Pure epoxy crosslinking system as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of insulating materials of high-voltage direct-current power transmission equipment, and discloses a pure epoxy crosslinking system and a preparation method and application thereof.The preparation method comprises the steps that fluorenyl bisphenol, epoxy chloropropane, a phase transfer catalyst and an alkaline solution are mixed to obtain a mixture, the mixture is subjected to impurity removal to obtain fluorenyl epoxy resin DGEBF, and the fluorenyl epoxy resin DGEBF is subjected to high-voltage direct-current power transmission equipment insulating materials. The preparation method comprises the following steps: uniformly mixing fluorene group epoxy resin DGEBF and an anhydride curing agent MTHPA, and then carrying out curing reaction to obtain a pure epoxy crosslinking system; according to the invention, the epoxy resin can have higher glass transition temperature and thermal decomposition temperature, the mechanical strength, modulus and dimensional stability of the material are improved, and good electrical insulation performance can still be maintained in a high-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission equipment insulation materials, and particularly relates to a pure epoxy crosslinking system and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the expansion of urbanization and the continuous integration of new energy technology, China's ultra-high voltage power grid has been developed vigorously, and the construction of ultra-high voltage and extra-high voltage direct current transmission projects has been further accelerated. The rapid development of high-voltage direct current transmission technology has stimulated the development of GIS. In the offshore wind power conversion platform, direct current GIS has become one of the key equipment for future lightweight and compact offshore converter stations due to its small footprint and strong weather resistance. So far, epoxy resin materials have been widely used in direct current GIS equipment as insulation materials due to their good dielectric properties, mechanical properties and weather resistance, and their comprehensive performance has gradually become one of the key factors affecting the actual application performance of existing direct current GIS equipment.

[0003] In the development process of high-performance insulation materials, epoxy resin plays a key role in fiber-reinforced composites due to its excellent heat resistance, excellent adhesion and good mechanical properties. The performance improvement of epoxy resin is closely related to its molecular network structure, and the network structure characteristics are significantly affected by the functional level of epoxy resin.

[0004] However, the existing epoxy resin generally has a low glass transition temperature (Tg), which leads to insufficient thermal mechanical properties and dimensional stability, and the material itself is brittle and has poor toughness, which is difficult to meet the requirements of high mechanical strength. At the same time, in a high-temperature environment, chain segment relaxation and thermal degradation easily occur, which significantly reduces the electrical insulation performance, limiting the application scenarios.

[0005] Therefore, the low glass transition temperature of epoxy resin, insufficient mechanical properties and deterioration of high-temperature insulation performance are problems that need to be overcome. With the increase of crosslinking density, the above defects are more prominent, which challenges the overall mechanical and electrical properties of the material. SUMMARY

[0006] The purpose of the present application is to provide a pure epoxy crosslinking system and a preparation method and application thereof to overcome the problems in the prior art. The present application can make the epoxy resin have a higher glass transition temperature and thermal decomposition temperature, improve the mechanical strength, modulus and dimensional stability of the material, and still maintain good electrical insulation performance in a high-temperature environment.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows: In a first aspect, the present application provides a preparation method of a pure epoxy crosslinking system, comprising the following steps: Mixing fluorenyl bisphenol, epichlorohydrin, phase transfer catalyst and alkaline solution to obtain a mixture; Carrying out impurity removal on the mixture to obtain fluorenyl group epoxy resin DGEBF; Mixing the fluorenyl group epoxy resin DGEBF and acid anhydride curing agent MTHPA uniformly and then carrying out curing reaction to obtain a pure epoxy crosslinking system.

[0008] In some embodiments, the mixing of the fluorenyl bisphenol, epichlorohydrin, phase transfer catalyst and alkaline solution to obtain a mixture specifically comprises: Carrying out heating reaction on the fluorenyl bisphenol, epichlorohydrin and phase transfer catalyst under an inert atmosphere, carrying out temperature reduction after the heating reaction is completed, obtaining a mixed solution, adding alkaline solution dropwise to the mixed solution to carry out epoxidation reaction, and obtaining a mixture.

[0009] In some embodiments, the molar ratio of the fluorenyl bisphenol, epichlorohydrin and phase transfer catalyst is (0.08-0.1) : (1.3-1.4) : (0.0035-0.0045). The phase transfer catalyst comprises tributylammonium bromide. The temperature of the heating reaction is 85-95 ℃, and the time of the heating reaction is 5-7 h. The temperature after the temperature reduction is 65-75 ℃, and the time of adding the alkaline solution dropwise is 30-40 min. The alkaline solution is NaOH solution, the mass fraction of the NaOH solution is 50%, and the NaOH solution is 0.2-0.22 mol. The time of the epoxidation reaction is 1.5-2.5 h.

[0010] In some embodiments, stirring is carried out in the process of the heating reaction, the dropwise addition of the alkaline solution and the epoxidation reaction, wherein the stirring speed in the heating reaction is 300-350 rpm, the stirring speed in the dropwise addition of the alkaline solution is 400-450 rpm, and the stirring speed in the epoxidation reaction is 300-350 rpm.

