Method for controlling the molecular structure of brominated polystyrene and product thereof

Abstract

The application provides a brominated polystyrene molecular structure regulation method and a product thereof, and relates to the field of brominated polystyrene preparation. The brominated polystyrene molecular structure regulation method is characterized in that, in the presence of a catalyst, polystyrene is reacted with 1.6-2 times the molar amount of bromine based on the molar number of benzene rings in the polystyrene at a temperature of 10-25 DEG C; and in the reaction process, ultraviolet light is used for irradiation to induce the generation of aliphatic substituted bromine. The application deviates from the technical prejudice in the prior art that aliphatic bromine is avoided as much as possible, and the ratio of aliphatic substituted bromine and aromatic substituted bromine is accurately controlled through ultraviolet light assisted bromination reaction, and the addition amount of bromine is matched to regulate the decomposition temperature and softening point, so that the brominated polystyrene is adapted to the processing requirements of ABS resin; the thermal stability and compatibility of the brominated polystyrene can be regulated while maintaining the flame retardant efficiency, and the brominated polystyrene and the ABS resin matrix can be uniformly blended and interfacially compatible.

Description

Technical Field

[0001] This invention relates to the field of brominated polystyrene preparation, and in particular to a method for regulating the molecular structure of brominated polystyrene and its products. Background Technology

[0002] ABS resin (acrylonitrile-butadiene-styrene copolymer) is a widely used engineering plastic, but it is inherently flammable and requires flame-retardant modification in many applications. Currently, brominated triazine is commonly used in the industry as a flame retardant to prepare flame-retardant ABS resin. The typical processing temperature of ABS resin is around 200℃, while the melting point of brominated triazine is as high as around 240℃. This mismatch in melting temperatures prevents brominated triazine from achieving homogeneous blending with ABS resin at the molecular level, often resulting in it existing as a dispersed phase. This leads to a significant decrease in the mechanical properties of the finished product compared to pure ABS resin.

[0003] Brominated polystyrene (BPS), a polymeric flame retardant, has attracted widespread attention due to its good compatibility with polymer matrices, resistance to precipitation, and non-frosting properties. There are two main technical routes for the synthesis of brominated polystyrene: one is to first brominated styrene monomers and then polymerize them (e.g., US Patent US005369202A); the other is to directly bromine polystyrene using a brominating agent (e.g., US Patent US005677390A). Among these, the direct bromination method is widely used due to its advantages such as simple process, readily available raw materials, and the ability to recycle waste polystyrene.

[0004] However, the direct bromination method faces a long-standing technical challenge: in the presence of Lewis acid catalysts (such as aluminum trichloride and aluminum tribromide), while the brominating agent electrophilically substitutes the benzene rings of polystyrene, it also uncontrollably undergoes a small amount of free radical substitution reactions on the main chain, generating aliphatic bromides. These aliphatic bromides, due to their low carbon-bromine bond energy and poor thermal stability, easily release hydrogen bromide gas during the processing of flame-retardant nylon. This not only causes discoloration and equipment corrosion of the nylon material during processing but also severely reduces the flame-retardant efficiency of brominated polystyrene flame retardants, directly limiting their application range.

[0005] However, the inventors discovered through research that there has long been a prevalent technical bias in the field regarding aliphatic bromides generated during the preparation of brominated polystyrene: aliphatic bromine (or "thermally unstable bromine") is a completely undesirable impurity that must be reduced or eliminated as much as possible. For example, a relevant patent from Albemarle Corporation explicitly states that brominated flame retardants with "low thermally unstable bromine (aliphatic bromine) content" require the reduction or avoidance of aliphatic bromine formation during preparation because the thermally unstable bromine can cause HBr waste gas, which can corrode processing equipment. Furthermore, US Patent 5328983A emphasizes that aliphatic bromine impurities on the main chain of brominated polystyrene "make a major contribution to thermal instability," and has developed a specialized post-treatment process to specifically remove these aliphatic bromines. Furthermore, since traditional brominated polystyrene is mainly used in engineering plastics products with high processing temperatures such as nylon (PA) and polyester (PBT, PET), the synthesis of brominated polystyrene requires extremely stringent process conditions (such as a light-proof environment and extremely low temperature reactions at around 0°C) in order to achieve high heat resistance (decomposition temperature > 330°C, softening point > 280°C). This not only results in high energy consumption and high production difficulty, but also directly leads to a mismatch between the melting temperatures of brominated polystyrene and ABS resin, limiting the application of brominated polystyrene in medium-processing-temperature resin materials such as ABS.

[0006] In recent years, research has begun to focus on the influence of different brominated structures on flame retardant properties. Studies by Gu Guangxin et al. have shown that aliphatic bromine structures have better fire retardant properties, while aromatic bromine structures have better compatibility. However, insufficient thermal stability of the flame retardant can lead to its decomposition at processing temperatures, reducing its fire retardant performance (Lu J, Tu H, Gu G. Synthesis of brominated flame retardants with different brominated structures and study on flame retardancy of polystyrene resin[J]. Reactive and Functional Polymers, 2023, 105769). It can be seen that aliphatic bromine has high flame retardant efficiency but poor thermal stability and compatibility, while aromatic bromine has good thermal stability and compatibility but low flame retardant efficiency. There is a contradictory relationship between the two, making it difficult to achieve a balanced control of various performance aspects. Meanwhile, Wang Hongxing's master's thesis studied the preparation and properties of brominated polystyrene and found that brominated polystyrene has poor compatibility with ABS resin matrix and exhibits encapsulated dispersion (Wang Hongxing, Study on Preparation and Properties of Brominated Polystyrene, East China University of Science and Technology, 2011). It can be seen that brominated polystyrene and ABS resin cannot achieve uniform blending and interfacial compatibility at the molecular level, which directly affects the mechanical properties of its products.

