The Relationship between Catalyst Precursors and Chain End Groups in Homogeneous Propene Polymerization Catalysis

The chain transfer to monomer reactions promoted by primary and secondary growing chains in the propene polymerization promoted by ansa-zirconocenes and postmetallocene precursors are studied by using DFT methods. From the theoretical results it comes out that the prevalence of propene insertion over b-hydrogen transfer to the monomer decreases drastically in the presence of a secondary chain. Furthermore, we explained the reason why C2-symmetric metallocene catalysts promote the selective formation of cis but-2-enyls end group after a 2,1 inserted unit whereas for octahedral bis(phenoxy- imine)titanium-based catalysts, chain release promotes exclusively the formation of allyl terminated chain end. These results might be useful to design ligand precursors able to obtain not only high Mn PP polymers but also tuned chain end groups to build new polymer architectures. Overall, a more general picture of the enantioselectivity of the chain transfer to monomer processes is reported.