Thermal properties of phthalonitrile functional polybenzoxazines

Phthalonitrile functional polybenzoxazines show high thermal stability with temperature at 5% weight loss (T5%) up to 450°C for monofunctional benzoxazine-based polymers, and up to 550°C for polymers from the bifunctional precursors. High char yield up to 80% by weight is obtained by thermogravimetric analysis in an inert atmosphere at 800°C. Char yield up to 70% by weight at 600°C is achieved in air with T5% in the 380–420°C range. Differential scanning calorimetry (DSC) is used to determine curing conditions. These resins do not require ultrahigh curing temperature as it is typical for the other phthalonitrile functional prepolymers and 250°C is used as a maximum post-cure temperature to achieve desired properties. Dynamic mechanical analysis (DMA) reveals unusually broad dependence of loss modulus vs. temperature with the maximum at 300°C for polybenzoxazines from bifunctional precursors and 278°C for polymer from monofunctional precursors. Additionally, these materials exhibit low flammability.