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Keywords:

  • bimodal;
  • catalyst mixture;
  • copolymerization;
  • dual-site;
  • metallocene catalysts

Abstract

Dual-site ethene/1-hexene copolymerizations with MAO-activated (1,2,4-Me3Cp)2ZrCl2 and (Me5Cp)2ZrCl2 catalysts were performed. Copolymers with narrow molecular weight distributions and bimodal short chain branching distributions could be produced. The combined catalyst system demonstrates a number of discrepancies from an expected average behavior of the individual sites. Dual-site (1,2,4-Me3Cp)2ZrCl2/(Me5Cp)2ZrCl2 systems produce copolymers with lower incorporation than expected. Clear evidences for relative activity enhancement of the (Me5Cp)2ZrCl2 catalyst in the mixture were observed in melting endotherms and Crystaf profiles. Molecular weights obtained by the mixture were higher than for any of the individual catalysts. A similar effect is observed for a dual-site system of the (1,2,4-Me3Cp)2ZrCl2 catalyst together with the Me4Si2(Me4Cp)2ZrCl2 catalyst as an alternative to (Me5Cp)2ZrCl2.