[0007] Therefore, this paper provides a method for controlling the molecular structure of brominated polystyrene, which can effectively control the thermal stability of brominated polystyrene and its compatibility with ABS resin while maintaining sufficient flame retardant efficiency. The softening point and decomposition temperature of brominated polystyrene are controlled to match the processing window of ABS resin (approximately 200°C). Furthermore, the preparation process avoids harsh low-temperature synthesis processes and enables uniform blending and interfacial compatibility between brominated polystyrene and the ABS resin matrix, avoiding adverse effects on the mechanical properties of ABS products. This method has significant technical implications and research value, greatly facilitating the preparation of high-quality flame-retardant ABS resin products, significantly reducing production costs, and further expanding the application range. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention provides a method for controlling the molecular structure of brominated polystyrene. This method can effectively control the thermal stability of brominated polystyrene and its compatibility with ABS resin while maintaining sufficient flame retardant efficiency. It controls the softening point and decomposition temperature to a level that matches the processing window of ABS resin (approximately 200°C). Furthermore, during the preparation process, it avoids the harsh low-temperature synthesis process and enables brominated polystyrene to achieve uniform blending and interfacial compatibility with the ABS resin matrix, thus avoiding adverse effects on the mechanical properties of ABS products.

[0009] The present invention also provides brominated polystyrene prepared by the aforementioned method.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for controlling the molecular structure of brominated polystyrene involves using polystyrene and bromine as raw materials. In the presence of a Lewis acid catalyst, polystyrene is reacted with bromine in a molar amount equal to 1.6-2 times the number of benzene rings in the polystyrene at a temperature of 10-25°C. During the reaction, ultraviolet light irradiation is used to induce the formation of aliphatic substituted bromine. The ratio of aliphatic substituted bromine to aromatic substituted bromine in the brominated polystyrene is controlled to be (1-5)%:(95-99)%, thereby obtaining brominated polystyrene with a decomposition temperature and softening point that meet the processing requirements of ABS resin.

[0011] Furthermore, the method for regulating the molecular structure of brominated polystyrene includes the following steps: placing polystyrene and a Lewis acid catalyst in dichloromethane, and adding bromine dropwise under ultraviolet light irradiation at a temperature of 10-25°C; after the bromine is added, maintaining the temperature for reaction to obtain a reaction solution, which is then purified to obtain brominated polystyrene.

[0012] Preferably, the wavelength range of the ultraviolet light is 200-400 nm, and the intensity of the ultraviolet light is 500-5000 μW / cm.2 .

[0013] Preferably, the wavelength range of the ultraviolet light is 254-365 nm, and the ultraviolet light intensity is 1000-3000 μW / cm². 2 .

[0014] Preferably, the Lewis acid catalyst is aluminum trichloride or aluminum tribromide; the molar amount of the Lewis acid catalyst is 0.8-1.2% of the molar amount of polystyrene, based on the number of benzene ring units in the polystyrene.

[0015] Preferably, the reaction time after the bromine is added is 5-30 minutes.

[0016] Furthermore, the above purification method is as follows: after neutralizing the excess bromine in the reaction solution with sodium sulfite solution, the mixture is allowed to stand and separate into layers; after washing the lower organic phase with deionized water, the mixture is allowed to stand and separate into layers; the lower organic phase is added dropwise to deionized water at 80-100℃, dichloromethane is evaporated and recovered, the precipitate is collected and dried to obtain brominated polystyrene.

[0017] A brominated polystyrene prepared by the aforementioned method has the molecular structure shown in general formula (1): (1); In equation (1), the x-segment and y-segment are randomly arranged. The values ​​of x and y represent the number of segment units, and the ratio of x to y is (1-5)%: (95-99)%; m represents the length of the macromolecular chain; n represents the average number of bromine atoms on the benzene ring in the macromolecular chain, and the value of n ranges from 1.5 to 2.

[0018] Furthermore, the brominated polystyrene has a softening point of 190-210℃ and a decomposition temperature of 298-310℃.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The molecular structure control method of brominated polystyrene of this invention, in contrast to the existing technology that strives to avoid the formation of aliphatic bromine, involves using ultraviolet light of specific wavelengths and intensities to assist the bromination reaction during the preparation of brominated polystyrene from polystyrene and bromine. Through the synergistic coordination of various process parameters, the content and substitution positions of bromine in the brominated polystyrene are effectively adjusted, controllably inducing the formation of a predetermined proportion of aliphatic bromine structures and precisely controlling the content of aliphatic and aromatic substituted bromine in the brominated polystyrene. The aforementioned technical means work together synergistically to effectively control the thermal stability and compatibility of brominated polystyrene while maintaining the required flame retardant efficiency, thereby controlling the decomposition temperature and softening point of brominated polystyrene to match the processing temperature and decomposition characteristics of ABS resin. Therefore, in subsequent applications, uniform blending and interfacial compatibility between brominated polystyrene and the ABS resin matrix are achieved, ultimately resulting in products that possess both excellent flame retardant effects and high mechanical property retention. Specifically: (1) The process conditions of the method of the present invention are mild and the preparation process is easy to control: Compared with the light-shielding and harsh low-temperature conditions required for the preparation of high heat-resistant brominated polystyrene, the present invention uses ultraviolet light of specific wavelength and intensity to assist the bromination reaction, and can effectively regulate the molecular structure at a relatively mild reaction temperature (10-25℃), which greatly reduces the production difficulty, energy consumption and cost.

