Copolymerization of ethylene with 1-hexene over highly active supported Ziegler–Natta catalysts with vanadium active component but different vanadium contents

Abstract

The kinetics of copolymerization of ethylene with 1-hexene over highly active V-Mg Ziegler–Natta catalysts [VMC: VCl₄/MgCl₂ + Al (i-Bu)₃] at different contents of vanadium (4 and 0.1 wt% of V) was studied. Data on copolymerization ability of these catalysts, molecular weight characteristics, and compositional homogeneity of the produced copolymers were attained. It was found that the introduction of 1-hexene led to broadening of the molecular weight distribution of copolymer (an increase in the M_w/M_n value) relative to homopolyethylene due to a decrease in the molecular weight (M_n) in the region of 1–100 kg mol⁻¹ without changes in the molecular weight in the region of M_n > 500 kg mol⁻¹ for two used VMCs catalysts. This result testified to non-uniformity of the active centers of these catalysts in the chain transfer reaction with participation of 1-hexene. Therefore, the active centers of VMCs producing high-molecular polyethylene were virtually not involved in the chain transfer reaction with 1-hexene. At the same time, these centers were more reactive in the incorporation of 1-hexene. This led to unusual distribution of butyl branches in ethylene–1-hexene copolymers produced over VMCs, namely, to an increased content of butyl branches in the high-molecular fraction of copolymers (M_w > 1000 kg mol⁻¹).

Graphical Abstract