Functional Upcycling of Crosslinked Polyurethanes via Reactive Extrusion Decrosslinking through Catalyzed Carbamate Exchange*

The thermoset nature of many commercial polyurethanes (PUs) prohibit common melt reprocessing methodologies. Dynamic carbamate exchange catalyzed by reactive extrusion emerges as a novel reprocessing pathway for covalently crosslinked PUs, however, is confined to network-to-network reprocessing. The introduction of monofunctional urethanes (serving as end-capping reagents) into a model PU network effectively decreases crosslink density and eventually deconstructs the network into a solvent-soluble, highly branched PU oligomer. The small-molecule urethane loading dictates the final material structures after reactive extrusion, consistent with the Flory-Stockmayer gelation theory. In addition, synthesis of a library of small-molecule decrosslinkers with variable molecular weight, functionality, and aromaticity valorizes the robustness of the depolymerization process. Furthermore, functional end groups installed onto PU oligomers by the urethane decrosslinkers provides post-decrosslinking reactivity. Altogether, this work seeks to develop an effective catalytic reactive-extrusion mediated depolymerization process where the feedstock materials are crosslinked PU networks, low molecular weight urethane end capping agents, and catalysts. We then seek to propose the decrosslinking technique as a platform to reprocess other polymer networks synthesized by step-growth reactions, such as polyureas.