Preparation method of bromo-triazine with improved thermal stability

Abstract

The invention relates to the technical field of fine chemical engineering and flame retardant preparation, and discloses a preparation method of bromo-triazine capable of improving thermal stability, and the preparation method comprises the following steps: mixing phenol, water and dichloromethane, controlling the temperature, and carrying out oxidative bromination reaction to prepare an organic phase containing tribromophenol; then, under the action of an organic amine catalyst, carrying out condensation reaction on the organic phase, liquid caustic soda and cyanuric chloride; after the reaction, washing with water to remove impurities; and in the presence of process water, firstly controlling the temperature at 38-42 DEG C for azeotropic desolvation, then raising the temperature to 85-95 DEG C for high-temperature crystallization and crystal growing, and finally cooling, filtering and drying to obtain the bromo-triazine product. By utilizing the high selectivity of the organic amine catalyst and a two-stage azeotropic crystallization process, the side reaction is effectively reduced, the solvent wrapped in the crystal is eliminated, the prepared product is high in main content and extremely low in volatile component, the temperature can reach 370 DEG C or above when the thermal weight loss is 2%, and the thermal stability is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals and flame retardant preparation technology, specifically to a method for preparing bromotriazine with improved thermal stability. Background Technology

[0002] Bromotriazine, a high-molecular-weight additive flame retardant, is widely used in the flame retardant modification of engineering plastics such as polybutylene terephthalate, acrylonitrile-butadiene-styrene copolymer, and high-impact polystyrene due to its excellent flame retardant efficiency, good photothermal stability, and anti-migration properties. With the increasing demands for material integration and processing precision in the electronics and electrical appliance industry, downstream processing manufacturers are imposing more stringent standards on the temperature resistance, appearance, and processing flowability of flame retardants.

[0003] Existing industrial production processes for bromotriazine mainly involve the nucleophilic substitution reaction of tribromophenol with cyanuric chloride under alkaline conditions. To overcome the mass transfer resistance between the organic and aqueous phases, current technologies typically rely on quaternary ammonium salt phase transfer catalysts to promote the reaction. However, due to their strong surface activity, these catalysts are difficult to completely remove during the layering and washing processes after the reaction. The trace amounts of catalyst remaining in the product are highly susceptible to thermal oxidative decomposition during subsequent drying or high-temperature processing, leading to a yellowing of the product and inducing degradation of the polymer matrix. Furthermore, in the crystallization and purification stage, existing processes often employ direct heating to evaporate organic solvents such as dichloromethane for solid-liquid separation. This solvent removal mode, lacking precise temperature control, easily leads to an imbalance between the solvent evaporation rate and the crystal growth rate, causing the crystal surface to harden and form a crust, thus trapping the solvent that has not yet escaped inside the crystal.

[0004] These product defects, caused by solvent and catalyst residues encapsulated within the crystals, not only significantly increase the volatile content of the finished flame retardant but also compromise the density and thermal stability of the crystal structure. When such flame retardants are applied to engineering plastics processed at high temperatures, they often release gases during injection molding or extrusion, leading to defects such as silver streaks and bubbles on the surface of the final product. In severe cases, they can even corrode the mold and reduce the mechanical properties of the material. Therefore, developing a brominated triazine preparation process that balances high reaction selectivity, high purity, and low volatile residues has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing bromotriazine with improved thermal stability, solving the problems of poor thermal stability and high volatile content in bromotriazine flame retardants prepared by existing technologies due to low reaction selectivity and solvent encapsulation in the crystallization process.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a method for preparing bromotriazine with improved thermal stability, the method comprising the following steps:

[0007] S1: Add phenol, water, and dichloromethane to the reactor, and control the system temperature within the range of 5℃ to 40℃ while stirring. Simultaneously add bromine and hydrogen peroxide to the system to carry out the oxidative bromination reaction.

[0008] After the reaction was completed, sodium sulfite solution was added to the reaction solution to remove unreacted oxidant. The reaction solution was then transferred to a washing vessel and washed with water at a temperature of 30°C to 35°C. After standing and separating, the lower organic phase containing tribromophenol was obtained.

[0009] S2: The organic phase containing tribromophenol is transferred to a synthesis reactor, and liquid alkali, cyanuric chloride and organic amine catalyst are added to carry out a condensation reaction.

