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 preparation method includes the steps that 2-(4-hydroxyphenyl) benzothiazole and phosphorus oxychloride serve as raw materials to react to prepare 2-(4-dichlorophosphoryloxyphenyl) benzothiazole; spirocyclic phosphate-terephthalyl alcohol diester is prepared by adopting a one-step method; 2-(4-dichlorophosphoryloxyphenyl) benzothiazole and spiro phosphate-terephthalyl alcohol diester are used as reactants, polycondensation is performed to generate a flame retardant precursor, and then aniline is used for end capping to obtain the polyphosphate flame retardant. According to the invention, a benzothiazole ring is introduced into a side chain of the polyphosphate flame retardant, and spirocyclic phosphate-terephthalyl alcohol ester with a charring effect is taken as a main chain of the polyphosphate flame retardant, so that the polyphosphate flame retardant with relatively high thermal stability is prepared.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant technology, specifically relating to a high thermal stability polyphosphate flame retardant and its preparation method. Background Technology

[0002] Polymer materials are ubiquitous in modern life. However, because many polymer materials do not contain phosphorus and nitrogen-based flame retardant elements, they have low LOI (flame retardancy index), are extremely flammable, and are difficult to extinguish once ignited. They may also produce a large amount of toxic gases, posing a huge threat to people's lives and property.

[0003] Flame retardants are additives that improve the flame resistance of materials. They can inhibit or prevent the combustion of polymeric materials, giving them flame-retardant, self-extinguishing, and smoke-suppressing properties, thus improving product safety. Polyphosphate flame retardants, due to their high efficiency, low toxicity, and environmental friendliness, have become one of the current research hotspots in the field of flame retardancy.

[0004] However, traditional polyphosphate flame retardants still have some key drawbacks in practical applications. First, most polyphosphate flame retardants lack thermal stability and are prone to decomposition during high-temperature processing or long-term use, leading to a decrease in flame retardant efficiency and even affecting the mechanical properties of the matrix material. Second, existing polyphosphate flame retardants often rely on a single flame retardant mechanism, such as gas-phase or condensed-phase flame retardancy, making it difficult to provide comprehensive and effective flame retardant protection in complex combustion environments. Summary of the Invention

[0005] The purpose of this invention is to provide a high thermal stability polyphosphate flame retardant and its preparation method to solve the above-mentioned technical problems.

[0006] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows: A method for preparing a high thermal stability polyphosphate flame retardant includes the following steps: S1. Mix 2-(4-hydroxyphenyl)benzothiazole and anhydrous pyridine, and add anhydrous acetonitrile to the mixture under stirring to obtain a mixed system. Place the mixed system in an ice-water bath and slowly add phosphorus oxychloride to the mixture. After the addition is complete, carry out the reaction. After the reaction is complete, cool the reaction system to 0°C and pour it into ice water while stirring. Then, extract, wash, dry and rotary evaporate in sequence to obtain 2-(4-dichlorophosphoryloxyphenyl)benzothiazole. S2. Using a one-step method, pentaerythritol dichlorophosphite is obtained by reacting pentaerythritol and phosphorus trichloride, followed by the addition of terephthalic acid to prepare spirocyclic phosphate-terephthalic acid diester. S3. Using 2-(4-dichlorophosphoryloxyphenyl)benzothiazole and spirocyclic phosphate-terephthalic acid diester as reactants, a flame retardant precursor is generated by polycondensation, which is then end-capped with aniline to obtain a polyphosphate flame retardant.

[0007] As a further improvement, in step S1, the preparation method of 2-(4-hydroxyphenyl)benzothiazole is as follows: 2,2'-dithiodiphenylamine, p-hydroxybenzaldehyde, sodium sulfide nonahydrate, and sodium bicarbonate are added to a reactor in sequence. Under nitrogen protection, N,N-dimethylformamide is added to the reactor, and the reaction is carried out at 100°C with magnetic stirring for 5-8 hours. After the reaction is completed, the reaction system is cooled, quenched with sodium bisulfite solution, extracted with dichloromethane, and finally dried, distilled under reduced pressure, and purified to obtain 2-(4-hydroxyphenyl)benzothiazole.

[0008] As a further improvement, the molar ratio of 2,2'-dithiodiphenylamine to p-hydroxybenzaldehyde is 1:2, and the molar ratio of sodium sulfide nonahydrate and sodium bicarbonate to 2,2'-dithiodiphenylamine is 0.5 to 1:1.

