Low-dielectric and high-temperature-resistant modified cyanate ester resin and preparation method thereof

Abstract

The invention relates to the technical field of high-performance polymer materials, in particular to low-dielectric and high-temperature-resistant modified cyanate ester resin and a preparation method thereof. Advantages and characteristics of bisphenol A type cyanate ester monomers and bisphenol M type cyanate ester monomers are combined, and the dielectric property and the thermal stability are remarkably improved. Diallyl bisphenol A is introduced as a network structure modifier, the phenolic hydroxyl group of the diallyl bisphenol A adjusts the curing reaction rate, and the allyl and bisphenol A structures of the diallyl bisphenol A finely regulate and control the rigid-flexible balance of a cross-linked network through chemical copolymerization, so that the curing process is controllable and the final network structure is optimized. Meanwhile, a toughening system is innovatively designed, epoxy-terminated liquid nitrile rubber is adopted for toughening, stable micron-scale rubber particles are formed in a resin matrix in a chemical bonding mode, and the fracture toughness is improved. The modified resin has excellent dielectric properties, high heat resistance and a wide process window, and meets the strict requirements of a new generation of low observability aircrafts on a bearing-stealth integrated composite material matrix.

Description

Technical Field

[0001] This invention relates to the field of high-performance polymer materials technology, and in particular to a low-dielectric, high-temperature resistant modified cyanate ester resin and its preparation method, which is suitable for low-observable aircraft. Background Technology

[0002] Low-observable aircraft place dual demands on the integrated load-bearing and stealth structural components, requiring both "wideband wave transmission and high-efficiency absorption," and their core resin matrix must maintain a wavelength above 10 GHz. , It possesses both high heat resistance and sufficient toughness. Cyanate ester resin (CE), due to the formation of a symmetrical triazine ring network after curing, exhibits superior intrinsic dielectric properties and heat resistance compared to epoxy, making it the preferred matrix for high-speed stealth platforms. However, commercial-grade CE... The temperature is still around 3.0, and the curing temperature is generally higher than 220℃, resulting in bottlenecks such as high mold energy consumption, high internal stress due to co-curing with quartz fiber / frequency selective surface, and short storage period of prepreg.

[0003] To lower the gelation temperature (CE), existing technologies mainly employ two approaches: ① Introducing co-curing agents such as organoximes and carboxylic anhydrides can reduce the gelation temperature to 180℃, but... Simultaneous temperature drops to below 200℃ significantly impairs the material's key heat resistance, stiffness, and low dielectric properties. ② While using acetylacetone metal salt catalysis shortens the gel time, it increases dielectric loss by more than 30%, without significantly improving toughness. On the other hand, toughening methods often involve adding thermoplastics or core-shell particles, requiring high-temperature melt blending, which causes a sharp increase in system viscosity, making it impossible to prepare low areal density prepregs. Although terminal epoxy-based liquid nitrile butadiene rubber (ETBN) has been proven effective in epoxy systems, it suffers from poor compatibility, rubber phase coarsening, and mismatched curing windows in CE systems. A complete solution simultaneously achieving "low dielectric, high heat resistance, high toughness, and low molding temperature" has yet to be found.

[0004] Patent CN116606529B employs a hydantoin-type epoxy / latent imidazole synergistic desealing method to achieve low-temperature curing at 100℃, but... With a curing temperature of only 140-150℃, poor heat resistance, and only applicable to epoxy systems, it cannot be extended to cyanate ester systems; CN111793193A uses a ternary compound of "liquid aromatic amine + alicyclic amine + ester accelerator" to replace the traditional anhydride / imidazole system, lowering the curing temperature to 150℃, but the glass transition temperature is only 180℃, resulting in insufficient heat resistance, and the introduction of more than 40% polyfunctional epoxy leads to a system viscosity >8000 mPa·s, which cannot meet the requirements of the hot melt prepreg process; patent CN109265922B utilizes hyperbranched polysiloxane to achieve epoxy self-catalytic toughening, reducing the curing temperature from 150℃ to 110℃, but... >3.5, the dielectric properties cannot meet the stealth requirements, and the heat resistance is insufficient.

[0005] In summary, existing technologies have not yet solved the problem of "decreasing molding temperature leading to..." The common contradiction of "simultaneous decline in dielectric properties and toughness" is further compounded by the fact that it cannot maintain its properties under curing conditions of ≤200℃. ≥200℃ Cyanate ester systems with a dielectric constant of ≤2.6 have been reported. Therefore, developing a modified cyanate ester resin that can maintain high heat resistance, low dielectric constant, and high toughness while being molded at low temperatures is of great significance for promoting the low-cost and high-reliability manufacturing of integrated load-bearing and stealth components for low-observable aircraft. Summary of the Invention

[0006] To address the aforementioned problems or shortcomings, and to solve the issue that existing cyanate ester systems cannot simultaneously achieve low-temperature molding while maintaining high heat resistance, low dielectric constant, and high toughness, this invention provides a low-dielectric, high-temperature resistant modified cyanate ester resin and its preparation method. This is a high-performance modified cyanate ester resin suitable for wave-transparent / stealth structural components of low-observable aircraft.

