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.