Leveraging Intramolecular 6-exo-trig Cyclization to Create a Chemically Triggered Degradable and Recyclable Polyurethane Plastic

Chemical recycling of polyurethanes is challenging because urethane linkages are highly stable and typically require harsh glycolysis conditions to depolymerize. Herein, we present a specialized diisocyanate monomer that enables mild and selective polyurethane degradation while being incorporated using standard diisocyanate/polyol chemistry. Structurally analogous to methylenediphenyl diisocyanate (MDI), the monomer contains protected benzyl alcohols that, upon deprotection, undergo 6-exo-trig intramolecular cyclization to cleave adjacent carbamate bonds under ambient conditions. The protecting group strategy is modular, allowing degradation to be triggered under different conditions depending on the protecting group identity. Both the small-molecule cyclization product and oligourethane fragments can be recycled: the former is converted back to the specialized monomer, and the latter are repolymerized with MDI to regenerate cross-linked elastomers. The oligourethane can also be degraded enzymatically; variations of pH can influence relative amounts of linear and cyclized products under biologically relevant conditions.