A new high-performance Ziegler–Natta catalyst with vanadium active component supported on highly-dispersed MgCl2 for producing polyethylene with broad/bimodal molecular weight distribution

Abstract

In this paper, we synthesized a highly-dispersed MgCl₂ support using the Grignard reagent method, and loaded it with TiCl₄ and VCl₄ to prepare polyethylene catalysts with titanium and vanadium active centers. The two catalysts demonstrated narrow particle distribution. The polymerization data demonstrated that the two catalysts both had good activity. And GPC and ¹³C NMR data indicated that polymer produced with vanadium active centers has some good characteristics, a broader molecular weight distribution and higher degree of methyl branching compared with polymer produced by catalysts with titanium active centers. Also, we found that the molecular weight distribution can be controlled by changing the hydrogen pressure in polymerization; because of the dual active sites have different responses to hydrogen pressure. Also, through ¹³C NMR data, we found that most of the methyl branching occurred in the high molecular weight part. The existence of methyl branching in the high molecular weight part and broader molecular weight distribution of polyethylene can solve the contradiction of mechanical properties and processing properties.