Polyphosphate flame retardant with high thermal stability and preparation method thereof

Abstract

The invention belongs to the technical field of flame retardants, and particularly relates to a high-thermal-stability polyphosphate flame retardant and a preparation method thereof. The DOPO is modified through the polyethylene glycol acrylate, methyl methacrylate and dicumyl peroxide composite solution, double bonds of the polyethylene glycol acrylate and P-H bonds of the DOPO can be subjected to nucleophilic addition to form stable C-P bonds, and thermal migration of the DOPO is hindered; dOPO has polymerization double bonds of methyl methacrylate and long carbon chains of polyethylene glycol acrylate, so that the compatibility of the polyphosphate flame retardant and a polymer substrate is improved, and phase separation is avoided; maleic anhydride grafted silicone oil is connected to the surface of an amino modified gamma-cyclodextrin-modified DOPO inclusion compound, so that the polyphosphate flame retardant has high thermal stability and high compatibility after long-chain alkyl modification; amino groups in the modified gamma-cyclodextrin react with maleic anhydride grafted silicone oil to generate an amido bond cross-linked network, so that the thermal migration of DOPO is reduced together, and the high thermal stability of the polyphosphate flame retardant is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardants, and particularly relates to a polyphosphate flame retardant with high thermal stability and a preparation method thereof. Background Art

[0002] Flame retardants are additives added to substrate materials to slow or even prevent combustion. They can be categorized by their constituent elements, including halogen, nitrogen, and silicon. Phosphorus-based flame retardants, due to their low smoke, low toxicity, and affordability, hold a prominent position in the modern flame retardant material market. Phosphorus-based flame retardants include both organic and inorganic phosphorus-based flame retardants. During combustion, they produce PO· free radicals, which combine with H· and OH· free radicals to form inert substances, exerting a vapor-phase flame retardant effect. They also generate semi-solid inorganic acids, such as phosphoric acid. These acids are not only highly acidic but also coat the substrate surface, exerting a strong solid-phase flame retardant effect. The water produced during combustion also lowers the surface temperature of the material, further enhancing its flame retardant effect.

[0003] Organophosphorus flame retardants primarily include diphenyl phosphate (RDP), triphenyl phosphate (TPP), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and phosphinates. Traditional organophosphorus flame retardants are mostly low-molecular-weight compounds with poor thermal stability, high volatility, easy migration, unsatisfactory compatibility with polymers, or significant impacts on the mechanical and physical properties of polymers. Therefore, the development of phosphate ester oligomers and high-molecular-weight polyphosphates with high thermal stability and good compatibility has become an inevitable trend in the development of phosphorus-based flame retardants.

[0004] The invention patent with authorization publication number CN113717443B discloses a modified β-cyclodextrin-DOPO composite material and its preparation method. The invention utilizes the cavity structure of β-cyclodextrin to encapsulate DOPO, solving the problem of the DOPO flame retardant easily migrating from the matrix material to the surface when added alone. The invention also modifies β-cyclodextrin with a silane coupling agent to improve the compatibility of the flame retardant with the matrix material. However, this is limited to compatibility with polar matrix materials and does not improve compatibility with non-polar matrix materials. Summary of the Invention

[0005] The object of the present invention is to provide a polyphosphate flame retardant with high thermal stability and a preparation method thereof, so as to solve the above-mentioned technical problems.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention is: A method for preparing a high thermal stability polyphosphate flame retardant comprises the following steps: S1. Dissolve the amino-modified γ-cyclodextrin and modified DOPO in anhydrous N,N-dimethylformamide, mix well, and react at 55°C and 800 rpm for 2 h to form an inclusion complex; S2. Under a nitrogen atmosphere, the obtained inclusion compound was mixed with maleic anhydride grafted silicone oil, 1,2,4-triazole and DBU were added, and the mixture was reacted at 50°C for 10 h. The mixture was subjected to reduced pressure distillation at 95°C and 10 mmHg for 20 min to obtain a polyphosphate flame retardant with high thermal stability.

[0007] As a further improvement, the preparation method of the maleic anhydride grafted silicone oil is as follows: under a nitrogen atmosphere, silicone oil and maleic anhydride are dissolved in a mixed solvent, chloroplatinic acid is added, stirred at 850-950 rpm, and heated to 130°C for reaction for 8 hours; after the reaction is completed, the temperature is lowered to 50°C, white clay is added, and after stirring, adsorption, suction filtration, and reduced pressure distillation, the resulting product is mixed with ethylene glycol methyl ether, butyl titanate, and xylene, and under a nitrogen atmosphere, reflux is maintained, stirred at 150°C for reaction for 10 hours, and after cooling to room temperature, reduced pressure distillation is performed to obtain maleic anhydride grafted silicone oil.

[0008] As a further improvement, the modified DOPO is prepared by dissolving 15 to 20 parts by weight of methyl methacrylate, 6 to 10 parts of dicumyl peroxide, and 4.5 to 6.5 parts of polyethylene glycol acrylate in anhydrous ethanol, and stirring and mixing at 150° C. to obtain a modifier; adding the modifier to DOPO at a molar ratio of 1:1, stirring at 600 rpm for 30 minutes, and maintaining the mixture in an electric forced air drying oven at 75° C. for 12 hours to obtain the modified DOPO.

