Patent ID: 7141635

Claim:
A catalyst composition for the polymerization of olefins comprising the combination of one or more Ziegler-Natta catalysts comprising one or more transition metal compounds; one or more aluminum containing cocatalysts; and a mixture of two or more different selectivity control agents (SCA's) in a molar ratio based on total transition metal of from 0.5 to 15, including in said mixture of selectivity control agents at least one normally dominating selectivity control agent (SCA 1 ) selected from the group consisting of dicyclopentyldimethoxysilane, di-tert-butyl-dimethoxy-silane, diphenyldimethoxysilane, diisopropyldimethoxysilane, di-n-propyldimethoxysilane, di-n-butyldimethoxysilane, cyclopentyltrimethoxysilane, ethyltriethoxysilane, cyclopentyl-pyrrolidinodimethoxysilane, bis(pyrrolidino)dimethoxysilane, and bis(perhydroisoquinolino)-dimethoxysilane in an amount from 0.1 to 60 mol percent of said mixture and at least one normally dominated selectivity control agent (SCA 2 ), characterized in that the individual selectivity control agents are present in the mixture in relative amounts with respect to each other and with respect to the one or more transition metal compounds, such that the effect of the selectivity control agents on the resulting polymer properties is not determined solely or substantially solely by the normally dominating selectivity control agent.