Covalent Adaptable Polyester Networks Based on Citric Acid with Fast Dynamic Behaviors and Closed-Loop Recyclability

Most covalent adaptable networks (CANs) based on citric acid (CA) exhibit low thermostability, low glass-transition temperatures (T_g), and poor mechanical properties. Moreover, their slow relaxation rates necessitate prolonged reprocessing time, resulting in issues such as degradation or side-reactions. Herein, a bicyclic tetracarboxylate (DMTE) derived from CA was prepared. A series of polyester CANs were prepared via catalyst-free melt-polycondensation of DMTE, CA, and 1,6-hexanediol (HDO). To our delight, the highly rigid DMTE simultaneously improved the T_g values and mechanical properties of the CANs based on CA. Furthermore, benefiting from its dissociative transesterification reaction (TER), the introduction of DMTE significantly improved their relaxation rates. This allows their reprocessing time to be significantly shortened to merely 10 s at 180 °C, compared to the long reprocessing time needed for the CAN solely based on CA (30 min). Lastly, these materials can be closed-loop recycled by catalyst-free methanolysis to recover the initial monomers in high yields.