Abstract: A process for polymerizing 1,3-butadiene into a low molecular weight high-cis polybutadiene is described using a catalyst system comprising: (a) a neodymium-containing compound, (b) an aluminoxane or a trialkyl aluminum compound, (c) an organoaluminum hydride, and (d) a halogen source. A blend of a high molecular weight high-cis polybutadiene and the low molecular weight high-cis polybutadiene is also disclosed for use in pneumatic tire treads. Desirably both the high and the low molecular weight polymers have high cis contents, with the low molecular weight polymer being at least 70 percent cis and the high molecular weight polymer being at least 92 percent cis. Desirably both polymers are made with a neodymium catalyst system. The blends provide a balance of properties including good snow traction, wet traction, and rolling resistance while providing a balance of good physical properties including tension at break, modulus etc.

Abstract: The present invention is directed to a process for the preparation of a gel-free hydrocarbon solution containing a lanthanide rare earth series compound by dissolving or synthesizing a lanthanide compound in an inert hydrocarbon solvent with a Lewis acid in an amount sufficient to prevent formation of highly viscous solutions. The present invention is also directed to the use of the gel-free Ln solutions formed by the recited process as co-catalysts for the polymerization of dienes. The Lewis acid is a group 2, 12, 13, 14 or 15 halide or organohalide, or a transition metal halide, excluding aluminum trialkyls.