A MULTI-STAGE PROCESS FOR THE PREPARATION OF alpha -OLEFIN POLYMERS HAVING CONTROLLED STEREOREGULARITY AND PRODUCTS PREPARED THEREOF

摘要

The invention relates to the preparation of an alpha -olefin polymer product having controlled stereoregularity, comprising the successive steps of: (i) producing a first polymerization product by contacting under polymerization conditions an alpha -olefin monomer with a polymerization catalyst system comprising a transition metal compound, a first organometal compound and a stereoregulating external electron donor to give a first polymerization reaction mixture; (ii) producing a second polymerization product by contacting additional alpha -olefin monomer with the first polymerization reaction mixture. The controlled stereoregularity is achieved in such a way that in step (ii) the second polymerization product is produced in the presence of a stereoregularity controlling agent. The stereoregularity controlling agent is e.g. a second organometal compound which contains, on an atom basis, more halogen per metal than the first organometal compound, and/or 0.01-1.2 % of an olefin which is not said alpha -olefin monomer, calculated on the total molar amount of olefin and alpha -olefin monomer.