Controlled Cationic Ring-Opening Polymerization Enables Chemically Recyclable Polyacetal-Based Polyurethanes.

The pursuit of a sustainable, circular polyurethane (PU) economy has created a pressing need to develop chemically recyclable polyols capable of reconciling the inherent conflicts between the performance requirements during and after their life span. Polyacetal polyols offer a promising candidate for this purpose; however, their widespread adoption in PUs manufacturing has been persistently hindered by challenges in precision synthesis. Here, we demonstrate a highly efficient anion-binding catalytic polymerization (ABCP) strategy for reversible-deactivation cationic ring-opening polymerization of cyclic acetals, using a selenocyclodiphosph(V)azane catalyst and a trimethylsilyl iodide initiator. This approach enables the long-sought precision synthesis of poly(1,3-dioxepane) (PDXP) diol-a representative polyacetal polyol-on the kilogram scale, with no detectable cyclic side-products. This chemistry further enables the utilization of hydroxyl-telechelic PDXP as an alternative to poly(tetramethylene ether glycol) diol in the preparation of both thermoplastic PUs and flexible foams. The resulting materials exhibit excellent mechanical properties and processability comparable to those of commercial polyether-based PUs, while the PDXP soft segments in representative thermoplastic PU and crosslinked flexible foam can be depolymerized to regenerate 1,3-dioxepane, and the hard-segment-enriched residue can be converted to 4,4'-diaminodiphenylmethane, thereby demonstrating closed-loop recycling of the PDXP soft segment together with chemical valorization of the hard-segment-derived fraction.