A high melting point high whiteness methyl octabromo ether flame retardant composition and a method for preparing the same

Abstract

This application relates to a high-melting-point, high-whiteness methyl octabromoether flame retardant composition and its preparation method, belonging to the fields of fine chemicals and flame retardant preparation technology. The method includes: etherifying tetrabromobisphenol A, sodium hydroxide, and allyl chloride; purifying the mixture by isothermal crystallization at 30–50°C to obtain a tetrabromoether intermediate; dissolving the intermediate in dichloromethane and reacting it with bromine at 10–40°C; and finally, obtaining the finished product through post-treatment. This invention effectively removes impurities such as monoethers through a specific intermediate crystallization process, and avoids overheating and oxidation side reactions by combining low-temperature bromination and optimized solvent ratios. The obtained flame retardant has a melting point ≥106°C, whiteness R457 ≥92, and bromine content ≥67%, exhibiting advantages such as good thermal stability, low volatility, and high purity. The process conditions are mild and suitable for industrial production.

Description

Technical Field

[0001] This application relates to the fields of fine chemicals and flame retardant preparation technology, and in particular to a high melting point, high whiteness methyl octabromoether flame retardant composition and its preparation method. Background Technology

[0002] Octabromobisphenol A ether, chemically known as tetrabromobisphenol A ether, is a highly efficient additive flame retardant widely used in polymer materials such as polypropylene, polyethylene, and ABS resin. Because its molecular structure contains both aromatic and aliphatic bromine, it features low addition amounts, high flame retardant efficiency, minimal impact on the physical and mechanical properties of the substrate, and excellent UV resistance and light stability. It is currently one of the important alternatives to decabromodiphenyl ether and hexabromocyclododecane in the modified plastics industry.

[0003] Despite the promising applications of octabromoether, existing industrial synthesis processes still face significant technical bottlenecks in product quality control, primarily manifested in the product's low melting point and poor color. The preparation of octabromoether typically involves two steps: first, tetrabromobisphenol A reacts with allyl chloride under alkaline conditions to form the intermediate tetrabromoether; subsequently, the intermediate undergoes an addition reaction with bromine to generate the final product. In the first etherification step, due to reaction equilibrium and kinetic limitations, monoether byproducts or unreacted tetrabromobisphenol A are easily generated. Current technologies often employ simple water washing or crude solvent washing methods to treat the intermediate, making it difficult to effectively separate these structurally similar organic impurities. Based on the principle of melting point reduction, these residual low-melting-point impurities significantly disrupt the integrity of the final product's crystal lattice, resulting in a melting point that is difficult to reach above 105°C. Consequently, thermal stability decreases, making the product prone to decomposition or precipitation in the high-temperature environments of downstream plastic processing, affecting the surface quality and flame retardant durability of the final product.

[0004] Furthermore, the second step, bromination, is a strongly exothermic reaction, extremely sensitive to temperature and reaction medium. Existing processes, in pursuit of production efficiency, often employ high reaction temperatures or low solvent dilution ratios, leading to localized overheating of the reaction system. High-temperature environments not only accelerate the oxidation of bromine but may also induce molecular chain breakage or dehydrobromination reactions, generating chromophores with conjugated double bonds or carbonized particles. This directly results in the produced octabromoether exhibiting a pale yellow or even grayish-yellow appearance with low whiteness. With increasingly stringent requirements for the appearance of materials used in high-end home appliances and electronic device casings, especially the extremely high demands for color difference control in white or light-colored products, the low whiteness and low thermal stability of octabromoether produced by traditional processes can no longer meet the demands of the high-end market. Therefore, developing a production process that can effectively remove intermediate impurities and precisely control the bromination process to prepare high-melting-point, high-whiteness octabromoether has become a pressing technical problem in this field.

[0005] In view of the above-mentioned related technologies, a high melting point and high whiteness methyl octabromoether flame retardant composition and its preparation method are provided. Summary of the Invention

[0006] The purpose of this application is to provide a high-melting-point, high-whiteness methyl octabromoether flame retardant composition and its preparation method. The aim is to improve the existing technology where the preparation process of methyl octabromoether is crude due to the crude purification of intermediates, resulting in the residue of impurities such as monoether, which lowers the melting point of the product. In addition, the bromination process is prone to oxidation and yellowing due to local overheating, which leads to insufficient whiteness and makes it difficult to meet the requirements of high-end applications for high thermal stability and excellent color.

[0007] By adopting the above technical solution, a high-melting-point, high-whiteness methyl octabromoether flame retardant composition is prepared from raw materials comprising the following proportions:

[0008] Raw materials used to prepare the intermediate tetrabromo ether: 100 parts by weight of tetrabromobisphenol A, 10-30 parts by weight of sodium hydroxide, and 20-40 parts by weight of allyl chloride;

[0009] The raw materials used to prepare the final product: the molar ratio of the intermediate tetrabromoether to bromine is 1:2.05 to 2.1;

[0010] The intermediate tetrabromoether is a crystalline material obtained by etherifying the raw material, cooling it to 30-50°C for constant temperature crystallization for 3-5 hours, and then drying it after solid-liquid separation.

