Preparation of phosphorus, nitrogen and silicon macromolecular flame retardant and application of phosphorus, nitrogen and silicon macromolecular flame retardant in epoxy resin

Abstract

The invention belongs to the technical field of flame-retardant materials, and particularly relates to preparation of a phosphorus, nitrogen and silicon macromolecular flame retardant and application of the phosphorus, nitrogen and silicon macromolecular flame retardant in epoxy resin. The preparation method comprises the following steps: firstly, carrying out substitution reaction on chlorosilane and syringaldehyde or vanillic aldehyde to synthesize a silicon-containing intermediate, then carrying out Schiff base reaction on the silicon-containing intermediate and an amine compound, and finally carrying out addition reaction on the silicon-containing intermediate and a phosphorus-containing compound to prepare the phosphorus, nitrogen and silicon macromolecular flame retardant. The flame retardant has a good flame-retardant effect, can be used for preparing flame-retardant epoxy resin, can effectively improve the limit oxygen index and the vertical combustion grade of the epoxy resin, and can endow the epoxy resin with good transparency and molten drop resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardant materials, and particularly relates to the preparation of a phosphorus, nitrogen, silicon macromolecular flame retardant and its application in epoxy resin. Background Art

[0002] With the development of society, high molecular polymers are applied in various fields of production and life. However, due to their flammability, most high molecular polymers pose a potential fire threat, seriously affecting human production and life. Therefore, the flame retardant modification of high molecular polymers has become the focus of current research.

[0003] Currently, the most commonly used method for flame retardancy of high molecular polymers is to add flame retardants containing flame retardant elements. Flame retardants are functional additives that endow high molecular polymers with flame retardant properties. According to the usage method, they are divided into additive flame retardants and reactive flame retardants. However, some flame retardants will produce toxic and harmful gases during combustion, thus causing great harm to human health and affecting the environment.

[0004] Phosphorus, nitrogen, silicon synergistic flame retardants not only combine the high flame retardant performance of phosphorus-based flame retardants, but also combine the advantages of low toxicity of nitrogen-based flame retardants and high heat resistance of silicon-based flame retardants. Such flame retardants not only improve the flame retardant efficiency of high molecular polymer products, but also reduce the impact of their combustion on the environment. However, there are still many deficiencies in current phosphorus, nitrogen, silicon flame retardants, such as poor dispersibility between the flame retardant and polymer resin, which brings many troubles to practical applications. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of a phosphorus, nitrogen, silicon macromolecular flame retardant and its application as a flame retardant in epoxy resin. The preparation method of this macromolecular flame retardant is as follows: First, a silicon-containing intermediate 1 is synthesized by the substitution reaction of chlorosilane with syringaldehyde or vanillin. Then, the silicon-containing intermediate 1 reacts with an amine compound through a Schiff base reaction to synthesize an intermediate 2 containing nitrogen and silicon elements. Finally, the intermediate 2 containing nitrogen and silicon elements reacts with a phosphorus-containing compound through an addition reaction to obtain the target product, the phosphorus, nitrogen, silicon macromolecular flame retardant. Further, the macromolecular flame retardant prepared by the present invention is applied to epoxy resin.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions.

[0007] The preparation method of the phosphorus, nitrogen, silicon macromolecular flame retardant specifically includes the following steps:

[0008] S1: Prepare raw materials. Prepare syringaldehyde, vanillin, chlorosilanes (dichlorodiphenylsilane, tert-butyldimethylchlorosilane), phosphorus-containing compounds (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or diphenylphosphine oxide), amine compounds (4,4'-diaminodiphenylmethane, p-phenylenediamine, 9,9-bis(4-aminophenyl)fluorene or 3,5-diamino-1,2,4-triazole), dichloromethane, triethylamine, N,N-dimethylformamide, tetrahydrofuran, deionized water, and set aside.

[0009] S2: Prepare Intermediate 1: A substitution reaction occurs between chlorosilane and syringaldehyde or vanillin to synthesize silicon-containing Intermediate 1;

[0010] Preheat the oil bath of the magnetic stirrer to 20 - 25°C in advance. Add 0.04 - 0.12 mol (7.28 - 21.84 g) of syringaldehyde or vanillin, 0.04 - 0.12 mol (4.04 - 12.12 g) of triethylamine, and 100 - 150 ml of dichloromethane into a three-necked flask in sequence. Place it in the oil bath of the magnetic stirrer. Then weigh 0.02 - 0.04 mol (5.06 - 10.12 g) of chlorosilane and place it in a beaker. Add 20 - 40 ml of dichloromethane to dissolve it fully. Slowly drip it into the above flask using a constant pressure dropping funnel. Set up a condensing reflux device and drip it under a nitrogen atmosphere for 0.5 - 1 h. After dripping, slowly raise the temperature of the oil bath to 40 - 45°C. After the temperature rise is completed, keep the temperature constant and react for 3 - 4 h. After the reaction is completed, turn off the cooling water and nitrogen. After cooling to room temperature, filter it by a Buchner funnel and a vacuum pump to remove the triethylamine hydrochloride generated by the reaction. Pour the filtrate into an extraction bottle, pour in excessive deionized water, shake it violently, let it stand for stratification, take out the lower organic layer, and repeat the above operation for three times. After washing, pour the organic layer into a distillation flask and perform rotary evaporation at 50°C. After rotary evaporation is completed, pour it into a beaker and place it in a vacuum drying oven with the temperature set at 65°C and dry it for 12 h to obtain a yellowish-brown solid (SASi), which is Intermediate 1. Grind it into powder and set it aside for later use.

