A process for the preparation of brominated polystyrene

Abstract

The application belongs to the technical field of bromine flame retardant polymer preparation, and particularly relates to a preparation method of brominated polystyrene, wherein, in the presence of a soluble catalyst, chlorinated bromine is used as a brominating agent to brominate high molecular weight polystyrene; after the reaction is completed, the product is separated from the reaction system through the action of temperature reduction and an additive; the solid is washed and dried to obtain the product; and the mother liquor is recycled for the next bromination reaction. The synthesis method not only realizes the recycling of the solvent and the catalyst, reduces energy consumption and wastewater discharge, but also has high bromine content, good whiteness, high weight average molecular weight and good thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of high molecular weight brominated flame retardants, specifically relating to a method for preparing brominated polystyrene. Background Technology

[0002] Brominated polystyrene is a bromine-based organic flame retardant with excellent flame retardancy, thermal stability, and light stability, as well as excellent physical and mechanical properties. It is widely used in engineering plastics such as polybutylene terephthalate, polyethylene terephthalate, and nylon-66.

[0003] Currently, there are two main industrial methods for synthesizing brominated polystyrene: brominated polystyrene synthesized via bromination followed by polymerization, and polystyrene synthesized via polymerization followed by bromination. The bromination-before-polymerization method uses styrene as a raw material, undergoing addition, bromination, and dehydrobromination reactions with hydrogen bromide to obtain brominated styrene monomer, which is then polymerized to obtain polybrominated polystyrene. The polymerization-before-bromination method uses polystyrene as a raw material, reacting it with a brominating agent to produce brominated polystyrene.

[0004] In China, the common process route is polymerization followed by bromination. This route is simple to synthesize, requires less sophisticated equipment, and yields products with high bromine content. However, after the reaction, water quenching is required to extinguish the reaction, leading to catalyst deactivation and preventing recycling. The solvent, after evaporation and crystallization, requires further dehydration before recycling, increasing energy consumption and wastewater volume. Furthermore, substitution reactions can cause side reactions, such as bromine substitution of hydrogen atoms in the polystyrene backbone and Friedel-Crafts reactions between the solvent and polystyrene, both of which result in a yellowish product color and lower thermal weight loss.

[0005] For example, Chinese patent document CN119241742A discloses a method for synthesizing highly thermally stable brominated polystyrene, including the following steps: S01, dissolving polystyrene in a haloalkanes solvent in a reaction flask to obtain a polystyrene solution; S02, adding aluminum chloride and bromine to another reaction flask; S03, introducing hydrogen bromide gas into the S02 reaction flask and starting stirring to react at room temperature; S04, after the S03 reaction is completed, lowering the temperature of the S01 polystyrene solution to the reaction temperature, starting stirring, adding a free radical inhibitor, and adding the bromine and catalyst mixture obtained in the S03 reaction dropwise into the polystyrene solution; S05, after the dropwise addition is completed, adjusting the temperature to the holding temperature and holding the reaction for a period of time; S06, after the holding temperature is completed, obtaining brominated polystyrene through post-treatment.

[0006] This patent utilizes the hydrogen bromide tail gas generated during the brominated polystyrene process to react with aluminum chloride in an online manner to prepare aluminum bromide, a catalyst with higher activity. This reduces the amount of catalyst to be fed and improves the thermal stability of the product. However, the catalyst cannot be recycled, and the solvent needs to be evaporated and crystallized to remove it, which increases energy consumption. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing brominated polystyrene, which is simple in process, low in production cost, high in yield, and produces high-quality products.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing brominated polystyrene includes the following steps:

[0010] (1) Polystyrene, soluble Lewis acid catalyst, and haloalkanes are mixed to obtain material A;

[0011] (2) Chlorine gas is passed into bromine and reacted at -5 to 5°C for 1 to 3 hours to obtain material B;

[0012] (3) Add material B dropwise to material A at a temperature of 0-10℃ for 1-3 hours to obtain material C. Then heat material C to 20-40℃ and keep it warm for 3-8 hours. Then cool it down to -25--5℃. Add an auxiliary agent to material C and filter to obtain solid and mother liquor. Wash the solid and vacuum dry it to obtain brominated polystyrene. Return the mother liquor to step (1) to mix with polystyrene to prepare material A. When the bromine content in the product is less than 66.5%, add a catalyst to the mother liquor. The amount added is 10% of the mass of the catalyst in step (1).