[0011] In some embodiments, the carrying out of impurity removal on the mixture to obtain fluorenyl group epoxy resin DGEBF specifically comprises: The mixture is sequentially subjected to first vacuum distillation, washing and vacuum drying to obtain primary fluorenyl group epoxy resin powder, and the primary fluorenyl group epoxy resin powder is sequentially subjected to dissolution, ultrasonic treatment, filtration and second vacuum distillation to obtain pure fluorenyl group epoxy resin DGEBF.

[0012] In some embodiments, the temperature of the first vacuum distillation is 115-125 ℃. The washing of the powdery solid comprises washing the powdery solid with 200 mL of deionized water for 3-4 times. The vacuum drying is performed for 8 h at 85 ℃. The dissolving comprises dissolving the primary fluorene group epoxy resin powder in a 1,4-dioxane solution for 30 min, and the molar ratio of the primary fluorene group epoxy resin powder to the 1,4-dioxane solution is 1:19. The ultrasonic treatment is performed for 1-2 h at a frequency of 30-40 kHz. The second time of the reduced pressure distillation is performed at 120 ℃.

[0013] In some embodiments, the curing reaction specifically comprises: After the mixture is uniformly mixed, a catalyst is added to the fluorene group epoxy resin DGEBF and the acid anhydride curing agent MTHPA, and then low-temperature reaction and high-temperature reaction are performed.

[0014] In some embodiments, the ratio of the epoxy equivalent weight of the fluorene group epoxy resin DGEBF to the acid anhydride equivalent weight of the acid anhydride curing agent MTHPA is (0.9-1.05):2. The catalyst is 2,4,6-tris(dimethylaminomethyl)phenol, and the mass percentage of the catalyst is 0.5-2 wt%. The low-temperature reaction is performed at 70~78 ℃ for 1.5~2 h. The high-temperature reaction is performed at 130~138 ℃ for 2~2.5 h.

[0015] In a second aspect, the present application provides a pure epoxy crosslinking system, which is obtained based on the preparation method of any one of the above pure epoxy crosslinking systems, and has a glass transition temperature (Tg) in the range of 158-165 ℃, a tensile strength in the range of 64-70 MPa, a bending strength in the range of 113-120 MPa, and a volume resistivity at 80 ℃ in the range of 2.5-3.2×10 15 Ω·m.

[0016] In a third aspect, the present application provides an application of the above pure epoxy crosslinking system in high-voltage direct-current GIS equipment and electrical insulation materials with high insulation and high heat resistance.

[0017] The above technical solutions have the following advantages or beneficial effects: In a first aspect, the present application provides a preparation method of a pure epoxy crosslinking system. By introducing rigid bulky fluorene groups, the rigidity and thermal stability of the crosslinking network are significantly improved, the cured product has a higher glass transition temperature and thermal decomposition temperature, and the problem of insufficient heat resistance of traditional epoxy resins is effectively solved. The introduction of fluorene groups also improves the dielectric properties and insulation stability of the material, and the material can still maintain good electrical insulation performance under high temperature environment, overcoming the technical difficulty of deterioration of high temperature insulation performance. The method of the present application adopts a staged temperature rising curing process, and by accurately controlling the temperature change in the curing process, the crosslinking reaction is effectively controlled, and a three-dimensional network structure with uniform structure and high crosslinking density is formed. The above optimized crosslinking structure not only improves the mechanical strength, modulus and dimensional stability of the material, but also increases the free volume inside the network by appropriately introducing methyl side chains in the molecular chain, thereby improving the toughness while maintaining high strength of the material, and solving the problem of insufficient mechanical properties.

[0018] Further, by first heating the fluorene-based bisphenol, epichlorohydrin and phase transfer catalyst under an inert atmosphere, the inert atmosphere can effectively prevent the raw materials from being oxidized, ensuring the purity of the reaction. The heating reaction can accelerate the collision between molecules and improve the reaction rate. After the reaction is completed, the temperature is lowered, and then a basic solution is added dropwise to perform the epoxidation reaction, which can accurately control the reaction process and avoid the occurrence of side reactions caused by excessive local concentration of the basic solution.

[0019] Further, by accurately limiting the molar ratio of fluorene-based bisphenol, epichlorohydrin and phase transfer catalyst, the reaction can be carried out according to the ideal stoichiometric ratio, improving the utilization rate of raw materials and reducing the generation of by-products. By selecting tributylammonium bromide as the catalyst, the reaction can be effectively promoted. Heating at 85-95 ℃ for 5-7 h can ensure that the reaction proceeds sufficiently. After the temperature is lowered to 65-75 ℃, a NaOH solution with a specific mass fraction and dosage is added dropwise within 30-40 min, which can accurately control the reaction rate. The epoxidation reaction time of 1.5-2.5 h can make the reaction complete, thereby obtaining a pure epoxy crosslinking system with high purity and high performance, improving the product quality and stability.