[0011] Among them, the chlorosilane is: dichlorodiphenylsilane, tert-butyldimethylchlorosilane.

[0012] S3: Prepare Intermediate 2. A Schiff base reaction occurs between the silicon-containing Intermediate 1 and the amine compound to synthesize nitrogen- and silicon-containing Intermediate 2;

[0013] Before the experiment, the intermediate 1 was dried in an oven overnight. 0.05 - 0.1 mol (27.2 - 54.4 g) of SASi and 150 ml of N,N - dimethylformamide were added to a three - necked flask in sequence, and it was placed in an oil bath with magnetic stirring at room temperature. Stir to dissolve SASi completely. Weigh 0.01 - 0.3 mol (15 - 45 g) of an amine compound and place it in a beaker. Add 50 - 100 ml of N,N - dimethylformamide to dissolve it completely. Then use a constant - pressure dropping funnel to slowly add it to the above - mentioned flask. Set up a condensing reflux device. After the dropping is completed, raise the temperature to 90 - 95 °C and react for 6 - 8 h.

[0014] Among them, the amine compound is: 4,4’ - diamino - diphenylmethane, p - phenylenediamine, 9,9 - bis(4 - aminophenyl)fluorene or 3,5 - diamino - 1,2,4 - triazole.

[0015] S4: The intermediate 2 containing nitrogen and silicon elements undergoes an addition reaction with the phosphorus - containing compound to obtain the target product;

[0016] After the reaction is completed, add 0.1 - 0.2 mol (21.62 - 43.24 g) of the phosphorus - containing compound, which was previously dissolved in 50 - 100 ml of N,N - dimethylformamide, to the above S3 system. Raise the temperature to 100 - 110 °C and react for 20 - 24 h. After the reaction ends, cool the system to room temperature. Prepare a large amount of deionized water for standby. Pour the product cooled to room temperature into a large amount of deionized water and stir continuously with a glass rod. After stirring, a large amount of white solid is formed. Use a vacuum pump and a Buchner funnel for suction filtration. Dissolve the solid after suction filtration in tetrahydrofuran, and then wash it with deionized water until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90 °C and dry it to constant weight to obtain a light - yellow powder of phosphorus, nitrogen, and silicon macromolecular flame retardant, namely PDSASi.

[0017] Among them, the phosphorus - containing compound is: 9,10 - dihydro - 9 - oxa - 10 - phosphaphenanthrene - 10 - oxide (DOPO) or diphenylphosphine oxide.

[0018] The preferred flame - retardant structural formula of the phosphorus, nitrogen, and silicon macromolecular flame retardant prepared by the above method is as follows:

[0019]

[0020] n = 1 - 50.

[0021] As a further scheme of the present invention: Pour the reaction product cooled to room temperature into a large amount of deionized water, and while pouring, stir rapidly with a glass rod. The solution precipitates a yellow - white solid. Stir for 20 - 30 min to ensure that no remaining product precipitates before performing suction filtration.

[0022] The present invention also proposes the application of phosphorus, nitrogen, and silicon macromolecular flame retardants. The prepared PDSASi is ground fine using a mortar, and then epoxy resin (EP) is poured into a beaker and preheated in an oil bath at 100°C. PDSASi is added in a proportion of 2% - 8%. Then, it is stirred with a rotor for 2 h to make it evenly mixed. After stirring is completed, the corresponding amount of 4,4'-diaminodiphenylmethane is added to the beaker and stirred with a glass rod for 30 s to make it evenly mixed. After stirring is completed, the beaker is taken out, and the product obtained after stirring is poured into a preheated silica gel template and placed in a vacuum oven. Curing is completed according to the curing sequence of 100°C / 2 h and 120°C / 2 h. After curing is completed, the obtained composite material is taken out of the oven and naturally cooled to room temperature to obtain the EP / PDSASi flame retardant composite material.