[0009] As a further improvement, in step S1, the molar ratio of 2-(4-hydroxyphenyl)benzothiazole to phosphorus oxychloride is 1:2, and the amount of anhydrous pyridine added is 3 to 3.5 times the molar amount of 2-(4-hydroxyphenyl)benzothiazole. The reaction process is as follows: the reaction system is naturally heated to room temperature, stirred for 2 hours, then heated to reflux, and the reaction is continued to be stirred for 4 to 6 hours.

[0010] As a further improvement, in step S2, the one-step preparation process of spirocyclic phosphate-terephthalic acid diester is specifically as follows: Under a nitrogen atmosphere, pentaerythritol, xylene, and pyridine were mixed, and phosphorus trichloride was added dropwise at 5°C over 30 minutes. The mixture was then stirred under constant temperature reflux for 1 hour to obtain pentaerythritol dichlorophosphite. The hydrogen chloride gas generated during the reaction was discharged through a condenser and absorbed by sodium hydroxide solution. After the reaction was completed, the nitrogen gas supply was stopped, and the hydrogen chloride in the reaction system was removed by a vacuum pump. At the same time, the pressure of the system was reduced to 3000 Pa. After stirring for 30 minutes, nitrogen gas was introduced into the reaction system again. Triethylamine and xylene were added to the reaction system, and then the reaction system was cooled to 5°C. A mixed solution of terephthalic acid and xylene was added dropwise. After the addition was completed, the mixture was refluxed for 1 hour, then cooled to room temperature. The solid was filtered, washed with xylene, and dried to obtain spirocyclic phosphate-terephthalic acid diester.

[0011] As a further improvement, the molar ratio of pentaerythritol, phosphorus trichloride and terephthalic acid is 1:2.1 to 2.3:2.

[0012] As a further improvement, step S3 is as follows: Under a nitrogen atmosphere, spirocyclic phosphate-terephthalic acid diester, triethylamine and dichloromethane are mixed and stirred in an ice-water bath. Then, a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole is slowly added to the mixture, and the reaction is carried out for 2 hours. Then, the mixture is heated to 70°C and reacted for 5 hours. Then, a dichloromethane solution of aniline is added to the mixture, and the reaction is continued at 70°C under a nitrogen atmosphere for 12 hours. After the reaction is completed, the mixture is filtered, rotary evaporated and dried to obtain the polyphosphate flame retardant.

[0013] As a further improvement, the molar ratio of the spirocyclic phosphate-terephthalic acid diester, 2-(4-dichlorophosphoryloxyphenyl)benzothiazole and aniline is 1:1:0.5, and the amount of triethylamine added is 1 to 1.2 times the molar amount of the spirocyclic phosphate-terephthalic acid diester.

[0014] The present invention also provides a polyphosphate flame retardant.

[0015] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: This invention provides a high thermal stability polyphosphate flame retardant and its preparation method. A benzothiazole ring is introduced into the side chain of the polyphosphate flame retardant, and a spirocyclic phosphate ester-terephthalic acid ester with char-forming properties is used as the main chain of the polyphosphate flame retardant to prepare a polyphosphate flame retardant with high thermal stability.

[0016] The polyphosphate flame retardant prepared by this invention has a high content of flame retardant elements, improves the catalytic carbonization ability of phosphoric acid, pyrophosphate and sulfonic acid, as well as the free radical capture efficiency of phosphorus-containing free radicals and sulfur dioxide and the fuel dilution efficiency.

[0017] The polyphosphate flame retardant prepared by this invention contains both +3 and +5 valence phosphorus. Compared with flame retardants with a single phosphorus-containing structure, the combination of different phosphorus-containing structures is beneficial to improving the thermal stability of the material. The +3 valence phosphorus can be thermally released into the gas phase, combine with free radicals, and play a gas phase flame retardant role. The +5 valence phosphorus can improve the high-temperature charring of the material and play a condensed phase flame retardant role.

[0018] The benzothiazole ring introduced in this invention not only improves the thermal stability of polyphosphate, but also, during the heating process, the ammonia formed by the nitrogen in it plays a further role in gas-phase flame retardancy, and the sulfonic acid generated by the sulfur is more acidic, which is more conducive to the formation of the char layer. Through the synergistic effect of P, N and S in flame retardancy, the flame retardant effect is further improved. Attached Figure Description