[0009] As a further improvement, the preparation method of the amino-modified γ-cyclodextrin is as follows: 10 to 13 parts of γ-cyclodextrin are taken by weight, dispersed in a 0.3M NaOH solution, and stirred in an ice bath at 0 to 5°C for 1 hour to obtain a γ-cyclodextrin solution; 5 to 8 parts of 3-bromopropylamine hydrobromide are dissolved in acetonitrile, and added dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere. After the addition is complete, the ice bath is removed, and the reaction is stirred at 25 to 28°C for 6 hours. After the reaction is completed, the filtrate is filtered, and the pH of the obtained filtrate is slowly adjusted to 7.0 to 8.5 with a saturated ammonium chloride solution. The precipitate is filtered again and collected. After recrystallization and vacuum drying, the amino-modified γ-cyclodextrin is obtained.

[0010] As a further improvement, the mixed solvent is obtained by mixing phenoxyethanol and diphenyl ether in a mass ratio of 1:1, and the amount of the mixed solvent is 35% of the total mass of the silicone oil and maleic anhydride; the molar ratio of the silicone oil to maleic anhydride is 1:1.5~2; and the amount of chloroplatinic acid added is 3% of the total mass of the silicone oil and maleic anhydride.

[0011] As a further improvement, the mass ratio of the total mass of the amino-modified γ-cyclodextrin and modified DOPO to anhydrous N,N-dimethylformamide is 1:5; the added amounts of 1,2,4-triazole and DBU are 8% and 5% of the total molar number of the inclusion complex and maleic anhydride grafted silicone oil, respectively.

[0012] The present invention also provides a high thermal stability polyphosphate flame retardant, which comprises the following components in parts by weight: 40 to 50 parts of maleic anhydride grafted silicone oil, 35 to 55 parts of modified DOPO and 5 to 15 parts of amino-modified gamma-cyclodextrin.

[0013] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: (1) DOPO was modified by a composite solution of polyethylene glycol acrylate, methyl methacrylate, and diisopropylbenzene peroxide. The double bond of polyethylene glycol acrylate can undergo nucleophilic addition with the PH bond of DOPO to generate a stable CP bond, which hinders the thermal migration of DOPO. DOPO has both the polymerized double bond of methyl methacrylate and the long carbon chain of polyethylene glycol acrylate, which respectively improves the compatibility of polyphosphate flame retardant with polar / non-polar polymers, thereby achieving uniform dispersion of DOPO in a wide range of polymer systems and avoiding phase separation.

[0014] (2) By connecting maleic anhydride grafted silicone oil to amino-modified γ-cyclodextrin-modified DOPO inclusion complex, the polyphosphate flame retardant has high thermal stability and high compatibility after long-chain alkyl modification; amino-modified γ-cyclodextrin reacts with maleic anhydride grafted silicone oil to form an amide bond cross-linking network, which reduces the thermal migration of DOPO and improves the high thermal stability of the polyphosphate flame retardant. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 a, b are infrared spectra of silicone oil and maleic anhydride, respectively; Figure 2 This is the infrared spectrum of maleic anhydride grafted silicone oil; Figure 3 a, b are the infrared spectra of modified DOPO and original DOPO, respectively; Figure 4 a, b are the infrared spectra of γ-cyclodextrin before and after amino modification, respectively; Figure 5 (a) and (b) are microscopic images of polypropylene flame retardant composites obtained by compounding polyphosphate obtained in Comparative Example 3 and Example 3 with polypropylene, respectively; Figure 6 (a) and (b) are microscopic images of epoxy resin flame retardant composites obtained by compounding the polyphosphate obtained in Comparative Example 3 and Example 3 with epoxy resin, respectively. DETAILED DESCRIPTION

[0016] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0017] Example 1 A method for preparing a polyphosphate flame retardant with high thermal stability comprises the following steps: S1. Phenoxyethanol and diphenyl ether were mixed in a mass ratio of 1:1 to obtain a mixed solvent; under a nitrogen atmosphere, silicone oil and maleic anhydride were dissolved in the mixed solvent in a molar ratio of 1:1.5, and the mixture was added to a 250 mL four-necked flask, chloroplatinic acid was added, and the mixture was stirred at 850 rpm and 130° C. for 8 h; after the reaction was completed, the temperature was lowered to 50° C., kaolin was added, and the mixture was stirred and adsorbed for 20 min. After filtration, the mixture was distilled under reduced pressure at 80° C. and 10 mmHg for 2 h to obtain a preliminary reaction product; the amount of the mixed solvent was 35% of the total mass of the silicone oil and maleic anhydride, the amount of chloroplatinic acid added was 3% of the total mass of the silicone oil and maleic anhydride, and the amount of kaolin was 8% of the mass of the silicone oil; the synthesis process of the preliminary reaction product was as follows: .