[0023] The beneficial effects of the present invention are as follows:

[0024] The macromolecular flame retardant prepared by the present invention integrates phosphorus, nitrogen, and silicon elements, can play a better synergistic flame retardant effect of multiple elements, and can effectively improve the dispersibility of the flame retardant in the matrix. When applied to epoxy resin, it can effectively improve the oxygen index and vertical burning grade of epoxy resin, and at the same time endow epoxy resin with good transparency and anti-dripping properties. Description of the Drawings

[0025] Figure 1 It is a schematic route diagram of the preparation method of the phosphorus, nitrogen, and silicon macromolecular flame retardant of the present invention.

[0026] Figure 2 The FT-IR diagrams of the raw materials, intermediates, and the macromolecular flame retardant PDSASi in Example 1 are shown.

[0027] Figure 3 The physical digital pictures of the epoxy resin composite materials obtained in Examples 1 - 4 and Comparative Example 1 are shown.

[0028] Figure 4 The UL-94 and LOI test result diagrams of the epoxy resin composite materials obtained in Examples 1 - 4 and Comparative Example 1 are shown. Detailed Embodiments

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the examples. Obviously, the described embodiments are only a part of the examples of the present invention, rather than all the examples.

[0030] Example 1

[0031] Referring to Figure 1 , the synthesis method of the phosphorus, nitrogen, and silicon macromolecular flame retardant includes the following steps:

[0032] Preparation of Intermediate: Heat the oil bath with magnetic stirring to 25 °C in advance. Add 0.04 mol (7.28 g) of syringaldehyde, 0.04 mol (4.04 g) of triethylamine and 100 ml of dichloromethane into a 500 ml three-necked flask in sequence, and place it in the oil bath with magnetic stirring. Weigh 0.02 mol (5.06 g) of dichlorodiphenylsilane and put it into a 250 ml beaker, add 20 ml of dichloromethane to dissolve it fully, and use a constant pressure dropping funnel to add it dropwise to the above flask. Set up a condensation reflux device. The dropping time under nitrogen atmosphere is 0.5 h. After the dropping is completed, raise the temperature of the oil bath to 40 °C and react for 3 h. After the reaction is completed, turn off the cooling water and nitrogen. After cooling to room temperature, perform suction filtration to remove the triethylamine hydrochloride generated in the reaction. Pour the filtrate into an extraction bottle, pour in excessive deionized water, shake and separate the layers, take out the organic layer, and repeat the above operation for three times. After washing, pour the organic layer into a distillation flask, perform rotary evaporation at 50 °C. After the rotary evaporation is completed, pour it into a 250 ml beaker, put it into a vacuum drying oven, and dry it at 65 °C for 12 h to obtain a brown-yellow solid (SASi), and grind it into powder for standby.

[0033] Preparation of PDSASi: Dry the intermediate SASi in a drying oven overnight before the experiment. Add 27 g of SASi and 150 ml of N,N-dimethylformamide to a 500 ml three-necked flask in sequence, and place it in an oil bath with magnetic stirring at room temperature, and stir to dissolve SASi fully. Weigh 15 g of 4,4'-diaminodiphenylmethane and put it into a 250 ml beaker, add 50 ml of N,N-dimethylformamide to dissolve it fully, and use a constant pressure dropping funnel to slowly add it to the above flask. Set up a condensation reflux device. After the dropping is completed, raise the temperature to 90 °C and react for 6 h. After the reaction is completed, add 21.62 g of DOPO, which has been previously dissolved in 50 ml of N,N-dimethylformamide, to the above system, raise the temperature to 110 °C, and react for 24 h. After the reaction is completed, cool the system to room temperature. Pour the product cooled to room temperature into 2000 ml of deionized water, and stir continuously with a glass rod. A large amount of white solid is generated after stirring. Perform suction filtration using a vacuum pump and a Buchner funnel. Dissolve the solid after suction filtration in tetrahydrofuran, and then wash it with deionized water until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90 °C and dry it to a constant weight to finally obtain a pale yellow powder, namely PDSASi.

[0034] The chemical structure of PDSASi was analyzed by FT-IR, and the results are as Figure 2 shown. In Figure 2 Syringaldehyde represents syringaldehyde. Figure 2It shows that the synthesis of SASi and PDSASi is successful. For example, the characteristic peaks of Syringaldehyde are retained in SASi, such as the -CHO absorption peak at 1677 cm-1. The -OH absorption peak in SASi disappears significantly, indicating that dehydrogenation reaction occurred between dichlorodiphenylsilane and Syringaldehyde. In addition, the -CHO characteristic peak in PDSASi weakens significantly, and a -P-C- characteristic absorption peak appears at 1381 cm-1, indicating that a Schiff base reaction occurred between SASi and 4,4'-diaminodiphenylmethane, and then an addition reaction occurred with DOPO. Therefore, the product is successfully synthesized.

