Bridging the Reactivity Discrepancy: Model Molecules vs. Polymers in Polyurethane Recycling

The prevailing approach to polymer recycling relies on small-molecule analogs to predict cleavage behavior, implicitly assuming that functional group reactivity translates directly from molecular to macromolecular systems. Here, we challenge this assumption by demonstrating diverged hydrolysis reactivities of carbamate and urea groups in polyurethanes from their small-molecule counterparts under Lewis acid-catalyzed, water-lean conditions. We trace this discrepancy to the distinct microenvironments surrounding each linkage within the polymer matrix: adjacent ether groups promote carbamate cleavage via a thermal decomposition pathway, while urea hydrolysis proceeds through a nucleophilic mechanism. The reactivity can be rationally regulated by Lewis acids and water-lean solvent selection. Furthermore, we uncover that the generated aniline can further react with carbamate groups to yield urea, while also coordinating with the Lewis acid catalyst, enabling its precipitation and thereby simplifying product separation. This fundamental understanding offers a new paradigm for chemical recycling that leverages the unique influence of the macromolecular microenvironment and enables the selective and efficient depolymerization of PUs.