[0020] (2) The method of the present invention can achieve precise control: by synergistic regulation of ultraviolet light irradiation and process parameters such as reaction temperature and time, a predetermined proportion of aliphatic bromine structure can be induced in a controllable manner, thereby achieving precise control of the aliphatic substituted bromine content in brominated polystyrene, thus effectively regulating the thermal properties (decomposition temperature and softening point) of brominated polystyrene while maintaining the required flame retardant efficiency.

[0021] (3) The method of the present invention has a high degree of performance matching: by introducing a predetermined proportion of aliphatic substituted bromine in the preparation process of brominated polystyrene, the decomposition temperature and softening point of brominated polystyrene are adjusted to a range that is more compatible with ABS resin, which is conducive to playing a better synergistic flame retardant effect during combustion.

[0022] (4) The solvent in the method of the present invention is recyclable and environmentally friendly: the hot water precipitation process is adopted, and the dichloromethane solvent is recovered and reused through the condenser, which effectively reduces production costs and solvent emissions, and the process is highly environmentally friendly.

[0023] (5) The brominated polystyrene prepared by the method of the present invention has excellent application performance: the flame-retardant ABS products prepared by blending brominated polystyrene prepared by the method of the present invention with ABS resin can maintain or even improve the original mechanical properties of ABS resin and obtain higher surface smoothness while meeting the UL94 V-0 flame retardant requirements. Attached Figure Description

[0024] Figure 1 The thermogravimetric curve of brominated polystyrene prepared in Example 1.

[0025] Figure 2 The thermogravimetric curve of brominated polystyrene prepared in Example 2.

[0026] Figure 3 The thermogravimetric curve of brominated polystyrene prepared in Example 3.

[0027] Figure 4 The thermogravimetric curve of brominated polystyrene prepared in Example 4.

[0028] Figure 5 Thermogravimetric curve of brominated polystyrene prepared for Comparative Example 1.

[0029] Figure 6 Thermogravimetric curve of brominated polystyrene prepared for Comparative Example 2.

[0030] Figure 7 Thermogravimetric curve of brominated polystyrene prepared for Comparative Example 3.

[0031] Figure 8 Thermogravimetric curve of brominated polystyrene prepared for Comparative Example 4. Detailed Implementation

[0032] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] This invention provides a method for controlling the molecular structure of brominated polystyrene. In the presence of a Lewis acid catalyst, polystyrene is reacted with bromine in a molar amount of 1.6-2 times the number of benzene rings in the polystyrene at a temperature of 10-25°C. During the reaction, ultraviolet light irradiation is used to induce the generation of aliphatic substituted bromine. The ratio of aliphatic substituted bromine to aromatic substituted bromine in the brominated polystyrene is controlled to be (1-5)%:(95-99)%, thus obtaining brominated polystyrene whose decomposition temperature, softening point, and flame retardant properties all meet the flame retardant and processing requirements of ABS resin.

[0035] The molecular structure of brominated polystyrene obtained by the method described above is shown in the following general formula (1): (1); In general formula (1), the x segment represents a structural unit containing aliphatic substituted bromine, and the y segment represents a structural unit containing only aromatic substituted bromine. The x and y segments are randomly arranged in the molecular chain of brominated polystyrene. The values ​​of x and y represent the number of segment units, and the ratio of x to y is (1-5)%:(95-99)%, that is, the ratio of aliphatic substituted bromine to aromatic substituted bromine in brominated polystyrene is (1-5)%:(95-99)%. m represents the degree of polymerization of the macromolecular chain of brominated polystyrene. n represents the average number of bromine atoms on each benzene ring in the macromolecular chain of brominated polystyrene, and the value ranges from 1.5 to 2.

[0036] In the method for controlling the molecular structure of brominated polystyrene, the molecular structure of the brominated polystyrene obtained is preferably any integer between 10 and 2000.

[0037] The method for regulating the molecular structure of brominated polystyrene produces brominated polystyrene with a softening point of 180-215℃ and a decomposition temperature of 295-315℃; preferably, the brominated polystyrene produced has a softening point of 190-210℃ and a decomposition temperature of 298-310℃.

[0038] The method for regulating the molecular structure of brominated polystyrene includes the following steps: placing polystyrene and a Lewis acid catalyst in dichloromethane solvent, and adding bromine dropwise under ultraviolet light irradiation at a temperature of 10-25°C; after the bromine is added, maintaining the temperature for reaction to obtain a reaction solution, which is then purified to obtain brominated polystyrene.

[0039] Preferably, the molar ratio of polystyrene (in terms of the number of molar benzene ring units) to bromine is 1:1.6-2.

[0040] Preferably, the Lewis acid catalyst is aluminum trichloride or aluminum tribromide, and the molar amount of the Lewis acid catalyst is 0.8-1.2% of the molar amount of polystyrene (based on the number of molar units of benzene rings).

[0041] Preferably, the reaction time after the bromine is added is 5-30 minutes.

