Controlling Reactivity by Geometry in Retro-Diels-Alder Reactions under Tension
Authors: Richard Stevenson, Guillaume De Bo
Journal: Journal of the American Chemical Society
Publication Date: 31 October, 2017
Department of: Chemistry
A molecular tug-of-war
Mechanical force, with its ability to distort, bend, and stretch chemical bonds, is unique in the way it activates chemical reactions. Now, researchers at the University of Manchester have shown that mechanical force can enhance or suppress the ability of polycyclic adducts to disassemble, in a process known as a retro-Diels-Alder reaction, in function of their geometry. In polymer mechanochemistry, mechanophores are embedded within a polymer backbone to enable their mechanical activation. The resulting macromolecule can be activated in solution using high-intensity ultrasound where the elongational flow surrounding collapsing bubbles stretches and deforms it until an eventual bond scission occurs. However, the efficiency of activation depends on how well the force is transduced from the polymer to the scissile bond. At zero force, the rate of retrocycloaddition depends primarily on the relative orientation of the rings composing the adduct. Under tension, the proximity of the polymer with the scissile bond proves more important to ensure an efficient mechanochemical coupling. Ultimately, the geometry can be adjusted to create a thermally labile, yet mechanically resistant, adduct. These results are particularly significant for the development of thermally mendable materials, in which the mechanical and self-healing properties can be finely tuned by combining different adducts.
- Ultrasound-induced cavitation provokes the nucleation, growth and collapse of microbubbles in a liquid.
- A mechanophore is a mechanosensitive molecule
- The mechanochemical coupling describes how well the force is transduced from the polymer to a particular chemical bond.
- Retrocycloaddition/retro-Diels-Alder: A cycloaddition is a reaction in which two or more unsaturated molecules combine with the formation of a cyclic adduct. A retrocycloaddition is the reverse process. The Diels Alder reaction is a type of cycloaddition yielding a 6-membered ring.