[0010] The organic amine catalyst is selected from one of dimethylamine, pyridine, or pyrrole;

[0011] The amount of the organic amine catalyst added is 0.05 times the mass of the cyanuric chloride. The nucleophilic properties of the organic amine catalyst are used to promote the substitution reaction. After the reaction is complete, the aqueous phase is separated, and the organic phase is washed with deionized water until the pH is neutral.

[0012] S3: Add process water to the washed organic phase and perform a two-stage temperature-controlled treatment. First, control the temperature within the range of 38℃ to 42℃ for azeotropic solvent removal, utilizing the azeotropic properties of dichloromethane and water to distill off the solvent until dichloromethane is distilled off;

[0013] The temperature was then raised to 85°C to 95°C, and the mixture was kept at this temperature and stirred for 8 to 10 hours to carry out crystallization and crystal growth treatment. Finally, the system was cooled, filtered, and dried to obtain the bromotriazine.

[0014] In a preferred embodiment, the mass ratio of each material in S1 is: phenol: bromine: hydrogen peroxide = 1:(2.5-2.8):(2.1-2.4);

[0015] In the mixed solvent, the mass ratio of water to phenol is 1:1, and the mass ratio of dichloromethane to phenol is 10:1.

[0016] In a preferred embodiment, the heat preservation reaction time after the addition of S1 is completed is 3 to 6 hours. The water washing process in S1 lasts for 1 hour.

[0017] In a preferred embodiment, the molar ratio of each material in S2 is: tribromophenol: liquid alkali: cyanuric chloride = (3.1-3.2):(3.1-3.2):1.

[0018] In a preferred embodiment, the volume of process water added in S3 is equal to the volume of the organic phase.

[0019] In a preferred embodiment, the azeotropic desolvation process described in S3 continues until the dichloromethane distillate reaches more than 90% of the theoretical solvent amount.

[0020] In a preferred embodiment, the final processing step S3 specifically involves cooling the crystallized suspension to below 60°C for filtration, and then washing and drying the filter cake.

[0021] In summary, this application includes at least one of the following beneficial technical effects:

[0022] 1. This invention uses organic amine catalysts to improve the selectivity of the condensation reaction, promotes the complete substitution of the three chlorine atoms of cyanuric chloride by tribromophenoxy groups, and reduces the generation of low-substituted byproducts with poor thermal stability; at the same time, combined with high-temperature crystal growth process, the crystal structure is further rearranged and densified, thereby significantly improving the heat resistance of the product.

[0023] 2. This invention utilizes the azeotropic properties of dichloromethane and water and the low interfacial tension of the organic amine system through a low-temperature azeotropic solvent removal step, enabling the solvent to escape smoothly and completely from the inside of the droplets. This effectively avoids the phenomenon of solvent being encapsulated due to the rapid formation of crystal shells in traditional crystallization processes, thereby preventing the flame retardant from generating bubbles or causing surface defects in the product during high-temperature injection molding or extrusion processing of engineering plastics.

[0024] 3. The organic amine catalyst selected in this invention does not have strong surface activity. Compared with traditional quaternary ammonium salt phase transfer catalysts, it is easier to separate and remove from the organic phase during the layering and water washing process after the reaction, avoiding the oxidation and discoloration problem caused by catalyst residue. Therefore, the obtained bromotriazine product can have a main content of more than 99.0%, an appearance whiteness of more than 94.0, and does not contain free bromine, which is beneficial for its application in light-colored plastic products with strict color requirements. Detailed Implementation

[0025] Example:

[0026] Example 1

[0027] A method for preparing bromotriazine with improved thermal stability includes the following steps:

[0028] (1) Add 100 kg of phenol, 100 kg of deionized water and 1000 kg of dichloromethane to the reactor, start stirring, and adjust and control the system temperature to 25°C.

[0029] At this temperature, 265 kg of bromine and 225 kg of hydrogen peroxide were simultaneously added dropwise to the reactor. After the addition was complete, the reaction was continued at 25°C for 4.5 hours.

[0030] After the reaction was completed, an appropriate amount of sodium sulfite solution was added to quench the oxidant. The reaction solution was then transferred to a washing vessel and washed with water at 32°C for 1 hour. After standing and separating into layers, the lower organic phase containing tribromophenol was collected.

[0031] (2) Take a sample of the above organic phase to test the tribromophenol content, and transfer it to the synthesis reactor. Based on the detected content, add liquid alkali and cyanuric chloride in a molar ratio of tribromophenol: liquid alkali: cyanuric chloride = 3.15: 3.15: 1.

