Functionalized star polymers

Abstract

Block polymers of the star type contain a central core of crosslinked bisunsaturated compound and a plurality of functionalized branches attached to the core, each branch containing at least a terminal portion of polymerized alkyl methacrylate, polymerized through the ethylenic unsaturation of the methacrylate moiety. The polymers are useful in adhesive formulations and as viscosity index improvers for hydrocarbon fluids.

What is claimed is: 
     
       1. A block polymer of the star type having a central core of crosslinked di(alkenyl) aromatic hydrocarbon and a plurality of functionalized branches wherein at least the terminal portion is polymerized alkyl methacrylate polymerized through the ethylenic unsaturation of the methacrylate moiety, the polymer having the formula ##STR2## wherein C is the core of crosslinked di(alkenyl) aromatic hydrocarbon, A independently is a block of polymerized anionically polymerizable monomer, M is a block of the polymeized alkyl methacrylate, r is 0 or 1, s is an average number from about 3 to about 50, and t is a number up to about 50 which is equal to or greater than s. 
     
     
       2. The polymer of claim 1 wherein the alkyl of the alkyl methacrylate moieties independently has up to 30 carbon atoms. 
     
     
       3. The polymer of claim 2 wherein the anionically polymerizable monomer is styrene or isoprene. 
     
     
       4. The polymer of claim 3 wherein C is no more than 10% of the molecular weight of the polymer. 
     
     
       5. The polymer of claim 4 wherein, in the branches .paren open-st.A.paren close-st. r  M, the polymerized alkyl methacrylate is at least about 50% of the molecular weight of the branches. 
     
     
       6. The polymer of claim 5 wherein r is zero. 
     
     
       7. The polymer of claim 6 wherein the di(alkenyl) aromatic hydrocarbon is divinylbenzene. 
     
     
       8. The polymer of claim 7 wherein the alkyl methacrylate is branched-butyl methacrylate. 
     
     
       9. The polymer of claim 8 wherein the branched-butyl is t-butyl. 
     
     
       10. A process of producing a block polymer of the star type having functionalized branches which consists essentially of a) contacting an anionically polymerizable monomer with a metal hydrocarbon compound in liquid phase solution under polymerizable conditions to produce a polymeric anionically polymerizable monomer having an organometallic site as a polymerization initiator,   b) contacting the initiator with a di(alkyl) aromatic hydrocarbon under polymerization conditions to produce a central core of crosslinked di(alkenyl) aromatic hydrocarbon having a plurality of organometallic sites as a first block polymer intermediate,   c) optionally contacting the core of di(alkenyl) aromatic hydrocarbon with an anionically polymerizable monomer under polymerization conditions to produce a second block polymer intermediate of a core of crosslinked di(alkenyl) aromatic hydrocarbon and a plurality of branches of polymerized anionically polymerizable monomer having terminal organometallic sites,   d) contacting the first or second block polymer intermediate with an alkyl methacrylate under polymerization conditions, and   e) terminating the polymerization with an active hydrogen compound.   
     
     
       11. The process of claim 10 wherein the anionically polymerizable monomer is alkenyl aromatic compound or conjugated alkadiene. 
     
     
       12. The process of claim 11 wherein the di(alkenyl) aromatic hydrocarbon has up to 20 carbon atoms and up to 2 aromatic rings. 
     
     
       13. The process of claim 12 wherein the alkyl moiety of the alkyl methacrylate has up to 30 carbon atoms. 
     
     
       14. The process of claim 13 wherein the metal hydrocarbon compound is an alkali metal alkyl. 
     
     
       15. The process of claim 14 wherein the alkali metal alkyl is a lithium alkyl. 
     
     
       16. The process of claim 15 wherein the di(alkenyl) aromatic hydrocarbon compound is divinylbenzene. 
     
     
       17. The process of claim 16 wherein the anionically polymerizable monomer is styrene, isoprene, butadiene, or 4-vinylpyridine. 
     
     
       18. The process of claim 17 wherein the alkyl methacrylate is branched-butyl methacrylate. 
     
     
       19. The process of claim 18 wherein the anionically polymerizable monomer is isoprene. 
     
     
       20. The process of claim 19 wherien the branched-butyl methacrylate is t-butyl methacrylate.