High-heat-stable polyphosphate flame retardant and method for preparing same

Abstract

The application belongs to the technical field of flame retardants, and particularly relates to a high-thermal-stability polyphosphate flame retardant and a preparation method thereof. 2-(4-dichlorophosphoryloxyphenyl) benzothiazole is prepared by taking 2-(4-hydroxyphenyl) benzothiazole and phosphorus oxychloride as raw materials and performing a reaction; spirocyclic phosphate-p-xylylene glycol diester is prepared by using a one-step method; the polyphosphate flame retardant is obtained by taking 2-(4-dichlorophosphoryloxyphenyl) benzothiazole and spirocyclic phosphate-p-xylylene glycol diester as reactants, performing polycondensation to generate a flame retardant precursor, and then performing end-capping with aniline. In the application, the benzothiazole ring is introduced into the side chain of the polyphosphate flame retardant, and the spirocyclic phosphate-p-xylylene glycol ester with a charring effect is used as the main chain of the polyphosphate flame retardant, so that the polyphosphate flame retardant with high thermal stability is prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flame retardants, and particularly relates to a high-thermal-stability polyphosphate flame retardant and a preparation method thereof. BACKGROUND

[0002] Polymer materials are everywhere in modern life, however, because many polymer materials do not contain phosphorus and nitrogen flame-retardant elements, the LOI is low, and the polymer materials are extremely flammable, and once burning, it is difficult to extinguish, and a large amount of toxic gas may be generated, which brings great hidden dangers to people's life and property safety.

[0003] The flame retardant is an additive for improving the flame resistance of materials, which can inhibit or prevent the combustion of polymer materials, and makes the materials have flame retardance, self-extinguishability and smokelessness, and improves the safety performance of products. The polyphosphate flame retardant has become one of the research hotspots in the current flame retardant field due to its high efficiency, low toxicity and environmental protection.

[0004] However, the traditional polyphosphate flame retardant still has some key defects in practical application. First, most of the polyphosphate flame retardants have insufficient thermal stability, and are prone to decomposition during high-temperature processing or long-term use, which leads to a decrease in flame-retardant efficiency, and even affects the mechanical properties of the matrix material; second, the polyphosphate flame retardants in the prior art often rely on a single flame-retardant mechanism, such as gas-phase flame retardation or condensed-phase flame retardation, and are difficult to provide comprehensive and effective flame-retardant protection in a complex combustion environment. SUMMARY

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

[0006] In order to achieve the above technical purpose, the technical scheme of the present application is as follows:

[0007] A preparation method of a high-thermal-stability polyphosphate flame retardant, comprising the following steps:

[0008] 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, carrying out reaction after dropwise addition is completed, cooling the reaction system to 0 DEG C after reaction is completed, and pouring into ice water while stirring, and then sequentially performing extraction, washing, drying and rotary evaporation to obtain 2-(4-dichlorophosphoryloxyphenyl) benzothiazole;

[0009] S2, using a one-step method, taking pentaerythritol and phosphorus trichloride as reactants to obtain pentaerythritol dichlorodiphosphite, and then adding p-xylylene glycol to prepare a spirocyclic phosphate-p-xylylene glycol diester;

[0010] S3, using 2-(4-dichlorophosphoryloxyphenyl) benzothiazole and spirocyclic phosphate-p-xylylene glycol diester as reactants, carrying out polycondensation to generate flame retardant precursor, and then using aniline to end-cap, to obtain polyphosphate flame retardant.

[0011] As a further improvement, in step S1, the preparation method of the 2-(4-hydroxyphenyl) benzothiazole is: sequentially adding 2,2'-dithiodianiline, p-hydroxybenzaldehyde, sodium sulfide nine hydrates, and sodium bicarbonate into a reactor, adding N,N-dimethylformamide into the reactor under nitrogen protection, stirring magnetically at 100°C for 5-8h, after the reaction is completed, cooling the reaction system, then 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.

