High-temperature-resistant low-dielectric thermosetting polyimide resin prepolymer as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a high-temperature-resistant low-dielectric thermosetting polyimide resin prepolymer as well as a preparation method and application thereof. The preparation method comprises the following steps: reacting a dianhydride monomer containing a fluorene structure, a diamine monomer containing a trifluoromethyl structure and an end-capping reagent by adopting a high-temperature one-step method to obtain a polyimide prepolymer; and carrying out hot-pressing curing molding on the prepolymer to obtain the high-temperature-resistant low-dielectric thermosetting polyimide resin. Through molecular structure design, a fluorene structure and a trifluoromethyl structure are introduced into thermosetting polyimide, and high-frequency low dielectric constant, low loss factor, high heat resistance and good prepolymer machinability are synergistically realized; the technical problem that the high-frequency dielectric property, the heat resistance and the processability of the traditional polyimide resin are difficult to optimize at the same time is effectively solved. The resin can be used as a high-performance resin matrix and is applied to high-temperature-resistant low-dielectric wave-transparent composite materials in the field of aerospace.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer, its preparation method, and its application. Background Technology

[0002] Polyimide, with its excellent thermal stability, chemical stability, mechanical stability, and dielectric properties, has become one of the key resin matrices in the field of high-temperature transparent composite materials for aerospace. With the rapid development of aerospace and electronic information technology, to meet the increasing communication and guidance needs of aircraft, ensure efficient and low-loss transmission of electromagnetic waves under extreme environments such as high temperature and high-speed aerodynamic loads, and protect antenna systems from external environmental damage, there is an urgent need to develop polymer-based transparent composite materials that combine lightweight, low dielectric constant, low loss factor, excellent heat resistance, and superior mechanical properties.

[0003] However, traditional polyimide resins, such as common aromatic polyimides, have a dielectric constant of 3.1-3.5 and a loss factor of 0.01-0.02 in the GHz band, which is insufficient to meet the requirements of next-generation hypersonic vehicles for polymer-based microwave-transparent composite materials. Furthermore, the rigid molecular structure introduced to achieve high thermal stability often results in excessively high melt viscosity and insufficient solubility of the prepolymer, posing challenges to the molding and processing of complex components. Therefore, the core challenge in this field is to synergistically optimize the dielectric constant, loss factor, and processability of polyimide resins through innovative molecular structure design while maintaining their high heat resistance.

[0004] To address the aforementioned challenges, molecular structure design is crucial. Introducing fluorene-containing structures into the polyimide molecular chain is considered an effective strategy for balancing high heat resistance and good processability. The rigidity of the fluorene structure and its significant large volume effect have a dual effect: on the one hand, its rigidity helps maintain the rigidity of the molecular chain and restricts chain segment movement, thereby maintaining the high glass transition temperature and thermal stability of the resin system; on the other hand, its large volume steric hindrance can effectively increase the interchain spacing, reduce the interchain packing density, and improve the solubility and melt flowability of the prepolymer in organic solvents. Furthermore, this increased free volume is also beneficial for reducing the dielectric constant of the material. However, the increase in free volume brought about by the introduction of the fluorene structure may also lead to an increase in the water absorption rate of the material. Since the dielectric loss of water molecules is much higher than the intrinsic loss of polyimide at high frequencies, the adsorbed water molecules will significantly increase the loss factor of polyimide, which becomes a disadvantage when using fluorene-containing structures to optimize dielectric properties. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a high-temperature resistant, low-dielectric thermosetting polyimide resin, which introduces a trifluoromethyl structure into the prepolymer and combines the fluorene structure with the trifluoromethyl structure to synergistically solve the technical problem that it is difficult to simultaneously optimize high-frequency dielectric properties, heat resistance and processability.

[0006] First aspect:

[0007] A high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer, with the following general structural formula:

[0008] Where m and n are the degree of aggregation, and m≧1, n≧0, 1≦m+n≦20, the arrangement of repeating units can be block or random. R' is each independently at least one of hydrogen atom, fluorine atom, methyl or trifluoromethyl; R1 and R2 are each independently selected from at least one of the following structures.

[0009] R a At least one of the following structures

[0010] The R1, R2 and R a In the structure, the dashed lines indicate the connection positions with other groups of the prepolymer.

[0011] Specifically, m can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.; n can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.; the two repeating units can be arranged and combined arbitrarily in the molecule.

