A Synthetic Approach to Active Site Deconvolution in Supported Cr Catalysts for Olefin Polymerization

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AbstractProposal Title: A Synthetic Approach to Active Site Deconvolution in Support Cr Catalysts for Olefin Polymerization Proposal Number: CTS-0500489Principal Investigator: Susannah L. ScottInstitution: University of California-Santa BarbaraAnalysis (rationale for decision): The goal of this project is to solve a longstanding and complex problem related to a class of catalysts based on chromium that have been extensively used for high-density polyethylene production. These catalysts have a remarkable ability to self-activate in the presence of olefin. Until the nature of the active sites is known, however, it is unlikely that it will be possible to determine how they are formed or why this catalyst is so effective at reviving deactivated sites. The proposed approach to this problem combines active site deconvolution for the heterogeneous catalyst using Flory analysis and kinetic modeling with synthesis of individual active site candidates using surface organometallic chemistry. Matching the activity profiles and polymer characteristics of the catalyst sites with those of well-defined organometallic sites will allow correlation of structure with reactivity. It may then be possible to reformulate the olefin polymerization catalysts by selecting combinations of sites that generate desired combinations of physical properties in the polyethylene. Furthermore, by shedding light on the activation mechanisms of the supported metal oxide catalysts, it will be possible to make the self-activation more efficient. The synthetic approach to active site investigation is complementary to combinatorial approaches to catalyst discovery. Once interesting catalyst formulations are identified and optimized by screening (parallel or otherwise), further improvements depend on the ability to manipulate active site structure. Identifying the structural features which control reactivity by synthesizing model compounds has been a promising strategy in homogeneous catalysis, and the approach is innovative and high risk for heterogeneous catalysis.The broader technological impacts of this project will be significant due to the widespread use of chromium-based polymerization catalysts by industry. The project will involve students in a very strong multidisciplinary environment that particularly emphasizes the key combination of chemical engineering and chemistry approaches that have been necessary for leading-edge catalysis research. The research program conducted by the principal investigator has a record of involving undergraduate students from underrepresented groups in research: 28 students including 18 women have been involved in projects during the past 10 years, and 13 of these students have pursued graduate studies.