Interaction between Two Active Sites of the Same Catalyst for Macromonomer Enchained Olefin Polymerization

A zirconium amine bis(phenolate) catalyst that is capable of simultaneously producing both oligomers and polymers of 1-hexene was investigated. It was found that the polymer produced has more branching than the commonly encountered poly(1-hexene), suggesting an oligomer macro-monomer enchainment. The polymer weight fraction and molecular weight are weakly dependent on conversion and are not affected by increasing the concentration of free oligomer macromonomers in solution. After considering a number of possible mechanisms, the most plausible supported by spectroscopic and kinetic data is a second-order reaction between an oligomer forming site and a polymer forming site, resulting in the transfer of oligomer macro-monomers into the growing polymer chain. The ratio between oligomer and polymer products can be precisely tuned by varying the precatalyst activation conditions.