261396 Kinetics of Olefin Polymerization Using Multi-Response Data Which Includes Fitting of Molecular Weight Distributions (MWDs)
In order to develop a thorough understanding of single-site olefin polymerization catalysis, we have developed a quantitative kinetic modeling framework. This allows us to determine microkinetic mechanisms and associated rate constants from experimental data such as monomer consumption, molecular weight distributions (MWDs), polymer end group analyses, and active-site counting. This methodology was applied to the batch polymerization of 1-hexene by rac-C2H4(1-Ind)2ZrMe2 activated with B(C6F5)3, one of the most studied single-site systems to date, and led to the discovery that only ca. 60% of the catalyst is active. The methodology has now been applied to other single-site systems, particularly those non-Cp Zr catalysts with tetradentate salan-type ancillary ligands. These ligands provide a wide variation in chemical and structural diversity. Studies of 1-hexene polymerization by these catalysts revealed two key features: the presence of misinserted monomers, which render a significant portion of the catalyst dormant; and how small perturbation in the ligand can impact the rate of chain transfer significantly- by orders of magnitude. It is noteworthy that these findings would not have been possible had it not been for a data set that included the MWDs at different percent monomer conversion.