Mechanics of vitrimer with hybrid networks

Vitrimer has recently emerged as a polymer combining great processability, self-healing capability and hightemperature mechanical properties. Most of those salient features of a vitrimer originate from the existence of dynamic covalent bonds in the polymer network. To further adjust the mechanical behaviors of vitrimer, regular covalent bonds have been mixed with dynamic covalent bonds to create a hybrid network. Percolation theory predicts that, if regular covalent bonds and dynamic covalent bonds are homogenously mixed, a high molar ratio of dynamic covalent bonds is needed to maintain the self-healing and reprocessing capabilities of the material. Herein, we experimentally show that, if the network with only regular covalent bonds and the network with dynamic covalent bonds are immiscible with each other, hybrid network can be synthesized with a low molar ratio of dynamic covalent bonds (less than 20 mol%), which still maintains its reprocessing and self-healing capabilities. Our discoveries will enable much greater tunability of the thermo-mechanical properties of vitrimers such as stress relaxation, creep resistance and fracture toughness, which can be important in many of their applications.