[0018] S2. The obtained preliminary reaction product is mixed with ethylene glycol methyl ether, butyl titanate and xylene, and the mixture is stirred at 150° C. for 10 h under a nitrogen atmosphere while being refluxed. After cooling to room temperature, the mixture is subjected to reduced pressure distillation at 90° C. and 10 mmHg to obtain maleic anhydride grafted silicone oil; wherein the molar ratio of the preliminary reaction product to ethylene glycol methyl ether and xylene is 1:1.5:0.1; the concentration of butyl titanate after mixing is 25 μg / g; the synthesis process of maleic anhydride grafted silicone oil is as follows: ; The free carboxyl groups generated by the above reaction will not exist stably in the system and will continue to esterify with excess ethylene glycol methyl ether.

[0019] S3. 15 g of methyl methacrylate, 6 g of dicumyl peroxide, and 4.5 g of polyethylene glycol acrylate were added to 200 mL of anhydrous ethanol, and the mixture was stirred at 150° C. and 200 rpm for 20 min to obtain a modifier. The modifier was added to DOPO at a molar ratio of 1:1, and the mixture was stirred at 600 rpm for 30 min. The mixture was then dried in an electric blast drying oven at 75° C. for 12 h to obtain modified DOPO. The mechanism of the modified DOPO was analyzed as follows: (1) Modifier synthesis mechanism: ; ; .

[0020] (2) Modification mechanism of DOPO: .

[0021] S4. Take 10 parts of γ-cyclodextrin by weight, disperse them in 200 mL of 0.3 M NaOH solution, and stir the mixture in an ice bath at 0°C for 1 hour to obtain a γ-cyclodextrin solution; dissolve 5 parts of 3-bromopropylamine hydrobromide in 50 mL of acetonitrile and add them dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere. After the addition is complete, remove the ice bath and stir the mixture at 25°C for 6 hours. After the reaction is completed, filter and remove the white insoluble matter. Slowly adjust the pH of the obtained filtrate to 7.0 with a saturated ammonium chloride solution, filter again and collect the precipitate. Recrystallize the precipitate twice in hot water and then dry it in a vacuum drying oven at 0.1 MPa and 35°C for 2 hours to obtain amino-modified γ-cyclodextrin. The synthesis process of amino-modified cyclodextrin is as follows: .

[0022] S5. Take 40 parts of maleic anhydride grafted silicone oil, 35 parts of modified DOPO, and 5 parts of amino-modified γ-cyclodextrin, by weight.

[0023] S6. After uniformly mixing the amino-modified γ-cyclodextrin and the modified DOPO, dissolve them in anhydrous N,N-dimethylformamide, and react at 55° C. and 800 rpm for 2 h to form an inclusion complex; wherein the mass ratio of the total mass of the amino-modified γ-cyclodextrin and the modified DOPO to the anhydrous N,N-dimethylformamide is 1:5.

[0024] S7. Under a nitrogen atmosphere, the obtained inclusion compound was mixed with maleic anhydride grafted silicone oil, 1,2,4-triazole and DBU (diazabicyclic) were added, and the mixture was reacted at 50°C for 10 hours. The mixture was then subjected to reduced pressure distillation at 95°C and 10 mmHg for 20 minutes to obtain a polyphosphate flame retardant with high thermal stability. The added amounts of 1,2,4-triazole and DBU were 8% and 5% of the total molar number of the inclusion compound and the maleic anhydride grafted silicone oil, respectively. The grafting process of the maleic anhydride grafted silicone oil onto the surface of the inclusion compound was as follows: .

[0025] Example 2 A method for preparing a polyphosphate flame retardant with high thermal stability comprises the following steps: S1. Phenoxyethanol and diphenyl ether were mixed in a mass ratio of 1:1 to obtain a mixed solvent; under a nitrogen atmosphere, silicone oil and maleic anhydride were dissolved in the mixed solvent in a molar ratio of 1:1.8, and the mixture was added to a 250 mL four-necked flask, chloroplatinic acid was added, and the mixture was stirred at 900 rpm and 130° C. for 8 h; after the reaction was completed, the temperature was lowered to 50° C., kaolin was added, and the mixture was stirred and adsorbed for 20 min. After filtration, the mixture was distilled under reduced pressure at 80° C. and 10 mmHg for 2 h to obtain a preliminary reactant; the amount of the mixed solvent was 35% of the total mass of the silicone oil and maleic anhydride, the amount of chloroplatinic acid added was 3% of the total mass of the silicone oil and maleic anhydride, and the amount of kaolin was 8% of the mass of the silicone oil.

[0026] S2. The obtained preliminary reaction product is mixed with ethylene glycol methyl ether, butyl titanate and xylene, and the mixture is stirred at 150° C. for 10 hours under a nitrogen atmosphere while maintaining reflux. After cooling to room temperature, the mixture is subjected to reduced pressure distillation at 90° C. and 10 mmHg to obtain maleic anhydride grafted silicone oil; wherein the molar ratio of the preliminary reaction product to ethylene glycol methyl ether and xylene is 1:1.5:0.1; and the concentration of butyl titanate after mixing is 25 μg / g.