[0013] The additive is one of zinc sulfate, aluminum sulfate, manganese chloride, or manganese sulfate, and the mass ratio of the additive, bromine, and polystyrene is 1-5:220-250:100.

[0014] Furthermore, the mass ratio of chlorine to bromine is 1:2.1 to 2.3.

[0015] Furthermore, the polystyrene has a number-average molecular weight of 300,000 to 350,000 and a molecular weight distribution of 1.2 to 1.5.

[0016] Furthermore, the soluble Lewis acid catalyst is one of antimony trichloride, tin tetrachloride, or titanium tetrachloride, and the mass ratio of the catalyst to polystyrene is 2 to 10:100.

[0017] Furthermore, the haloalkane solvent is one of dichloromethane, 1,2-dichloroethane, chloroform, and 1-chlorobromomethane, and the mass ratio of polystyrene to haloalkane solvent is 5-15:100.

[0018] Furthermore, the vacuum drying temperature is 120–150°C, and the drying time is 8–20 hours.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Existing technologies generally use aluminum trichloride and aluminum tribromide as catalysts. After the reaction is completed, water is added to quench the reaction. The catalyst undergoes hydrolysis in the aqueous phase and is a disposable catalyst that cannot be recycled. This not only wastes the catalyst but also increases the amount of saline wastewater. The organic phase needs to be washed with water and alkali before evaporation and crystallization to remove the solvent. Then, it needs to be filtered and dried to obtain the product. Moreover, the solvent needs to be further dehydrated before it can be recycled.

[0021] This invention uses a moderately Lewis acid soluble in the reaction system as a catalyst, such as antimony trichloride, tin tetrachloride, or titanium tetrachloride, to catalyze the preparation of brominated polystyrene. After the reaction is complete, the temperature of the reaction system is lowered to -25 to -5°C to promote the precipitation of brominated polystyrene from the reaction system, followed by filtration. During the precipitation process of brominated polystyrene, a cationic additive is added to the reaction system to effectively reduce intermolecular repulsion, further promoting the precipitation of brominated polystyrene from the reaction system and improving the product yield. Because the catalyst used in this invention is a moderately Lewis acid soluble in the reaction system, the above operations facilitate the precipitation of brominated polystyrene from the reaction system. The catalyst is filtered out, while the catalyst remains in the mother liquor, thus achieving effective separation of the product from the catalyst and organic solvent. The mother liquor can be reused in the next bromination reaction, that is, the mother liquor is used to replace the catalyst and haloalkane solvent in step (1), realizing the recycling of the catalyst and solvent. After the mother liquor is recycled 5 to 7 times, only a small amount of catalyst needs to be added for recycling. Compared with the prior art, the present invention does not require water quenching reaction after the bromination reaction, and the catalyst will not be deactivated; it also does not require evaporation, crystallization and dehydration of the reaction system, thus realizing the recycling of the catalyst and organic solvent, reducing material consumption, energy consumption, reaction cost, simplifying post-treatment process and reducing wastewater discharge.

[0022] The inventors discovered that commonly used strong Lewis acid catalysts such as aluminum trichloride and aluminum tribromide in the prior art cannot be used in the technical solution of this invention. Because strong Lewis acid catalysts are insoluble in the reaction system, during the cooling and precipitation of brominated polystyrene from the reaction system, the strong Lewis acid catalyst will adhere to the surface of the brominated polystyrene and precipitate together, preventing it from entering the mother liquor and making catalyst recovery impossible. In addition, during the precipitation process, strong Lewis acid catalysts can cause side reactions such as chain scission of brominated polystyrene, affecting product quality and reducing product yield.

[0023] (2) Existing technologies use strong Lewis acids such as aluminum trichloride and aluminum tribromide as catalysts, which easily lead to Friedel-Crafts reactions between polystyrene and solvents, resulting in cross-linking of the product. Moreover, aluminum trichloride and aluminum tribromide are insoluble in the reaction system, which easily leads to catalyst agglomeration, resulting in decreased activity and making polystyrene prone to side reactions such as chain scission, thus reducing the thermal stability and molecular weight of the product. The present invention uses soluble moderate Lewis acids as catalysts, which can effectively solve the Friedel-Crafts reaction between polystyrene and solvents and the side reactions such as chain scission of polystyrene. As a result, the prepared brominated polystyrene product not only has a high molecular weight (weight average molecular weight of 184,000 to 192,000) and good whiteness (whiteness of 85.2% to 90.2%), but also has high thermal stability and bromine content, with 1% TGA at 342.3% to 354.9% and 5% TGA at 372.8% to 377.1%, and bromine content at 68.2% to 69.4%. Attached Figure Description

[0024] Figure 1 This is the GPC spectrum of brominated polystyrene;

[0025] Figure 2 This is the thermogravimetric spectrum of brominated polystyrene. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0027] Its 1% and 5% thermal weight loss were determined using a thermogravimetric analyzer; its whiteness was determined using a whiteness meter; its bromine content was determined using a combustion method and potentiometric titration; and its molecular weight was determined using gel permeation chromatography.

