Ethylene bistetrabromophthalimide, process for its preparation and use

Abstract

This invention relates to the field of flame retardant chemical synthesis technology, and discloses ethylene bis(tetrabromophthalimide) and its preparation method and applications. The method includes reacting phthalic anhydride and ethylenediamine in an aqueous medium at a controlled mass ratio of 3.0-5.5:1 to obtain an intermediate; reacting the intermediate with bromine in a fuming sulfuric acid medium, controlling the dropping temperature at 45-60℃ and the holding temperature at 130-150℃; and washing the reaction product followed by high-temperature heat treatment at 150-220℃ to constant weight. This invention effectively inhibits residual active amino groups and organic carbonization by strictly controlling the intermediate synthesis ratio and the temperature range of the bromination reaction. By utilizing high-temperature heat treatment, it thoroughly removes deep-seated acidic volatiles that cannot be removed by conventional drying, solving the problems of yellowing appearance, poor heat resistance, and easy corrosion of processing equipment in existing products. It is applicable to the field of flame-retardant engineering plastics.

Description

Technical Field

[0001] This invention relates to the field of flame retardant chemical synthesis technology, and in particular to ethylene bis(tetrabromophthalimide) and its preparation method and application. Background Technology

[0002] Ethylene bis(tetrabromophthalimide) (commonly known as RDT-5) is a high-performance additive brominated flame retardant. This flame retardant features high bromine content, good thermal stability, strong UV resistance, and excellent electrical insulation properties. It is widely used in the flame retardant modification of engineering plastics such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and polyamide (PA), as well as polymers such as polyolefins and polystyrene. Particularly in the white goods and electronic connectors industry, extremely high requirements are placed on the whiteness, thermal stability, and exudation resistance of flame retardants.

[0003] Currently, the industrial preparation of ethylenebistetrabromophthalimide typically employs a two-step method: first, phthalic anhydride reacts with ethylenediamine to synthesize the intermediate N,N'-ethylenebisphthalimide; then, the intermediate is dissolved in fuming sulfuric acid or an organic solvent, and bromine is added to initiate a bromination reaction to obtain the final product. However, existing preparation processes still have shortcomings in terms of raw material ratio control, reaction process control, and post-processing, resulting in product quality that fails to meet the demands of high-end applications.

[0004] In the intermediate synthesis stage, existing processes often fail to strictly control the stoichiometric ratio of reactants. When phthalic anhydride is insufficient or the reaction is incomplete, unreacted terminal amino groups or monoimide byproducts may remain in the product. These amino-containing substances are chemically reactive and readily undergo oxidation reactions in the subsequent strongly acidic and oxidizing bromination environment to generate chromophores with azo or quinone structures. This results in a yellowish appearance and reduced whiteness in the final product, and this color difference is difficult to remove through subsequent washing processes.

[0005] During the bromination stage, this reaction is an exothermic electrophilic substitution reaction, and the steric hindrance effect increases significantly with the degree of substitution. Existing technologies often rely on a single approach to temperature control. If the initial temperature is too high, the intense exothermic reaction can lead to localized overheating, causing carbonization of organic materials and resulting in black spot impurities in the product. Conversely, if the temperature is insufficient in the later stages of the reaction, the high energy barrier of polybromination reactions cannot be overcome, leading to incomplete bromination, lower bromine content in the product, and reduced flame retardant efficiency.

[0006] Furthermore, the post-processing of the product mainly focuses on water washing and conventional drying (usually below 120°C). While this can remove free acid from the surface, it is difficult to remove trace amounts of hydrogen bromide and sulfuric acid mist adsorbed within the crystal lattice or deep within the particles. These deeply adsorbed acidic volatiles have a strong binding force with the product, and conventional drying cannot remove them. When flame retardants containing such residues are used in the high-temperature (usually above 250°C) processing of engineering plastics, the acidic gases will be released upon heating, not only corroding metal molds but also catalyzing the degradation of the polymer matrix, leading to a decrease in the mechanical properties and appearance defects of the composite material. Therefore, how to prepare ethylene bis(tetrabromophthalimide) with high whiteness, high bromine content, and high thermal stability is a problem that urgently needs to be solved in the field. Summary of the Invention

[0007] The purpose of this invention is to provide ethylene bis(tetrabromophthalimide) and its preparation method and application. This invention solves the problems in the preparation of existing ethylene bis(tetrabromophthalimide) products, such as low conversion rate of intermediate synthesis leading to amino residue, incomplete bromination reaction, or incomplete acid removal in post-treatment, resulting in low whiteness, low thermal decomposition temperature, and bromine content deviating from theoretical values ​​in the final product, thus limiting its application in high-end engineering plastics.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: The first aspect of the present invention provides ethylene bis(tetrabromophthalimide), which is made from raw materials comprising the following parts by weight: 200 parts of intermediate N,N'-ethylene bis(phthalimide) and 900-1100 parts of bromine; wherein the intermediate N,N'-ethylene bis(phthalimide) is prepared by reacting phthalic anhydride with ethylenediamine.