[0012] As a further improvement, the molar ratio of the 2,2'-dithiodianiline and the p-hydroxybenzaldehyde is 1:2, and the molar ratio of the sodium sulfide nine hydrates, the sodium bicarbonate, and the 2,2'-dithiodianiline is 0.5-1:1.

[0013] As a further improvement, 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;

[0014] The reaction process specifically is: naturally warming the reaction system to room temperature, stirring for 2h, then heating to reflux, and continuing to stir for 4-6h.

[0015] As a further improvement, in step S2, the one-step preparation process of the spirocyclic phosphate-p-xylylene glycol diester specifically is:

[0016] Under a nitrogen atmosphere, mixing pentaerythritol, xylene, and pyridine, adding phosphorus trichloride dropwise thereto at 5°C, completing the dropwise addition in 30min, then constant-temperature reflux stirring for 1h to obtain pentaerythritol dichlorodiphosphite, absorbing the hydrogen chloride gas generated in the reaction process through a condenser tube and then absorbing with a sodium hydroxide solution, stopping the nitrogen introduction after the reaction is completed, removing the hydrogen chloride in the reaction system through a vacuum pump, and at the same time, reducing the pressure of the system to 3000Pa, continuing to introduce nitrogen into the reaction system after stirring for 30min;

[0017] Adding triethylamine and xylene into the reaction system, then cooling the reaction system to 5°C, dropwise adding a mixed solution of p-xylylene glycol and xylene thereto, after the dropwise addition is completed, refluxing for 1h, then reducing to room temperature, washing the solid with xylene after filtration, and drying to obtain the spirocyclic phosphate-p-xylylene glycol diester.

[0018] As a further improvement, the molar ratio of the pentaerythritol, the phosphorus trichloride and the p-xylylene glycol is 1:2.1~2.3:2.

[0019] As a further improvement, step S3 is specifically: mixing the spirocyclic phosphate-p-xylylene glycol diester, triethylamine and dichloromethane under a nitrogen atmosphere, stirring in an ice water bath, then slowly adding a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl) benzothiazole thereto, reacting for 2h, then heating to 70℃ and reacting for 5h, then adding a dichloromethane solution of aniline thereto, continuing to react at 70℃ under a nitrogen atmosphere for 12h, after the reaction is completed, filtering, rotary evaporation and drying to obtain the polyphosphate flame retardant.

[0020] As a further improvement, the molar ratio of the spirocyclic phosphate-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 the molar amount of the spirocyclic phosphate-p-xylylene glycol diester.

[0021] The application also provides a polyphosphate flame retardant.

[0022] Due to the adoption of the above technical solutions, the application has the following beneficial effects:

[0023] The application provides a high-thermal-stability polyphosphate flame retardant and a preparation method thereof. A benzothiazole ring is introduced into the side chain of the polyphosphate flame retardant, and a spirocyclic phosphate-p-xylylene glycol ester with a charring effect is used as the main chain of the polyphosphate flame retardant, so that a polyphosphate flame retardant with high thermal stability is prepared.

[0024] The polyphosphate flame retardant prepared by the application has a high content of flame-retardant elements, and the catalytic carbonization capacity of phosphoric acid, pyrophosphoric acid and sulfonic acid, and the free radical capture and fuel dilution efficiency of phosphorus-containing free radicals and sulfur dioxide are improved.

[0025] The polyphosphate flame retardant prepared by the application contains both +3 valence state and +5 valence state phosphorus. Compared with a flame retardant containing only a single phosphorus structure, the combination of different phosphorus structures is beneficial to the improvement of the thermal stability of the material. The +3 valence state P can be released into the gas phase and combine with free radicals to play a gas-phase flame-retardant role, and the +5 valence state P can improve the high-temperature charring property of the material to play a condensed-phase flame-retardant role.