[0020] Further, by first vacuum distillation, the low-boiling-point impurities in the mixture can be effectively removed, the product purity is initially improved, washing can further remove residual polar impurities, reduce interference with subsequent reactions, and vacuum drying can remove volatile substances such as water to ensure the stability of the resin. By dissolving the primary powder and then ultrasonicating, the possible agglomeration can be broken, and the components can be uniformly dispersed. Filtration can remove insoluble impurities. The second vacuum distillation further purifies the product, and the trace impurities are accurately removed. Through the above ordered and targeted impurity removal operations, a fluorene group epoxy resin DGEBF with high purity can be obtained.

[0021] Further, the first reduced pressure distillation temperature of 115-125 ℃ can effectively remove low-boiling impurities while avoiding decomposition of the target product due to excessive temperature. Washing the powder-like solid with 200 mL of deionized water for 3-4 times can sufficiently wash off the polar impurities on the surface of the powder-like solid, ensuring purity. Vacuum drying at 85 ℃ for 8 h can completely remove moisture, preventing its impact on the performance of the resin. Dissolving the resin in a 1,4-dioxane solution for 30 min facilitates subsequent operations. Ultrasonic treatment for 1-2 h can sufficiently disperse the resin and remove small impurities. The second reduced pressure distillation at 120 ℃ can further purify, ultimately obtaining high-purity fluorenyl epoxy resin DGEBF, improving product quality.

[0022] Further, the low-temperature reaction first allows the catalyst to fully play its role, enabling the fluorenyl epoxy resin and the acid anhydride curing agent to be initially mixed uniformly and react slowly, avoiding defects caused by intense reaction. The high-temperature reaction then accelerates the curing process, making the cross-linked structure more compact and perfect, improving the performance and stability of the cross-linked system.

[0023] Further, precise control of the equivalent ratio of epoxy and acid anhydride can ensure that the curing reaction is sufficient and moderate, avoiding incomplete curing or performance degradation due to improper proportioning. The specific catalyst and dosage can effectively catalyze the reaction, improving the reaction rate. The reaction temperature and time are set in stages, with low temperature to start the reaction smoothly and high temperature to make the curing complete, thereby obtaining a pure epoxy cross-linked system with excellent performance and stable structure.

[0024] In the second aspect, the present application provides a pure epoxy cross-linked system. In terms of thermal performance, the glass transition temperature (Tg) of the system ranges from about 158-165 ℃, which is higher than that of the traditional DGEBA / MTHPA system (about 120-130 ℃), showing excellent thermal stability and enabling the system to maintain insulation performance and structural stability in the high-temperature working environment of DC GIS equipment. In terms of mechanical performance, the cross-linked system exhibits good tensile strength and bending strength, with a tensile strength range of about 64-70 MPa and a bending strength range of about 113-120 MPa, ensuring that the material remains stable under complex mechanical loads. In terms of electrical performance, the volume resistivity of the pure epoxy cross-linked system under normal conditions at 80 ℃ ranges from about 2.5-3.2 × 10 15 Ω·m (electric field intensity 10 kV / mm), which is significantly higher than that of the traditional DGEBA / MTHPA system, indicating that the fluorenyl-modified epoxy resin can effectively suppress free electron migration and reduce the risk of charge accumulation by introducing high-energy electron traps and enhancing electron adsorption capacity, thereby improving the surface insulation properties and long-term stability of the material in DC GIS.

[0025] In a third aspect, the present application provides an application of the above-mentioned pure epoxy cross-linking system in high-voltage direct-current GIS devices and electrical insulation materials with high insulation and high heat resistance, which expands the application range; at the same time, the proportion of epoxy resin and anhydride and the curing temperature gradient are reasonably designed, so that the prepared material has good controllability and repeatability, can stably achieve the expected performance, is convenient for batch industrial production, and effectively meets the urgent needs of high-voltage direct-current GIS and other high insulation scenes for high-performance materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A preparation method flowchart of a pure epoxy cross-linking system according to some embodiments of the present application is shown. Figure 2 A preparation principle diagram of a fluorene group epoxy resin DGEBF according to some embodiments of the present application is shown. Figure 3 A cross-linking structural formula of the fluorene group epoxy resin DGEBF and anhydride according to some embodiments of the present application is shown. DETAILED DESCRIPTION

[0027] Hereinafter, only certain exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and the description are considered to be exemplary in nature rather than limiting.