[0035] Preparation of flame-retardant epoxy resin composite:

[0036] 23.52 g of bisphenol A diglycidyl ether, 5.88 g of curing agent 4,4'-diaminodiphenylmethane and 0.6 g of flame retardant PDSASi were mixed and completely dissolved, and then defoamed under vacuum for 30 min to remove the air bubbles in the system. The obtained mixture was poured into a mold and kept at 100 °C for 2 h and at 120 °C for 2 h for complete curing to obtain the composite material, and finally the composite material was taken out of the mold.

[0037] Example 2

[0038] The intermediate was prepared in the same manner as in Example 1:

[0039] PDSASi was prepared in the same manner as in Example 1:

[0040] Preparation of flame-retardant epoxy resin composite:

[0041] 23.04 g of bisphenol A diglycidyl ether, 5.76 g of curing agent 4,4'-diaminodiphenylmethane and 1.2 g of flame retardant PDSASi were mixed and completely dissolved, and then defoamed under vacuum for 30 min to remove the air bubbles in the system. The obtained mixture was poured into a mold and kept at 100 °C for 2 h and at 120 °C for 2 h for complete curing to obtain the composite material, and finally the composite material was taken out of the mold.

[0042] Example 3

[0043] The intermediate was prepared in the same manner as in Example 1:

[0044] PDSASi was prepared in the same manner as in Example 1:

[0045] Preparation of flame-retardant epoxy resin composite:

[0046] 22.56 g of bisphenol A diglycidyl ether, 5.64 g of curing agent 4,4'-diaminodiphenylmethane, and 1.8 g of flame retardant PDSASi were mixed and completely dissolved, and then defoamed under vacuum for 30 min to remove the bubbles in the system. The obtained mixture was poured into a mold and maintained at 100 °C for 2 h and at 120 °C for 2 h for complete curing to obtain the composite material, and finally the composite material was taken out of the mold.

[0047] Example 4

[0048] The intermediate was prepared in the same manner as in Example 1.

[0049] PDSASi was prepared in the same manner as in Example 1.

[0050] Preparation of flame-retardant epoxy resin composite material:

[0051] 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane, and 2.4 g of flame retardant PDSASi were mixed and completely dissolved, and then defoamed under vacuum for 30 min to remove the bubbles in the system. The obtained mixture was poured into a mold and maintained at 100 °C for 2 h and at 120 °C for 2 h for complete curing to obtain the composite material, and finally the composite material was taken out of the mold.

[0052] Example 5

[0053] The intermediate was prepared in the same manner as in Example 1, except that vanillin was replaced with syringaldehyde.

[0054] Preparation of PDSASi: Before the experiment, the intermediate product SASi was dried overnight in an oven. 27 g of SASi and 150 ml of N,N-dimethylformamide were sequentially added to a 500 ml three-necked flask, and it was placed in an oil bath with magnetic stirring at room temperature, and stirred to fully dissolve SASi. 20 g of p-phenylenediamine was weighed and placed in a 250 ml beaker, and 50 ml of N,N-dimethylformamide was added to fully dissolve it. It was slowly added to the above flask using a constant pressure dropping funnel, and a reflux condenser was set up. After the dropping was completed, the temperature was raised to 90 °C and reacted for 6 h. After the reaction was completed, 21.62 g of DOPO previously dissolved in 50 ml of N,N-dimethylformamide was added to the above system, and the temperature was raised to 110 °C and reacted for 24 h. After the reaction was completed, the system was cooled to room temperature. The product cooled to room temperature was poured into 2000 ml of deionized water, and continuously stirred with a glass rod. After stirring, a large amount of white solid was formed. It was filtered by a vacuum pump and Buchner funnel. The solid after filtration was dissolved in tetrahydrofuran, and then washed with deionized water multiple times until the filtrate became clear. Finally, it was placed in a vacuum drying oven at 90 °C and dried to constant weight to finally obtain a pale yellow powder, namely PDSASi.

[0055] Preparation of flame-retardant epoxy resin composite material:

[0056] Completely dissolve 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane, and 1.2 g of flame retardant PDSASi, and then defoam under vacuum for 30 min to remove the air bubbles in the system. Pour the obtained mixture into a mold, and keep it at 100 °C for 2 h and at 120 °C for 2 h to complete curing, thus obtaining the composite material. Finally, take out the composite material from the mold.

[0057] Example 6

[0058] Preparation of intermediate: The same as in Example 1.

[0059] Preparation of PDSASi: Before the experiment, dry the intermediate product SASi in an oven overnight. Add 27 g of SASi and 150 ml of N,N-dimethylformamide to a 500 ml three-necked flask in sequence, and place it in an oil bath with magnetic stirring at room temperature, and stir to fully dissolve SASi. Weigh 40 g of 9,9-bis(4-aminophenyl)fluorene and place it in a 250 ml beaker, add 50 ml of N,N-dimethylformamide to fully dissolve it, and slowly add it to the above flask using a constant pressure dropping funnel. Set up a condensing reflux device. After the dropping is completed, raise the temperature to 90 °C and react for 6 h. After the reaction is completed, add 21.62 g of DOPO previously dissolved in 50 ml of N,N-dimethylformamide to the above system, raise the temperature to 110 °C, and react for 24 h. After the reaction is over, cool the system to room temperature. Pour the product cooled to room temperature into 2000 ml of deionized water, and continuously stir with a glass rod. After stirring, a large amount of white solid is generated. Use a vacuum pump and a Buchner funnel for suction filtration. Dissolve the suction-filtered solid in tetrahydrofuran, and then wash it with deionized water multiple times until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90 °C and dry it to constant weight to finally obtain a pale yellow powder, namely PDSASi.