[0027] S3. To 200 mL of anhydrous ethanol, 18 g of methyl methacrylate, 8 g of dicumyl peroxide, and 5.5 g of polyethylene glycol acrylate were added and stirred at 150° C. and 200 rpm for 20 min to obtain a modifier. The obtained modifier was added to DOPO at a molar ratio of 1:1, stirred at 600 rpm for 30 min, and dried in an electric forced air drying oven at 75° C. for 12 h to obtain modified DOPO.

[0028] S4. Take 12 parts of γ-cyclodextrin by weight, disperse them in 200 mL of 0.3 M NaOH solution, and stir to react in an ice bath at 3°C ​​for 1 hour to obtain a γ-cyclodextrin solution; dissolve 7 parts of 3-bromopropylamine hydrobromide in 50 mL of acetonitrile, and add them dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere. After the addition is complete, remove the ice bath, and stir to react at 27°C for 6 hours. After the reaction is completed, filter and remove the white insoluble matter, slowly adjust the pH of the obtained filtrate to 8.0 with a saturated ammonium chloride solution, filter again and collect the precipitate, recrystallize the precipitate twice in hot water, and then place it in a vacuum drying oven at 0.1 MPa and 35°C and dry it for 2 hours to obtain amino-modified γ-cyclodextrin.

[0029] S5. Take 45 parts of maleic anhydride grafted silicone oil, 45 parts of modified DOPO, and 10 parts of amino-modified γ-cyclodextrin, by weight.

[0030] S6. After uniformly mixing the amino-modified γ-cyclodextrin and the modified DOPO, dissolve them in anhydrous N,N-dimethylformamide, and react at 55° C. and 800 rpm for 2 h to form an inclusion complex; wherein the mass ratio of the total mass of the amino-modified γ-cyclodextrin and the modified DOPO to the anhydrous N,N-dimethylformamide is 1:5.

[0031] S7. Under a nitrogen atmosphere, the obtained inclusion compound was mixed with maleic anhydride grafted silicone oil, 1,2,4-triazole and DBU were added, and the mixture was reacted at 50°C for 10 hours. The mixture was subjected to reduced pressure distillation at 95°C and 10 mmHg for 20 minutes to obtain a polyphosphate flame retardant with high thermal stability; wherein the added amounts of 1,2,4-triazole and DBU were 8% and 5% of the total molar number of the inclusion compound and the maleic anhydride grafted silicone oil, respectively.

[0032] Example 3 A method for preparing a high thermal stability polyphosphate flame retardant comprises the following steps: S1. Phenoxyethanol and diphenyl ether were mixed in a mass ratio of 1:1 to obtain a mixed solvent; under a nitrogen atmosphere, silicone oil and maleic anhydride were dissolved in the mixed solvent in a molar ratio of 1:2, and the mixture was added to a 250 mL four-necked flask, chloroplatinic acid was added, and the mixture was stirred at 950 rpm and 130° C. for 8 h; after the reaction was completed, the temperature was lowered to 50° C., kaolin was added, and the mixture was stirred and adsorbed for 20 min. After filtration, the mixture was distilled under reduced pressure at 80° C. and 10 mmHg for 2 h to obtain a preliminary reaction product; the amount of the mixed solvent was 35% of the total mass of the silicone oil and maleic anhydride, the amount of chloroplatinic acid added was 3% of the total mass of the silicone oil and maleic anhydride, and the amount of kaolin was 8% of the mass of the silicone oil.

[0033] S2. The obtained preliminary reaction product is mixed with ethylene glycol methyl ether, butyl titanate and xylene, and the mixture is stirred at 150° C. for 10 hours under a nitrogen atmosphere while maintaining reflux. After cooling to room temperature, the mixture is subjected to reduced pressure distillation at 90° C. and 10 mmHg to obtain maleic anhydride grafted silicone oil; wherein the molar ratio of the preliminary reaction product to ethylene glycol methyl ether and xylene is 1:1.5:0.1; and the concentration of butyl titanate after mixing is 25 μg / g.

[0034] S3. To 200 mL of anhydrous ethanol, 20 g of methyl methacrylate, 10 g of dicumyl peroxide, and 6.5 g of polyethylene glycol acrylate were added, and the mixture was stirred at 150° C. and 200 rpm for 20 min to obtain a modifier. The obtained modifier was added to DOPO at a molar ratio of 1:1, and the mixture was stirred at 600 rpm for 30 min. The mixture was then dried in an electric forced air drying oven at 75° C. for 12 h to obtain modified DOPO.

[0035] S4. Take 13 parts of γ-cyclodextrin by weight, disperse them in 200 mL of 0.3 M NaOH solution, and stir in an ice bath at 5°C for 1 hour to obtain a γ-cyclodextrin solution; dissolve 8 parts of 3-bromopropylamine hydrobromide in 50 mL of acetonitrile, and add them dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere. After the addition is complete, remove the ice bath, and stir and react at 28°C for 6 hours. After the reaction is completed, filter and remove the white insoluble matter, slowly adjust the pH of the obtained filtrate to 8.5 with a saturated ammonium chloride solution, filter again and collect the precipitate, recrystallize the precipitate twice in hot water, and then place it in a vacuum drying oven at 0.1 MPa and 35°C and dry it for 2 hours to obtain amino-modified γ-cyclodextrin.

