Synthesis of Phosphazene-Containing, Bisphenol A-Based Benzoxazines and Properties of Corresponding Polybenzoxazines

Abstract

With the aim of obtaining halogen-free polybenzoxazazines with reduced flammability, phosphazene-containing benzoxazines (PhBZ) were synthesized in a two-stage method. In the first stage of the reaction of hexachlorocycotriphosphazene with bisphenol A at molar ratios of 1:12, 1:16, and 1:24, respectively, mixtures of bisphenol and hydroxyaryloxycyclotriphosphazenes were obtained, which mainly contained P3N3[OC6H4C(CH3)3C6H4OH]6. In the second stage, when these mixtures interacted with aniline and an excess of paraformaldehyde in toluene at 80–90 °C, PhBZ containing 20–50% of the phosphazene component with Mw 1200–5800 were formed. According to 1H and 13C NMR spectroscopy, PhBZ contain a small amount of oligomeric compounds with Mannich aminomethylene bridges. With an increase of the content of the phosphazene component, the curing temperature of PhBZ decreases from 242 °C to 215 °C. Cured PhBZ samples with a phosphorus content of more than 1.5% have increased flammability resistance according to UL-94.