Mechanochemistry of an Interlocked Poly[2]catenane: From Single Molecule to Bulk Gel

Mechanically interlocked molecules (MIMs) are prototypical molecular machines with parts that enable controlled, large-amplitude movement with one component positioned relative to another. Incorporating MIMs into polymeric matrices is promising for the designing of functional materials with unprecedented properties. However, the central issue is the challenges involved with establishing the mechanistic linkage between the single-molecule and the bulk material. Herein, we explore the mechanochemical properties and energetic details of a linear poly[2] catenane with strong intercomponent hydrogen bonding (IHB) revealed by single-molecule force spectroscopy. Our results showed that the individual linear poly[2]catenane chain exhibited typical sawtooth pattern, corresponding to the reversible unlocking and relocking transitions under external force or upon stimulations to dissociate or re-form the strong IHB. Furthermore, when a poly[2]catenane-based polymer gel was prepared using a thiol-ene click reaction between thiol-ended poly[2] catenane and a low-molecule-weight cross-linker, the resultant gel showed excellent mechanical adaptability and dynamic properties, which correlated well with the molecular-level observations. The unique poly[2]catenane structure also contributed to the gel formation with an extraordinary IHB-mediated swelling behavior and shape memory property. Thus our present results demonstrate the functioning of bulk material in a linear tandem manner from the behavior of a single molecule, a finding which should be applicable to other systems with versatile properties and promising applications.