Structure–Property Relationships of Doubly-Threaded Interlocked Polymer Networks

Mechanically interlocked polymers (MIPs) represent a unique class of materials in which topological constraints impart dynamic and tunable physical properties using mechanical bond. Among these, slide-ring networks—where interlocked rings can move along polymer backbones—have attracted significant attention due to their unusual mechanical behavior, such as greater extensibility, flexibility, toughness, and energy dissipation. This thesis mainly focuses on the design, synthesis, and structure–property relationships of slide ring networks, with an emphasis on the mobility of the doubly-threaded ring crosslinks as a key molecular parameter. In Chapter 2, a series of doubly threaded slide-ring gel networks (dt-SRGs) is developed using metal-templated pseudo[3]rotaxane (P3R) crosslinkers formed from a photo-curable ligand-containing thread. These networks incorporate doubly threaded rings as mobile crosslinking moieties. Compared to the corresponding covalent gel and entangled gel, dt-SRGs exhibit enhanced swelling, unique viscoelasticity, and faster stress relaxation, demonstrating the critical role of mobile interlocked crosslinks. Furthermore, the ability to modulate network properties by “locking” ring mobility through remetalation highlights the direct relationship between crosslink mobility and macroscopic behavior. In Chapter 3, this concept is extended to the synthesis of slide-ring polycatenane networks (SR-PCNs), where doubly threaded rings are integrated into a covalent polymer network as additional topological constraints. By optimizing monomer structure, the reaction kinetics of P3R formation are improved, enabling high gel fractions and increased ring incorporation while minimizing side reactions. These well-defined SR-PCNs allow for systematic investigation of the influence of interlocked rings on network properties. Relative to covalent and tangled control networks, SR-PCNs exhibit enhanced swelling and frequency-dependent viscoelastic behavior, which are attributed to ring mobility. In addition, their properties can be tuned through external stimuli, such as solvent, metalation, and protonation, which modulate ring dynamics. Molecular simulations further provide mechanistic insight into how ring motion governs stress redistribution and network mechanics. In Chapter 4, the impact of ring size on the properties of SR-PCNs is systematically explored. Varying ring size provides a direct means of tuning ring mobility and, consequently, network behavior. Networks containing larger rings exhibit increased swelling, faster stress relaxation, lower modulus, and higher extensibility, with mechanical responses approaching those of lower-crosslink-density systems. In contrast, networks with smaller rings behave more like conventional covalent networks, displaying greater hysteresis and energy dissipation due to constrained sliding. These results establish ring size as a critical design parameter that governs the balance between elasticity, dissipation, and stress redistribution in mechanically interlocked networks. In Chapter 5, the synthesis of [3]catenane with a new heteroleptic metal-ligand system is explored. This initial work uses zinc (II) binding with a bidentate phenanthroline and a terdentate 2,6-bis(N-alkyl-benzimidazolyl)pyridine ligand to self-assemble the thread and macrocycle components to form pseudorotaxanes. The crude product in the ring closing reactions of the thread and the pseudorotaxanes are explored and analyzed by gel permeation chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy. In Chapter 6, steps toward more complex poly[n]catenane networks have been taken. Overall, this thesis demonstrates that the incorporation of mobile interlocked crosslinks into polymers and networks provides a powerful strategy for tuning material properties. By elucidating the relationships between network structure, ring mobility, and macroscopic behavior, this work establishes key molecular design principles for the development of next-generation mechanically interlocked materials.