A Material Platform Based on Dissociative CO₂-Derived N,O-Acetals for Tunable Degradation of 3D Printable Materials

Modern-day thermosetting polymers should be designed with circular economy principles in mind, considering both their recyclability and end-of-life options. Covalent adaptable networks (CANs) have the potential to address the environmental challenges we face today as, in spite of being thermosets, they can be reprocessed by conventional thermoprocessing methods and are thus recyclable. While in the last years intensive efforts have been devoted to the preparation of CANs using sustainable sources, less attention has been paid to their end-of-life options in case they escape from plastic sorting. Herein, we report the development of a new type of dynamic bond, the N,O-acetal bond based on the coupling between CO₂-based oxazolidone moieties and abundant, potentially biobased polyols. Computational and kinetic studies revealed that this bond underwent rapid dissociative exchange and, crucially, was also susceptible to hydrolytic degradation. We then prepared a range of thermoset materials endowed by double end-of-life features, i.e., CAN behavior and hydrolytic degradation. This was achieved by radical thiol-ene photo-cross-linking of a diallyl monomer bearing the N,O-acetal moiety with another alkene-functionalized monomer that did not bear this dynamic bond. CANs with tunable mechanical properties and hydrolytic degradation features were easily obtained by modulating the monomer compositions. The fast-photocuring of the N,O-functionalized monomer was then exploited for producing three-dimensional (3D) printed objects, offering the potential for on-demand hydrolytic behavior.