Wave-transparent resin for aircraft equipment compartment and preparation method of wave-transparent resin

Abstract

The invention relates to the technical field of wave-transparent materials, in particular to wave-transparent resin for an aircraft equipment compartment and a preparation method of the wave-transparent resin. The method comprises the following steps: reacting 5-bromine-2-fluorine-trifluorotoluene with chirality-1, 1 '-co-2-naphthol under the protection of nitrogen to obtain a chiral monomer, polymerizing the chiral monomer with biphenyl phthalazinone through an initiator to obtain a prepolymer, and finally terminating with 4-nitrophthalonitrile to obtain the target resin. According to the method, regular accumulation of molecules is destroyed by mixing 1, 1 '-bi-2-naphthol with different configurations, and the low polarity of-CF3 and a rigid framework of biphenyl phthalazinone are combined, so that the dielectric property and the thermal stability of the resin are cooperatively regulated and controlled. The obtained wave-transparent resin is low in dielectric constant and loss, high in thermal decomposition temperature and glass transition temperature, excellent in mechanical property and high-temperature retention rate, low in softening point and good in solubility, can be easily compounded and molded with quartz fiber cloth, is suitable for preparation of wave-transparent composite materials for aircraft equipment cabins, and meets the requirements of broadband high-temperature service.

Description

Technical Field

[0001] This invention relates to the field of wave-transparent materials technology, and in particular to a wave-transparent resin for use in aircraft equipment compartments and its preparation method. Background Technology

[0002] The core function of wave-transparent materials is to achieve efficient transmission of electromagnetic waves. Their wave-transmitting performance is mainly determined by the dielectric constant and dielectric loss: the lower the dielectric constant and the smaller the dielectric loss, the weaker the reflection and energy attenuation of electromagnetic waves when propagating in the material, and the higher the wave-transmitting efficiency. The dielectric properties are essentially regulated by the molecular structure of the material. The degree of regularity of molecular chain packing, the dipole synergistic effect of polar groups, and the interface polarization between crystalline and amorphous regions are key factors affecting the dielectric constant. The hysteresis effect of molecular dipoles following the movement of an external electric field and the ability of charge traps to capture free charges directly determine the dielectric loss. In addition, the service environment of aircraft equipment compartments places stringent comprehensive performance requirements on wave-transparent materials: they must withstand temperatures above 400°C caused by aerodynamic heating (requiring materials with high glass transition temperature and thermal decomposition temperature), while also withstanding mechanical forces such as vibration and assembly loads (requiring good flexural strength and modulus), and must also possess excellent processability (such as low softening point and good solvent solubility) to adapt to prepreg preparation and composite material molding processes.

[0003] To meet the fundamental performance requirements of microwave-transparent materials, various resin matrices have been developed using existing technologies. While epoxy resins, widely used in the early stages, offer excellent processability, they suffer from high dielectric constants and glass transition temperatures mostly below 200°C. This results in a sharp increase in dielectric loss at high temperatures, failing to meet the broadband, high-temperature service requirements of aircraft. Cyanate ester resins, by introducing rigid structures such as benzene rings, reduce dielectric constants and losses, but the curing process easily leads to the formation of locally ordered structures, resulting in enhanced interfacial polarization, poor broadband dielectric stability, and insufficient retention of high-temperature mechanical properties. In recent years, phthalonitrile resins, due to their aromatic and heterocyclic aromatic structures, have shown significantly improved heat resistance, becoming a research hotspot for high-temperature microwave-transparent materials. However, traditional phthalonitrile resins are mostly polymerized using single-configuration monomers, exhibiting a tendency for directional stacking of molecular chains, easily forming microcrystalline regions and leading to high dielectric constants. Some studies have attempted to reduce polarity by introducing fluorine-containing groups, but the steric hindrance of these groups often leads to increased resin softening points, decreased solubility, and a narrowed processing window.

[0004] To further optimize dielectric properties, a few studies have attempted to introduce twisted planar molecules to regulate the molecular chain stacking of polymers. For example, using biphenyldiazepine as a comonomer can suppress tight stacking through the twisted structure of biphenyldiazepine, but the single configuration still has a tendency for quasi-ordered arrangement, and the dipole synergistic effect is not completely destroyed, so the effect of reducing the dielectric constant is limited. In addition, existing microwave-transparent resins face obvious bottlenecks when balancing the four requirements of low dielectric, high heat resistance, strong mechanical properties, and easy processing: emphasizing dielectric properties sacrifices heat resistance or processability, while improving heat resistance leads to a decrease in mechanical properties or microwave transmission stability, making it difficult to meet the stringent requirements of aircraft equipment compartments for microwave-transparent materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a microwave-transparent resin for use in aircraft equipment compartments and its preparation method.

