AbstractA promising high temperature phthalonitrile (PN) resin composed of a polyetherketoneketone (PEKK) core bridged by two bisphenol A linkers and end capped with PN groups is presented. This PEKK‐PN resin was characterized via differential scanning calorimetry, thermogravimetric analysis, proton nuclear magnetic resonance spectroscopy, scanning electron microscopy, dynamic mechanical analysis, attenuated total reflection Fourier transform infrared, and rheometry. The PEKK‐PN resin was evaluated with two different compositions containing 1) 70:30 PEKK‐PN to bisphenol A PN (n = 0) and 2) pure PEKK‐PN. The 70:30 PEKK‐PN resin was mixed with bis[4‐(3‐aminophenoxy)phenyl]sulfone and exhibited a melt viscosity of 271 cP, much lower than the 657 cP viscosity of the pure PEKK‐PN mixture. Void‐free PEKK‐PN polymers were easily prepared by degassing and curing up to 380°C, resulting in fully crosslinked networks exhibiting thermal stability above 500°C and a 75% char yield. Additionally, the cured PEKK‐PN polymer samples displayed good mechanical integrity retaining 50% stiffness at 300°C. This combination of properties suggests these new PEKK‐PN resins are excellent materials for high temperature thermosets in composite applications.