Mechanistic Studies of ε-Caprolactone Polymerization by (salen)AlOR Complexes and a Predictive Model for Cyclic Ester Polymerizations

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• 作者：Elodie E. Marlier ; Joahanna A. Macaranas ; Daniel J. Marell ; Christine R. Dunbar ; Michelle A. Johnson ; Yvonne DePorre ; Maria O. Miranda ; Benjamin D. Neisen ; Christopher J. Cramer ; Marc A. Hillmyer ; William B. Tolman
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：February 5, 2016
• 年：2016
• 卷：6
• 期：2
• 页码：1215-1224
• 全文大小：458K
• ISSN：2155-5435

文摘

Aluminum alkoxide complexes (<b>2b>) of salen ligands with a three-carbon linker and para substituents having variable electron-withdrawing capabilities (X = NOb>2b>, Br, OMe) were prepared, and the kinetics of their ring-opening polymerization (ROP) of ε-caprolactone (CL) were investigated as a function of temperature, with the aim of drawing comparisons to similar systems with two-carbon linkers investigated previously (<b>1b>). While <b>1b> and <b>2b> exhibit saturation kinetics and similar dependences of their ROP rates on substituents X (invariant Kb>eqb>, similar Hammett ρ = +1.4(1) and 1.2(1) for kb>2b>, respectively), ROP by <b>2b> was significantly faster than for <b>1b>. Theoretical calculations confirm that, while the reactant structures differ, the transition state geometries are quite similar, and by analyzing the energetics of the involved distortions accompanying the structural changes, a significant contribution to the basis for the rate differences was identified. Using this knowledge, a simplified computational method for evaluating ligand structural influences on cyclic ester ROP rates is proposed that may have utility for future catalyst design.