[0060] Preparation of flame-retardant epoxy resin composite material:

[0061] Completely dissolve 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane, and 1.2 g of flame retardant PDSASi, and then defoam under vacuum for 30 min to remove the air bubbles in the system. Pour the obtained mixture into a mold, and keep it at 100 °C for 2 h and at 120 °C for 2 h to complete curing, thus obtaining the composite material. Finally, take out the composite material from the mold.

[0062] Example 7

[0063] Preparation of intermediate: The same as in Example 1.

[0064] Preparation of PDSASi: Before the experiment, the intermediate SASi was dried in an oven overnight. 27 g of SASi and 150 ml of N,N-dimethylformamide were sequentially added to a 500 ml three-necked flask, and it was placed in an oil bath with magnetic stirring at room temperature. Stir to fully dissolve SASi. Weigh 10 g of 3,5-diamino-1,2,4-triazole and place it in a 250 ml beaker. Add 50 ml of N,N-dimethylformamide to fully dissolve it, and slowly add it to the above flask using a constant pressure dropping funnel. Set up a condensing reflux device. After the addition, raise the temperature to 90 °C and react for 6 h. After the reaction, add 21.62 g of DOPO, which was previously dissolved in 50 ml of N,N-dimethylformamide, to the above system, raise the temperature to 110 °C, and react for 24 h. After the reaction, cool the system to room temperature. Pour the product cooled to room temperature into 2000 ml of deionized water, and continuously stir with a glass rod. After stirring, a large amount of white solid is formed. Use a vacuum pump and a Buchner funnel for suction filtration. Dissolve the solid after suction filtration in tetrahydrofuran, and then wash it with deionized water multiple times until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90 °C and dry it to constant weight to obtain a pale yellow powder, namely PDSASi.

[0065] Preparation of flame-retardant epoxy resin composite:

[0066] Completely dissolve 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane, and 1.2 g of flame retardant PDSASi, and then defoam under vacuum for 30 min to remove the bubbles in the system. Pour the obtained mixture into a mold, and keep it at 100 °C for 2 h and at 120 °C for 2 h to fully cure to obtain the composite material. Finally, take out the composite material from the mold.

[0067] Example 8

[0068] Preparation of intermediate: Heat the oil bath with magnetic stirring to 25 °C in advance. In a 500 ml three-necked flask, successively add 0.04 mol (6.09 g) of vanillin, 0.04 mol (4.04 g) of triethylamine, and 100 ml of dichloromethane. Place it in the oil bath with magnetic stirring. Weigh 0.04 mol (6.02 g) of tert-butyldimethylchlorosilane and put it in a 250 ml beaker. Add 20 ml of dichloromethane to dissolve it fully. Use a constant pressure dropping funnel to add it dropwise to the above flask. Set up a reflux condenser. The dropping time under a nitrogen atmosphere is 0.5 h. After the dropping is completed, raise the temperature of the oil bath to 40 °C and react for 3 h. After the reaction is completed, turn off the cooling water and nitrogen. After cooling to room temperature, filter by suction to remove the triethylamine hydrochloride generated in the reaction. Pour the filtrate into an extraction bottle, add an excessive amount of deionized water, shake and separate the layers. Take out the organic layer and repeat the above operation for three washes. After the washing is completed, pour the organic layer into a distillation flask and perform rotary evaporation at 50 °C. After the rotary evaporation is completed, pour it into a 250 ml beaker and put it in a vacuum drying oven to dry at 65 °C for 12 h to obtain a pale yellow solid (SASi). Grind it into powder for later use.

[0069] Preparation of PDSASi: Dry the intermediate SASi in a drying oven overnight before the experiment. Add 27 g of SASi and 150 ml of N,N-dimethylformamide to a 500 ml three-necked flask in sequence. Place it in an oil bath with magnetic stirring at room temperature and stir to dissolve SASi fully. Weigh 15 g of 4,4'-diaminodiphenylmethane and put it in a 250 ml beaker. Add 50 ml of N,N-dimethylformamide to dissolve it fully. Use a constant pressure dropping funnel to slowly add it to the above flask. Set up a reflux condenser. After the dropping is completed, raise the temperature to 90 °C and react for 6 h. After the reaction is completed, add 21.62 g of DOPO, which has been pre-dissolved in 50 ml of N,N-dimethylformamide, to the above system, raise the temperature to 110 °C, and react for 24 h. After the reaction is completed, cool the system to room temperature. Pour the product cooled to room temperature into 2000 ml of deionized water and stir continuously with a glass rod. A large amount of white solid is generated after stirring. Use a vacuum pump and Buchner funnel to filter by suction. Dissolve the filtered solid in tetrahydrofuran and then wash it with deionized water multiple times until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90 °C and dry it to constant weight to finally obtain a pale yellow powder, namely PDSASi.

