Synthesis of narrow-distribution polycyclopentene using a ruthenium ring-opening metathesis initiator

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 ≈ 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.