Effect of Phosphate-Bridged Monomer on Thermal Oxidative Behavior of Phthalonitrile Thermosets

• Published in: Polymers 2024-08, Vol.16 (16), p.2239
• Main Authors: Lobanova, Marina Sergeevna, Babkin, Alexandr Vladimirovich, Kepman, Alexey Valeryevich, Avdeev, Victor Vasil'evich, Morozov, Oleg Sergeevich, Bulgakov, Boris Anatol'evich
• Format: Article
• Language: English
• Subjects: Aerospace engineering; Aging; Chemical tests; Crack propagation; Curing; Flame retardants; Flexural strength; Heat resistance; High temperature; Hydrocarbons; Mechanical engineering; Mechanical properties; Melt temperature; Monomers; Oxidation; Phosphorus; Polymers; Resins; Structural stability; Temperature; Thermal stability; Thermogravimetric analysis
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym16162239

Phthalonitrile thermosets are known for their excellent mechanical, physico-chemical, and fire-retardant properties, making them attractive for aerospace and mechanical engineering applications. When producing and applying phthalonitrile-based structural parts, it is essential to consider aspects such as processability and the long-term stability of the material's properties at high temperatures. In our previous studies, we demonstrated that resins containing phosphate-bridged bisphthalonitrile monomers are easily processable due to their low melting temperature and wide processing window. In this study, we investigated the impact of bis(3-(3,4-dicyanophenoxy)phenyl)phenyl phosphate (PPhPN) monomer content on physico-chemical and mechanical properties, thermal stability, and thermal oxidative stability. This research highlights the importance of conducting long-term thermal oxidative aging studies in addition to thermogravimetric analysis to properly assess the stability of thermosets. The findings indicate that adding less than 15% of PPhPN results in the formation of a crystalline phase, which impairs the resin's processability. Conversely, a high PPhPN content reduces the material's thermal oxidative stability. Therefore, based on mechanical and physico-chemical tests after thermal oxidative aging, it can be concluded that a 10-15% concentration of the phosphate-containing monomer enables easy processability of the phthalonitrile resin and provides excellent long-term thermal oxidative stability at temperatures up to 300 °C, while maintaining a flexural strength exceeding 120 MPa and an elasticity modulus of 4.3 GPa.