Ethene polymerization with bis(2-dimethylsilyl-indenyl)zirconium(IV) dichloride (
1)/MAO and bis(2-trimethylsilyl-indenyl)zirconium(IV) dichloride (
2)/MAO and ethene-
co-1-hexene polymerization with
1/MAOare presented. The end
group analysis of homopolymers reveals a pronounced dependence of the terminationrate on temperature chan
ges. In combination with the hi
gh molecular wei
ghts obtained, these results are inaccord with theoretical predictions. Gel permeation chromato
graphy, Fourier transform infrared, and
13C NMRanalyses of copolymerization products from
1/MAO as a function of comonomer concentration at two differenttemperature series denote its tendency to form inhomo
geneous polymer blends. Thermal analysis andfractionation results of one such blend indicate an inhomo
geneity in the enchainment process and the existenceof multiple active sites of differin
g geometry. These indications are further supported by AMBER force fieldand density functional theory studies of the catalyst precursors and the active site of
1/MAO. For this system,
ges/
gifchars/delta.
gif" BORDER=0 >-a
gostic interactions for the stabilization of the zirconium cation are favored over
ges/
gifchars/beta2.
gif" BORDER=0 ALIGN="middle">-a
gostic interactions,which, in contrast to the situation in studies on bis-Cp systems, is a sparsely populated species. The
gap inactivation enthalphies for
ges/
gifchars/beta2.
gif" BORDER=0 ALIGN="middle">-hydride transfer and elimination is mar
ginalized for these bulky zirconocenes,and conceptually new mechanisms for the isomerization of the vinyl end
groups are discussed. Further,unexpected activation of the silicon-hydro
gen bond within the li
gand framework is observed with an activationenthalpy as low as 14 kcal/mol.