[0006] To achieve the above objectives, the present invention provides a method for preparing a microwave-transparent resin for use in aircraft equipment compartments, comprising the following steps:

[0007] S1. Under nitrogen protection, 5-bromo-2-fluoro-trifluorotoluene, chiral-1,1'-bi-2-naphthol, and potassium carbonate were added to dimethyl sulfoxide. The mixture was stirred and heated to 150-170℃ for 6-10 hours. After cooling to room temperature, the precipitate was poured into a dilute hydrochloric acid solution, filtered, and the solid was collected. Recrystallization from ethanol yielded the chiral monomer. Since chiral-1,1'-bi-2-naphthol is prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol configurations, two reactions occur during this process. The specific chemical reaction equations are as follows:

[0008]

[0009] S2. Under nitrogen protection, chiral monomers, biphenyldiazepinene, and cesium carbonate are added to anhydrous sulfolane. The mixture is heated to 135-145°C with stirring for 1-2 hours, then cooled to 80°C, an initiator is added, and the mixture is heated to 190-200°C for 18-30 hours to obtain the prepolymer. During this process, biphenyldiazepinene first forms a salt under the action of cesium carbonate. The chemical reaction equation is as follows:

[0010] Then, because the chiral monomer contains two compounds with two different configurations, the polymerization reaction will result in a prepolymer containing repeating units with two different configurations. The chemical reaction equation is as follows:

[0011]

[0012] S3. Under nitrogen protection, the reaction temperature was lowered to 80-90℃, and 4-nitrophthalonitrile was added to the prepolymer. The reaction was carried out for 8-10 hours. After cooling to room temperature, a phthalonitrile-terminated polymer solution was obtained. This solution was then poured into a dilute hydrochloric acid solution to precipitate the polymer. The precipitate was filtered, the solid was collected, washed with ethanol, and dried to obtain a microwave-transparent resin for aircraft equipment compartments. The chemical reaction equations that occurred during this process are as follows:

[0013]

[0014] Preferably, the chiral-1,1'-bi-2-naphthol in S1 is prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 1:1.

[0015] Preferably, the molar ratio of 5-bromo-2-fluoro-trifluorotoluene, chiral-1,1'-bi-2-naphthol, and potassium carbonate in S1 is 1:2-2.4:2-3.

[0016] Preferably, the 5-bromo-2-fluoro-trifluorotoluene, dimethyl sulfoxide, and dilute hydrochloric acid solution in S1 are in a weight ratio of 1:8-12:20-30.

[0017] Preferably, the mass concentration of the dilute hydrochloric acid solution in S2 is 10%.

[0018] Preferably, the chiral monomer, biphenyldiazepinene, and cesium carbonate in S2 are in a molar ratio of 1:1-1.2:1.5-2.

[0019] Preferably, the chiral monomer, anhydrous sulfolane, and initiator in S2 are in a weight ratio of 1:8-12:0.03-0.07.

[0020] Preferably, the initiator in S2 is a mixture of cuprous chloride and quinoline in a molar ratio of 1:2.

[0021] Preferably, the molar ratio of 4-nitrophthalonitrile in S3 to biphenyldiazepine in the prepolymer is 1.2-2:1.

[0022] Preferably, in S3, the phthalonitrile-terminated polymer solution and the dilute hydrochloric acid solution are in a weight ratio of 1:2-3.

[0023] Preferably, the mass concentration of the dilute hydrochloric acid solution in S3 is 10%.

[0024] Furthermore, the present invention also provides a microwave-transparent resin for aircraft equipment compartments, which is prepared using the above-described method.

[0025] Preferably, the working mechanism of the wave-transparent resin for aircraft equipment compartments in this invention is as follows:

[0026] In this invention, chiral molecules improve the wave transmission performance of materials by reducing their dielectric constant. The asymmetric interference effect of chiral configuration disrupts the regular stacking of molecular chains and the synergistic effect of dipoles, thereby weakening dielectric polarization ability from the root and suppressing the generation of dielectric loss.

[0027] Although the molecular chains of single chiral configurations (such as pure R-type or pure S-type 1,1'-bi-2-naphthol) are difficult to pack tightly due to the twisted structure of the binaphthyl skeleton, they still have a tendency to be oriented. The binaphthyl planes of adjacent molecules will tilt in the same direction, forming a quasi-ordered loose packing. This arrangement will cause the polar groups in the molecule to tend to be aligned, resulting in a dipole cooperative effect and an increase in dielectric constant.

