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EP-4741429-A1 - LOW MOLECULAR WEIGHT POLYBROMOSTYRENE AS FLAME RETARDANT, PROCESS OF MANUFACTURE AND APPLICATIONS THEREOF

EP4741429A1EP 4741429 A1EP4741429 A1EP 4741429A1EP-4741429-A1

Abstract

Low molecular weight polybromostyrene having a molecular weight of about 1,000 to about 10,000 g/mol, based on gel permeation chromatography and polystyrene standards, and processes for producing the same by polymerization of bromostyrene monomer.

Inventors

  • HE, Qingliang
  • SIMPSON, CHRISTOPHER
  • CLARKE, JOSHUA
  • BARTLEY, DAVID W.

Assignees

  • LANXESS Corporation

Dates

Publication Date
20260513
Application Date
20241209

Claims (20)

  1. A process for the polymerization of brominated styrenes having a molecular weight below 10,000, comprising the steps of: dissolving a hydrocarbon soluble initiator and a hydrocarbon soluble chain transfer agent in a bromostyrene monomer to form a dissolved mixture; and dispersing the dissolved mixture in an aqueous medium containing an organic suspending agent, wherein pH of the aqueous medium does not need to be controlled.
  2. The process according to claim 1, further comprising the step of agitating the dispersed reaction mixture at a temperature of about 30 to about 60°C, preferably about 40 to about 55°C, more preferably about 50°C, most preferably about 50°C, to form droplets.
  3. The process according to claim 2, further comprising increasing the temperature to about 70 to about 140°C, preferably about 80 to less than 110°C, more preferably about 85 to about 100°C, most preferably about 90°C, to polymerize and form beads.
  4. The process according to any of the preceding claims, wherein the hydrocarbon soluble initiator is charged as about 0.05 to about 5.0 wt%, preferably about 0.5 to about 2.5 wt%, more preferably about 1.0 to about 2.0 wt%, based on the weight of the bromostyrene monomer.
  5. The process according to any of the preceding claims, wherein the hydrocarbon soluble initiator is an azo compound, preferably 2,2'-azobis(2,4-dimethylvaleronitrile).
  6. The process according to any of the preceding claims, wherein the hydrocarbon soluble chain transfer agent is charged as about 0.05 to about 5.0 wt%, preferably about 0.5 to about 2.5 wt%, more preferably about 1.5 to about 2.0 wt%, based on weight of the bromostyrene monomer.
  7. The process according to any of the preceding claims, wherein the hydrocarbon soluble chain transfer agent is a thiol compound, preferably dodecylmercaptan.
  8. The process according to any of the preceding claims, wherein the bromostyrene monomer comprises a mixture of mono-, di-, and tribromostyrene monomers.
  9. The process according to any of the preceding claims, wherein the bromostyrene monomer comprises about 50 to about 70 wt% bromine, preferably about 55 to about 65 wt% bromine, more preferably about 60 to about 64 wt% bromine.
  10. The process according to any of the preceding claims, wherein the concentration of the organic suspending agent is about 0.5 to about 5.0 g/L, preferably about 1.0 to about 2.5 g/L, more preferably about 1.5 to about 1.75 g/L, most preferably about 1.7 g/L.
  11. The process according to any of the preceding claims, wherein the organic suspending agent is polyvinyl alcohol, preferably 87-89% hydrolyzed polyvinyl alcohol having a weight-average molecular weight of 146,000-186,000 g/mol.
  12. The process according to any of the preceding claims, wherein pH of the aqueous medium does not need to be maintained above 5.9.
  13. A process for preparing polydibromostyrene having a molecular weight below 10,000, comprising the steps of dissolving 2,2'-azobis(2,4-dimethylvaleronitrile) and dodecylmercaptan in a mixture of mono-, di-, and tribromostyrene monomers to form a dissolved mixture; dispersing the dissolved mixture in an aqueous medium containing hydrolyzed polyvinyl alcohol having a weight-average molecular weight of 146,000-186,000 g/mol; agitating the dispersion at temperature of about 45 to about 55°C to form droplets; and increasing the temperature to about 85 to about 95°C to polymerize the droplets.
  14. The process according to claim 13, wherein the hydrocarbon soluble initiator is charged as 0.05 to about 5.0 wt%, preferably about 0.5 to about 2.5 wt%, more preferably about 1.0 to about 2.0 wt%, based on the weight of the bromostyrene monomer, and the hydrocarbon soluble chain transfer agent is charged as about 0.05 to about 5.0 wt%, preferably about 0.5 to about 2.5 wt%, more preferably about 1.5 to about 2.0 wt%, based on weight of the bromostyrene monomer.
  15. A flame retardant comprising polybromostyrene produced by the process according to any of the preceding claims, wherein the molecular weight of the polymer is about 1,000 to about 10,000 g/mol based on gel permeation chromatography and polystyrene standards.
  16. The flame retardant according to claim 15, wherein the polybromostyrene has a color value of less than 1, preferably less than 0.7, more preferably less than 0.6, when a 20 mg/mL solution of the flame retardant in toluene is measured in accordance with ASTM D1500-33mm.
  17. A flame retardant composition comprising the flame retardant according to claims 15 or 16 and an impact modifier, preferably selected from, chlorinated polyolefins, and rubber elastomers, such as Styrene-Ethylene-Butylene-Styrene (SEBS), ethylene propylene diene monomer (EPDM), styrene-butadiene-styrene (SBS), and poly(Styrene-block-lsoButylene-block-Styrene) (SIBS), and optionally, a compatibilizer, such as maleic anhydride grafted polyolefins.
  18. A flame retardant polymer composition comprising the flame retardant of claims 15 or 16 or the flame retardant composition of claim 17 and a thermoplastic polymer.
  19. A process for preparing polydibromostyrene having a molecular weight below 10,000, comprising the steps of heating a first hydrocarbon soluble initiator, preferably 2,2'-azobis(2,4-dimethylvaleronitrile), a thiol compound, preferably dodecylmercaptan, and a liquid bromostyrene monomer comprising a mixture of mono-, di-, and tribromostyrene monomers in a prepolymerizer at about 150 to about 180 °C to form a monomer mixture; feeding the heated monomer mixture into an extruder; adding a second hydrocarbon soluble initiator, preferably cumyl hydroperoxide, into the extruder; and extruding pellets of polybromostyrene, wherein the first hydrocarbon soluble initiator is charged as about 0.05 to about 5.0 wt%, preferably about 0.25 to about 2.5 wt%, more preferably about 0.5 to about 1.0 wt%, based on the weight of the bromostyrene monomer, wherein the thiol compound is charged as about 0.05 to about 5.0 wt%, preferably about 0.5 to about 3.0 wt%, more preferably about 1.0 to about 2.0 wt%, based on weight of the of bromostyrene monomer, wherein the bromostyrene monomer comprises about 50 to about 70 wt% bromine, preferably about 55 to about 65 wt% bromine, more preferably about 60 to about 64 wt% bromine, and wherein the second hydrocarbon soluble initiator is charged as about 0.1 to about 2.5 wt%, preferably about 0.2 to about 1.5 wt%, more preferably about 0.3 to about 1.0 wt%, based on the weight of the bromostyrene monomer.
  20. The process according to claim 19, wherein the extruder is a twin screw extruder, and feed rate into the extruder is about 900 Ib/h (6804 g/min).

