Extending the Stretchability Limit of Elastomers Through Mechanical Bond Motion

Elastomers with superior mechanical properties are imperative for next generation technologies spanning soft robotics, implantable bioelectronics, and adaptive aerospace systems. However, in conventional chemically crosslinked elastomers, increasing crosslinking density usually enhances modulus while reducing the attainable deformation before fracture, leading to a persistent stiffness-extensibility trade-off. Here, we report polymer networks incorporating a single type of [2]rotaxane crosslinker that combines hidden length activation and stress redistribution through mechanical bond motion, enabling greater extensibility at comparable stiffness. Increasing the rotaxane crosslinker content raises Young's modulus from 0.08 to 1.83 MPa while decreasing fracture strain from 10.24 to 2.70. The resulting networks exhibit an empirical stiffness-extensibility relationship of $E\propto {\lambda }_{\max }^{-2.84}$ , compared with the classical scaling $E\propto {\lambda }_{\max }^{-2}$ . This relationship corresponds to a smaller proportional loss of extensibility for the same proportional increase in modulus. The fracture energy reaches 5.57 kJ/m², compared with 1.01 kJ/m² for control networks, demonstrating enhanced fracture resistance. Similar stretchability enhancements are observed in networks prepared from other acrylate monomers, supporting the applicability of this design across different acrylate matrices. This work provides a molecular strategy for designing stiff, stretchable, and damage tolerant elastomers.