Process for preparing substantially gel-free cis-1,4-polybutadiene

An improved process for the production of substantially gel-free cis-1,4-polybutadiene in the presence of a catalyst comprising a mixture of cobalt octoate or cobalt stearate and at least one aluminum compound selected from the group consisting of trialkyl aluminum, dialkyl aluminum chloride, alkyl aluminum dichloride and aluminum chloride or a mixture thereof, wherein said alkyls having 1 to 4 carbon atoms, the improvement comprising

• (a) adding to the polymerization vessel butadiene, water, and a solution of the cobalt catalyst and then adding a solvent in which butadiene monomer and polymer are substantially soluble, provided that if the solvent is an aromatic or a chlorinated solvent at most 15 percent by weight based on the weight of total charge is added at this stage;
• (b) after the mixture has become substantially homogeneous, adding the entire amount of an aromatic or a chlorinated solvent, or the balance of such a solvent if part thereof was added earlier;
• (c) thereafter adding at least one aluminum compound, said compound having a chlorine to aluminum ratio of between 0.7:1 and 1.6:1;
• said polymerization system containing an aluminum to cobalt ratio between 40:1 and 300:1 and a water to aluminum ratio between 0.1:1 and 0.6:1;
• and finally
• (d) polymerizing said butadiene-1,3 to a conversion of 30 to 90 percent producing gel-free cis-polybutadiene.