[0019] Figure 1These are the mass spectrum and 1H NMR spectrum of 2-(4-hydroxyphenyl)benzothiazole in Example 1, where A is the mass spectrum of 2-(4-hydroxyphenyl)benzothiazole and B is the 1H NMR spectrum of 2-(4-hydroxyphenyl)benzothiazole. Figure 2 This is the infrared spectrum of 2-(4-hydroxyphenyl)benzothiazole in Example 1; Figure 3 This is the infrared spectrum of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole in Example 1; Figure 4 This is the infrared spectrum of spirocyclic phosphate-terephthalic acid ester in Example 1; Figure 5 These are the TG and DTG curves of the thermogravimetric analysis of polyphosphate flame retardants, where a is the TG curve and b is the DTG curve. Figure 6 These are characteristic curves of the heat release rate (HRR) and total heat release (THR) of the composite material, where a is the HRR curve of the composite material and b is the THR curve of the composite material. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0021] Example 1: A method for preparing a high thermal stability polyphosphate flame retardant, specifically including the following steps: S1. 0.4 mmol of 2,2'-dithiodiphenylamine, 0.8 mmol of p-hydroxybenzaldehyde, 0.2 mmol of sodium sulfide nonahydrate, and 0.2 mmol of sodium bicarbonate were added sequentially to the reactor. Under a nitrogen atmosphere, 3 mL of the reaction solvent N,N-dimethylformamide was added. The reaction was magnetically stirred at 100 °C for 5 h. After the reaction was completed, the reaction system was cooled to room temperature. The reaction system was then placed in a separatory funnel, and sodium bisulfite solution was added to quench the reaction. Dichloromethane was then added for extraction to separate the organic phase. The organic phase was then dried with anhydrous magnesium sulfate for 30 min. The anhydrous magnesium sulfate was removed by filtration, and the dichloromethane solvent was removed by vacuum distillation to obtain the crude product. The crude product was separated by column chromatography (using a 200-mesh silica gel column) with a 1:1 volume ratio of petroleum ether and ethyl acetate to obtain 2-(4-hydroxyphenyl)benzothiazole. The reaction equation is: ; S2. Mix 5 mmol of 2-(4-hydroxyphenyl)benzothiazole and 1.21 mL of anhydrous pyridine. Add 15 mL of anhydrous acetonitrile to the mixture under stirring to obtain a mixed system. Place the mixed system in an ice-water bath and slowly add 10 mmol of phosphorus oxychloride dropwise. After the addition is complete, remove the ice bath and allow the reaction system to naturally warm to room temperature. Stir for 2 h, then heat to reflux and continue stirring for 4 h. After the reaction is complete, cool the reaction system to 0 °C. Pour the reaction system into 100 mL of ice water under stirring. Extract three times with dichloromethane. Combine the organic phases and wash them successively with cold saturated sodium bicarbonate solution and saturated brine. Dry with anhydrous magnesium sulfate, filter to remove anhydrous magnesium sulfate, and then remove the solvent dichloromethane by rotary evaporation at 30 °C to obtain 2-(4-dichlorophosphoryloxyphenyl)benzothiazole. The reaction equation is as follows: ; S3. Under a nitrogen atmosphere, 0.2 mol pentaerythritol, 80 mL xylene, and 0.01 mol pyridine were mixed to obtain a mixture. The mixture was placed in an ice-water bath at 5 °C, and 0.42 mol phosphorus trichloride was added dropwise over 30 min. The temperature was then raised to 80 °C, and the mixture was stirred and refluxed at a constant temperature of 80 °C for 1 h to obtain pentaerythritol dichlorophosphite. The hydrogen chloride gas generated during the reaction was discharged through a condenser and absorbed by sodium hydroxide solution. After the reaction was completed, the nitrogen gas was stopped, and the hydrogen chloride in the reaction system was removed by a vacuum pump. At the same time, the pressure of the system was reduced to 3000 Pa. The mixture was then stirred for 30 min, and nitrogen gas was continued to be introduced into the reaction system. Then, 0.4 mol of triethylamine and 100 mL of xylene were added to the reaction system. The reaction system was then cooled to 5 °C. A mixed solution of 0.4 mol of terephthalic acid and 100 mL of xylene was slowly added dropwise to the reaction system. After the addition was complete, the temperature of the reaction system was raised by 8-10 °C and then refluxed for 1 h. After the reaction was complete, the temperature was lowered to room temperature, the solid was collected by filtration, washed with xylene, and dried to obtain spirocyclic phosphate-terephthalic acid ester. The reaction equation is: ; ; S4. Dissolve 10 mol of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole in 100 mL of dichloromethane to obtain a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole; 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline; Under a nitrogen atmosphere, 10 mol of spirocyclic phosphate-terephthalic acid ester, 10 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in an ice-water bath at 5 °C and stirred. Then, a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added to the solution, and the reaction was allowed to proceed for 2 h. The solution was then heated to 70 °C and reacted for 5 h. Next, a dichloromethane solution of aniline was added to the solution, and the reaction was continued at 70 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the triethylamine and dichloromethane were removed by filtration and rotary evaporation. After drying, a polyphosphate flame retardant was obtained. The reaction equation is: ; .

