Controlled distribution of active sites in ziegler-natta catalyst systems

A method for activating a Ziegler-Natta pre-catalyst component comprising:

• providing a Ziegler-Natta pre-catalyst component, wherein the Ziegler-Natta pre-catalyst component comprises magnesium, titanium, an amount of chlorine sufficient to chlorinate Mg and Ti and form MgCl2 and TiCl4 and internal electron donor(s) that comprise at least two distinct oxygen-containing functions;
• submitting the pre-catalyst component to a thermal treatment carried out at a temperature of from 80 to 150° C. under vacuum better than 10−5 bars;
• treating the pre-catalyst component by adding a Lewis acid BX3 that is a boron compound soluble in apolar solvents, wherein X is halogen or alkyl group;
• optionally further treating the Ziegler-Natta pre-catalyst component with a titanium compound TiX4 before or after treatment with the Lewis acid;
• adding aluminium compound of general formula AlRnZ3-n wherein R is alkyl group having from 1 to 10 carbon atoms, Z is halogen and n is 0, 1, 2 or 3;
• and
• optionally adding an external electron donor either of general formula SiRam(ORb)4-m or of general formula R′O—(CH2—CR1R2—CH2)—OR′ wherein Ra and Rb are each independently selected from alkyl, aryl, cycloalkyl, arylalkyl or alkylaryl having at most 12 carbon atoms, and two neighbouring R can be linked together to make a ring, m is 0 or an integer from 1 to 4, wherein each R′, R1 and R2 is independently selected from alkyl, aryl, cycloalkyl, arylalkyl or alkylaryl having at most 12 carbon atoms, and R1 and R2 can be linked together to make a ring or rings.