[0042] Preferably, the wavelength range of the ultraviolet light is 200-400 nm, more preferably 254-365 nm, and even more preferably 365 nm; the intensity of the ultraviolet light is 500-5000 μW / cm². 2 (Measured at the surface of the reaction liquid), preferably 1000-3000 μW / cm 2 More preferably 2000±500μW / cm 2 In the above reaction process, ultraviolet light irradiation is a key technical means to regulate the generation of aliphatic substituted bromine; the generation of aliphatic substituted bromine mainly proceeds through a free radical reaction mechanism, and ultraviolet light can effectively excite bromine molecules to generate bromine free radicals, thereby promoting the free radical substitution reaction on the polystyrene backbone.

[0043] Furthermore, the method for controlling the molecular structure of brominated polystyrene includes the following steps: dissolving polystyrene in dichloromethane solvent, adding aluminum tribromide (a Lewis acid catalyst), heating to 10-25°C under ultraviolet light irradiation, and adding bromine dropwise while maintaining the temperature; after the bromine is added, maintaining the temperature for reaction, then neutralizing the unreacted bromine with sodium sulfite solution, allowing the mixture to stand and separate into layers, washing the lower organic phase with water, allowing it to stand and separate into layers again, and then adding the lower organic phase dropwise to hot water at 80-100°C, evaporating and recovering the dichloromethane solvent, collecting the solid and drying it to obtain brominated polystyrene with a softening point of 180-215°C and a decomposition temperature of 295-315°C.

[0044] Preferably, the volume of deionized water used in the water washing is 20-50% of the volume of the lower organic phase.

[0045] Preferably, the lower organic phase is added dropwise to 1.5-2.5 times its volume of hot water to evaporate the solvent and precipitate.

[0046] Furthermore, the method for controlling the molecular structure of brominated polystyrene includes the following steps: dissolving 1 mol (based on benzene ring units) of polystyrene in 500 mL of dichloromethane, adding 0.8-1.2% mol (based on benzene ring units) of Lewis acid catalyst aluminum tribromide, and adding 1.6-2.0 mol of bromine dropwise at a temperature of 10-25°C under ultraviolet light irradiation through the sight glass of the reactor, while controlling the system temperature within the range of 10-25°C by adjusting the bromine addition rate during the bromine addition process; after the bromine addition is complete, maintaining the temperature at the same temperature as the addition temperature (i.e., 10-25°C) for 5-30 min to obtain a reaction solution; then adding sulfurous acid to the reaction solution. Unreacted bromine is neutralized and removed by a sodium saturated solution. After standing and separating into layers, the lower organic phase is introduced into a water-washing reactor and washed with 20-50% of the organic phase volume of deionized water. After standing and separating into layers again, 1.5-2.5 times the volume of the lower organic phase of deionized water is added to a precipitation reactor, and the temperature is raised to 80-100℃. The lower organic phase is stirred and added dropwise to hot water at 80-100℃. The dichloromethane solvent in the lower organic phase evaporates and is recovered and reused through a condenser connected to the precipitation reactor. Solids are precipitated in the precipitation reactor. The solids are collected and dried at 100-120℃ to obtain brominated polystyrene with a softening point of 180-215℃ and a decomposition temperature of 295-315℃.

[0047] The method for regulating the molecular structure of brominated polystyrene can achieve precise control over the final decomposition temperature and softening point of the product by synergistically controlling four dimensions: ultraviolet light irradiation intensity, reaction temperature, reaction time, and bromine dosage. Preferably, the amount of aliphatic substituted bromine generated is controlled by synergistically controlling the ultraviolet light irradiation intensity, bromine drop temperature, and / or heat preservation reaction time, and the content of aromatic substituted bromine is controlled by controlling the amount of bromine added.

[0048] The present invention also provides brominated polystyrene prepared by the aforementioned method, with a softening point of 180-215°C and a decomposition temperature of 295-315°C; preferably, the softening point is 190-210°C and the decomposition temperature is 298-310°C.

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with some specific embodiments.

[0050] The testing equipment and raw materials used in each embodiment are described below: Testing equipment: Digital melting point tester (for determining softening point); bromine content tester by sample combustion method; potentiometric titrator (for determining the ratio of aliphatic bromine to aromatic bromine); vertical combustion tester; simply supported beam testing machine; electronic universal tensile testing machine; TGA thermogravimetric analyzer (for determining decomposition temperature, referring to the 5% thermal weight loss temperature in this article).

[0051] The method for detecting the bromine content in segment x is as follows: Accurately weigh 1.000±0.002g of brominated polystyrene sample (accurate to 0.1mg) into a 250mL iodine flask containing a rotor, then add 100mL of tetrahydrofuran, start stirring, and heat. When the solution begins to reflux, add 25mL of 0.5mol / L potassium hydroxide ethanol solution, reflux for 15min, then add 100mL of deionized water, cool to room temperature, add 3-4 drops of 50% nitric acid solution for acidification, then add 0.1g of dextrin, and titrate with 0.01mol / L silver nitrate solution according to the operating procedure of a potentiometric titrator to obtain the volume V of silver nitrate solution consumed at the titration endpoint; simultaneously perform a blank test to obtain the volume V0 of silver nitrate solution consumed for the blank sample; the bromine content (wt%) in segment x is calculated using the following formula: ; In the formula, V - the volume of silver nitrate solution consumed to the titration endpoint, mL; V0 - the volume of silver nitrate solution consumed for the blank titration, mL; C - the molar concentration of the silver nitrate solution, mol / L; m - the weight of the brominated polystyrene sample, g.