[0028] Yield = Product quality obtained / (Polystyrene quality / (1 - Bromine content of product)). Example 1

[0029] (1) 20g of polystyrene (the number average molecular weight of polystyrene is 300,000 and the molecular weight distribution is 1.2), 0.4g of antimony trichloride and 400g of 1,2-dichloroethane are mixed in a 1L four-necked bottle to obtain material A;

[0030] (2) 24g of chlorine gas was passed into 50g of bromine and reacted at -5℃ for 3h to obtain material B;

[0031] (3) Add material B dropwise to material A at a temperature of 0°C for 3 hours to obtain material C. Then heat material C to 20°C and keep it warm for 8 hours. Then cool it down to -25°C and add 0.2g of zinc sulfate. After the product precipitates out of the system, filter to obtain solid and mother liquor. Wash the solid with water until neutral and then vacuum dry at 150°C for 8 hours to obtain 61.2g of brominated polystyrene product with a yield of 96.7%. The bromine content of the product is 68.4%, the weight average molecular weight Mw is 189,000, the whiteness is 90.2°, the 1% TGA is 345.9°, and the 5% TGA is 377.1°. Example 2

[0032] (1) Add the mother liquor recovered in Example 1 to a 1L four-necked flask and add 20g of polystyrene (the number average molecular weight of polystyrene is 300,000 and the molecular weight distribution is 1.2).

[0033] (2) 24g of chlorine gas was passed into 50g of bromine and reacted at -5℃ for 3h to obtain material B;

[0034] (3) Add material B dropwise to material A at a temperature of 0°C for 3 hours to obtain material C. Then heat material C to 20°C and keep it at that temperature for 8 hours. Then cool it down to -25°C and add 0.2g of zinc sulfate. After the product precipitates out of the system, filter to obtain solid and mother liquor. Wash the solid with water until it is neutral and then vacuum dry it at 150°C for 8 hours to obtain 61.4g of brominated polystyrene product with a yield of 97.6%. The bromine content of the product is 68.2%, the weight average molecular weight Mw is 187,000, the whiteness is 88.9°, the 1% TGA is 344.1°C, and the 5% TGA is 374.5°C. Example 3

[0035] Repeat the above process. When the bromine content in the product is lower than 66.5%, add 10% of the original catalyst mass to the mother liquor obtained this time and repeat the above reaction process. The product obtained is 61.6g, with a yield of 97.0%, a bromine content of 68.5%, a weight-average molecular weight (Mw) of 188,000, a whiteness of 87.2°, a TGA temperature of 344.6℃ for 1% and 376.2℃ for 5%. Example 4

[0036] (1) 20g of polystyrene (the number average molecular weight of polystyrene is 350,000 and the molecular weight distribution is 1.5), 2g of tin tetrachloride and 133g of 1-bromomethane are mixed in a 1L four-necked flask to obtain material A;

[0037] (2) 21g of chlorine gas was passed into 44g of bromine and reacted at 5°C for 1h to obtain material B;

[0038] (3) Add material B dropwise to material A at a temperature of 10°C for 1 hour to obtain material C. Then heat material C to 40°C and keep it warm for 3 hours. Then cool it down to -5°C and add 1g of aluminum sulfate. After the product precipitates out of the system, filter to obtain the product and mother liquor. The liquid is reused for the next bromination reaction. The solid is washed with water until neutral and then vacuum dried at 130°C for 10 hours to obtain 60.4g of brominated polystyrene product with a yield of 96.7%. The bromine content of the product is 68.3%, the weight average molecular weight Mw is 184,000, the whiteness is 85.9°, the 1% TGA is 342.8°C, and the 5% TGA is 372.5°C. Example 5

[0039] (1) 20g of polystyrene (the number average molecular weight of polystyrene is 320,000 and the molecular weight distribution is 1.3), 1g of titanium tetrachloride and 200g of dichloromethane are mixed in a 1L four-necked bottle to obtain material A;

