Method for preparing asymmetric radial copolymers having two first arms and two second arms

Abstract

A method for preparing asymmetric radial polymers wherein the different polymeric arms are contacted sequentially with a coupling agent. The method narrows the relative arm distribution of the several asymmetric radial polymers produced and significantly increases the amount of total product having the desired ratio of polymeric arms. Any coupling agent known in the prior art to be useful in the production of asymmetric radial polymers may be used in the method of this invention but coupling agents having from three to about twelve functional groups are most effective.

Having thus described and illustrated the invention; what is claimed is: 
     
       1. A method for preparing an asymmetric radial polymer comprising the steps of: p1 (a) contacting a first conjugated diene polymer having a single reactive end group per molecule with a coupling agent containing four functional groups which will react with the reactive end group such that said first conjugated diene polymer reacts with two of the functional groups on each molecule of the coupling agent; (b) contacting a second conjugated diene polymer having a single reactive end group per molecule with the reaction product from step (a) under conditions such that reaction between said second polymer and the reaction product from step (a) proceeds substantially to completion; and   (c) recovering an asymmetric radial polymer having four-arm radial polymer molecules having a ratio of two polymeric arms from the first conjugated diene polymer to two polymeric arms from the second conjugated diene polymer.   
     
     
       2. The method of claim 1 wherein the coupling agent comprises four halogen functional groups. 
     
     
       3. The method of claim 2 wherein the first conjugated diene polymer comprises living isoprene homopolymer and the second conjugated diene polymer comprises living polystyrene-polyisoprene or living polystyrene-polybutadiene diblock copolymers. 
     
     
       4. The method of claim 3 wherein said coupling agent contains four chlorine functional groups. 
     
     
       5. The method of claim 4 wherein said coupling agent is silicon tetrachloride. 
     
     
       6. The method of claim 5 wherein the living isoprene homopolymers have weight average molecular weights from 1,000 to 150,000, the living block copolymers have weight average molecular weights from 1,000 to 150,000. 
     
     
       7. An asymmetric radial polymer prepared with a method comprising the steps of: (a) contacting a first conjugated diene polymer having a single reactive end group per molecule with a coupling agent containing four functional groups which will react with the reactive end group such that said first conjugated diene polymer reacts with two of the functional groups on each molecule of the coupling agent;   (b) contacting a second conjugated diene polymer having a single reactive end group per molecule with the reaction product from step (a) under conditions such that reaction between said second polymer and the reaction product from step (a) proceeds substantially to completion; and   (c) recovering an asymmetric radial polymer having four-arm radial polymer molecules having a ratio of two polymeric arms from the first conjugated diene polymer to two polymeric arms from the second conjugated diene polymer.   
     
     
       8. The asymmetric radial polymer of claim 7 wherein the coupling agent comprises four halogen functional groups. 
     
     
       9. The asymmetric radial polymer of claim 8 wherein the first conjugated diene polymer comprises living isoprene homopolymer and the second conjugated diene polymer comprises living polystyrene-polyisoprene or living polystyrene-polybutadiene diblock copolymers. 
     
     
       10. The asymmetric radial polymer of claim 9 wherein said coupling agent contains four chlorine functional groups. 
     
     
       11. The asymmetric radial polymer of claim 10 wherein said coupling agent is silicon tetrachloride. 
     
     
       12. The asymmetric radial polymer of claim 11 wherein the living isoprene homopolymers have weight average molecular weights from 1,000 to 150,000, the living block copolymers have weight average molecular weights from 1,000 to 150,000.