Halogen-free flame-retardant temperature-resistant epoxy resin and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, and discloses a halogen-free flame-retardant temperature-resistant epoxy resin and a preparation method thereof.The halogen-free flame-retardant temperature-resistant epoxy resin is prepared by taking epoxy resin, nitrogen-phosphorus-silicon four-functionality epoxy resin, a curing agent and a diluent as raw materials through blending and curing, 2, 3-bis (3-aminopropyl) tetramethyldisiloxane, bis (4-methoxyphenyl) phosphine oxide and epichlorohydrin are used as raw materials and are subjected to condensation, addition and substitution reactions to obtain the flame retardant, nitrogen, phosphorus and silicon have a synergistic flame retardant effect, and good heat insulation, mass insulation and oxygen insulation effects are achieved; the four-functionality epoxy resin molecules contain more epoxy groups, and can react with the curing agent to form more crosslinking points, so that the crosslinking density is improved, and the stress can be dispersed and resisted more effectively; the epoxy resin prepared by the invention is excellent in flame retardant effect, halogen-free and environment-friendly, and has very good temperature resistance and mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, in particular to a halogen-free flame-retardant and heat-resistant epoxy resin and a preparation method thereof. Background Art

[0002] As an important polymer material, epoxy resin is widely used in electronics, electrical, aerospace, construction, transportation and other fields due to its excellent physical properties, chemical stability and good processing performance. However, epoxy resin is a flammable material with a low limiting oxygen index of only 19.5%. Due to its deficiencies in thermal stability and flame retardancy, there are great safety hazards in practical applications, which limits its further application. Traditional epoxy resins may produce toxic gases when burned and have limited high temperature resistance, which to a certain extent limits its scope of application. With the enhancement of global environmental awareness and the increasingly stringent relevant regulations, the development of an epoxy resin that is both flame retardant, high temperature resistant and environmentally friendly has become a hot topic in the industry.

[0003] Traditional halogen flame retardants, such as bromine and chlorine flame retardants, have good flame retardant effects, but they may release toxic gases during the combustion process, which does not meet modern environmental protection requirements. Therefore, halogen-free flame retardant technology came into being. Currently, commonly used halogen-free flame retardants include phosphorus-based, nitrogen-based and inorganic flame retardants. These flame retardants can form a stable carbon layer when the material burns, preventing the transfer of oxygen and heat, thereby achieving a flame retardant effect; however, the addition of halogen-free flame retardants often affects the mechanical properties and processing properties of epoxy resins. How to maintain or improve the comprehensive performance of the material while ensuring flame retardancy is an important direction that halogen-free flame retardant epoxy resins need to improve.

[0004] In order to improve the heat resistance of epoxy resin, the prior art generally achieves this by adding heat-resistant fillers, such as adding inorganic fillers with high melting points (such as alumina, silicon nitride, etc.) to epoxy resin to improve its heat resistance, but there are problems such as poor dispersibility and easy reduction of mechanical properties; although there are currently a variety of preparation methods for halogen-free flame retardant and heat-resistant epoxy resins, there are still some shortcomings. How to maintain the balance between the flame retardant properties, mechanical properties and heat resistance of epoxy resins to ensure that environmental protection requirements are met without significantly increasing production costs is an urgent problem to be solved. Patent No. CN115232445B discloses a flame-retardant epoxy resin and a preparation method thereof, wherein a modified composite flame retardant is obtained by reacting 2,2-bis(4-aminophenyl)propane, tris(2-aminoethyl)amine and ammonium polyphosphate, but ammonium polyphosphate has poor compatibility with epoxy resin substrates, and there are problems such as easy precipitation, moisture absorption, and low flame retardant efficiency, which will lead to a decrease in mechanical properties such as strength and toughness of epoxy resin, and the patent does not improve the heat resistance of epoxy resin.

[0005] In view of the above background, the present invention provides a halogen-free flame-retardant and heat-resistant epoxy resin and a preparation method thereof. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a halogen-free flame-retardant and heat-resistant epoxy resin and a preparation method thereof, which solves the problem of poor flame retardancy and heat resistance of existing epoxy resins, is halogen-free and environmentally friendly, and can be applied on a large scale.

