Diketoenamine-Based Vitrimers via Thiol-ene Photopolymerization

Likened to both thermosets and thermoplastics, vitrimers are a unique class of materials that combine remarkable stability, healability, and reprocessability. Herein, this work describes a photopolymerized thiol-ene-based vitrimer that undergoes dynamic covalent exchanges through uncatalyzed transamination of enamines derived from cyclic beta-triketones, whereby the low energy barrier for exchange facilitates reprocessing and enables rapid depolymerization. Accordingly, an alkene-functionalized beta-triketone, 5,5-dimethyl-2-(pent-4-enoyl)cyclohexane-1,3-dione, is devised which is then reacted with 1,6-diaminohexane in a stoichiometrically imbalanced fashion (approximate to 1:0.85 primary amine:triketone). The resulting networks exhibit subambient glass transition temperature (T-g = 5.66 degrees C) by differential scanning calorimetry. Using a Maxwell stress-relaxation fit, the topology-freezing temperature (T-v) is calculated to be -32 degrees C. Small-amplitude oscillatory shear rheological analysis enables to identify a practical critical temperature above which the vitrimer can be successfully reprocessed (T-v,T-eff). Via the introduction of excess primary amines, this work can readily degrade the networks into monomeric precursors, which are in turn reacted with diamines to regenerate reprocessable networks. Photopolymerization provides unique spatiotemporal control over the network topology, thereby opening the path for further investigation of vitrimer properties. As such, this work expands the toolbox of chemical upcycling of networks and enables their wider implementation.