Patent ID: 7884155

Claim:
A process for producing a vinyl-cis-polybutadiene rubber, which comprises mixing (A) and (B), wherein (A) comprises a vinyl-cis-polybutadiene solution where a proportion (HI) of a boiling n-hexane insoluble matter of the vinyl-cis-polybutadiene is from 30 to 60% by weight, the vinyl-cis-polybutadiene being obtained by (1) a step of adding a cis-1,4-polymerization catalyst, comprising a first organoaluminum compound and a soluble cobalt compound, to a mixture containing 1,3-butadiene and a cyclohexane solvent as major components, where a water content is adjusted to a range of 0.1 to 1.0 moles of water per mole of the first organoaluminum compound, thereby subjecting the 1,3-butadiene to cis-1,4-polymerization to obtain a resulting polymerization reaction mixture, and (2) a step of exposing a second catalyst to the resulting polymerization reaction mixture, thereby subjecting 1,3-butadiene to 1,2-polymerization, wherein the second catalyst comprises a soluble cobalt compound, a second organoaluminum compound represented by the general formula AlR 3 , and carbon disulfide, and wherein R represents an alkyl group having from 1 to 6 carbon atoms, a phenyl group, or a cycloalkyl group, and wherein (B) comprises a cis-polybutadiene solution obtained by a step of adding said cis-1,4-polymerization catalyst to 1,3-butadiene to subject the 1,3-butadiene to cis-1,4-polymerization.