A process for preparing a polydiene, the process comprising the step of polymerizing conjugated diene monomer in the presence of a dihydrocarbyl ether, where said step of polymerizing takes place within a polymerization mixture that includes less than 20% by weight of organic solvent based on the total weight of the polymerization mixture, and where said step of polymerizing employs a lanthanide-based catalyst system that includes the combination of or reaction product of ingredients including (a) a lanthanide compound, (b) an aluminoxane, (c) an organoaluminum compound other than an aluminoxane, and (d) a bromine-containing compound selected from the group consisting of elemental bromine, bromine-containing mixed halogens, and organic bromides.