AbstractRigid thermosets show great potential application value in several fields; however, enhancing their extensibility without losing the required mechanical strength is always a huge challenge. In this work, a new class of rigid thermosets, poly(triethylenetetramine bisphenol A epoxy phenylimidazole)s, with both multiple supramolecular interactions, including “face–face” π–π stacking, “point–point” hydrogen bond, and ion‐pair electrostatic interaction, and covalent crosslinks is developed by introducing the special functional group 2‐phenylimidazole into the crosslinked thermoset. Owing to the synergistic effect of the strong covalent crosslinks and the multiple supramolecular interactions, synchronously improved tensile strengths and elongation at break have been successfully obtained with these rigid thermosets.