[0040] (2) 21g of chlorine gas was passed into 46g of bromine and reacted at 0℃ for 2h to obtain material B;

[0041] (3) Add material B dropwise to material A at a temperature of 5°C for 1 hour to obtain material C. Then heat material C to 30°C and keep it warm for 5 hours. Then cool it down to -10°C and add 0.5g of manganese chloride. After the product precipitates out of the system, filter to obtain the product and mother liquor. The liquid is reused for the next bromination reaction. The solid is washed with water until neutral and then vacuum dried at 140°C for 15 hours to obtain 61.5g of brominated polystyrene product with a yield of 95.9%. The bromine content of the product is 68.8%, the weight average molecular weight Mw is 192,000, the whiteness is 88.2°, the 1% TGA is 343.7°, and the 5% TGA is 376.4°. Example 6

[0042] (1) 20g of polystyrene (the number average molecular weight of polystyrene is 300,000 and the molecular weight distribution is 1.2), 1g of antimony trichloride and 300g of chloroform are mixed in a 1L four-necked bottle to obtain material A;

[0043] (2) 22g of chlorine gas was passed into 48g of bromine and reacted at 2℃ for 2h to obtain material B;

[0044] (3) Add material B dropwise to material A at a temperature of 0°C for 2 hours to obtain material C. Then heat material C to 30°C and keep it warm for 3 hours. Then cool it down to -15°C and add 0.6g of manganese sulfate. After the product precipitates out of the system, filter to obtain the product and mother liquor. The liquid is reused for the next bromination reaction. The solid is washed with water until neutral and then vacuum dried at 120°C for 15 hours to obtain 62.6g of brominated polystyrene product with a yield of 95.8%. The bromine content of the product is 69.4%, the weight average molecular weight Mw is 186,000, the whiteness is 85.2°, the 1% TGA is 342.3°C, and the 5% TGA is 372.8°C. Example 7

[0045] (1) 20g of polystyrene (the number average molecular weight of polystyrene is 300,000 and the molecular weight distribution is 1.2), 1g of antimony trichloride and 200g of 1,2-dichloroethane are mixed in a 1L four-necked flask to obtain material A;

[0046] (2) 22g of chlorine gas was passed into 47g of bromine and reacted at 0℃ for 3h to obtain material B;

[0047] (3) Add material B dropwise to material A at a temperature of 3°C for 2 hours to obtain material C. Then heat material C to 25°C and keep it warm for 5 hours. Then cool it down to -20°C and add 0.6g of manganese sulfate. After the product precipitates out of the system, filter to obtain the product and mother liquor. The liquid is reused for the next bromination reaction. The solid is washed with water until neutral and then vacuum dried at 150°C for 8 hours to obtain 62.0g of brominated polystyrene product with a yield of 97.0%. The bromine content of the product is 68.7%, the weight average molecular weight Mw is 190,000, the whiteness is 87.8°, the 1% TGA is 343.2°C, and the 5% TGA is 375.6°C. Comparative Example 1

[0048] The difference from Example 1 is that the additive used is sodium chloride. After vacuum drying, 56.2g of brominated polystyrene product was obtained with a yield of 88.5%. The bromine content of the product was 68.5%, the weight average molecular weight (Mw) was 189,000, the whiteness was 89.6°, the temperature of 1% TGA was 345.2°C, and the temperature of 5% TGA was 376.7°C. Comparative Example 2

[0049] The difference from Example 1 is that the added zinc sulfate additive is 0.1g, and after vacuum drying, 56.8g of brominated polystyrene product is obtained with a yield of 89.2%. The bromine content of the product is 68.3%, the weight average molecular weight (Mw) is 188,000, the whiteness is 89.8°, the temperature of 1% TGA is 344.8°, and the temperature of 5% TGA is 376.5°. Comparative Example 3

[0050] The difference from Example 1 is that the catalyst used is aluminum trichloride. After washing with water multiple times, it was vacuum dried to obtain 58.4g of brominated polystyrene product with a yield of 94.3%. The bromine content of the product is 67.7%, the weight average molecular weight (Mw) is 142,000, the whiteness is 65.4°, the temperature of 1% TGA is 308.7°, and the temperature of 5% TGA is 360.4°. Comparative Example 4

[0051] Polystyrene (2.5g) was placed in a three-necked flask, and dichloroethane solvent (25mL) was added. The mixture swelled for 24h. Then, liquid bromine was used as the brominating agent (the reaction ratio was n(Br2):n(PS)=3:1). The bromine was added at a rate of 1 drop / s, starting at 15℃. Fe powder was selected as the catalyst, with a dosage of 1g. Dichloroethane was used as the solvent, the reaction temperature was 40℃, and the reaction time was maintained for 3h. The product was yellowish-white in color and contained 63.34% bromine. (See "Synthesis of Polybrominated Styrene", Guangdong Chemical Industry, 2022, 49(12): 14-16).

