Recyclable Poly(urethane-urea) Covalent Adaptable Network Foams via Catalyst-, Isocyanate-, and Additive-Free Synthesis

Abstract

For decades, poly(urethane-urea) (PUU) foam production has relied on hazardous isocyanates and a complex array of external catalysts and blowing agents, resulting in chemically persistent materials that defy recycling. Herein, we break this convention by reporting the first-ever synthesis of high-performance PUU foams through an entirely autonomous, isocyanate-free, and additive-free pathway. By leveraging the ring-opening of thiazolidin-2-one with multifunctional amines, we establish a streamlined reaction that simultaneously constructs a covalent adaptable network (CAN) and triggers in situ CO₂ evolution. This chemistry bypasses traditional reagents; instead, internal thiol groups react with ethylene carbonate to drive foaming under entirely catalyst-free conditions. By precisely tuning the tris(2-aminoethyl)amine ratio, we synchronize gas expansion with matrix vitrification, overcoming the structural collapse typical of nontraditional systems. The resulting foams feature hindered urea linkages that impart dissociative CAN behavior, enabling full chemical reprocessability and structural recovery over multiple cycles without compromising mechanical integrity. With an open-cell architecture and acoustic performance comparable to those of the tested commercial reference materials under the present measurement conditions, this work provides a promising strategy for designing circular cellular materials that contribute to a zero-waste chemical economy.