[0011] The final product is prepared by dissolving the crystalline material of the intermediate tetrabromoether, and then adding the bromine dropwise at a system temperature of 10–40°C to carry out a bromination reaction, while controlling the reaction temperature to not exceed 40°C during the dropwise addition process.

[0012] Furthermore, the flame retardant composition has a melting point ≥105.5℃ and a whiteness R457 ≥92.

[0013] Preferably, the flame retardant composition has a bromine content ≥67%, volatile matter ≤0.15%, acetone insoluble matter ≤0.05%, and a carbonization temperature ≥250℃.

[0014] Preferably, in the raw materials used to prepare the intermediate tetrabromoether, the weight ratio of tetrabromobisphenol A, sodium hydroxide and allyl chloride is 1:0.2:0.3.

[0015] A method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition includes the following steps:

[0016] S1. Etherification reaction: Tetrabromobisphenol A is mixed with sodium hydroxide and allyl chloride and reacted to generate a tetrabromoether reaction solution;

[0017] S2. Crystallization and purification: After the etherification reaction is completed, the product of step S1 is cooled down to 30-50℃ and crystallized at a constant temperature for 3-5 hours. After solid-liquid separation, it is dried to obtain tetrabromoether crystals.

[0018] S3, bromination reaction: Dissolve the tetrabromoether crystal material obtained in step S2 in dichloromethane, adjust the system temperature to 10-40℃, and then start adding bromine dropwise to carry out the reaction, while controlling the reaction temperature not to exceed 40℃ during the dropwise addition process;

[0019] S4. Post-treatment: After bromination, the mixture is decolorized, washed, the dichloromethane solvent is removed, and dried to obtain the flame retardant composition.

[0020] Preferably, in step S1, the reaction temperature is 45–90°C and the reaction time is 6–10 hours.

[0021] Preferably, in step S2, the purity of the dried tetrabromoether crystal material is such that its acetone-insoluble content is ≤0.05%.

[0022] Preferably, in step S3, the mass ratio of the tetrabromoether crystal material to dichloromethane is 1:2.5 to 3.5.

[0023] Preferably, step S3 is implemented by first completely dissolving the tetrabromoether crystal material in dichloromethane, and controlling the reaction temperature through a cooling medium during the dropwise addition process.

[0024] Preferably, in step S4, the decolorization involves adding an aqueous sodium sulfite solution to the reacted solution until the organic phase is colorless or pale yellow; the washing involves allowing the decolorized solution to stand and separate into layers, then washing the organic phase with deionized water until the pH value is 7.

[0025] Preferably, in step S4, the removal of the dichloromethane solvent is carried out by flash evaporation, and the final drying is carried out by airflow drying.

[0026] In summary, this application includes at least one of the following beneficial technical effects:

[0027] 1. This application introduces a constant temperature crystallization and drying process at 30-50℃ after the etherification reaction, which effectively removes monoether byproducts and unreacted raw materials in the intermediate by utilizing the difference in solubility, thereby significantly improving the purity of the intermediate; this key step enables the final methyl octabromoether flame retardant to reach a melting point of over 106℃, which is better than the common 100-103℃ level of the prior art, and exhibits better thermal stability;

[0028] 2. This application effectively avoids local overheating, oxidation, and carbonization and yellowing during the reaction process by strictly controlling the bromination reaction temperature in the low-temperature range of 10 to 40°C and using an optimized solvent ratio; the whiteness of the obtained product can reach more than 92, which meets the stringent requirements of high-end modified plastics for the color of flame retardants.

[0029] 3. This application precisely defines the mass ratio of tetrabromobisphenol A, sodium hydroxide, and allyl chloride in the etherification reaction, which ensures the reaction proceeds fully while suppressing side reactions to the greatest extent. This optimized ratio ensures the chemical structural uniformity of the product from the source, which is beneficial for obtaining high-purity tetrabromoether intermediates. Detailed Implementation

[0030] Examples 1-3:

[0031] Example 1:

[0032] This embodiment provides a method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition, the specific steps of which are as follows:

[0033] Step S1, etherification reaction:

[0034] In a reactor equipped with a stirrer, thermometer, and reflux condenser, 500 kg of tetrabromobisphenol A, 100 kg of sodium hydroxide, and 150 kg of allyl chloride were added sequentially; the stirrer was turned on and the temperature was raised, and the reaction system temperature was controlled at 70°C and kept at this temperature for 8 hours.

