Chemical and Physical Tailoring of Guanidine-based Covalent Adaptable Networks

We present the synthesis of two different guanidine-based CAN materials which, unlike traditional thermoset polymer networks, can undergo an exchange reaction called thermal guanidine metathesis (TGM) and be reprocessed. Thermosets, which are polymer networks characterized by permanent covalent crosslinks between chains, have a myriad of commercial applications. However, a major drawback to thermosets is their inability to be reprocessed. To develop a more sustainable thermoset-like material, CANs exhibit breaking and reforming of crosslinks under certain conditions that enable reprocessing. To elucidate the effects of varied guanidine structure on the rheological and mechanical properties of these dissociative CANs, we synthesized two guanidine-based CANs via reaction of a carbodiimide-containing polymer with two bifunctional amines. We found that the CAN with a more sterically congested guanidine was able to relax stress more quickly than the less sterically hindered CAN, supporting the influence of steric bulkiness on the kinetic and thermodynamic properties of the TGM reaction in guanidine-based CANs