Role of Molecular Topology Elucidated in Unified Gels

Incorporating topologically nontrivial molecules (e.g., catenanes) is an emerging strategy for tuning properties of polymer networks, but the fundamental roles of these molecules remain poorly understood. Herein, we report a unified gel system employing isomeric linkers with distinct topologies, which allows for cross-gel comparison and elucidation of how topology governs mechanical and dynamic properties in polymeric materials. Our gels feature a panel of phenanthroline-based macrocyclic molecules as linkers, which adopt structures including a large macrocycle, a flexible catenane, and, through metal coordination, a rigidified catenane and a twisted figure-eight structure. By mechanical and thermodynamic analysis and simulations, we identify topology-dependent coordination and conformational entropy as the key factors driving the gels' mechanical responses. We reveal that the toughness and energy dissipation capacity of the gels correlate directly to the conformational change allowed by each topology, proportional to the "hidden length" that can be released by the linkers. Surprisingly, metal-ligand bonds primarily tune the initial linker conformation rather than dissipate energy through bond dissociation, while they simultaneously enhance network dynamics. Our findings could guide the selection of topological molecules for engineering advanced polymer materials.