A cyclotriphosphazene-based silicon-containing flame retardant, a preparation method and application thereof

Abstract

The application relates to a cyclotriphosphazene-based silicon-containing flame retardant as well as a preparation method and application thereof. The flame retardant is based on hexachlorocyclotriphosphazene, a silicon-containing compound is introduced through a nucleophilic substitution reaction between the hexachlorocyclotriphosphazene and an allyl-containing phenolic compound and a silicon-hydrogen addition reaction between the hexachlorocyclotriphosphazene and a silane compound, a flame retardant containing phosphorus, nitrogen and silicon elements is obtained, and the molecular structure is shown as formula (I). The flame retardant can significantly improve the smoke suppression and charring performance of a polymer, has excellent flame retardant efficiency, and has a wide application prospect in polymer materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flame-retardant materials, and particularly relates to a cyclotriphosphazene-based silicon-containing flame-retardant agent, a preparation method and application thereof, and especially application of the flame-retardant agent in epoxy resin. BACKGROUND

[0002] Hexachlorocyclotriphosphazene can react with different nucleophiles to generate a variety of derivatives with different properties and functions due to the presence of six active chlorine atoms. These compounds are widely used as flame retardants due to the presence of efficient flame-retardant elements phosphorus and nitrogen and good synergistic flame-retardant effect. Cyclotriphosphazene derivatives decompose to generate non-flammable gases such as NH3 and N2 when heated, which can dilute the concentration of combustible and supporting gases near the material surface and absorb a large amount of energy required for the reaction, thereby reducing the material surface temperature. At the same time, cyclotriphosphazene derivatives generate compounds containing P-O bonds or P-O-C bonds during the decomposition process. These compounds can catalyze the further degradation of the matrix and promote the formation of a dense and stable carbonized layer on the material surface, while isolating the outside air and flame from the inside of the matrix and inhibiting the dehydration, cracking and oxidation reactions in the matrix. Therefore, hexachlorocyclotriphosphazene is often used as a flame-retardant material. Another common flame-retardant material is a silicon-containing flame-retardant agent, which is also called a "green" flame-retardant agent because it does not generate substances harmful to the environment and human health after thermal decomposition. Due to the low surface energy of silicon atoms, organic silicon flame-retardant agents can migrate to the surface of the matrix during the initial stage of combustion, and then form stable inorganic compounds such as SiO2 and SiC. These inorganic compounds cover the surface of the matrix to form a dense and stable silicon-containing heat-insulating carbon layer. This protective layer can effectively block the outward release of combustible components and the inward transmission of external oxygen and heat, thereby achieving the purpose of preventing or delaying the spread of flames.

[0003] The activity of chlorine atoms in hexachlorocyclotriphosphazene makes chlorine easy to be replaced by nucleophiles, so that a series of phosphazene compounds can be prepared by side-group derivatization. The modified cyclotriphosphazene containing silicon elements prepared by combining hexachlorocyclotriphosphazene with silicon is one of such compounds. The presence of silicon elements enables the phosphazene compound to have flame-retardant properties, as well as far-reaching application prospects in surface modification, fabric finishing and organic-inorganic hybrid modification fields. However, the existing cyclotriphosphazene derivatives containing silicon elements still have problems such as complex synthesis reaction and poor flame-retardant effect.

[0004] CN102250147A discloses a preparation method and application of a silicon functional group-containing cyclotriphosphazene, and adds the cyclotriphosphazene as a synergistic agent to a flame-retardant polypropylene system, and simultaneously as a toughening agent and a flame retardant to endow the polypropylene with good comprehensive performance, but the highest limiting oxygen index is only 26.5%, the flame-retardant efficiency needs to be further enhanced, and the synthesis steps are relatively complex.

[0005] CN114805442A discloses a preparation method of a siloxane cyclotriphosphazene with a Schiff base structure, which is prepared through a nucleophilic substitution reaction of hexachlorocyclotriphosphazene and p-hydroxybenzaldehyde and a Schiff base reaction of an aldehyde group and an amino group, has the advantages of high reaction degree, easy separation of the product, and short reaction time, but still needs to be reacted in an organic solvent, which increases the use cost and the difficulty of post-processing. Moreover, the siloxane cyclotriphosphazene is not applied in a polymer material, and thus the flame-retardant effect needs to be further explored.

