Catalyst Mileage in Olefin Polymerization: The Peculiar Role of Toluene

Ti-C homolysis is generally regarded as a catalyst deactivation step in olefin polymerization catalyzed by titanium complexes. The present work demonstrates that for industrially relevant Ti catalysts in toluene and related solvents a "detour" via radical activation of the solvent can prolong catalyst lifetime and productivity, leading to chain transfer to solvents (CTS). For differently substituted phosphinimide half-titanocenes and other Ti catalyst classes, i.e. constrained geometry (CGC) and amidinate catalysts, CTS leads to formation of up to ∼60% benzylated chains. The efficiency of the reactivation pathway depends mostly on steric factors and correlates well with the percentage of buried volume, %VBur, as well with as DFT predictors. Thus, the solvent is far from innocent, and catalyst behavior in such solvents may not be representative of polymerizations in more innocent saturated hydrocarbons. On the other hand, it might be the case that, in truly innocent solvents, the monomer itself can play a less innocent role.