Depolymerization of Polyurethanes and Recovery of Isocyanates to Aid Plastic Circularity

Polyurethanes are a ubiquitous group of polymers used in a myriad of applications, including foams, coatings, and textiles; however, their versatility leads to a large amount of polyurethane waste with diverse chemical structures, resulting in challenges with end-of-life recycling. Polyurethanes are composed of polyols, isocyanates, and chain extenders, and current polyurethane recycling methods focus on polyol/chain extender recovery with some efforts aimed at recovering amines from the isocyanate component – yet, there have been no significant steps towards the recovery of isocyanates directly, limiting the overall circularity of polyurethane materials. This work demonstrates a first-of-its-kind depolymerization approach that enables nearly quantitative recovery of isocyanates from laboratory-made and commercially sourced polyurethanes, both thermoplastics and thermosets, using an organoboron Lewis acid under mild conditions (60-80 °C, toluene or tetrahydrofuran, ambient pressure). The recovered isocyanates were used to prepare second-generation polyurethanes that exhibited molecular weights and thermal properties similar to virgin material. Additionally, the impact of polymer additives (e.g., antioxidants, dyes) was explored. Overall, this work demonstrates a significant advancement toward complete circularity of polyurethanes and could mitigate the need for the production of new polyurethane precursors (i.e., new isocyanates using phosgene-intensive routes) that are toxic and harmful to the environment.