Mechanistic Detail Revealed via Comprehensive Kinetic Modeling of [rac-C₂H₄(1-indenyl)₂ZrMe₂]-Catalyzed 1-Hexene Polymerization

Abstract

Thorough kinetic characterization of single-site olefin polymerization catalysis requires comprehensive, quantitative kinetic modeling of a rich multiresponse data set that includes monomer consumption, molecular weight distributions (MWDs), end group analysis, etc. at various conditions. Herein we report the results obtained via a comprehensive, quantitative kinetic modeling of all chemical species in the batch polymerization of 1-hexene by rac-C(2)H(4)(1-Ind)(2)ZrMe(2) activated with B(C(6)F(5))(3). While extensive studies have been published on this catalyst system, the previously acknowledged kinetic mechanism is unable to predict the MWD. We now show it is possible to predict the entire multiresponse data set (including the MWDs) using a kinetic model featuring a catalytic event that renders 43% of the catalyst inactive for the duration of the polymerization. This finding has significant implications regarding the behavior of the catalyst and the polymer produced and is potentially relevant to other single-site polymerization catalysts, where it would have been undetected as a result of incomplete kinetic modeling. In addition, comprehensive kinetic modeling of multiresponse data yields robust values of rate constants (uncertainties of less than 16% for this catalyst) for future use in developing predictive structure-activity relationships.

Low‐Temperature Kinetic NMR Studies on the Insertion of a Single Olefin Molecule into a ZrC Bond: Assessing the Counterion–Solvent Interplay

“…In many studies the kinetic parameters of the olefin insertion into the metal–carbon bond are determined 11–15. Nevertheless, to the best of our knowledge, the activation enthalpy (Δ H ≠ ) and entropy (Δ S ≠ ) values have never been reported for the same catalytic system featuring the two most frequently used counterions, that is, the “sticky” MeB(C 6 F 5 ) 3 − and the weakly coordinating B(C 6 F 5 ) 4 − anion.…”

Quantification of active sites in single-site group 4 metal olefin polymerization catalysis

“…Typical steps that can be embedded into such a model are chain transfer (to monomer, H2, AlR3…), β-H elimination with differentiation between vinyl and vinylidene chain-ends formation, misinsertions (i.e., regioirregular insertions) of the -olefin monomer, restitution after these misinsertions (i.e., reactivation of a dormant chain), etc. An example of a comprehensive model involving up to 12 elementary processes is delineated in Scheme 2 [35].…”

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

“…It is evident that kinetic studies based on direct measurement of the active center concentration in the polymerization system can lead to easier construction of a comprehensive mechanistic model. Many such studies have been reported based on various methods of counting the active center in metallocene catalysts . In most of the literatures, the determined active center ratios ([C * ]/[Mt], where [Mt] is concentration of the metallocene complex) in homogeneous metallocene catalysis systems were evidently lower than 1, meaning that only a part of the metallocene complex could be turned to active center.…”