[0007] The technical solution of the present invention is: A method for preparing a halogen-free flame-retardant and heat-resistant epoxy resin is carried out according to the following steps: Step (1), under nitrogen atmosphere, add tetrahydroxynitrogenphosphorus silicon intermediate and epichlorohydrin into a reaction flask, stir evenly, add sodium hydroxide and a catalyst, react at 60-80° C. for 5-10 hours, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain a tetrafunctional nitrogenphosphorus silicon epoxy resin.

[0008] Step (2), adding 100 parts by weight of E51 epoxy resin, 10-50 parts of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 10-15 parts of diluent into a stirring kettle, stirring evenly, adding 30-45 parts of curing agent, mixing evenly, pouring into a mold, curing at 120-160° C. for 2-4 hours, cooling to room temperature, and demolding to obtain a halogen-free flame retardant and heat-resistant epoxy resin.

[0009] Furthermore, in step (1), the catalyst is any one of tetrabutylammonium bromide, tetrabutylammonium iodide or N,N-dimethylbenzylamine.

[0010] Furthermore, in step (1), the molar ratio of tetrahydroxynitrogenphosphorus silicon intermediate, epichlorohydrin, sodium hydroxide and catalyst is 1:8-10:4.5-6:0.05-0.1.

[0011] Furthermore, in step (2), the diluent is any one of resorcinol diglycidyl ether, 1,4-butanediol diglycidyl ether or phenyl glycidyl ether.

[0012] Furthermore, in step (2), the curing agent is any one of 4-methylhexahydrophthalic anhydride, trimellitic anhydride or diethylenetriamine.

[0013] Furthermore, the preparation method of the tetrahydroxynitrogenphosphorus silicon intermediate in step (1) is carried out according to the following steps: Step S1, under a nitrogen atmosphere, add 4-maleimidobenzoic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, p-dimethylaminopyridine and dichloromethane to a reaction flask, stir evenly, add 1,3-bis(3-aminopropyl)tetramethyldisiloxane, react at 20-35° C. for 16-24 h, concentrate under reduced pressure, purify by column chromatography (elution with chloroform / methanol=20:1), and dry to obtain a maleimidosiloxane intermediate.

[0014] Step S2, under a nitrogen atmosphere, add the maleimidosiloxane intermediate and acetonitrile to a microwave reaction bottle, stir evenly, add bis(4-methoxyphenyl)phosphine oxide, and carry out microwave reaction. After the reaction is completed, concentrate under reduced pressure, purify by column chromatography (elution with dichloromethane / methanol = 15:1), add boron tribromide and dichloromethane after drying, react at room temperature for 12-24h, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain a tetrahydroxynitrogenphosphorus silicon intermediate.

[0015] Furthermore, in step S1, the molar ratio of 4-maleimidobenzoic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, p-dimethylaminopyridine, and 1,3-bis(3-aminopropyl)tetramethyldisiloxane is 1:1.1-1.25:0.08-0.12:0.5-0.6.

[0016] Furthermore, in step S2, the molar ratio of the maleimide siloxane intermediate, bis(4-methoxyphenyl)phosphine oxide, and boron tribromide is 1:2.05-2.2:5-8.

[0017] Furthermore, in step S2, the microwave reaction temperature is 150-170° C., the microwave reaction time is 2-5 h, and the microwave reaction power is 200-300 W.

[0018] The beneficial technical effects of the present invention are: (1) Excellent flame retardant properties: The silicon, nitrogen and phosphorus retardant elements rich in the nitrogen-phosphorus-silicon tetrafunctional epoxy resin can form a dense expanded carbon layer of deposited silicon when the epoxy resin cured product burns, so that the modified epoxy resin releases NH4+ by self-decomposition when heated. 3 After these non-combustible gases diffuse into the flame zone, they can dilute the oxygen concentration in the gas phase, thereby inhibiting the spread of the flame and playing a gas phase flame retardant role; at the same time, the decomposed acidic substances can promote the decomposition of epoxy resin and form viscous polymers containing P and N, changing the composition and properties of the carbon layer, making the carbon layer dense and continuous, playing a good role in heat insulation, insulation, and oxygen isolation, reducing the diffusion of combustion heat to the unburned part, and playing a condensed phase flame retardant role. In addition, the introduced siloxane is oxidized to SiO 2, making the formed carbon layer denser and further protecting the carbon layer from oxidative decomposition, thereby greatly enhancing the flame retardant properties of epoxy resin.