[0022] In this embodiment, the mass spectrum and 1H NMR spectrum of 2-(4-hydroxyphenyl)benzothiazole are as follows: Figure 1 As shown, A is the mass spectrum of 2-(4-hydroxyphenyl)benzothiazole, and B is the 1H NMR spectrum of 2-(4-hydroxyphenyl)benzothiazole. Figure 1 It can be seen that, 1 H-NMR (500MHz, DMSO, TMS) δ: 10.21 (s, 1H), 8.09 (d, 1H, J=7.5Hz), 7.98 (dd, 1H, J=8.0 , 0.5Hz), 7.93-7.95 (m, 2H), 7.49-7.52 (m, 1H), 7.39-7.42 (m, 1H), 6.93-6.95 (m, 2H); MS (ESI): m / z calcd for C 13 H 10 NOS ([M+H))+ ): 228.04, found 228.05.

[0023] Figure 2 This is the infrared spectrum of 2-(4-hydroxyphenyl)benzothiazole in this embodiment, obtained by... Figure 2 It can be seen that 3400cm -1 A characteristic peak for the hydroxyl group on the benzene ring appears nearby, at 1230 cm⁻¹. -1 The presence of a moderately strong characteristic peak for the carbon-oxygen bond in the benzene ring indicates the presence of a para-substituted hydroxyl group in the benzene ring, at 1620-1580 cm⁻¹. -1 A stretching vibration peak of a carbon-nitrogen double bond appears nearby, at 500 cm⁻¹. -1 Characteristic peaks of carbon-sulfur bonds appear nearby.

[0024] In this embodiment, the infrared spectrum of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole is as follows: Figure 3 As shown, by Figure 3 It can be seen that 3400cm -1 The characteristic peak of the hydroxyl group on the benzene ring disappears in the vicinity, 1280-1330 cm⁻¹ -1 A characteristic peak of the P=O bond appears nearby, at 520 cm⁻¹. -1 A stretching vibration peak of P-Cl appeared nearby.

[0025] In this embodiment, the infrared spectrum of spirocyclic phosphate-terephthalic acid ester is as follows: Figure 4 As shown, by Figure 4 It can be seen that 3349cm -1 A stretching vibration absorption peak of hydroxyl groups appears nearby, at 3027 cm⁻¹. -1 The nearby peaks are the stretching vibration peaks of methyl and methylene groups, at 1238 cm⁻¹. -1 and 1178cm -1 The characteristic absorption peak of POC appears nearby, at 830 cm⁻¹. -1 The characteristic peaks appearing nearby indicate that the benzene ring is a p-disubstituted benzene ring.

