquid reactor obtained in step S2, and stir at 0-20℃ for 2 hours to fully mix the rigid and flexible materials. Then add the dynamic crosslinking premix prepared in step S4 and continue stirring for 1.5 hours to form a preliminary mixed system, allowing the materials to initially exert a synergistic effect.

[0058] S6. Degassing treatment: Transfer the preliminary mixture obtained in step S5 into a vacuum degassing machine and degas for 30 minutes under vacuum conditions of 0.08-0.1MPa and <70℃ to remove air bubbles in the slurry and avoid pinhole defects after film forming.

[0059] S7. Addition of additives: Add the flake boron nitride treated in step S1 to the raw material after complete degassing treatment in step S6, and stir at 0-20℃ for 2.5-3.5 hours to ensure that the flake boron nitride is evenly dispersed in the system to form a thermally conductive network. At the same time, the effect of silane coupling agent is used to enhance its binding with the system.

[0060] S8. Casting film: After adding the boron nitride slurry in step S7, cast it evenly on a clean glass plate and use a film scraper to control the film thickness.

[0061] S9. Gradient temperature curing: Place the film cast in step S8 along with the glass plate into an oven and dry it at 80°C for 2 hours to remove most of the solvent; then raise the temperature to 150°C and hold for 2 hours to promote the action of the dynamic crosslinking agent; then raise the temperature to 250°C and hold for 1.5 hours to further cure the film; finally, raise the temperature to 350°C and treat for 1 hour to complete the curing process, so that the film forms a stable structure and achieves the characteristic of low thermal expansion coefficient.

[0062] S10. Peeling and Cutting: After the oven temperature in step S9 drops to room temperature, peel the film off the glass plate and cut it to the required size to obtain the finished polyimide film with low thermal expansion coefficient by catalytic method.

[0063] Please see the appendix Figure 1 Embodiment 1 of the present invention provides a polyimide film with low thermal expansion coefficient by catalytic method, comprising 43% rigid polyimide material (23.9% homophenylene polyimide, 19.1% fluorinated biphenyl polyimide), 28% flexible polyimide material, 4% dynamic crosslinking agent (2.4% maleimide-terminated polyamide, 1.6% bisfuran compound), 7% component agent (5% sheet boron nitride, 2% silane coupling agent), and solvent to make up the balance.

[0064] Example 1 is the minimum proportion in the formulation of this invention. Example 1 has the following effects: it maintains stable low thermal expansion characteristics in conventional hot and cold cycles, meets the dimensional stability requirements of basic industrial scenarios, and is suitable for low-frequency temperature fluctuation environments.

[0065] Please see the appendix Figure 1Embodiment 2 of the present invention provides a polyimide film with low thermal expansion coefficient by catalytic method, comprising 45% rigid polyimide material (25% homophenylene polyimide, 20% fluorinated biphenyl polyimide), 30% flexible polyimide material, 5% dynamic crosslinking agent (3% maleimide-terminated polyamide, 2% bisfuran compound), 8% component agent (5.7% flake boron nitride, 2.3% silane coupling agent), and solvent to make up the balance.

[0066] Example 2 is a medium proportion in the formulation of this invention. Example 1 has the following effects: it balances low thermal expansion and dynamic repair performance, inhibits expansion and can autonomously repair micro-damage under medium intensity temperature alternation, and is suitable for most industrial application scenarios.

[0067] Please see the appendix Figure 1 Embodiment 3 of the present invention provides a polyimide film with low thermal expansion coefficient by catalytic method, comprising 47% rigid polyimide material (26.1% homophenylene polyimide, 20.9% fluorinated biphenyl polyimide), 32% flexible polyimide material, 6% dynamic crosslinking agent (3.6% maleimide-terminated polyamide, 2.4% bisfuran compound), 9% component agent (6.4% flake boron nitride, 2.6% silane coupling agent), and solvent to make up the balance.

[0068] Example 3 represents the maximum proportion in the formulation of this invention. Example 1 has the following effects: it can withstand extreme temperature difference shocks, has a more lasting low thermal expansion effect, and exhibits significant synergistic effects of dynamic cross-linking and thermal conduction, making it suitable for high-end precision scenarios with high frequency and wide temperature range changes.

[0069] Comparative experiment:

[0070] I. Experimental Design

[0071] This experiment was conducted in accordance with standards such as "Determination of Linear Expansion Coefficient of Plastics" (GB / T1036-2008) and "Environmental Test Temperature Change" (GB / T2423.22-2012). Five parallel samples were tested (n=5 for each group), and the data were analyzed using 95% confidence intervals.

[0072] II. Experimental Subjects

[0073] Examples 1 / 2 / 3: Prepared according to the patented formula, corresponding to low / medium / high dynamic crosslinking densities respectively;

[0074] Control group A: Commercially available high-performance polyimide film (UBEUPILEXVT, CTE = 18ppm / ℃);

[0075] Control group B: Traditional biaxially oriented homopolymer PI film (self-made, process parameters: stretch ratio 1.5:1.5, curing temperature 350℃).

