Rediscovering phthalonitrile resins: a novel liquid monomer towards high-performance resins

Abstract

The superior high-temperature resistance of phthalonitrile resins shows great application potential in extreme environments. However, the high rigidity and strong intermolecular force lead to a high melting point and harsh processing conditions. To improve the processability of phthalonitrile resins, Si–O–Si chain segments with long bond lengths and large bond angles were introduced, and a liquid phthalonitrile monomer was successfully prepared. The flexible segment effectively improved the processing performance of the monomer, which was characterized by a low melting point (−10.8 °C), low viscosity (∼4.3 Pa s at 30 °C), and good solubility in common solvents. The cured resin showed excellent thermal properties, credited to the high bond energy from Si–O bonds and the aromatic heterocyclic structures formed during curing. Moreover, the resin also demonstrated good flame retardancy without flame retardant additives, and low heat release capacity (32.7 J g⁻¹ K⁻¹), and passed the V-0 rate of the UL 94 test. This high-performance resin, integrating easy processing, high-temperature resistance, and flame retardancy, makes phthalonitrile a suitable resin to serve in harsh environments.