[0028] In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0030] Embodiment 1: Figure 1 A preparation method flowchart of a pure epoxy cross-linking system according to some embodiments of the present application is shown. The preparation method of the pure epoxy cross-linking system includes the following steps: Step one, place a three-necked flask equipped with a mechanical stirrer and a condenser in a constant temperature heating device, and under nitrogen protection, the following operations are carried out: 0.1 mol of fluorene-based bisphenol (BHPF), 1.35 mol of epichlorohydrin (ECH) and 0.004 mol of tributylammonium bromide (TEBAC) are added to the flask, heated and stirred at 300 rpm for 6 h at 85 ℃ to fully dissolve BHPF and carry out etherification reaction, then the temperature is reduced to 70 ℃, and 17 g (0.21 mol) of 50% NaOH aqueous solution is slowly added under stirring at 400 rpm, the dropwise addition process is controlled to be completed in 35 min, and after dropwise addition, the epoxy reaction is continued at 300 rpm for 2 h at 70 ℃ to promote complete epoxy reaction, and a mixture is obtained.

[0031] Step two, the mixture is distilled under reduced pressure at 121 ℃ to remove excess ECH, and a powdery solid is obtained, which is washed with 200 mL of deionized water for 3 times to remove by-product salt, and then vacuum dried at 85 ℃ for 8 h to obtain a primary fluorene group epoxy resin powder, the primary fluorene group epoxy resin powder is dissolved in 1,4-dioxane and stirred for 30 min, wherein the molar ratio of the primary fluorene group epoxy resin powder to the 1,4-dioxane solution is 1:19, then filtered after ultrasonic treatment at a frequency of 30 kHz for 1.5 h to remove insoluble impurities, and then distilled under reduced pressure at 120 ℃ to remove the solvent to obtain pure fluorene group epoxy resin DGEBF with a yield of 87%.

[0032] Step three, the fluorene group epoxy resin DGEBF is uniformly mixed with an acid anhydride curing agent MTHPA at an epoxy equivalent weight to anhydride equivalent weight ratio of 1:2, and 1 wt% of DMP-30, i.e. 2,4,6-tris (dimethylaminomethyl) phenol, is added, and then a curing reaction is carried out under a predetermined temperature rising curing program, which specifically includes: first reacting at a lower temperature of 75 ℃ for 2 h to promote uniform dispersion of the reactants and partial ring-opening reaction, and then reacting at a higher temperature of 135 ℃ for 2.5 h to achieve full crosslinking, to obtain a dense and stable pure epoxy crosslinking system.

[0033] The glass transition temperature (Tg) of the pure epoxy crosslinking system obtained in Example 1 of the present specification is 165 ℃, the tensile strength is 70 MPa, the bending strength is 120 MPa, and the volume resistivity at 80 ℃ normal working condition is 3.2×10 15 Ω·m, showing extremely excellent heat resistance, mechanical properties and electrical insulation properties.

[0034] Figure 2A flow chart for preparing the fluorene-based epoxy resin DGEBF according to some embodiments of the present specification, Figure 3 A cross-linking structure formula of the fluorene-based epoxy resin DGEBF and an anhydride according to some embodiments of the present specification, Figure 2 and Figure 3 It can be seen that the theoretical molar ratio of the reaction involved is DGEBF: MTHPA = 1:2.

[0035] Example 2: Figure 1 A flow chart for preparing a pure epoxy cross-linking system according to some embodiments of the present specification, the method for preparing the pure epoxy cross-linking system comprising the following steps: Step one, place a three-necked flask equipped with a mechanical stirrer and a condenser in a constant temperature heating device, and perform the following operations under nitrogen protection: Add 0.09 mol of fluorene-based bisphenol (BHPF), 1.32 mol of epichlorohydrin (ECH), and 0.0038 mol of tributylammonium bromide (TEBAC) to the flask, heat and stir at a speed of 300 rpm at 90 °C for 5.5 h, so that the BHPF is fully dissolved and undergoes etherification reaction, then reduce the temperature to 68 °C, slowly add 16 g (0.2 mol) of 50% NaOH aqueous solution at a stirring speed of 400 rpm, control the dropwise addition process to be completed in 40 min, continue to perform the epoxidation reaction at 68 °C for 1.8 h at a stirring speed of 300 rpm to promote the completion of the epoxidation, and obtain a mixture.

[0036] Step two, perform vacuum distillation on the mixture at 120 °C to remove the excess ECH, obtain a powder-like solid, wash the powder-like solid with 200 mL of deionized water for 3 times to remove the byproduct salt, then vacuum dry at 85 °C for 8 h to obtain a primary fluorene-based epoxy resin powder, dissolve the primary fluorene-based epoxy resin powder in 1,4-dioxane and stir for 30 min, wherein the molar ratio of the primary fluorene-based epoxy resin powder to the 1,4-dioxane solution is 1:19, then perform ultrasonic treatment at 30 kHz for 1.5 h, filter to remove insoluble impurities, and perform vacuum distillation at 120 °C to remove the solvent, to obtain the pure fluorene-based epoxy resin DGEBF, with a yield of 83%.