[0076] III. Experimental Procedure (Standardization of Key Parameters)

[0077] CTE test (GB / T1036-2008)

[0078] Sample size: 50mm × 10mm × 25μm;

[0079] Test equipment: Netzsch TMA402F3 (load 0.05N, heating rate 5℃ / min);

[0080] Test range: -50℃~200℃ (covering the requirements of GJB150.3A-2009 military standard);

[0081] Thermal cycling test (GB / T2423.22-2012);

[0082] Cyclic conditions: -55℃ (1h) → 150℃ (1h), for a total of 1000 cycles;

[0083] Temperature change rate: 10℃ / min (meets industrial-grade testing standards);

[0084] Crack detection: Olympus BX53 metallurgical microscope (500x magnification) was used.

[0085] Dynamic repair test

[0086] Scratch preparation: diamond scribing needle (load 50mN, speed 0.1mm / s);

[0087] Repair conditions: 120℃ × 30 min (designed based on the ring-opening temperature of the dynamic crosslinking agent);

[0088] Characterization method: Hitachi SU8010 SEM (1 nm resolution).

[0089] Surface roughness test (GB / T1031-2009)

[0090] Test equipment: Bruker Multimode 8AFM;

[0091] Scan range: 5μm × 5μm (compliant with ISO 25178 standard);

[0092] Evaluation parameter: Ra (arithmetic mean deviation).

[0093] IV. Experimental Data (including error analysis)

[0094]

[0095] V. Comparative Analysis of Key Indicators

[0096] CTE modulation effect

[0097] In Example 3, the CTE (14.5 ppm / ℃) was reduced by 49.5% compared to the control group B, meeting the Class A requirement (≤15 ppm / ℃) for high-frequency substrate materials in the IPC-4101F standard.

[0098] Compared to commercially available products (control group A), the reduction was further 19.4%, demonstrating the advantages of catalytic molecular design.

[0099] Thermomechanical stability

[0100] After 1000 cycles, no visible cracks were found in the example group, while control group B showed an average of 4.3 cracks / mm. 2 Microcracks;

[0101] Control group A still showed a small number of cracks due to fluorine modification, verifying the necessity of dynamic cross-linking network.

[0102] Dynamic repair mechanism

[0103] Example 3: The scratch healing rate reached 91%, and SEM observation showed that a new covalent bond network was formed at the fracture site;

[0104] Repair efficiency is positively correlated with the content of dynamic crosslinking agent (R 2 =0.98).

[0105] Surface quality

[0106] The Ra value of the example group was reduced by 65% ​​compared with the control group B, meeting the requirements of semiconductor packaging materials (Ra≤5nm);

[0107] Solvent system optimization (NMP / γ-butyrolactone = 4:1) significantly suppressed phase separation.

[0108] VI. Standard Compliance Conclusion

[0109] CTE performance: Examples 1 / 2 / 3 meet the requirements of Class I (≤25ppm / ℃), Class II (≤20ppm / ℃), and Class III (≤15ppm / ℃) in GB / T1036-2008, respectively;

[0110] Environmental adaptability: Meets the requirements of GB / T2423.22-2012 test Nb (temperature change) severity level 2;

[0111] Surface quality: Meets the standard of Ra3.2μm for precision electronic device substrates in GB / T1031-2009.

[0112] VII. Verification of Innovation Points

[0113] Low thermal expansion mechanism: Plate-like boron nitride (5-6.4%) forms a thermally conductive network, reducing the local temperature difference by 30% (detected by infrared thermal imager);

[0114] Advantages of dynamic crosslinking: Energy storage modulus at 150℃ is increased by 40% compared to control group A (TAQ800DMA test);

[0115] Process compatibility: The uniformity of film thickness in cast film (±2%) is better than that in traditional stretching process (±8%).

[0116] 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 with a low coefficient of thermal expansion obtained by catalytic method, characterized in that, It includes 43-47% rigid polyimide material, 28-32% flexible polyimide material, 4-6% dynamic crosslinking agent, 7-9% component agent, and solvent to make up the balance; The rigid polyimide material and the flexible polyimide material are prepared by stirring, mixing and dissolving in two sets of reaction vessels, respectively. The dynamic crosslinking agent is prepared by mixing using a high-speed mixer.

2. The polyimide film with low thermal expansion coefficient obtained by catalytic method according to claim 1, characterized in that, The rigid polyimide material includes: homophenylene polyimide.

3. The polyimide film with low thermal expansion coefficient obtained by catalytic method according to claim 2, characterized in that, The rigid polyimide material further includes: fluorinated biphenyl polyimide, wherein the ratio of pyromellitic polyimide to fluorinated biphenyl polyimide is 5:

4.

4. The polyimide film with low thermal expansion coefficient obtained by catalytic method according to claim 1, characterized in that, The flexible polyimide material includes: etheroxy chain polyimide.