[0028] When R / S-1,1'-bi-2-naphthol is used in combination, the spatial orientation of the molecular chains of the two configurations is completely opposite, forming a random stacking structure: the binaphthol planes of adjacent molecules intersect each other, the intermolecular distance increases, the dipole orientation of the polar groups is random (the dipole moments cancel each other out), and the dipole synergy is completely destroyed. This configuration disorder reduces the molecular polarizability, which meets the core requirement of low dielectric for microwave transparent materials.

[0029] Another important contribution to the dielectric constant comes from interfacial polarization (charge accumulation at the interface between different phases), and the high regularity of the molecular chain is a prerequisite for crystallization. Due to their uniform configuration, single-chiral binaphthol derivatives are prone to forming locally ordered microcrystalline regions during the curing process, resulting in a two-phase structure of crystalline and amorphous regions in the material.

[0030] The molecules in the crystalline region are closely packed, resulting in a high dielectric constant.

[0031] The molecules in the amorphous region are loosely arranged, resulting in a lower dielectric constant.

[0032] Charge accumulation occurs at the interface between two phases due to the difference in dielectric constant, resulting in interface polarization, which increases the overall dielectric constant and disrupts wave transmission stability.

[0033] After R / S chiral mixing, the asymmetry of the configuration completely suppresses the ordered arrangement of molecules, resulting in a completely amorphous structure after resin curing, with no obvious crystalline-amorphous region interface, the disappearance of charge accumulation phenomenon, and a decrease in the contribution of interfacial polarization to the dielectric constant.

[0034] Dielectric loss mainly stems from the hysteresis effect of molecular dipoles following the movement of an external electric field. The regularity of molecular chains directly affects the coordination of movement. In a single-chiral resin, although the molecular chains are twisted, their orientation is consistent. When the temperature or electric field changes, the chain segments of adjacent molecules are prone to coordinated vibration: the dipoles rotate synchronously following the electric field, and the hysteresis effect is obvious, leading to an increase in dielectric loss.

[0035] After R / S chiral mixing, the random arrangement of molecular chains causes the chain segment motion to lose its synergy: the direction of motion of molecular chains with different configurations restricts each other, and the dipoles can only vibrate independently within a limited range, making it difficult to form a synchronous hysteresis effect. At the same time, the rigid structure of the binaphthyl skeleton itself restricts the internal rotation of the molecular chains, further reducing the motion capability of the dipoles. Under the synergistic effect of the two, the dielectric loss decreases, and the thermal stability provided by the naphthalene ring avoids the problem of the sharp increase in high temperature loss of traditional resins.

[0036] The twisted structure of chiral molecules can also optimize the polarity distribution within the molecule: the twisting of the binaphthyl skeleton places the cyanophenoxy groups on both sides in an asymmetric spatial position, avoiding the strong dipole moment formed by symmetric polar groups. After R / S chiral mixing, this asymmetric polarity distribution is further averaged on a macroscopic scale, and the overall dipole moment of the molecule decreases.

[0037] The low dipole moment reduces the ability of molecules to trap free charges: In traditional resins, strongly polar groups are prone to forming charge traps, which are difficult to escape at high frequencies, resulting in increased dielectric loss; while the chiral structure of the present invention has a uniform polarity distribution and a lower charge trap density, which reduces dielectric loss at high frequencies and meets the requirements of broadband communication for aircraft.

[0038] Furthermore, the present invention also provides the application of a microwave-transparent resin for aircraft equipment compartments in the preparation of microwave-transparent composite materials for aircraft equipment compartments, comprising the following steps:

[0039] (1) At room temperature, microwave-transparent resin for aircraft equipment compartment, zinc chloride and 4,4-diaminodiphenyl sulfone are added to N,N-dimethylformamide and stirred for 30-60 minutes to obtain resin solution;

[0040] (2) On a heating plate heated to 60°C, quartz fiber cloth is immersed in resin solution and waited for 10-20 minutes. After completion, it is placed in an oven at 150-160°C to dry. After removing the solvent, a prepreg is obtained. Then, it is placed in a molding machine for hot pressing and curing. After hot pressing and curing, it is cooled to room temperature and demolded to obtain a wave-transparent composite material, which is used to cover the antenna for receiving signals in the equipment cabin of the aircraft.