[0052] The method for detecting the bromine content corresponding to n is as follows: Brominated polystyrene is treated with an ethanol solution of 0.5 mol / L potassium hydroxide to remove aliphatic bromine. After thorough washing and drying, 1 g of the powder is weighed and ground in a mortar, then passed through a 40-mesh sieve to obtain powder. 0.0150 ± 0.001 g of the powder is weighed and wrapped in ashless filter paper. Simultaneously, 10 mL of 0.5 mol / L sodium hydroxide solution and 5 mL of 6 wt% hydrogen peroxide solution are added to a 500 mL oxygen combustion flask. Oxygen is bubbled into the flask for 2 minutes, then the filter paper is ignited and quickly placed into the combustion flask and inverted. After combustion, the combustion flask is shaken vigorously for about 30 seconds. The flask is then placed at 20 ± 3℃ and allowed to stand for 1 hour. Finally, the powder is transferred to a 250 mL beaker and distilled water is added to a final volume of 200 mL. The sample preparation is now complete. Add 0.1g of dextrin to the sample, then add 2mL of 50% nitric acid. Titrate with 0.01mol / L silver nitrate solution according to the operating procedure of the potentiometric titrator, and obtain the volume V1 of silver nitrate solution consumed at the titration endpoint. Simultaneously, perform a blank test to obtain the volume V0 of silver nitrate solution consumed for the blank sample. The bromine content (wt%) corresponding to n is calculated using the following formula: ; In the formula, V0 is the volume of silver nitrate solution consumed in the blank titration (mL); V1 is the volume of silver nitrate solution consumed in the titration to the endpoint (mL); C is the molar concentration of the silver nitrate solution (mol / L); and m is the mass of the ground powder weighed (g).

[0053] The method for detecting total bromine content is as follows: Weigh 1g of brominated polystyrene and grind it in a mortar, then pass it through a 40-mesh sieve to obtain ground powder; weigh 0.0150±0.001g of the ground powder and wrap it in ashless filter paper. At the same time, add 10mL of 0.5mol / L sodium hydroxide solution and 5mL of 6wt% hydrogen peroxide solution to a 500mL oxygen combustion flask. After bubbling oxygen into the flask for 2min, ignite the filter paper and quickly place it into the combustion flask and invert it. After combustion, shake the combustion flask vigorously for about 30s. Place the combustion flask at 20±3℃ and let it stand for 1h. Then transfer it to a 250mL beaker and add distilled water to 200mL. The sample preparation is complete. Add 0.1g of dextrin to the sample, then add 2mL of 50% nitric acid. Titrate with 0.01mol / L silver nitrate solution according to the operating procedure of the potentiometric titrator, and obtain the volume V2 of silver nitrate solution consumed at the titration endpoint. Simultaneously, perform a blank test to obtain the volume V0 of silver nitrate solution consumed for the blank sample. The total bromine content (wt%) is calculated using the following formula: ; In the formula, V0 is the volume of silver nitrate solution consumed in the blank titration (mL); V2 is the volume of silver nitrate solution consumed in the titration to the endpoint (mL); C is the molar concentration of the silver nitrate solution (mol / L); and m is the mass of the ground powder weighed (g).

[0054] Furthermore, the calculation method for the values ​​of x, y, and n is as follows: based on the aforementioned formula (1) for brominated polystyrene, the theoretical calculation formulas for the three bromine contents detected are as follows: The theoretical formula for calculating the bromine content (wt%) in segment x: ; The theoretical formula for calculating the bromine content (wt%) corresponding to n is as follows: ; The theoretical formula for calculating total bromine content (wt%): ; Substitute the aforementioned detection results of the three bromine contents into the corresponding theoretical formulas to calculate the values ​​of x, y, and n.

[0055] Production equipment: twin-screw extruder.

[0056] Equipment for preparing the sample strip: injection molding machine.

[0057] Bromotriazine: Commercially available, softening point 242℃, decomposition temperature 320℃.

[0058] Polystyrene (GPPS): General grade, commercially available, molecular weight 200,000 (i.e., m≈2000).

[0059] PA grade brominated polystyrene: commercially available, softening point 280℃, decomposition temperature 340℃.

[0060] ABS resin: Commercially available, general grade.

[0061] Antioxidant 1010: Commercially available.

[0062] Antimony trioxide: Commercially available, particle size 1-2μm.

[0063] The basic preparation method of brominated polystyrene (nBPS) used in each embodiment is as follows: 1 mol (based on benzene ring units) of polystyrene is dissolved in 500 mL of dichloromethane, and 0.01 mol of Lewis acid catalyst aluminum tribromide is added. Under the illumination of a UV lamp installed in the sight glass of the reactor, 1.6-2.0 mol of bromine is added dropwise at a temperature of 10-25°C. During the bromine addition, the system temperature is controlled within the range of 10-25°C by adjusting the bromine addition rate. After the bromine addition is complete, the mixture is kept at the same temperature as the addition temperature for 5-30 min to obtain the reaction solution. A saturated sodium sulfite solution was added to the reaction solution to neutralize and remove unreacted bromine. After standing and separating the layers, the lower organic phase was introduced into a water-washing reactor and washed with 20% of the volume of the organic phase in deionized water. After standing and separating the layers again, twice the volume of the lower organic phase in deionized water was added to the precipitation reactor, and the temperature was raised to 90°C. The lower organic phase was stirred and added dropwise to hot water at 90°C. The dichloromethane solvent in the lower organic phase evaporated and was recovered and reused through a condenser connected to the precipitation reactor. Solid precipitated in the precipitation reactor, the solid was collected and dried at 120°C to obtain brominated polystyrene.

