Controlled Sol-Gel Transitions by Actuating Molecular Machine Based Supramolecular Polymers.

The implementation of artificial molecular machines in polymer science is an important objective that challenges chemists and physicists in order to access an entirely new class of smart materials. To design such systems, the amplification of a mechanical actuation from the nanoscale up to a macroscopic response in the bulk material is a central issue. In this article we show that bistable [c2]daisy chain rotaxanes (i.e., molecular muscles) can be linked into main-chain Upy-based supramolecular polymers. We then reveal by an in depth quantitative study that the pH actuation of the mechanically active rotaxane at the nanoscale influences the physical reticulation of the polymer chains by changing the supramolecular behavior of the Upy units. This nanoactuation within the local structure of the main chain polymer results in a mechanically controlled sol-gel transition at the macroscopic level.