A halogen-free flame-retardant and temperature-resistant epoxy resin and its preparation method

Abstract

The present invention relates to the technical field of polymer materials, and discloses a halogen-free flame-retardant and temperature-resistant epoxy resin and a preparation method thereof. The epoxy resin is prepared from epoxy resin, nitrogen-phosphorus-silicon tetrafunctional epoxy resin, curing agent and diluent through blending and curing. The nitrogen-phosphorus-silicon tetrafunctional epoxy resin is obtained by using 4-maleimidobenzoic acid, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, bis(4-methoxyphenyl)phosphine oxide and epichlorohydrin as raw materials through condensation, addition and substitution reactions. The nitrogen-phosphorus-silicon has a synergistic flame-retardant effect and plays a good role in heat insulation, mass isolation and oxygen isolation. The tetrafunctional epoxy resin molecule contains more epoxy groups, can react with the curing agent to form more cross-linking points, improve the cross-linking density, and can more effectively disperse and resist stress. The epoxy resin prepared by the present invention has excellent flame-retardant effect, is halogen-free and environmentally friendly, and has good temperature resistance and mechanical properties at the same time.

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 temperature-resistant epoxy resin and its preparation method. Summary of the Invention

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

[0007] The technical solution of the present invention is as follows:

[0008] The preparation method of a halogen-free flame-retardant and temperature-resistant epoxy resin is carried out according to the following steps:

[0009] Step (1): Under a nitrogen atmosphere, add a tetrahydroxy nitrogen phosphorus silicon intermediate and epichlorohydrin into a reaction flask. After stirring evenly, add sodium hydroxide and a catalyst, and react at 60 - 80 °C for 5 - 10 h. Then perform centrifugal separation, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and dry to obtain a nitrogen phosphorus silicon tetra-functional epoxy resin.

[0010] Step (2): Add 100 parts of E51 type epoxy resin, 10 - 50 parts of nitrogen phosphorus silicon tetra-functional epoxy resin, and 10 - 15 parts of a diluent by weight fraction into a stirring kettle. After stirring evenly, add 30 - 45 parts of a curing agent, mix evenly, pour into a mold, cure at 120 - 160 °C for 2 - 4 h, cool to room temperature, and demold to obtain a halogen-free flame-retardant and temperature-resistant epoxy resin.

[0011] Further, in step (1), the catalyst is any one of tetrabutylammonium bromide, tetrabutylammonium iodide, or N,N-dimethylbenzylamine.

[0012] Further, in step (1), the molar ratio of the tetrahydroxy nitrogen phosphorus silicon intermediate, epichlorohydrin, sodium hydroxide, and the catalyst is 1:8 - 10:4.5 - 6:0.05 - 0.1.

[0013] Further, in step (2), the diluent is any one of resorcinol diglycidyl ether, 1,4-butanediol diglycidyl ether, or phenyl glycidyl ether.

[0014] Further, in step (2), the curing agent is any one of 4-methylhexahydrophthalic anhydride, trimellitic anhydride, or diethylenetriamine.

[0015] Further, the preparation method of the tetrahydroxy nitrogen phosphorus silicon intermediate in step (1) is carried out according to the following steps:

[0016] Step S1: Under a nitrogen atmosphere, 4-maleimidobenzoic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, p-dimethylaminopyridine, and dichloromethane are added to a reaction flask. After stirring evenly, 1,3-bis(3-aminopropyl)tetramethyldisiloxane is added, and the reaction is carried out at 20 - 35 °C for 16 - 24 h. Then, it is concentrated under reduced pressure and purified by column chromatography (eluted with chloroform / methanol = 20:1). After drying, a maleimidopolysiloxane intermediate is obtained.