[0037] Step three, the fluorene group epoxy resin DGEBF and acid anhydride curing agent MTHPA are mixed uniformly according to the ratio of epoxy equivalent to acid anhydride equivalent 1:2, and 0.5 wt% of DMP-30, i.e. 2,4,6-tris (dimethylaminomethyl) phenol, is added, and then the curing reaction is carried out under a predetermined temperature curing program, which specifically includes: first, the reaction is carried out at a lower temperature of 75 ℃ for 1.5 h to promote uniform dispersion of the reactants and partial ring-opening reaction, and then the reaction is carried out at a higher temperature of 130 ℃ for 2 h to achieve sufficient crosslinking, thereby obtaining a dense and stable pure epoxy crosslinking system.

[0038] The glass transition temperature (Tg) of the pure epoxy crosslinking system obtained in Example 2 of the present specification is 162 ℃, the tensile strength is 67 MPa, the bending strength is 117 MPa, and the volume resistivity at 80 ℃ normal working condition is 2.9×10 15 Ω·m, showing excellent heat resistance, mechanical properties and electrical insulation properties.

[0039] Example 3: Figure 1 A flowchart of a preparation method of a pure epoxy crosslinking system according to some embodiments of the present specification is shown, and the preparation method of the pure epoxy crosslinking system comprises the following steps: Step one, a three-necked flask equipped with a mechanical stirrer and a condenser is placed in a constant temperature heating device, and the following operations are carried out under nitrogen protection: 0.08 mol of fluorene-based bisphenol (BHPF), 1.3 mol of epoxy chloropropane (ECH) and 0.0042 mol of tributylammonium bromide (TEBAC) are added to the flask, and the BHPF is fully dissolved and subjected to etherification reaction by heating and stirring at a speed of 300 rpm at 88 ℃ for 7 h, then the temperature is lowered to 65 ℃, and 18 g (0.22 mol) of 50% NaOH aqueous solution is slowly added dropwise under the condition of stirring at a speed of 400 rpm, the dropwise process is controlled to be completed in 40 min, and then the epoxy reaction is carried out at 65 ℃ for 2.5 h at a speed of 300 rpm to promote complete epoxy reaction, thereby obtaining a mixture.

[0040] Step two, the mixture was distilled under reduced pressure at 115 ℃ to remove excess ECH, to obtain a powdery solid, the powdery solid was washed with 200 mL deionized water for 4 times to remove by-product salt, and then vacuum dried at 85 ℃ for 8 h to obtain a primary fluorene group epoxy resin powder, the primary fluorene group epoxy resin powder was dissolved in 1,4-dioxane for 30 min, wherein the molar ratio of the primary fluorene group epoxy resin powder to the 1,4-dioxane solution was 1:19, then filtered after ultrasonic treatment at 35 kHz for 2 h to remove insoluble impurities, and then distilled under reduced pressure at 120 ℃ to remove the solvent to obtain a pure fluorene group epoxy resin DGEBF with a yield of 80%.

[0041] Step three, the fluorene group epoxy resin DGEBF was uniformly mixed with the acid anhydride curing agent MTHPA at an epoxy equivalent weight to acid anhydride equivalent weight ratio of 0.95:2, and 2 wt% of DMP-30, i.e. 2,4,6-tris(dimethylaminomethyl)phenol, was added, and then a curing reaction was carried out under a predetermined temperature curing program, which specifically included: first, incubating at a lower temperature of 70 ℃ for 2 h to promote uniform dispersion of the reactants and partial ring-opening reaction, and then incubating at a higher temperature of 135 ℃ for 2.5 h to achieve sufficient crosslinking, to obtain a dense and stable pure epoxy crosslinking system.

[0042] The glass transition temperature (Tg) of the pure epoxy crosslinking system obtained in Example 3 of the present specification was 160 ℃, the tensile strength was 65.5 MPa, the bending strength was 114.5 MPa, and the volume resistivity at 80 ℃ normal working condition was 2.8×10 15 Ω·m, showing excellent heat resistance, mechanical properties and electrical insulation properties.

[0043] Example 4: Figure 1 A flowchart of a preparation method of a pure epoxy crosslinking system according to some embodiments of the present specification, the preparation method of the pure epoxy crosslinking system comprising the following steps: Step one, a three-necked flask equipped with a mechanical stirrer and a condenser was placed in a constant temperature heating device, and the following operations were carried out under nitrogen protection: A flask was charged with 0.095 mol of fluorene-based bisphenol (BHPF), 1.34 mol of epichlorohydrin (ECH), and 0.004 mol of tributylammonium bromide (TEBAC), and heated and stirred at 87 ℃ at a rotation speed of 350 rpm for 6.5 h to fully dissolve the BHPF and allow the etherification reaction to occur. Then the temperature was lowered to 69 ℃, and 16.5 g (0.205 mol) of a 50% NaOH aqueous solution was slowly added dropwise under stirring at a rotation speed of 450 rpm, and the dropwise addition was controlled to be completed in 38 min. After the dropwise addition, the epoxidation reaction was continued at 69 ℃ at a rotation speed of 350 rpm for 2 h to promote the completion of the epoxidation, and a mixture was obtained.

