Brominated polystyrene (BPS) is a derivative of polystyrene. Its polymer structure makes it highly compatible with matrix resins, especially plastics containing aromatic rings such as PBT, PET, and PA, resulting in excellent resistance to exudation. During long-term use, BPS does not migrate to the material surface like some small-molecule flame retardants, commonly known as "non-frosting," thus maintaining the product's appearance, performance, and electrical properties.

I. Basic Information

Chemical name: BPS; Brominated Polystyrene

Other chemical name: Ethenyl-benzene homopolymer brominated

Molecular formula : (C8H5.3 Br2.7)n

CAS NO.: 88497-56-7

II. Flame Retardant Mechanism

Brominated polystyrene (BPS) is almost always used in combination with antimony trioxide (Sb₂O₃), which is the classic halogen-antimony synergistic effect. During combustion, the HBr produced by the decomposition of brominated polystyrene reacts with antimony trioxide to generate volatile antimony bromide such as antimony tribromide (SbBr₃). SbBr₃ has high density and moderate volatility, allowing it to remain in the combustion zone for a longer period and more effectively capture free radicals. Simultaneously, it promotes char formation on the material surface in the condensed phase, forming a denser protective layer. This synergistic effect can significantly reduce the amount of flame retardant added while achieving a superior flame retardant rating.

III. Product Specifications

Appearance: white yellow powder/granule

Softening point: 220oCmin

Free bromine:12mg/kg max

Organic bromine: 67% min

Volatile matter: 0.3%max

Molecular weight:200,000min

IV. Applications

Brominated polystyrene (BPS) flame retardant possesses excellent thermal stability and electrical properties. It is particularly suitable for PA, PET, PBT, and PCT. Due to its excellent thermal stability, it is an ideal choice for high-temperature applications such as engineering plastics. Due to its stability, it is generally suitable for applications where other flame retardants cannot withstand it. Because of its polymer structure, it does not exhibit whitening in any application. Its excellent electrical properties also make it an ideal flame retardant for demanding engineering plastics applications.

V. Flame Retardant Formulations

PA66/6: BPS 21, ATO 8, UL94 (1.6mm) V-0

PBT, PET: BPS 17, ATO 6, UL94 (1.6mm) V-0

PBT, PET Reinforced: BPS 10, ATO 4, UL94 (1.6mm) V-0

VI. Production Process

The mainstream production process for brominated polystyrene (BPS) is solution bromination. The core process involves electrophilic substitution of the benzene ring in polystyrene (PS) under Lewis acid catalysis, using bromine chloride (BrCl) as the brominating agent. The complete process flow is as follows:

A. Raw Material Preparation: Polystyrene (PS, granules/powder), bromine (Br₂), chlorine (Cl₂), haloalkanes solvent (1,2-dichloroethane/dichloromethane), antimony trichloride (SbCl₃), antimony tribromide (SbBr₃), aluminum chloride (AlCl₃), Lewis acids, sodium sulfite, sodium bicarbonate, deionized water, methanol (for post-treatment).

B. Preparation of Bromine Chloride (BrCl) (brominating agent):

1. Add dichloroethane and bromine to a low-temperature reactor and stir to dissolve.

2. Maintain the temperature below 0℃ and slowly introduce chlorine gas to induce the reaction: Br₂ + Cl₂ → 2BrCl.

3. After the reaction is complete, a 40% bromine chloride solution is obtained and stored at low temperature for later use.

C. Catalyst Preparation (As Needed)

Taking antimony tribromide as an example: Antimony powder reacts with liquid bromine at 30°C and is maintained at this temperature for 2 hours to obtain a catalyst solution.

D. Polystyrene Dissolution

1. Add PS granules to a dissolving vessel, add 1,2-dichloroethane, and heat to 40–60°C while stirring until completely dissolved.

2. Cool to 5–15°C and transfer to a bromination reactor.

E. Bromination Reaction (Core Step)

1. Add a Lewis acid catalyst (such as SbCl₃/SbBr₃) to the PS solution and stir until homogeneous.

2. Maintain the temperature at 5–10°C and slowly add bromine chloride solution dropwise (strict temperature control to prevent side reactions).

3. After the addition is complete, raise the temperature to 20–30°C and maintain the reaction for 3–8 hours until the bromine content reaches the target (usually 65–68%).

4. The exhaust gas (HBr, unreacted Cl₂/Br₂) is treated by alkaline absorption.

F. Post-treatment and Purification

1. Reduction and Decolorization: Add sodium sulfite solution to reduce residual bromine, whitening the material.

2. Water Washing and Neutralization: Wash repeatedly with water, add sodium bicarbonate to adjust pH to neutral, removing catalyst and salts.

3. Solvent Removal and Precipitation: Add the organic phase dropwise to 85–90℃ hot water, dichloroethane is evaporated, and BPS solid precipitates.

4. Filtration and Washing: Centrifuge/filter, wash with hot water to remove residual solvent and impurities.

5. Drying and Pulverizing: Dry at 100–120℃, pulverize to the target particle size, obtaining the finished BPS product.

G. Quality Control and Testing

Testing Indicators: Bromine content, thermal stability, whiteness, molecular weight, volatile matter, ash content, etc.

Package and warehousing after passing inspection.

H. Process Key Points

Low Temperature Control: Temperature control throughout the reaction process to avoid main chain degradation and side reactions.

Brominizing Agent Selection: Bromine chloride has high activity and good selectivity, making it the mainstream industrial agent.

Solvent Recovery: Dichloroethane requires efficient recovery to reduce costs and environmental impact.

Tail Gas Treatment: HBr, Cl₂, etc., must be absorbed through alkaline scrubbing to meet emission standards.

BPS has a high decomposition temperature; its 5% thermal decomposition temperature typically exceeds 330°C, and some high-quality products can even reach above 340°C. This allows it to withstand high-temperature processing conditions of PBT, PA, and other engineering plastics at around 300°C without premature decomposition, avoiding corrosion of processing equipment and problems such as blistering and discoloration of materials. Due to its large molecular structure and good compatibility with substrates, BPS provides flame retardancy while preserving the original mechanical, electrical, and antistatic properties of the substrate to the greatest extent possible. BPS does not contain polybrominated diphenyl ethers (PBDEs) or polybrominated biphenyls (PBBPs) during its preparation, thus complying with RoHS and considered a safer and more environmentally friendly alternative to brominated flame retardants.