Chemical composition distributions and microstructures of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst

Abstract

A silica-magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for a metallocene/Ziegler–Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl 4 and rac-Et(Ind) 2ZrCl 2. The prepared rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst was applied to the ethylene–hexene copolymerization with variable amounts of 1-hexene used. The catalytic activity of rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB showed a volcano feature with respect to the amount of comonomer used. The melting point attributed to the Ziegler–Natta catalyst was not changed significantly, while that attributed to the metallocene catalyst was broadened and gradually shifted to the lower temperature with increasing 1-hexene content. The number of chemical composition distribution (CCD) peaks was increased and the short chain branches were distributed over the lower temperature region with increasing 1-hexene content. The majorities of lamella distributions whose content was more than 50 wt.% shifted to the smaller lamella size with increasing 1-hexene content. The average sequence length of ethylene was steadily decreased with increasing comonomer content, while that of 1-hexene was not changed significantly. Both blocky sequence ([EHH]) and non-blocky sequence ([EHE]) were increased with increasing comonomer content. However, the increasing rate of blocky sequence formation was much higher than that of non-blocky sequence.