[0041] Preferably, in (1), the aircraft equipment compartment uses a microwave-transparent resin, zinc chloride, and 4,4-diaminodiphenyl sulfone, with N,N-dimethylformamide added in a weight ratio of 1:0.02-0.04:0.02-0.04:2.5-3.5.

[0042] Preferably, the pressure of the film press in (2) is 1-1.5 MPa.

[0043] Preferably, the curing temperature rise procedure in (2) is as follows: first, cure at 250-260℃ for 2 hours, then raise the temperature to 290℃ and cure for 2 hours, and finally raise the temperature to 360℃ and cure for 2 hours.

[0044] The beneficial effects of this invention are:

[0045] 1. This invention forms a racemic mixture by mixing (R)-1,1'-bi-2-naphthol and (S)-1,1'-bi-2-naphthol in a 1:1 weight ratio. The two molecular chains have completely opposite spatial orientations, forming a random stacking structure. This completely destroys the dipole synergistic effect of the polar groups, causing the dipole moments to cancel each other out. At the same time, it inhibits the ordered arrangement of molecules to eliminate the crystalline-amorphous region interface, significantly reducing the contribution of interfacial polarization. The low polarity of the -CF3 group introduced by 5-bromo-2-fluoro-trifluorotoluene further weakens the molecular polarizability, resulting in a low dielectric constant and dielectric loss of the resin in the 8-18 GH wide frequency band. Moreover, at a high temperature of 400℃, the rigid skeleton restricts chain segment movement, resulting in a weak dipole hysteresis effect and excellent dielectric stability. This allows for efficient electromagnetic wave transmission, meeting the wave transmission requirements of antenna communication in aircraft equipment compartments.

[0046] 2. In the resin molecular chain of this invention, the rigid aromatic ring of biphenyldiazepine and the binaphthyl skeleton form a double rigid structure, which synergistically enhances the heat-resistant skeleton support of the molecular chain. At the same time, the strong CF bond of the -CF3 group has excellent thermal stability, which can reduce molecular chain breakage and volatilization at high temperatures. In addition, the three-dimensional cross-linked network of triazine rings formed by end-capping and curing of phthalonitrile is dense and stable, further improving the structural integrity of the resin. The above design enables the resin to have a high glass transition temperature, thermal decomposition temperature and 800℃ char residue. Even under the high temperature environment caused by aerodynamic heating of aircraft, it can still maintain a stable chemical and physical structure without obvious thermal degradation, meeting the reliability requirements of long-term high-temperature service in equipment compartments.

[0047] 3. The random stacking structure formed by the mixture of (R)-1,1'-bi-2-naphthol and (S)-1,1'-bi-2-naphthol in this invention weakens intermolecular forces and lowers the resin softening point. Simultaneously, the amorphous structure, without microcrystalline regions hindering solvent penetration, exhibits good solubility in polar solvents such as DMF, allowing for the rapid formation of a homogeneous resin solution. This resin solution can efficiently wet quartz fiber cloth at 60°C, and after drying to remove the solvent, a uniform prepreg sheet can be prepared. Furthermore, the resin is suitable for curing processes with pressures of 1-1.5 MPa and stepped temperature increases, exhibiting moderate fluidity, low shrinkage, and no significant bubbles or defects during curing. The overall processing window is wide, and the operation is convenient, enabling the efficient preparation of microwave-transparent composite materials, which is beneficial for industrial-scale mass production.

[0048] 4. The random stacking structure of the resin in this invention results in a uniform distribution of molecular chains. When impregnated with quartz fiber cloth, it can fully fill the gaps between fibers, forming a tight resin-fiber interface bond. Under stress, stress can be efficiently transferred from the resin to the main fiber carrier, significantly improving the room temperature flexural strength and flexural modulus of the composite material. At the same time, the high glass transition temperature of the resin ensures that it remains rigid at 400°C and is not easily softened, maintaining the integrity of the interface bond and preventing fiber-resin delamination. This ensures that the composite material retains a high mechanical property retention rate in high-temperature environments, enabling it to withstand the mechanical effects of vibration and assembly loads during aircraft service, thus ensuring the structural stability of the equipment compartment.