[0026] The benzothiazole ring introduced in the application not only improves the thermal stability of the polyphosphate, but also further plays a role in gas-phase flame retardation in the process of heating, the ammonia gas formed by N is more conducive to the formation of a carbon layer, and the sulfonic acid formed by S is more acidic, and the flame-retardant effect is further improved through the synergistic effect of P, N and S. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the mass spectrum and the nuclear magnetic hydrogen spectrum of 2-(4-hydroxyphenyl) benzothiazole in Example 1, wherein A is the mass spectrum of 2-(4-hydroxyphenyl) benzothiazole, B is the nuclear magnetic hydrogen spectrum of 2-(4-hydroxyphenyl) benzothiazole;

[0028] Figure 2 is the infrared spectrum of 2-(4-hydroxyphenyl) benzothiazole in Example 1;

[0029] Figure 3 is the infrared spectrum of 2-(4-dichlorophosphoryloxyphenyl) benzothiazole in Example 1;

[0030] Figure 4 is the infrared spectrum of spirocyclic phosphate-p-xylylene glycol ester in Example 1;

[0031] Figure 5 is the TG curve and the DTG curve of the thermal gravimetric analysis test of the polyphosphate flame retardant, wherein a is the TG curve, and b is the DTG curve;

[0032] Figure 6 is the characteristic curve of the heat release rate (HRR) and the total heat release (THR) of the composite material, wherein a is the HRR curve of the composite material, and b is the THR curve of the composite material. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described clearly and completely in combination with the specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0034] Example 1 A method for preparing a high-thermal-stability polyphosphate flame retardant, specifically comprising the following steps:

[0035] S1, 0.4 mmol of 2,2'-dithiodianiline, 0.8 mmol of p-hydroxybenzaldehyde, 0.2 mmol of sodium sulfide nonahydrate and 0.2 mmol of sodium bicarbonate were sequentially added to the reactor, 3 mL of reaction solvent N,N-dimethylformamide was added under a nitrogen atmosphere, and the reaction was stirred magnetically at 100°C for 5 h. After the reaction was completed, the reaction system was cooled to room temperature, then placed in a separatory funnel, quenched by adding sodium bisulfite solution, then extracted with dichloromethane, the organic phase was separated and dried with anhydrous magnesium sulfate for 30 min, filtered to remove anhydrous magnesium sulfate, then the dichloromethane solvent was removed by reduced pressure distillation to obtain a crude product, which was separated by column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 1:1 (using a 200-mesh silica gel column) to obtain 2-(4-hydroxyphenyl)benzothiazole;

[0036] The reaction equation is:

[0037] ;

[0038] S2, 5 mmol of 2-(4-hydroxyphenyl)benzothiazole and 1.21 mL of anhydrous pyridine were mixed under stirring to obtain a mixed system, which was placed in an ice water bath, and 10 mmol of phosphorus oxychloride was slowly added dropwise. After the dropwise addition was completed, the ice bath was removed, and the reaction system was naturally warmed to room temperature and stirred for 2 h, then heated to reflux and continued to stir for 4 h. After the reaction was completed, the reaction system was cooled to 0°C, and then poured into 100 mL of ice water under stirring. The organic phase was extracted with dichloromethane three times, then combined, and the organic phase was sequentially washed with cold saturated sodium bicarbonate solution and saturated brine, then dried with anhydrous magnesium sulfate, filtered to remove anhydrous magnesium sulfate, and then rotary evaporated at 30°C to remove the dichloromethane solvent to obtain 2-(4-dichlorophosphoryloxyphenyl)benzothiazole;

[0039] The reaction equation is as follows:

[0040] ;

[0041] S3, 0.2 mol of pentaerythritol, 80 mL of xylene and 0.01 mol of pyridine were mixed to obtain a mixed solution, which was placed in a 5°C ice water bath, and 0.42 mol of phosphorus trichloride was added dropwise. The dropwise addition was completed in 30 min, then the temperature was increased to 80°C, and the reaction was stirred at a constant temperature of 80°C for 1 h to obtain pentaerythritol dichlorodiphosphite. During the reaction, the generated hydrogen chloride gas was discharged through a condenser and absorbed with a sodium hydroxide solution. After the reaction was completed, the nitrogen gas was stopped, the hydrogen chloride in the reaction system was removed by a vacuum pump, the pressure of the system was reduced to 3000 Pa, then stirred for 30 min, and the nitrogen gas was continued to be introduced into the reaction system.