5. The polyimide film with low thermal expansion coefficient obtained by catalytic method according to claim 1, characterized in that, The dynamic crosslinking agent comprises maleimide-terminated polyamide and a bisfuran compound, wherein the ratio of maleimide-terminated polyamide to bisfuran compound is 3:2; the component comprises flake boron nitride and a silane coupling agent, wherein the ratio of flake boron nitride to silane coupling agent is 5:2; the solvent comprises N-methylpyrrolidone and γ-butyrolactone, wherein the ratio of N-methylpyrrolidone to γ-butyrolactone is 4:

1.

6. A method for preparing a polyimide film with a low coefficient of thermal expansion by catalysis according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Raw material pretreatment: Weigh out the following in proportion: pyromellitic polyimide, fluorinated biphenyl polyimide, ether oxygen chain polyimide, maleimide-terminated polyamide, bisfuran compound, flake boron nitride, silane coupling agent, N-methylpyrrolidone and γ-butyrolactone. S2. Mixing of rigid polyimide materials: Add the homopolymer polyimide and fluorinated biphenyl polyimide prepared in step S1 to a set of reaction vessels in a ratio of 5:4, and add the N-methylpyrrolidone prepared in step S1 at the same time, wherein the N-methylpyrrolidone accounts for 60% of the total amount; under nitrogen protection, stir and mix to fully dissolve the two rigid materials to form a rigid premixed liquid, which provides a preliminary skeleton structure for the overall material. S3. Dissolving the flexible polyimide material: Add the ether-oxygen chain polyimide prepared in step S1 to another set of reaction vessels, add the remaining N-methylpyrrolidone and all of the γ-butyrolactone from step S2 until completely dissolved to obtain a flexible solution, so that it can be better integrated with the rigid premixed liquid in the future and play the role of absorbing expansion stress. S4. Dynamic crosslinking agent premix: The maleimide-terminated polyamide and the bisfuran compound prepared in step S1 are placed in a high-speed mixer at a ratio of 3:2 and stirred at 0-20℃ for 0.8-1.2 hours to form a dynamic crosslinking premix, ensuring that the two can stably play a dynamic crosslinking role in subsequent steps. S5. Mixing the main system: Slowly add the flexible solution prepared in step S3 to the rigid premixed liquid reactor obtained in step S2, and stir at 0-20℃ for 1.5-2.5 hours to fully mix the rigid and flexible materials. Then add the dynamic crosslinking premix prepared in step S4 and continue stirring for 1-2 hours to form a preliminary mixed system, allowing each material to initially exert a synergistic effect. S6. Degassing treatment: Transfer the preliminary mixture obtained in step S5 into a vacuum degassing machine to remove air bubbles from the slurry and avoid pinhole defects after film forming. S7. Addition of additives: Add the flake boron nitride treated in step S1 to the raw material after complete degassing treatment in step S6, and stir at 0-20℃ for 2.5-3.5 hours to ensure that the flake boron nitride is evenly dispersed in the system to form a thermally conductive network. At the same time, the effect of silane coupling agent is used to enhance its binding with the system. S8. Casting film: After adding the boron nitride slurry in step S7, cast it evenly on a clean glass plate and use a film scraper to control the film thickness. S9. Gradient temperature curing: The film cast in step S8, along with the glass plate, is placed in an oven. A heating scheme is used to form a stable structure in the film, achieving the characteristic of a low coefficient of thermal expansion. The heating scheme includes: First, heat in an oven at 75-85℃ and dry for 1.5-2.5 hours to remove most of the solvent; Then, the oven temperature is raised to 145-155℃ and maintained for 1.5-2.5 hours to promote the action of the dynamic crosslinking agent; Next, the oven temperature is raised to 200-300℃ and maintained for 1-2 hours to further cure the film; Finally, heat the oven to 400-500℃ and treat for 0.8-1.2 hours to complete the curing process; S10. Peeling and Cutting: After the oven temperature in step S9 drops to room temperature, peel the film off the glass plate and cut it to the required size to obtain the finished polyimide film with low thermal expansion coefficient by catalytic method.

7. The method for preparing a polyimide film with a low coefficient of thermal expansion by catalysis according to claim 6, characterized in that, In step S1, the flake boron nitride needs to be processed separately, specifically: the flake boron nitride is placed in an ethanol solution containing a silane coupling agent, ultrasonically dispersed for 25-35 minutes, refluxed at <70℃ for 1.5-2.5 hours, filtered and dried for later use; the surface of the flake boron nitride is modified by the silane coupling agent to enhance its bonding with other materials.

8. The method for preparing a polyimide film with a low coefficient of thermal expansion by catalysis according to claim 6, characterized in that, In step S2, the parameters of the set of reaction vessels include: heating temperature <70℃, stirring for 1.5-2.5 hours.

9. The method for preparing a polyimide film with a low coefficient of thermal expansion by catalysis according to claim 6, characterized in that, In step S3, the parameters of the other set of reaction vessels include: heating temperature <70℃, stirring for 1-2 hours.

10. The method for preparing a polyimide film with a low coefficient of thermal expansion by catalysis according to claim 6, characterized in that, In step S6, the parameters of the vacuum degassing machine include: vacuum degree 0.08-0.1MPa, and degassing for 25-35 minutes at <70℃.

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