[0035] Step S2, Crystallization and Purification:

[0036] After the etherification reaction was completed, the material in the reactor was cooled to 40°C and maintained at this temperature for 4 hours for crystallization. After crystallization, the material was centrifuged and filtered to remove the mother liquor. The solid filter cake was collected and dried to obtain the intermediate tetrabromoether crystals. The structural characterization data of the intermediate tetrabromoether crystals were obtained from sampling and analysis as follows: Mass spectrometry (ESI-MS): m / z = 624.8 [M+H] + ;H1N NMR spectrum ( 1 HNMR, 400MHz, CDCl3): δ 7.38 (s, 4H, Ar-H), 6.15–6.05 (m, 2H, -CH=), 5.45 (dd, 2H, =CH2), 5.32 (dd, 2H, =CH2), 4.55 (d, 4H, -OCH2-), 1.62 (s, 6H, -CH3); The above data confirm the successful insertion of the allyl group, identifying it as tetrabromobisphenol A dielyl ether.

[0037] Step S3, bromination reaction:

[0038] 500 kg of the tetrabromoether crystalline intermediate prepared in step S2 was transferred into a bromination reactor; 1500 kg of dichloromethane was added, and stirring was started until the intermediate was completely dissolved; the temperature inside the reactor was adjusted to 25°C, and bromine was slowly added dropwise; the total amount of bromine added was controlled so that the molar ratio of the intermediate to bromine was 1:2.08; during the dropwise addition, the reaction temperature was always maintained at 25°C by adjusting the cooling water.

[0039] Step S4, Post-processing:

[0040] After the bromination addition reaction is completed, sodium sulfite aqueous solution is added to the reaction solution for decolorization treatment until the solution is colorless or pale yellow; the solution is allowed to stand and separate into layers, the organic phase is separated, and the organic phase is washed with deionized water until the pH of the washing solution is 7; the solvent is removed by flash evaporation of the washed organic phase, and the high melting point and high whiteness methyl octabromoether flame retardant product is obtained by air drying.

[0041] The structure of the prepared methyl octabromoether flame retardant was characterized, and the data are as follows: Mass spectrometry (ESI-MS): m / z = 944.5 [M+H] + ;H1N NMR spectrum ( 1 HNMR, 400MHz, CDCl3): δ 7.42 (s, 4H, Ar-H), 4.48–4.38 (m, 2H, -CHBr-), 4.35–4.20 (m, 4H, -OCH2-), 3.95–3.82 (m, 4H, -CH2Br), 1.65 (s, 6H, -CH3); The disappearance of the olefinic proton peak in the NMR spectrum confirmed the complete bromination addition of the double bond and confirmed the structure of the target product.

[0042] The performance of the methyl octabromoether flame retardant prepared in this embodiment was tested and found to be as follows: melting point 106.5℃, whiteness 92.5, bromine content 67.21%, volatile matter 0.12%, acetone insoluble matter 0.03%, and carbonization temperature 254℃.

[0043] Example 2:

[0044] This embodiment provides a method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition, the specific steps of which are as follows:

[0045] Step S1, etherification reaction:

[0046] In a reactor equipped with a stirrer, thermometer, and reflux condenser, 500 kg of tetrabromobisphenol A, 50 kg of sodium hydroxide, and 100 kg of allyl chloride were added sequentially; the stirrer was turned on and the temperature was raised, and the reaction system temperature was controlled at 45°C and kept at this temperature for 10 hours.

[0047] Step S2, Crystallization and Purification:

[0048] After the etherification reaction was completed, the material in the reactor was cooled to 30°C and maintained at this temperature for 3 hours for crystallization. After crystallization, the material was centrifuged and filtered to remove the mother liquor. The solid filter cake was collected and dried to obtain the intermediate tetrabromoether crystals. Sampling and analysis revealed the following structural characterization data for this intermediate: Mass spectrometry (ESI-MS): m / z = 624.8 [M+H] + ;H1N NMR spectrum ( 1 ¹H NMR, 400 MHz, CDCl₃: δ 7.38 (s, 4H), 6.15–6.05 (m, 2H), 5.45 (dd, 2H), 5.32 (dd, 2H), 4.55 (d, 4H), 1.62 (s, 6H); confirmed as tetrabromobisphenol A dielyl ether.

[0049] Step S3, bromination reaction:

[0050] 500 kg of the tetrabromoether crystalline intermediate prepared in step S2 was transferred into a bromination reactor; 1250 kg of dichloromethane was added, and stirring was started until the intermediate was completely dissolved; the temperature inside the reactor was adjusted to 10°C, and bromine was slowly added dropwise; the total amount of bromine added was controlled so that the molar ratio of the intermediate to bromine was 1:2.05; during the dropwise addition, the reaction temperature was always maintained at 10°C by adjusting the cooling water.

[0051] Step S4, Post-processing:

[0052] After the bromination addition reaction is completed, sodium sulfite aqueous solution is added to the reaction solution for decolorization treatment until the solution is colorless or pale yellow; the solution is allowed to stand and separate into layers, the organic phase is separated, and the organic phase is washed with deionized water until the pH of the washing solution is 7; the solvent is removed by flash evaporation of the washed organic phase, and the high melting point and high whiteness methyl octabromoether flame retardant product is obtained by air drying.