[0042] Then 0.4 mol of triethylamine and 100 mL of dimethylbenzene were added to the reaction system, and then the reaction system was cooled to 5°C. A mixture solution of 0.4 mol of p-xylylene glycol and 100 mL of dimethylbenzene was slowly added dropwise to the reaction system. After the dropwise addition was completed, the temperature of the reaction system was increased by 8-10°C, and then the reaction was refluxed for 1 h. After the reaction was completed, the temperature was lowered to room temperature. The solid was collected after filtration, washed with dimethylbenzene, and dried to obtain the spirocyclic phosphonate-p-xylylene glycol ester;

[0043] The reaction equation is as follows:

[0044]

[0045]

[0046] S4, 10 mol of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole;

[0047] 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline;

[0048] Under a nitrogen atmosphere, 10 mol of spirocyclic phosphonate-p-xylylene glycol ester, 10 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in a 5°C ice water bath and stirred, and then the dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added thereto. The reaction was carried out for 2 h, and then the temperature was increased to 70°C and the reaction was carried out for 5 h. Then the dichloromethane solution of aniline was added thereto. Under a nitrogen atmosphere, the reaction was continued at 70°C for 12 h. After the reaction was completed, triethylamine and dichloromethane were removed by filtration and rotary evaporation, and then dried to obtain a polyphosphate flame retardant;

[0049] The reaction equation is as follows:

[0050]

[0051]

[0052] In this embodiment, the mass spectrum and the nuclear magnetic hydrogen spectrum of 2-(4-hydroxyphenyl)benzothiazole are shown in Figure 1 , wherein A is the mass spectrum of 2-(4-hydroxyphenyl)benzothiazole, and B is the nuclear magnetic hydrogen spectrum of 2-(4-hydroxyphenyl)benzothiazole. Figure 1 It can be seen from 1 ​​​​H-NMR (500 MHz, DMSO, TMS) δ: 10.21 (s, 1H), 8.09 (d, 1H, J = 7.5 Hz), 7.98 (dd, 1H, J = 8.0, 0.5 Hz), 7.93-7.95 (m, 2H), 7.49-7.52 (m, 1H), 7.39-7.42 (m, 1H), 6.93-6.95 (m, 2H);

[0053] MS (ESI): m / z calcd for C 13 H 10 NOS ([M+H] + ): 228.04, found 228.05.

[0054] Figure 2 is the infrared spectrum of 2-(4-hydroxyphenyl)benzothiazole in this example, which is shown in Figure 2 It can be seen that the characteristic peak of hydroxyl on benzene ring appears near 3400 cm -1 , the characteristic peak of carbon-oxygen bond in benzene ring appears at 1230 cm -1 with medium intensity, indicating that the benzene ring is substituted with hydroxyl at para position, the stretching vibration peak of carbon-nitrogen double bond appears near 1620-1580 cm -1 , the characteristic peak of carbon-sulfur bond appears near 500 cm -1 .

[0055] In this example, the infrared spectrum of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole is shown in Figure 3 , which is shown in Figure 3 It can be seen that the characteristic peak of hydroxyl on benzene ring near 3400 cm -1 disappears, the characteristic peak of P=O bond appears near 1280-1330 cm -1 , the stretching vibration peak of P-Cl appears near 520 cm -1 .

[0056] In this example, the infrared spectrum of spirocyclic phosphonate-p-xylylene ester is shown in Figure 4 , which is shown in Figure 4 It can be seen that the stretching vibration absorption peak of hydroxyl appears near 3349 cm -1 , the stretching vibration peaks of methyl and methylene appear near 3027 cm -1 , the characteristic absorption peaks of P-O-C appear near 1238 cm -1 and 1178 cm -1 , the characteristic peaks appearing near 830 cm -1 indicate that the benzene ring is para-disubstituted benzene ring.