[0012] In the preparation of microwave-transparent composite materials, good processing performance is a crucial prerequisite for material molding. Thermoplastic polyimides typically have high molecular weight and rigid chain segments, resulting in high melt viscosity and poor solubility, making them difficult to composite with reinforcing materials through conventional injection molding and extrusion processes. In contrast, thermosetting polyimides, by introducing active end groups into the molecular chain, form prepolymers with lower molecular weights, making them easier to melt during processing and exhibiting lower melt viscosity. Subsequently, they can form a stable three-dimensional network structure through crosslinking reactions. This structure not only effectively maintains the inherent high heat resistance, mechanical strength, and dimensional stability of polyimides but also better meets the process requirements for molding complex components and preparing composite materials. Therefore, from the perspective of practical composite material applications, this invention chooses thermosetting polyimide resins as the design direction.

[0013] To mitigate the negative hygroscopic effects of the fluorene structure, this invention introduces trifluoromethyl (-CF3) groups into the prepolymer. On one hand, the strong hydrophobicity of trifluoromethyl groups helps reduce the water absorption rate of the resin, thereby reducing the increase in the loss factor caused by water molecules. On the other hand, trifluoromethyl groups have low electronic polarizability, which helps reduce the dielectric constant of the material. More importantly, its steric hindrance effect can synergistically work with the fluorene structure to further increase the interchain spacing and free volume. This not only contributes to a further reduction in the dielectric constant but also further improves the processability of the material.

[0014] Furthermore, this invention balances the processability of the prepolymer and the heat resistance of the cured resin by controlling the degree of polymerization (i.e., limiting m and n). If the polymerization degree is too high, the molecular weight of the prepolymer increases, leading to a higher melting temperature, significantly increased melt viscosity, and decreased solubility, which is detrimental to the processing and molding of the prepolymer. More importantly, a high polymerization degree means a reduction in the number of active end groups per unit volume, and active end groups are the reaction sites for forming crosslinking networks. A decrease in their concentration directly leads to a decrease in the crosslinking density of the final cured resin, and crosslinking density is a core factor determining the thermal stability and mechanical strength of thermosetting resins. Therefore, controlling the degree of polymerization within a suitable range is a necessary condition to ensure that the prepolymer has good processing fluidity while enabling the cured product to obtain high crosslinking density and excellent heat resistance.

[0015] As a preferred embodiment, the minimum melt viscosity of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is 1-1000 Pa·s; the dissolved solids content of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer in a polar aprotic solvent is 10-50 wt%. More preferably, the minimum melt viscosity of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is 1-10 Pa·s.

[0016] The melt viscosity of a prepolymer is mainly related to its main chain structure and molecular weight. By controlling the degree of polymerization, the melt viscosity can be adjusted within a certain range. If the melt viscosity is too low, the prepolymer will have excessive fluidity, which can easily cause overflow problems in processes such as lamination or injection molding. If the viscosity is too high, the fluidity will be significantly reduced, greatly increasing the difficulty of processing and molding. Based on the fluorene structure, this invention also introduces trifluoromethyl groups into the prepolymer structure, synergistically utilizing the steric hindrance effect of these two structures to further increase the free volume of the molecular chain, thereby optimizing the minimum melt viscosity of the prepolymer to 1-1000 Pa·s and increasing the solubility to 10-50 wt%, significantly improving the molding and processing performance of complex components.

[0017] The second aspect: A method for preparing a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer includes the following steps: S1, Under an inert atmosphere, a diamine monomer containing a trifluoromethyl structure is completely dissolved in an organic solvent at room temperature to obtain the first solution; S2, add a fluorene-containing dianhydride monomer to the first solution and react at room temperature for 6-8 hours to obtain a second solution; S3, add a capping agent to the second solution and react at room temperature for 6-8 hours to obtain a third solution; S4, add a dehydrating agent and a catalyst to the third solution, heat to 180-200℃, and react for 8-10 hours to obtain a fourth solution; the fourth solution includes the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer.

[0018] In steps S2 and S3, reaction temperature and reaction time are two key process parameters. Room temperature is the preferred choice in this invention. Excessively high reaction temperatures may accelerate the reaction rate but can lead to a wider molecular weight distribution and potential side reactions (such as hydrolysis of unreacted carboxyl groups). Conversely, low reaction temperatures may reduce the reaction rate, resulting in incomplete reactions. Therefore, room temperature is the optimal choice that balances reaction rate and process control. Given a fixed reaction temperature, a reaction time of 6-8 hours is controlled to ensure the reaction is essentially complete and does not affect the prepolymer properties. In polymer synthesis, due to equilibrium constraints, even extending the reaction time cannot guarantee complete reaction. Excessively extended reaction time may cause changes in molecular weight distribution, which is detrimental to subsequent processing and molding. Therefore, 6-8 hours is the optimal choice that strikes a balance between reaction completion and product uniformity.

