Revealing the Interactions between the Flexible Polymer and Counteranion during Propagation and Termination for Olefin Polymerization with the Ti(IV) Constrained Geometry Catalyst

The structure and behavior of counteranions MeB(C6F5)3– and B(C6F5)4– interacting with a constrained-geometry Ti olefin polymerization catalyst and its growing polymer chain are examined through conformer sampling and reaction pathway simulations. The results show that the length of the polymer chain substantially influences the counteranion position, where longer polymer chains have a tendency to limit the counteranion’s access to the monomer coordination site. Conformations affect not only ion pair preferences but also the effective free energy of activation for monomer insertion and chain termination. Ion pair orientations of the π-complex where the counteranion is on the opposite side of the Ti catalyst as the ethylene monomer are preferred for productive insertion and chain termination reaction pathways. These result in ion pairs of B(C6F5)4– having orientations conducive to ethylene insertion as well as chain termination via β-hydrogen transfer, which can explain why B(C6F5)4– results in lower molecular weight of the polymer.