[0032] Simultaneously, pyridine catalyst was added, in an amount 0.05 times the mass of cyanuric chloride. The condensation reaction was carried out under stirring. After the reaction was complete, the aqueous phase was separated, and the organic phase was washed with deionized water until neutral.

[0033] (3) Add an equal volume of process water to the washed organic phase. First, control the temperature of the crystallization vessel at 40°C to perform azeotropic desolvation until the dichloromethane distillate reaches more than 90% of the theoretical amount. Then, slowly raise the temperature to 90°C and maintain the temperature with stirring for 9 hours to carry out crystallization and crystal growth treatment. Finally, cool the suspension to 50°C, filter, wash the filter cake with water, and dry it to obtain the bromotriazine product.

[0034] Example 2

[0035] A method for preparing bromotriazine with improved thermal stability includes the following steps:

[0036] (1) Add 100 kg of phenol, 100 kg of deionized water and 1000 kg of dichloromethane to the reactor. Turn on the stirring and adjust and control the system temperature to 5℃.

[0037] At this temperature, 250 kg of bromine and 210 kg of hydrogen peroxide were added dropwise to the reactor simultaneously. After the addition was complete, the reactor was kept at 5°C for 3 hours. After the reaction was completed, an appropriate amount of sodium sulfite solution was added for treatment. The reaction solution was then transferred to a washing vessel and washed with water at 30°C for 1 hour. The mixture was allowed to stand and separate into layers. The lower organic phase containing tribromophenol was collected.

[0038] (2) Transfer the above organic phase to the synthesis reactor. Based on the detected content, add liquid alkali and cyanuric chloride in a molar ratio of tribromophenol: liquid alkali: cyanuric chloride = 3.1:3.1:1.

[0039] Simultaneously, dimethylamine, a catalyst, was added in an amount 0.05 times the mass of cyanuric chloride. The condensation reaction was carried out under stirring. After the reaction was complete, the aqueous phase was separated, and the organic phase was washed with deionized water until neutral.

[0040] (3) Add an equal volume of process water to the washed organic phase. First, control the temperature of the crystallization vessel to 38°C and carry out azeotropic desolvation until the dichloromethane distillation amount reaches more than 90% of the theoretical amount.

[0041] The temperature was then slowly increased to 85°C, and the mixture was kept at this temperature and stirred for 8 hours to allow for crystallization and crystal growth. Finally, the suspension was cooled to 45°C, filtered, and the filter cake was washed with water and dried to obtain the bromotriazine product.

[0042] Example 3

[0043] A method for preparing bromotriazine with improved thermal stability includes the following steps:

[0044] (1) Add 100 kg of phenol, 100 kg of deionized water and 1000 kg of dichloromethane to the reactor. Turn on the stirring and adjust and control the system temperature to 40°C.

[0045] At this temperature, 280 kg of bromine and 240 kg of hydrogen peroxide were simultaneously added dropwise to the reactor. After the addition was complete, the reaction was continued at 40°C for 6 hours.

[0046] After the reaction was completed, an appropriate amount of sodium sulfite solution was added for treatment. The reaction solution was then transferred to a washing vessel and washed with water at 35°C for 1 hour. After standing and separating into layers, the lower organic phase containing tribromophenol was collected.

[0047] (2) Transfer the above organic phase to the synthesis reactor, and add liquid alkali and cyanuric chloride according to the detected content in a molar ratio of tribromophenol: liquid alkali: cyanuric chloride = 3.2:3.2:1.

[0048] Simultaneously, pyrrole catalyst was added, at an amount equal to 0.05 times the mass of cyanuric chloride. The condensation reaction was carried out under stirring. After the reaction was complete, the aqueous phase was separated, and the organic phase was washed with deionized water until neutral.

[0049] (3) Add an equal volume of process water to the washed organic phase. First, control the temperature of the crystallization vessel to 42°C and carry out azeotropic desolvation until the dichloromethane distillation reaches more than 90% of the theoretical amount.

[0050] The temperature was then slowly increased to 95°C and maintained at this temperature with stirring for 10 hours to induce crystallization and crystal growth. Finally, the suspension was cooled to 55°C, filtered, and the filter cake was washed with water and dried to obtain the bromotriazine product.

[0051] Comparative Example 1

[0052] Compared with Example 1, the difference is that in step (2), the catalyst pyridine is replaced with an equal mass of tetrabutylammonium bromide (a conventional phase transfer catalyst), and the rest are the same.