[0019] In step S4, 180-200℃ is the typical temperature for the imidization reaction (dehydration cyclization). If the reaction temperature is too high, cyclization may be accelerated, but this is limited by the solvent's boiling point, as excessively high temperatures can cause solvent vaporization. If the reaction temperature is too low, the dehydration reaction will be incomplete, resulting in insufficient imidization and residual ammonium acid structures in the prepolymer. These residual structures are prone to causing defects during subsequent thermosetting, thus affecting resin properties. Therefore, a reaction temperature of 180-200℃ is the optimal choice that balances reaction efficiency and product structural integrity. Given a fixed reaction temperature, controlling the reaction time to 8-10 hours typically achieves a high degree of imidization, resulting in a structurally stable prepolymer. Insufficient reaction time may lead to incomplete dehydration and residual ammonium acid structures, affecting prepolymer performance. While a prolonged reaction time may further increase the degree of imidization, prolonged high temperatures can easily trigger side reactions, such as molecular chain breakage, affecting prepolymer performance. Therefore, a reaction time of 8-10 hours is the optimal choice that strikes a balance between ensuring high conversion rates and suppressing side reactions.

[0020] As a preferred embodiment, the molar ratio of the dianhydride monomer, the diamine monomer, and the capping agent is (m+n):(m+n+1):2, wherein m≧1, n≧0, and 1≦m+n≦20.

[0021] As a preferred embodiment, the diamine monomer is at least one selected from 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 2,2'-bis(trifluoromethoxy)-biphenyldiamine, 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, and 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]propane; The dianhydride monomer is at least one selected from 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), 5,5'-(2,7-difluoro-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), 5,5'-(2,7-dimethyl-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), and 5,5'-(2,7-bis(trifluoromethyl)-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione). The capping agent is at least one of 4-phenylethynyl phthalic anhydride, norbornene phthalic anhydride, and ethynyl phthalic anhydride.

[0022] As a preferred embodiment, the inert atmosphere includes at least one of nitrogen and argon, the organic solvent includes at least one of N-methylpyrrolidone, m-cresol, phenol and p-chlorophenol, the dehydrating agent includes at least one of toluene and xylene, and the catalyst includes at least one of isoquinoline, quinoline and pyridine.

[0023] As a preferred embodiment, the following steps are also included: S5, the fourth solvent is added to the cleaning agent, the powder is precipitated, the powder is washed, filtered, and dried at 200-220°C to obtain the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer; the cleaning agent includes at least one of ethanol and water.

[0024] Third aspect: A thermosetting polyimide resin is prepared by the following method: P1, using a hot-press curing molding process, the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is placed in a mold, and the mold is heated to 250-310℃ and held for 0.5-1.5h. P2 is used for exhaust treatment by pressurization or depressurization, and then pressurized to 1-10MPa; P3. Heat the mold to 370-400℃ and keep it at that temperature for 2-3 hours. After the mold cools down to below 200℃, release the pressure to obtain the thermosetting polyimide resin.

[0025] In step P2, the mold temperature (250-310℃) is a temperature parameter determined based on the melt rheological curve of the prepolymer. Specifically, this temperature range is generally taken about 20℃ before the inflection point of the curve (the inflection point corresponds to the lowest melt viscosity of the prepolymer), aiming to ensure that the prepolymer reaches a low melt viscosity while avoiding premature initiation of crosslinking and curing. This parameter is crucial for optimizing processing performance; deviations from this temperature will directly affect the resin's flowability, venting efficiency, and subsequent molding quality. Insufficient temperature results in incomplete resin melting, leading to a higher melt viscosity, which reduces the flowability of the prepolymer in the mold, making it difficult to spread evenly and fill mold voids. Excessive temperature, approaching the inflection point of the rheological curve, causes the prepolymer to begin crosslinking and curing before complete melting, affecting the completeness of the prepolymer's reaction.

[0026] In step P3, the crosslinking of the phenylacetylene groups is a thermally activated reaction. If the temperature is too low, the activation energy will be insufficient, the crosslinking rate will decrease, and it will be difficult to achieve a high degree of crosslinking. Insufficient crosslinking will significantly affect the heat resistance of the resin. On the other hand, if the set temperature is too high, it may cause molecular chain degradation, reducing the resin's thermal stability and mechanical properties.

[0027] As a preferred embodiment, the thermosetting polyimide resin has a glass transition temperature ≥340℃, a tensile strength ≥40.8MPa, and an elongation at break ≥2.3%; at an ambient humidity of 50%RH, a temperature of 25℃, and a 10GHz frequency, it has a dielectric constant ≤2.95 and a loss factor ≤0.0098; and a 5% thermal weight loss temperature in air ≥538℃.

[0028] Fourth aspect: A thermosetting polyimide resin is used in high-temperature resistant, low-dielectric, and microwave-transparent composite materials in the aerospace field.

