Mechanism and kinetics of homogeneous catalysis

Silei Xiong, Purdue University

Abstract

A model-based approach using a diverse set of data including monomer consumption, evolution of molecular weight, and end-group analysis was employed to determine each of the reaction specific rate constants involved in 1-hexene polymerization process catalyzed by a family of group IV single-site catalysts. The primary set of elementary reaction steps included initiation, normal propagation, misinsertion, recovery from misinsertion, monomer independent and dependent chain transfer. Robust determination of kinetic constants and reaction mechanisms for a series of Group IV amine bis-phenolate complexes led to the development of several structure−activity relationships. For some of the catalysts of the bis-phenolate family the primary set of elementary reactions had proven inadequate and further investigation using the analysis developed here revealed the presence of additional key reaction steps. The kinetic study of the Zr[tBu-ONTHFO]Bn2/B(C 6F5)3 system under sub-stoichiometric activator conditions uncovered the formation of the binuclear complex (BNC) consisting of the neutral catalytic species and an active site connected via degenerative transfer of benzyl ligand. The kinetic study of the Zr[tBu-ONNEt2O]Bn 2/B(C6F5)3 system showed that a special polymeric site was formed which was capable to incorporate the growing oligomer chains attached to the normal active site to form branched polymer. The approach was next applied to studying the kinetics of other catalytic systems, e.g., the zwitterionic ring-opening polymerization using N-heterocyclic carbene, where several new reaction steps were proposed and then experimentally validated, including the attack of active zwitterions on cyclic chains that leads to high molecular weight cyclic poly(caprolactones).

Degree

Ph.D.

Advisors

Caruthers, Purdue University.

Subject Area

Chemical engineering

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