[0070] Preparation of flame-retardant epoxy resin composite materials:

[0071] 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane, and 1.8 g of flame retardant PDSASi were completely dissolved, and then defoamed under vacuum for 30 min to remove the bubbles in the system. The resulting mixture was poured into a mold and kept at 100 °C for 2 h and at 120 °C for 2 h for complete curing to obtain the composite material. Finally, the composite material was taken out of the mold.

[0072] Example 9

[0073] Preparation of intermediate: The oil bath of the magnetic stirrer was preheated to 25 °C. In a 500 ml three-necked flask, 0.04 mol (6.09 g) of vanillin, 0.04 mol (4.04 g) of triethylamine, and 100 ml of dichloromethane were added in sequence, and then placed in the oil bath of the magnetic stirrer. 0.02 mol (5.06 g) of dichlorodiphenylsilane was weighed and placed in a 250 ml beaker, and 20 ml of dichloromethane was added to dissolve it fully. It was added dropwise to the above flask using a constant pressure dropping funnel. A condensing reflux device was set up, and the dropping time under a nitrogen atmosphere was 0.5 h. After the dropping was completed, the temperature of the oil bath was raised to 40 °C and the reaction was carried out for 3 h. After the reaction was completed, the cooling water was turned off, the nitrogen was turned off, and after cooling to room temperature, suction filtration was carried out to remove the triethylamine hydrochloride generated by the reaction. The filtrate was poured into an extraction bottle, and an excessive amount of deionized water was poured in, and it was shaken and layered. The organic layer was taken out, and the above operation was repeated for three washes. After washing, the organic layer was poured into a distillation flask and rotary evaporated at 50 °C. After the rotary evaporation was completed, it was poured into a 250 ml beaker and placed in a vacuum drying oven and dried at 65 °C for 12 h to obtain a pale yellow solid (SASi), which was ground into powder for standby.

[0074] Preparation of PDSASi: Before the experiment, the intermediate product SASi was dried overnight in an oven. 27 g of SASi and 150 ml of N,N-dimethylformamide were added to a 500 ml three-necked flask in sequence, and it was placed in an oil bath with magnetic stirring at room temperature. Stir to fully dissolve SASi. Weigh 15 g of 4,4'-diaminodiphenylmethane and place it in a 250 ml beaker. Add 50 ml of N,N-dimethylformamide to fully dissolve it, and slowly add it to the above flask using a constant pressure dropping funnel. Set up a condensing reflux device. After dropping, raise the temperature to 90 °C and react for 6 h. After the reaction is completed, add 20.21 g of diphenylphosphine oxide previously dissolved in 50 ml of N,N-dimethylformamide to the above system, raise the temperature to 110 °C, and react for 24 h. After the reaction ends, cool the system to room temperature. Pour the product cooled to room temperature into 2000 ml of deionized water, stir continuously with a glass rod. After stirring, a large amount of white solid is generated. Use a vacuum pump and Buchner funnel for suction filtration. Dissolve the suction-filtered solid in tetrahydrofuran, and then wash it several times with deionized water until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90 °C and dry it to constant weight to obtain a pale yellow powder, namely PDSASi.

[0075] Preparation of flame-retardant epoxy resin composite materials:

[0076] Mix 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane, and 1.8 g of flame retardant PDSASi completely dissolved, and then defoam under vacuum for 30 min to remove the bubbles in the system. Pour the obtained mixture into a mold, and keep it at 100 °C for 2 h and at 120 °C for 2 h to fully cure to obtain the composite material. Finally, take out the composite material from the mold.

[0077] Comparative Example 1

[0078] The preparation process of the epoxy resin composite material includes the following steps:

[0079] Mix 30 g of bisphenol A diglycidyl ether and 7.5 g of curing agent 4,4'-diaminodiphenylmethane completely dissolved, and then defoam under vacuum for 30 min to remove the bubbles in the system. Pour the obtained mixture into a mold, and keep it at 100 °C for 2 h and at 120 °C for 2 h to fully cure to obtain the composite material. Finally, take out the composite material from the mold.

[0080] To illustrate the actual effects of the present invention, the composite materials of the examples and comparative examples were tested for conventional flame retardancy and mechanical properties according to the following standards. The test results are shown in Table 1 and Figure 3 .