[0036] S5. Take 50 parts of maleic anhydride grafted silicone oil, 55 parts of modified DOPO, and 15 parts of amino-modified γ-cyclodextrin by weight.

[0037] S6. After uniformly mixing the amino-modified γ-cyclodextrin and the modified DOPO, dissolve them in anhydrous N,N-dimethylformamide, and react at 55° C. and 800 rpm for 2 h to form an inclusion complex; wherein the mass ratio of the total mass of the amino-modified γ-cyclodextrin and the modified DOPO to the anhydrous N,N-dimethylformamide is 1:5.

[0038] S7. Under a nitrogen atmosphere, the obtained inclusion compound was mixed with maleic anhydride grafted silicone oil, 1,2,4-triazole and DBU were added, and the mixture was reacted at 50°C for 10 hours. The mixture was subjected to reduced pressure distillation at 95°C and 10 mmHg for 20 minutes to obtain a polyphosphate flame retardant with high thermal stability; wherein the added amounts of 1,2,4-triazole and DBU were 8% and 5% of the total molar number of the inclusion compound and the maleic anhydride grafted silicone oil, respectively.

[0039] Comparative Example 1 A method for preparing a polyphosphate flame retardant with high thermal stability, which differs from Example 1 in that no maleic anhydride grafted silicone oil is added, specifically comprising the following steps: S1. To 200 mL of anhydrous ethanol, 15 g of methyl methacrylate, 6 g of dicumyl peroxide, and 4.5 g of polyethylene glycol acrylate were added and stirred at 150°C and 200 rpm for 20 min to obtain a modifier. The modifier was added to DOPO at a molar ratio of 1:1, stirred at 600 rpm for 30 min, and dried in an electric forced air drying oven at 75°C for 12 h to obtain modified DOPO.

[0040] S2. Take 10 parts of γ-cyclodextrin by weight, disperse them in 200 mL of 0.3 M NaOH solution, and stir to react in an ice bath at 0°C for 1 hour to obtain a γ-cyclodextrin solution; dissolve 5 parts of 3-bromopropylamine hydrobromide in 50 mL of acetonitrile, and add them dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere. After the addition is complete, remove the ice bath, and stir to react at 25°C for 6 hours. After the reaction is completed, filter and remove the white insoluble matter, slowly adjust the pH of the obtained filtrate to 7.0 with a saturated ammonium chloride solution, filter again and collect the precipitate, recrystallize the precipitate twice in hot water, and then place it in a vacuum drying oven at 0.1 MPa and 35°C and dry it for 2 hours to obtain amino-modified γ-cyclodextrin.

[0041] S3. Take 35 parts of modified DOPO and 5 parts of amino-modified γ-cyclodextrin by weight.

[0042] S4. After uniformly mixing the amino-modified γ-cyclodextrin and the modified DOPO, dissolve them in anhydrous N,N-dimethylformamide, and react at 55°C and 800 rpm for 2 hours to form an inclusion complex; wherein the mass ratio of the total mass of the amino-modified γ-cyclodextrin and the modified DOPO to the anhydrous N,N-dimethylformamide is 1:5; the obtained inclusion complex is subjected to reduced pressure distillation at 95°C and 10 mmHg for 20 minutes to obtain a polyphosphate flame retardant with high thermal stability.

[0043] Comparative Example 2 A method for preparing a polyphosphate flame retardant with high thermal stability, which differs from Example 1 in that amino-modified γ-cyclodextrin is not added, specifically comprising the following steps: S1. Phenoxyethanol and diphenyl ether were mixed in a mass ratio of 1:1 to obtain a mixed solvent; under a nitrogen atmosphere, silicone oil and maleic anhydride were dissolved in the mixed solvent in a molar ratio of 1:1.5, and the mixture was added to a 250 mL four-necked flask, chloroplatinic acid was added, and the mixture was stirred at 850 rpm and 130° C. for 8 h; after the reaction was completed, the temperature was lowered to 50° C., kaolin was added, and the mixture was stirred and adsorbed for 20 min. After filtration, the mixture was distilled under reduced pressure at 80° C. and 10 mmHg for 2 h to obtain a preliminary reaction product; the amount of the mixed solvent was 35% of the total mass of the silicone oil and maleic anhydride, the amount of chloroplatinic acid added was 3% of the total mass of the silicone oil and maleic anhydride, and the amount of kaolin was 8% of the mass of the silicone oil.

[0044] S2. The obtained preliminary reaction product is mixed with ethylene glycol methyl ether, butyl titanate and xylene, and the mixture is stirred at 150° C. for 10 hours under a nitrogen atmosphere while maintaining reflux. After cooling to room temperature, the mixture is subjected to reduced pressure distillation at 90° C. and 10 mmHg to obtain maleic anhydride grafted silicone oil; wherein the molar ratio of the preliminary reaction product to ethylene glycol methyl ether and xylene is 1:1.5:0.1; and the concentration of butyl titanate after mixing is 25 μg / g.

