Abstract: A catalyst composition for the polymerization of olefins and process for the use thereof, comprising the combination of one or more Ziegler-Natta catalysts, comprising one or more transition metal compounds, one or more aluminum containing cocatalyts, and a mixture of different selectivity control agents, including in said mixture of selectivity control agents at least one normally dominating selectivity control agent and one normally dominated selectivity control agent, characterized in that the individual selectivity control agents are present in the mixture in relative amounts to each other and relative 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.

Abstract: A method of making a solid procatalyst composition for use in a Ziegler-Natta olefin polymerization catalyst composition, said method comprising: contacting a precursor composition comprising a magnesium compound with a titanium halide compound and an internal electron donor in any order, in a suitable reaction medium to prepare a solid procatalyst composition, separating the solid procatalyst from the reaction medium, extracting the solid procatalyst composition by contacting the same one or more times with a liquid diluent at an elevated temperature for a period of time sufficient to prepare a solid procatalyst composition having a decreased titanium content compared to the titanium content of the solid procatalyst composition before said extraction, and recovering the solid procatalyst composition.