[0044] Step two, the mixture was subjected to vacuum distillation at 125 ℃ to remove the excess ECH, and a powdery solid was obtained. The powdery solid was washed with 200 mL of deionized water for 3 times to remove the byproduct salt, and then vacuum dried at 85 ℃ for 8 h to obtain a primary fluorene group epoxy resin powder. The primary fluorene group epoxy resin powder was dissolved in 1,4-dioxane by stirring for 30 min, wherein the molar ratio of the primary fluorene group epoxy resin powder to the 1,4-dioxane solution was 1:19. Then the solution was filtered after being treated with ultrasound at 40 kHz for 1.5 h to remove insoluble impurities, and then subjected to vacuum distillation at 120 ℃ to remove the solvent, and a pure fluorene group epoxy resin DGEBF was obtained with a yield of 85%.

[0045] Step three, the fluorene group epoxy resin DGEBF was uniformly mixed with an acid anhydride curing agent MTHPA at an epoxy equivalent weight to acid anhydride equivalent weight ratio of 1.05:2, and 1.5 wt% of DMP-30, i.e., 2,4,6-tris(dimethylaminomethyl)phenol, was added, and then a curing reaction was performed under a predetermined temperature rising curing program, which specifically included: first, being kept at a lower temperature of 78 ℃ for 2 h to promote the uniform dispersion of the reactants and the partial ring-opening reaction, and then being kept at a higher temperature of 132 ℃ for 2 h to achieve sufficient crosslinking, and a dense and stable pure epoxy crosslinking system was obtained.

[0046] The glass transition temperature (Tg) of the pure epoxy crosslinking system obtained in Example 4 was 161 ℃, the tensile strength was 66.8 MPa, the bending strength was 115.2 MPa, and the volume resistivity at 80 ℃ under normal working conditions was 2.95×10 15 Ω·m, which showed excellent heat resistance, mechanical properties, and electrical insulation properties.

[0047] Example 5: Figure 1A flow chart of a preparation method of a pure epoxy crosslinking system according to some embodiments of the present specification, the preparation method of the pure epoxy crosslinking system comprising the following steps: Step one, place a three-necked flask equipped with a mechanical stirrer and a condenser in a constant temperature heating device, and perform the following operations under nitrogen protection: Add 0.085 mol of fluorene-based bisphenol (BHPF), 1.31 mol of epichlorohydrin (ECH), and 0.0045 mol of tributylammonium bromide (TEBAC) into the flask, heat and stir at 350 rpm for 6 h at 89 ℃ to make BHPF fully dissolved and undergo etherification reaction, then reduce the temperature to 66 ℃, slowly add 18 g (0.22 mol) of 50% NaOH aqueous solution at a stirring speed of 400 rpm, control the dropwise addition process to be completed within 35 min, continue the epoxidation reaction at 66 ℃ for 2.2 h at a stirring speed of 350 rpm to promote complete epoxidation, and obtain a mixture.

[0048] Step two, perform vacuum distillation on the mixture at 120 ℃ to remove excess ECH, obtain a powder-like solid, wash the powder-like solid with 200 mL of deionized water for 4 times to remove by-product salts, then vacuum dry at 85 ℃ for 8 h to obtain a primary fluorene group epoxy resin powder, dissolve the primary fluorene group epoxy resin powder in 1,4-dioxane, stir for 30 min, wherein the molar ratio of the primary fluorene group epoxy resin powder to the 1,4-dioxane solution is 1:19, then filter after ultrasonic treatment at 40 kHz for 2 h to remove insoluble impurities, and perform vacuum distillation at 120 ℃ to remove the solvent, to obtain a pure fluorene group epoxy resin DGEBF with a yield of 80%.

[0049] Step three, uniformly mix the fluorene group epoxy resin DGEBF with the acid anhydride curing agent MTHPA at an epoxy equivalent weight to acid anhydride equivalent weight ratio of 0.9:2, and add DMP-30, i.e., 2,4,6-tris (dimethylaminomethyl) phenol, in an amount of 2 wt%, then perform a curing reaction under a predetermined temperature rising curing program, which specifically includes: first, heat at a lower temperature of 72 ℃ for 2 h to promote uniform dispersion of the reactants and partial ring-opening reaction, then heat at a higher temperature of 138 ℃ for 2.5 h to achieve full crosslinking, to obtain a pure epoxy crosslinking system that is dense and stable in performance.

[0050] The glass transition temperature (Tg) of the pure epoxy crosslinking system obtained in Example 5 of the present specification is 159 ℃, the tensile strength is 65.2 MPa, the bending strength is 113.8 MPa, and the volume resistivity at 80 ℃ normal operating conditions is 2.85×10 15Ω·m, which exhibits excellent heat resistance, mechanical properties and electrical insulation properties.

