Structure–Activity Correlation for Relative Chain Initiation to Propagation Rates in Single-Site Olefin Polymerization Catalysis

Abstract

We have determined what makes the first monomer insertion (initiation) facile or slow for many homogeneous olefin polymerization catalysts. Specifically, we have developed the first comprehensive and mechanistically detailed quantitative structure–activity relationship (QSAR) that successfully predicts relative chain initiation to propagation rates for a large series of group 4 single-site olefin polymerization catalysts. This QSAR correctly predicts (a) whether initiation is facile or slow and (b) the ki/kp ratio for a catalyst family with slow initiation. Monomer concentration versus time profiles were measured for batch polymerization of 1-hexene catalyzed by 27 Cp′Ti(OAr)Me2 and Cp*Zr(OC6H-2,3,5,6-Ph4)J2 (J = Me, CH2Ph) complexes activated with B(C6F5)3. Comparison of DFT calculations to experimental data revealed that the underlying cause of slow versus facile initiation is the difference in docking site opening sizes between the initiation kinetically dominant ion pair (i-KDIP) and the propagation k...