Effects of Electronic Perturbations on 1-Hexene Polymerization Catalyzed by Zirconium Amine Bisphenolate Complexes

Abstract

The kinetics of 1-hexene polymerization using four zirconium amine bisphenolate catalysts, Zr[tBu-ONXO]Bn2 (where, X = pyr-CF3 (1), pyr (2), pyr-CH3 (3), pyr-OMe (4)) has been investigated to elucidate the effect of varying the electronic nature of the pyridine pendant ligand X. A model-based approach using a diverse set of data, including monomer consumption, evolution of molecular weight, and end-group analysis was employed to determine each of the reaction-specific rate constants involved in polymerization. The mechanisms of polymerization for 1–4 was similar, and the necessary elementary reaction steps included initiation, propagation, misinsertion, recovery from misinsertion, and chain transfer. It was observed that the electronic nature of the pendant pyridine ligand affects each monomer insertion event (propagation, misinsertion, and recovery) in a similar fashion, in concert with changes in the Hammett parameters of the ligand substituents. These findings underscore the importance of kinetic modeling to establish robust structure–activity relationships.