Over 8 billion tons of plastic have been produced to date, and a 100% reclamation recycling strategy is not foreseeable. This review summarizes how the mechanochemistry of polymers may contribute to a sustainable polymer future by controlling the degradation not only of de novo developed designer polymers but also of plastics in existing waste streams. The historical development of polymer mechanochemistry is presented while highlighting current examples of mechanochemically induced polymer degradation. Additionally, theoretical and computational frameworks are discussed that may lead to the discovery and better understanding of new mechanochemical reactions in the future. This review takes into account technical and engineering perspectives converging the fields of trituration and polymer mechanochemistry with a particular focus on the fate of commodity polymers and potential technologies to monitor mechanochemical reactions while they occur. Therefore, a unique perspective of multiple communities is presented, highlighting the need for future transdisciplinary research to tackle the high-leverage parameters governing an eventually successful mechanochemical degradation approach for a circular economy.

Shear selectivity: Chemical reactions typically proceed by distributing energy statistically among all accessible molecular vibrations. Liu et al. report that external shear forces can sometimes pry open strained carbon rings without dissipating energy into adjacent bond rotations. Through careful design and synthesis of polymer-embedded cyclobutyl rings, the authors showed that certain relative substituent geometries are preserved when sonication induces ring opening. Accompanying simulations support the instigation of “flyby” trajectories that channel energy narrowly to cleave the cyclic sigma bonds and then rapidly form acyclic pi bonds. Science , abi7609, this issue p. 208