title: Mechanistic Studies of ε-Caprolactone Polymerization by (salen)AlOR Complexes and a Predictive Model for Cyclic Ester Polymerizations.
abstract: Aluminum alkoxide complexes (2) of salen ligands with a three-carbon linker and para substituents having variable electron-withdrawing capabilities (X = NO2, 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 (1). While1and2exhibit saturation kinetics and similar dependences of their ROP rates on substituents X (invariantKeq, similar Hammett ρ = +1.4(1) and 1.2(1) fork2, respectively), ROP by2was significantly faster than for1. 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.
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Elodie E
authors.initials: EE
authors.lastname: Marlier
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Joahanna A
authors.initials: JA
authors.lastname: Macaranas
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Marell
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Christine R
authors.initials: CR
authors.lastname: Dunbar
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Johnson
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: DePorre
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Maria O
authors.initials: MO
authors.lastname: Miranda
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Neisen
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Cramer
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Hillmyer
authors.affiliation: Department of Chemistry, Center for Sustainable Polymers, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors.forename: William B
authors.initials: WB
authors.lastname: Tolman
keywords: catalysis; computation; ligand effects; ring-opening polymerization; saturation kinetics