[0064] The ultraviolet lamps used were low-pressure mercury lamps or UV-LED light sources, emitting ultraviolet light with a dominant wavelength of 365 nm. The ultraviolet intensity measured at the reaction liquid surface was 2000±500 μW / cm². 2 The power and irradiation distance of the ultraviolet lamp can be adjusted according to the size of the reactor to ensure that the reaction system receives appropriate ultraviolet irradiation intensity. The ultraviolet lamp tube is protected by a quartz sleeve and fixed to the sight glass by a sealing flange to ensure the sealing of the reactor. This ensures that stable and controllable ultraviolet radiation is continuously provided throughout the reaction process, precisely controlling the formation rate and final content of aliphatic substituted bromine.

[0065] Example 1 This embodiment provides a method for regulating the molecular structure of brominated polystyrene, specifically as follows: Following the aforementioned basic preparation method, 1 mol of polystyrene (based on benzene ring units) was dissolved in 500 mL of dichloromethane, and 0.01 mol of Lewis acid catalyst aluminum tribromide was added. Under the illumination of an ultraviolet lamp installed in the sight glass of the reactor, 1.6 mol of bromine was added dropwise at 12 °C. After the addition was complete, the mixture was kept at the same temperature (12 °C) as the addition temperature for 30 min to obtain the reaction solution. The subsequent purification steps for the reaction solution were the same as those in the aforementioned basic preparation method, and white brominated polystyrene (nBPS) was obtained.

[0066] This embodiment also provides brominated polystyrene prepared by the aforementioned method. Its structural parameters and properties are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) is 1.3:98.7; the average number of bromine atoms on the benzene ring is n=1.62; the softening point is 190℃; and the decomposition temperature is 310℃ (thermogravimetric curve as shown). Figure 1 (As shown).

[0067] Furthermore, 100 parts by weight of ABS resin, 12 parts by weight of the aforementioned nBPS, 1 part by weight of antioxidant 1010, and 4 parts by weight of antimony trioxide were added to a twin-screw extruder, and a flame-retardant ABS resin composition was obtained by melt extrusion granulation. After the granules were dried, they were injection molded into standard test strips with a thickness of 1.6 mm using an injection molding machine, and their mechanical properties and flame-retardant properties were tested. The results are shown in Table 1.

[0068] Example 2 This embodiment provides a method for regulating the molecular structure of brominated polystyrene, specifically as follows: Following the aforementioned basic preparation method, 1 mol of polystyrene (based on benzene ring units) was dissolved in 500 mL of dichloromethane, and 0.01 mol of Lewis acid catalyst aluminum tribromide was added. Under the illumination of an ultraviolet lamp installed in the sight glass of the reactor, 1.6 mol of bromine was added dropwise at 15 °C. After the addition was complete, the mixture was kept at the same temperature (15 °C) as the addition temperature for 25 min to obtain the reaction solution. The subsequent purification steps for the reaction solution were the same as those in the aforementioned basic preparation method, and white brominated polystyrene (nBPS) was obtained.

[0069] This embodiment also provides brominated polystyrene prepared by the aforementioned method. Its structural parameters and properties are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) is 3.6:96.4; the average number of bromine atoms on the benzene ring is n=1.63; the softening point is 190℃; and the decomposition temperature is 305℃ (thermogravimetric curve as shown). Figure 2 (As shown).

[0070] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0071] Example 3 This embodiment provides a method for regulating the molecular structure of brominated polystyrene, specifically as follows: Following the aforementioned basic preparation method, 1 mol of polystyrene (based on benzene ring units) was dissolved in 500 mL of dichloromethane, and 0.01 mol of Lewis acid catalyst aluminum tribromide was added. Under the illumination of an ultraviolet lamp installed in the sight glass of the reactor, 1.6 mol of bromine was added dropwise at 25 °C. After the addition was complete, the mixture was kept at the same temperature (25 °C) as the addition temperature for 5 min to obtain the reaction solution. The subsequent purification steps for the reaction solution were the same as those in the aforementioned basic preparation method, and white brominated polystyrene (nBPS) was obtained.

[0072] This embodiment also provides brominated polystyrene prepared by the aforementioned method. Its structural parameters and properties are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) is 4.7:95.3; the average number of bromine atoms on the benzene ring is n=1.64; the softening point is 190℃; and the decomposition temperature is 298℃ (thermogravimetric curve as shown). Figure 3 (As shown).

[0073] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0074] Example 4 This embodiment provides a method for regulating the molecular structure of brominated polystyrene, specifically as follows: Following the aforementioned basic preparation method, 1 mol of polystyrene (based on benzene ring units) was dissolved in 500 mL of dichloromethane, and 0.01 mol of Lewis acid catalyst aluminum tribromide was added. Under the illumination of an ultraviolet lamp installed in the sight glass of the reactor, 2.0 mol of bromine was added dropwise at 12 °C. After the addition was complete, the mixture was kept at the same temperature (12 °C) as the addition temperature for 20 min to obtain the reaction solution. The subsequent purification steps for the reaction solution were the same as those in the aforementioned basic preparation method, and white brominated polystyrene (nBPS) was obtained.

[0075] This embodiment also provides brominated polystyrene prepared by the aforementioned method. Its structural parameters and properties are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) is 1.6:98.4; the average number of bromine atoms on the benzene ring is n=1.95; the softening point is 210℃; and the decomposition temperature is 301℃ (thermogravimetric curve as shown). Figure 4 (As shown).

