Polyurethane depolymerization by dialkyl carbonates: toward sustainable chemical recycling

Abstract

Polyurethane foams (PUFs), a major component of common consumer products such as mattresses, generally end up in landfills because they cannot be properly recycled. As thermoset, PUFs cannot be remolten to new products either. As condensation polymer, they can be depolymerized to recover one monomer, the polyol, but generally not the diisocyanate co-monomer without using phosgene, a toxic and wasteful reagent. We show here the possibility to depolymerize PUF in a way that enables a harmless, waste-free and phosgene-free recovery of both diisocyanate and polyol. Accordingly, the PUF is depolymerized with a dialkyl carbonate – providing carbonyl exchange at low concentrations of nucleophile – to deliver a carbonated polyol with 90% yield and aromatic dicarbamates with 70% yield under non-optimized conditions. These precursors are known to be converted to the original polyols and diisocyanates at high yield by alcoholysis and pyrolysis, respectively. We present advanced analytical methods to characterize and quantify the depolymerization products. We also report model reactions to show that the depolymerization proceeds through a thermodynamic equilibration of carbonates, carbamates and ureas.