Kinetic Peculiarities of Ethylene Polymerization over Homogeneous Bis(imino)pyridine Fe(II) Catalysts with Different Activators

Abstract

AbstractSummary: Method of polymerization inhibition by radioactive carbon monoxide (14CO) has been used to determine the number of active centers (CP) and propagation rate constant (kP) for ethylene polymerization with homogeneous complex 2,6‐(2,6‐(Me)2C6H3NCMe)2C5H3NFeCl2 (LFeCl2), activated with methylalumoxane (MAO) or Al(i‐Bu)3. With both activators the rate profile of polymerization was unstable: high activity [0.8 × 103–1.5 × 103 kg PE per (molFe · h · atm) at 35 °C] of the initial period sharply decreases (sevenfold in 10 min). In the beginning of polymerization with the catalysts LFeCl2/MAO and LFeCl2/Al(i‐Bu)3, the CP values were found to be 8 and 41% of total Fe‐complex content in catalysts, respectively, and decreased 1.5–2‐fold in 9 min. As polymerization proceeds, the kP value for LFeCl2/MAO system decreases from 5 × 104 to 1.5 × 104 L · (mol · s)−1 LFeCl2/MAO, and for LFeCl2/Al(i‐Bu)3 system from 2.6 × 104 to 0.82 × 104 L · (mol · s)−1. Data on the effect of polymerization time on polyethylene molar mass distribution are presented. Basing on the obtained results it was suggested that highly reactive, but unstable centers, dominating at short polymerization times, produce low‐molar‐mass polyethylene, while polyethylene with higher molar mass is produced by less active (low kP) and more stable centers.Data showing change in molar mass distribution of polyethylene with polymerization time.magnified imageData showing change in molar mass distribution of polyethylene with polymerization time.