Control of molecular weight and molecular weight distribution in ethylene polymerization with metallocene catalysts

Abstract

SUMMARY:The molecular weight (MW) and the molecular weight distribution (MWD) of polyethylene (PE) prepared with various metallocene catalysts were investigated. The weight-average molecular weight (MW) of PE prepared with dicyclopentadienyltitanium dichloride/ aluminoxane (Cp,TiCl,/MAO) was about 4,O. lo', while that of PE obtained withPE of bimodal MWD was obtained with the mixed catalyst Cp,TiCl,/Cp,ZrCl,. Narrow MWD PE was obtained with the mixed catalyst Cp2ZrC1,/Et(ind),ZrC1,, because each catalyst produced an M, of 1,0 * lo5. However, the change of temperature during the polymerization with the mixture Cp,ZrC1,/Et(ind)2ZrClz produced PE with a bimodal MWD and a value of the ratio of weight-to number-average molecular weights of a w / M n = 4.

Effect of hydrogen on ethylene polymerization using in-situ supported metallocene catalysts

“…These intermediate hydride complexes can be reactivated for propagation by insertion of a monomer unit. Hydrogen may coordinate to the metal atom and make more metal hydride complexes resulting in a lower propagation rate 14) . In addition, hydrogen can cause reduction of ethylene concentration around active sites because of its characteristics (hydrogenation of olefinic monomer).…”

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

“…Controlling the (m j ) overall MWD is then merely a matter of controlling the values for a particular polymerization. This is m j done using eqn (2) …”

“…These include the work of Heiland and Kaminsky,1 Han et al 2 and Lee et al 3 There is also great interest in supporting metallocene catalysts, and many patents and articles have been published which describe the combination of multiple catalyst types on supports.4h7…”

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.…”