Description

FIELD OF THE INVENTION The present invention relates generally to polymers of brominated styrene, and more particularly to methods for polymerization of brominated styrenes, as well as their application as a flame retardant. BACKGROUND OF THE INVENTION Brominated polystyrene has been identified by the US Environmental Protection Agency (EPA) as a potential alternative to decabromodiphenyl ethane (DBDPE) and decabromodiphenyl ether (DecaBDE) flame retardants used in a variety of applications, including textiles, plastics, wiring insulation, and building and construction materials. Low molecular weight versions of brominated polystyrenes are desirable for their high bromine content relative to size, better integration into polymers, improved processing properties and compatibility with other additives. Additionally, they exhibit reduced blooming, low volatility, and cost efficiency. Polymers of brominated styrene are produced by one of two basic methods--the bromination of polystyrene or the polymerization of bromostyrene monomers. In general, the materials made by the two production methods are not equivalent. For example, bromination of polystyrene will result in undesirable side chain halogenation, causing a reduction in thermal stability or requiring expensive treatment to remove the more labile bromine atoms. Polymers prepared by the polymerization of bromostyrene do not have undesirable side chain halogenation and are preferred for their relatively greater thermal stability. Not only do the two methods of preparing brominated polystyrenes provide different end products, but there are also numerous disadvantages inherent to the bromination of polystyrene approach. First, such methods require that the polymer be solubilized, necessitating isolation and purification procedures that may add significantly to production costs. Also, because the product is recovered from solution, the final product will be a dusty powder unless some type of compaction step is included at additional cost. Similarly, unless a post-production compounding step is used, the introduction of co-additives is limited to dry blending with other powders. US 2007/0004870 A1 discloses bromination of polystyrene (prepared by anionic polymerization), having a weight-average molecular weight of 8,000-50,000, where bromine (Br2) was used as a brominating agent and AIX3 (where X is Cl or Br) was used as Lewis acid catalyst to increase the rate of reaction, giving brominated polystyrene with 66-72 wt% bromine content. Low orthobromine substitution leads to higher melt flow and lower color compared to previous examples of brominated polystyrene. Bromination reactions were carried out in bromochloromethane. However, thermally labile bromines in the aliphatic chain cause HBr to release at high temperatures and discoloration occurs, which must be treated post-reaction. Additionally, bromochloromethane is a halogenated solvent that may be considered hazardous waste and a regular expense if not recycled. Likewise, US 2010/0087620 A1 discloses bromination of polystyrene with Br2 and AIX3. The brominated polystyrene has a weight-average molecular weight of 2,000-30,000 and is brominated to 60-71 wt% with methylene chloride solvent. Reaction workup includes washes to remove bromides and quench residual acid. Methylene chloride is banned by the EPA and washes decrease productivity and incur cost. This process also produces thermally labile bromines in the aliphatic chain that cause HBr to release at high temperatures and results in discoloration, which must be treated post-reaction. US 8,802,787B2 and WO 2010/065462 also describes an approach to manufacture low molecular weight polystyrene through an anionic polymerization technique. Tetramethylethylene diamine-stabilized alkyl lithium initiates the polymerization of styrene (through the intermediacy of a benzyl anion) under inert atmosphere and rigorously dried solvents. The final product must be treated with aqueous sodium hydroxide to quench residual hydrobromic acid and sodium borohydride to reduce brominated amines and thermally labile bromines on the polymer alkyl backbone caused by the bromination reaction. The washes decrease productivity and incur cost. In addition to the issues with thermally labile bromines in the aliphatic chain and hazardous waste from the bromochloromethane solvent, alkyl lithium reagents are pyrophoric and require rigorous drying of reaction solvents, adding to cost. US20230272185A1 discloses a very low molecular weight brominated polystyrene produced by anionic polymerization of styrene, followed by bromination of such polystyrene, and used as flame retardant alternative to DBDPE in polyolefins. The process creates thermally labile bromine in the polymer product and a glow suppressant is necessary in filled polyolefin to mitigate afterglow issue during UL 94 flame test. The polymerization of bromostyrene has several advantages over the bromination of polystyrene. As mentio