[0051] Example 6: Figure 1 A flowchart of a preparation method of a pure epoxy crosslinking system according to some embodiments of the present specification, the preparation method of the pure epoxy crosslinking system comprising the following steps: Step one, place a three-necked flask equipped with a mechanical stirrer and a condenser in a constant temperature heating device, and perform the following operations under nitrogen protection: Add 0.1 mol of fluorene-based bisphenol (BHPF), 1.4 mol of epichlorohydrin (ECH), and 0.0035 mol of tributylammonium bromide (TEBAC) into the flask, heat and stir at 325 rpm for 5 h at 95 ℃ to make BHPF fully dissolved and undergo etherification reaction, then reduce the temperature to 75 ℃, slowly add 17 g (0.21 mol) of 50% mass fraction NaOH aqueous solution under the condition of 425 rpm stirring, control the dropwise addition process to be completed within 30 min, continue the epoxidation reaction at 68 ℃ for 1.5 h at 325 rpm to promote complete epoxidation, and obtain a mixture.

[0052] Step two, perform vacuum distillation on the mixture at 120 ℃ to remove excess ECH, obtain a powdery solid, wash the powdery solid with 200 mL of deionized water for 3 times to remove byproduct salts, then vacuum dry at 85 ℃ for 8 h to obtain a primary fluorene group epoxy resin powder, dissolve the primary fluorene group epoxy resin powder in 1,4-dioxane, stir for 30 min, wherein the molar ratio of the primary fluorene group epoxy resin powder to the 1,4-dioxane solution is 1:19, then filter after ultrasonic treatment at 40 kHz for 1 h to remove insoluble impurities, and perform vacuum distillation at 120 ℃ to remove the solvent, to obtain a pure fluorene group epoxy resin DGEBF with a yield of 83%.

[0053] Step three, mix the fluorene group epoxy resin DGEBF and the acid anhydride curing agent MTHPA uniformly according to the ratio of epoxy equivalent to acid anhydride equivalent of 1:2, and add DMP-30, i.e. 2,4,6-tris(dimethylaminomethyl)phenol, in an amount of 0.5 wt%, then perform a curing reaction under a predetermined temperature rising curing program, which specifically includes: first, heat at a lower temperature of 75 ℃ for 2 h to promote uniform dispersion of the reactants and partial ring-opening reaction, then heat at a higher temperature of 135 ℃ for 2 h to achieve sufficient crosslinking, to obtain a pure epoxy crosslinking system that is dense and stable in performance.

[0054] The glass transition temperature (Tg) of the pure epoxy crosslinking system obtained in Example 6 of the present specification is 162 DEG C, the tensile strength is 68.3 MPa, the bending strength is 116.4 MPa, and the volume resistivity under normal working conditions at 80 DEG C is 3.10 x 10 15 Ω·m, showing excellent heat resistance, mechanical properties and electrical insulation properties.

[0055] The performance evaluation of the pure epoxy crosslinking system prepared in Examples 1-6 of the present specification is shown in Table 1 below: Table 1 Performance test table of the pure epoxy crosslinking system prepared in Examples 1-6

[0056] The fluorene group is a rigid and highly conjugated aromatic structure, and the double benzene ring is enhanced by the bridging five-membered ring, which enhances the rigidity and thermal stability of the molecular chain, and at the same time reduces the free volume, inhibits the movement of chain segments at high temperature, thereby significantly improving the glass transition temperature (Tg) and dielectric strength of the material. In the design of high-voltage direct-current insulation materials, the introduction of fluorene group not only improves the thermal performance, but also improves the dimensional stability and mechanical strength of the material by enhancing the π-π stacking effect between molecules.

[0057] By uniformly mixing the epoxy resin with anhydride MTHPA and an appropriate amount of catalyst, a high crosslinking density pure epoxy curing system is obtained by staged temperature curing. This method can effectively control the functional group distribution and crosslinking structure of the epoxy resin, so that a stable and uniform three-dimensional network structure is formed during the curing process, improving the thermal stability, mechanical properties and electrical insulation properties of the system. By introducing fluorene groups and methyl side chains, the proportion of free volume in the crosslinking system increases, which helps to improve the molecular chain movement ability, while maintaining the controllability of the material deformation under high temperature conditions.

[0058] The present application significantly improves the rigidity and thermal stability of the system by introducing fluorene structure into the molecular chain of the epoxy resin, and the anhydride curing system can form a highly crosslinked network structure, so that the material has a high glass transition temperature and excellent heat resistance. Compared with the traditional bisphenol A type epoxy system, the system has significantly improved heat resistance, dimensional stability and chemical corrosion resistance while maintaining good mechanical strength, and is suitable for the preparation of high-end electronic packaging materials, high-temperature insulation structural parts and high-temperature resistant composite components. By optimizing the reaction conditions and curing program, the process repeatability and industrialized production can be realized.

[0059] The foregoing merely illustrates the principles of the application and application of its leading features. This application is not limited to the exact details shown above and described herein, and obvious modifications will occur to those skilled in the art upon reading the foregoing description. Therefore, the scope of the application is not to be determined by the specific examples shown above, but only by the claims below. Any reference signs in the claims should not be construed as limiting the scope of the claims.

