Method of producing essentially cis rubbery polyisoprene

Isoprene is polymerized to an essentially cis1,4-polyisoprene in the presence of metallic lithium and a saturated hydrocarbon solvent liquid under reaction conditions and in the substantial absence of oxygen and oxygen-containing compounds. The hydrocarbon diluent may be petroleum ether, or aliphatic and cycloaliphatic hydrocarbon solvents such as propane, n-butane, n-pentane, n-heptane and other normal and branched chain liquid hydrocarbons up to dodecane, cyclopentane and cyclohexane. Low molecular weight solvents are preferred in an amount of at least 50% by weight of the total reactant charge. The process is otherwise similar to that of Specification 814,676, examples being given to illustrate the advantages in polymer properties gained by the use of the diluent.