[0007] A low dielectric and high temperature resistant modified cyanate ester resin comprises the following components by mass fraction: cyanate ester monomer: 80-120 parts; toughening agent: 8-12 parts; co-curing-toughening agent: 0.5-1.5 parts; metal complex catalyst: 100-500 ppm.

[0008] The cyanate monomers include bisphenol A type cyanate resin monomers and bisphenol M type cyanate monomers, with a molar ratio of 1:2 to 2:1.

[0009] The toughening agent is terminal epoxy-terminated liquid nitrile rubber; the co-curing toughening agent is diallyl bisphenol A; and the metal complex catalyst is cobalt acetylacetonate.

[0010] Furthermore, the preparation method of the above-mentioned low-dielectric, high-temperature resistant modified cyanate ester resin includes the following steps:

[0011] Step 1: Using a molar ratio of 1:2-2:1, melt-mix the two cyanate monomers, bisphenol A type cyanate resin monomer and bisphenol M type cyanate monomer, at 110-130℃ and 300-500r / min, and prepolymerize at a constant temperature for 0.5-1 h to obtain homogeneous prepolymer a.

[0012] Step 2: Add toughening agent to the homogeneous prepolymer a obtained in step 1, and stir until the mixture is homogeneous to obtain mixture b.

[0013] Step 3: Add co-curing toughening agent to mixture b obtained in step 2, mix evenly, and allow to cool naturally to obtain mixture c.

[0014] Step 4: Add the metal complex catalyst to the mixture c obtained in step 3, and stir for 5-15 minutes until the mixture is uniform to obtain the pre-cured modified cyanate ester resin.

[0015] Step 5: After pouring the modified cyanate resin obtained in Step 4 into the mold, vacuum defoaming is performed, followed by step curing (120-220℃) to obtain a low dielectric and high temperature resistant modified cyanate resin.

[0016] Furthermore, the aforementioned low-dielectric, high-temperature resistant modified cyanate ester resin is used to manufacture high-performance transparent radar domes, stealth antenna domes, and low RCS load-bearing structural components.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) This invention innovatively designs the curing system in the resin formulation, constructing a stepwise controllable synergistic curing system based on cyanate monomers, multifunctional comonomers, and metal complex catalysts, significantly optimizing the resin's processability and network structure. Specifically, this invention combines the advantageous characteristics of bisphenol A and bisphenol M cyanate monomers, significantly improving the dielectric properties and thermal stability of the material, and enhancing processing fluidity. Specifically, bisphenol A cyanate provides good electrical insulation and low dielectric loss, while bisphenol M cyanate enhances the material's thermal stability through its excellent high-temperature resistance. Furthermore, by introducing bisphenol compounds as network structure modifiers, such as diallyl bisphenol A, its phenolic hydroxyl groups can regulate the curing reaction rate, and its allyl group and bisphenol A structure can finely control the rigid-flexible balance of the crosslinked network through chemical copolymerization, achieving controllable curing process and optimized final network structure.

[0019] (2) The present invention also innovatively designs a toughening system, which uses rubber elastomers for toughening, such as terminal epoxy liquid nitrile rubber, to form stable micron-scale rubber particles in the resin matrix through chemical bonding, thereby significantly improving the fracture toughness of the material without sacrificing the inherent heat resistance and dielectric properties of the material.

[0020] (3) The curing system and toughening system of the present invention achieve synergistic effect through step heating, so that the final resin has excellent dielectric properties, high heat resistance and wide process window, which meets the stringent requirements of the new generation of low observable aircraft for the load-bearing-stealing integrated composite material matrix. It can be used to manufacture high-performance transparent radar domes, stealth antenna domes and low RCS load-bearing structural components. Attached Figure Description

[0021] Figure 1 Dynamic thermomechanical analysis (DMA) curves of the modified cyanate ester resins in Examples 1-6 and 7-12;

[0022] Figure 2The dielectric constant and dielectric loss test results of the modified cyanate ester resins in Examples 1-6 are shown.

[0023] Figure 3 The dielectric constant and dielectric loss test results of the modified cyanate ester resins in Examples 7-12 are shown below.

[0024] Figure 4 The impact strength test results are for the modified cyanate ester resins in Examples 1-6 and 7-12.