[0053] The structural characterization data of the obtained product are as follows: Mass spectrometry (ESI-MS): m / z = 944.5 [M+H] + ;H1N NMR spectrum ( 1 HNMR, 400MHz, CDCl3): δ 7.42 (s, 4H), 4.48–4.38 (m, 2H), 4.35–4.20 (m, 4H), 3.95–3.82 (m, 4H), 1.65 (s, 6H); The structure of the target product was confirmed.

[0054] The performance of the methyl octabromoether flame retardant prepared in this embodiment was tested and found to be as follows: melting point 106.8℃, whiteness 93.1, bromine content 67.08%, volatile matter 0.15%, acetone insoluble matter 0.04%, and carbonization temperature 252℃.

[0055] Example 3:

[0056] This embodiment provides a method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition, the specific steps of which are as follows:

[0057] Step S1, etherification reaction:

[0058] In a reactor equipped with a stirrer, thermometer, and reflux condenser, 500 kg of tetrabromobisphenol A, 150 kg of sodium hydroxide, and 200 kg of allyl chloride were added sequentially; the stirrer was turned on and the temperature was raised, and the reaction system temperature was controlled at 90°C and kept at this temperature for 6 hours.

[0059] Step S2, Crystallization and Purification:

[0060] After the etherification reaction was completed, the material in the reactor was cooled to 50°C and maintained at this temperature for 5 hours for crystallization. After crystallization, the material was centrifuged and filtered to remove the mother liquor. The solid filter cake was collected and dried to obtain the intermediate tetrabromoether crystals. Sampling and analysis revealed the following structural characterization data for this intermediate: Mass spectrometry (ESI-MS): m / z = 624.8 [M+H] + ;H1N NMR spectrum ( 1 ¹H NMR, 400 MHz, CDCl₃: δ 7.38 (s, 4H), 6.15–6.05 (m, 2H), 5.45 (dd, 2H), 5.32 (dd, 2H), 4.55 (d, 4H), 1.62 (s, 6H); confirmed as tetrabromobisphenol A dielyl ether.

[0061] Step S3, bromination reaction:

[0062] 500 kg of the tetrabromoether crystals prepared in step S2 were transferred into a bromination reactor; 1750 kg of dichloromethane was added, and stirring was started until the intermediate was completely dissolved; the temperature inside the reactor was adjusted to 40°C, and bromine was slowly added dropwise. The total amount of bromine added was controlled so that the molar ratio of the intermediate to bromine was 1:2.1; during the dropwise addition, the reaction temperature was always maintained at 40°C by adjusting the cooling water.

[0063] Step S4, Post-processing:

[0064] After the bromination addition reaction is completed, sodium sulfite aqueous solution is added to the reaction solution for decolorization treatment until the solution is colorless or pale yellow; the solution is allowed to stand and separate into layers, the organic phase is separated, and the organic phase is washed with deionized water until the pH of the washing solution is 7; the solvent is removed by flash evaporation of the washed organic phase, and the high melting point and high whiteness methyl octabromoether flame retardant product is obtained by air drying.

[0065] The structural characterization data of the obtained product are as follows: Mass spectrometry (ESI-MS): m / z = 944.5 [M+H]+ ;H1N NMR spectrum ( 1 HNMR, 400MHz, CDCl3): δ 7.42 (s, 4H), 4.48–4.38 (m, 2H), 4.35–4.20 (m, 4H), 3.95–3.82 (m, 4H), 1.65 (s, 6H); The structure of the target product was confirmed.

[0066] The performance of the methyl octabromoether flame retardant prepared in this embodiment was tested and found to be as follows: melting point 105.9℃, whiteness 92.1, bromine content 67.28%, volatile matter 0.13%, acetone insoluble matter 0.05%, and carbonization temperature 253℃.

[0067] Comparative Examples 1-4:

[0068] Comparative Example 1:

[0069] Compared to Example 1, the difference lies in the omission of the isothermal crystallization and filtration steps in step S2. The specific operation is adjusted as follows: after the etherification reaction, the reaction mixture is directly washed with water to separate the layers. The organic layer is then distilled under reduced pressure to remove unreacted allyl chloride. The resulting oily crude intermediate is directly fed into step S3 for bromination. All other steps and raw material ratios are the same as in Example 1.

[0070] Comparative Example 2:

[0071] The difference from Example 1 is that the crystallization temperature in step S2 is adjusted to 10°C. All other steps and parameters are the same as in Example 1.

[0072] Comparative Example 3:

[0073] The difference from Example 1 is that the bromination reaction temperature in step S3 is adjusted to 55°C. All other steps and parameters are the same as in Example 1.

[0074] Comparative Example 4:

[0075] Compared with Example 1, the difference is that the mass ratio of the intermediate to dichloromethane in step S3 is adjusted to 1:1.5. The remaining steps and parameters are the same as in Example 1.

