Method for producing brominated and halohydrated polymers
Conjugated diene polymers such as a styrene-butadiene copolymer are sequentially brominated by reaction with a quaternary ammonium tribromide or quaternary phosphonium tribromide and halohydrated by reaction with an N-haloimide compound. This produces a brominated and halohydrated polymer with very good thermal stability. The product is useful as a flame retardant in a variety of polymer systems.
1. A process for preparing a brominated and halohydrated polymer of at least one conjugated diene, comprising (a) reacting a starting polymer of at least one conjugated diene with a quaternary ammonium tribromide, quaternary phosphonium tribromide compound or both a quaternary ammonium tribromide and a quaternary phosphonium tribromide to brominate 50% to 98% of the conjugated diene repeating units in the starting polymer to form a partially brominated polymer and then (b) reacting the partially brominated polymer with an N-haloimide compound in the presence of water and a water-miscible solvent system for the partially brominated polymer to halohydrate at least a portion of the remaining conjugated diene repeating units and produce a brominated and halohydrated polymer.
2. The process of claim 1 wherein the N-haloimide is an N-halosuccinimide.
3. The process of claim 1 wherein the N-haloimide is an N-bromoimide.
4. The process of claim 1 wherein 65 to 95% of the conjugated diene units are brominated in step (a), 5 to 35% of the conjugated diene units are halohydrated in step (b), and 0 to 5% of the conjugated diene units are unreacted.
5. The process of claim 1 wherein 75 to 98% of the conjugated diene units are brominated in step (a), 2 to 25% of the conjugated diene units are halohydrated in step (b) and 0 to 5% of the conjugated diene units are unreacted.
6. The process of claim 1 , wherein in step (b) the concentration of the partially brominated polymer in the water-miscible solvent system is 2 to 25 weight percent based on the combined weight of partially brominated polymer and solvent system.
7. The process of claim 1 wherein in step (b), water is present in an amount from 0.25 to 1 parts by weight per part by weight of the solvent system.
8. The process of claim 1 wherein the starting polymer is a copolymer of styrene and butadiene having a weight average molecular weight of at least 20,000 by gel permeation chromatography against a polystyrene standard.
9. The process of claim 1 wherein the brominated and halohydrated polymer obtained from the process is a thermoplastic material that contains no more than 3 weight percent of gel material.
10. The process of claim 1 wherein the brominated and halohydrated is crosslinked in step (b) or in a subsequent step.
11. The process of claim 1 wherein the brominated and halohydrated polymer is formed into particles.