[0006] SUMMARY

[0007] The present application aims to solve the problems of complex synthesis reaction, poor flame-retardant effect, etc. of the existing cyclotriphosphazene derivative containing silicon elements, and provides a preparation method and application of a novel and efficient cyclotriphosphazene-based silicon-containing flame retardant. The cyclotriphosphazene-based silicon-containing flame retardant of the present application combines the structures of silicon-containing compounds and cyclotriphosphazene, has good thermal stability, high char yield, and excellent flame-retardant effect.

[0008] To solve the problems of the prior art, the present application provides the following technical solutions:

[0009] In one aspect, the present application provides a cyclotriphosphazene-based silicon-containing flame retardant, the molecular structure formula of which is shown as formula (I):

[0010]

[0011] (I)

[0012] wherein X1-X6 are independently selected from or a vinyl group, and at least one of X1-X6 is ;

[0013] R1 is selected from H or a methoxy group; R2, R3, R4 are independently selected from a methyl group, an ethyl group, an isopropyl group, an isobutyl group, a tert-butyl group or a phenyl group.

[0014] In different raw material ratios, different numbers of vinyl groups in X1-X6 are substituted, and different cyclotriphosphazene-based silicon-containing flame retardants are obtained accordingly. In one example, all the vinyl groups in X1-X6 are substituted, and the molecular structure formula of the obtained cyclotriphosphazene-based silicon-containing flame retardant is shown as formula (I-1):

[0015] (I-1)

[0016] wherein R1 is selected from H or methoxy; R2, R3, R4 are independently selected from methyl, ethyl, isopropyl, isobutyl, tert-butyl or phenyl.

[0017] Further, the initial thermal decomposition temperature of the cyclotriphosphazene-based silicon-containing flame retardant is higher than 350 ℃, preferably higher than 360 ℃, and in one example, the initial thermal decomposition temperature is up to 365 ℃.

[0018] Further, the carbon residue rate of the cyclotriphosphazene-based silicon-containing flame retardant is higher than 35%, preferably higher than 36%, and in one example, the carbon residue rate can reach 36.84%.

[0019] In another aspect, the present application provides a preparation method of a cyclotriphosphazene-based silicon-containing flame retardant, comprising the following steps:

[0020] (1) generating an intermediate by a nucleophilic substitution reaction between hexachlorocyclotriphosphazene and an allyl-containing phenolic compound;

[0021] (2) adding Karstedt catalyst under nitrogen atmosphere, and obtaining the cyclotriphosphazene-based silicon-containing flame retardant by a hydrosilylation reaction between the intermediate and a silane compound.

[0022] Further, in step (1), the allyl-containing phenolic compound is one or a combination of eugenol and p-allylphenol.

[0023] Further, in step (1), the reaction is carried out at 40-70 ℃ for 48 hours by using dioxane as an organic solvent and adding a catalyst and an acid-binding agent.

[0024] Further, in step (1), the molar ratio of hexachlorocyclotriphosphazene to the allyl-containing phenolic compound is (2-3):20.

[0025] Further, in step (1), the amount of the organic solvent is 1 g of raw material: 4-6 mL of solvent, and specifically, 1 g of hexachlorocyclotriphosphazene or the allyl-containing phenolic compound is dissolved in 4-6 mL of solvent; preferably, the amount of the organic solvent is 1 g of raw material: 5 mL of solvent.

[0026] Further, in step (1), the mass of the catalyst is 0.5-0.6 wt% of the mass of the allyl-containing phenolic compound.

[0027] Further, in step (1), the catalyst is a phase transfer catalyst, including one or a combination of tetrabutylammonium bromide, benzyltriethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, and in one example, the catalyst is tetrabutylammonium bromide.

[0028] Further, the acid-binding agent includes one or a combination of sodium hydroxide, potassium carbonate, sodium carbonate, triethylamine, and pyridine.

[0029] Further, the molar ratio of the acid-binding agent to the double bond compound is 1:1, where the double bond compound refers to the allyl-containing phenolic compound. The acid-binding agent reacts with the chlorine atoms on the hexachlorocyclotriphosphazene to form sodium chloride precipitate.

