Two-step process for brominating butadiene copolymers
View Patent ↗Butadiene copolymers are brominated using certain quaternary ammonium tribromides as the brominating agent in a first step, and then with elemental bromine in a second bromination step. The bromination process proceeds easily under mild conditions, and produces a brominated product that has excellent thermal stability. The bromination proceeds to high conversions in shorter reaction times, when the bromination is performed using only the first bromination step.
1. A process comprising reacting in a first step a butadiene polymer containing unsaturated butadiene repeating units with a phenyltrialkylammonium tribromide, benzyltrialkylammonium tribromide or tetraalkylammonium tribromide in the presence of at least one solvent for the butadiene polymer, to form a partially brominated butadiene polymer in which from about 50 to about 96% of the butadiene repeating units are brominated, and then further reacting the partially brominated butadiene polymer in a second step with elemental bromine until greater than 96% of the butadiene repeating units have been brominated.
2. The process of claim 1 , wherein from 60 to 90% of the butadiene units of the butadiene polymer are brominated in the first step.
3. The process of claim 2 , wherein the phenyltrialkylammonium tribromide, benzyltrialkylammonium tribromide or tetraalkylammonium tribromide is phenyltrimethylammonium tribromide, benzyltrimethylammonium tribromide, tetramethylammonium tribromide, tetraethylammonium tribromide, tetrapropylammonium tribromide or tetra-n-butylammonium tribromide.
4. The process of claim 3 , wherein water is added into the first step after 50-70% of the butadiene units of the starting butadiene polymer are brominated.
5. The process of claim 4 , wherein an aliphatic alcohol is present in the second step.
6. The process of claim 5 , wherein the butadiene polymer is a homopolymer of butadiene or a copolymer of butadiene and a vinyl aromatic monomer.
7. The process of claim 6 , wherein the butadiene polymer is a block copolymer of styrene and butadiene.
8. The process of claim 7 , wherein the temperature during the first step is from 0 to 90° C.
9. The process of claim 8 wherein the temperature during the first step is from 40 to 80° C.
10. The process of claim 9 wherein the temperature during the second step is from 0 to 40° C.
11. The process of claim 10 wherein the second step is conducted in the presence of from 0.5 to 6 moles of an aliphatic alcohol per mole of elemental bromine, and further wherein the butadiene polymer remains in solution during said second step.