[0029] Compared with the prior art, the present invention has the following beneficial effects: This invention, through innovative molecular structure design, organically combines the fluorene structure with the trifluoromethyl structure, synergistically solving the problems of excessively high dielectric constant and loss factor, insufficient heat resistance, and poor prepolymer processability of traditional polyimide resins at the GHz frequency band. Specifically, while maintaining a certain glass transition temperature and high heat resistance with a 5% thermogravimetric temperature loss in air ≥538℃, it achieves dielectric properties of ≤2.95 dielectric constant and ≤0.0098 at an ambient humidity of 50%RH, a temperature of 25℃, and a frequency of 10GHz, significantly superior to traditional materials. Simultaneously, the hydrophobicity of the trifluoromethyl group effectively suppresses the hygroscopic problem caused by the fluorene structure, reducing the negative impact of moisture on the loss factor. Furthermore, through synergistic steric hindrance effects, it further increases the free volume of the molecular chain, thereby optimizing the minimum melt viscosity of the prepolymer to 1-1000 Pa·s and increasing the solubility to 10-50 wt%, significantly improving the molding and processing performance of complex components. In addition, the material also possesses good mechanical stability, ensuring its reliable application in extreme aerospace environments. This comprehensive optimization enables the high-temperature resistant, low-dielectric thermosetting polyimide resin prepared in this invention to be used as a high-performance resin matrix for high-temperature resistant, low-dielectric microwave-transparent composite materials in the aerospace field. Attached Figure Description

[0030] Figure 1 The image shows the FT-IR spectrum of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer prepared in Example 1.

[0031] Figure 2 The DSC curve of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer prepared in Example 1 is shown.

[0032] Figure 3 The rheological curve of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer prepared in Example 1 is shown.

[0033] Figure 4 The DMA curve of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepared in Example 1 is shown.

[0034] Figure 5 The TGA curve of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepared in Example 1 is shown.

[0035] Figure 6 The mechanical property curves of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepared in Example 1 are shown. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] A high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer, with the following general structural formula:

[0042] Where m and n are the degree of aggregation, and m≧1, n≧0, 1≦m+n≦20, the arrangement of repeating units can be block or random. R' is each independently at least one of hydrogen atom, fluorine atom, methyl or trifluoromethyl; R1 and R2 are each independently selected from at least one of the following structures.

[0043] R a At least one of the following structures

[0044] R1, R2 and R a In the structure, the dashed lines indicate the connection positions with other groups of the prepolymer.

[0045] The minimum melt viscosity of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is 1-1000 Pa·s, and the dissolved solids content in polar aprotic solvents is 10-50 wt%.

[0046] To better optimize the processing performance of the prepolymer and enhance the heat resistance of the resin, a homopolymer / copolymer prepolymer structure with a degree of polymerization of m=1 and n=0 was specifically designed and prepared in this embodiment of the invention (structural formula shown below). This specific structure was chosen because of its significant synergistic advantages: the low degree of polymerization endows the prepolymer chain segments with stronger mobility, which not only helps improve the solubility of the prepolymer in organic solvents but also reduces the melt viscosity of the prepolymer, thereby improving the processing performance of the prepolymer. More importantly, the prepolymer structure at this degree of polymerization has a high content of terminal reactive groups, which is beneficial for forming a higher crosslinking network density during curing, thereby effectively increasing the glass transition temperature of the cured resin and ultimately endowing the resin with excellent heat resistance, which is crucial for the high-temperature performance requirements in the application scenarios of this invention.

[0047]

[0048] A method for preparing a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer includes the following steps: S1, Under an inert atmosphere, a diamine monomer containing a trifluoromethyl structure is completely dissolved in an organic solvent at room temperature to obtain a first solution.

[0049] S2, add a fluorene-containing dianhydride monomer to the first solution and react at room temperature for 6-8 hours to obtain the second solution.

[0050] S3, add a capping agent to the second solution and react at room temperature for 6-8 hours to obtain the third solution.

[0051] S4, add a dehydrating agent and a catalyst to the third solution, heat to 180-200℃, react for 8-10 hours to obtain the fourth solution; the fourth solution includes a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer.

[0052] S5, the fourth solvent is added to the cleaning agent, the powder is precipitated, the powder is washed, filtered and dried at 200-220℃ to obtain a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer; the cleaning agent includes at least one of ethanol and water.

[0053] In this embodiment of the invention, room temperature refers to 20-30°C.

[0054] The molar ratio of dianhydride monomer, diamine monomer, and capping agent is (m+n):(m+n+1):2, where m≧1, n≧0, and 1≦m+n≦20. The mass of the organic solvent is 1.5 to 4 times the total mass of the dianhydride monomer, diamine monomer, and capping agent.

