A Model Elastomer with Modular Metal-Ligand Crosslinking
Metallosupramolecular polymers are increasingly of interest for functional and degradable polymeric materials. In these materials, the metal-ligand bonds often bear an external mechanical load, but little is yet understood about the nature of mechanically-triggered reactions of metal-ligand bonds and how that reactivity influences the mechanical limits of the material. This dissertation presents a poly(cyclooctene) polymer bearing 2,6-bis(1′-methyl-benzimidazolyl)pyridine (Mebip) ligands on sidechains, which provides easy incorporation into polymer backbones and sidechains, binding to a large variety of metal species, and facile synthesis with sites for future study substituent effects. This platform is employed in proof-of-concept studies comparing the crosslinking behavior of iron(II) trifluoromethanesulfonate and copper(II) trifluoromethanesulfonate. It was found through small molecule spectroscopic studies that both metal species bind in the desired 2:1 MeBip:metal stoichiometry for crosslinking. When these small molecule complexes are polymerized as crosslinkers in gel and solid networks, though the extent of crosslinking is found to be similar, the copper(II)-crosslinked networks exhibited a faster relaxation than the iron(II)-crosslinked networks. Further, under high strains, the copper(II)-crosslinked networks exhibited significantly higher extensibility. This work lays the foundation for further investigations of the effect of metal-ligand bonding on force-coupled properties of materials.
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