Studies on the Activation Patterns and the Catalytic Behaviors of Binuclear Organotitanium Complexes towards Olefin PolymerizationPublic Deposited
Bimetallic polymerization catalysis represents a small, though active, area of research due largely to the interesting properties observed in the resulting product polymers, including higher molecular weight, increased comonomer incorporation, and enhanced tacticity. Current work is focused on furthering an understanding of the active catalytic species that give rise to these desirable polymer properties. Presented here are the synthesis and reactivity of two series of bimetallic organotitanium catalysts. The active species of both catalysts are extensively studied, and the catalytic performance is evaluated based on this knowledge of the active species. It will be seen that one catalyst series is comprised of separable diastereomers, which display distinct modes of reactivity with stoichiometric boron-based cocatalysts and produce widely varying polymers depending on stereochemistry of the catalyst and identity of cocatalyst. The second catalyst series, on the other hand, will be seen to rearrange and produce a chemically distinct, yet highly active species upon activation with a boron-based cocatalyst. Thus, though they differ largely in reactivity with activators, both catalyst series highlight the importance of knowing the nature of the active species in order to explain the observed polymerization characteristics.