[0019] (2) Excellent heat resistance: Nitrogen-phosphorus-silicon tetrafunctional epoxy resin contains an imide ring with high chemical and thermal stability and a siloxane with high bond energy. It can resist thermal decomposition under high temperature conditions and maintain the stability of its chemical structure. At the same time, the tetrafunctional epoxy resin has a high cross-linking density and is not prone to thermal decomposition or deformation, which makes the prepared epoxy resin have high heat resistance.

[0020] (3) Excellent mechanical properties: The silicon-oxygen chains are evenly distributed in the cross-linked network of the epoxy resin, dispersing and reducing the internal stress of the resin when it breaks under impact. In addition, since the Si-O bond is softer and has a higher bond energy than the CC bond, it plays a toughening role in the resin. The tetrafunctional epoxy resin molecule contains more epoxy groups, which can react with the curing agent to form more cross-linking points, making the cured product of the epoxy resin have a tighter and stronger network structure, thereby improving its mechanical properties. At the same time, due to the increase in cross-linking density, the product of the tetrafunctional epoxy resin after curing can more effectively disperse and resist stress when subjected to external force, so that the prepared epoxy resin has stronger mechanical properties. DETAILED DESCRIPTION

[0021] The present invention will be specifically described below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments and examples are for illustrating the present invention, but not for limiting the present invention. Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. If there is a conflict, this specification takes precedence.

[0022] Unless otherwise specified, the raw materials and reagents used in this application are commercially available or can be prepared by known methods.

[0023] 4-Maleimidobenzoic acid, CAS number is 17057-04-4.

[0024] 1,3-Bis(3-aminopropyl)tetramethyldisiloxane 2469-55-8.

[0025] Bis(4-methoxyphenyl)phosphine oxide, CAS number is 15754-51-5.

[0026] Example 1 (1) Under nitrogen atmosphere, add 25 mmol of 4-maleimidobenzoic acid, 29.5 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, 0.25 mmol of p-dimethylaminopyridine and 100 mL of dichloromethane to the reaction flask, stir evenly, add 14 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, react at 25°C for 20 h, concentrate under reduced pressure, purify by column chromatography (elution with chloroform / methanol = 20:1), and dry to obtain a maleimidosiloxane intermediate. The preparation reaction formula is as follows:

[0027] (2) Under nitrogen atmosphere, 22 mmol of maleimidosiloxane intermediate and 175 mL of acetonitrile were added to a microwave reaction bottle. After stirring, 47.3 mmol of bis(4-methoxyphenyl)phosphine oxide was added. The reaction was carried out at a temperature of 160 °C and a power of 260 W for 4 h. The reaction was concentrated under reduced pressure and purified by column chromatography (elution with dichloromethane / methanol = 15:1). After drying, 143 mmol of boron tribromide and 300 mL of dichloromethane were added. The reaction was carried out at room temperature for 16 h. The reaction was extracted with ethyl acetate and deionized water. The organic phase was concentrated and dried to obtain tetrahydroxynitrogenphosphorus silicon intermediate.

[0028] (3) Under nitrogen atmosphere, add 18 mmol of tetrahydroxynitrogen phosphosilane intermediate and 155 mmol of epichlorohydrin to the reaction flask, stir evenly, add 94.5 mmol of sodium hydroxide and 1.35 mmol of tetrabutylammonium bromide, react at 70°C for 8 h, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain tetrafunctional nitrogen phosphosilane epoxy resin. The preparation reaction is as follows:

[0029] (4) Add 100 g of E51 epoxy resin, 10 g of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 12 g of resorcinol diglycidyl ether into a stirring kettle and stir evenly. Then add 40 g of 4-methylhexahydrophthalic anhydride and mix evenly. Pour the mixture into a mold and cure at 135 °C for 3 h. Then cool the mixture to room temperature and demold the mixture to obtain a halogen-free, flame-retardant and heat-resistant epoxy resin.

[0030] Example 2 (1) Under nitrogen atmosphere, 80 mmol of 4-maleimidobenzoic acid, 88 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, 6.4 mmol of p-dimethylaminopyridine and 240 mL of dichloromethane were added to a reaction flask. After stirring, 40 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added. The mixture was reacted at 35°C for 16 h, concentrated under reduced pressure, purified by column chromatography (elution with chloroform / methanol = 20:1), and dried to obtain a maleimidosiloxane intermediate.