[0076] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0077] Comparative Example 1 This comparative example demonstrates the effect of carrying out the bromination reaction at a lower temperature. This comparative example uses the technical solution of Example 1, except that the bromine addition temperature and the reaction holding temperature are both 0°C.

[0078] The structural parameters and properties of the brominated polystyrene prepared in this comparative example are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) = 0.1:99.9, the average number of bromine atoms in the benzene ring n = 1.96, the softening point is 225℃, and the decomposition temperature is 331℃ (thermogravimetric curves are shown in the figure). Figure 5 (As shown).

[0079] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0080] Comparative Example 2 This comparative example demonstrates the effect of carrying out the bromination reaction at a lower temperature. This comparative example uses the technical solution of Example 1, except that the bromine addition temperature and the holding reaction temperature are both -5°C.

[0081] The structural parameters and properties of the brominated polystyrene prepared in this comparative example are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) = 0.05:99.95, the average number of bromine atoms in the benzene ring n = 1.97, the softening point is 228℃, and the decomposition temperature is 341℃ (thermogravimetric curves are shown below). Figure 6 (As shown).

[0082] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0083] Comparative Example 3 This comparative example demonstrates the effect of deep bromination at a lower temperature using excess bromine. This comparative example adopts the technical solution of Example 1, with the following differences: 1) the bromine dropping temperature and the holding reaction temperature are both -5°C; 2) the molar amount of bromine is 2.7 mol.

[0084] The structural parameters and properties of the brominated polystyrene obtained in this comparative example are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) = 0.06:99.94, the average number of bromine atoms in the benzene ring n = 2.45, the softening point is 282℃, and the decomposition temperature is 351℃ (thermogravimetric curves are shown in the figure). Figure 7 (As shown).

[0085] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0086] Comparative Example 4 This comparative example demonstrates the effect of bromination without the use of ultraviolet light irradiation, aiming to simulate the traditional preparation route of PA-grade brominated polystyrene. This comparative example adopts the technical solution of Example 1, with the following differences: 1) the bromine dropping temperature and the holding reaction temperature are both 0°C; 2) the molar amount of bromine is 2.7 mol; 3) ultraviolet light irradiation is not used.

[0087] The structural parameters and properties of the brominated polystyrene prepared in this comparative example are as follows: in the aforementioned general formula (I), the ratio of aliphatic substituted bromine segments (x):aromatic substituted bromine segments (y) = 0.01:99.99, the average number of bromine atoms in the benzene ring n = 2.65, the softening point is 286℃, and the decomposition temperature is 361℃ (thermogravimetric curves are shown in the figure). Figure 8 (As shown).

[0088] Standard test strips of the flame-retardant ABS resin composition were prepared according to the same formulation and process as in Example 1, and their performance was tested. The results are shown in Table 1.

[0089] Comparative Example 5 In the preparation of the flame-retardant ABS resin composition, commercially available brominated triazine was used instead of brominated polystyrene in Example 1. Specifically, 100 parts by weight of ABS resin, 16 parts by weight of commercially available brominated triazine, 1 part by weight of antioxidant 1010, and 4 parts by weight of antimony trioxide were added to a twin-screw extruder. The flame-retardant ABS resin composition was obtained by melt extrusion granulation. After the granules were dried, they were injection molded into standard test strips with a thickness of 1.6 mm using an injection molding machine. Their mechanical properties and flame-retardant properties were tested, and the results are shown in Table 1.

[0090] Comparative Example 6 In the preparation of the flame-retardant ABS resin composition, commercially available PA-grade brominated polystyrene was used instead of the brominated polystyrene in Example 1. Specifically, 100 parts by weight of ABS resin, 12 parts by weight of commercially available PA-grade brominated polystyrene, 1 part by weight of antioxidant 1010, 1 part by weight of antioxidant 168, and 3 parts by weight of antimony trioxide were added to a twin-screw extruder. The flame-retardant ABS resin composition was obtained by melt extrusion granulation. After drying the granules, they were injection molded into standard test strips with a thickness of 1.6 mm using an injection molding machine. Their mechanical properties and flame-retardant properties were tested, and the results are shown in Table 1.

[0091] Table 1 Summary of Product Parameters and Performance Indicators

[0092] Based on the product parameters and performance indicators in the table above, it is clear that: Examples 1-4 of this invention: By conducting the reaction under the mild conditions (10-25℃) specified in this invention, the aliphatic bromine content (x ratio) can be successfully controlled between 1-5%. The softening point (190-210℃) and decomposition temperature (298-310℃) of the product are highly matched with the processing temperature window of ABS resin. Among them, the n values ​​of Examples 1-3 are 1.62, 1.63, and 1.64, respectively, and the n values ​​are very close. Therefore, the softening point of all of them is 190℃, which is in line with scientific principles (the softening point is mainly affected by the number of bromine atoms n on the benzene ring and the molecular weight, and the aliphatic bromine content has a small impact on it). In Example 4, the amount of bromine is increased to twice the molar amount of polystyrene (based on the benzene ring unit of polystyrene), and the n value increases to 1.95, so the softening point rises to 210℃. At the same time, the flame-retardant ABS resin prepared therefrom all achieves the UL94 V-0 rating, and has excellent mechanical properties and surface finish.