[0057] Embodiment 2 A method for preparing a high-thermal-stability polyphosphate flame retardant, specifically comprising the following steps:

[0058] S1, 0.4 mmol of 2,2'-dithiodianiline, 0.8 mmol of p-hydroxybenzaldehyde, 0.4 mmol of sodium sulfide nonahydrate and 0.4 mmol of sodium bicarbonate were sequentially added to a reactor, 3 mL of reaction solvent N,N-dimethylformamide was added thereto under a nitrogen atmosphere, and the reaction was stirred magnetically at 100°C for 8 h. After the reaction was completed, the reaction system was cooled to room temperature, then placed in a separatory funnel, quenched by adding sodium bisulfite solution thereto, then extracted with dichloromethane, the organic phase was separated, dried with anhydrous magnesium sulfate for 30 min, filtered to remove the anhydrous magnesium sulfate, then the dichloromethane solvent was removed by reduced pressure distillation to obtain a crude product, and the crude product was separated by column chromatography (using a 200-mesh silica gel column) with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 1:1 to obtain 2-(4-hydroxyphenyl)benzothiazole;

[0059] S2, 5 mmol of 2-(4-hydroxyphenyl)benzothiazole and 1.42 mL of anhydrous pyridine were mixed, 15 mL of anhydrous acetonitrile was added thereto under stirring to obtain a mixed system, the mixed system was placed in an ice water bath, and 10 mmol of phosphorus oxychloride was slowly added dropwise thereto. After the dropwise addition was completed, the ice bath was removed, the reaction system was naturally warmed to room temperature, stirred for 2 h, then heated to reflux, and the stirring reaction was continued for 6 h. After the reaction was completed, the reaction system was cooled to 0°C, poured into 100 mL of ice water under stirring, extracted with dichloromethane three times, the organic phases were combined, then sequentially washed with cold saturated sodium bicarbonate solution and saturated brine, dried with anhydrous magnesium sulfate, filtered to remove the anhydrous magnesium sulfate, then the dichloromethane solvent was removed by rotary evaporation at 30°C to obtain 2-(4-dichlorophosphoryloxyphenyl)benzothiazole;

[0060] S3, 0.2 mol of pentaerythritol, 80 mL of dimethylbenzene and 0.01 mol of pyridine were mixed to obtain a mixed liquid, the mixed liquid was placed in a 5°C ice water bath, 0.46 mol of phosphorus trichloride was added dropwise thereto, the dropwise addition was completed in 30 min, then the temperature was increased to 80°C, and the stirring reflux reaction was carried out at a constant temperature of 80°C for 1 h to obtain pentaerythritol dichlorodiphosphite. During the reaction, the generated hydrogen chloride gas was discharged through a condenser and absorbed with a sodium hydroxide solution. After the reaction was completed, the nitrogen gas was stopped, the hydrogen chloride in the reaction system was removed by a vacuum pump, the pressure of the system was reduced to 3000 Pa, and the system was stirred for 30 min. Then, the nitrogen gas was continuously introduced into the reaction system;

[0061] Then 0.4 mol of triethylamine and 100 mL of xylene were added to the reaction system, and then the reaction system was cooled to 5°C. A mixture solution of 0.4 mol of p-xylylene glycol and 100 mL of xylene was slowly added dropwise to the reaction system. After the dropwise addition was completed, the temperature of the reaction system was increased by 8-10°C, and then the reaction was refluxed for 1 h. After the reaction was completed, the reaction system was cooled to room temperature, and then the solid was collected by filtration, washed with xylene, and dried to obtain the spirocyclic phosphonate-p-xylylene glycol ester;

[0062] S4, 10 mol of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole;

[0063] 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain an aniline dichloromethane solution;

[0064] Under a nitrogen atmosphere, 10 mol of spirocyclic phosphonate-p-xylylene glycol ester, 12 mol of triethylamine, and 100 mL of dichloromethane were mixed to obtain a mixed solution. The mixed solution was placed in a 5°C ice water bath and stirred, and then the dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added thereto. The reaction was carried out for 2 h, and then the temperature was increased to 70°C and the reaction was carried out for 5 h. Then the dichloromethane solution of aniline was added thereto. Under a nitrogen atmosphere, the reaction was continued at 70°C for 12 h. After the reaction was completed, triethylamine and dichloromethane were removed by filtration and rotary evaporation, and then dried to obtain a polyphosphate flame retardant.