[0031] (2) Under nitrogen atmosphere, 70 mmol of maleimide siloxane intermediate and 420 mL of acetonitrile were added to a microwave reaction bottle. After stirring, 143.5 mmol of bis(4-methoxyphenyl)phosphine oxide was added. The reaction was carried out at a temperature of 170 °C and a power of 300 W for 2 h. The reaction was concentrated under reduced pressure and purified by column chromatography (elution with dichloromethane / methanol = 15:1). After drying, 350 mmol of boron tribromide and 840 mL of dichloromethane were added. The reaction was carried out at room temperature for 12 h. The reaction was extracted with ethyl acetate and deionized water. The organic phase was concentrated and dried to obtain tetrahydroxynitrogenphosphorus silicon intermediate.

[0032] (3) Under nitrogen atmosphere, add 60 mmol of tetrahydroxynitrogen phosphosilane intermediate and 480 mmol of epichlorohydrin into the reaction flask, stir evenly, then add 270 mmol of sodium hydroxide and 3 mmol of tetrabutylammonium iodide, react at 80 °C for 5 h, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain tetrafunctional nitrogen phosphosilane epoxy resin.

[0033] (4) Add 100 g of E51 epoxy resin, 20 g of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 10 g of 1,4-butanediol diglycidyl ether into a stirring kettle, stir evenly, add 30 g of trimellitic anhydride, mix evenly, pour into a mold, cure at 160°C for 2 h, cool to room temperature, and demold to obtain a halogen-free flame retardant and heat-resistant epoxy resin.

[0034] Example 3 (1) Under nitrogen atmosphere, 16 mmol of 4-maleimidobenzoic acid, 20 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, 1.92 mmol of p-dimethylaminopyridine and 80 mL of dichloromethane were added to a reaction flask. After stirring, 9.6 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added. The mixture was reacted at 20°C for 24 h, concentrated under reduced pressure, purified by column chromatography (elution with chloroform / methanol = 20:1), and dried to obtain a maleimidosiloxane intermediate.

[0035] (2) Under nitrogen atmosphere, 12 mmol of maleimidosiloxane intermediate and 120 mL of acetonitrile were added to a microwave reaction bottle. After stirring, 26.4 mmol of bis(4-methoxyphenyl)phosphine oxide was added. The reaction was carried out at a temperature of 150 °C and a power of 200 W for 5 h. The reaction was concentrated under reduced pressure and purified by column chromatography (elution with dichloromethane / methanol = 15:1). After drying, 96 mmol of boron tribromide and 180 mL of dichloromethane were added. The reaction was carried out at room temperature for 24 h. The reaction was extracted with ethyl acetate and deionized water. The organic phase was concentrated and dried to obtain tetrahydroxynitrogenphosphorussilicon intermediate.

[0036] (3) Under nitrogen atmosphere, add 20 mmol of tetrahydroxynitrogen phosphosilane intermediate and 100 mmol of epichlorohydrin into the reaction flask, stir evenly, then add 120 mmol of sodium hydroxide and 2 mmol of N,N-dimethylbenzylamine, react at 60 °C for 10 h, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain tetrafunctional nitrogen phosphosilane epoxy resin.

[0037] (4) Add 100 g of E51 epoxy resin, 30 g of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 15 g of phenyl glycidyl ether into a stirring kettle, stir evenly, add 45 g of diethylenetriamine, mix evenly, pour into a mold, cure at 120 ° C for 4 h, cool to room temperature, and demold to obtain a halogen-free flame retardant and heat-resistant epoxy resin.

[0038] Example 4 (1) Under nitrogen atmosphere, 50 mmol of 4-maleimidobenzoic acid, 60 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, 4.75 mmol of p-dimethylaminopyridine and 175 mL of dichloromethane were added to a reaction flask. After stirring, 28 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added. The mixture was reacted at 30°C for 18 h, concentrated under reduced pressure, purified by column chromatography (elution with chloroform / methanol = 20:1), and dried to obtain a maleimidosiloxane intermediate.