[0055] The diamine monomer is at least one of 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 2,2'-bis(trifluoromethoxy)biphenyldiamine, 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, and 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]propane, and its structural formula is shown sequentially as (I) to (IX):

[0056] The dianhydride monomer is at least one of 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), 5,5'-(2,7-difluoro-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), 5,5'-(2,7-dimethyl-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), and 5,5'-(2,7-bis(trifluoromethyl)-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), and its structural formulas are shown in (X) to (XIII) in sequence:

[0057] The capping agent is at least one of 4-phenylethynylphthalic anhydride, norbornene phthalic anhydride, and ethynylphthalic anhydride, and its structural formulas are shown in (XIV) to (XVI) in sequence:

[0058] In this embodiment of the invention, the capping agent is 4-phenylethynylphthalic anhydride, which has the structural formula (XIV).

[0059] The inert atmosphere includes at least one of nitrogen and argon, the organic solvent includes at least one of N-methylpyrrolidone, m-cresol, phenol and p-chlorophenol, the dehydrating agent includes at least one of toluene and xylene, and the catalyst includes at least one of isoquinoline, quinoline and pyridine.

[0060] A method for preparing a thermosetting polyimide resin includes the following steps: P1 uses a hot-press curing molding process, in which a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is placed in a mold, the mold is heated to 250-310℃, and held at that temperature for 0.5-1.5 hours.

[0061] P2 is used for exhaust treatment by pressurizing or depressurizing, and then pressurized to 1-10MPa.

[0062] P3. Heat the mold to 370-400℃ and hold for 2-3 hours. After the mold cools to below 200℃, release the pressure to obtain thermosetting polyimide resin.

[0063] The prepared thermosetting polyimide resin has a glass transition temperature ≥340℃, tensile strength ≥40.8MPa, and elongation at break ≥2.3%; at an ambient humidity of 50%RH, a temperature of 25℃, and a 10GHz frequency, it has a dielectric constant ≤2.95 and a loss factor ≤0.0098; and a 5% thermal weight loss temperature in air ≥538℃. It is suitable for use in high-temperature resistant, low-dielectric, and microwave-transparent composite materials in the aerospace field.

[0064] Example 1 A method for preparing a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer includes the following steps: Under nitrogen protection, 2,2-bis(4-aminophenyl)hexafluoropropane (16.7130 g, 50 mmol) and N-methylpyrrolidone (50 mL) were added to a dry 250 mL three-necked flask. The mixture was stirred at room temperature until the diamine was completely dissolved. Then, 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione) (11.4605 g, 25 mmol) and N-methylpyrrolidone (30 mL) were added. The reaction mixture was stirred at room temperature for 6 h under nitrogen protection. Then, 4-phenylethynylphthalic anhydride (12.4115 g, 50 mmol) and N-methylpyrrolidone (15 mL) were added to the system to bring the solid content of the solution to 30 wt%. After stirring at room temperature for 8 hours, xylene (11 mL) and isoquinoline (0.4 mL) were added to the reaction solution, and the mixture was heated to 180 °C for azeotropic dehydration and refluxed for 8 hours. Afterward, the reaction system was cooled to room temperature, and the mixture was poured into ethanol, resulting in powder precipitation. After stirring at room temperature for 8 hours, the mixture was filtered, washed, and vacuum dried at 205 °C for 6 hours to obtain the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer shown in (i).

[0065]

[0066] The FT-IR spectrum of the prepared high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is shown below. Figure 1 As shown, the DSC curve is as follows Figure 2 As shown, the rheological curves are as follows: Figure 3As shown. Analysis of the FT-IR spectrum of the prepolymer reveals that at 2210 cm⁻¹... -1 The characteristic absorption peak near the 1780 cm⁻¹ is attributed to the C≡C stretching vibration of the benzoynyl group. -1 and 1720cm -1 The characteristic absorption peaks nearby are attributed to the symmetric and asymmetric stretching vibrations of the C=O bond in the imide ring, respectively, at 1370 cm⁻¹. -1 The characteristic absorption peaks in the vicinity are attributed to the stretching vibration peaks of CN in the imide ring, indicating that the present invention successfully prepared a phenylacetylene-terminated polyimide prepolymer. Analysis of the DSC curve of the prepolymer reveals an exothermic peak at 339-433℃, with a peak temperature of 372℃. This exothermic peak is attributed to the exothermic reaction caused by the crosslinking of the terminal phenylacetylene groups in the prepolymer structure. Analysis of the rheological curve of the prepolymer shows that the melt viscosity gradually decreases with increasing temperature as the prepolymer softens at high temperatures; however, with further temperature increases, the terminal phenylacetylene groups in the prepolymer structure begin to undergo crosslinking and curing reactions, and the melt viscosity gradually increases. The prepolymer exhibits the lowest melt viscosity (5.61 Pa·s) at 313℃, indicating a wide processing window, which is beneficial for processing and molding. Furthermore, the dissolved solids content of this prepolymer in the polar aprotic solvent N-methylpyrrolidone is 40%.