[0045] S3. To 200 mL of anhydrous ethanol, 15 g of methyl methacrylate, 6 g of dicumyl peroxide, and 4.5 g of polyethylene glycol acrylate were added and stirred at 150° C. and 200 rpm for 20 min to obtain a modifier. The obtained modifier was added to DOPO at a molar ratio of 1:1, and stirred at 600 rpm for 30 min. The mixture was then dried in an electric forced air drying oven at 75° C. for 12 h to obtain modified DOPO.

[0046] S4. Take 40 parts of maleic anhydride grafted silicone oil and 35 parts of modified DOPO by weight.

[0047] S5. The modified DOPO and maleic anhydride grafted silicone oil were mixed, stirred at 600 rpm and 70° C. for 65 min, and subjected to reduced pressure distillation at 95° C. and 10 mmHg for 20 min to obtain a polyphosphate flame retardant with high thermal stability.

[0048] Comparative Example 3 A method for preparing a polyphosphate flame retardant with high thermal stability, which differs from Example 1 in that DOPO is not modified, specifically comprises the following steps: S1. Phenoxyethanol and diphenyl ether were mixed in a mass ratio of 1:1 to obtain a mixed solvent; under a nitrogen atmosphere, silicone oil and maleic anhydride were dissolved in a solvent in a molar ratio of 1:1.5, and the mixture was added to a 250 mL four-necked flask, chloroplatinic acid was added, and the mixture was stirred and reacted at 850 rpm and 130° C. for 8 h; after the reaction was completed, the temperature was lowered to 50° C., kaolin was added, and the mixture was stirred and adsorbed for 20 min. After filtration, the mixture was distilled under reduced pressure at 80° C. and 10 mmHg for 2 h to obtain a preliminary reaction product; the amount of the mixed solvent was 35% of the total mass of the silicone oil and maleic anhydride, the amount of chloroplatinic acid added was 3% of the total mass of the silicone oil and maleic anhydride, and the amount of kaolin was 8% of the mass of the silicone oil.

[0049] S2. The obtained preliminary reaction product is mixed with ethylene glycol methyl ether, butyl titanate and xylene, and the mixture is stirred at 150° C. for 10 hours under a nitrogen atmosphere while maintaining reflux. After cooling to room temperature, the mixture is subjected to reduced pressure distillation at 90° C. and 10 mmHg to obtain maleic anhydride grafted silicone oil; wherein the molar ratio of the preliminary reaction product to ethylene glycol methyl ether and xylene is 1:1.5:0.1; and the concentration of butyl titanate after mixing is 25 μg / g.

[0050] S3. Take 10 parts of γ-cyclodextrin by weight, disperse them in 200 mL of 0.3 M NaOH solution, and stir to react in an ice bath at 0°C for 1 hour to obtain a γ-cyclodextrin solution; dissolve 5 parts of 3-bromopropylamine hydrobromide in 50 mL of acetonitrile, and add them dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere. After the addition is complete, remove the ice bath, and stir to react at 25°C for 6 hours. After the reaction is completed, filter and remove the white insoluble matter, slowly adjust the pH of the obtained filtrate to 7.0 with a saturated ammonium chloride solution, filter again and collect the precipitate, recrystallize the precipitate twice in hot water, and then place it in a vacuum drying oven at 0.1 MPa and 35°C and dry it for 2 hours to obtain amino-modified γ-cyclodextrin.

[0051] S4. Take 40 parts of maleic anhydride grafted silicone oil, 35 parts of DOPO, and 5 parts of amino-modified γ-cyclodextrin by weight.

[0052] S5. After uniformly mixing the amino-modified γ-cyclodextrin and DOPO, dissolve them in anhydrous N,N-dimethylformamide, and react at 55° C. and 800 rpm for 2 h to form an inclusion complex; wherein the mass ratio of the total mass of the amino-modified γ-cyclodextrin and DOPO to anhydrous N,N-dimethylformamide is 1:5.

[0053] S6. Under a nitrogen atmosphere, the obtained inclusion compound was mixed with maleic anhydride grafted silicone oil, 1,2,4-triazole and DBU were added, and the mixture was reacted at 50°C for 10 hours. The mixture was distilled under reduced pressure at 95°C and 10 mmHg for 20 minutes to obtain a polyphosphate flame retardant with high thermal stability; wherein the added amounts of 1,2,4-triazole and DBU were 8% and 5% of the total molar number of the inclusion compound and the maleic anhydride grafted silicone oil, respectively.

[0054] Comparative Example 4 A method for preparing a polyphosphate flame retardant with high thermal stability is different from Example 1 in that only unmodified DOPO is used as the polyphosphate flame retardant.

[0055] The maleic anhydride grafted silicone oil, modified DOPO and amino-modified γ-cyclodextrin obtained in Example 1 were tested by infrared spectra to verify the actual formation of the products.

