Rotaxane cross-linked polymers (RCPs) have been attracted attentions because of their excellent capacities to dissipate local stress accumulated at the cross-linked points. However, the correlation between microscopic and macroscopic failure mechanism derived from a ring-sliding process has not been revealed yet. In this study, to reveal the failure mechanism of RCPs, deformation and stress relaxation processes derived from rotaxane structures at the cross-linked points were visualized through the activation of mechanophore. Namely, mechanochromic rotaxane-linked polymers(MCRPs) was developed by the introduction of difluorenylsuccinonitrile (DFSN) mechanophore which is homolytically cleaved into pink-colored stable radicals upon mechanical stress, into the rotaxane cross-linked points. The generated carbon-centered radicals can be evaluated quantitatively by electron paramagnetic resonance (EPR) spectroscopy in the bulk, which enables the quantitative evaluation of the extent of DFSN activation.The mechanocromic properties of the resulting MCRPs were characterized by comparison with covalently cross-linked polymers which were cross-linked by DFSN without rotaxane structure.

Synthesis of rotaxane cross linkers with a radical type mechanophore to visualize dynamic behavior of slide ring materials

ACS Fall 2021

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