Advancing Non-isocyanate Polyurethane Foams: exo-Vinylene Cyclic Carbonate–Amine Chemistry Enabling Room-Temperature Reactivity and Fast Self-Blowing

Abstract

Though widely used, polyurethane foams raise health concerns stemming from their isocyanate precursors. Nonisocyanate polyurethane foams (NIPUFs), synthesized by aminolysis of 5-membered cyclic carbonates, represent safer and more sustainable alternatives. Despite their potential, achieving efficient self-blowing NIPUFs from room temperature (RT) formulations has proven highly challenging, as previous methods rely on external heat sources, prolonged reaction times, or are based on hybrid formulations involving epoxides. In this study, we demonstrate a new concept that makes rapid the production of full NIPUFs (i.e., with exclusive urethane linkages) from RT solvent-free formulations through the incorporation of exovinylene cyclic carbonate (αCC). This approach incorporated hydroxyoxazolidone groups, i.e., cyclic hydroxyurethanes, as pendant groups of the polyhydroxyurethane backbone. We investigated the reactions occurring in this foaming system and identified optimal foaming formulations to rapidly produce the foams within 1–5 min, with a high gel content. The study explored monomer variations as amine mixtures and different αCCs. Compression tests revealed that the foam’s mechanical properties were easily tuned by adapting the formulation composition, giving access to both flexible and rigid foams with pore sizes in the range of conventional PU foams. Moreover, we highlighted the importance of the hydrophilic nature of NIPUFs on their mechanical properties, with a decrease in the Young’s modulus when exposed to increased humidity contents. While these foams, like many NIPUs, exhibit inherent hydrophilicity, this limitation may be addressed through additives or future formulation optimization. Our new concept paves the way for the rapid preparation of the next generation of full isocyanate-free polyurethane foams with modular properties.