[0060] In addition, it should be understood that although the present specification describes particular embodiments, each of which contains only a single independent technical solution, the specification is merely a description of certain embodiments of the application, and the skilled person should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that the skilled person can understand. The above is only to illustrate the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made on the basis of the technical idea of the present application, which is formed on the basis of the technical solutions, falls within the protection scope of the claims of the present application.

Claims

1. A method for preparing a pure epoxy crosslinking system, characterized in that, Includes the following steps: Fluorenylbisphenol, epichlorohydrin, phase transfer catalyst and alkaline solution are mixed to obtain a mixture; The mixture was purified to obtain fluorene-based epoxy resin DGEBF; Fluorene-based epoxy resin DGEBF was mixed evenly with an anhydride curing agent MTHPA and then cured to obtain a pure epoxy crosslinking system.

2. The method for preparing a pure epoxy crosslinking system according to claim 1, characterized in that, The mixture obtained by mixing fluorenylbisphenol, epichlorohydrin, phase transfer catalyst, and alkaline solution specifically includes: Fluorenylbisphenol, epichlorohydrin, and a phase transfer catalyst were heated and reacted under an inert atmosphere. After the heating reaction was completed, the mixture was cooled to obtain a mixed solution. An alkaline solution was then added dropwise to the mixed solution to carry out an epoxidation reaction, resulting in a final mixture.

3. The method for preparing a pure epoxy crosslinking system according to claim 2, characterized in that, The molar ratio of fluorenylbisphenol, epichlorohydrin and phase transfer catalyst is (0.08-0.1):(1.3-1.4):(0.0035-0.0045). The phase transfer catalyst includes tributylammonium bromide; The heating reaction is carried out at a temperature of 85-95 ℃ for 5-7 h. The temperature after cooling is 65-75℃; the time for adding the alkaline solution is 30-40 min; The alkaline solution is a NaOH solution with a mass fraction of 50% and a concentration of 0.2-0.22 mol. The epoxidation reaction takes 1.5-2.5 hours.

4. The method for preparing a pure epoxy crosslinking system according to claim 2, characterized in that, Stirring is performed during the heating reaction, the dropwise addition of alkaline solution, and the epoxidation reaction. Specifically, the stirring speed is 300-350 rpm during the heating reaction, 400-450 rpm during the dropwise addition of alkaline solution, and 300-350 rpm during the epoxidation reaction.

5. The method for preparing a pure epoxy crosslinking system according to claim 1, characterized in that, The process of removing impurities from the mixture to obtain fluorene-based epoxy resin DGEBF specifically includes: The mixture was subjected to a first vacuum distillation, washing, and vacuum drying to obtain primary fluorene group epoxy resin powder. The primary fluorene group epoxy resin powder was then dissolved, sonicated, filtered, and subjected to a second vacuum distillation to obtain pure fluorene group epoxy resin DGEBF.

6. The method for preparing a pure epoxy crosslinking system according to claim 5, characterized in that, The temperature of the first vacuum distillation is 115-125℃; The washing of the powdered solid includes: washing the powdered solid with 200 mL of deionized water 3-4 times; The vacuum drying time is 8 hours, and the vacuum drying temperature is 85 ℃; The dissolution process includes: dissolving primary fluorene-based epoxy resin powder in a 1,4-dioxane solution and reacting for 30 min; the molar ratio of primary fluorene-based epoxy resin powder to 1,4-dioxane solution is 1:

19. The duration of the ultrasound is 1-2 hours, and the frequency of the ultrasound is 30-40 kHz. The temperature of the second vacuum distillation was 120 °C.

7. The method for preparing a pure epoxy crosslinking system according to claim 1, characterized in that, The curing reaction specifically includes: A catalyst was added to the uniformly mixed fluorene-based epoxy resin DGEBF and anhydride-based curing agent MTHPA, and a low-temperature reaction was carried out first, followed by a high-temperature reaction.

8. The method for preparing a pure epoxy crosslinking system according to claim 7, characterized in that, The epoxy equivalent ratio of the fluorene-based epoxy resin DGEBF to the anhydride equivalent ratio of the anhydride curing agent MTHPA is (0.9-1.05):

2. The catalyst is 2,4,6-tris(dimethylaminomethyl)phenol, and the mass percentage of the catalyst is 0.5-2 wt%. The low-temperature reaction is carried out at a temperature of 70~78 ℃ for 1.5~2 h. The high-temperature reaction is carried out at a temperature of 130~138 ℃ for a duration of 2~2.5 h.

9. A pure epoxy crosslinking system, characterized in that, The method for preparing a pure epoxy crosslinking system according to any one of claims 1-8 is obtained.

10. An application of a pure epoxy crosslinking system based on claim 9 in high-voltage DC GIS equipment and electrical insulation materials requiring high insulation and high heat resistance.

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