[0017] Step S2: Under a nitrogen atmosphere, the maleimidopolysiloxane intermediate and acetonitrile are added to a microwave reaction flask. After stirring evenly, bis(4-methoxyphenyl)phosphine oxide is added, and a microwave reaction is carried out. After the reaction ends, it is concentrated under reduced pressure and purified by column chromatography (eluted with dichloromethane / methanol = 15:1). After drying, boron tribromide and dichloromethane are added, and the reaction is carried out at room temperature for 12 - 24 h. It is extracted with ethyl acetate and deionized water, the organic phase is concentrated, and after drying, a tetrahydroxy nitrogen phosphorus silicon intermediate is obtained.

[0018] 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.

[0019] Furthermore, in step S2, the molar ratio of the maleimidopolysiloxane intermediate, bis(4-methoxyphenyl)phosphine oxide, and boron tribromide is 1:2.05 - 2.2:5 - 8.

[0020] 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.

[0021] The beneficial technical effects of the present invention are:

[0022] (1) Excellent flame retardancy: The silicon, nitrogen, and phosphorus elements rich in the nitrogen-phosphorus-silicon tetrafunctional epoxy resin can form a dense expanded carbon layer with deposited silicon during the combustion of the epoxy resin cured product. When the modified epoxy resin is heated, it releases non-combustible gases such as NH 3 etc. These non-combustible gases can dilute the oxygen concentration in the gas phase after diffusing to the flame zone, 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 the epoxy resin and form a viscous polymer 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, mass insulation, and oxygen insulation, reducing the diffusion of combustion heat to the unburned part, and playing a condensed-phase flame retardant role. In addition, the introduced polysiloxane is oxidized to SiO when heated 2, making the formed carbon layer more dense and further protecting the carbon layer from being oxidized and decomposed, thereby greatly enhancing the flame retardancy of the epoxy resin.

[0023] (2) Excellent temperature resistance: The nitrogen, phosphorus, and silicon tetra-functional epoxy resin contains imide rings with high chemical stability and thermal stability and siloxanes 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 tetra-functional epoxy resin has a high crosslinking density and is not prone to thermal decomposition or deformation, so that the prepared epoxy resin has high temperature resistance.

[0024] (3) Excellent mechanical properties: The silicon-oxygen chains are evenly distributed in the epoxy resin crosslinking network, dispersing and reducing the internal stress when the resin is impacted and fractured. And because the Si-O bond is softer and has a higher bond energy than the C-C bond, it plays a toughening role in the resin; the tetra-functional epoxy resin molecule contains more epoxy groups and can react with the curing agent to form more crosslinking points, making the cured product of the epoxy resin have a more compact and firm network structure, thereby improving its mechanical properties; at the same time, due to the increase in crosslinking density, the cured product of the tetra-functional epoxy resin can more effectively disperse and resist stress when subjected to external forces, so that the prepared epoxy resin has stronger mechanical properties. Detailed implementation manners

[0025] The following will specifically describe the present invention in combination with specific implementation manners and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these specific implementation manners and examples are used to illustrate the present invention, rather than limiting the present invention. Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the art to which the present invention belongs. In case of conflict, this specification shall prevail.

[0026] Unless otherwise specified, the raw materials and reagents used in this application are all commercially available products or can be prepared by known methods.

[0027] 4-Maleimidobenzoic acid, CAS number is 17057-04-4.

[0028] 1,3-Bis(3-aminopropyl)tetramethyldisiloxane 2469-55-8.

[0029] Bis(4-methoxyphenyl)phosphine oxide, CAS number is 15754-51-5.

