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

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.