[0049] 5. This invention, through precise molecular structure design, combines chiral regulation, fluorine modification, and rigid framework construction to simultaneously achieve a synergistic effect of low dielectric constant, high heat resistance, strong mechanical properties, and easy processing. Compared to traditional microwave-transparent resins that prioritize dielectric properties at the expense of heat resistance or processability, or improve heat resistance at the expense of mechanical properties, this invention's resin does not compromise on core properties: random stacking and fluorine-containing structures ensure dielectric properties, rigid framework and cross-linked networks enhance heat resistance, interface optimization strengthens mechanical properties, and intermolecular force regulation improves processability. This comprehensive performance advantage allows the resin to be directly applied to the preparation of microwave-transparent composite materials for aircraft equipment compartments, perfectly meeting the stringent requirements of equipment compartments for microwave-transparent materials. Attached Figure Description

[0050] Figure 1 The HNMR spectrum of the chiral monomer prepared in Example 2 of this invention;

[0051] Figure 2 The image shows the FTIR infrared spectrum of the prepolymer prepared in Example 2 of this invention.

[0052] Figure 3 The image shows the FTIR infrared spectrum of the wave-transparent resin for aircraft equipment compartments prepared in Example 2 of this invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0054] Example 1: A specific preparation method of a microwave-transparent resin for aircraft equipment compartments, comprising the following steps:

[0055] S1. Under nitrogen protection, 100g of 5-bromo-2-fluoro-trifluorotoluene, 235.65g of chiral-1,1'-bi-2-naphthol (prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 1:1), and 113.75g of potassium carbonate were added to 800g of dimethyl sulfoxide. The mixture was stirred and heated to 150℃ for 6h. After cooling to room temperature, the solid was precipitated in 2kg of 10% dilute hydrochloric acid solution, filtered, and the solid was collected. After recrystallization with ethanol, the chiral monomer was obtained.

[0056] S2. Under nitrogen protection, 200g of chiral monomer, 65.07g of biphenyldiazepine, and 133.47g of cesium carbonate were added to 1.6kg of anhydrous sulfolane. The mixture was heated to 135℃ with stirring and stirred for 1h. Then the temperature was lowered to 80℃, and 6g of initiator (prepared by mixing cuprous chloride and quinoline in a molar ratio of 1:2) was added. The temperature was then raised to 190℃ and the reaction was carried out for 18h to obtain the prepolymer.

[0057] S3. Under nitrogen protection, the reaction temperature was lowered to 80℃, and 56.74g of 4-nitrophthalonitrile was added to the prepolymer. The reaction was carried out for 8 hours. After cooling to room temperature, a phthalonitrile-terminated polymer solution was obtained. Then, it was poured into a 10% dilute hydrochloric acid solution (the mass ratio of dilute hydrochloric acid to the phthalonitrile-terminated polymer solution was 2:1) to precipitate the polymer. The solution was filtered, the solid was collected, washed with ethanol, and dried to obtain a microwave-transparent resin for aircraft equipment compartments.

[0058] Example 2: A specific preparation method of a microwave-transparent resin for aircraft equipment compartments, comprising the following steps:

[0059] S1. Under nitrogen protection, 100g of 5-bromo-2-fluoro-trifluorotoluene, 269.19g of chiral-1,1'-bi-2-naphthol (prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 1:1), and 147.66g of potassium carbonate were added to 1kg of dimethyl sulfoxide. The mixture was stirred and heated to 160℃ for 8h. After cooling to room temperature, the solid was precipitated in 2.5kg of 10% dilute hydrochloric acid solution, filtered, and the solid was collected. After recrystallization with ethanol, the chiral monomer was obtained.

[0060] S2. Under nitrogen protection, 200g of chiral monomer, 71.57g of biphenyldiazepine, and 155.72g of cesium carbonate were added to 2kg of anhydrous sulfolane. The mixture was heated to 140℃ with stirring and stirred for 1.5h. Then the temperature was lowered to 80℃, and 10g of initiator (prepared by mixing cuprous chloride and quinoline in a molar ratio of 1:2) was added. The temperature was then raised to 195℃ and the reaction was carried out for 24h to obtain the prepolymer.

[0061] S3. Under nitrogen protection, the reaction temperature was lowered to 85°C, and 83.21g of 4-nitrophthalonitrile was added to the prepolymer. The reaction was carried out for 9 hours. After cooling to room temperature, a phthalonitrile-terminated polymer solution was obtained. Then, the solution was poured into a 10% dilute hydrochloric acid solution (the mass ratio of dilute hydrochloric acid to the phthalonitrile-terminated polymer solution was 2.5:1) to precipitate the polymer. The solution was filtered, the solid was collected, washed with ethanol, and dried to obtain a microwave-transparent resin for aircraft equipment compartments.