[0076] Test Example 1-3:

[0077] Test Example 1: Product Appearance and Whiteness Test

[0078] This test case aims to determine the appearance and whiteness value of the methyl octabromoether flame retardant samples prepared in Examples 1 to 3 and Comparative Examples 1 to 4.

[0079] Experimental steps:

[0080] Sampling: Randomly select 20g powder samples from the dried finished products prepared in each example and comparative example, place them in a clean, dry self-sealing bag, and label them for later use.

[0081] Appearance observation: Lay the sample flat on a white standard colorimetric plate and observe the color uniformity and powder state of the sample under natural diffused light, and record the observation results.

[0082] Instrument Calibration: Using a whiteness meter, preheat for 30 minutes. Zero the instrument using the supplied black tube and calibrate it using a standard white board to ensure stable instrument readings.

[0083] Sample preparation and measurement:

[0084] Take an appropriate amount of the powder to be tested and put it into the powder forming machine, then scrape the surface smooth.

[0085] Apply constant pressure to make the powder surface compact and flat, ensuring no cracks or powder shedding.

[0086] The pressed sample was placed under the test hole of the whiteness meter to measure the blue light whiteness value.

[0087] Each sample was rotated 90 degrees and the measurement was repeated three times. The readings were recorded and the arithmetic mean was calculated.

[0088] Test data:

[0089] The test results for each sample are shown in Table 1 below.

[0090] Table 1: Appearance and Whiteness Test Data of Methyl Octabromoether Samples Prepared Under Different Process Conditions

[0091] Sample number Appearance description Measured value 1 Measured value 2 Measured value 3 Average whiteness value Example 1 White powder 92.4 92.6 92.5 92.5 Example 2 White powder 92.1 92.4 92.2 92.2 Example 3 White powder 91.9 92.2 92.1 92.1 Comparative Example 1 White powder with a slight yellow tinge 90.3 90.7 90.5 90.5 Comparative Example 2 White powder 90.8 91.1 90.9 90.9 Comparative Example 3 pale yellow powder 87.2 87.8 87.5 87.5 Comparative Example 4 White powder with a slight yellow tinge 89.1 89.4 89.1 89.2

[0092] Results analysis:

[0093] A comparison of the data from Examples 1 to 3 with Comparative Example 3 shows that the bromination reaction temperature has a decisive influence on the color of the final product. In Comparative Example 3, because the bromination reaction temperature was set at 55°C, exceeding the low-temperature range of 10–40°C defined in this invention, the average whiteness value significantly decreased to 87.5, and the appearance was pale yellow. The mechanism is that the high-temperature environment during the synthesis of methyl octabromoether exacerbates the oxidizing ability of bromine, triggering local carbonization or oxidation side reactions in the material, generating colored impurities; simultaneously, high temperature may cause some unstable aliphatic bromine bonds to undergo elimination reactions, generating conjugated double bond structures, thereby increasing the number of chromophores. Examples 1 to 3, by strictly controlling the low-temperature reaction environment, suppressed the occurrence of the above-mentioned side reactions, thus maintaining the high whiteness of the product.

[0094] The differences in data between Examples 1 to 3 and Comparative Example 4 reveal the importance of the reaction solvent ratio for controlling the thermal effect. In Comparative Example 4, the mass ratio of the intermediate to dichloromethane was 1:1.5, with a relatively small amount of solvent, and the measured whiteness value was 89.2, lower than that of the Example group. In the bromination addition reaction, dichloromethane not only acts as a solvent but also plays a role in dispersing the heat of reaction. When the solvent ratio is too low, the viscosity of the reaction system increases, the heat dissipation efficiency decreases, leading to heat accumulation in local areas and the formation of instantaneous high-temperature micro-regions. This local overheating phenomenon also induces thermal degradation or side reactions of some materials, thereby affecting the color of the final product. This invention, by maintaining a solvent ratio of 1:2.5 to 3.5, ensures a homogeneous reaction system and sufficient heat exchange, avoiding quality degradation caused by local overheating.

[0095] The comparison between Examples 1 to 3 and Comparative Examples 1 and 2 demonstrates the heritable influence of intermediate purity on the whiteness of the finished product. Comparative Example 1 omitted the crystallization step, and Comparative Example 2 had an excessively low crystallization temperature; neither achieved the whiteness level of the Example group. This indicates that if colored byproducts or impurities generated during the etherification reaction are not effectively removed during the intermediate stage using a specific isothermal crystallization process of 30–50°C, they will be carried into subsequent processes or undergo further chemical transformation, ultimately remaining in the finished product and affecting whiteness. Only by crystallizing within the specific temperature range described in this invention, utilizing the difference in solubility between impurities and the main product in the solvent for separation, can a high-purity substrate be provided for the subsequent bromination reaction, thereby obtaining a high-whiteness final product.

[0096] Test Example 2: Melting Point and Thermal Stability Test

[0097] This test case aims to determine the melting point range and charring temperature of the methyl octabromoether flame retardant samples prepared in Examples 1 to 3 and Comparative Examples 1 to 4, in order to evaluate the thermal performance of the products.