[0025] Figure 5 This is a flowchart illustrating the preparation process of the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0027] Examples 1-6:

[0028] As shown in Table 1, 50 parts of bisphenol A type cyanate resin monomer and 50 parts of bisphenol M type cyanate resin monomer were weighed and added to a reaction vessel. The temperature was raised to 100℃, and the mixture was stirred at 400 r / min until the monomers were completely melted and homogeneous. Subsequently, the system was heated to 120℃ and reacted for 1 hour to obtain a homogeneous prepolymer mixture a.

[0029] Subsequently, X parts of terminal epoxy-terminated liquid nitrile rubber were added, and the mixture was heated to 130°C and stirred at 400 r / min for 1 hour to obtain mixture b.

[0030] Then, 1 part of diallyl bisphenol A was added to mixture b, and the mixture was stirred at 130°C and 400 r / min for 2 hours. The temperature was then raised to 150°C and maintained for 1.5 hours. After the reaction was completed, the heating was stopped and the mixture was allowed to cool naturally to 70°C to obtain mixture c.

[0031] Subsequently, 250 ppm of cobalt acetylacetone was added to mixture c, and the mixture was stirred at 600 r / min for 10 minutes to obtain a pre-cured modified cyanate ester resin composition.

[0032] The pre-cured modified cyanate ester resin composition was then degassed under vacuum at 120°C for 2 hours. Subsequently, curing was performed using a stepped temperature increase program. After curing, the mixture was cooled to room temperature and demolded to obtain a low-dielectric, high-temperature resistant modified cyanate ester resin. As shown in Table 1, with the increase of the amount of terminal epoxy-based liquid nitrile rubber, the glass transition temperature generally showed a decreasing trend, but in Example 2, a relatively high glass transition temperature of 183.6°C was still maintained.

[0033] X takes values ​​of 0, 2, 4, 6, 8, and 10, respectively, constituting Examples 1-6. Specific component parameters are shown in Table 1 below:

[0034]

[0035] Examples 7-12:

[0036] As shown in Table 2, 66.6 parts of bisphenol A type cyanate resin monomer and 33.3 parts of bisphenol M type cyanate resin monomer were weighed and added to a reaction vessel. The temperature was raised to 100℃, and the mixture was stirred at 400 r / min until the monomers were completely melted and homogeneous. Subsequently, the system was heated to 120℃ and reacted for 1 hour to obtain a homogeneous prepolymer mixture a.

[0037] Subsequently, Y-part terminal epoxy-terminated liquid nitrile rubber was added, and the mixture was heated to 130°C and stirred at 400 r / min for 1 hour to obtain mixture b.

[0038] Then, 1 part of diallyl bisphenol A was added to mixture b, and the mixture was stirred at 130°C and 400 r / min for 2 hours. The temperature was then raised to 150°C and maintained for 1.5 hours. After the reaction was completed, the heating was stopped and the mixture was allowed to cool naturally to 70°C to obtain mixture c.

[0039] Subsequently, 250 ppm of cobalt acetylacetone was added to mixture c, and the mixture was stirred at 600 r / min for 10 minutes to obtain a pre-cured modified cyanate ester resin composition.

[0040] The pre-cured modified cyanate ester resin composition was then degassed under vacuum at 120°C for 2 hours. Subsequently, curing was performed using a stepped temperature increase program. After curing, the mixture was cooled to room temperature and demolded to obtain the cured low-dielectric modified cyanate ester resin. As shown in Table 2, compared with Examples 1-6, the glass transition temperatures in Examples 7-12 were generally higher, but still showed an overall decreasing trend. Example 8 maintained a relatively high glass transition temperature of 209.6°C.

[0041] Y takes values ​​of 0, 2, 4, 6, 8, and 10, respectively, constituting Examples 7-12. The specific component parameters are shown in Table 2 below:

[0042]

[0043] Figure 1 a and b are the dynamic thermomechanical analysis (DMA) curves of the modified cyanate ester resins in Examples 1-6 and 7-12 listed in Tables 1 and 2, respectively; Figure 2 a and b are the dielectric constant and dielectric loss test results of the modified cyanate ester resins in Examples 1-6 of Table 1, respectively; Figure 3 a′ and b′ are the dielectric constant and dielectric loss test results of the modified cyanate ester resins in Examples 7-12 in Table 2, respectively; Figure 4 a and b are the impact strength test results of the modified cyanate ester resins in Examples 1-6 and 7-12 listed in Tables 1 and 2, respectively.

