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

Abstract

The number of active centers Cp and propagation rate constant kp upon ethylene polymerization with a homogeneous catalyst based on a cobalt complex with bis[imino]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 bis[imino]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.