Synergistically Mediated Nitrile Curing Chemistry via Episulfide Ring-Opening Chemistry For High-Performance Polymer

Abstract Phthalonitrile (PN) resins have attracted considerable attention across diverse application fields owing to their outstanding thermal stability. However, their intrinsically high melting points and low curing reactivity have long hindered large-scale processing and practical implementation. In this work, a synergistic design strategy is proposed by blending an episulfide-containing resin (2,2-bis[4-(2,3-epithiopropoxy) phenyl]propane, DGTBA) with an allyl-functionalized phthalonitrile (4-(2-methoxy-4-allylphenoxy) phthalonitrile, EPN) matrix to simultaneously improve processability and curing activity. The equimolar blending system exhibits pronounced pseudo-eutectic characteristics, with a significantly reduced melting temperature of 76 °C and a broad low-viscosity processing window of approximately 175 °C. FTIR combined with 2DCS reveals that sulfur-centered active species generated from episulfide ring-opening can induce the synchronous addition of cyano and allyl groups, thereby accelerating the formation of a densely crosslinked network. Meanwhile, the cured resin demonstrates excellent thermal stability, with a glass transition temperature (Tg) of 351 °C and a char yield exceeding 68% at 800 °C under nitrogen. In addition, SEM observations revealed no obvious void defects on the fracture cross-section of the cured resin. Overall, this work provides a facile and effective strategy for the design of high-performance, readily processable phthalonitrile resins.