Roles of Monomer Binding and Alkoxide Nucleophilicity in Aluminum-Catalyzed Polymerization of 蔚-Caprolactone

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• 作者：Keying Ding ; Maria O. Miranda ; Beth Moscato-Goodpaster ; Noureddine Ajellal ; Laurie E. Breyfogle ; Eric D. Hermes ; Chris P. Schaller ; Stephanie E. Roe ; Christopher J. Cramer ; Marc A. Hillmyer ; William B. Tolman
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：July 10, 2012
• 年：2012
• 卷：45
• 期：13
• 页码：5387-5396
• 全文大小：495K
• 年卷期：v.45,no.13(July 10, 2012)
• ISSN：1520-5835

文摘

The kinetics of polymerization of 蔚-caprolactone (CL) initiated by aluminum-alkoxide complexes supported by the dianionic forms of N,N-bis[methyl-(2-hydroxy-3-tert-butyl-5-R-phenyl)]-N,N-dimethylethylenediamines, (L^R)Al(Oi-Pr) (R = OMe, Br, NO₂) were studied. The ligands are sterically similar but have variable electron donating characteristics due to the differing remote (para) ligand substituents R. Saturation kinetics were observed using [CL]₀ = 2鈥?.6 M and [complex]₀ = 7 mM, enabling independent determination of the substrate coordination (K_eq) and insertion (k₂) events in the ring-opening polymerization process. Analysis of the effects of the substituent R as a function of temperature on both K_eq and k₂ yielded thermodynamic parameters for these steps. The rate constant k₂, related to alkoxide nucleophilicity, was strongly enhanced by electron-donating R substituents, but the binding parameter K_eq is invariant as a function of ligand electronic properties. Density functional calculations provide atomic-level detail for the structures of key reaction intermediates and their associated thermochemistries.