End-of-life upcycling of robust polyurethanes using a room temperature, mechanism-based degradation

Abstract

A major challenge in developing recyclable polymeric materials is the inherent conflict between the properties required during and after its life span. In particular, materials must be strong and durable when in use, but undergo complete and rapid degradation upon end-of-life. We report a new mechanism for degrading polyurethanes called CyclizAtion-Triggered CHain (CATCH) cleavage that achieves this duality. CATCH cleavage features a simple glycerol-based acyclic acetal unit as a kinetic and thermodynamic trap for gated chain-shattering. Thus, an organic acid induces transient chain breaks with oxocarbenium ion formation and subsequent intramolecular cyclization to depolymerize fully the polyurethane backbone at room temperature. With minimal chemical modification, the resulting degradation products can be repurposed into strong adhesives and photochromic coatings demonstrating the potential for upcycling. The CATCH cleavage strategy for low-energy input breakdown and subsequent upcycling may be generalizable to a broader range of synthetic polymers and their end-of-life waste streams. The global challenge to reduce polymeric waste entering oceans and landfills has increased in urgency as the scale of problem has come into focus.1,2 Of the many approaches to make polymeric materials more sustainable, closed loop recycling have been especially interesting where depolymerization produces the original monomer.3,4 The process can be quite efficient for some materials, however others, especially thermosets require harsh conditions and most often the breakdown is insufficiently clean and too energy intensive to be practical.5 Dynamic