We describe here a well-behaved initiator for ring-opening alkyne metathesis polymerization (ROAMP) of dibenzocyclooctynes. The reaction produces living polymers with low polydispersities and predictable molecular weights. We activate the well-known alkyne metathesis precatalyst, [(N(tBu)Ar)(3)Mo CCH2CH3], with phenolic ligands that have a-electron donating substituents. We show that the chelating ability of these ligands as well as the nature of the propagating molybdenum center have dramatic effects on the outcome of the polymerization reaction.