Catalyst-Free Covalent Adaptable Polyurethane Foams for Closed-Loop Recycling and Programmable Mechanical Performance

Thermoset flexible polyurethane foams (PUFs) are widely used in impact absorption and thermal insulation applications because of their low density, excellent energy dissipation, and insulating properties. However, their permanently crosslinked networks hinder recyclability, resulting in disposal through landfilling or incineration and raising sustainability concerns.

To address this limitation, a β-amino ester motif capable of inducing covalent adaptable network (CAN) behavior was incorporated into acrylate-functionalized polyols. The β-amino ester units act as internal catalytic motifs that promote dynamic bond exchange without requiring external catalysts, enabling simultaneous foaming, network rearrangement, and chemical recycling. As a result, the crosslinked PUFs can be depolymerized into reusable monomeric or oligomeric components, which were subsequently reused for foam fabrication, demonstrating the feasibility of closed-loop recycling.

In addition, residual acrylate functionalities provide reactive sites for dicumyl peroxide (DCP)-assisted thermal post-curing. Localized post-curing induces additional crosslinking in selected regions, generating a crosslink-density gradient within the foam structure. This gradient enables spatial control of mechanical properties, allowing selected regions to transition from compliant to rigid behavior. Such localized reinforcement promotes progressive deformation and stress dissipation, thereby enhancing energy absorption performance.

Overall, the acrylate-functionalized polyol platform combines CAN-enabled closed-loop recyclability with spatially programmable mechanical properties, providing a versatile strategy for sustainable and multifunctional thermoset polyurethane foams.