posted on 2020-03-04, 21:44authored byYuval Vidavsky, Michael R. Buche, Zachary M. Sparrow, Xinyue Zhang, Steven J. Yang, Robert A. DiStasio, Meredith N. Silberstein
Metal–ligand
interactions provide a means for modulating
the mechanical properties of metallopolymers as well as an avenue
toward understanding the connection between cross-link interaction
strength and macroscale mechanical properties. In this work, we used
nickel carboxylate as the tunable cross-linking interaction in a metallopolymer.
Different numbers and types of neutral ligands that coordinate to
the metal center are introduced as an easy approach to adjust the
strength of the ionic interactions in the nickel carboxylate cross-links,
thus allowing macroscale mechanical properties to be tuned. Density
functional theory (DFT) calculations, with the external forces explicitly
included (EFEI) approach, were used to quantify how the number and
type of ligands affect the stiffness, strength, and thermodynamic
stability of the nickel carboxylate cross-linking interactions. Interpreting
the bulk material properties in the context of these DFT results suggests
that the stiffness and strength of the cross-linking interactions
primarily control the initial stiffness and yield strength of the
metallopolymer, while the mechanical behavior at higher strain is
controlled by dynamical bond re-formation and interactions with the
polymer environment. The physicochemical insight gained from this
work can be used in the rational design of metallopolymers with a
wide scope of targeted mechanical properties.