[0026] Example 2: A method for preparing a high thermal stability polyphosphate flame retardant, specifically including the following steps: S1. 0.4 mmol of 2,2'-dithiodiphenylamine, 0.8 mmol of p-hydroxybenzaldehyde, 0.4 mmol of sodium sulfide nonahydrate, and 0.4 mmol of sodium bicarbonate were added sequentially to the reactor. Under a nitrogen atmosphere, 3 mL of the reaction solvent N,N-dimethylformamide was added. The reaction was magnetically stirred at 100 °C for 8 h. After the reaction was completed, the reaction system was cooled to room temperature. The reaction system was then placed in a separatory funnel, and sodium bisulfite solution was added to quench the reaction. Dichloromethane was then added for extraction to separate the organic phase. The organic phase was then dried with anhydrous magnesium sulfate for 30 min. The anhydrous magnesium sulfate was removed by filtration, and the dichloromethane solvent was removed by vacuum distillation to obtain the crude product. The crude product was separated by column chromatography (using a 200-mesh silica gel column) with a 1:1 volume ratio of petroleum ether and ethyl acetate to obtain 2-(4-hydroxyphenyl)benzothiazole. S2. Mix 5 mmol of 2-(4-hydroxyphenyl)benzothiazole and 1.42 mL of anhydrous pyridine. Add 15 mL of anhydrous acetonitrile to the mixture under stirring to obtain a mixed system. Place the mixed system in an ice-water bath and slowly add 10 mmol of phosphorus oxychloride dropwise. After the addition is complete, remove the ice bath and allow the reaction system to naturally warm to room temperature. Stir for 2 h, then heat to reflux and continue stirring for 6 h. After the reaction is complete, cool the reaction system to 0 °C. Pour the reaction system into 100 mL of ice water under stirring. Extract three times with dichloromethane. Combine the organic phases and wash them successively with cold saturated sodium bicarbonate solution and saturated brine. Dry with anhydrous magnesium sulfate, filter to remove anhydrous magnesium sulfate, and then remove the solvent dichloromethane by rotary evaporation at 30 °C to obtain 2-(4-dichlorophosphoryloxyphenyl)benzothiazole. S3. Under a nitrogen atmosphere, 0.2 mol pentaerythritol, 80 mL xylene, and 0.01 mol pyridine were mixed to obtain a mixture. The mixture was placed in an ice-water bath at 5 °C, and 0.46 mol phosphorus trichloride was added dropwise over 30 minutes. The temperature was then raised to 80 °C, and the mixture was stirred and refluxed at a constant temperature of 80 °C for 1 hour to obtain pentaerythritol dichlorophosphite. The hydrogen chloride gas generated during the reaction was discharged through a condenser and absorbed by sodium hydroxide solution. After the reaction was completed, the nitrogen gas was stopped, and the hydrogen chloride in the reaction system was removed by a vacuum pump. At the same time, the pressure of the system was reduced to 3000 Pa. The mixture was then stirred for 30 minutes, and nitrogen gas was continued to be introduced into the reaction system. Then, 0.4 mol of triethylamine and 100 mL of xylene were added to the reaction system. The reaction system was then cooled to 5 °C. A mixed solution of 0.4 mol of terephthalic acid and 100 mL of xylene was slowly added dropwise to the reaction system. After the addition was complete, the temperature of the reaction system was raised by 8-10 °C and then refluxed for 1 h. After the reaction was complete, the temperature was lowered to room temperature, the solid was collected by filtration, washed with xylene, and dried to obtain spirocyclic phosphate-terephthalic acid ester. S4. Dissolve 10 mol of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole in 100 mL of dichloromethane to obtain a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole; 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline; Under a nitrogen atmosphere, 10 mol of spirocyclic phosphate-terephthalic acid ester, 12 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in an ice-water bath at 5 °C and stirred. Then, a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added to the solution, and the reaction was allowed to proceed for 2 h. The solution was then heated to 70 °C and reacted for 5 h. Next, a dichloromethane solution of aniline was added to the solution, and the reaction was continued at 70 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the triethylamine and dichloromethane were removed by filtration and rotary evaporation. The product was then dried to obtain a polyphosphate flame retardant.

