Catalyst-Free and Room-Temperature Synthesis of Reprocessable Nonisocyanate Polythiourethane Foams via Self-Induced Exothermic Aminolysis

Abstract

Conventional polyurethane foams rely on toxic isocyanates and energy-intensive processes, posing environmental and health concerns. Herein, we report a sustainable and catalyst-free strategy for the rapid synthesis of nonisocyanate polyurethane foams under ambient conditions. By integrating trimethylolpropane trithiocarbonate as a highly reactive monomer and citric acid (CA) as a multifunctional reactive foaming modifier, we achieved autonomous foaming within 2 min without external heating or toxic additives. Through a combination of Fourier transform infrared spectroscopy, rheology, thermogravimetric analysis, scanning electron microscopy, and dynamic mechanical analysis, we demonstrate that CA simultaneously enhances cross-linking, therebyincreasing the gel content to 88% and elevating T g from 7.2 °C to 35.9 °C, and activates NaHCO 3 via acid–base neutralization, reducing its decomposition temperature to 50 °C for controlled CO 2 release. The resulting foams exhibit a uniform cellular architecture (6.04 × 10 4 cells/cm 3 ), a high compressive modulus (3.58 MPa), and robust thermal stability. Furthermore, the dynamic thiocarbonate bonds facilitate closed-loop recyclability, enabling the reprocessing into dense films with enhanced mechanical properties. This work establishes a green and scalable pathway to high-performance recyclable polyurethanes, aligning with the principles of the circular polymer economy.