[0062] Example 3: A specific method for preparing a microwave-transparent resin for an aircraft equipment compartment, comprising the following steps:

[0063] S1. Under nitrogen protection, 100g of 5-bromo-2-fluoro-trifluorotoluene, 282.79g of chiral-1,1'-bi-2-naphthol (prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 1:1), and 170.63g of potassium carbonate were added to 1.2kg of dimethyl sulfoxide. The mixture was stirred and heated to 170℃ for 10h. After cooling to room temperature, the solid was precipitated in 3kg of 10% dilute hydrochloric acid solution, filtered, and the solid was collected. After recrystallization with ethanol, the chiral monomer was obtained.

[0064] S2. Under nitrogen protection, 200g of chiral monomer, 78.08g of biphenyldiazepine, and 177.97g of cesium carbonate were added to 2.4kg of anhydrous sulfolane. The mixture was heated to 145℃ with stirring and stirred for 2 hours. Then the temperature was lowered to 80℃, and 14g of initiator (prepared by mixing cuprous chloride and quinoline in a molar ratio of 1:2) was added. The temperature was then raised to 200℃ and the reaction was carried out for 30 hours to obtain the prepolymer.

[0065] S3. Under nitrogen protection, the reaction temperature was lowered to 90℃, and 113.48g of 4-nitrophthalonitrile was added to the prepolymer. The reaction was carried out for 10h, and after cooling to room temperature, a phthalonitrile-terminated polymer solution was obtained. Then, it was poured into a 10% dilute hydrochloric acid solution (the mass ratio of dilute hydrochloric acid to the phthalonitrile-terminated polymer solution was 3:1) to precipitate the polymer. The solution was filtered, the solid was collected, washed with ethanol, and dried to obtain a microwave-transparent resin for aircraft equipment compartments.

[0066] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that chiral-1,1'-bi-2-naphthol is replaced with (S)-1,1'-bi-2-naphthol.

[0067] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that chiral-1,1'-bi-2-naphthol is replaced with (R)-1,1'-bi-2-naphthol.

[0068] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that chiral-1,1'-bi-2-naphthol is prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 3:1.

[0069] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that chiral-1,1'-bi-2-naphthol is prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 5:1.

[0070] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that 5-bromo-2-fluoro-trifluorotoluene is replaced with 5-bromo-2-fluorotoluene.

[0071] Performance testing:

[0072] 1. Softening point and solubility test: The softening point and DMF solubility of the microwave-transparent resins for aircraft equipment compartments prepared in Examples 1-4 and Comparative Examples 1-5 were tested. The DMF solubility test method was as follows: 2g of sample was placed in a 25mL conical flask, 5g of DMF was added, and the time for complete dissolution of the sample was recorded. The experimental results are shown in Table 1.

[0073] Table 1 Softening point and solubility

[0074] Softening point / °C Complete dissolution time / min Example 1 136 19 Example 2 141 22 Example 3 143 25 Comparative Example 1 158 48 Comparative Example 2 157 49 Comparative Example 3 148 36 Comparative Example 4 153 45 Comparative Example 5 162 54

[0075] 2. Thermal and dielectric properties testing: The microwave-transparent resins for aircraft equipment compartments prepared in Examples 1-3 and Comparative Examples 1-5 were cured according to the following steps:

[0076] (1) At room temperature, the microwave-transparent resin for the aircraft equipment compartment, zinc chloride and 4,4-diaminodiphenyl sulfone were added to N,N-dimethylformamide at a weight ratio of 1:0.02-0.04:0.02-0.04:2.5-3.5, and stirred for 30-60 minutes to obtain a resin solution;

[0077] (2) It is dried in an oven at 150-160℃ to remove the solvent, and then placed in a molding machine for hot pressing and curing. The pressure of the molding machine is 1-1.5MPa. First, it is cured at 250-260℃ for 2 hours, then the temperature is raised to 290℃ for 2 hours, and finally the temperature is raised to 360℃ for 2 hours. After hot pressing and curing, it is cooled to room temperature and demolded to obtain the cured product.

[0078] The glass transition temperature, thermal decomposition temperature, char residue at 800℃, dielectric constant range of 8-18 GHz at room temperature, dielectric loss range of 8-18 GHz, and dielectric constant range of 8-18 GHz at 400℃ were tested. The experimental results are shown in Table 2.