[0030] Example 1

[0031] (1) Under a nitrogen atmosphere, 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 were added to a reaction flask. After stirring evenly, 14 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added. The reaction was carried out at 25 °C for 20 h, concentrated under reduced pressure, purified by column chromatography (eluted with chloroform / methanol = 20:1), and dried to obtain the maleimidopolysiloxane intermediate. The preparation reaction formula is as follows:

[0032] (2) Under a nitrogen atmosphere, 22 mmol of the maleimidopolysiloxane intermediate and 175 mL of acetonitrile were added to a microwave reaction flask. After stirring evenly, 47.3 mmol of bis(4-methoxyphenyl)phosphine oxide was added. The microwave reaction was carried out at a temperature of 160 °C and a power of 260 W for 4 h, concentrated under reduced pressure, purified by column chromatography (eluted with dichloromethane / methanol = 15:1), and dried. Then 143 mmol of boron tribromide and 300 mL of dichloromethane were added, and the reaction was carried out at room temperature for 16 h. Extraction was carried out with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain the tetrahydroxy nitrogen-phosphorus-silicon intermediate.

[0033] (3) Under a nitrogen atmosphere, 18 mmol of the tetrahydroxy nitrogen-phosphorus-silicon intermediate and 155 mmol of epichlorohydrin were added to a reaction flask. After stirring evenly, 94.5 mmol of sodium hydroxide and 1.35 mmol of tetrabutylammonium bromide were added. The reaction was carried out at 70 °C for 8 h, centrifuged, washed with deionized water until neutral, extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain the nitrogen-phosphorus-silicon tetrafunctional epoxy resin. The preparation reaction formula is as follows:

[0034] (4) 100 g of E51-type epoxy resin, 10 g of the nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 12 g of resorcinol diglycidyl ether were added to a stirring kettle. After stirring evenly, 40 g of 4-methylhexahydrophthalic anhydride was added. After mixing evenly, it was poured into a mold and cured at 135 °C for 3 h, cooled to room temperature, and demolded to obtain the halogen-free flame-retardant and temperature-resistant epoxy resin.

[0035] Example 2

[0036] (1) Under a 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 evenly, 40 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added, and the reaction was carried out at 35 °C for 16 h. The mixture was concentrated under reduced pressure and purified by column chromatography (eluted with chloroform / methanol = 20:1), and the maleimidopolysiloxane intermediate was obtained after drying.

[0037] (2) Under a nitrogen atmosphere, 70 mmol of the maleimidopolysiloxane intermediate and 420 mL of acetonitrile were added to a microwave reaction flask. After stirring evenly, 143.5 mmol of bis(4-methoxyphenyl)phosphine oxide was added, and the microwave reaction was carried out at a temperature of 170 °C and a power of 300 W for 2 h. The mixture was concentrated under reduced pressure and purified by column chromatography (eluted with dichloromethane / methanol = 15:1). After drying, 350 mmol of boron tribromide and 840 mL of dichloromethane were added, and the reaction was carried out at room temperature for 12 h. The mixture was extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a tetrahydroxy nitrogen-phosphorus-silicon intermediate.

[0038] (3) Under a nitrogen atmosphere, 60 mmol of the tetrahydroxy nitrogen-phosphorus-silicon intermediate and 480 mmol of epichlorohydrin were added to a reaction flask. After stirring evenly, 270 mmol of sodium hydroxide and 3 mmol of tetrabutylammonium iodide were added, and the reaction was carried out at 80 °C for 5 h. The mixture was centrifuged, washed with deionized water until neutral, extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a nitrogen-phosphorus-silicon tetrafunctional epoxy resin.

[0039] (4) 100 g of E51 type epoxy resin, 20 g of the nitrogen-phosphorus-silicon tetrafunctional epoxy resin and 10 g of 1,4-butanediol diglycidyl ether were added to a stirring kettle. After stirring evenly, 30 g of trimellitic anhydride was added. After mixing evenly, the mixture was poured into a mold and cured at 160 °C for 2 h. After cooling to room temperature and demolding, a halogen-free flame-retardant and temperature-resistant epoxy resin was obtained.

[0040] Example 3

[0041] (1) Under a 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 evenly, 9.6 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added, and the reaction was carried out at 20 °C for 24 h. The mixture was concentrated under reduced pressure and purified by column chromatography (eluted with chloroform / methanol = 20:1), and the maleimidopolysiloxane intermediate was obtained after drying.