[0027] Example 3: A method for preparing a high thermal stability polyphosphate flame retardant, specifically including the following steps: S1. 0.4 mmol 2,2'-dithiodiphenylamine, 0.8 mmol p-hydroxybenzaldehyde, 0.3 mmol sodium sulfide nonahydrate, and 0.3 mmol sodium bicarbonate were added sequentially to the reactor. Under a nitrogen atmosphere, 3 mL of the reaction solvent N,N-dimethylformamide was added. The reaction was magnetically stirred at 100 °C for 7 h. After the reaction was completed, the reaction system was cooled to room temperature. The reaction system was then placed in a separatory funnel, and sodium bisulfite solution was added to quench the reaction. Dichloromethane was then added for extraction to separate the organic phase. The organic phase was then dried with anhydrous magnesium sulfate for 30 min. The anhydrous magnesium sulfate was removed by filtration, and the dichloromethane solvent was removed by vacuum distillation to obtain the crude product. The crude product was separated by column chromatography (using a 200-mesh silica gel column) with a 1:1 volume ratio of petroleum ether and ethyl acetate to obtain 2-(4-hydroxyphenyl)benzothiazole. S2. Mix 5 mmol of 2-(4-hydroxyphenyl)benzothiazole and 1.3 mL of anhydrous pyridine. Add 15 mL of anhydrous acetonitrile to the mixture under stirring to obtain a mixed system. Place the mixed system in an ice-water bath and slowly add 10 mmol of phosphorus oxychloride dropwise. After the addition is complete, remove the ice bath and allow the reaction system to naturally warm to room temperature. Stir for 2 h, then heat to reflux and continue stirring for 5 h. After the reaction is complete, cool the reaction system to 0 °C. Pour the reaction system into 100 mL of ice water under stirring. Extract three times with dichloromethane. Combine the organic phases and wash them successively with cold saturated sodium bicarbonate solution and saturated brine. Dry with anhydrous magnesium sulfate, filter to remove anhydrous magnesium sulfate, and then remove the solvent dichloromethane by rotary evaporation at 30 °C to obtain 2-(4-dichlorophosphoryloxyphenyl)benzothiazole. S3. Under a nitrogen atmosphere, 0.2 mol pentaerythritol, 80 mL xylene, and 0.01 mol pyridine were mixed to obtain a mixture. The mixture was placed in an ice-water bath at 5 °C, and 0.44 mol phosphorus trichloride was added dropwise over 30 min. The temperature was then raised to 80 °C, and the mixture was stirred and refluxed at a constant temperature of 80 °C for 1 h to obtain pentaerythritol dichlorophosphite. The hydrogen chloride gas generated during the reaction was discharged through a condenser and absorbed by sodium hydroxide solution. After the reaction was completed, the nitrogen gas was stopped, and the hydrogen chloride in the reaction system was removed by a vacuum pump. At the same time, the pressure of the system was reduced to 3000 Pa. The mixture was then stirred for 30 min, and nitrogen gas was continued to be introduced into the reaction system. Then, 0.4 mol of triethylamine and 100 mL of xylene were added to the reaction system. The reaction system was then cooled to 5 °C. A mixed solution of 0.4 mol of terephthalic acid and 100 mL of xylene was slowly added dropwise to the reaction system. After the addition was complete, the temperature of the reaction system was raised by 8-10 °C and then refluxed for 1 h. After the reaction was complete, the temperature was lowered to room temperature, the solid was collected by filtration, washed with xylene, and dried to obtain spirocyclic phosphate-terephthalic acid ester. S4. Dissolve 10 mol of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole in 100 mL of dichloromethane to obtain a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole; 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline; Under a nitrogen atmosphere, 10 mol of spirocyclic phosphate-terephthalic acid ester, 11 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in an ice-water bath at 5 °C and stirred. Then, a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added to the solution, and the reaction was allowed to proceed for 2 h. The solution was then heated to 70 °C and reacted for 5 h. Next, a dichloromethane solution of aniline was added to the solution, and the reaction was continued at 70 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the triethylamine and dichloromethane were removed by filtration and rotary evaporation. The product was then dried to obtain a polyphosphate flame retardant.

[0028] Comparative Example 1: A method for preparing a polyphosphate flame retardant, comprising using phenyl phosphate dichloride and spirocyclic phosphate-terephthalic acid ester as reactive monomers, polycondensing to obtain a polyphosphate prepolymer, and then using aniline as a capping agent to obtain the polyphosphate flame retardant. The specific preparation method is as follows: 10 mol of phenyl phosphate dichloride was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of phenyl phosphate dichloride; 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline; Under a nitrogen atmosphere, 10 mol of spirocyclic phosphate-terephthalic acid ester, 12 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in an ice-water bath at 5 °C and stirred. Then, a dichloromethane solution of phenyl phosphate dichloride was slowly added to the solution, and the reaction was allowed to proceed for 2 h. The solution was then heated to 70 °C and reacted for 5 h. Next, a dichloromethane solution of aniline was added to the solution, and the reaction was continued at 70 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the solution was filtered and the triethylamine and dichloromethane were removed by rotary evaporation. After drying, the polyphosphate flame retardant was obtained.

[0029] Comparative Example 2: A method for preparing a polyphosphate flame retardant, comprising using phenyl phosphate dichloride and 4,4-dihydroxybiphenyl as reactive monomers, polycondensing to obtain a polyphosphate prepolymer, and then using aniline as a capping agent to obtain the polyphosphate flame retardant. The specific preparation method is as follows: 10 mol of phenyl phosphate dichloride was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of phenyl phosphate dichloride; 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline; Under a nitrogen atmosphere, 10 mol of 4,4-dihydroxybiphenyl, 12 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in an ice-water bath at 5 °C and stirred. Then, a dichloromethane solution of phenyl dichloride phosphate was slowly added to the solution, and the reaction was allowed to proceed for 2 h. The solution was then heated to 70 °C and reacted for 5 h. Next, a dichloromethane solution of aniline was added to the solution, and the reaction was continued at 70 °C for 12 h under a nitrogen atmosphere. After the reaction was completed, the solution was filtered and the triethylamine and dichloromethane were removed by rotary evaporation. After drying, the polyphosphate flame retardant was obtained.

[0030] The thermal stability and flame retardancy of the polyphosphate flame retardants prepared in Example 1 and Comparative Examples 1-2 were tested.