[0065] Example 3, a method for preparing a high-thermal-stability polyphosphate flame retardant, specifically comprising the following steps:

[0066] S1, 0.4 mmol of 2,2'-dithiodianiline, 0.8 mmol of p-hydroxybenzaldehyde, 0.3 mmol of sodium sulfide nonahydrate, and 0.3 mmol of sodium bicarbonate were sequentially added to a reactor. Under a nitrogen atmosphere, 3 mL of a reaction solvent N,N-dimethylformamide was added thereto. The reaction was carried out at 100°C under magnetic stirring for 7 h. After the reaction was completed, the reaction system was cooled to room temperature, and then placed in a separatory funnel. Sodium bisulfite solution was added thereto for quenching, and then dichloromethane was added for extraction. The organic phase was separated, dried with anhydrous magnesium sulfate for 30 min, filtered to remove the anhydrous magnesium sulfate, and then the dichloromethane solvent was removed by reduced pressure distillation to obtain a crude product. The crude product was separated by column chromatography using a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 1:1 (a 200-mesh silica gel column was used). 2-(4-hydroxyphenyl)benzothiazole was obtained.

[0067] S2, 5 mmol of 2-(4-hydroxyphenyl) benzothiazole and 1.3 mL of anhydrous pyridine were mixed, 15 mL of anhydrous acetonitrile was added thereto under stirring to obtain a mixed system, the mixed system was placed in an ice water bath, 10 mmol of phosphorus oxychloride was slowly added dropwise thereto, after the dropwise addition was completed, the ice bath was removed, the reaction system was naturally warmed to room temperature, and stirring was continued for 2 h, then heating was continued to reflux, and stirring was continued for 5 h, after the reaction was completed, the reaction system was cooled to 0℃, the reaction system was poured into 100 mL of ice water under stirring, extraction was performed with dichloromethane three times, the organic phase was combined, the organic phase was sequentially washed with a cold saturated sodium bicarbonate solution and a saturated brine solution, then dried with anhydrous magnesium sulfate, the anhydrous magnesium sulfate was removed by filtration, then dichloromethane was removed by rotary evaporation at 30℃ to obtain 2-(4-dichlorophosphoryloxyphenyl) benzothiazole;

[0068] S3, 0.2 mol of pentaerythritol, 80 mL of xylene and 0.01 mol of pyridine were mixed to obtain a mixed solution, the mixed solution was placed in a 5℃ ice water bath, 0.44 mol of phosphorus trichloride was added dropwise thereto, dropwise addition was completed in 30 min, then the temperature was increased to 80℃, and reflux reaction was performed under constant temperature of 80℃ for 1 h to obtain pentaerythritol dichlorodiphosphite, hydrogen chloride gas generated in the reaction process was discharged through a condenser and then absorbed with a sodium hydroxide solution, after the reaction was completed, the nitrogen was stopped, hydrogen chloride in the reaction system was removed through a vacuum pump, at the same time, the pressure of the system was reduced to 3000 Pa, then stirring was continued for 30 min, and nitrogen was continuously introduced into the reaction system;

[0069] Then 0.4 mol of triethylamine and 100 mL of xylene were added to the reaction system, then the reaction system was cooled to 5℃, a mixed solution of 0.4 mol of p-xyleneglycol and 100 mL of xylene was slowly added dropwise to the reaction system, after the dropwise addition was completed, the temperature of the reaction system was increased by 8~10℃, then reflux reaction was continued for 1 h, after the reaction was completed, the temperature was decreased to room temperature, the solid was collected after filtration, then washed with xylene and dried to obtain the spirocyclic phosphonate-p-xyleneglycol ester;

[0070] S4, 10 mol of 2-(4-dichlorophosphoryloxyphenyl) benzothiazole was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl) benzothiazole;

[0071] 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline;

[0072] A mixture solution of 10 mol of spirocyclic phosphate-p-xylylene glycol ester, 11 mol of triethylamine and 100 mL of dichloromethane was prepared under a nitrogen atmosphere, the mixture solution was stirred in a 5°C ice water bath, then a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added thereto, the reaction was carried out for 2 h, then heating was carried out at 70°C for 5 h, then a dichloromethane solution of aniline was added thereto, the reaction was continuously carried out at 70°C for 12 h under a nitrogen atmosphere, after the reaction was completed, triethylamine and dichloromethane were removed by filtration and rotary evaporation, and a polyphosphate flame retardant was obtained after drying.