[0039] (2) Under nitrogen atmosphere, 45 mmol of maleimidosiloxane intermediate and 390 mL of acetonitrile were added to a microwave reaction bottle. After stirring, 96.5 mmol of bis(4-methoxyphenyl)phosphine oxide was added. The reaction was carried out at a temperature of 165 °C and a power of 240 W for 3 h. The reaction was concentrated under reduced pressure and purified by column chromatography (elution with dichloromethane / methanol = 15:1). After drying, 306 mmol of boron tribromide and 612 mL of dichloromethane were added. The reaction was carried out at room temperature for 15 h. The reaction was extracted with ethyl acetate and deionized water. The organic phase was concentrated and dried to obtain tetrahydroxynitrogenphosphorussilicon intermediate.

[0040] (3) Under nitrogen atmosphere, 40 mmol of tetrahydroxynitrogen phosphosilane intermediate and 340 mmol of epichlorohydrin were added to the reaction flask. After stirring, 220 mmol of sodium hydroxide and 3.4 mmol of tetrabutylammonium bromide were added. The mixture was reacted at 75 °C for 8 h. The mixture was centrifuged and washed with deionized water until neutral. The mixture was extracted with ethyl acetate and deionized water. The organic phase was concentrated and dried to obtain a tetrafunctional nitrogen phosphosilane epoxy resin.

[0041] (4) Add 100 g of E51 epoxy resin, 40 g of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 14 g of resorcinol diglycidyl ether into a stirring kettle and stir evenly. Then add 36 g of 4-methylhexahydrophthalic anhydride and mix evenly. Pour the mixture into a mold and cure at 145 °C for 3 h. Then cool the mixture to room temperature and demold the mixture to obtain a halogen-free, flame-retardant and heat-resistant epoxy resin.

[0042] Example 5 (1) Under nitrogen atmosphere, 32 mmol of 4-maleimidobenzoic acid, 38.5 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, 3.2 mmol of p-dimethylaminopyridine and 140 mL of dichloromethane were added to a reaction flask. After stirring, 17.2 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added. The mixture was reacted at 25°C for 24 h, concentrated under reduced pressure, purified by column chromatography (elution with chloroform / methanol = 20:1), and dried to obtain a maleimidosiloxane intermediate.

[0043] (2) Under nitrogen atmosphere, 28 mmol of maleimidosiloxane intermediate and 235 mL of acetonitrile were added to a microwave reaction bottle. After stirring, 60.2 mmol of bis(4-methoxyphenyl)phosphine oxide was added. The reaction was carried out at a temperature of 165 °C and a power of 280 W for 4 h. The reaction was concentrated under reduced pressure and purified by column chromatography (elution with dichloromethane / methanol = 15:1). After drying, 210 mmol of boron tribromide and 405 mL of dichloromethane were added. The reaction was carried out at room temperature for 15 h. The reaction was extracted with ethyl acetate and deionized water. The organic phase was concentrated and dried to obtain tetrahydroxynitrogenphosphorus silicon intermediate.

[0044] (3) Under nitrogen atmosphere, add 25 mmol of tetrahydroxynitrogen phosphosilane intermediate and 215 mmol of epichlorohydrin into the reaction flask, stir evenly, then add 130 mmol of sodium hydroxide and 1.5 mmol of tetrabutylammonium iodide, react at 65 °C for 10 h, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain tetrafunctional nitrogen phosphosilane epoxy resin.

[0045] (4) Add 100 g of E51 epoxy resin, 50 g of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 14 g of 1,4-butanediol diglycidyl ether into a stirring kettle, stir evenly, add 40 g of trimellitic anhydride, mix evenly, pour into a mold, cure at 1450°C for 3 h, cool to room temperature, and demold to obtain a halogen-free flame retardant and heat-resistant epoxy resin.

[0046] Comparative Example 1 (1) Under nitrogen atmosphere, add 18 mmol of 1,1'-biphenyl-3,3',4,4'-tetrol (CAS No. 3598-30-9, structural formula ) and 155mmol epichlorohydrin, stir evenly, add 94.5mmol sodium hydroxide and 1.35mmol tetrabutylammonium bromide, react at 70℃ for 8h, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain biphenyl tetrafunctional epoxy resin.

[0047] (2) Add 100 g of E51 epoxy resin, 10 g of biphenyl tetrafunctional epoxy resin and 12 g of resorcinol diglycidyl ether into a stirring kettle and stir evenly. Then add 40 g of 4-methylhexahydrophthalic anhydride and mix evenly. Pour the mixture into a mold and cure at 135 °C for 3 h. Then cool to room temperature and demold to obtain a heat-resistant epoxy resin.

