A new mending chemistry exhibiting stability at extreme temperatures and holding mechanical properties as well as mechanical stability comparable to widely used engineering plastics is reported here. This mendable thermoset polymer is synthesized using commodity reactants through the formation of an isocyanurate-oxazolidone network which exhibit a high service temperature as shown by their T-g of 270 degrees C and T-d of 365 degrees C. We demonstrate that this network polymer is repeatedly self-mendable in the presence of a macroscopic crack, yielding considerable recovery of the polymer's strength after thermal annealing. This self-mending behavior is derived from a high density of mechano-responsive isocyanurate rings which are introduced as cross-links in the network. After mechanically initiated cyclo-reversion, the recovery of isocyanurate rings in a solid state is thermally initiated. This research is the first demonstration of an isocyanurate ring as a repairing moiety. We developed a new class of intrinsic self-mendable polymers withstanding high temperatures, which will greatly impact the application of thermoset polymers in the field of structural laminates and electronics packaging. (C) 2017 Elsevier Ltd. All rights reserved.