[0098] Experimental steps:

[0099] Sample pretreatment: Place the sample to be tested in a vacuum drying oven and dry it at 50°C for 2 hours, then place it in a desiccator to cool to room temperature.

[0100] Sample loading: Take the dried sample powder and load it into a clean, dry capillary tube using the vertical drop method. Gently tap the tube repeatedly to ensure the sample is compacted, with the filling height controlled between 3mm and 4mm.

[0101] Melting point determination:

[0102] Use a fully automatic melting point apparatus.

[0103] The initial temperature is set to 90℃, and the heating rate is set to 1.0℃ / min.

[0104] Insert the capillary tube containing the sample into the heating furnace and start the measurement program.

[0105] The instrument automatically records the initial melting temperature and final melting temperature of the sample.

[0106] Each sample was measured three times, and the arithmetic mean was calculated.

[0107] Carbonization temperature determination:

[0108] Place 0.5g of sample at the bottom of a glass test tube.

[0109] Place the test tube in a thermally conductive oil bath, and start the oil bath temperature at 200℃, increasing the temperature at a rate of 5℃ / min.

[0110] Continuously observe the sample's condition and record the instantaneous temperature at which the sample color changes significantly from white or slightly yellow to charred black, as the carbonization temperature.

[0111] Test data:

[0112] The melting point and carbonization temperature test results of each sample are shown in Table 2 below.

[0113] Table 2: Thermal performance data of methyl octabromoether samples prepared under different process conditions

[0114] Sample number Initial melting temperature (°C) Final melting temperature (°C) Melting range (°C) Carbonization temperature (°C) Example 1 106.3 107.8 1.5 254 Example 2 106 107.6 1.6 252 Example 3 105.9 107.4 1.5 253 Comparative Example 1 102.8 105.1 2.3 246 Comparative Example 2 103.4 105.5 2.1 248 Comparative Example 3 105.2 107.1 1.9 241 Comparative Example 4 104.5 106.8 2.3 249

[0115] Results analysis:

[0116] A comparison of the melting point data of Examples 1 to 3 with Comparative Examples 1 and 2 reveals the decisive role of the intermediate crystallization and purification process in the physical constants of the product. Comparative Example 1 did not include a crystallization step, and its initial melting temperature was only 102.8℃, with a relatively wide melting range. Although Comparative Example 2 underwent crystallization, the temperature was set at 10℃, resulting in an initial melting temperature of 103.4℃, which is also lower than the 105.9–106.3℃ of the Example group. The mechanism lies in the fact that the synthesis of tetrabromobisphenol A diallyl ether is accompanied by the formation of monoether byproducts and low molecular weight oligomers. According to the principle of solid-liquid phase equilibrium, within a specific temperature range of 30–50℃, the target diether product precipitates in a supersaturated state, while the monoether and other impurities remain in the mother liquor due to differences in solubility. If crystallization is omitted or the crystallization temperature is too low, the impurities will co-precipitate with the main product. According to Raoult's law and the principle of melting point depression, the presence of impurities in the crystal lattice disrupts the regularity of the crystal structure, leading to a significant decrease in the melting point and a widening of the melting range of the final product. Examples 1 to 3 achieved effective separation of impurities through precise temperature-controlled crystallization, thereby obtaining pure products with high melting points and narrow melting ranges.

[0117] The difference in carbonization temperature between Examples 1 to 3 and Comparative Example 3 demonstrates the influence of bromination reaction temperature on the thermal stability of the product. Comparative Example 3 employed a high-temperature bromination at 55°C. Although its melting point data was relatively close to that of the Examples, its carbonization temperature was significantly lower than that of the Example group. This is because at higher bromination temperatures, the free radical activity within the reaction system increases, making over-bromination or oxidation reactions more likely, introducing thermally unstable tertiary carbon-bromine bonds or oxidation structural defects into the molecular chain. These structural defects become initiation points for thermal degradation upon heating, causing the molecular chain to break and carbonize at lower temperatures. Examples 1 to 3 employed a low-temperature bromination process of 10–40°C, ensuring the selectivity of the addition reaction, reducing the formation of structural defects, and thus improving the material's resistance to thermal decomposition.

[0118] The comparison of data from Examples 1 to 3 with Comparative Example 4 reflects the effect of reaction medium concentration on reaction homogeneity. In Comparative Example 4, the amount of dichloromethane used was less, resulting in a lower initial melting temperature than the Example group and an increased melting range of 2.3°C. In the exothermic bromination reaction, the solvent acts as a heat capacity buffer and mass transfer medium. An excessively low solvent ratio leads to increased local viscosity and impeded heat dissipation in the reaction system, forming localized overheated micro-regions. This heterogeneous thermal history results in the inclusion of some incompletely brominated or thermally rearranged isomer molecules in the product. The presence of these isomers reduces the orderliness of the molecular arrangement, macroscopically manifested as a lower melting point and a wider melting range. This invention ensures the thermal homogeneity of the reaction process by controlling the mass ratio of intermediate to solvent between 1:2.5 and 3.5, thereby obtaining a structurally homogeneous high-melting-point product.