[0009] By employing the above technical solution, this invention controls the stoichiometric ratio of materials in the bromination reaction. Theoretically, each molecule of the intermediate N,N'-ethylenebisphthalimide requires 8 molecules of bromine to completely replace 8 hydrogen atoms, with a theoretical mass ratio of approximately 1:4.0. This solution sets the mass ratio of the intermediate to bromine to be 1:4.5 to 1:5.5 (i.e., 200 parts correspond to 900-1100 parts), placing bromine in an excess of 1.1 to 1.4 times the theoretical amount. This excess ratio increases the bromine concentration in the reaction system, promoting the substitution reaction towards the formation of the octabromoproduct and reducing the formation of hexabromo or heptabromoby-products, thereby increasing the bromine content and flame retardant efficiency of the product. Simultaneously, the excess bromine acts as a co-solvent in the fuming sulfuric acid medium, improving the mass transfer effect of the reaction system, which helps suppress carbonization side reactions caused by local overheating and improves the whiteness of the product.

[0010] Preferably, the intermediate N,N'-ethylenebisphthalimide is made from raw materials comprising the following parts by weight: 10 parts ethylenediamine and 30-55 parts phthalic anhydride.

[0011] By adopting the above technical solution, the formation of the monoimide byproduct (N-aminoethyl phthalimide) is reduced. The theoretical mass ratio of ethylenediamine to phthalic anhydride in the reaction to form diimides is approximately 1:4.93. This solution sets the amount of phthalic anhydride near or in excess of the theoretical value to promote the complete conversion of the amino groups at both ends of ethylenediamine into chemically stable imide ring structures. If the amount of phthalic anhydride is insufficient, the residual terminal amino (-NH2) structure in the reaction system has high reactivity. In the subsequent high-temperature bromination and strong oxidizing environment of fuming sulfuric acid, it is easily oxidized to form chromophores with azo or quinone structures, resulting in a yellowing of the final product. This solution, by ensuring a sufficient supply of anhydride, helps to improve the color quality of the product.

[0012] Preferably, the product has at least one of the following performance parameters: Hunter whiteness ≥87%, 1% thermogravimetric temperature ≥310℃, and bromine content ≥65.5%.

[0013] By adopting the above technical solution, the performance indicators reflect the purity and thermal stability of the product. A 1% thermogravimetric temperature (T1%) exceeding 310℃ indicates that trace amounts of solvent and free acidic gases (such as HBr) adsorbed within the product have been removed. The presence of free acid can corrode processing equipment and act as an acidic catalyst to induce molecular decomposition, reducing the material's heat resistance. High whiteness (≥87) reflects the control of oxidation side reactions during synthesis and the low content of carbonized impurities.

[0014] Preferably, the raw materials also include fuming sulfuric acid, wherein the fuming sulfuric acid is present in 1000-1200 parts by weight.

[0015] By adopting the above technical solution, fuming sulfuric acid serves as both the reaction medium and catalyst in this system. The high proportion of fuming sulfuric acid (5-6 times the weight of the intermediate) provides a homogeneous reaction environment. The free sulfur trioxide (SO3) in the sulfur trioxide acts as a Lewis acid, promoting the electrophilic substitution reaction. This allows the deep bromination reaction to proceed under relatively mild conditions, avoiding material decomposition and color deterioration caused by excessively increasing the reaction temperature to improve the degree of substitution.

[0016] A second aspect of this invention provides a method for preparing ethylene bis(tetrabromophthalimide), comprising the following steps:

[0017] In an aqueous medium, phthalic anhydride and ethylenediamine are mixed and subjected to an imidization reaction, followed by separation and drying to obtain the intermediate N,N'-ethylenebisphthalimide;

[0018] In a fuming sulfuric acid medium, the obtained intermediate N,N'-ethylenebisphthalimide was subjected to a bromination reaction with bromine. After the reaction was completed, the mixture was filtered and washed to obtain a wet material.

