Comparison of zirconocene and hafnocene catalysts for the polymerization of ethylene and 1‐butene

Abstract

In polymerizations with ethylene and copolymerizations with ethylene and 1-butene the catalyst system rac-ethylene(bisindeny1)zirconium dichloride (ra~-Et(Ind)~ZrCI~/methylaluminoxane (MAO) shows lower activities than the analogous Hafnium catalyst. The polymers obtained with the hafnium-catalyst have average molar masses up to ten times higher than those synthesized with the zirconium compound. It is remarkable that rac-Et(Ind),HfCI, is much more able to incorporate the comonomer. This is expressed by the copolymerization parameters. At a polymerization temperature of + 30"C, e. g., the r,-parameter of the hafnium-catalyst is 5,4, the corresponding parameter of the zirconium catalyst is 19,4. Polymerizations with a catalyst mixture ruc-Et(Ind),(Hf, Zr)CI, (containing 95% rac-Et(Ind),HfCI, and 5% rac-Et(Ind),ZrCI,) show that each catalyst compound produces its own polymer independently.

A critical examination of polyethylene molecular weight distribution control through the combination of soluble metallocene/methylalumoxane catalysts

“…The catalysts available should be evaluated for their molecular weight behaviour at the proposed polymerization conditions. Once the MWDs for individual catalysts versus (w j (M i ) M i ) are available, these data can be fed into eqn (1). Using an ordinary spreadsheet, the values of can easily be m j manipulated to change the global MWD versus (W (M i ) control over which is ultimately desired.…”

Effects of propylene prepolymerization on ethylene/1‐hexene and ethylene/1‐octene copolymerization with an immobilized metallocene catalyst

“…In the case of ethylene homopolymerization, the lower molecular weight obtained with the prepolymerized catalyst could also arise from the presence of some unreacted propylene from the prepolymerization stage, taking into account the effect of a-olefin comonomers on chain transfer in ethylene polymerization. 19,20 DSC thermograms of the ethylene/1-hexene copolymers prepared without and with prepolymerization are shown in Figure 2. In each case, two distinct melting peaks are apparent, which could be indicative of the presence of polymer fractions differing in the comonomer content.…”

Copolymerization of ethylene and ?-olefins with combined metallocene catalysts. I. A formal criterion for molecular weight bimodality

“…Use of two or more types of metallocene catalysts during polymerization. [11][12][13][14][15] These resins are commonly called reactor blends because they are mixtures, at the molecular level, of polymer chains of different average properties. Dual reactor cascades are used with heterogeneous Ziegler-Natta and single-site-type catalysts for the commercial production of impact copolymers and a variety of reactor blends.…”