The Hafnium-Pyridyl Amido-Catalyzed Copolymerization of Ethene and 1-Octene: How Small Amounts of Ethene Impact Catalysis

Abstract

Copolymerization of ethene and 1-octene is catalyzed by the Hf-pyridyl amido complex used in chain-shuttling polymerization. Active site counts and the molar mass distribution of catalyst-bound polymeryls are determined by chromophore quench-labeling. Catalytic data for copolymerization (1-octene consumption, active site counts, molar mass distributions of polymers, and I2-labeling of Zn-polymeryls) are compared with similar data for the homopolymerization of 1-octene. Such comparisons reveal that small amounts of ethene have a significant impact on catalysis. The rate of 1-octene consumption increases in a copolymerization ∼3-fold compared to a homopolymerization; this likely results from in situ ligand modification. The first insertion of alkene occurs into the Hf–naphthyl bond of the Hf-pyridyl amido catalyst; in copolymerization, competition between ethene and 1-octene for this insertion creates multiple active species. We propose that ethene insertion into the Hf–naphthyl bond leads to a faster polym...