[0067] A method for preparing a thermosetting polyimide resin includes the following steps: The thermosetting polyimide prepolymer prepared in this embodiment is placed in a mold, the mold is heated to 295°C and held for 0.5 hours; the pressure is released by pressurization or depressurization, and then the pressure is increased to 5 MPa; the mold is heated to 370°C and held for 2 hours, and the pressure is released after the mold cools to below 200°C to obtain a thermosetting polyimide resin sheet.

[0068] The DMA curve of the prepared thermosetting polyimide resin is as follows: Figure 4 As shown, the TGA curve is as follows Figure 5 As shown, the mechanical curve is as follows Figure 6 As shown. Analysis of the resin's DMA curve reveals that its glass transition temperature is >400℃, indicating high heat resistance. Analysis of the resin's TGA curve shows that its 5% thermogravimetric analysis (TGA) temperature in air is 539℃, indicating high thermal stability. In the mechanical property testing of the resin, five specimens from the application example were tested, and the average value was used as the final result. The tensile strength of the resin was found to be 40.8 MPa, and the elongation at break was 2.3%, indicating good mechanical properties. Furthermore, this thermosetting polyimide resin exhibits a dielectric constant of 2.95 and a loss factor of 0.0098 at an ambient humidity of 50% RH, a temperature of 25℃, and a 10 GHz frequency, indicating excellent dielectric properties.

[0069] Example 2 A method for preparing a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer includes the following steps: Under nitrogen protection, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (25.9225 g, 50 mmol) and N-methylpyrrolidone (70 mL) were added to a dry 250 mL three-necked flask. The mixture was stirred at room temperature until the diamine was completely dissolved. Then, 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione) (11.4605 g, 25 mmol) and N-methylpyrrolidone (30 mL) were added. The reaction mixture was stirred at room temperature for 6 h under nitrogen protection. Then, 4-phenylethynylphthalic anhydride (12.4115 g, 50 mmol) and N-methylpyrrolidone (15 mL) were added to the system to bring the solid content of the solution to 30 wt%. After stirring at room temperature for 8 hours, xylene (11 mL) and isoquinoline (0.5 mL) were added to the reaction solution, and the mixture was heated to 180 °C for azeotropic dehydration and refluxed for 8 hours. Afterward, the reaction system was cooled to room temperature, and the mixture was poured into ethanol, resulting in powder precipitation. The mixture was stirred at room temperature for 8 hours, filtered, washed, and then vacuum dried at 205 °C for 6 hours to obtain the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer shown in (ⅰⅰ).

[0070]

[0071] The prepared high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer has a dissolved solids content of 20% in the polar aprotic solvent N-methylpyrrolidone and a minimum melt viscosity of 1.67 Pa·s.

[0072] A method for preparing a thermosetting polyimide resin includes the following steps: The thermosetting polyimide prepolymer prepared in this embodiment is placed in a mold, the mold is heated to 290°C and held for 0.5 hours; the venting is performed by pressurizing or depressurizing, and then the pressure is increased to 5 MPa; the mold is heated to 370°C and held for 2 hours, and the pressure is released after the mold cools to below 200°C to obtain a thermosetting polyimide resin sheet.

[0073] The prepared thermosetting polyimide resin exhibits the following properties at an ambient humidity of 50%RH, a temperature of 25℃, and a 10GHz frequency: dielectric constant of 2.95, loss factor of 0.0063, glass transition temperature of 340℃, 5% thermal weight loss temperature in air of 538℃, tensile strength of 84.2MPa, and elongation at break of 8.4%.

[0074] Example 3 A method for preparing a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer includes the following steps: Under nitrogen protection, 2,2-bis(4-aminophenyl)hexafluoropropane (8.3565 g, 25 mmol), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (12.9613 g, 25 mmol), and N-methylpyrrolidone (60 mL) were added to a dry 250 mL three-necked flask. The mixture was stirred at room temperature until the diamine was completely dissolved. Then, 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione) (11.4605 g, 25 mmol) and N-methylpyrrolidone (30 mL) were added, and the reaction mixture was stirred at room temperature for 6 h under nitrogen protection. Then, 4-phenylethynylphthalic anhydride (12.4115 g, 50 mmol) and N-methylpyrrolidone (15 mL) were added to the system to bring the solid content of the solution to 30 wt%. After stirring at room temperature for 8 hours, xylene (12 mL) and isoquinoline (0.4 mL) were added to the reaction solution, and the mixture was heated to 180 °C for azeotropic dehydration and refluxed for 8 hours. Afterward, the reaction system was cooled to room temperature, and the mixture was poured into ethanol, resulting in powder precipitation. The mixture was stirred at room temperature for 8 hours, filtered, washed, and then vacuum dried at 205 °C for 6 hours to obtain the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer shown in (ⅰⅰⅰ).