[0030] Further, in step (2), the silane compound is one or a combination of triethylsilane, triisopropylsilane, triisobutylsilane, triphenylsilane, diphenylmethylsilane, t-butyldiphenylsilane, t-butyldimethylsilane, or dimethylphenylsilane.

[0031] Further, in step (2), the reaction temperature is 80-100 ℃, and the reaction time is 8-12 hours.

[0032] Further, in step (2), the molar ratio of the silane compound to the intermediate is 1-10:1. Different molar ratios of the silane compound to the intermediate can result in different numbers of vinyl groups in X1-X6 being replaced by , and different cyclotriphosphazene-based silicon-containing flame retardants are obtained accordingly, such as:

[0033] In one example, when the molar ratio of the silane compound to the intermediate is 1:1, only one of the vinyl groups in X1-X6 is replaced by , and the others are all vinyl groups.

[0034] Similarly, in another example, when the molar ratio of the silane compound to the intermediate is 2:1, two of the vinyl groups in X1-X6 are replaced by , and the others are all vinyl groups. When the molar ratio of the silane compound to the intermediate is 3:1, 4:1, 5:1, 6:1, and so on.

[0035] In another example, an excess amount of the silane compound is used to react with the intermediate, i.e., the molar ratio of the two is higher than 6:1, such as 6.6:1. In this case, the reaction is fully complete, and all the vinyl groups are replaced, and X1-X6 are all , and the obtained cyclotriphosphazene-based silicon-containing flame retardant has a molecular structure as shown in the above formula (I-1).

[0036] Further, the yield of the preparation method of the cyclotriphosphazene-based silicon-containing flame retardant is greater than 80%, preferably greater than 82%, and more preferably 82% to 93%. In another aspect, the present application provides the use of the cyclotriphosphazene-based silicon-containing flame retardant in the preparation of a flame-retardant epoxy resin.

[0037] In another aspect, the present application provides a preparation method of a flame-retardant epoxy resin, comprising the following steps: stirring the cyclotriphosphazene-based silicon-containing flame retardant prepared above or according to any of the above-mentioned methods with an epoxy resin prepolymer to form a homogeneous liquid, then adding a curing agent and stirring until dissolved, and then performing a curing treatment, and cooling to obtain the flame-retardant epoxy resin.

[0038] Further, the cyclotriphosphazene-based silicon-containing flame retardant and the epoxy resin prepolymer are stirred at 110 to 130°C for 15 to 30 minutes to form a homogeneous liquid.

[0039] Further, the curing treatment comprises pouring the homogeneous liquid into a mold after adding the curing agent, placing the mold in a drying oven, and curing at 120°C, 140°C, 160°C, and 180°C for 1 to 2 hours each.

[0040] Further, the mass ratio of the epoxy resin prepolymer, the curing agent, and the cyclotriphosphazene-based silicon-containing flame retardant is 100:25:0 to 12.

[0041] Further, the preparation method of the flame-retardant epoxy resin comprises the following steps:

[0042] The prepared cyclotriphosphazene-based silicon-containing flame retardant and the epoxy resin prepolymer are stirred at 110°C for 30 minutes to form a homogeneous liquid, then a curing agent is added and stirred until dissolved, and then quickly poured into a preheated stainless steel mold, and then the mold is placed in a forced air drying oven and cured at 120°C, 140°C, 160°C, and 180°C for 1 to 2 hours each, and the mass ratio of the epoxy resin prepolymer, the curing agent, and the cyclotriphosphazene-based silicon-containing flame retardant is 100:25:0 to 12, and the flame-retardant epoxy resin is obtained after cooling.

[0043] Further, the epoxy resin is one or a combination of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, or alicyclic epoxy resin.

[0044] Further, the curing agent is one or a combination of anhydride, polyamine, dicyandiamide, or phenolic resin.

[0045] In another aspect, the present application provides a flame-retardant epoxy resin.

[0046] Further, the limiting oxygen index of the flame-retardant epoxy resin is greater than 29%.

