Expanding Mechanically Mediated Polymerization via Mechanistic Understanding

University Of Chicago, Chicago IL

Investigators

Abstract

With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professor Aaron P. Esser-Kahn of University of Chicago is investigating the mechanism and reactivity of polymerization reactions mediated by piezoelectric catalysis. Piezoelectric compounds are solid materials, such as crystals, certain ceramics or even biological matter like bone, which have the ability to generate electrical charge from applied mechanical stress. In this work, piezoelectric particles composed of zinc and oxygen are agitated with sound waves (mechanical stress) to build electric charge. The charged particles are then used to speed up the formation of polymers in which the chain-ends contain carbon-sulfur bonds. These bonds are very unique because they enable reversible cross-linking of polymer chains resulting in the formation of materials with self-modelling properties. In addition to a mechanistic understanding of how piezoelectric particles speed up the polymerization process, several studies are performed to determine their surface composition and crystalline structure using a variety of sophisticated X-ray experimental techniques. This research actively engages students across a broad age range with a focus on high-school age children. The team is further developing burgeoning high-school summer “Pathways” program that aims to increase the number of STEM degree seeking college freshman. This research is focused on mechanistic and reactivity studies of polymerization mediated by piezoelectric catalysis. Piezo-mediated thiol-ene polymerization is extended to include new radical and metathesis monomers, disulfide bond formation, and novel reactivity. Radical based reactivity is expanded to include metathesis and ring-opening processes. In parallel, the mechanism by which piezo-particles mediate polymerization activity is explored. Combining these two approaches, the results of this research have the potential to greatly expand both the knowledge of mechanically controlled polymerization and the monomers and polymers accessible via this technique. Beyond simply improving polymer properties, mechanically driven electron ejection events could be used to harden solid materials through reduction/oxidation processes mediated by embedded piezo particles while serving as self-reporting strain and stress sensors. The potential to form new polymers in demanding environments could also be possible using mechanically initiated polymerization events. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.