[0075]

[0076] The prepared high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer has a dissolved solids content of 20% in the polar aprotic solvent N-methylpyrrolidone and a minimum melt viscosity of 2.60 Pa·s.

[0077] A method for preparing a thermosetting polyimide resin includes the following steps: The thermosetting polyimide prepolymer prepared in this embodiment is placed in a mold, the mold is heated to 280°C and held for 0.5 hours; the pressure is released by pressurization or depressurization, and then the pressure is increased to 5 MPa; the mold is heated to 370°C and held for 2 hours, and the pressure is released after the mold cools to below 200°C to obtain a thermosetting polyimide resin sheet.

[0078] The prepared thermosetting polyimide resin exhibits the following properties at an ambient humidity of 50%RH, a temperature of 25℃, and a 10GHz frequency: dielectric constant of 2.90, loss factor of 0.0077, glass transition temperature of 368℃, 5% thermal weight loss temperature in air of 546℃, tensile strength of 78.1MPa, and elongation at break of 6.8%.

[0079] Example 4 A method for preparing a high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer includes the following steps: Under nitrogen protection, 2,2'-di(trifluoromethyl)diaminobiphenyl (8.0058 g, 25 mmol), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (12.9613 g, 25 mmol), and N-methylpyrrolidone (60 mL) were added to a dry 250 mL three-necked flask. The mixture was stirred at room temperature until the diamine was completely dissolved. Then, 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione) (11.4605 g, 25 mmol) and N-methylpyrrolidone (30 mL) were added. The reaction mixture was stirred at room temperature for 6 h under nitrogen protection. Then, 4-phenylethynylphthalic anhydride (12.4115 g, 50 mmol) and N-methylpyrrolidone (15 mL) were added to the system to bring the solid content of the solution to 30 wt%. After stirring at room temperature for 8 hours, xylene (12 mL) and isoquinoline (0.4 mL) were added to the reaction solution, and the mixture was heated to 180 °C for azeotropic dehydration and refluxed for 8 hours. Afterward, the reaction system was cooled to room temperature, and the mixture was poured into ethanol, resulting in powder precipitation. After stirring at room temperature for 8 hours, the mixture was filtered, washed, and vacuum dried at 205 °C for 6 hours to obtain the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer shown in (iv).

[0080]

[0081] The prepared high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer has a dissolved solids content of 20% in the polar aprotic solvent N-methylpyrrolidone and a minimum melt viscosity of 3.47 Pa·s.

[0082] A method for preparing a thermosetting polyimide resin includes the following steps: The thermosetting polyimide prepolymer prepared in this embodiment is placed in a mold, the mold is heated to 280°C and held for 0.5 hours; the pressure is released by pressurization or depressurization, and then the pressure is increased to 5 MPa; the mold is heated to 370°C and held for 2 hours, and the pressure is released after the mold cools to below 200°C to obtain a thermosetting polyimide resin sheet.

[0083] The prepared thermosetting polyimide resin exhibits the following properties at an ambient humidity of 50%RH, a temperature of 25℃, and a 10GHz frequency: dielectric constant of 2.88, loss factor of 0.0077, glass transition temperature of 369℃, 5% thermal weight loss temperature in air of 552℃, tensile strength of 64.3MPa, and elongation at break of 4.7%.

[0084] The above embodiments clearly demonstrate that the thermosetting polyimide with fluorene and trifluoromethyl structures synthesized according to the present invention possesses excellent comprehensive properties: high frequency, low dielectric constant, low loss factor, high heat resistance, and good prepolymer processability. The rigidity of the fluorene structure contributes to the high heat resistance, specifically manifested in a high glass transition temperature and a 5% thermogravimetric loss temperature in air ≥538℃. The synergistic effect of the large volume of the fluorene and trifluoromethyl structures reduces the molecular chain packing density, thereby improving the solubility (20-40% solubility in N-methylpyrrolidone) and melt flowability (minimum melt viscosity of 1-10 Pa·s) of the prepolymer. Furthermore, this effect increases the free volume of the polymer, effectively reducing the high-frequency dielectric constant (≤2.95 at 50% RH, 25℃, and 10 GHz). Meanwhile, the hydrophobicity of the trifluoromethyl structure helps suppress the polymer's moisture absorption, reducing the high-frequency loss factor (≤0.0098 at 10GHz with an ambient humidity of 50%RH and a temperature of 25℃). This comprehensive optimization not only solves the challenge of traditional polyimide resins in balancing high-frequency dielectric properties, heat resistance, and processability, but also ensures the material's mechanical stability, making it suitable as a high-performance resin matrix for high-temperature resistant, low-dielectric, and microwave-transparent composite materials in the aerospace field.