[0047] Further, the limiting oxygen index of the flame-retardant epoxy resin is 29% to 35%, preferably 29% to 34%, and more preferably 29% to 33.5%.

[0048] Further, the vertical burning grade of the flame-retardant epoxy resin is V-0 or above.

[0049] Further, the vertical burning test time of the flame-retardant epoxy resin is less than 10+7 s.

[0050] Further, the initial decomposition temperature of the flame-retardant epoxy resin is less than 360 ℃, preferably 350 ℃ to 360 ℃, and more preferably 356 ± 2 ℃.

[0051] Further, the residual carbon content of the flame-retardant epoxy resin is higher than 15%, preferably higher than 20%, and more preferably 20% to 25%, and more preferably 20% to 23%.

[0052] In another aspect, the present application provides the use of the flame-retardant epoxy resin in the field of flame-retardant materials, including the flame-retardant epoxy resin as a flame-retardant material, or for preparing other flame-retardant epoxy resin compositions.

[0053] Compared with the prior art, the present application has the following beneficial effects:

[0054] 1. The cyclotriphosphazene-based silicon-containing flame retardant can exert the synergistic flame-retardant effect of phosphorus-nitrogen-silicon elements, and the flame-retardant epoxy resin prepared by applying the cyclotriphosphazene-based silicon-containing flame retardant to the epoxy resin has good flame-retardant effect.

[0055] 2. The flame retardant has good compatibility with the epoxy resin, is easy to disperse in the resin matrix, and improves the stability of the resin cured product in processing.

[0056] 3. In the synthesis step (2) of the flame retardant, a solvent-free synthesis reaction is used, the operation is simple, the yield of the obtained product is higher than 80%, and the post-treatment is simple. BRIEF DESCRIPTION OF DRAWINGS

[0057] The preferred mode of the present application will be further described in detail below with reference to the accompanying drawings.

[0058] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the intermediate prepared for Example 1 of the present application;

[0059] Figure 2 The nuclear magnetic resonance hydrogen spectrum of the cyclotriphosphazene-based silicon-containing flame retardant prepared for Example 2 of the present application;

[0060] Figure 3 The thermogravimetric curve of the cyclotriphosphazene-based silicon-containing flame retardant prepared for Example 2 of the present application. DETAILED DESCRIPTION

[0061] The present application is further illustrated by the following examples and figures, but is not limited in any way by the examples, any variations or substitutions made based on the present application are within the scope of the present application. It is noted that the examples of the present application use excess silane compound and intermediates to fully react to obtain the cyclophosphazene-based silicon-containing flame retardant with all vinyl groups substituted, but those skilled in the art can know that when the molar ratio of silane compound to intermediate is changed, different amounts of products with substituted vinyl groups will be obtained, which are not described one by one in the present application.

[0062] Example 1

[0063] The preparation method of one of the intermediates of the cyclophosphazene-based silicon-containing flame retardant described in the present application specifically includes the following steps:

[0064] First, 49.2 g (0.3 mol) of eugenol is added to a three-necked flask equipped with mechanical stirring and nitrogen, 250 mL of dioxane is added to stir and dissolve, then 0.26 g of tetrabutylammonium bromide is added and stirred at room temperature for 30 minutes. Then 11.73 g (0.3 mol) of sodium hydroxide is added to the flask, and the temperature is raised to 40 °C for 3 hours. Then 15.62 g (0.045 mol) of hexachlorocyclotriphosphazene is dissolved in 80 mL of dioxane, and the solution is added dropwise to the reaction system, and the temperature is raised to 70 °C and stirred for 48 hours. After the reaction is completed, the solution is cooled to room temperature and the generated solid is filtered off, then the filtrate is concentrated by rotary evaporation to remove the solvent, and the crude product is washed with ethanol three times to obtain a white solid powder with a yield of 79%, which is the intermediate, and its nuclear magnetic resonance hydrogen spectrum is shown in Figure 1. The molecular structure of the intermediate is shown below, and is named HEP. Figure 1

[0065] The reaction equation is as follows:

[0066]

[0067] Example 2

[0068] The preparation method of the cyclophosphazene-based silicon-containing flame retardant described in the present application specifically includes the following steps:

[0069] ​​5 mmol of the intermediate prepared in Example 1 was weighed into a three-necked flask equipped with magnetic stirring and nitrogen, then 30 mmol of triethylsilane was added, 10 μL of Karstedt catalyst was added, and the temperature was raised to 80 °C for 8 hours. After the reaction was completed, the solution was dried in a vacuum oven at 120 °C overnight to obtain a tan solid, and the yield was 92.2%. The product was a cyclotriphosphazene-based silicon-containing flame retardant, and its 1H NMR spectrum is shown in Figure 2 .