[0053] Comparative Example 2

[0054] Compared with Example 1, the difference is that in step (3), the temperature of the crystallization vessel is controlled at 40°C to carry out the first stage of temperature control operation for azeotropic desolvation. Instead, after adding process water, the system is directly heated to 90°C to distill off dichloromethane and crystallize at the same time. All other steps are the same.

[0055] Comparative Example 3

[0056] Compared with Example 1, the difference is that in step (3), after the dichloromethane distillation amount reaches more than 90% of the theoretical amount, the second stage crystal growth operation of slowly heating to 90°C and stirring for 9 hours is cancelled. Instead, the suspension is directly cooled to 50°C for filtration and drying. The rest are the same.

[0057] Compared with Example 1, Comparative Example 4 differs in that: in step (2), the catalyst is replaced with an equal mass of tetrabutylammonium bromide; and in step (3), the azeotropic crystallization process is not carried out, but the dichloromethane solvent is directly heated and evaporated to obtain a solid product. All other aspects are the same.

[0058] Test Example 1: Product Purity and Appearance Color Test

[0059] 1. Experiment Description

[0060] This test case mainly focuses on the determination of chemical purity (main content) and appearance whiteness of the bromotriazine samples prepared in Examples 1 to 3 and Comparative Examples 1 to 4.

[0061] Determination of main content (high performance liquid chromatography, HPLC)

[0062] Instrument configuration: High performance liquid chromatograph equipped with a UV detector was used.

[0063] Chromatographic conditions:

[0064] Chromatographic column: C18 reversed-phase column (size: 250mm×4.6mm, 5μm).

[0065] Mobile phase: Methanol (chromatographic grade): Water = 95:5 (volume ratio).

[0066] Flow rate: 1.0 mL / min.

[0067] Column temperature: 30℃.

[0068] Detection wavelength: 254nm.

[0069] Injection volume: 10 μL.

[0070] Determination Procedure: Weigh 0.05 g (accurate to 0.0001 g) of the dried sample to be tested, place it in a 50 mL volumetric flask, add tetrahydrofuran to dissolve and dilute to the mark, shake well, filter through a 0.45 μm organic filter membrane, and inject into the liquid chromatograph for analysis. Record the chromatogram, and calculate the percentage of the main peak area of ​​2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine using the area normalization method, as the main content of the sample.

[0071] Whiteness measurement

[0072] Instrument configuration: WSB-3A digital whiteness meter.

[0073] Measurement Procedure: Preheat the whiteness meter for 30 minutes, zero the instrument using a black tube, calibrate the instrument using a standard white plate, place an appropriate amount of the powder sample to be tested into the sample holder, flatten the surface, and press it into a smooth sample cake under the specified pressure. Place the sample cake under the test hole and measure the blue light whiteness. Measure each sample three times and take the arithmetic mean.

[0074] The experimental results are shown in Table 1.

[0075] The purity and whiteness test results of each group of samples are shown in Table 1.

[0076] Table 1: Purity and Whiteness Test Data of Each Example and Comparative Sample

[0077] Group Main content (%) Whiteness (R457) Example 1 99.23 94.9 Example 2 99.14 94.5 Example 3 99.08 94.2 Comparative Example 1 97.94 92.1 Comparative Example 2 98.86 93.6 Comparative Example 3 98.92 93.8 Comparative Example 4 97.42 90.5

[0078] Based on the test data in Table 1, the mechanism of influence of different preparation processes on product purity and appearance is analyzed as follows:

[0079] The main content of the samples in Examples 1 to 3 remained above 99.0%, and the whiteness value was above 94.0%. This is because the organic amine catalyst used in the condensation reaction stage has specific nucleophilicity. This type of catalyst can form a highly active intermediate with cyanuric chloride, reducing the activation energy of the substitution reaction, thereby promoting the complete substitution of the three chlorine atoms on the cyanuric chloride molecule by tribromophenoxy groups. This highly selective catalytic effect inhibits the formation of mono- or di-substituted byproducts, ensuring the high purity of the product from the source of the chemical reaction. In contrast, the main content of Comparative Examples 1 and 4, which used tetrabutylammonium bromide as a catalyst, was significantly lower, indicating that the limitations of conventional phase transfer catalysts in terms of steric hindrance or interfacial transport efficiency led to incomplete reactions or increased side reactions.