[0085] The above embodiments are merely illustrative of several implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the invention patent. For those skilled in the art, any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer, characterized in that, The general formula for the structure is: Where m and n are the degree of aggregation, and m≧1, n≧0, 1≦m+n≦20, the arrangement of repeating units can be block or random. R' is each independently at least one of hydrogen atom, fluorine atom, methyl or trifluoromethyl; R1 and R2 are each independently selected from at least one of the following structures. R a At least one of the following structures The R1, R2 and R a In the structure, the dashed lines indicate the connection positions with other groups of the prepolymer.

2. The high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer according to claim 1, characterized in that, The minimum melt viscosity of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer is 1-1000 Pa·s; the dissolved solids content of the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer in polar aprotic solvents is 10-50 wt%.

3. A method for preparing the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S1, Under an inert atmosphere, a diamine monomer containing a trifluoromethyl structure is completely dissolved in an organic solvent at room temperature to obtain the first solution; S2, add a fluorene-containing dianhydride monomer to the first solution and react at room temperature for 6-8 hours to obtain a second solution; S3, add a capping agent to the second solution and react at room temperature for 6-8 hours to obtain a third solution; S4, add a dehydrating agent and a catalyst to the third solution, heat to 180-200℃, and react for 8-10 hours to obtain a fourth solution; the fourth solution includes the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer.

4. The method for preparing the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer according to claim 3, characterized in that, The molar ratio of the dianhydride monomer, diamine monomer, and capping agent is (m+n):(m+n+1):2, where m≧1, n≧0, and 1≦m+n≦20.

5. The method for preparing the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer according to claim 3, characterized in that, The diamine monomer is at least one of 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 2,2'-bis(trifluoromethoxy)-biphenyldiamine, 1,4-bis(4'-amino-2'-trifluoromethylphenoxy)benzene, and 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]propane; The dianhydride monomer is at least one selected from 5,5'-(9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), 5,5'-(2,7-difluoro-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), 5,5'-(2,7-dimethyl-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione), and 5,5'-(2,7-bis(trifluoromethyl)-9H-fluorene-9,9-diyl)bis(isobenzofuran-1,3-dione). The capping agent is at least one of 4-phenylethynyl phthalic anhydride, norbornene phthalic anhydride, and ethynyl phthalic anhydride.

6. The method for preparing the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer according to claim 3, characterized in that, The inert atmosphere includes at least one of nitrogen and argon, the organic solvent includes at least one of N-methylpyrrolidone, m-cresol, phenol and p-chlorophenol, the dehydrating agent includes at least one of toluene and xylene, and the catalyst includes at least one of isoquinoline, quinoline and pyridine.

7. The method for preparing the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer according to claim 3, characterized in that, It also includes the following steps: S5, the fourth solvent is added to the cleaning agent, the powder is precipitated, the powder is washed, filtered, and dried at 200-220°C to obtain the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer; the cleaning agent includes at least one of ethanol and water.

8. A thermosetting polyimide resin, characterized in that, Prepared by the following method: P1, using a hot-press curing molding process, the high-temperature resistant, low-dielectric thermosetting polyimide resin prepolymer of claim 1 is placed in a mold, and the mold is heated to 250-310℃ and kept at that temperature for 0.5-1.5h. P2 is used for exhaust treatment by pressurization or depressurization, and then pressurized to 1-10MPa; P3. Heat the mold to 370-400℃ and keep it at that temperature for 2-3 hours. After the mold cools down to below 200℃, release the pressure to obtain the thermosetting polyimide resin.

9. A thermosetting polyimide resin as described in claim 8, characterized in that, Glass transition temperature ≥340℃, tensile strength ≥40.8MPa, elongation at break ≥2.3%; dielectric constant ≤2.95, loss factor ≤0.0098 at 10GHz and ambient humidity 50%RH, temperature 25℃; 5% thermal weight loss temperature in air ≥538℃.

10. An application of the thermosetting polyimide resin as described in claim 8, characterized in that, It is used in high-temperature resistant, low-dielectric, wave-transparent composite materials in the aerospace field.

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