Polyurethane Depolymerization With Alkyl, Aryl, and Mixed Carbonates
Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine
Chemical recycling of polyurethane foams (PUFs) remains challenging due to their crosslinked structure. Depolymerization with organic carbonates offers a phosgene‐free route to recover both polyols and aromatic monomers through carbonate‐mediated carbonyl exchange. Here, we evaluate the reactivity of a series of carbonates, including dimethyl carbonate (DMC), diphenyl carbonate (DPC), methyl phenyl carbonate (MPC), and mixed DMC/DPC, in the depolymerization of TDI‐based flexible PUF (190°C, 4 h, with Zn(OAc)as a catalyst). DPC promotes equilibration between urea and carbamate species but generates side products resulting in lower selectivity. MPC behaves similarly to the DMC/DPC mixture, resulting in the formation of mixed carbamate species, thus confirming carbonyl exchange as the underlying mechanism. In contrast, DMC yields cleaner products but suffers from limited dissolution of the aromatic hard blocks at lower temperatures. Using anisole as a cosolvent resolves this limitation, enhancing the accessibility of the hard domains, resulting in the recovery of 85% of methyl‐functionalized toluene dicarbamate (Me‐TDC) and of 95% of the polyol. Additionally, DMC also allows easy product separation. Overall, this study clarifies how carbonate structure affects depolymerization pathways, side‐product formation, and hard‐domain accessibility providing selective and phosgene‐free chemical recycling strategies for PUFs. The depolymerization of polyurethane foams strongly depends on
Abstract
Chemical recycling of polyurethane foams (PUFs) remains challenging due to their crosslinked structure. Depolymerization with organic carbonates offers a phosgene‐free route to recover both polyols and aromatic monomers through carbonate‐mediated carbonyl exchange. Here, we evaluate the reactivity of a series of carbonates, including dimethyl carbonate (DMC), diphenyl carbonate (DPC), methyl phenyl carbonate (MPC), and mixed DMC/DPC, in the depolymerization of TDI‐based flexible PUF (190°C, 4 h, with Zn(OAc)as a catalyst). DPC promotes equilibration between urea and carbamate species but generates side products resulting in lower selectivity. MPC behaves similarly to the DMC/DPC mixture, resulting in the formation of mixed carbamate species, thus confirming carbonyl exchange as the underlying mechanism. In contrast, DMC yields cleaner products but suffers from limited dissolution of the aromatic hard blocks at lower temperatures. Using anisole as a cosolvent resolves this limitation, enhancing the accessibility of the hard domains, resulting in the recovery of 85% of methyl‐functionalized toluene dicarbamate (Me‐TDC) and of 95% of the polyol. Additionally, DMC also allows easy product separation. Overall, this study clarifies how carbonate structure affects depolymerization pathways, side‐product formation, and hard‐domain accessibility providing selective and phosgene‐free chemical recycling strategies for PUFs. The depolymerization of polyurethane foams strongly depends on carbonate structure. Aryl carbonates improve hard‐segment solubility but generate side products. Alkyl carbonates give cleaner products yet suffer from limited hard‐block solubility and require anisole as a cosolvent. Mixed carbonate systems balance these effects, improving solubility while reducing side products. The methyl carbonate system also shows favorable phase separation, facilitating product work‐up. graphical