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 2p3/2 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. CA‐assisted CrV Phillips catalyst prepared in the presence of citric acid benefits the dispersion of bimetallic active sites. For the ethylene/1‐hexene copolymerization, the CrV‐1/2‐CA catalysts presents higher activity and broader molecular weight distribution than the counterpart without CA‐assisted impregnation, suggesting more active sites involved in the reaction.