Impact of Threading State on the Mechanics of γ-Cyclodextrin-Pyrene Gels

Conventional covalent and supramolecular crosslinks impose inherent trade-offs between mechanical robustness and environmental adaptability in polymer networks. Mechanically interlocked junctions offer an alternative route by enabling topological motion without compromising structural integrity. Here, a modular approach is reported to construct topology-engineered gels by copolymerizing 2-hydroxyethyl acrylate (HEA) with doubly threaded (dt-) pseudo[4]rotaxane crosslinkers, formed via the complexation of γ-cyclodextrin (γ-CD) and acrylate-end-capped pyrene derivatives. By tuning the HEA/water ratio in pre-gel formulations, the supramolecular assembly can be shifted from dt- to singly threaded (st-) entities, enabling access to gels with the same chemical composition but different architectures-dt-slide ring network versus st-polyrotaxane covalent network. The dt-network exhibits solvent-dependent fluorescence, swelling, and viscoelasticity that is not observed in either the st-network or a covalent control gel. Mechanical testing of the bulk networks reveals that the dt-network exhibits high extensibility (>1050% strain at break), strain rate-dependent stiffening and rupture, and a favorable combination of high toughness and comparatively low hysteresis under cyclic deformation that is not observed in the networks lacking the dt-architecture. Overall, these results establish a structure-property relationship dictated by crosslinking topology, demonstrating how dt-interlocked motifs can encode both mechanical performance and environmental responsiveness in soft materials.