Novel liquid phthalonitrile monomers towards high performance resin

[Display omitted] •Phthalonitrile monomer with melting point below room temperature was reported.•The harsh processing conditions of phthalonitrile resins were improved.•Liquid monomer functioned as solvent for high melting phthalonitrile monomers.•Enable the processing of high melting monomers at room temperature. Phthalonitrile resins are one of the high temperature resistant polymers which can be potentially used for harsh environments in both military and domestic fields. The high melting points of the monomers led to short processing windows and made processing procedure challenging and energy intensive. To solve this problem, liquid phthalonitrile monomers containing flexible siloxane segments were designed and synthesized. The long bond length and large bond angle of Si-O-Si chain segments introduced flexibility into the monomers and effectively reduced the melting point to −35.9 °C. Meanwhile, the high bond energy preserved the thermal stability of the resulting cured resin. The high fluidity (viscosity of ∼ 2 Pa·s at 30 °C) allows the monomers to be processed at room temperature without additional heating. In addition, the monomers can be dissolved in common organic solvents, such as ethyl acetate and ethanol. The resins cured at 250 °C demonstrated good thermal and thermal oxygen stability. The weight loss of 5 % in argon and air at temperatures of 428.6 °C and 434.9 °C, respectively. Furthermore, blending this liquid monomer blended with powdered monomers improved both the processibility of the high melting monomers and the overall temperature resistance of the cured resin. The resin showed a weight loss of 5 % in argon and air of 534.4 °C and 532.3 °C, respectively.