[0042] (2) Under a nitrogen atmosphere, 12 mmol of maleimide-based siloxane intermediate and 120 mL of acetonitrile were added to a microwave reaction flask. After stirring evenly, 26.4 mmol of bis(4-methoxyphenyl)phosphine oxide was added. Microwave reaction was carried out at a temperature of 150 °C and a power of 200 W for 5 h. Then, it was concentrated under reduced pressure and purified by column chromatography (eluted with dichloromethane / methanol = 15:1). After drying, 96 mmol of boron tribromide and 180 mL of dichloromethane were added, and the reaction was carried out at room temperature for 24 h. It was extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a tetra-hydroxy nitrogen-phosphorus-silicon intermediate.

[0043] (3) Under a nitrogen atmosphere, 20 mmol of tetra-hydroxy nitrogen-phosphorus-silicon intermediate and 100 mmol of epichlorohydrin were added to a reaction flask. After stirring evenly, 120 mmol of sodium hydroxide and 2 mmol of N,N-dimethylbenzylamine were added. The reaction was carried out at 60 °C for 10 h. After centrifugal separation, it was washed with deionized water until neutral, extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a nitrogen-phosphorus-silicon tetra-functional epoxy resin.

[0044] (4) 100 g of E51-type epoxy resin, 30 g of nitrogen-phosphorus-silicon tetra-functional epoxy resin, and 15 g of phenyl glycidyl ether were added to a stirring kettle. After stirring evenly, 45 g of diethylenetriamine was added. After mixing evenly, it was poured into a mold and cured at 120 °C for 4 h. After cooling to room temperature and demolding, a halogen-free flame-retardant and temperature-resistant epoxy resin was obtained.

[0045] Example 4

[0046] (1) Under a 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 evenly, 28 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added. The reaction was carried out at 30 °C for 18 h. Then, it was concentrated under reduced pressure and purified by column chromatography (eluted with chloroform / methanol = 20:1). After drying, a maleimide-based siloxane intermediate was obtained.

[0047] (2) Under a nitrogen atmosphere, 45 mmol of maleimide-based siloxane intermediate and 390 mL of acetonitrile were added to a microwave reaction flask. After stirring evenly, 96.5 mmol of bis(4-methoxyphenyl)phosphine oxide was added. Microwave reaction was carried out at a temperature of 165 °C and a power of 240 W for 3 h. Then, it was concentrated under reduced pressure and purified by column chromatography (eluted with dichloromethane / methanol = 15:1). After drying, 306 mmol of boron tribromide and 612 mL of dichloromethane were added, and the reaction was carried out at room temperature for 15 h. It was extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a tetra-hydroxy nitrogen-phosphorus-silicon intermediate.

[0048] (3)Under a nitrogen atmosphere, 40 mmol of the tetra-hydroxy nitrogen-phosphorus-silicon intermediate was added to a reaction flask, and 340 mmol of epichlorohydrin was added. After stirring evenly, 220 mmol of sodium hydroxide and 3.4 mmol of tetrabutylammonium bromide were added, and the reaction was carried out at 75 °C for 8 h. After centrifugal separation, it was washed with deionized water until neutral, extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a nitrogen-phosphorus-silicon tetra-functional epoxy resin.

[0049] (4)100 g of E51-type epoxy resin, 40 g of nitrogen-phosphorus-silicon tetra-functional epoxy resin and 14 g of resorcinol diglycidyl ether were added to a stirring kettle. After stirring evenly, 36 g of 4-methylhexahydrophthalic anhydride was added. After mixing evenly, it was poured into a mold and cured at 145 °C for 3 h. After cooling to room temperature, the mold was removed to obtain a halogen-free flame-retardant and temperature-resistant epoxy resin.

