Molecular Origin of the Stretchability and Fatigue-Resistance of Rotaxane-Based Mechanically Interlocked Polymer...

Rotaxane-based polymer networks leveraging host-guest recognition have recently emerged as a versatile platform for developing smart materials. Despite numerous studies on these polymers, their unique mechanical properties are mostly associated with the sliding motion of the macrocycle along the axle, leaving the impact of the presence or absence of interlocked structures on the mechanical performance of materials yet to be directly demonstrated. In this work, we present a densely (pseudo)rotaxane-based supramolecular polymeric network (SPN) and a mechanically interlocked network (MIN) as model systems to explore how the mechanical interlocking unit dominates the material properties. Specifically, we have achieved a significant transition from SPN to MIN by finely tuning the stopper size, just substituting a methyl with a dimethyl group attached to the phenyl ring. Although their stereochemical structures are similar, a subtle increase in the stopper size can lead to striking improvements in stretchability and anti-fatigue performance. The stopper size-relevant dethreading behavior, as evidenced by a combined approach of solid-state NMR spectroscopy and rheology, is the underlying molecular mechanism for the difference in the macroscopic mechanical properties. We anticipate that the fundamental understanding gained from this work will advance the development of rotaxane-based materials with emergent functions and applications.