(385an) Functional Upcycling of Polyurethane Thermosets into Value-Added Thermoplastics Via Small-Molecule Carbamate-Assisted Decrosslinking Extrusion

Polyurethanes (PUs) deliver exceptional, versatile properties and find a home in most aerospace, insulation, and comfort applications. The thermoset nature of many commercial PUs, however, prohibit common melt reprocessing methodologies. Kinetic and thermodynamic limitations fundamental to the urethane linkage hinder the wholesale recovery of viable PU monomers from solvolytic depolymerization processes. Dynamic carbamate exchange empowered by reactive extrusion emerges as a novel reprocessing methodology to transform PU thermosets into reprocessable covalent adaptable networks (CANs). This approach, however, has been limited to thermoset-to-thermoset reprocessing, which requires high reaction temperatures due to their well preserved, viscous network structure. This study reports the development of a reactive extrusion decrosslinking process which converts PU networks into thermoplastics in a rapid, solvent-free manner. Low molecular weight, carbamate-functionalized small molecules simultaneously decrosslink the PU network while functionalizing the thermoplastic in the melt state. Amendable to both crosslinked PU films and foams, the process is generalizable towards multiple photoactive functionalities, with chain-end functionalization confirmed by analyzing purified extrudates after dialysis. We seek to propose the decrosslinking technique as a platform to transform crosslinked PU waste into a library of thermoplastic PUs for diverse applications, such as adhesives, photoresins, and stimuli-responsive materials. Altogether, this process represents a powerful reaction extrusion mediated decrosslinking methodology applicable towards other commercial thermosets capable of dynamic exchange reactions, such as polyurea and polyester networks.