[0080] Regarding appearance and color, the high whiteness of the example samples is attributed to the physicochemical properties of the organic amine catalyst. Organic amine catalysts have a small molecular weight and lack strong surface activity, making them easily transferred from the organic phase to the aqueous phase and removed during the post-reaction washing step via dissolution or salt formation. Comparative Examples 1 and 4, due to the use of quaternary ammonium salt phase-transfer catalysts, possess surfactant properties, are prone to residues in the organic phase, and are susceptible to oxidative degradation during subsequent drying or thermal processing, leading to yellowing of the product. Therefore, their whiteness values ​​are significantly lower than those of the example samples.

[0081] Furthermore, the data from Comparative Examples 2 and 3 indicate that differences in crystallization processes also have a microscopic impact on the purity of the final product. The process employed in the examples—low-temperature azeotropic solvent removal followed by high-temperature crystal growth—allowed the crystals to grow orderly during the slow evaporation of dichloromethane, resulting in a dense lattice arrangement and reducing the inclusion of mother liquor within the crystals. Comparative Example 2, however, omitted the low-temperature azeotropic stage, leading to excessively rapid solvent evaporation and a crystal growth rate exceeding the impurity removal rate, resulting in some impurities being trapped within the crystals. Comparative Example 3, by omitting the high-temperature crystal growth stage, suffered from insufficient crystal density, and surface-adsorbed impurities were not adequately replaced. The absence of these physical processes resulted in slightly lower main content and whiteness in Comparative Examples 2 and 3 compared to Example 1, but they were still superior to Comparative Examples 1 and 4, which modified the catalyst system. This demonstrates that catalyst selection is the primary factor determining chemical purity, while the crystallization process is a crucial auxiliary means to further improve product quality.

[0082] Test Example 2: Volatile Matter and Solvent Residue Test

[0083] Experimental instructions

[0084] This test case aims to quantitatively evaluate the impact of different preparation processes on the residual amount of volatile substances in bromotriazine products, especially to test the removal effect of dichloromethane solvent used in the production process.

[0085] The instrument configuration for volatile matter determination includes: an electric heating drying oven, an analytical balance (sensitivity 0.0001g), and a flat weighing bottle.

[0086] Measurement steps:

[0087] Place the clean weighing bottle in a 125℃ drying oven for 1 hour, remove it and place it in a desiccator to cool to room temperature, then weigh it. ).

[0088] Weigh approximately 2g of the sample to be tested, spread it evenly at the bottom of the weighing bottle, and accurately determine its mass. ).

[0089] Place the weighing bottle containing the sample (with the cap off) in a 125℃ forced-air drying oven and heat at a constant temperature for 2 hours.

[0090] Remove the weighing bottle, cap it, and place it in a desiccator to cool to room temperature (about 30 minutes). Weigh the bottle and determine its mass. ).

[0091] Calculation formula: Volatile matter content (%) = .

[0092] Determination of dichloromethane residue

[0093] Instrument configuration: Gas chromatograph (equipped with FID detector and headspace sampler).

[0094] Chromatographic conditions:

[0095] Chromatographic column: DB-624 capillary column (30m×0.32mm×1.8μm).

[0096] Column temperature program: Initial temperature 40℃, hold for 5 minutes, then increase to 200℃ at 10℃ / min.

[0097] Inlet temperature: 220℃; Detector temperature: 250℃.

[0098] Headspace equilibrium temperature: 80℃; equilibrium time: 30 minutes.

[0099] Determination Procedure: Weigh 0.5 g of sample into a headspace vial, add 5 mL of N,N-dimethylformamide to dissolve and seal. Place the headspace vial in a headspace sampler and heat to equilibrate. Extract headspace gas and inject it into the gas chromatograph. Using the external standard method, calculate the residual amount of dichloromethane in the sample based on the peak area of ​​dichloromethane standard.

[0100] The experimental results are shown in Table 2.

[0101] The test results of volatile matter and dichloromethane residue in each embodiment and comparative sample are shown in Table 2.