[0048] Comparative Example 2 100g of E51 epoxy resin, 10g of pentaerythritol glycidyl ether (CAS No. 3126-63-4, structural formula ) and 12g of resorcinol bisglycidyl ether are added into a stirring kettle. After stirring evenly, 40g of 4-methylhexahydrophthalic anhydride is added. After mixing evenly, the mixture is poured into a mold and cured at 135°C for 3h. The mixture is cooled to room temperature and demolded to obtain a modified epoxy resin.

[0049] Comparative Example 3 Add 110g of E51 epoxy resin and 12g of resorcinol diglycidyl ether into a stirring kettle, stir evenly, add 40g of 4-methylhexahydrophthalic anhydride, mix evenly, pour into a mold, cure at 135°C for 3h, cool to room temperature, and demold to obtain a modified epoxy resin.

[0050] Limiting oxygen index test: Tested in accordance with GB / T 2406.2-2009 standard.

[0051] UL-94 grade test: Tested in accordance with UL94-2009 standard.

[0052] Table 1 Flame retardant performance test

[0053] It can be seen from the test results in the above table that with the increase of the content of the nitrogen-phosphorus-silicon tetrafunctional epoxy resin, the flame retardant performance of the epoxy resin is gradually enhanced. The limiting oxygen index in Example 5 reaches 36.0%, and the UL-94 grade reaches V-0, which is a flame retardant material level. This is because the silicon, nitrogen, and phosphorus barrier elements rich in the nitrogen-phosphorus-silicon tetrafunctional epoxy resin can form a dense expanded carbon layer of deposited silicon when the epoxy resin cured product burns, so that the modified epoxy resin releases NH4+ by self-decomposition when heated. 3After these non-combustible gases diffuse into the flame zone, they can dilute the oxygen concentration in the gas phase, thereby inhibiting the spread of the flame and playing a gas phase flame retardant role; at the same time, the decomposed acidic substances can promote the decomposition of epoxy resin and form viscous polymers containing P and N, changing the composition and properties of the carbon layer, making the carbon layer dense and continuous, playing a good role in heat insulation, insulation, and oxygen isolation, reducing the diffusion of combustion heat to the unburned part, and playing a condensed phase flame retardant role. In addition, the introduced siloxane is oxidized to SiO 2 , making the formed carbon layer more compact and further protecting the carbon layer from oxidation and decomposition, thereby greatly enhancing the flame retardant properties of the epoxy resin. Comparative Examples 1, 2, and 3 do not contain nitrogen, phosphorus, and silicon flame retardant elements, and have poor flame retardant properties.

[0054] Temperature resistance test: The glass transition temperature test was carried out using a differential scanning calorimeter in a nitrogen environment with a heating rate of 20°C / min.

[0055] Table 2 Temperature resistance test

[0056] Generally speaking, the higher the glass transition temperature, the higher the temperature resistance of the material. This is because a high glass transition temperature means that the molecular structure of the material is tighter, and the molecular motion caused by heat is more strongly restricted, thus showing the high temperature resistance of the material. From the test results in the above table, it can be seen that with the increase of the content of nitrogen-phosphorus-silicon tetrafunctional epoxy resin, the temperature resistance of the epoxy resin gradually increases. This is because nitrogen-phosphorus-silicon tetrafunctional epoxy resin contains an imide ring with high chemical stability and thermal stability and a siloxane with high bond energy, which can resist thermal decomposition under high temperature conditions and maintain the stability of its chemical structure. At the same time, the tetrafunctional epoxy resin has a high crosslinking density and is not prone to thermal decomposition or deformation, so that the prepared epoxy resin has a higher temperature resistance. Comparative Example 1 contains a biphenyl group with better temperature resistance, and its temperature resistance is better than that of Comparative Examples 2 and 3.

[0057] Tensile performance test: a universal tensile testing machine was used to test the material according to GB / T 1040-2008 standard, with a tensile rate of 10 mm / min.

[0058] Impact strength test: The test was conducted using a simply supported beam impact tester with reference to ASTM D638-2008 standard, and the sample had no notch.