[0070] The reaction equation is as follows:

[0071]

[0072] The thermal gravimetric curve of the cyclotriphosphazene-based silicon-containing flame retardant of the embodiment of the present application is shown in Figure 3 From the figure, it can be seen that the initial thermal decomposition temperature is high, reaching 365 °C. The carbon residue rate can reach 36.84%, showing strong carbon formation ability and thermal stability.

[0073] Example 3

[0074] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant comprises the following steps:

[0075] 5 mmol of the intermediate prepared in Example 1 was weighed into a three-necked flask equipped with magnetic stirring and nitrogen, then 35 mmol of triisopropylsilane was added, 10 μL of Karstedt catalyst was added, and the temperature was raised to 85 °C for 10 hours. After the reaction was completed, the solution was dried in a vacuum oven at 120 °C overnight to obtain a tan solid, and the yield was 89.3%.

[0076] Example 4

[0077] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant comprises the following steps:

[0078] 5 mmol of the intermediate prepared in Example 1 was weighed into a three-necked flask equipped with magnetic stirring and nitrogen, then 40 mmol of triisobutylsilane was added, 10 μL of Karstedt catalyst was added, and the temperature was raised to 90 °C for 9 hours. After the reaction was completed, the solution was dried in a vacuum oven at 120 °C overnight to obtain a tan solid, and the yield was 90.1%.

[0079] Example 5

[0080] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant comprises the following steps:

[0081] Take 5 mmol of the intermediate prepared in Example 1 into a three-necked flask equipped with magnetic stirring and nitrogen, then add 35 mmol of tert-butyldimethylsilane, add 10 μL of Karstedt catalyst, and heat to 85 °C for 11 hours. After the reaction is completed, dry the solution in a vacuum oven at 120 °C overnight to obtain a tan solid with a yield of 88.4%.

[0082] Example 6

[0083] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant according to the present application specifically comprises the following steps:

[0084] Take 5 mmol of the intermediate prepared in Example 1 into a three-necked flask equipped with magnetic stirring and nitrogen, then add 40 mmol of dimethylphenylsilane, add 10 μL of Karstedt catalyst, and heat to 95 °C for 12 hours. After the reaction is completed, dry the solution in a vacuum oven at 120 °C overnight to obtain a light brown solid with a yield of 85.0%.

[0085] Example 7

[0086] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant according to the present application specifically comprises the following steps:

[0087] Take 5 mmol of the intermediate prepared in Example 1 into a three-necked flask equipped with magnetic stirring and nitrogen, then add 45 mmol of diphenylmethylsilane, add 10 μL of Karstedt catalyst, and heat to 95 °C for 12 hours. After the reaction is completed, dry the solution in a vacuum oven at 120 °C overnight to obtain a light brown solid with a yield of 86.9%.

[0088] Example 8

[0089] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant according to the present application specifically comprises the following steps:

[0090] Take 5 mmol of the intermediate prepared in Example 1 into a three-necked flask equipped with magnetic stirring and nitrogen, then add 50 mmol of tert-butyldiphenylsilane, add 10 μL of Karstedt catalyst, and heat to 95 °C for 12 hours. After the reaction is completed, dry the solution in a vacuum oven at 120 °C overnight to obtain a light brown solid with a yield of 83.2%.

[0091] Example 9

[0092] The preparation method of the cyclotriphosphazene-based silicon-containing flame retardant according to the present application specifically comprises the following steps:

[0093] Take 5 mmol of the intermediate prepared in Example 1 into a three-necked flask equipped with magnetic stirring and nitrogen, then add 50 mmol of triphenylsilane, and 10 μL of Karstedt catalyst, and heat to 100 °C for 12 hours. After the reaction is completed, dry the solution in a vacuum oven at 120 °C overnight to obtain a light brown solid with a yield of 82.4%.