[0073] A preparation method of a polyphosphate flame retardant, using phenyl dichlorophosphate and spirocyclic phosphate-p-xylylene glycol ester as reaction monomers, polycondensation to obtain a polyphosphate prepolymer, and then using aniline as an end-capping agent to obtain a polyphosphate flame retardant, the specific preparation method is as follows:

[0074] 10 mol of phenyl dichlorophosphate was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of phenyl dichlorophosphate;

[0075] 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline;

[0076] A mixture solution of 10 mol of spirocyclic phosphate-p-xylylene glycol ester, 11 mol of triethylamine and 100 mL of dichloromethane was prepared under a nitrogen atmosphere, the mixture solution was stirred in a 5°C ice water bath, then a dichloromethane solution of 2-(4-dichlorophosphoryloxyphenyl)benzothiazole was slowly added thereto, the reaction was carried out for 2 h, then heating was carried out at 70°C for 5 h, then a dichloromethane solution of aniline was added thereto, the reaction was continuously carried out at 70°C for 12 h under a nitrogen atmosphere, after the reaction was completed, triethylamine and dichloromethane were removed by filtration and rotary evaporation, and a polyphosphate flame retardant was obtained after drying.

[0077] A preparation method of a polyphosphate flame retardant, using phenyl dichlorophosphate and 4,4-dihydroxydiphenyl as reaction monomers, polycondensation to obtain a polyphosphate prepolymer, and then using aniline as an end-capping agent to obtain a polyphosphate flame retardant, the specific preparation method is as follows:

[0078] 10 mol of phenyl dichlorophosphate was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of phenyl dichlorophosphate;

[0079] 5 mol of aniline was dissolved in 100 mL of dichloromethane to obtain a dichloromethane solution of aniline;

[0080] Under nitrogen atmosphere, 10 mol 4,4-dihydroxydiphenyl, 12 mol triethylamine and 100 mL dichloromethane were mixed to obtain a mixed solution, the mixed solution was stirred in a 5 ℃ ice water bath, then a dichloromethane solution of phenyl phosphate dichloride was slowly added, the reaction was carried out for 2 h, then heated to 70 ℃ and reacted for 5 h, then a dichloromethane solution of aniline was added, and the reaction was continued at 70 ℃ for 12 h under nitrogen atmosphere. After the reaction was completed, triethylamine and dichloromethane were removed by filtration and rotary evaporation, and the polyphosphate flame retardant was obtained after drying.

[0081] The polyphosphate flame retardants prepared in Example 1 and Comparative Examples 1-2 were tested for thermal stability and flame retardancy.

[0082] The thermal stability of the polyphosphate flame retardant was studied by thermogravimetric analysis (TGA) under nitrogen atmosphere, the gas flow was 20 mL / min, the heating rate was 20 ℃ / min, the temperature range was 40-700 ℃, the sample amount was about 10 mg, and the results are shown in Figure 5 , wherein a is the TG curve of the polyphosphate flame retardant thermal gravimetric analysis test, b is the DTG curve of the polyphosphate flame retardant thermal gravimetric analysis test; the initial decomposition temperature (T 5% ), the temperature at the maximum weight loss rate (T max ) and the carbon residue amount at 700 ℃ are shown in Table 1.

