Fluorine-containing phthalonitrile resin: Synthesis, curing behavior, and thermal properties

A novel fluorinated phthalonitrile monomer is synthesized via nucleophilic substitution reactions using 4,4′-difluorobenzophenone, bisphenol AF, and 4-nitrophthalimide. Two resins with distinct curing temperatures are obtained using 4-(aminophenoxy) benzonitrile (APPH) as the curing agent. The successful synthesis of the monomer is confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) is employed to determine the melting point and curing behavior of the monomer, revealing a melting point of 102°C and a calculated processing window of 148°C. Furthermore, a relatively low average apparent activation energy was calculated. The morphology of the polymer cross-section was characterized using scanning electron microscopy (SEM), and the resin cross-section exhibited characteristics consistent with brittle fracture. Thermodynamic properties of the polymers are investigated via dynamic mechanical analysis (DMA), revealing storage modulus of 2313 MPa and 2433 MPa for the two resins at room temperature. Thermal stability is evaluated by thermogravimetric analysis (TGA), revealing that both resins exhibited temperatures for 5% weight loss above 500°C under both nitrogen and air atmospheres.