Activation Energies of Phthalonitrile Resins Using Sulfur- and Oxygen-Based Curing Agents

High-performance polymers characterized by their exceptional thermal stability are crucial across various industries. Here, phthalonitrile resins have attracted significant attention due to their ability to form highly cross-linked networks upon curing, leading to outstanding properties suitable for demanding applications in aerospace, electronics, and automotive sectors. This study investigated the thermal curing kinetics and resulting thermal stability of phthalonitrile resins cured with 4,4'-diaminodiphenyl sulfone (DDS) and bisphenol A diglycidyl ether (DGEBA). Kissinger and Friedman methods were employed to analyze the curing process using thermogravimetric analysis data at various heating rates. The results revealed that DGEBA-cured networks exhibited higher thermal stability and activation energy compared to DDS-cured networks. This was attributed to the stronger C–O bonds formed in DGEBA networks. The higher bond dissociation energy of C–O bonds, arising from factors including electronegativity difference, bond length, orbital overlap, and hybridization necessitates a greater energy input for bond cleavage during thermal degradation. These findings highlight the critical role of curing agent selection in tailoring the thermal properties of phthalonitrile-based materials for high-performance applications.