[0019] The obtained wet material was subjected to high-temperature heat treatment and dried to constant weight to obtain ethylene bis(tetrabromophthalimide);

[0020] The temperature of the high-temperature heat treatment is 150-220℃.

[0021] By employing the above technical solution, this invention utilizes high-temperature heat treatment to remove deep-seated volatiles. Conventional drying processes are typically carried out at 100-120℃, which can only remove adsorbed water on the surface of the material. Since the bromination reaction takes place in a fuming sulfuric acid and high-concentration hydrogen bromide environment, acidic volatiles (mainly HBr and trace amounts of sulfuric acid mist) are easily adsorbed into the interior of the product particles or in the intercrystalline lattice. These volatile components have a strong binding force with the matrix, making them difficult to remove at conventional drying temperatures. Residual acidic substances can catalyze the breakage of polymer chains in subsequent high-temperature processing applications, leading to a decrease in the material's initial decomposition temperature. This solution sets the post-treatment temperature at 150-220℃, providing the energy required for desorption, promoting the diffusion and escape of internally adsorbed acidic volatiles, thereby improving the product's thermal stability (T1%) and reducing corrosion of processing equipment due to acidic residues.

[0022] Preferably, in the imidization reaction, the reaction temperature is 70-105℃ and the reaction time is 5-8 hours; the mass ratio of phthalic anhydride to ethylenediamine is 3.0-5.5:1.

[0023] By employing the above technical solution, the intermediate is synthesized using an aqueous phase method, reducing the use of organic solvents. The feed ratio is controlled at 3.0-5.5:1, i.e., phthalic anhydride is in excess, suppressing the formation of monoimide byproducts. The excess phthalic anhydride promotes the complete conversion of the amino groups at both ends of ethylenediamine into imide ring structures. This reduces the residual active amino groups in the intermediate, preventing their oxidation to chromophores in subsequent bromination steps, thereby improving the whiteness of the final product.

[0024] Preferably, the bromination reaction is performed as follows: the intermediate N,N'-ethylenebisphthalimide is dispersed in fuming sulfuric acid, bromine is slowly added dropwise while controlling the temperature at 45-60°C, and after the addition is complete, the temperature is increased to 130-150°C and the reaction is maintained at this temperature for 6-10 hours.

[0025] By adopting the above technical solution, a segmented temperature control process was used. During the dropping stage, the temperature was controlled at 45-60℃ to reduce liquid bromine volatilization and control the rate of exothermic reaction, preventing localized overheating that could lead to product carbonization. During the holding stage, the temperature was increased to 130-150℃ to overcome the steric hindrance in the later stages of the polybromination reaction. As the number of bromine atoms on the benzene ring increases, the activation energy for further electrophilic substitution reactions rises. The high-temperature holding provides the energy required for the reaction, promoting the full substitution of hydrogen atoms on the benzene ring to generate the octabromoform product, thereby increasing the bromine content of the product.

[0026] Preferably, the high-temperature heat treatment is performed at 180°C for 3-6 hours until the moisture and volatile matter content of the product is ≤0.2%.

[0027] By adopting the above technical solution, 180℃ is the optimal temperature for balancing the removal efficiency of volatiles and the thermal stability of the product. Below 150℃, the removal of acidic residues adsorbed inside the particles is incomplete, affecting thermal stability; above 220℃, the product may undergo slight thermo-oxidative aging under prolonged high temperatures, leading to a decrease in whiteness. Treatment at 180℃ can remove deeply adsorbed volatiles, increasing T1% to above 310℃, while maintaining the product's whiteness (WI≥87).

[0028] A third aspect of this invention provides the application of ethylene bis(tetrabromophthalimide) in the field of flame retardant materials, employing the following technical solution:

[0029] Application of ethylene bis(tetrabromophthalimide) as a flame retardant in the preparation of flame-retardant polymer materials.

[0030] By adopting the above technical solution, the ethylene bis(tetrabromophthalimide) prepared by the present invention has high bromine content, high thermal stability and high whiteness, which can overcome the problems of traditional flame retardants of the same type being prone to decomposition and discoloration and corrosion of equipment during high-temperature processing.

[0031] The specific mechanism of action is as follows: The high bromine content (≥65.5%) provides the basis for flame retardancy. When the material is heated during combustion, the product decomposes and releases hydrogen bromide (HBr). As a free radical scavenger, HBr can consume highly reactive free radicals (such as HO·, H·) in the combustion chain reaction, thereby inhibiting the combustion reaction and achieving gas-phase flame retardancy.

