Elastomers having reduced hysteresis prepared with vinyl polycyclic aromatic hydrocarbon

An endcapped polymer comprising:

• (a) a polymeric backbone, said backbone being a polymer of one or more conjugated dienes having from 4 to about 12 carbon atoms or a copolymer of one or more conjugated dienes having from 4 to about 12 carbon atoms within one or more monovinyl aromatic monomers having from 8 to about 18 carbon atoms;
• (b) at least one short chain polymeric end block, said end block being a short chain polymer of a vinyl substituted bicyclic or tricyclic aromatic hydrocarbon having an average chain length of about 2.2 to about 15 monomer units.

A process for preparing an endcapped polymer which comprises reacting a living polymer having at least one functional site with about 2.2 to about 15 equivalents of an endcapping agent, said endcapping agent being a vinyl substituted bicyclic or tricyclic aromatic hydrocarbon,

• wherein said living polymer is formed by polymerization of a monomer or mixture thereof in solution in the presence of a polymerization initiator, said monomer or mixture thereof being selected from the group consisting of conjugated dienes having 4 to about 12 carbon atoms and mixtures of one or more said conjugated dienes with one or more monovinyl aromatic monomers having from 8 to about 18 carbon atoms.