[0050] Example 5

[0051] (1)Under a 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 evenly, 17.2 mmol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane was added, and the reaction was carried out at 25 °C for 24 h. After concentration under reduced pressure, it was purified by column chromatography (eluted with chloroform / methanol = 20:1), and after drying, a maleimide-based siloxane intermediate was obtained.

[0052] (2)Under a nitrogen atmosphere, 28 mmol of the maleimide-based siloxane intermediate and 235 mL of acetonitrile were added to a microwave reaction flask. After stirring evenly, 60.2 mmol of bis(4-methoxyphenyl)phosphine oxide was added, and the microwave reaction was carried out at a temperature of 165 °C and a power of 280 W for 4 h. After concentration under reduced pressure, it was purified by column chromatography (eluted with dichloromethane / methanol = 15:1). After drying, 210 mmol of boron tribromide and 405 mL of dichloromethane were added, and the reaction was carried out at room temperature for 15 h. After extraction with ethyl acetate and deionized water, the organic phase was concentrated and dried to obtain a tetra-hydroxy nitrogen-phosphorus-silicon intermediate.

[0053] (3)Under a nitrogen atmosphere, 25 mmol of the tetra-hydroxy nitrogen-phosphorus-silicon intermediate and 215 mmol of epichlorohydrin were added to a reaction flask. After stirring evenly, 130 mmol of sodium hydroxide and 1.5 mmol of tetrabutylammonium iodide were added, and the reaction was carried out at 65 °C for 10 h. After centrifugal separation, it was washed with deionized water until neutral, extracted with ethyl acetate and deionized water, and the organic phase was concentrated and dried to obtain a nitrogen-phosphorus-silicon tetra-functional epoxy resin.

[0054] (4) Add 100 g of E51-type epoxy resin, 50 g of nitrogen-phosphorus-silicon tetrafunctional epoxy resin, and 14 g of 1,4-butanediol diglycidyl ether to a stirring kettle. After stirring evenly, add 40 g of trimellitic anhydride. After mixing evenly, pour it into a mold and cure at 1450 °C for 3 h. Cool to room temperature, and after demolding, a halogen-free flame-retardant and temperature-resistant epoxy resin is obtained.

[0055] Comparative Example 1

[0056] (1) Under a nitrogen atmosphere, add 18 mmol of 1,1'-biphenyl]-3,3',4,4'-tetrol (CAS No. 3598-30-9, structural formula ) and 155 mmol of epichlorohydrin to a reaction flask. After stirring evenly, add 94.5 mmol of sodium hydroxide and 1.35 mmol of tetrabutylammonium bromide, and react at 70 °C for 8 h. Centrifuge and separate, wash with deionized water until neutral, extract with ethyl acetate and deionized water, concentrate the organic phase, and after drying, a biphenyl tetrafunctional epoxy resin is obtained.

[0057] (2) Add 100 g of E51-type epoxy resin, 10 g of biphenyl tetrafunctional epoxy resin, and 12 g of resorcinol diglycidyl ether to a stirring kettle. After stirring evenly, add 40 g of 4-methylhexahydrophthalic anhydride. After mixing evenly, pour it into a mold and cure at 135 °C for 3 h. Cool to room temperature, and after demolding, a temperature-resistant epoxy resin is obtained.

[0058] Comparative Example 2

[0059] Add 100 g of E51-type epoxy resin, 10 g of pentaerythritol glycidyl ether (CAS No. 3126-63-4, structural formula ) and 12 g of resorcinol diglycidyl ether to a stirring kettle. After stirring evenly, add 40 g of 4-methylhexahydrophthalic anhydride. After mixing evenly, pour it into a mold and cure at 135 °C for 3 h. Cool to room temperature, and after demolding, a modified epoxy resin is obtained.

[0060] Comparative Example 3

[0061] Add 110 g of E51-type epoxy resin and 12 g of resorcinol diglycidyl ether to a stirring kettle. After stirring evenly, add 40 g of 4-methylhexahydrophthalic anhydride. After mixing evenly, pour it into a mold and cure at 135 °C for 3 h. Cool to room temperature, and after demolding, a modified epoxy resin is obtained.

