The Dynamics of Bulk Polymers with Metal-ligand Coordination Crosslinking*

The dynamics of polymer networks consisting of metal-ligand coordination as crosslinks have been widely studied in solution and gel systems. However, understanding the dynamics of bulk polymers with metal-ligand coordination crosslinking remains a challenge because it is hard to decouple the polymer relaxation and association/dissociation of the dynamic bonds. To address this problem, we carefully designed both the polymer structure and the intramolecular dynamic bond in the system. A series of copolymers containing ethyl acetoacetate ligands have been synthesized by RAFT polymerization. The ethyl acetoacetate ligands can form coordination complexes with different metal ions (Ni(II), Cu(II), and Zn(II)) and act as reversible crosslinks. We investigated the dynamic responses of these polymer networks by rheometer and DMA. These lightly crosslinked networks have behavior that varies both with choice of metal and quantity of metal, thereby revealing the kinetic differences due to the metal-ligand coordination bonds in bulk polymers. We show that these non-covalent dynamic bonds in the bulk polymer networks play an important role in determining their mechanical properties.