[0081] Flame retardancy performance: The limiting oxygen index (LOI) test was carried out in accordance with GB / T 2406.2-2009. The vertical burning test was carried out in accordance with GB / T 2408-2021. Samples with dimensions of 100mm×100mm×3mm were prepared in accordance with ASTM ISO 5660 for the cone calorimeter test.

[0082] Mechanical properties: The tensile strength was tested in accordance with the standard of GB / T 2567-2021; the impact strength was tested in accordance with the standard of GB / 1043.2-2018.

[0083] Table 1

[0084]

[0085] The flame retardancy performance and mechanical properties of Comparative Example 1 and Examples 1-9 are shown in Table 1. It can be seen from the table that with the increase of the flame retardant, the flame retardant grade of the composite material gradually increases. The comparative example has no grade because no flame retardant is added. Example 1 reaches the V-1 grade, while Examples 2, 3, 4, 5, 6, 7, 8, and 9 all reach the V-0 grade. This shows that the addition of the flame retardant greatly improves the flame retardancy performance of epoxy resin. The phosphorus, nitrogen, and silicon macromolecular flame retardant designed in the present invention significantly reduces the total heat release of EP, greatly improving the fire safety of the material. Compared with the comparative example, the mechanical properties of the examples are significantly improved. This is mainly because there is an interaction between the structure of the flame retardant and the epoxy resin matrix, thereby improving the mechanical properties of the composite material. However, excessive addition will lead to poor interfacial compatibility between the flame retardant and EP, resulting in a decrease in its mechanical properties.

[0086] Figure 3 Digital photos of Comparative Example 1 and Examples 1, 2, 3, and 4 are shown. It can be clearly seen from the figure that the composite material after adding the flame retardant has a certain color change but still remains somewhat transparent. It should be noted here that from Figure 3 In it, the background pattern and text are only used to reflect the transparency of the composite material and have no other meaning.

[0087] Comparative Example 2

[0088] Synthesis method of the phosphorus, nitrogen, and silicon-containing flame retardant, comprising the following steps:

[0089] Preparation of intermediate: Preheat the oil bath with magnetic stirring to 25°C in advance. Add 0.04 mol (7.28 g) of syringaldehyde, 0.04 mol (4.04 g) of triethylamine, and 100 ml of dichloromethane into a 500 ml three-necked flask in sequence. Place it in the oil bath with magnetic stirring. Weigh 5.06 g of dichlorodiphenylsilane and put it into a 250 ml beaker. Add 20 ml of dichloromethane to dissolve it fully. Slowly add it dropwise into the above flask using a constant-pressure dropping funnel. Set up a condensation reflux device. After the dropping is completed, raise the temperature of the oil bath to 40°C and react for 3 h. After the reaction is completed, turn off the cooling water. After cooling to room temperature, perform suction filtration to remove the triethylamine hydrochloride generated in the reaction. Pour the filtrate into an extraction bottle, add an excessive amount of deionized water, shake and separate the layers. Take out the organic layer and repeat the above operation three times. After washing, pour the organic layer into a distillation flask and perform rotary evaporation at 50°C. After the rotary evaporation is completed, pour it into a 250 ml beaker and place it in a vacuum drying oven to dry at 65°C for 12 h to obtain a brown oily substance (SASi).

[0090] Preparation of PDSASi: Dry the intermediate SASi in a drying oven overnight before the experiment. Add 27 g of SASi and 150 ml of N,N-dimethylformamide into a 500 ml three-necked flask in sequence. Place it in an oil bath with magnetic stirring at room temperature and stir to dissolve SASi fully. Weigh 15 g of 4,4'-diaminodiphenylmethane and put it into a 250 ml beaker. Add 50 ml of N,N-dimethylformamide to dissolve it fully. Slowly add it dropwise into the above flask using a constant-pressure dropping funnel. Set up a condensation reflux device. After the dropping is completed, raise the temperature to 90°C and react for 6 h. After the reaction is completed, add 21.62 g of DOPO, which has been pre-dissolved in 50 ml of N,N-dimethylformamide, into the above system and raise the temperature to 110°C and react for 24 h. After the reaction is completed, cool the system to room temperature. Pour the product cooled to room temperature into a large amount of deionized water and stir continuously with a glass rod. After stirring, a large amount of white solid is generated. Perform suction filtration using a vacuum pump and a Buchner funnel. Dissolve the solid after suction filtration in tetrahydrofuran and then wash it with deionized water multiple times until the filtrate becomes clear. Finally, place it in a vacuum drying oven at 90°C and dry it to constant weight to finally obtain a pale yellow powder, namely PDSASi.

[0091] Experimental results: Since nitrogen was not introduced in the first-step reaction, the synthesized intermediate aggregated in the rotary evaporation flask in an oily state, with a dark brown color, showing a large difference from the state of the target product.