[0032] Its high thermal stability (T1%≥310℃, T5%≥450℃) makes it suitable for high-temperature processing of engineering plastics (such as PBT, PET, PA66, etc.). Conventional flame retardants with insufficient thermal stability decompose at processing temperatures of 250-300℃, releasing acidic substances that catalyze the degradation of the matrix resin, leading to decreased mechanical properties, surface defects, and corrosion of metal molds. This product's high initial decomposition temperature maintains its stability during processing, reducing these processing defects.

[0033] The high whiteness (WI≥87) gives downstream flame-retardant materials a better appearance and color. Compared with traditional products that tend to yellow, this product reduces the impact on the color matching system of modified plastics and is suitable for fields such as white appliance casings and electronic and electrical connectors where appearance requirements are high.

[0034] In summary, the present invention has at least one of the following beneficial technical effects:

[0035] 1. This invention reduces the formation of residual active-terminal amino groups and monoimide byproducts by controlling the excess of phthalic anhydride during the intermediate synthesis stage and maintaining an excess of bromine during the bromination stage. This control of the raw material ratio avoids the transformation of easily oxidized structures into chromophores under strong acid and high-temperature environments, resulting in a final product with a Hunter whiteness of over 87, thus solving the problem of yellowing appearance caused by impurities in traditional process products.

[0036] 2. This invention employs a high-temperature heat treatment process of 150-220℃ to remove deeply adsorbed volatiles that cannot be removed by conventional drying. This process promotes the escape of trace amounts of hydrogen bromide and sulfuric acid mist adsorbed in lattice defects and interparticle gaps, raising the product's 1% thermal weight loss temperature to over 310℃. This improves the product's thermal stability and reduces the risk of flame retardants releasing acidic gases during downstream high-temperature processing, which could corrode molds or degrade the base resin.

[0037] 3. This invention utilizes fuming sulfuric acid as the reaction medium and employs a segmented temperature-controlled bromination strategy to control side reactions while ensuring the degree of reaction. The process of low-temperature dropwise addition combined with high-temperature insulation controls the exothermic reaction in the initial stage to prevent localized carbonization of the materials, and overcomes steric hindrance in the later stage of the reaction to ensure complete bromination. The resulting product has a bromine content ≥65.5% and a melting point ≥450℃, meeting the requirements of high-end modified plastics for flame retardant efficiency and heat resistance. Attached Figure Description

[0038] Figure 1 This is a test curve diagram of the present invention;

[0039] Figure 2 This is a comparison curve diagram of the present invention;

[0040] Figure 3This is the infrared spectrum of the present invention. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Preparation Examples 1-4:

[0043] Preparation Example 1:

[0044] This preparation example provides a method for preparing the intermediate N,N'-ethylenebisphthalimide, including the following steps:

[0045] Water was added as the reaction medium to a reactor equipped with a stirrer, and phthalic anhydride was added at a mass ratio of 5.0:1 to ethylenediamine. The stirrer was turned on and the temperature was raised to 90°C. The reaction was kept at this temperature for 6.5 hours. After the reaction was completed, the reaction mixture was centrifuged, the solid precipitate was collected, and after drying, the intermediate N,N'-ethylenebisphthalimide was obtained with a yield of about 99% (based on ethylenediamine).

[0046] Preparation Example 2:

[0047] This preparation example provides a method for preparing the intermediate N,N'-ethylenebisphthalimide, including the following steps:

[0048] Water was added as the reaction medium to a reactor equipped with a stirrer, and the phthalic anhydride to ethylenediamine was added in a mass ratio of 3.0:1. The stirrer was turned on and the temperature was raised to 70°C. The reaction was kept at this temperature for 5 hours. After the reaction was completed, the reaction mixture was centrifuged and the solid precipitate was collected and dried to obtain the intermediate N,N'-ethylenebisphthalimide.

[0049] Preparation Example 3:

[0050] This preparation example provides a method for preparing the intermediate N,N'-ethylenebisphthalimide, including the following steps:

[0051] Water was added as the reaction medium to a reactor equipped with a stirrer, and phthalic anhydride and ethylenediamine were added in a mass ratio of 5.5:1. Stirring was started and the temperature was raised to 105°C. The reaction was kept at this temperature for 8 hours. After the reaction was completed, the reaction mixture was centrifuged, the solid precipitate was collected, and the intermediate N,N'-ethylenebisphthalimide was obtained after drying.