[0119] Test Example 3: Chemical Composition and Purity Index Testing

[0120] This test aims to quantitatively analyze the chemical composition and purity of the methyl octabromoether flame retardant samples prepared in Examples 1 to 3 and Comparative Examples 1 to 4. Specific test items include bromine content, volatile matter, and acetone-insoluble matter content.

[0121] Experimental steps:

[0122] Bromine content determination:

[0123] Accurately weigh 0.1g of the sample to be tested and wrap it with ashless filter paper.

[0124] Add hydrogen peroxide absorbent to an oxygen-filled combustion flask, place the wrapped sample in a platinum basket, ignite, and decompose under sealed conditions.

[0125] After combustion is complete and the mixture has cooled, shake the combustion flask to ensure that the combustion products are completely absorbed by the absorbent liquid.

[0126] Transfer the absorption solution to a titration cup, add isopropanol to adjust the medium, and insert the silver electrode and calomel electrode.

[0127] Potentiometric titration was performed using a standard silver nitrate solution. The volume at the titration endpoint was recorded, and the total bromine mass fraction in the sample was calculated based on the amount consumed.

[0128] Each sample was measured in triplicate, and the arithmetic mean was taken.

[0129] Volatile matter determination:

[0130] Place the clean weighing bottle in a 105℃ oven and dry it until constant weight. Record the tare weight. .

[0131] Weigh approximately 2g of sample into a weighing bottle and record the total weight. .

[0132] Place the open weighing bottle containing the sample in a 105℃ forced-air drying oven and heat for 2 hours.

[0133] Remove the bottle and place it in a desiccator to cool to room temperature. Seal the bottle and weigh it, recording the mass after heating. .

[0134] According to the formula Calculate the volatile matter content.

[0135] Determination of acetone-insoluble matter:

[0136] Weigh approximately 5g of sample (accurate to 0.01g) and place it in a beaker.

[0137] Add 100 mL of acetone solvent and stir magnetically for 30 minutes at room temperature to fully dissolve the main component, methyl octabromoether.

[0138] Vacuum filtration was performed using a pre-weighed G4 sand core funnel.

[0139] Wash the residue in the beaker and funnel several times with a small amount of acetone until the filtrate is colorless.

[0140] Place the sand core funnel in an oven at 105℃ and dry it for 1 hour. After cooling, weigh it and calculate the mass percentage of the residual insoluble matter.

[0141] Test data:

[0142] The chemical composition and purity test results of each sample are shown in Table 3 below.

[0143] Table 3: Chemical purity data of methyl octabromoether samples prepared under different process conditions

[0144] Sample number Bromine content determination value 1 (%) Bromine content determination value 2 (%) Average bromine content (%) Volatile matter (%) Acetone-insoluble matter (%) Example 1 67.18 67.24 67.21 0.12 0.03 Example 2 67.05 67.11 67.08 0.15 0.04 Example 3 67.25 67.31 67.28 0.13 0.05 Comparative Example 1 66.42 66.55 66.49 0.35 0.12 Comparative Example 2 66.71 66.83 66.77 0.18 0.08 Comparative Example 3 66.85 66.92 66.89 0.16 0.05 Comparative Example 4 66.58 66.74 66.66 0.22 0.09

[0145] Results analysis:

[0146] The differences in acetone-insoluble matter and volatile matter between Examples 1 to 3 and Comparative Examples 1 and 2 confirm the necessity of a specific temperature crystallization process for impurity removal. Data shows that the uncrystallized sample of Comparative Example 1 had an acetone-insoluble matter content as high as 0.12% and a volatile matter content of 0.35%, significantly higher than the Example group. The mechanism lies in the fact that the monoether byproducts generated in the etherification reaction, unreacted phenolic salts, and residual inorganic salts typically have different solubility characteristics than the target diether product. Organic impurities such as monoethers are easily volatile or have poor thermal stability at high temperatures, while inorganic salts are insoluble in acetone. The isothermal crystallization step of 30–50°C used in this invention utilizes the difference in solubility of the target product and impurities in the solvent with temperature, allowing the impurities to be separated while remaining in the mother liquor. The low-temperature crystallization of 10°C in Comparative Example 2 resulted in the co-precipitation of some impurities with the main product; therefore, although its insoluble matter and volatile matter content were better than Comparative Example 1, it still did not reach the high purity level of the Examples.

