High-temperature-resistant hybrid phthalonitrile resins with good processability

Phthalonitrile resins are ideal candidates for next-generation of high-temperature resin matrices due to their good thermo-oxidative stability, low moisture absorption, and high residual carbon rate, which arise from their unique molecular structure. However, processability and thermal resistance/mechanical properties at high temperatures are mutually exclusive. To solve this problem, a novel resin system (xSi2Pn + yBPn) through copolymerization of liquid silicon-modified liquid phthalonitrile (Si2Pn) and powder boron-modified phthalonitrile (BPn) monomers was developed. The mixtures of monomers exhibited adequate fluidity at 30 °C, and the hydroxyl group in BPn expedites the copolymerization reaction of cyan groups, thereby accelerating the curing reaction process and expanding the processing window from 79 °C to 110 °C, indicating good processability. Concurrently, the thermo-oxidative stability of xSi2Pn + yBPn surpassed that of the resins prepared from pure Si2Pn or BPn due to synergistic effect of B and Si. The optimized P–5Si2Pn+5BPn resin showed onset decomposition temperatures of 520.1 °C (Air) and 509.2 °C (Argon), which are 18.9 °C & 89.8 °C and 22.1 °C & 94.6 °C higher than those of BPn and Si2Pn resins. Furthermore, it demonstrates stable mechanical properties across broad temperature range, with storage moduli of 2481 MPa at 50 °C and 1095 MPa at 400 °C, making it a robust material for extreme thermal environments.