[0052] Preparation Example 4:

[0053] This preparation example provides a method for preparing the intermediate N,N'-ethylenebisphthalimide for comparative experiments, including the following steps:

[0054] Water was added as the reaction medium to a reactor equipped with a stirrer, and phthalic anhydride to ethylenediamine was added in a mass ratio of 2.5:1. Stirring was started and the temperature was raised to 90°C, and the reaction was kept at this temperature for 6.5 hours. After the reaction was completed, the reaction mixture was centrifuged, the solid precipitate was collected, and the intermediate N,N'-ethylenebisphthalimide was obtained after drying.

[0055] Examples 1-5:

[0056] Example 1:

[0057] This embodiment provides a method for preparing ethylene bis(tetrabromophthalimide), corresponding to the attached... Figure 1 and attached Figure 3 Preparation of the sample shown. In a bromination reactor equipped with a stirrer, condenser, tail gas absorption device, and temperature control system, 1000g of fuming sulfuric acid was added as the reaction medium. Under stirring, 200g of the intermediate N,N'-ethylenebisphthalimide obtained from Preparation Example 1 was added. After uniform dispersion, the temperature was controlled at approximately 45°C, and 1000g of bromine was slowly added dropwise (at this point, the mass ratio of the intermediate to bromine was 1:5, with a theoretical excess of approximately 25%). After the addition was complete, the reaction system was controlled using a programmed temperature increase method, gradually raising the temperature to 150°C. The reaction was maintained within this temperature range for 8 hours until no significant hydrogen bromide gas was emitted. After the reaction was completed, the reaction solution was cooled to room temperature, and the solid product was separated by filtration. The solid product was deacidified and repeatedly washed with deionized water until the washing solution was neutral. Subsequently, the washed wet material was placed in a drying device and subjected to high-temperature heat treatment at 180℃ for 4 hours until the moisture and volatile matter content was ≤0.2%. The dried material was then crushed, sieved, and packaged to obtain a white powdered ethylene bis(tetrabromophthalimide) product (RDT-5).

[0058] Example 2:

[0059] This embodiment provides a method for preparing ethylenebis(tetrabromophthalimide). In a bromination reactor equipped with a stirrer, condenser, tail gas absorption device, and temperature control system, 1000 g of fuming sulfuric acid is added. While stirring, 200 g of the intermediate N,N'-ethylenebis(phthalimide) obtained in Preparation Example 2 is added, and 900 g of bromine is slowly added dropwise (at this point, the mass ratio of intermediate to bromine is 1:4.5, close to the theoretical excess limit). The reaction system temperature is controlled within the range of 45°C to 130°C, and the reaction time is 10 hours. After the reaction is complete, the reaction solution is cooled, and the solid product is separated by filtration. The solid product is then deacidified and repeatedly washed with deionized water until the washing solution is neutral. Next, the washed wet material is placed in a drying device and subjected to high-temperature heat treatment at 150°C for 6 hours until the moisture and volatile matter content is ≤0.2%. The dried material is then crushed, sieved, and packaged to obtain ethylene bis(tetrabromophthalimide) product.

[0060] Example 3:

[0061] This embodiment provides a method for preparing ethylenebis(tetrabromophthalimide). In a bromination reactor equipped with a stirrer, condenser, tail gas absorption device, and temperature control system, 1200 g of fuming sulfuric acid is added. While stirring, 200 g of the intermediate N,N'-ethylenebis(phthalimide) obtained in Preparation Example 3 is added, and 1100 g of bromine is slowly added dropwise (at this point, the mass ratio of intermediate to bromine is 1:5.5 to ensure complete bromination). The reaction system temperature is controlled within the range of 60°C to 150°C, and the reaction time is 6 hours. After the reaction is complete, the reaction solution is cooled, and the solid product is separated by filtration. The solid product is then deacidified and repeatedly washed with deionized water until the washing solution is neutral. Subsequently, the washed wet material is placed in a drying device and subjected to high-temperature heat treatment at a controlled temperature of 220℃ for 3 hours until the moisture and volatile matter content is ≤0.2%. The dried material is then crushed, sieved, and packaged to obtain the ethylene bis(tetrabromophthalimide) product.

[0062] Example 4:

[0063] This embodiment provides a method for preparing ethylenebistetrabromophthalimide. Except for adjusting the drying temperature in the drying process to 160°C, the other raw materials (using the intermediate of Preparation Example 1, the amount of bromine and fuming sulfuric acid are the same as in Example 1) and preparation steps are consistent with Example 1.