[0093] Comparative Examples 1-3 demonstrate the effects of bromination at lower temperatures. It can be seen that as the reaction temperature decreases (from 0℃ to -5℃), the formation of aliphatic bromine is significantly suppressed (x percentage < 0.1%), while the decomposition temperature and softening point of the product increase accordingly. In particular, Comparative Example 3, through low temperature and excess bromine, produced a product with properties similar to commercially available PA-grade brominated polystyrene (softening point 282℃, decomposition temperature 351℃). However, when used with ABS resin, due to its excessively high softening point (>280℃), it cannot effectively melt and disperse at processing temperatures around 200℃, resulting in a mismatch with the processing temperature range of ABS resin. This leads to flame retardant agglomeration, significant deterioration of the material's mechanical properties and surface appearance, and a flame retardant rating of only V-2. This demonstrates, conversely, that higher thermal stability is not always better; rather, it needs to be compatible with the target substrate.

[0094] Comparative Example 4: This demonstrates the conventional production process of PA-grade brominated polystyrene without the use of ultraviolet light irradiation. The aliphatic substituted bromine in the prepared brominated polystyrene is significantly reduced, and the decomposition temperature and softening point are too high, which are completely mismatched with the processing temperature window of ABS resin. This directly leads to poor dispersion of the polystyrene in the ABS resin matrix and poor overall performance of the ABS resin composition.

[0095] Comparative Example 5: Using the traditional small-molecule flame retardant component brominated triazine, the flame retardant rating of the flame-retardant ABS resin composition prepared with it can reach V-0. However, due to the poor compatibility between brominated triazine and ABS, the mechanical properties of the flame-retardant ABS resin composition are significantly reduced, and the stability is poor, with a risk of precipitation.

[0096] Comparative Example 6: Commercially available PA-grade brominated polystyrene was used. However, due to its excessively high decomposition temperature and softening point, which were completely mismatched with the processing temperature window of ABS resin, it was directly caused to poor dispersion in the ABS resin matrix, resulting in poor overall performance of the ABS resin composition.

[0097] In summary, this invention, through the deliberate introduction and precise control of an appropriate amount of aliphatic substituted bromine during the preparation of brominated polystyrene, successfully modulates the thermal properties of the resulting brominated polystyrene product to a range perfectly matched with ABS resin. This effectively controls the thermal stability of brominated polystyrene and its compatibility with ABS resin while maintaining sufficient flame retardant efficiency, promoting uniform blending and interfacial compatibility between brominated polystyrene and the ABS resin matrix, thus avoiding adverse effects on the mechanical properties of ABS products.

[0098] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0099] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for regulating the molecular structure of brominated polystyrene, characterized in that, In the presence of a Lewis acid catalyst, polystyrene is reacted with bromine in a molar amount of 1.6-2 times the number of benzene rings in the polystyrene at a temperature of 10-25℃. During the reaction, ultraviolet light irradiation is used to induce the generation of aliphatic substituted bromine. The ratio of aliphatic substituted bromine to aromatic substituted bromine in the brominated polystyrene is controlled to be (1-5)%:(95-99)%, so as to obtain brominated polystyrene with decomposition temperature and softening point that meet the processing requirements of ABS resin.

2. The method for regulating the molecular structure of brominated polystyrene according to claim 1, characterized in that, The process includes the following steps: placing polystyrene and a Lewis acid catalyst in dichloromethane, adding bromine dropwise under ultraviolet light at a temperature of 10-25°C; after the bromine is added, maintaining the temperature to react and obtaining a reaction solution; purifying the reaction solution to obtain brominated polystyrene.

3. The method for regulating the molecular structure of brominated polystyrene according to claim 1, characterized in that, The wavelength range of the ultraviolet light is 200-400 nm, and the intensity of the ultraviolet light is 500-5000 μW / cm. 2 .

4. The method for regulating the molecular structure of brominated polystyrene according to claim 1, characterized in that, The wavelength range of the ultraviolet light is 254-365 nm, and the intensity of the ultraviolet light is 1000-3000 μW / cm. 2 .

5. The method for regulating the molecular structure of brominated polystyrene according to claim 1, characterized in that, The Lewis acid catalyst is aluminum trichloride or aluminum tribromide; Based on the number of molar units of benzene rings in polystyrene, the molar amount of Lewis acid catalyst is 0.8-1.2% of the molar amount of polystyrene.

6. The method for regulating the molecular structure of brominated polystyrene according to claim 2, characterized in that, After the bromine is added, the reaction should be kept at a constant temperature for 5-30 minutes.

7. The method for regulating the molecular structure of brominated polystyrene according to claim 2, characterized in that, The purification method described above is as follows: after neutralizing excess bromine in the reaction solution with sodium sulfite solution, the mixture is allowed to stand and separate into layers; the lower organic phase is washed with deionized water and allowed to stand and separate into layers; the lower organic phase is added dropwise to deionized water at 80-100℃, dichloromethane is evaporated and recovered, the precipitate is collected and dried to obtain brominated polystyrene.

8. A brominated polystyrene prepared by the method according to any one of claims 1-7, characterized in that, The molecular structure of brominated polystyrene is shown in general formula (1): （1）； In equation (1), the x-segment and y-segment are randomly arranged. The values ​​of x and y represent the number of segment units, and the ratio of x to y is (1-5)%: (95-99)%; m represents the length of the macromolecular chain; n represents the average number of bromine atoms on the benzene ring, and the value of n ranges from 1.5 to 2.

9. The brominated polystyrene according to claim 8, characterized in that, The brominated polystyrene has a softening point of 190-210℃ and a decomposition temperature of 298-310℃.

Images