Fig. 12. Ultrasound-induced retro [3+2] cycloaddition of an embedded triazole moiety. Triazole bond formation can be reversed by the application of mechanical force, resulting in azide and alkyne functional groups. The generated azide and alkyne moieties of the functionalized poly(methyl acrylate) (PMA) were subsequently ‘clicked’ (Cu, CH₃CN) to form the triazole-based starting material. Image reprinted from Brantley et al. ²⁹⁹ with permission from Nature publishing group. Copyright (2011).