[0102] Table 2: Volatility characteristics and solvent residue test data of each group of samples

[0103] Group Volatile content (%) Dichloromethane residue (ppm) Example 1 0.043 8.2 Example 2 0.038 6.5 Example 3 0.049 11.4 Comparative Example 1 0.075 35.6 Comparative Example 2 0.215 452.8 Comparative Example 3 0.128 185.3 Comparative Example 4 0.355 892.1

[0104] Table 2 reveals the solvent removal mechanism under the synergistic effect of the two-stage azeotropic crystallization process and the catalyst system. The volatile matter content of the samples from Examples 1 to 3 was controlled below 0.05%, and the residual dichloromethane was extremely low. This is mainly attributed to the low-temperature azeotropic desolvation step at 38°C to 42°C. In this temperature range, dichloromethane forms an azeotrope with water. Utilizing the low interfacial tension environment created by the organic amine catalytic system, solvent molecules can continuously and smoothly migrate from the inside of the droplet to the water-oil interface and escape. This process prevents the premature formation of a hard solid shell on the droplet surface, thus avoiding solvent encapsulation.

[0105] In contrast, Comparative Example 2 eliminated the low-temperature azeotropic stage, directly raising the temperature to cause dichloromethane to boil violently and evaporate rapidly. This led to rapid crystallization and hardening of the product surface, trapping any remaining solvent inside the crystals. Consequently, its dichloromethane residue reached a high of 452.8 ppm, and the volatile matter content increased significantly. Comparative Example 3, while retaining the azeotropic step, eliminated the high-temperature crystal growth process. The crystal structure failed to achieve densification through lattice rearrangement at high temperatures, and the trace amounts of solvent adsorbed in the interstitial spaces or micropores were not replaced and expelled by water molecules. Therefore, its volatile matter content (0.128%) was between that of the Example and Comparative Example 2. This indicates that low-temperature azeotropism is fundamental to preventing large amounts of solvent from being trapped, while high-temperature crystal growth is a necessary supplement to further reduce trace residues and achieve deep devolatification.

[0106] Furthermore, data from Comparative Example 1 show that, under the same crystallization process, simply replacing the organic amine with a quaternary ammonium salt catalyst also resulted in an increase in volatile matter and solvent residue. This is because quaternary ammonium salt catalysts have strong surface activity and easily form a stable emulsion layer at the dichloromethane-water interface, increasing the mass transfer resistance of solvent molecules crossing the interface into the gas phase, leading to some solvent being physically trapped by emulsion droplets during crystallization. In contrast, the organic amine catalyst used in the examples does not produce an emulsification effect, ensuring the mass transfer efficiency at the oil-water interface and maximizing the effect of the azeotropic desolvation process. Comparative Example 4, representing a traditional process, exhibited the highest solvent residue, confirming the significant improvement of the present invention compared to existing conventional technologies.

[0107] Test Example 3: Thermal Stability Test

[0108] Experimental instructions

[0109] In this test case, thermogravimetric analysis was used to determine the thermal decomposition behavior of each group of bromotriazine samples in order to quantitatively characterize their thermal stability.

[0110] Instrument configuration: TGA-4000 thermogravimetric analyzer.

[0111] Test conditions:

[0112] Atmosphere: High-purity nitrogen gas flow rate of 20 mL / min.

[0113] Heating program: Starting temperature is 30℃, heating to 600℃ at a heating rate of 10℃ / min.

[0114] Crucible material: alumina ceramic crucible.

[0115] Measurement steps:

[0116] Turn on the instrument and warm it up for 30 minutes before performing baseline calibration.

[0117] Weigh 5 mg to 8 mg of the powder sample to be tested, record the mass accurately, and place it in a crucible.

[0118] Once the heating program is started, the instrument automatically records the curve of sample mass changing with temperature (TGA curve).

[0119] Extract the temperature at which sample mass loss reaches 1% from the data ( ), the temperature at which mass loss reaches 2% ( ) and the temperature at which mass loss reaches 5% ( Among them, T2% is a key indicator for evaluating the heat resistance stability of this material during engineering plastics processing.

[0120] 2. The experimental results are shown in Table 3.

[0121] The thermogravimetric characteristic temperature data of each embodiment and comparative sample are shown in Table 3.