[0147] A comparison of the bromine content and purity data of Examples 1 to 3 with Comparative Example 3 reveals the controlling effect of bromination reaction temperature on the stoichiometric reaction. Comparative Example 3, which underwent high-temperature bromination at 55°C, had an average bromine content of 66.89%, lower than the 67% or more in the Example group. Under high-temperature conditions, the oxidizing power of bromine is enhanced, and the reaction competition mechanism changes: in addition to the expected allyl double bond addition reaction, free radical substitution reactions or oxidative chain scission reactions may also occur. The bromine content of the products generated by these side reactions often deviates from the theoretical value, and some oxidation products constitute acetone-insoluble matter. This invention, by strictly limiting the reaction temperature to 10–40°C, ensures that the reaction follows the electrophilic addition mechanism, maximizing the utilization rate of bromine atoms and the chemical structural uniformity of the product, thereby guaranteeing a high bromine content and low impurity residue in the final product.

[0148] The differences in data between Examples 1 to 3 and Comparative Example 4 reflect the influence of solvent dosage on the microenvironment of the reaction system. In Comparative Example 4, the reduced solvent dosage led to an increase in acetone-insoluble matter to 0.09%, and a lower bromine content. In the preparation of methyl octabromoether, the bromination reaction is a strongly exothermic reaction, and the solvent acts as a medium for diluting the reactants and conducting heat. When the solvent ratio is too low, the system viscosity increases, the mixing uniformity decreases, resulting in excessively high bromine concentrations in localized areas where heat cannot dissipate in time. This localized high-temperature, high-concentration environment induces intermolecular cross-linking or polymerization side reactions, generating high molecular weight substances insoluble in acetone. The solvent mass ratio of 1:2.5 to 3.5 set in this invention provides a suitable dilution environment and heat capacity buffer, suppressing side reactions caused by localized overheating and ensuring the high purity of the product.

Claims

1. A high-melting-point, high-whiteness methyl octabromoether flame retardant composition, characterized in that, This flame retardant composition is prepared from raw materials containing the following proportions: Raw materials used to prepare the intermediate tetrabromo ether: 100 parts by weight of tetrabromobisphenol A, 10-30 parts by weight of sodium hydroxide, and 20-40 parts by weight of allyl chloride; The raw materials used to prepare the final product: the molar ratio of the intermediate tetrabromoether to bromine is 1:2.05 to 2.1; The intermediate tetrabromoether is a crystalline material obtained by etherifying the raw material, cooling it to 30-50°C for constant temperature crystallization for 3-5 hours, and then drying it after solid-liquid separation. The final product is prepared by dissolving the crystalline material of the intermediate tetrabromoether, and then adding the bromine dropwise at a system temperature of 10–40°C to carry out a bromination reaction, while controlling the reaction temperature to not exceed 40°C during the dropwise addition process. Furthermore, the flame retardant composition has a melting point ≥105.5℃ and a whiteness R457 ≥92.

2. The high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 1, characterized in that, The flame retardant composition has a bromine content ≥67%, volatile matter ≤0.15%, acetone insoluble matter ≤0.05%, and a carbonization temperature ≥250℃.

3. The high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 1, characterized in that, In the raw materials used to prepare the intermediate tetrabromoether, the weight ratio of tetrabromobisphenol A, sodium hydroxide and allyl chloride is 1:0.2:0.

3.

4. A method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Etherification reaction: Tetrabromobisphenol A is mixed with sodium hydroxide and allyl chloride and reacted to generate a tetrabromoether reaction solution; S2. Crystallization and purification: After the etherification reaction is completed, the product of step S1 is cooled down to 30-50℃ and crystallized at a constant temperature for 3-5 hours. After solid-liquid separation, it is dried to obtain tetrabromoether crystals. S3, bromination reaction: Dissolve the tetrabromoether crystal material obtained in step S2 in dichloromethane, adjust the system temperature to 10-40℃, and then start adding bromine dropwise to carry out the reaction, while controlling the reaction temperature not to exceed 40℃ during the dropwise addition process; S4. Post-treatment: After bromination, the mixture is decolorized, washed, the dichloromethane solvent is removed, and dried to obtain the flame retardant composition.

5. The method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 4, characterized in that, In step S1, the reaction temperature is 45–90°C and the reaction time is 6–10 hours.

6. The method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 4, characterized in that, In step S2, the purity of the dried tetrabromoether crystal material is such that its acetone-insoluble content is ≤0.05%.

7. The method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 4, characterized in that, In step S3, the mass ratio of the tetrabromoether crystal material to dichloromethane is 1:2.5 to 3.

5.

8. The method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 4, characterized in that, The specific implementation method of step S3 is as follows: first, the tetrabromoether crystal material is completely dissolved in dichloromethane, and the reaction temperature is controlled by a cooling medium during the dropwise addition process.

9. The method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 4, characterized in that, In step S4, the decolorization involves adding an aqueous sodium sulfite solution to the reacted solution until the organic phase is colorless or pale yellow; the washing involves allowing the decolorized solution to stand and separate into layers, then washing the organic phase with deionized water until the pH value is 7.

10. The method for preparing a high-melting-point, high-whiteness methyl octabromoether flame retardant composition according to claim 4, characterized in that, In step S4, the dichloromethane solvent is removed by flash evaporation, and the final drying is performed by airflow drying.