Two-site silica supported Fe/Cr catalysts for tailoring bimodal polyethylenes with variable content of UHMWPE

• We immobilized two single-site catalysts producing bimodal PE-blends.
• The influence of the immobilization procedure was investigated.
• Sequential cosupporting was preferred with respect to the simultaneous procedure.
• The blend composition was also determined by the ratio of the so-supported catalysts.

A new family of silica supported two-site Fe/Cr catalysts were prepared by means of sequential and simultaneous immobilization (“cosupporting”) of both 2,6-bis-[1-(2,6-dimethylphenyliminio)ethyl]pyridine iron(II) chloride (Fe) and η5-[3,4,5-trimethyl-1-(8-quinolyl)-2-trimethyl-silylcyclopentadienyl]chromium(III) chloride (Cr) on MAO-pretreated silica. The influence of catalyst preparation, catalyst composition, and of Fe/Cr molar ratio on catalyst activity, polyethylene (PE) molecular weight (MW), and PE molecular weight distribution (MWD), as determined by high temperature size exclusion chromatography, was examined. Catalyst activity increased with decreasing transition metal content. The average molar masses of the two PE fractions, UHMWPE (3 × 106 g/mol), produced on Cr sites, and PE (3 × 105 g/mol), produced on Fe sites, are independent of the Fe/Cr molar ratio. The sequential immobilization of the Fe complex prior to the Cr complex affords the highest catalyst activities and highest UHMWPE contents. Here, the UHMWPE content consequently increases from 0 to 32 wt% with increasing Cr content at constant Fe concentration.

A new family of Fe/Cr-based supported dual-site catalysts were prepared by means of sequential and simultaneous immobilization (“cosupporting”) of two single-site catalysts on MAO pretreated silica. The influence of catalyst preparation, catalyst composition, and of Fe/Cr molar ratio on catalyst activity, polyethylene (PE) molecular weight (MW), and PE molecular weight distribution (MWD), as determined by high temperature size exclusion chromatography, was examined.Figure optionsDownload high-quality image (83 K)Download as PowerPoint slide