Comparative Life Cycle Assessment of Recyclable Polyhydroxyurethanes Synthesized from Five- and Six-Membered Carbonates

Polyhydroxyurethanes (PHUs) synthesized from cyclic carbonates are promising alternatives to conventional polyurethanes due to their advantageous isocyanate-free synthesis and reprocessability characteristics. While many studies focus on PHUs derived from five-membered cyclic carbonates (5CCs) for more sustainable synthesis routes, PHUs from six-membered cyclic carbonates (6CCs) exhibit enhanced reactivity towards amines. Their reprocessability is facilitated by the presence of hydroxyl groups along the polymer chain, enabling transcarbamoylation reactions. However, since non-catalyzed transcarbamoylation is typically a sluggish reaction, catalysts are often required to enhance network reprocessability. This study presents a life cycle assessment (LCA) of PHU-5CC and PHU-6CC syntheses, with catalysts, for recycling applications targeting end-of-life scenarios. Environmental impact categories, including climate change, particulate matter, fossil resource depletion, mineral and metal resource use and freshwater eutrophication, were evaluated. Sensitivity analyses were also conducted to assess key variables. Our results indicate that PHUs from 6CCs show a higher environmental footprint due to their solvent-intensive synthesis process. Despite the increased reactivity and shorter reaction times associated with the 6CC monomer, these benefits do not fully offset the environmental impacts of the synthesis process. In conclusion, this study highlights potential improvements for future PHU synthesis, such as solvent-free processes, metal-free catalysts and optimized reaction monitoring.