Effect of Fluoride‐Modification on the Phillips Cr/SiO2 Catalyst for Ethylene Polymerization

Abstract

AbstractIn this work, a fluoride‐modified Phillips catalyst was investigated by using combined experimental and computational methods. The addition of fluoride to the Phillips Cr/SiO2 catalyst can increase the activity of the catalyst calcined at a low temperature and the molecular weight of the polyethylene product. DFT calculations were performed to show that the difference of the Gibbs free energy barriers between chain transfer and chain propagation increased after the introduction of the fluoride onto the silica surface, which is in accordance with the increased molecular weight of the polyethylene produced by the fluoride‐modified Phillips Cr/F‐SiO2 catalyst. The computational results also reflect the increase of the activity of the ethylene/1‐hexene copolymerization after the introduction of fluoride, although the modification has little effect on the regioselectivity of the produced ethylene/1‐hexene copolymer. Moreover, copolymers produced by the fluoride‐modified Phillips catalyst with more short‐chain branches (SCBs) in the high‐molecular‐weight fraction and a significant enhancement of the environmental stress crack resistance can be explained from the results of the DFT calculations.