[0092] Comparative Example 3

[0093] The preparation of the intermediate is the same as that in Example 1.

[0094] The preparation of PDSASi is the same as that in Example 1.

[0095] Preparation of flame-retardant epoxy resin composite material:

[0096] 22.08 g of bisphenol A diglycidyl ether, 5.52 g of curing agent 4,4'-diaminodiphenylmethane and 2.4 g of flame retardant PDSASi were completely dissolved, and then defoamed under vacuum for 5 min to remove the bubbles in the system. The obtained mixture was poured into a mold and kept at 100 °C for 2 h and at 120 °C for 2 h for complete curing to obtain the composite material, and finally the composite material was taken out of the mold.

[0097] The test results of the mechanical properties of the composite material obtained in Comparative Example 3 are as follows:

[0098] Table 2

[0099] sample Tensile strength (MPa) Comparative Example 2 73.3 Comparative Example 3 85.2

[0100] It can be seen that when the defoaming time was shortened to 5 min, there were visible tiny bubbles inside the cured mechanical spline, so the mechanical property characteristics were greatly affected.

[0101] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A preparation method of a phosphorus, nitrogen, silicon macromolecular flame retardant, characterized in that, The steps of the preparation method of the phosphorus, nitrogen and silicon macromolecular flame retardant are as follows: S1, chlorosilane and syringaldehyde or vanillin undergo substitution reaction to synthesize intermediate 1 containing silicon element; S2, the silicon-containing intermediate 1 reacts with an amine compound to undergo a Schiff base reaction to synthesize the nitrogen- and silicon-containing intermediate 2; S3, the intermediate 2 containing nitrogen and silicon elements undergoes addition reaction with the compound containing phosphorus element to obtain the target product phosphorus, nitrogen and silicon macromolecular flame retardant.

2. The preparation method of the phosphorus, nitrogen, and silicon macromolecular flame retardant according to claim 1, wherein, In step S1, the chlorosilane is: dichlorodiphenylsilane, tert-butyldimethylchlorosilane; the molar ratio of chlorosilane to syringaldehyde or vanillin is: 2-4:4-12, the reaction temperature is: 40-45°C, and the reaction time is: 3-4h.

3. The preparation method of the phosphorus, nitrogen, silicon macromolecular flame retardant according to claim 1, characterized in that, In step S2, the amine compound is: 4,4'-diaminodiphenylmethane, p-phenylenediamine, 9,9-bis(4-aminophenyl)fluorene or 3,5-diamino-1,2,4-triazole; the molar ratio of intermediate 1 to the amine compound is: 5-10:1-30, the reaction temperature is: 90-95°C, and the reaction time is: 6-8h.

4. The preparation method of the phosphorus, nitrogen, silicon macromolecular flame retardant according to claim 1, characterized in that, In step S3, the compound containing phosphorus is: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or diphenylphosphine oxide; the molar ratio of intermediate 2 to the compound containing phosphorus is: 1:1-2, the reaction temperature is: 100-110°C, and the reaction time is: 20-24h.

5. A phosphorus, nitrogen and silicon macromolecular flame retardant prepared according to the method according to any one of claims 1 to 4.

6. The phosphorus, nitrogen, silicon macromolecular flame retardant according to claim 5, characterized in that, The structural formula of the phosphorus, nitrogen and silicon macromolecular flame retardant is shown below: n＝1-50。 7. Use of a phosphorus, nitrogen, silicon macromolecular flame retardant prepared by the method according to any one of claims 1-4, characterized in that, The phosphorus, nitrogen and silicon macromolecular flame retardants are used for preparing flame-retardant epoxy resins.

8. Use of the phosphorus, nitrogen, silicon macromolecular flame retardant according to claim 7, characterized in that, The preparation method of the flame retardant epoxy resin comprises: preheating the epoxy resin in an oil bath to obtain an epoxy resin solution, then adding phosphorus, nitrogen and silicon macromolecular flame retardants into the epoxy resin solution and stirring the mixture, and then adding a curing agent to obtain an epoxy resin mixed liquid; pouring the epoxy resin mixed liquid into a preheated silica gel template, placing the mixture in a vacuum oven for curing reaction, and obtaining the flame retardant epoxy resin.

9. The application of the phosphorus, nitrogen, and silicon macromolecular flame retardant according to claim 8, wherein The mass percentage of the phosphorus, nitrogen and silicon macromolecular flame retardants in the epoxy resin is 2-8wt%; the stirring time after the phosphorus, nitrogen and silicon macromolecular flame retardants are added into the epoxy resin solution is 2h.

10. The application of the phosphorus, nitrogen, and silicon macromolecular flame retardant according to claim 8, characterized in that, The curing agent is: 4,4'-diaminodiphenylmethane, and the added amount thereof is 25% of the mass of the epoxy resin; the curing reaction conditions are: 100°C / 2h and 120°C / 2h.

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