[0044] from Figure 1 The DMA analysis results show that when the molar ratio of bisphenol A to bisphenol M cyanate monomers is 2:1, the prepared modified cyanate resin exhibits a higher glass transition temperature and superior heat resistance. Figure 2 A comparison of the dielectric properties of Examples 1-6 and Examples 7-12 in Section 3 shows that the dielectric constants of Examples 1-6 are generally lower than those of Examples 7-12. Furthermore, with the increase of toughening agent content, the dielectric constant of the resin system generally shows a trend of first decreasing and then increasing. Among them, Example 2 exhibits the best dielectric properties, with a dielectric constant of only 2.68; among Examples 7-12, Example 10 exhibits the best dielectric properties, with a dielectric constant of only 2.71, but slightly higher than that of Example 2.

[0045] Figure 4 The impact test results show that the impact strength of Examples 7-12 is generally higher than that of Examples 1-6, indicating better toughness. Further analysis shows that the impact strength of the resin system generally increases with the addition of toughening agent, and the impact strength reaches its maximum when the toughening agent content is 6%. Among them, Example 10 has the highest impact strength, at 5.2 KJ / m². 2 It exhibits the best toughness, while in Examples 1-6, Example 4 shows the highest impact strength of 4.25 KJ / m. 2 .

[0046] As can be seen from the above embodiments, this invention combines the advantageous characteristics of bisphenol A and bisphenol M cyanate monomers, significantly improving the dielectric properties and thermal stability of the material, and enhancing its processing fluidity. By introducing the bisphenol compound diallylbisphenol A as a network structure modifier, its phenolic hydroxyl groups regulate the curing reaction rate, while its allyl group and bisphenol A structure finely control the rigidity-flexibility balance of the crosslinked network through chemical copolymerization, achieving controllable curing process and optimized final network structure. Simultaneously, an innovative toughening system is designed, employing terminal epoxy-based liquid nitrile rubber for toughening. Stable micron-scale rubber particles are formed in the resin matrix through chemical bonding, significantly improving the fracture toughness of the material without sacrificing its inherent heat resistance and dielectric properties. Furthermore, a metal complex catalyst is used to construct a stepwise controllable synergistic curing system, enabling the modified resin to possess excellent dielectric properties, high heat resistance, and a wide process window. This meets the stringent requirements of next-generation low-observable aircraft for integrated load-bearing and stealth composite material matrices, and can be used to manufacture high-performance radar domes, stealth antenna radomes, and low RCS load-bearing structural components.

Claims

1. A low-dielectric, high-temperature resistant modified cyanate ester resin, characterized in that: By mass fraction, it includes 80-120 parts of cyanate ester monomer and 8-12 parts of toughening agent; Co-curing toughening agent: 0.5-1.5 parts; Metal complex catalyst: 100-500 ppm; The cyanate monomers include bisphenol A type cyanate resin monomers and bisphenol M type cyanate monomers, with a molar ratio of 1:2 to 2:

1. The toughening agent is terminal epoxy-terminated liquid nitrile rubber; The co-curing toughening agent is diallyl bisphenol A; The metal complex catalyst is cobalt acetylacetonate.

2. The low dielectric and high temperature resistant modified cyanate ester resin as described in claim 1, characterized in that: The molar ratio of the bisphenol A type cyanate resin monomer to the bisphenol M type cyanate resin monomer is 2:

1.

3. The low dielectric and high temperature resistant modified cyanate ester resin as described in claim 1, characterized in that: The toughening agent content is 6%.

4. The low dielectric and high temperature resistant modified cyanate ester resin as described in claim 1, characterized in that: Used to manufacture high-performance transparent radar domes, stealth antenna domes, and low RCS load-bearing structural components.

5. The method for preparing the low-dielectric, high-temperature resistant modified cyanate ester resin as described in claim 1, characterized in that, Includes the following steps: Step 1: Using a molar ratio of 1:2-2:1, melt-mix the two cyanate monomers, bisphenol A type cyanate resin monomer and bisphenol M type cyanate monomer, at 110-130℃ and 300-500r / min, and prepolymerize at a constant temperature for 0.5-1 h to obtain homogeneous prepolymer a; Step 2: Add toughening agent to the homogeneous prepolymer a obtained in step 1, and stir until the mixture is homogeneous to obtain mixture b; Step 3: Add the co-curing toughening agent to the mixture b obtained in Step 2, mix evenly, and allow to cool naturally to obtain mixture c; Step 4: Add the metal complex catalyst to the mixture c obtained in step 3, and stir for 5-15 minutes until the mixture is uniform to obtain the pre-cured modified cyanate ester resin; Step 5: Pour the modified cyanate resin obtained in Step 4 into a mold, defoam under vacuum, and then cure it in stages at 120-220℃ to obtain a low dielectric and high temperature resistant modified cyanate resin.

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