Divinylbenzene cross-linked polystyrene bound neodymium and cerium catalysts that polymerize butadiene stereospecifically to form cis-1, 4-polybutadiene in the presence of organoaluminum reagents are described. These immobilized catalysts can be recycled without significant loss of activity or selectivity. Neodymium chloride was also attached to carboxylated polyethylene to form a polyethylene-bound neodymium carboxylate that formed a homogeneous diene polymerization catalyst in solutions of aromatic solvents in the presence of triethylaluminum and ethylaluminum dichloride. Polybutadiene was successfully separated from the precipitated polyethylene-bound catalyst at room temperature after dilution of the reaction mixture with additional solvent but the activity of these polyethylene-entrapped catalysts was not significantly better than the activity of the polystyrene-bound catalysts. 1985, American Chemical Society. All rights reserved.