Achieving rapid foaming in self-blown non-isocyanate polyurethane foams via controlled epoxy functionality in cyclic carbonates

Abstract

Non-isocyanate polyurethane (NIPU) foams present a safer and more environmentally friendly alternative to conventional polyurethane (PU) foams, which rely on toxic, petrochemical-based isocyanates. Efficient in-situ CO₂ generation, achieved through the simultaneous aminolysis and hydrolysis of cyclic carbonates, enables replication of traditional PU foaming processes. This study provides the first systematic investigation of the effect of aromatic and aliphatic epoxy functionalities on these reactions and their quantitative correlation with the self-blowing behavior of NIPU foams. Detailed kinetic analysis of model monomers showed significant differences in activation energy, with aromatic systems exhibiting lower activation energy, leading to faster reaction rates, while aliphatic systems had higher activation energy, indicating slower curing. These differences in reactivity were later revealed in the foaming process, where the aromatic groups contributed to rapid foam formation and improved thermal stability, with a glass transition temperature (T_g) of 60 °C. Conversely, aliphatic substituents provided greater material flexibility but revealed a critical threshold, leading to unsuccessful foaming when their content exceeded 30 %, due to slower reaction kinetics. By integrating kinetic data with foaming behavior, we demonstrate that balancing aromatic and aliphatic functionalities enables precise control over foam properties, including T_g, density, and mechanical performance. This work provides new insights into tailoring NIPU foams through epoxy functionality, advancing their potential for sustainable industrial applications.