Mechanically interlocked mechanophores by living-radical polymerization from rotaxane initiators

Two [2]rotaxane initiators for single-electron-transfer living-radical-polymerization were synthesized and used for the controlled polymerization of methyl acrylate. The mechanically interlocked polymers exhibited distinct responses to mechanical activation by ultrasound. Monitoring the fate of the rotaxanes' charge transfer absorption bands provides evidence for preferential mechanical degradation of a midsection rotaxane unit as compared to a terminal rotaxane entity as a consequence of mechanical forces accumulating in the central region of the polymer chain.