Polycyclopentene was synthesized by ring-opening metathesis polymerization (ROMP) at room temperature, using a ruthenium-based initiator in the presence of tricyclohexylphosphine, which acts as a polymerization regulator by shifting the metal-ligand binding equilibrium. A kinetic model was developed for the monomer conversion and polymer molecular weight as a function of time, monomer concentration, and monomer-to-initiator and phosphine-to-initiator ratios, and was fit to experimental data to extract a single rate parameter. By eliminating impurities which act as chain-transfer agents, and optimizing reaction conditions to minimize secondary metathesis, polycyclopentenes of controllable molecular weight (M-n = 6-40 kg/mol) and narrow distributions (PDI approximate to 1.15) can be routinely obtained, which could be hydrogenated to perfectly linear polyethylenes. This work extends existing ROMP methods for the synthesis of precursors to narrow-distribution polyethylene, which have employed tungsten or molybdenum catalysts, to a commercially available, robust ruthenium initiator. (C) 2008 Elsevier Ltd. All rights reserved.