Y. Chen, Chang‐lin Wang, Özgün Dağlar, Ashok Ramakrishnan, Brahim Mezari, Pascal Vermeeren, Célia Fonseca Guerra, Fabian Eisenreich, Željko Tomović
Thermosets are made to last. Yet, this very durability creates significant challenges for responsible end-of-life management, rendering conventional recycling nearly impossible. Developing recyclable-by-design thermosets that can be selectively broken down through targeted chemical reactions offers a promising path forward but requires innovative chemistry. While most reported recyclable thermosets are optimized for a single end-of-life route (e.g., chemical depolymerization or reprocessing), achieving multiple distinct circularity pathways in one high-performance thermoset remains challenging. Here, we uncover that hexahydrotriazines─widely used as stable cross-linking units in thermosets─can undergo nucleophilic attack by amines and engage in metathesis reactions, unlocking new avenues for circular material design. Adopting a holistic approach, we first conduct detailed mechanistic studies to elucidate this previously unexplored reactivity, then apply these insights to polyhexahydrotriazine-based thermosets. We demonstrate a single material platform that uniquely combines closed-loop recycling, postsynthetic property reprogramming, repurposing into distinct material architectures, and thermal reprocessing. This multifold circularity introduces a flexible and adaptive strategy for thermoset recycling, addressing the increasing complexity of a circular economy.