[0056] Figure 1 a, b are the infrared spectra of original silicone oil and maleic anhydride respectively. Figure 2 This is the infrared spectrum of maleic anhydride grafted silicone oil. Figure 1 As can be seen from a and b, 2874~2959cm -1 and 1000~1100cm -1 The characteristic absorption peaks at 2150cm are strong. Maleic anhydride contains -CH3, -CH2 and COC, which enhance the absorption peaks at these two locations. -1 The peak at is the characteristic peak of Si-H bond in silicone oil; Figure 2 This is the infrared spectrum of maleic anhydride grafted silicone oil. It can be seen that 2150cm -1 The characteristic peak of Si-H bond at the bottom has basically disappeared, indicating that there is no silicon-hydrogen bond in the silicone oil at this time; Figure 1 b medium 1770cm -1 and 1870cm -1 is the infrared absorption peak of the two conjugated carbonyl groups in maleic anhydride, and Figure 2 Only 1740cm appears in -1 An enhanced ester carbonyl infrared absorption peak was observed at the center of the gel, proving that the anhydride ring-opening in the maleic anhydride grafted silicone oil resulted in esterification reaction and the target product was synthesized.

[0057] Figure 3 a, b are infrared spectra of modified DOPO and original DOPO respectively; the infrared spectrum of original DOPO is 2366cm -1 The characteristic absorption peak of pH appeared at 1100 cm -1 An obvious PC characteristic absorption peak appeared at , indicating that the PH in DOPO reacted with the double bond in polyethylene glycol acrylate and the reaction was basically complete.

[0058] Figure 4 a, b are the infrared spectra of γ-cyclodextrin before and after amino modification, respectively. Figure 4 b, 3395cm -1 The corresponding peak is the OH stretching vibration peak. Figure 4 The infrared spectrum of amino-modified γ-cyclodextrin a is compared with that of original γ-cyclodextrin. -1 and 1231cm -1 New peaks appeared at , belonging to NH bending and CN stretching, indicating that the amino group had successfully modified γ-cyclodextrin.

[0059] 1. Measure the initial decomposition temperature T of the polyphosphate flame retardant obtained in each embodiment and comparative example d (temperature at which mass loss is 5%), maximum decomposition temperature T max The polyphosphate flame retardant was aged in a 120°C oven for 170 hours, and then analyzed by XPS to measure the atomic concentration of the P element on the surface and calculate the thermal mobility. The test results are shown in Table 1.

[0060] Table 1 Thermal stability test results of polyphosphate flame retardants ; As can be seen from Table 1, the initial decomposition temperature and maximum decomposition temperature of the polyphosphate flame retardants of Examples 1-3 are higher than those of Comparative Examples 1-4, and significantly higher than those of Comparative Examples 1 and 2. The carbon residue rate of Comparative Examples 1-4 is also significantly lower than that of Examples 1-3, and the thermal migration rate is higher than that of Examples 1-3. The double bond of polyethylene glycol acrylate is added to the DOPO structure, converting the unstable PH bond in the DOPO structure into a stable CP bond, thereby improving the thermal stability of DOPO. Therefore, the thermal stability of the polyphosphate flame retardant obtained in Comparative Example 3 is reduced. The amino-modified γ-cyclodextrin reacts with the maleic anhydride-grafted silicone oil to form an amide bond cross-linked network. Combined with the inclusion effect of the amino-modified γ-cyclodextrin, this jointly resists the thermal migration of DOPO and improves the high thermal stability of the polyphosphate heat-resistant agent. Therefore, the stability of the polyphosphate flame retardants obtained in Comparative Examples 1 and 2 is also reduced.

[0061] 2. Composite samples were prepared by combining the polyphosphate flame retardant obtained in Example 3, Comparative Example 3, and Comparative Example 4 with polar and non-polar polymer matrix materials to test the compatibility of the polyphosphate flame retardant.

[0062] Non-polar composite material: Polypropylene and polyphosphate flame retardant were uniformly mixed in a mass ratio of 4:1, melt-blended and extruded into pellets using a twin-screw extruder. The pellets were then oven-dried at 100°C to produce a polypropylene flame-retardant composite. Extrusion conditions were: twin-screw temperature at 200°C, main screw speed at 20 rpm, and feeder screw speed at 10 rpm.

[0063] Polar composite material: Add the prepared polyphosphate flame retardant to epoxy resin at 60°C. Stir at 1000 rpm for 30 minutes, then raise the temperature to 85°C and add the curing agent, 4,4'-diaminodiphenylmethane. Continue stirring until the liquid becomes clear and transparent. Vacuum degassing for 15 minutes. Pour the mixture into a mold and pre-cure at 80°C for 1 hour, then at 120°C for 2 hours, and finally at 150°C for 1 hour to obtain the epoxy resin flame-retardant composite.

[0064] The obtained polypropylene flame retardant composite was subjected to microstructure test, and the results were as follows: Figure 1 As shown, it can be seen that there are larger agglomerated particles at the interface between the polyphosphate flame retardant and polypropylene in comparative example 3, and the polyphosphate flame retardant is unevenly dispersed in the polypropylene; while there is no obvious interface separation between the polyphosphate flame retardant and polypropylene in embodiment 3, indicating that the polyphosphate flame retardant in embodiment 3 has good interaction with polypropylene, while the compatibility of the polyphosphate flame retardant in comparative example 3 with polypropylene is relatively poor.