[0064] Example 5:

[0065] This embodiment provides a method for preparing ethylenebistetrabromophthalimide. Except for adjusting the drying temperature in the drying process to 200°C, the other raw materials (using the intermediate from Preparation Example 1, the amount of bromine and fuming sulfuric acid are the same as in Example 1) and preparation steps are consistent with Example 1.

[0066] Comparative Examples 1-4:

[0067] Comparative Example 1: This comparative example selects commercially available mainstream N,N'-ethylenebistetrabromophthalimide products from DaHu Chemical or similar manufacturers as the comparison sample.

[0068] Comparative Example 2: Compared with Example 1, the difference is that the drying temperature is set to the conventional 105°C until the moisture and volatile content meet the standard, and high-temperature heat treatment above 150°C is not performed. The rest of the preparation steps and parameters are the same.

[0069] Comparative Example 3: Compared with Example 1, the difference is that the intermediate used was replaced with the intermediate obtained by Preparation Example 4 (the mass ratio of phthalic anhydride to ethylenediamine was 2.5:1), and the rest of the preparation steps and parameters were the same.

[0070] Comparative Example 4: Compared with Example 1, the difference is that the maximum temperature of the bromination reaction is set to 170°C (higher than 150°C), while the rest of the preparation steps and parameters are the same.

[0071] Test Example 1-2:

[0072] Test Example 1: Product Structure Validation and Physicochemical Index Testing

[0073] Experimental Procedure: Infrared spectroscopy analysis was performed using the potassium bromide pellet method. The dried sample from Example 1 was mixed with spectrally pure potassium bromide at a mass ratio of 1:100, ground, and pelleted. A full-band scan was then performed on a Fourier transform infrared spectrometer with a resolution set to 4 cm⁻¹. -1 A total of 32 scans were performed. The bromine content was determined by alkaline fusion-potential titration. Approximately 0.1 g of sample was weighed and placed in a nickel crucible. A mixed flux of potassium hydroxide and anhydrous sodium carbonate was added, and the mixture was melted and decomposed in a high-temperature muffle furnace to convert organically bound bromine into inorganic bromide ions. After cooling, the sample was leached with hot water and acidified. Titration was performed using an automatic potentiometric titrator with 0.1 mol / L silver nitrate standard solution. The total bromine content was calculated based on the volume consumed at the titration endpoint.

[0074] Melting point was determined using the capillary method. The ground sample was loaded into a capillary tube and compacted, then placed in a microscopic melting point apparatus. The heating rate was controlled at 10℃ / min, and the temperature range from initial melting to complete melting was recorded. Average particle size was determined using laser diffraction. The sample was dispersed in deionized water with sodium hexametaphosphate added as a dispersant, ultrasonically dispersed for 3 minutes, and the particle size distribution was detected using a laser particle size analyzer, with the D50 value recorded.

[0075] The loss on drying (moisture and volatile matter) was determined by the oven drying method. Approximately 2g of sample was weighed and spread evenly in a weighing bottle that had been kept at constant weight. The sample was then placed in a 125℃ forced-air drying oven and dried for 2 hours. After being removed and cooled to room temperature in a desiccator, the sample was weighed. The operation was repeated until a constant weight was achieved, and the mass loss ratio was calculated.

[0076] Experimental data: The RDT-5 product prepared in Example 1 was subjected to the above tests. Three different production batches were randomly selected for testing. The specific data are shown in Table 1.

[0077] Table 1. Physicochemical index test data of the product in Example 1

[0078] Testing items Reference Standard Batch number 20240101 Batch number 20240105 Batch number 20240109 average value Appearance White powder White powder White powder White powder - Bromine content (%) ≥65.5 66.88 67.05 66.92 66.95 Melting point (°C) ≥450 453.8 452.4 455.2 453.8 Average particle size D50 (µm) ≤5.0 3.79 4.21 3.65 3.88 Drying loss (%) ≤0.20 0.09 0.11 0.08 0.09

[0079] Note: The symbol "-" in the table indicates that the item has no value or cannot be calculated as a mathematical average.

[0080] Results Analysis and Conclusions: Infrared Spectroscopy (attached) Figure 3 ) at 1772cm -1 and 1710cm -1 A strong absorption peak is observed at 1394 cm⁻¹, attributed to the asymmetric and symmetric stretching vibrations of the imide ring carbonyl group; -1 The characteristic absorption peak of the CN bond is shown at 3200-3400 cm⁻¹. -1 The absence of an NH stretching vibration absorption peak in the region indicates that the reactant ethylenediamine reacted completely, and no monoimide structure remains in the product system. The spectral fingerprint region characteristics are consistent with the standard structure of N,N'-ethylenebistetrabromophthalimide.