[0122] Table 3: Thermogravimetric analysis data of each group of samples

[0123] Group (℃) (℃) (℃) Example 1 361.5 372.4 385.2 Example 2 359.8 371.8 384.6 Example 3 362.1 373.1 386.5 Comparative Example 1 345.3 358.5 372.1 Comparative Example 2 310.4 342.3 368.9 Comparative Example 3 352.7 364.7 378.4 Comparative Example 4 305.6 336.9 361.2

[0124] Table 3 shows the test results for samples from Examples 1 to 3. The temperatures remained above 371℃, indicating a high thermal decomposition threshold. This high thermal stability primarily stems from the chemoselectivity of the organic amine catalyst during the condensation reaction stage. Comparing the data from Example 1 and Comparative Example 1, it is evident that, under the same post-processing conditions, the sample using the organic amine catalyst... The temperature is about 14°C higher than that of the sample using the quaternary ammonium salt catalyst. This is because the high nucleophilicity of the organic amine catalyst promotes the full substitution of the three active sites of cyanuric chloride, minimizing the formation of thermally unstable phenolic hydroxyl intermediates or incompletely substituted byproducts, thereby improving the overall chemical bond energy and pyrolysis resistance of the material.

[0125] Secondly, the low-temperature azeotropic solvent removal process directly affected the initial stage of the thermogravimetric analysis (TGA) curve. In Comparative Example 2, the elimination of the azeotropic solvent removal step from 38°C to 42°C resulted in some dichloromethane solvent being trapped inside the crystals. During the heating process in the TGA test, this trapped solvent expanded and escaped, resulting in significant mass loss even at a relatively low temperature, leading to its... and The values ​​are significantly lower than those of the example samples. The example samples completely removed the solvent through an azeotropic process, ensuring that the thermogravimetric curves reflect the skeletal decomposition temperature of the bromotriazine molecule itself, rather than the pseudo-weight loss caused by solvent evaporation.

[0126] Furthermore, the high-temperature crystal growth step at 85°C to 95°C further enhanced thermal stability through physical structure regulation. Comparing the data of Example 1 and Comparative Example 3, although the difference in chemical purity between the two is small, the sample of Example 1, which underwent high-temperature crystal growth... The temperature remains approximately 8°C higher. This is because in the high-temperature aqueous environment, the crystals undergo rearrangement and ripening, eliminating lattice defects and forming a more compact crystal structure with a smaller specific surface area. This compact crystal structure can more effectively resist heat transfer and decomposition caused by lattice vibrations when heated, thus delaying the occurrence of thermal degradation reactions. In summary, this invention achieves improved thermal stability through a dual mechanism of chemical structure purification and physical crystal densification.

Claims

1. A method for preparing bromotriazine with improved thermal stability, characterized in that, Includes the following steps: S1: Phenol, water and dichloromethane are added to the reaction vessel, and the temperature is controlled at 5-40℃. Bromine and hydrogen peroxide are added dropwise to carry out the reaction. After the reaction is completed, the mixture is treated with sodium sulfite and washed with water to separate the organic phase containing tribromophenol. S2: The organic phase containing tribromophenol is transferred to a synthesis reactor, and liquid alkali, cyanuric chloride and organic amine catalyst are added to carry out a condensation reaction; The organic amine catalyst is selected from dimethylamine, pyridine, or pyrrole, and the amount of the organic amine catalyst added is 0.05 times the mass of the cyanuric chloride. After the reaction is complete, the aqueous phase is separated, and the organic phase is washed until neutral. S3: Add process water to the washed organic phase, and first control the temperature at 38-42℃ to carry out azeotropic desolvation until dichloromethane is distilled off; Then the temperature is raised to 85-95℃, and the mixture is kept at this temperature and stirred for 8-10 hours to crystallize. Finally, the bromotriazine was obtained by cooling, filtering, and drying.

2. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S1, the mass ratio of phenol, bromine and hydrogen peroxide is 1:(2.5-2.8):(2.1-2.4).

3. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S1, the mass ratio of water to phenol is 1:1, and the mass ratio of dichloromethane to phenol is 10:

1.

4. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S1, the reaction time after the addition is completed is 3-6 hours.

5. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, The water washing process described in S1 is as follows: Transfer the reaction solution into a washing vessel and wash for 1 hour at 30-35°C.

6. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S2, the molar ratio of tribromophenol, liquid alkali and cyanuric chloride is (3.1-3.2):(3.1-3.2):

1.

7. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S3, the volume of the added process water is equal to the volume of the organic phase.

8. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S3, the azeotropic desolvation process continues until the dichloromethane distillate reaches more than 90% of the theoretical solvent amount.

9. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, In S3, the final process of cooling, filtration, and drying is as follows: The crystallized suspension was cooled to below 60°C and filtered. The filter cake was washed with water and then dried.

10. The method for preparing bromotriazine with improved thermal stability according to claim 1, characterized in that, The organic amine catalyst is pyridine.