[0031] The thermal stability of polyphosphate flame retardants under a nitrogen atmosphere was studied using thermogravimetric analysis (TGA). The gas flow rate was 20 mL / min, the heating rate was 20 °C / min, the heating range was 40–700 °C, and the sample amount was approximately 10 mg. The results are as follows: Figure 5 As shown, a is the TG curve of the polyphosphate flame retardant obtained by thermogravimetric analysis, and b is the DTG curve of the polyphosphate flame retardant obtained by thermogravimetric analysis; the initial decomposition temperature (T) is also shown. 5% ), temperature at maximum weightlessness rate (T) max The data for carbon residue at 700℃ and 700℃ are shown in Table 1.

[0032] Table 1. Results of thermal stability study of polyphosphate flame retardants

[0033] Depend on Figure 5As can be seen from Table 1, the initial decomposition temperature (T) of the polyphosphate flame retardant in Example 1 is... 5% The temperature at which the maximum rate of weight loss occurs is 375℃ (T). max The temperature was 568.27℃, and the residual char content at 700℃ was 55.12wt%, exhibiting excellent thermal stability and char-forming performance. The thermal stability of the polyphosphate flame retardants in Comparative Examples 1 and 2 was not as good as that in Example 1. Compared with Example 1, Comparative Example 1 did not have a benzothiazole ring in its side chain, which led to a decrease in the thermal stability of the polyphosphate flame retardant. Comparative Example 2 only had a single +5 valence phosphorus, which further reduced its thermal stability.

[0034] The polyphosphate flame retardants of Example 1 and Comparative Examples 1-2 were used to prepare composite materials. The specific method was as follows: 10g of polyphosphate flame retardant was added to 50g of bisphenol A type epoxy resin (DGEBA, E-44, epoxy value 0.44) by physical addition. The mixture was heated to 65°C and stirred continuously until the system was homogeneous. Then, 25g of curing agent m-phenylenediamine was added and stirred evenly. After vacuuming to remove air bubbles, the mixture was poured into a preheated mold and cured at 80°C for 2 hours, followed by curing at 120°C for 2 hours.

[0035] The composite material was subjected to limiting oxygen index and vertical burning tests. The limiting oxygen index test was conducted according to the standard ASTM D2863-1970, and the vertical burning test was conducted according to the standard ANSI / UL-94-2010. The results of the limiting oxygen index test and vertical burning test are shown in Table 2.

[0036] Table 2 Results of Limiting Oxygen Index Test and Vertical Burning Test of Composite Materials

[0037] As can be seen from Table 2, the composite material prepared by the polyphosphate flame retardant in Example 1 has the best flame retardant performance. Comparative Examples 1 and 2 are not as good as Example 1. Among them, the LOI value of Comparative Example 1 is slightly lower than that of Example 1, and the LOI value of Comparative Example 2 is very low. This indicates that the +5 valence phosphorus mainly plays a role in the flame retardancy of the condensed phase and has a poor effect on improving the LOI.

[0038] To further characterize the actual combustion performance of the composite material, cone calorimetry (CONE) was performed on the composite material, with a radiation power of 50 kW / m². 2 ,like Figure 6 As shown, the characteristic curves of heat release rate (HRR) and total heat release (THR) of the composite material are presented, where a is the HRR curve of the composite material and b is the THR curve of the composite material. The cone calorimetry test results are shown in Table 3.

[0039] Table 3. Cone calorimetry test results of composite materials

[0040] Depend on Figure 6 As shown in Table 3, the peak heat release and total heat release of Comparative Examples 1-2 are higher than those of Example 1, indicating that the flame retardant of Example 1 has the best effect. The polyphosphate flame retardant of Comparative Example 1 does not have a benzothiazole ring in its side chain, which leads to a certain degree of decrease in both gas-phase and condensed-phase flame retardancy. Compared with Example 1 and Comparative Example 1, Comparative Example 2 only contains phosphorus in the +5 oxidation state in its structure and uses 4,4-dihydroxybiphenyl as the raw material monomer, which further reduces its gas-phase and condensed-phase flame retardancy. Therefore, Comparative Example 2 has the worst flame retardant effect.

