Depolymerization of Polyurethanes via Imidazolysis: A Chemical Recycling Approach to Recover Polyols and Imidazole-Carboxamides

Polyurethane (PU) materials are the most common form of thermoset polymers and also comprise a major source of waste at the end of their useful lives. There are limited and generally low-value opportunities to recycle PU foams (e.g., carpet underlayment). However, the ability of PU to be chemically depolymerized using water, alcohols, or amines to obtain polyols and analogues of the parent isocyanate has motivated significant efforts toward realizing circularity within PU. Previously, we showed that imidazole could depolymerize esters, specifically poly(ethylene terephthalate) (PET), and in this work, we demonstrate imidazolysis for the depolymerization of urethane linkages found in PU materials and small molecule model compounds, yielding alcohols and imidazole carboxamide molecules. Although imidazole is capable of depolymerizing PU without any additional catalysts, the introduction of triazobicyclodecene (TBD) as an organocatalyst improves the depolymerization rate upon heating. This study shows that imidazolysis of PU materials is a promising and scalable technique that benefits from straightforward processing and relatively mild reaction conditions.