Controlled Distribution of Active Sites in Ziegler-Natta Catalyst Systems

Abstract

The present invention provides a method for improving and controlling the activity of Ziegler-Natta catalyst systems.

1 - 11 . (canceled) 
     
     
         12 . A method for polymerizing ethylene or propylene comprising:
 injecting the active modified Ziegler-Natta catalyst system into a reactor, wherein the modified Ziegler-Natta catalyst system is formed by:   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 MgCl 2  and TiCl 4  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 BX 3  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 TiX 4  before or after treatment with the Lewis acid;   adding aluminium compound of general formula AlR n Z 3-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 SiR a   m (OR b ) 4-m  or of general formula R′O—(CH2-CR 1 R 2 —CH2)-OR′ wherein R a  and R b  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′, R 1  and R 2  is independently selected from alkyl, aryl, cycloalkyl, arylalkyl or alkylaryl having at most 12 carbon atoms, and R 1  and R 2  can be linked together to make a ring or rings;   injecting an ethylene or propylene monomer into the reactor;   maintaining the reactor under polymerisation conditions; and   retrieving a polymer.   
     
     
         13 . The method of  claim 12 , wherein the molar ratio B/Mg is of less than 1. 
     
     
         14 . The method of  claim 13 , wherein the molar ratio B/Mg is between 0.02 to 0.03. 
     
     
         15 . The method of  claim 13 , wherein the molar B/Mg ratio is equal to or less than 0.01. 
     
     
         16 . The method of  claim 12 , wherein the monomer is propylene. 
     
     
         17 . The method of  claim 16 , wherein the method further comprises injecting a comonomer into the reactor. 
     
     
         18 . The method of  claim 17 , wherein the comonomer is ethylene or hexene. 
     
     
         19 . The method of  claim 12 , wherein the monomer is ethylene. 
     
     
         20 . The method of  claim 19 , wherein the titanium content of the Ziegler-Natta pre-catalyst component is between 0.1 to 0.3 wt % based on the weight of the Ziegler-Natta pre-catalyst component. 
     
     
         21 . The method of  claim 19 , wherein the Ziegler-Natta pre-catalyst component does not contain an internal Lewis base. 
     
     
         22 . The method of  claim 19 , wherein the BX 3 /Ti molar ratio is between 20 and 50. 
     
     
         23 . The method of  claim 19 , wherein the method further comprises injecting a comonomer into the reactor. 
     
     
         24 . The method of  claim 19 , wherein the comonomer is hexene.