[0081] Appendix Figure 3 RDT-5 in the text is ethylene bis(tetrabromophthalimide).

[0082] Physicochemical testing results showed that the bromine content of all three batches of samples fluctuated around 66.0%, consistent with theoretical stoichiometric expectations. The first-step synthesis process employed a phthalic anhydride to ethylenediamine mass ratio of 5.0:1, which suppressed impurity formation. In the second-step bromination reaction, excess bromine was added to ensure the degree of substitution. Melting points were all above 450℃, and the drying loss was controlled below 0.15%, indicating that the 180℃ high-temperature heat treatment removed trace amounts of solvent and acidic volatiles adsorbed within the crystal lattice, improving the product's thermal stability. All test indicators met the requirements for industrial applications.

[0083] Test Example 2: Comparison Test of Thermal Stability and Whiteness Performance

[0084] Experimental Procedure: Thermal stability testing was conducted using a thermogravimetric analyzer (TGA). 5-10 mg of the sample was weighed and placed in an alumina crucible. Under a nitrogen atmosphere (gas flow rate 50 mL / min), the heating rate was set to 10 °C / min, and the temperature range was 30 °C to 600 °C. The temperatures at which the sample mass loss reached 1% (T1%) and 5% (T5%) were recorded. T1% represents the initial decomposition temperature of the sample, and T5% represents the sample's heat resistance limit. Whiteness and color difference testing were performed using a computer colorimeter, according to ASTM E313 standard. The powder sample was pressed into a smooth, circular sheet, and Hunter Whiteness (WI) and Yellowness Index (YI) were measured. Three different measurement points were selected for each sample, and the average value was taken to evaluate the sample's appearance and color.

[0085] Experimental data: Samples prepared in Examples 1, 4, and 5, as well as Comparative Examples 1 to 4, were subjected to the above tests. The TGA test curve for the sample in Example 1 corresponds to the attached figure. Figure 1 The TGA comparison curves of Example 1 and Comparative Example 2 are attached. Figure 2 .

[0086] Appendix Figure 1 and attached Figure 2 RDT-5 in the text is ethylene bis(tetrabromophthalimide).

[0087] The test results are summarized in Table 2.

[0088] Table 2. Results of thermal stability and whiteness tests for each group of samples.

[0089] Sample number <![CDATA[T1%(℃)]]> <![CDATA[T5%(℃)]]> Hunter Biden (WI) Yellowness Index (YI) Remark Example 1 315.4 460.7 91.2 1.8 Process Optimization Group Example 4 308.1 455.3 90.8 2.1 Drying temperature 160℃ Example 5 316.0 459.9 89.5 3.2 Drying temperature 200℃ Comparative Example 1 310.5 456.2 88.9 3.5 Commercially available comparison samples Comparative Example 2 288.6 448.1 88.5 3.6 Drying temperature 105℃ Comparative Example 3 298.3 441.5 75.7 12.6 Raw material ratio deviation Comparative Example 4 311.8 455.6 81.2 8.9 Bromination temperature too high

[0090] Results Analysis and Conclusions: From Appendix Figure 1 As can be seen from the thermogravimetric analysis curve and the data in Table 2, the initial decomposition temperature (T1%) of the RDT-5 product prepared in Example 1 is 312.4℃, the 5% thermogravimetric temperature (T5%) is 458.7℃, the Hunter whiteness is 91.2, and the yellowness index is 1.8. Compared with Comparative Example 1 (commercially available product), Example 1 shows improvements in both thermal stability and whiteness.

[0091] Appendix Figure 2The thermogravimetric analysis (TGA) curves of Example 1 and Comparative Example 2 are shown for comparison. Comparative Example 2, using conventional drying at 105°C, had a T1% of only 288.6°C, lower than Example 1. The difference in curves indicates that conventional drying temperatures cannot completely remove trace amounts of moisture and acidic volatiles (such as residual HBr) adsorbed deep within the crystal lattice or within particle aggregates. These residual components volatilize first during the initial TGA heating phase (200-300°C range), leading to a lower apparent initial decomposition temperature, and the residual acidic substances may catalyze the degradation of the matrix resin during high-temperature processing. Example 1, using high-temperature heat treatment at 180°C, effectively removed these stubborn residues, thereby improving the thermal stability of the material. In Example 5, after increasing the treatment temperature to 200°C, the T1% did not increase, but the whiteness decreased to 89.5, and the yellowness index increased, indicating that the excessively high post-treatment temperature caused slight thermal oxidation discoloration.