[0041] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A process for the preparation of a high thermal stability polyphosphate flame retardant characterized in that, The method comprises the following steps: S1, mixing 2-(4-hydroxyphenyl) benzothiazole and anhydrous pyridine, adding anhydrous acetonitrile to the mixture under stirring, slowly adding phosphorus oxychloride to the mixture in an ice water bath, and then carrying out reaction after dropwise addition, cooling the reaction system to 0℃ after the reaction is completed, pouring into ice water under stirring, and then sequentially carrying out extraction, washing, drying, and rotary evaporation to obtain 2-(4-dichlorophosphoryloxyphenyl) benzothiazole; S2, using pentaerythritol and phosphorus trichloride as reactants to obtain pentaerythritol dichlorodiphosphite by one-step method, and then adding p-xylylene glycol to prepare the spirocyclic phosphate-p-xylylene glycol diester; S3, using 2-(4-dichlorophosphoryloxyphenyl) benzothiazole and the spirocyclic phosphate-p-xylylene glycol diester as reactants to carry out polycondensation to obtain a flame retardant precursor, and then using aniline to carry out end-capping to obtain a polyphosphate flame retardant.

2. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 1, characterized in that, In step S1, the preparation method of the 2-(4-hydroxyphenyl) benzothiazole comprises the following steps: sequentially adding 2,2'-dithiodiphenylamine, p-hydroxybenzaldehyde, sodium sulfide nine hydrates, and sodium bicarbonate into a reactor, adding N,N-dimethylformamide into the reactor under nitrogen protection, carrying out reaction under magnetic stirring at 100℃ for 5-8h, cooling the reaction system after the reaction is completed, adding sodium bisulfite solution to quench, extracting with dichloromethane, and finally drying, reducing pressure distillation, and separation and purification to obtain 2-(4-hydroxyphenyl) benzothiazole.

3. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 2, characterized in that, The molar ratio of the 2,2'-dithiodiphenylamine and the p-hydroxybenzaldehyde is 1:2, and the molar ratio of the sodium sulfide nine hydrates, the sodium bicarbonate, and the 2,2'-dithiodiphenylamine is 0.5-1:

1.

4. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 1, characterized in that, In step S1, the molar ratio of the 2-(4-hydroxyphenyl) benzothiazole and the phosphorus oxychloride is 1:2, and the amount of the anhydrous pyridine added is 3-3.5 times the molar amount of the 2-(4-hydroxyphenyl) benzothiazole. The reaction process specifically comprises the following steps: naturally heating the reaction system to room temperature, stirring for 2h, then heating to reflux, and continuing to stir for 4-6h.

5. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 1, characterized in that, In step S2, the one-step preparation process of the spirocyclic phosphate-p-xylylene glycol diester specifically comprises the following steps: Under a nitrogen atmosphere, pentaerythritol, xylene, and pyridine are mixed, and phosphorus trichloride is added dropwise at 5℃, and the dropwise addition is completed in 30min, then constant temperature reflux stirring reaction is carried out for 1h to obtain pentaerythritol dichlorodiphosphite, the hydrogen chloride gas generated in the reaction process is discharged through a condenser and then absorbed with a sodium hydroxide solution, nitrogen is stopped after the reaction is completed, hydrogen chloride in the reaction system is removed through a vacuum pump, the pressure of the system is reduced to 3000Pa, and nitrogen is continued to be introduced into the reaction system after stirring for 30min; Triethylamine and xylene are added to the reaction system, then the reaction system is cooled to 5℃, a mixed solution of p-xylylene glycol and xylene is added dropwise, after the dropwise addition is completed, reflux reaction is carried out for 1h, then the temperature is reduced to room temperature, and the solid is washed with xylene after filtration, and then dried to obtain the spirocyclic phosphate-p-xylylene glycol diester.

6. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 5, characterized in that, The molar ratio of the pentaerythritol, the phosphorus trichloride, and the p-xylylene glycol is 1:2.1-2.3:

2.

7. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 1, characterized in that, The step S3 is specifically: mixing the spirocyclic phosphonate-p-xylylene glycol diester, triethylamine and dichloromethane under nitrogen atmosphere, stirring in an ice water bath, then slowly adding 2-(4-dichlorophosphoryloxyphenyl) benzothiazole in dichloromethane solution, reacting for 2h, then heating to 70℃ for 5h, then adding aniline in dichloromethane solution, continuing to react for 12h under nitrogen atmosphere at 70℃, after the reaction is completed, filtering, rotary evaporation and drying to obtain the polyphosphate flame retardant.

8. The method for preparing the high thermal stability polyphosphate flame retardant according to claim 7, characterized in that, The molar ratio of the spirocyclic phosphonate-p-xylylene glycol diester, 2-(4-dichlorophosphoryloxyphenyl) benzothiazole and aniline is 1:1:0.5, and the amount of the triethylamine added is 1-1.2 times of the molar amount of the spirocyclic phosphonate-p-xylylene glycol diester.

9. The polyphosphate flame retardant prepared by the method for preparing the high-thermal-stability polyphosphate flame retardant according to any one of claims 1-8.

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