[0059] Table 3 Mechanical properties test

[0060] It can be seen from the test results in the above table that with the increase of the content of nitrogen-phosphorus-silicon tetrafunctional epoxy resin, the mechanical properties of epoxy resin gradually increase. This is because on the one hand, the silicon-oxygen chain is evenly distributed in the cross-linked network of the epoxy resin, dispersing and reducing the internal stress of the resin when it is broken by impact, and because the Si-O bond is softer and has a higher bond energy than the CC bond, it plays a toughening role in the resin; on the other hand, the tetrafunctional epoxy resin molecule contains more epoxy groups, which can react with the curing agent to form more cross-linking points, so that the cured product of the epoxy resin has a tighter and stronger network structure, thereby improving its mechanical properties; at the same time, due to the increase in cross-linking density, the product after the tetrafunctional epoxy resin is cured can more effectively disperse and resist stress when subjected to external force, so that the prepared epoxy resin has stronger mechanical properties. Comparative Examples 1 and 2 both contain tetrafunctional epoxy groups, which can form more cross-linking sites, so that the mechanical properties are better than those of Comparative Example 3.

[0061] Based on the ideal embodiment of the present invention, through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing a halogen-free flame-retardant and heat-resistant epoxy resin, characterized in that: The preparation method is carried out according to the following steps: Step (1), under a nitrogen atmosphere, add tetrahydroxynitrogen phosphosilane intermediate and epichlorohydrin into a reaction flask, stir evenly, add sodium hydroxide and a catalyst, react at 60-80° C. for 5-10 hours, centrifuge, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain a tetrafunctional nitrogen phosphosilane epoxy resin; Step (2), adding 100 parts of epoxy resin, 10-50 parts of nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 10-15 parts of diluent by weight into a stirring kettle, stirring evenly, adding 30-45 parts of curing agent, mixing evenly, pouring into a mold, curing at 120-160° C. for 2-4 hours, cooling to room temperature, and demolding to obtain a halogen-free flame retardant and heat-resistant epoxy resin; The preparation method of the tetrahydroxynitrogenphosphorus silicon intermediate in step (1) is carried out according to the following steps: Step S1, under a nitrogen atmosphere, add 4-maleimidobenzoic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, p-dimethylaminopyridine and dichloromethane to a reaction flask, stir evenly, add 1,3-bis(3-aminopropyl)tetramethyldisiloxane, react at 20-35° C. for 16-24 h, concentrate under reduced pressure, purify by column chromatography, and dry to obtain a maleimidosiloxane intermediate; Step S2, under a nitrogen atmosphere, add the maleimidosiloxane intermediate and acetonitrile to a microwave reaction bottle, stir evenly, add bis(4-methoxyphenyl)phosphine oxide, and carry out microwave reaction. After the reaction is completed, concentrate under reduced pressure, purify by column chromatography, add boron tribromide and dichloromethane after drying, react at room temperature for 12-24h, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain the tetrahydroxynitrogenphosphorus silicon intermediate.

2. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: The catalyst in step (1) is any one of tetrabutylammonium bromide, tetrabutylammonium iodide or N,N-dimethylbenzylamine.

3. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: In the step (1), the molar ratio of the tetrahydroxynitrogenphosphorus silicon intermediate, epichlorohydrin, sodium hydroxide and the catalyst is 1:8-10:4.5-6:0.05-0.

1.

4. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: In the step (2), the diluent is any one of resorcinol diglycidyl ether, 1,4-butanediol diglycidyl ether or phenyl glycidyl ether.

5. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: In the step (2), the curing agent is any one of 4-methylhexahydrophthalic anhydride, trimellitic anhydride or diethylenetriamine.

6. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: In the step S1, the molar ratio of 4-maleimidobenzoic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, p-dimethylaminopyridine, and 1,3-bis(3-aminopropyl)tetramethyldisiloxane is 1:1.1-1.25:0.08-0.12:0.5-0.

6.

7. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: In the step S2, the molar ratio of the maleimide siloxane intermediate, bis(4-methoxyphenyl)phosphine oxide and boron tribromide is 1:2.05-2.2:5-8.

8. The method for preparing the halogen-free flame-retardant and heat-resistant epoxy resin according to claim 1, characterized in that: In step S2, the microwave reaction temperature is 150-170° C., the microwave reaction time is 2-5 h, and the microwave reaction power is 200-300 W.

9. A halogen-free flame-retardant and heat-resistant epoxy resin, characterized in that: Obtained by the preparation method according to any one of claims 1 to 8.

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