CrV Bimetallic Phillips Catalyst Prepared by Citric Acid-Assisted Impregnation on Ethylene Polymerization

Three CrV bimetallic Phillips catalysts are developed by a citric acid-assisted impregnation method and studied in ethylene homopolymerization and ethylene/1-hexene copolymerization. The method benefits to the dispersion of bimetallic active sites, especially for the V ones. The electron binding energy shift of V 2p(3/2) in CrV-1/2-CA suggests the increased electron deficiency of V active center. The CrV-1/2-CA, CrV-1/3-CA catalysts present higher activity, broader molecular weight distribution, than the counterparts without CA-assisted impregnation, suggesting more active sites involved in the reaction. The 1-hexene is higher inserted in the polyethylene by CrV-1/2 than the CrV-1/2-CA. But the results of temperature rising elution fractionation-successive self-nucleation and annealing (TREF-SSA) show the thinner platelet thickness at the high molecular weight parts of high-density polyethylene by CrV-1/2-CA, suggesting the higher insertion of 1-hexene and higher tensile properties. The CrV-1/2-CA also shows the more hydrogen-regulated response in the polymerization. The deconvolution of the gel permeation chromatography curves presents the higher fractions of high molecular weight polymer component.