The Effect of Polymer Chain Alignment and Relaxation on ForceInduced Chemical Reactions in an Elastomer

Traditionally chemical reactions are driven by light, thermal, chemical, or electrical potential. Mechanically induced bond cleavage can also be achieved, but is typically non-selective and/ or destructive. [ 1 ] By synthesizing and linking force-sensitive molecules (mechanophores) into a polymer backbone, mechanical deformation can be used to drive site-specifi c in situ chemical reactions. A variety of mechanophore chemistries have been incorporated into polymer backbones, and numerous force-stimulated chemical reactions have been demonstrated using pulsed sonication in the solution state. [ 2–12 ] Only a small number of mechanophores have shown activation in the solid state. [ 11,13,14 ] Notably, Davis et al. achieved force-induced activation of spiropyran (SP), which undergoes a 6π electro-cyclic ring-opening reaction under tensile deformation to a merocyanine (MC) form. The reaction of SP to MC is indicated by a strong color change, due to absorbance in the visible range, as well as the emergence of a fl uorescence signal. [ 13,15,16 ] This mechanically induced color change could serve as a sensor for mechanical deformation or stress in a polymer sample. Mechanochromic functionality has been demonstrated in previous polymer systems, [ 17,18 ]