[0094] Example 10

[0095] The preparation method of the flame-retardant epoxy resin described in the present application comprises the following steps:

[0096] The cyclotriphosphazene-based silicon-containing flame retardant 4 g prepared in Example 2 is stirred with 100 g of an epoxy resin prepolymer at 110 °C for 30 minutes to form a uniform liquid, then 25 g of a curing agent (4,4'-diaminodiphenylmethane) is added and stirred until dissolved, then quickly poured into a preheated stainless steel mold, and then the mold is placed in a forced air drying oven and cured at 120 °C, 140 °C, 160 °C, and 180 °C for 2 hours each, and after cooling, a flame-retardant epoxy resin sample is obtained.

[0097] Example 11

[0098] The preparation method of the flame-retardant epoxy resin described in the present application comprises the following steps:

[0099] The cyclotriphosphazene-based silicon-containing flame retardant 8 g prepared in Example 2 is stirred with 100 g of an epoxy resin prepolymer at 110 °C for 30 minutes to form a uniform liquid, then 25 g of a curing agent (4,4'-diaminodiphenylmethane) is added and stirred until dissolved, then quickly poured into a preheated stainless steel mold, and then the mold is placed in a forced air drying oven and cured at 120 °C, 140 °C, 160 °C, and 180 °C for 2 hours each, and after cooling, a flame-retardant epoxy resin sample is obtained.

[0100] Example 12

[0101] The preparation method of the flame-retardant epoxy resin described in the present application comprises the following steps:

[0102] The cyclotriphosphazene-based silicon-containing flame retardant 12 g prepared in Example 2 is stirred with 100 g of an epoxy resin prepolymer at 110 °C for 30 minutes to form a uniform liquid, then 25 g of a curing agent (4,4'-diaminodiphenylmethane) is added and stirred until dissolved, then quickly poured into a preheated stainless steel mold, and then the mold is placed in a forced air drying oven and cured at 120 °C, 140 °C, 160 °C, and 180 °C for 2 hours each, and after cooling, a flame-retardant epoxy resin sample is obtained.

[0103] Comparative Example 1

[0104] The preparation method of the flame-retardant epoxy resin comprises the following steps:

[0105] Take 20 g of the epoxy resin prepolymer and 5 g of the curing agent (4,4'-diaminodiphenyl methane) to mix at 90 ℃ to form a uniform liquid, pour it into a preheated stainless steel mold, and then put the mold into a blast drying oven, and cure at 120 ℃, 140 ℃, 160 ℃ and 180 ℃ for 2 hours respectively, and then cool to obtain an epoxy resin sample for further comparative test.

[0106] Test example

[0107] The flame-retardant epoxy resin prepared by adding the cyclotriphosphazene-based silicon-containing flame retardant to Examples 10-12 and the flame-retardant epoxy resin of the comparative example are tested for flame-retardant performance, and the performance test data are shown in Table 1:

[0108] Table 1 Flame-retardant performance test results of the flame-retardant epoxy resin

[0109] Component name Example 10 Example 11 Example 12 Comparative Example 1 Flame retardant 4 g 8 g 12 g 0 Vertical burn rating V-1 V-0 V-0 No rating Limiting oxygen index (%) 29.4±0.5 33.2±0.2 33.0±0.4 26.8±0.2 Vertical burn test time t1 + t2 (s) 10+7 2+1 3+1 Sustained burning Initial decomposition temperature (°C) 356.8 356.3 357.3 372.5 Residual carbon amount (%) 20.6 21.3 22.3 12.6

[0110] As can be seen from the comparison of Examples 10-12 and Comparative Example 1 (shown in Table 1), the addition of the cyclotriphosphazene-based silicon-containing flame retardant of the present application (Example 2) can significantly improve the limiting oxygen index and vertical burning grade of the epoxy resin sample, and the amount of residual carbon is also increased, wherein the limiting oxygen index of the flame-retardant epoxy resin is greater than 29%, as high as 35%; the vertical burning grade is V-0 or above, the vertical burning test time is less than 10+7 s, the initial decomposition temperature is less than 360 ℃, the amount of residual carbon is higher than 15%, even higher than 20%, as high as 23%. That is, the flame retardant modified epoxy resin of the present application can significantly improve the flame-retardant performance of the epoxy resin.

