Process for brominating butadiene polymers using ester solvent mixtures
View Patent ↗Butadiene copolymers are brominated using certain quaternary ammonium or phosphonium tribromides as the brominating agent. The bromination is performed in solution in a mixture of n-butyl acetate and ethyl acetate. The bromination process proceeds easily under mild conditions, and produces a brominated product that has excellent thermal stability.
1. A process comprising brominating a butadiene polymer by contacting the butadiene polymer with a solution of a tribromide brominating agent selected from the group consisting of phenyltrialkylammonium tribromide, benzyltrialkylammonium tribromide, tetraalkylammonium tribromide and quaternary phosphonium tribromide, where the solution further comprises an n-butyl acetate/ethyl acetate solvent mixture, under conditions sufficient to brominate at least 85 percent of non-aromatic carbon-carbon double bonds in the butadiene polymer.
2. The process of claim 1 wherein the tribromide brominating agent is phenyltrimethylammonium tribromide, benzyltrimethylammonium tribromide, tetraethylammonium tribromide, tetrapropylammonium tribromide, tetra-n-butylammonium tribromide or a mixture of two or more thereof.
3. The process of claim 1 wherein the tribromide brominating agent is tetramethylphosphonium tribromide, tetraethylphosphonium tribromide, tetra(n-propyl)phosphonium tribromide, tetra(n-butyl)phosphonium tribromide, tetrahexylphosphonium tribromide, tetraoctylphosphonium tribromide, trihexyltetradecylphosphonium tribromide, and the like, or a mixture of two or more thereof.
4. The process of claim 3 wherein the brominated butadiene polymer is recovered by adding an antisolvent to the reaction mixture or a portion thereof to precipitate the brominated butadiene polymer from the solvent mixture.
5. The process of claim 3 wherein
a. contacting the starting butadiene polymer with a solution of the quaternary ammonium or phosphonium tribromide in the n-butyl acetate/ethyl acetate solvent mixture under conditions such that the starting butadiene polymer and the quaternary ammonium tribromide react to produce a brominated butadiene polymer and a quaternary ammonium or phosphonium monobromide byproduct, and a solution or slurry of the brominated butadiene polymer in the solvent mixture is formed in the reaction,
b. continuously or semi-continuously contacting the solution or slurry of the brominated butadiene polymer with an aqueous phase to form an aqueous quaternary ammonium or phosphonium monobromide solution or slurry and a washed solution or slurry of the brominated butadiene polymer, and
c. continuously or semi-continuously contacting the aqueous quaternary ammonium or phosphonium monobromide solution or slurry obtained in step b with elemental bromine and a mixture of n-butyl acetate and ethyl acetate to form an aqueous raffinate stream and a solution of the quaternary ammonium or phosphonium tribromide in the mixture of n-butyl acetate and ethyl acetate, and
d. recycling the quaternary ammonium or phosphonium tribromide solution obtained in step c into step a.