[0079] Table 2 Thermal and Dielectric Properties

[0080]

[0081] 3. Mechanical property testing: Referring to ASTM D790 standard, a universal testing machine was used to test the room temperature flexural strength and flexural modulus of the radar-transparent resin and quartz fiber cloth composite materials for aircraft equipment compartments prepared in Examples 1-3 and Comparative Examples 1-5, as well as the flexural performance retention rate at 400℃. The preparation process of the composite materials is as follows:

[0082] (1) At room temperature, the microwave-transparent resin for the aircraft equipment compartment, zinc chloride and 4,4-diaminodiphenyl sulfone were added to N,N-dimethylformamide at a weight ratio of 1:0.02-0.04:0.02-0.04:2.5-3.5, and stirred for 30-60 minutes to obtain a resin solution;

[0083] (2) On a heating plate heated to 60°C, quartz fiber cloth is immersed in resin solution and waited for 10-20 minutes. After completion, it is placed in an oven at 150-160°C to dry. After removing the solvent, a prepreg is obtained. Then, it is placed in a molding machine for hot pressing and curing. The pressure of the molding machine is 1-1.5 MPa. First, it is cured at 250-260°C for 2 hours, then heated to 290°C for 2 hours, and finally heated to 360°C for 2 hours. After hot pressing and curing, it is cooled to room temperature and demolded to obtain the composite material.

[0084] The composite material was cut into samples with external dimensions of 80mm×10mm×4mm for testing. The experimental results are shown in Table 3.

[0085] Table 3 Mechanical Properties

[0086]

[0087]

[0088] Performance Analysis:

[0089] As can be seen from the experimental data in Tables 1-3, the microwave-transparent resins prepared in Examples 1-3 of this invention are significantly superior to the comparative examples in terms of softening point, solubility, thermal properties, dielectric properties, and mechanical properties of the resin / quartz fiber cloth composite material.

[0090] The examples exhibit lower softening points and faster dissolution rates because (R / S)-1,1'-bi-2-naphthol, when mixed in a 1:1 weight ratio, forms a racemic mixture. The two configurations have completely opposite molecular chain orientations, resulting in a random stacking structure. This increases intermolecular distance and weakens intermolecular forces, making it easier to soften. Simultaneously, the amorphous structure eliminates the obstruction of microcrystalline regions, allowing DMF solvent to quickly penetrate and dissolve intermolecular forces through polar interactions, resulting in high dissolution efficiency. Comparative Examples 1-2, employing a single chiral configuration, exhibit a tendency for directional molecular chain alignment, forming a quasi-ordered structure. Due to the stacking of molecules and strong intermolecular forces, the softening point is high, and the microcrystalline region hinders DMF penetration, resulting in slow dissolution. Comparative Examples 3-4 have a higher softening point and slower dissolution rate than the Examples due to the deviation of the chiral ratio from 1:1 and insufficient proportion of the secondary configuration, resulting in increased molecular stacking order. However, they are still better than the single-chiral Comparative Examples 1-2. Comparative Example 5 has the highest softening point and slowest dissolution rate because it is replaced with 5-bromo-2-fluorotoluene without the -CF3 group, which loses the steric hindrance effect of trifluoromethyl, resulting in more compact molecular chain stacking and enhanced intermolecular forces.

[0091] The embodiment exhibits superior thermal properties (glass transition temperature, thermal decomposition temperature, and char residue at 800°C) and dielectric properties (low dielectric constant, low dielectric loss, and high-temperature stability). Regarding thermal properties, the 1:1 weight ratio of (R / S)-1,1'-bi-2-naphthol results in random molecular packing. The rigid aromatic ring of biphenyldiazepinene forms a heat-resistant synergy with the binaphthyl skeleton, and the strong CF bond of the -CF3 group enhances thermal stability. Therefore, the thermal decomposition temperature and char residue are high, and the uniform crosslinking also improves the glass transition temperature. Regarding dielectric properties, random packing disrupts the dipole synergy of polar groups, causing the dipole moments to cancel each other out, and eliminating the crystalline-amorphous region interface. The surface polarization contribution is extremely low, and the low polarity of the -CF3 group further weakens the polarizability, resulting in low dielectric constant and loss. The rigid skeleton restricts chain segment movement at high temperatures, resulting in good dielectric stability. Comparative Examples 1-2 form microcrystalline regions due to single chirality, leading to uneven cross-linking networks, decreased thermal performance, and significant interfacial polarization between the microcrystalline and amorphous regions, resulting in deteriorated dielectric performance. Comparative Examples 3-4 have a chirality ratio that deviates from 1:1, resulting in insufficient dipole disorder and weaker interfacial polarization suppression effect than the examples. Their performance is better than Comparative Examples 1-2 but not as good as the examples. Comparative Example 5 has no -CF3 group, resulting in weakened thermal stability and polarization suppression effect, and its thermal and dielectric performance is the worst.