[0062] Limiting oxygen index test: The test is carried out with reference to the standard of GB / T 2406.2-2009.

[0063] UL-94 rating test: The test is carried out with reference to the standard of UL94-2009.

[0064] Table 1 Flame Retardancy Performance Test

[0065]

[0066] As can be seen from the test results in the above table, with the increase in the content of the nitrogen, phosphorus, and silicon tetrafunctional epoxy resin, the flame retardancy of the epoxy resin gradually increases. Among them, the limiting oxygen index in Example 5 reaches 36.0%, and the UL-94 rating reaches V-0 level, belonging to the level of flame-retardant materials. This is because the silicon, nitrogen, and phosphorus flame-retardant elements rich in the nitrogen, phosphorus, and silicon tetrafunctional epoxy resin can form a dense expanded carbon layer with deposited silicon during the combustion of the epoxy resin cured product, so that the modified epoxy resin releases NH 3 and other non-combustible gases through its own decomposition when heated. 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 the epoxy resin and form a viscous polymer 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, mass insulation, and oxygen insulation, 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 into SiO 2 when heated, making the formed carbon layer more dense and further protecting the carbon layer from being oxidized and decomposed, so that the flame retardancy of the epoxy resin can be greatly enhanced. In Comparative Examples 1, 2, and 3, there are no nitrogen, phosphorus, and silicon flame-retardant elements, and the flame retardancy is poor.

[0067] Temperature Resistance Test: A differential scanning calorimeter was used to conduct a glass transition temperature test under a nitrogen atmosphere, and the heating rate was 20 °C / min.

[0068] Table 2 Temperature Resistance Test

[0069]

[0070] 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 more compact, and the molecular motion caused by heat is more strongly restricted, thus showing the high-temperature resistance of the material; as can be seen from the test results in the above table, with the increase in the content of the nitrogen, phosphorus, and silicon tetrafunctional epoxy resin, the temperature resistance of the epoxy resin gradually increases. This is because the nitrogen, phosphorus, and silicon tetrafunctional epoxy resin contains imide rings with high chemical stability and thermal stability and siloxanes 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 easy to undergo thermal decomposition or deformation, so that the prepared epoxy resin has high temperature resistance. Comparative Example 1 contains a biphenyl group with good temperature resistance, and its temperature resistance is better than that of Comparative Example 2 and Comparative Example 3.

[0071] Tensile property test: A universal tensile testing machine was used, and the test was carried out with reference to the standard of GB / T 1040-2008. The tensile rate was 10 mm / min.

[0072] Impact strength test: A simply supported beam impact testing machine was used, and the test was carried out with reference to the standard of ASTM D638-2008. The sample had no notch.

[0073] Table 3 Mechanical property test

[0074]

[0075] From the test results in the above table, it can be seen that as the content of the tetra-functional epoxy resin of nitrogen, phosphorus and silicon increases, the mechanical properties of the epoxy resin gradually increase. This is because on the one hand, the silicon-oxygen chain is evenly distributed in the epoxy resin cross-linking network, dispersing and reducing the internal stress when the resin is impacted and fractured. And because the Si-O bond is softer and has a higher bond energy than the C-C bond, it plays a toughening role in the resin; on the other hand, the tetra-functional 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 more compact and solid network structure, thus improving its mechanical properties; at the same time, due to the increase in the cross-linking density, the product cured by the tetra-functional epoxy resin can more effectively disperse and resist stress when subjected to external force, so that the prepared epoxy resin has stronger mechanical properties. Both Comparative Example 1 and Comparative Example 2 contain tetra-functional epoxy groups, which can form more cross-linking sites, making the mechanical properties better than those of Comparative Example 3.

[0076] Enlightened by the ideal embodiments of the present invention, through the above description, relevant personnel can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this 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.

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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.

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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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