(495c) 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.