N-Sulfonyl Guanidine Urea to Design Ultrastrong, Stable, and Recyclable Associative Dynamic Polyurea Networks

Dynamic covalent adaptive networks can solve the recycling issue of thermosets. However, dissociative dynamic covalent networks may suffer from instability and network incompleteness at high temperatures or in solvents. Here, we report a novel dynamic covalent bond, N-sulfonyl guanidine urea (SGUA), that can undergo catalyst-free metathesis reactions, in which a passivation strategy of increasing the dissociation temperature of guanidine urea by introducing electron-withdrawing N-sulfonyl groups into adjacent positions was developed. Unlike conventional dissociative dynamic urea bonds, SGUAs exhibit associative metathesis reactions at around 120–180 °C, with a high dissociation threshold of 180 °C. The dynamic covalent polyurea constructed by SGUAs, named PSGUAs, exhibits ultrastrong (Young's modulus exceeding 4 GPa and tensile strength exceeding 60 MPa) and stable (thermal stability, network structure integrity under reprocessing, and dimensional stability) performances. Furthermore, due to the excellent dynamic characteristics of SGUAs, PSGUAs were successfully reprocessed after 30–60 min of hot pressing at 160 °C and 20 MPa. Combining the long-lasting antibacterial properties of PSGUAs with long-term use, this study marks a substantial improvement in the field of dynamic polymer networks, giving a solution for balancing material stability, high performance, and reprocessability.