[0092] The composite materials prepared using the microwave-transparent resins obtained in Examples 1-3 exhibit superior room temperature flexural strength, flexural modulus, and performance retention at 400°C. This is because the amorphous structure of the resins in these examples lacks microcrystalline regions, resulting in good wettability with the quartz fiber cloth. The resin solution can quickly penetrate the fiber gaps, forming a tight interfacial bond, allowing stress to be efficiently transferred from the resin to the fiber (main load-bearing structure) under load. Furthermore, the resin's glass transition temperature exceeds 400°C, maintaining interfacial integrity and preventing interfacial failure due to resin softening. In contrast, the composites in Comparative Examples 1-2, due to the microcrystalline region resistance of the single chiral resin... The resin solution hinders uniform wetting of the fibers, and the presence of voids and defects at the interface impedes stress transmission, resulting in low mechanical properties. At high temperatures, the resin softens easily near its glass transition temperature, leading to poor performance retention. Comparative Examples 3-4, due to a deviation of the chiral ratio from 1:1, have a lower proportion of microcrystalline regions than single-chiral examples, resulting in better wettability and interfacial bonding than Comparative Examples 1-2, but still inferior to the examples, with mechanical properties and performance retention at an intermediate level. Comparative Example 5, lacking -CF3 groups, exhibits weak physical entanglement between the resin and fibers, low interfacial bonding strength, and easy softening and peeling of the resin at high temperatures, resulting in the worst mechanical properties and performance retention.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a microwave-transparent resin for aircraft equipment compartments, characterized in that, Includes the following steps: S1. Under nitrogen protection, 5-bromo-2-fluoro-trifluorotoluene, chiral-1,1'-bi-2-naphthol, and potassium carbonate were added to dimethyl sulfoxide. The mixture was stirred and heated to 150-170℃ for 6-10 h. After cooling to room temperature, the mixture was poured into dilute hydrochloric acid solution to precipitate. The precipitate was filtered, the solid was collected, and the solid was recrystallized from ethanol to obtain the chiral monomer. S2. Under nitrogen protection, chiral monomers, biphenyldiazepinene and cesium carbonate are added to anhydrous sulfolane, heated to 135-145℃ with stirring, stirred for 1-2 hours, then cooled to 80℃, initiator is added, heated to 190-200℃, and reacted for 18-30 hours to obtain the prepolymer; S3. Under nitrogen protection, reduce the reaction temperature to 80-90℃, add 4-nitrophthalonitrile to the prepolymer, react for 8-10 hours, cool to room temperature to obtain a phthalonitrile-terminated polymer solution, then pour it into a dilute hydrochloric acid solution to precipitate, filter, collect the solid, wash with ethanol, and dry to obtain a microwave-transparent resin for aircraft equipment compartments.

2. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 1, characterized in that, The chiral-1,1'-bi-2-naphthol in S1 is prepared by mixing (S)-1,1'-bi-2-naphthol and (R)-1,1'-bi-2-naphthol in a weight ratio of 1:

1.

3. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 1, characterized in that, The molar ratio of 5-bromo-2-fluoro-trifluorotoluene, chiral-1,1'-bi-2-naphthol, and potassium carbonate in S1 is 1:2-2.4:2-3.

4. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 1, characterized in that, In S1, the weight ratio of 5-bromo-2-fluoro-trifluorotoluene, dimethyl sulfoxide, and dilute hydrochloric acid solution is 1:8-12:20-30, and the mass concentration of the dilute hydrochloric acid solution is 10%.

5. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 1, characterized in that, The chiral monomer, biphenyldiazepinene, and cesium carbonate in S2 are in a molar ratio of 1:1-1.2:1.5-2.

6. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 5, characterized in that, In S2, the chiral monomer, anhydrous sulfolane, and initiator are in a weight ratio of 1:8-12:0.03-0.

07.

7. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 5, characterized in that, The initiator in S2 refers to a mixture of cuprous chloride and quinoline in a molar ratio of 1:

2.

8. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 5, characterized in that, The molar ratio of 4-nitrophthalonitrile in S3 to biphenyldiazepine in the prepolymer is 1.2-2:

1.

9. The method for preparing the microwave-transparent resin for aircraft equipment compartments according to claim 5, characterized in that, In S3, the phthalonitrile-terminated polymer solution and the dilute hydrochloric acid solution are in a weight ratio of 1:2-3, and the mass concentration of the dilute hydrochloric acid solution is 10%.

10. A microwave-transparent resin for an aircraft equipment compartment, prepared by the preparation method described in any one of claims 1-9.

Images