[0092] Comparing the data of Example 1 and Comparative Example 3, Comparative Example 3, due to insufficient phthalic anhydride ratio (2.5:1) in the first synthesis step, showed a significant drop in whiteness value to 75.7, an increase in yellowness index to 12.6, and a lower T5%. This confirms the influence of raw material ratio on product purity and color. Insufficient phthalic anhydride feeding leads to the formation of monoimide byproducts or residual amino components in the reaction system. These amino-containing structures are unstable and are easily oxidized to form chromophores during subsequent high-temperature bromination and drying processes, resulting in a yellowing of the product and lowering the thermal decomposition temperature of the final product.

[0093] The data from Comparative Example 4 show that although its thermal stability is acceptable, its whiteness is only 81.2 due to the high bromination reaction temperature of 170℃. The excessively high reaction temperature causes some organic matter to carbonize or generate dark tar-like byproducts, which seriously affects the appearance of the product.

[0094] In summary, this technical solution, by controlling the synthesis ratio of intermediates and introducing a 180℃ high-temperature heat treatment process, solves the problems of easy yellowing and insufficient heat resistance of traditional process products while ensuring high bromine content, and prepares ethylene bis(tetrabromophthalimide) with both high whiteness and high thermal stability.

Claims

1. Ethylenebistetrabromophthalimide, characterized in that it is made from raw materials comprising the following parts by weight: 200 parts of intermediate N,N'-ethylenebisphthalimide; 900-1100 parts of bromine; The intermediate N,N'-ethylenebisphthalimide is prepared by reacting phthalic anhydride with ethylenediamine.

2. The ethylene bis(tetrabromophthalimide) according to claim 1, characterized in that the intermediate N,N'-ethylene bis(phthalimide) is made from raw materials comprising the following parts by weight: 10 parts of ethylenediamine; Phthalic anhydride 30-55 parts.

3. The ethylene bis(tetrabromophthalimide) according to claim 1, characterized in that, The product has at least one of the following performance parameters: Hunter whiteness ≥87%, 1% thermal weight loss temperature ≥310℃, and bromine content ≥65.5%.

4. The ethylene bis(tetrabromophthalimide) according to claim 1, characterized in that, The raw materials also include fuming sulfuric acid, which is present in 1000-1200 parts by weight.

5. A method for preparing ethylene bis(tetrabromophthalimide), characterized in that, The application of the ethylene bis(tetrabromophthalimide) according to any one of claims 1-4 comprises the following steps: In an aqueous medium, phthalic anhydride and ethylenediamine are mixed and subjected to an imidization reaction, followed by separation and drying to obtain the intermediate N,N'-ethylenebisphthalimide; In a fuming sulfuric acid medium, the obtained intermediate N,N'-ethylenebisphthalimide was subjected to a bromination reaction with bromine. After the reaction was completed, the mixture was filtered and washed to obtain a wet material. The obtained wet material was subjected to high-temperature heat treatment and dried to constant weight to obtain ethylene bis(tetrabromophthalimide); The temperature of the high-temperature heat treatment is 150-220℃.

6. The method for preparing ethylene bis(tetrabromophthalimide) according to claim 5, characterized in that, In the imidization reaction, the reaction temperature is 70-105℃ and the reaction time is 5-8 hours.

7. The method for preparing ethylene bis(tetrabromophthalimide) according to claim 5, characterized in that, The mass ratio of phthalic anhydride to ethylenediamine is 3-5.0:

1.

8. The method for preparing ethylene bis(tetrabromophthalimide) according to claim 5, characterized in that, The bromination reaction is performed as follows: The intermediate N,N'-ethylenebisphthalimide was dispersed in the fuming sulfuric acid, and bromine was slowly added dropwise while controlling the temperature at 45-60°C. After the addition was complete, the temperature was increased to 130-150°C and the reaction was maintained at this temperature for 6-10 hours.

9. The method for preparing ethylene bis(tetrabromophthalimide) according to claim 5, characterized in that, The high-temperature heat treatment is performed at 180°C for 3-6 hours until the moisture and volatile matter content of the product is ≤0.2%.

10. The application of the ethylene bis(tetrabromophthalimide) according to any one of claims 1-4 in the field of flame retardant materials.

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