[0052]

[0053] As can be seen from Table 1, the yield of brominated polystyrene obtained in the examples was 95.6%–97.6%, the bromine content was 68.2%–69.4%, the whiteness was 85.2%–90.2%, the weight-average molecular weight was 184,000–192,000, the 1% TGA was 342.3%–354.9%, and the 5% TGA was 372.8%–377.1%.

[0054] In Comparative Example 1, using sodium chloride instead of zinc sulfate resulted in some product remaining in the organic phase, leading to a decrease in product yield. This may be because high-valent cations are more effective at reducing intermolecular repulsion and promoting rapid product precipitation compared to monovalent cations.

[0055] In Comparative Example 2, reducing the amount of zinc sulfate resulted in a decrease in the product precipitation rate, with some product remaining in the organic phase, leading to a decrease in product yield.

[0056] Comparative Example 3 uses aluminum trichloride as a catalyst, which leads to side reactions such as Friedel-Crafts reaction between the raw material polystyrene and the solvent, as well as chain scission of the raw material polystyrene. This results in a decrease in the molecular weight of the product, a decrease in thermal weight loss, and a yellowing of the product color.

[0057] Comparative Example 4 uses iron powder as a catalyst and bromine as a brominating agent, which leads to side reactions such as Friedel-Crafts reaction between the raw material polystyrene and the solvent, as well as chain scission of the raw material polystyrene. This results in a yellowish product color and a low bromine content.

[0058] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

[0059] Figure 1 This is the GPC spectrum of the product from Example 1. Figure 1 It can be seen that the weight-average molecular weight of the product is 189,000 (Mw), and the polydispersity is 1.5, indicating that the prepared brominated polystyrene has a high molecular weight and a narrow molecular distribution.

[0060] Figure 2 This is the thermogravimetric spectrum of the product from Example 1. Figure 2 It can be seen that the product's 1% thermal weight loss is 345.9℃ and the 5% thermal weight loss is 377.1℃, indicating that the prepared brominated polystyrene product has good thermal stability.

Claims

1. A method for preparing brominated polystyrene, characterized in that, Includes the following steps: (1) Polystyrene, a soluble Lewis acid catalyst and haloalkanes are mixed to obtain material A, wherein the polystyrene has a number-average molecular weight of 300,000 to 350,000 and a molecular weight distribution of 1.2 to 1.5; (2) Chlorine gas is passed into bromine and reacted at -5 to 5°C for 1 to 3 hours to obtain material B; (3) Add material B dropwise to material A at a temperature of 0-10℃ for 1-3 hours to obtain material C. Then heat material C to 20-40℃ and keep it warm for 3-8 hours. Cool it down to -25--5℃ and add an additive to material C. Filter to obtain solid and mother liquor. Wash the solid and vacuum dry it to obtain brominated polystyrene. Return the mother liquor to step (1) to mix with polystyrene to prepare material A. When the bromine content in the product is less than 66.5%, add a catalyst to the mother liquor. The amount added is 10% of the mass of the catalyst in step (1). The additive is one of zinc sulfate, aluminum sulfate, manganese chloride, and manganese sulfate, and the mass ratio of the additive, bromine, and polystyrene is 1-5:220-250:

100. The soluble Lewis acid catalyst is one of antimony trichloride, tin tetrachloride, or titanium tetrachloride, and the mass ratio of the catalyst to polystyrene is 2 to 10:

100.

2. The method for preparing brominated polystyrene according to claim 1, characterized in that, The mass ratio of chlorine to bromine is 1:2.1 to 2.

3.

3. The method for preparing brominated polystyrene according to claim 1, characterized in that, The haloalkane solvent is one of dichloromethane, 1,2-dichloroethane, chloroform, and 1-chlorobromomethane, and the mass ratio of polystyrene to haloalkane solvent is 5-15:

100.

4. The method for preparing brominated polystyrene according to claim 1, characterized in that, The vacuum drying temperature is 120–150°C, and the drying time is 8–20 hours.

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