[0065] The obtained epoxy resin flame retardant composite was subjected to microstructure test, and the results were as follows: Figure 2As shown, it can be seen that the surface of the material after the polyphosphate flame retardant and epoxy resin are compounded in Comparative Example 3 is loose, with many cracks and wrinkles, which is conducive to the release of internal combustible volatiles, thereby intensifying the combustion reaction; while the surface of the material after the polyphosphate flame retardant and epoxy resin are compounded in Example 3 is denser, continuous and smoother, which is conducive to the formation of a large amount of stable residual carbon during the combustion process, isolating oxygen and heat, and playing a flame retardant role.

[0066] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high thermal stability polyphosphate flame retardant, characterized in that: The following steps are involved: S1. Dissolve the amino-modified γ-cyclodextrin and modified DOPO in anhydrous N,N-dimethylformamide, mix well, and react at 55°C and 800 rpm for 2 h to form an inclusion complex; S2. Under a nitrogen atmosphere, the obtained inclusion compound was mixed with maleic anhydride grafted silicone oil, 1,2,4-triazole and DBU were added, and the mixture was reacted at 50°C for 10 h. The mixture was subjected to reduced pressure distillation at 95°C and 10 mmHg for 20 min to obtain a polyphosphate flame retardant with high thermal stability.

2. The method for preparing a high thermal stability polyphosphate flame retardant according to claim 1, wherein: The preparation method of the maleic anhydride grafted silicone oil comprises the following steps: dissolving silicone oil and maleic anhydride in a mixed solvent under a nitrogen atmosphere, adding chloroplatinic acid, stirring at 850-950 rpm, heating to 130° C. and reacting for 8 hours; after the reaction is completed, cooling to 50° C., adding white clay, stirring and adsorbing, filtering, and distilling under reduced pressure, mixing the obtained product with ethylene glycol methyl ether, butyl titanate, and xylene, maintaining reflux under a nitrogen atmosphere, stirring and reacting at 150° C. for 10 hours, cooling to room temperature, and distilling under reduced pressure to obtain the maleic anhydride grafted silicone oil.

3. The method for preparing a high thermal stability polyphosphate flame retardant according to claim 1, wherein: The modified DOPO is prepared by dissolving 15 to 20 parts by weight of methyl methacrylate, 6 to 10 parts of dicumyl peroxide, and 4.5 to 6.5 parts of polyethylene glycol acrylate in anhydrous ethanol, and stirring and mixing at 150° C. to obtain a modifier; adding the modifier to DOPO at a molar ratio of 1:1, stirring at 600 rpm for 30 minutes, and then placing the modified DOPO in an electric forced air drying oven at 75° C. for 12 hours to obtain the modified DOPO.

4. The method for preparing a high thermal stability polyphosphate flame retardant according to claim 1, wherein: The preparation method of the amino-modified γ-cyclodextrin comprises the following steps: dispersing 10 to 13 parts of γ-cyclodextrin by weight in a 0.3M NaOH solution, stirring and reacting in an ice bath at 0 to 5°C for 1 hour to obtain a γ-cyclodextrin solution; dissolving 5 to 8 parts of 3-bromopropylamine hydrobromide in acetonitrile, and adding the solution dropwise to the γ-cyclodextrin solution under a nitrogen atmosphere; removing the ice bath after the addition is complete, stirring and reacting at 25 to 28°C for 6 hours, and filtering after the reaction is complete. Slowly adjusting the pH of the obtained filtrate to 7.0 to 8.5 with a saturated ammonium chloride solution, filtering again and collecting the precipitate. After recrystallization and vacuum drying, the amino-modified γ-cyclodextrin is obtained.

5. The method for preparing a high thermal stability polyphosphate flame retardant according to claim 2, wherein: The mixed solvent is obtained by mixing phenoxyethanol and diphenyl ether in a mass ratio of 1:1, and the amount of the mixed solvent is 35% of the total mass of the silicone oil and maleic anhydride; the molar ratio of the silicone oil to maleic anhydride is 1:1.5-2; and the amount of chloroplatinic acid added is 3% of the total mass of the silicone oil and maleic anhydride.

6. The method for preparing a high thermal stability polyphosphate flame retardant according to claim 1, wherein: The mass ratio of the total mass of the amino-modified γ-cyclodextrin and the modified DOPO to anhydrous N,N-dimethylformamide is 1:5; the added amounts of 1,2,4-triazole and DBU are 8% and 5% of the total molar number of the inclusion complex and the maleic anhydride grafted silicone oil, respectively.

7. The high thermal stability polyphosphate flame retardant prepared by the preparation method of claim 1, characterized in that: The invention comprises the following components in parts by weight: 40 to 50 parts of maleic anhydride grafted silicone oil, 35 to 55 parts of modified DOPO and 5 to 15 parts of amino-modified gamma-cyclodextrin.

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