Cleavable Additives for Deconstructable, Recyclable Polyurethane Thermosets.

Polyurethane (PU) thermosets, particularly those derived from aliphatic components, are challenging to chemically deconstruct due to their permanent cross-linking. Current approaches to impart deconstructability typically rely on complete substitution of network precursors with cleavable analogs, limiting practicality. Cleavable additives (CAs) offer a potentially simple and cost-effective alternative, yet their application has been largely confined to chain-growth networks and remains unexplored in end-linked systems such as PUs. Here, we present a generalizable reverse gel-point theory that predicts the minimum CA loading required for deconstruction of end-linked networks. We validate this framework experimentally through the incorporation of two classes of silyl ether-based CAsbifunctional cleavable strands (BCSs) and trifunctional cleavable junctions (TCJs)into PU thermosets. Both additives enable selective PU dissolution at low loadings (5-12 wt %), with TCJs demonstrating enhanced efficiency. The combined use of BCSs and TCJs also allows fine-tuning of material properties. Furthermore, we show that polyol fragments generated from the deconstruction of TCJ-containing PUs can be chemically repolymerized to regenerate PU materials without loss of mechanical performance over multiple cycles. This work establishes CAs as a viable strategy for advancing PU circularity and offers a foundational framework for their broader application in end-linked polymer networks.