Force-decoupled strategies in mechanochemically active polymers

Abstract

Polymer mechanochem. is a rapidly emerging area of research that investigates the use of external mech. forces to stimulate covalent chem. transformations. Polymers transduce mech. stress to force-sensitive mols. called mechanophores, resulting in specific chem. reactions ranging from small mol. release to changes in visible properties such as color or fluorescence. The development of mechanochromic mechanophores in particular promises to impact the important application area of stress sensing and damage detection by enabling the direct visualization of crit. stress and/or strain in polymeric materials. Mechanophores like spiropyran, for example, undergo a direct, force-mediated electrocyclic ring-opening reaction to generate a highly colored merocyanine dye in polymers and polymeric materials; however, the color generation is transient and upon removal of stress from the system, the merocyanine dye reverts to the colorless ring-closed state. A unique mechanophore design strategy that decouples the mech. activation from the visual response will be presented. This methodol., termed mechanochem. gated photoswitching, allows the mech. history of a material to be permanently recorded and read on-demand. Alternative force-decoupled mol. design approaches beyond stress sensing will also be discussed for achieving multifunctional, force-responsive polymeric materials for a wide variety of applications.