Effect of methylaluminoxane/transition-metal ratio on the physical properties and chemical composition distributions 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 the impregnation of TiCl 4 and rac-Et(Ind) 2ZrCl 2. The prepared rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO(methylaluminoxane)/SMB catalyst was applied to the ethylene–hexene copolymerization under the conditions of variable Al(MAO)/Zr ratio and fixed Al(TEA, triethylaluminum)/Ti ratio. The effect of Al(MAO)/Zr ratio on the physical properties and chemical composition distributions of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst was investigated. The catalytic activity of rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB was steadily increased with increasing Al(MAO)/Zr ratio from 200 to 500. The ethylene–hexene copolymer produced with Al(MAO)/Zr = 300, 400, and 500 showed two melting points at around 110 °C and 130 °C, while that produced with Al(MAO)/Zr = 200 showed one melting point at 136 °C. The number of chemical composition distribution (CCD) peaks was increased from 4 to 7 and the short chain branches of ethylene–hexene copolymer were distributed over lower temperature region with increasing Al(MAO)/Zr ratio. The lamellas in the copolymer were distributed over lower temperature region and the small lamellas in the copolymer were increased with increasing Al(MAO)/Zr ratio. The rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst preferably produced a ethylene–hexene copolymer with non-blocky sequence ([EHE]) with increasing Al(MAO)/Zr ratio.