Masud M. Monwar, Jared L. Barr, Kathy S. Clear, Carlos A. Cruz, Mitchell Refvik, Max P. McDaniel
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Initiation of the Phillips Cr(VI) Catalyst by Alkenes
As part of a continuing effort to better understand the initiation (i.e., the reduction and self-alkylation) of the Phillips commercial Cr(VI)/silica catalyst, this study attempted to isotopically label the initiating group on the starting PE chain. The hexavalent catalyst was reduced by deuterated olefin (C2D4 or C3D6), then polymerization of C2H4 was conducted. This amplified the starting group signal during the subsequent 2H NMR analysis of the polymer. In a second method, the Cr(VI) catalyst was reduced by various olefins, then hydrolyzed by injection of protic liquids. Redox products were then analyzed by GC–MS. These data indicate that the initial chain made on a Cr(VI) site begins with a methyl group. No unsaturation was observed. In addition, oxygen was found in many of the resultant chains, apparently incorporated from the original Cr(VI) as part of the initiation process. It demonstrates that reduction and alkylation are not necessarily separate and independent reactions, but often occur in a concerted process. It further suggests that there is not one initiation mechanism, but many, depending on the reactivity of the individual sites and the monomer used.
期刊介绍:
ACS Catalysis is an esteemed journal that publishes original research in the fields of heterogeneous catalysis, molecular catalysis, and biocatalysis. It offers broad coverage across diverse areas such as life sciences, organometallics and synthesis, photochemistry and electrochemistry, drug discovery and synthesis, materials science, environmental protection, polymer discovery and synthesis, and energy and fuels.
The scope of the journal is to showcase innovative work in various aspects of catalysis. This includes new reactions and novel synthetic approaches utilizing known catalysts, the discovery or modification of new catalysts, elucidation of catalytic mechanisms through cutting-edge investigations, practical enhancements of existing processes, as well as conceptual advances in the field. Contributions to ACS Catalysis can encompass both experimental and theoretical research focused on catalytic molecules, macromolecules, and materials that exhibit catalytic turnover.