A Novel SiO₂‐Supported Cr–V Bimetallic Catalyst Making Polyethylene and Ethylene/1‐Hexene Copolymers with Bimodal Molecular Weight Distribution

Abstract

A novel SiO 2 ‐supported Cr–V bimetallic catalyst for ethylene and ethylene/α‐olefin polymerization is investigated. This catalyst is prepared using the residual surface hydroxyl groups in a SiO 2 ‐supported vanadium catalyst to support bis(triphenysilyl) chromate (BC) in order to get the merits from both the vanadium‐based catalyst and the S‐2 catalyst. By investigation of the polymerization behavior and the microstructures of their polymers, several vital factors, such as the addition amount of vanadium species and the dosage of 1‐hexene, on the ethylene/1‐hexene copolymerization are systematically investigated. The results show that the activity of each bimetallic catalyst is higher than that of the S‐2 catalyst, and the product from the bimetallic catalyst shows a higher molecular weight (MW) with a bimodal molecular weight distribution (MWD). The copolymers obtained using the bimetallic catalyst also show a better short‐chain branch distribution (SCBD) than that using the S‐2 catalyst through a temperature rising elution fractionation (TREF) cross successive self‐nucleation and annealing (SSA) characterization. image