The number of active centers and propagation rate constant in ethylene polymerization with a homogeneous catalyst based on cobalt 2,6-bis[imino]pyridyl complex with methylaluminoxane activator

The number of active centers C _p and propagation rate constant k _p upon ethylene polymerization with a homogeneous catalyst based on a cobalt complex with bisimino]pyridyl ligands (LCoCl₂, where L is 2,6-(2,6-(Me)₂C₆H₃N=CMe)₂C₅H₃N) using methylaluminoxane as an activator was determined by quenching by radioactive carbon monoxide (¹⁴CO). It was found that the drop in activity during polymerization on the above catalyst is due to the decreasing number of active centers (from 0.23 to 0.14 mol/mol Co within 15 min of polymerization); the propagation rate constant remained unchanged, 3.5 × 10³ l/(mol s) at 35°C, which is substantially lower than for a catalyst based on an iron complex with analogous bisimino]pyridyl ligands. It follows from the data on molecular mass characteristics of the produced polymer that the homogeneous catalyst LCoCl₂/methylaluminoxane is of monocenter type, and the obtained value of the propagation rate constant reflects the true reactivity of its active centers.