[0083] Table 1 Thermal stability research results of polyphosphate flame retardant

[0084]

[0085] From Figure 5 and Table 1, it can be seen that the initial decomposition temperature (T 5% ) of the polyphosphate flame retardant of Example 1 is 375 ℃, the temperature at the maximum weight loss rate (T max ) is 568.27 ℃, and the carbon residue amount at 700 ℃ is 55.12 wt%, showing excellent thermal stability and carbonization performance;

[0086] The thermal stability of the polyphosphate flame retardants of Comparative Examples 1-2 is not as good as that of Example 1. Compared with Example 1, there is no benzylpropylthiazole ring in the side chain of Comparative Example 1, resulting in a decrease in the thermal stability of the polyphosphate flame retardant. In Comparative Example 2, there is only a single +5 valence state of phosphorus, and its thermal stability is further reduced.

[0087] 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.

[0088] 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.

[0089] Table 2 Results of Limiting Oxygen Index Test and Vertical Burning Test of Composite Materials

[0090]

[0091] 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.

[0092] 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.

[0093] Table 3. Cone calorimetry test results of composite materials

[0094]

[0095] 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.

[0096] The above description of the specific embodiments of the present application is not intended to limit the scope of the present application. Various other changes and modifications of the present application, which are based on the technical concept of the present application, can be made by those skilled in the art. Such changes and modifications are intended to be covered by the claims of the present application.

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, 2-(4-hydroxyphenyl) benzothiazole and anhydrous pyridine are mixed, and anhydrous acetonitrile is added thereto under stirring to obtain a mixed system, the mixed system is cooled in an ice water bath, and phosphorus oxychloride is slowly added thereto dropwise, and after dropwise addition is completed, reaction is carried out, after reaction is completed, the reaction system is cooled to 0 DEG C, and ice water is poured in while stirring, and then extraction, washing, drying and rotary evaporation are carried out in sequence to obtain 2-(4-dichlorophosphoryloxyphenyl) benzothiazole; S2, a one-step method is adopted to obtain pentaerythritol dichlorodiphosphite by using pentaerythritol and phosphorus trichloride as reactants, and then p-xylylene glycol is added to prepare the spirocyclic phosphate p-xylylene glycol diester; S3, 2-(4-dichlorophosphoryloxyphenyl) benzothiazole and the spirocyclic phosphate p-xylylene glycol diester are used as reactants to carry out polycondensation to obtain a flame retardant precursor, and then aniline is used for 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 is as follows: 2,2'-dithiodiphenylamine, p-hydroxybenzaldehyde, sodium sulfide nine hydrates and sodium bicarbonate are sequentially added into a reactor, N,N-dimethylformamide is added into the reactor under nitrogen protection, and then the reactor is subjected to magnetic stirring at 100 DEG C for 5-8 h; after reaction is completed, the reaction system is cooled, and then sodium bisulfite solution is added for quenching, followed by extraction with dichloromethane; finally, drying, reduced pressure distillation and separation and purification are carried out to obtain the 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 to the p-hydroxybenzaldehyde is 1:2, and the molar ratio of the sodium sulfide nine hydrates and the sodium bicarbonate to 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 to 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 is as follows: the reaction system is naturally warmed to room temperature, stirred for 2 h, then heated to reflux, and continuously stirred for 4-6 h.

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 is as follows: Under a nitrogen atmosphere, pentaerythritol, xylene and pyridine are mixed, and phosphorus trichloride is added dropwise thereto at 5 DEG C, and then the reaction is carried out under constant temperature reflux stirring for 1 h to obtain pentaerythritol dichlorodiphosphite; during the reaction, the generated hydrogen chloride gas is discharged through a condenser and then absorbed by a sodium hydroxide solution; after reaction is completed, the nitrogen is stopped, and the hydrogen chloride in the reaction system is removed by a vacuum pump; at the same time, the pressure of the system is reduced to 3000 Pa, and then nitrogen is continuously introduced into the reaction system after stirring for 30 min; Triethylamine and xylene are added into the reaction system, and then the reaction system is cooled to 5 DEG C; a mixed solution of p-xylylene glycol and xylene is added dropwise thereto dropwise, and then the reaction is carried out under reflux for 1 h; after the reaction is completed, the system is cooled to room temperature, and then filtration is carried out; the obtained solid is washed with xylene, 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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