[0111] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A cyclotriphosphazene-based silicon-containing flame retardant, having a molecular structure as shown in formula (I-1): wherein R 1 is methoxy; R 2, R 3 and R 4 are independently selected from methyl, ethyl, isopropyl, isobutyl, tert-butyl or phenyl. （I-1）； comprising the following steps:

2. The process for the preparation of cyclotriphosphazene-based silicon-containing flame retardants according to claim 1, characterized in that, (2) under a nitrogen atmosphere, adding Karstedt catalyst to obtain the cyclotriphosphazene-based silicon-containing flame retardant through a silicon-hydrogen addition reaction between the intermediate and a silane compound, wherein the silane compound is triethylsilane, triisopropylsilane, triisobutylsilane, triphenylsilane, tert-butyldiphenylsilane, tert-butyldimethylsilane or dimethylphenylsilane, and the molar ratio of the silane compound to the intermediate is 6:

1. (1) An intermediate is generated through a nucleophilic substitution reaction between hexachlorocyclotriphosphazene and an allyl-containing phenolic compound. The allyl-containing phenolic compound is eugenol; In step (1), the nucleophilic substitution reaction is carried out in dioxane as an organic solvent, and a catalyst and an acid-binding agent are added, and the reaction is carried out at 40-70 ℃ for 48 hours to obtain the intermediate; 3. The method of claim 2, wherein: The molar ratio of the hexachlorocyclotriphosphazene to the allyl-containing phenolic compound is (2-3):20; The amount of the organic solvent is 4-6 mL per 1 g of the hexachlorocyclotriphosphazene or the allyl-containing phenolic compound; The mass of the catalyst is 0.5-0.6 wt% of the mass of the allyl-containing phenolic compound; The catalyst is a phase transfer catalyst selected from one or a combination of tetrabutylammonium bromide, benzyltriethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, trioctylmethylammonium chloride and dodecyltrimethylammonium chloride; The acid-binding agent is selected from one or a combination of sodium hydroxide, potassium carbonate, sodium carbonate, triethylamine and pyridine, and the molar ratio of the acid-binding agent to the allyl-containing phenolic compound is 1:

1. In step (2), the reaction temperature is 80-100 ℃, and the reaction time is 8-12 hours.

4. The method of claim 2, wherein: 5.Use of the cyclotriphosphazene-based silicon-containing flame retardant of claim 1 in the preparation of a flame-retardant epoxy resin. The preparation method of the flame-retardant epoxy resin comprises the following steps:

6. A process for the preparation of a flame retardant epoxy resin characterized by: The cyclotriphosphazene-based silicon-containing flame retardant of claim 1 is stirred with an epoxy resin prepolymer to form a uniform liquid, then a curing agent is added and stirred until dissolved, and then a curing treatment is performed, and after cooling, a flame-retardant epoxy resin is obtained. The epoxy resin prepolymer is one or a combination of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin or alicyclic epoxy resin; and the curing agent is one or a combination of acid anhydride, polyamine, dicyandiamide or phenolic resin.

7. The method for preparing the flame-retardant epoxy resin according to claim 6, characterized in that: The cyclotriphosphazene-based silicon-containing flame retardant and the epoxy resin prepolymer are stirred at 110-130 ℃ for 15-30 minutes to form a uniform liquid; The curing treatment comprises pouring the uniform liquid into a mold after adding the curing agent, and placing the mold in a drying oven, and curing at 120 ℃, 140 ℃, 160 ℃ and 180 ℃ for 1-2 hours each time; The mass ratio of the epoxy resin prepolymer, the curing agent and the cyclotriphosphazene-based silicon-containing flame retardant is 100:25:

12. 8.A flame-retardant epoxy resin prepared according to the method of claim 6 or 7. The limiting oxygen index of the flame-retardant epoxy resin is greater than 29%.

9. The flame retardant epoxy resin of claim 8, wherein: ​

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