Solution diene elastomers by alkyl lithium catalysis

A process for preparing conjugated diene copolymers which comprises contacting a monomeric mixture of a conjugated diene hydrocarbon and from about 5 to about 50 parts by weight, based on 100 parts by weight of total monomers, of a vinyl-substituted aromatic hydrocarbon in which the vinyl group is attached to a nuclear carbon atom with a catalyst consisting essentially of (a) a complex having the formula

• R'.sub.y - Ar - OK .sup.. HOR"
• wherein R' is an alkyl group containing a minimum of 8 carbon atoms per group and a maximum of 26 carbon atoms in one or more such groups, R" is selected from the group consisting of hydrogen and aliphatic, cycloaliphatic and aromatic hydrocarbon radicals, Ar is an arylene radical containing one aromatic ring, and y is an integer from 1 to 3, inclusive, and from about 0.1 to about 20 millimoles, per 100 grams of said monomeric mixture, of (b) an organolithium compound having the formula R Li wherein R is a hydrocarbon radical selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, said contacting occurring in the presence of a solvent which is liquid at the polymerization temperature and is selected from the group consisting of saturated aliphatic hydrocarbons and aromatic hydrocarbons which do not contain benzylic hydrogen atoms, the Li/K molar ratio of the cocatalyst being from about 4/1 to about 25/1 when an aliphatic hydrocarbon solvent is used and from about 20/1 to 90/1 when an aromatic hydrocarbon solvent is used.