Synthesis and properties of the optical resin composed of cyclotriphosphazenes

Cyclomatrix polyphosphazenes attract more and more interest because they possess thermal stability and halogen-free flame retardant property. The hexa(Allyl 4-hydroxybenzoate)cyclotriphosphazene is synthesized using hexachlorocyclotriphosphazene (HCTP), 4-hydroxybenzoic acid and allyl alcohol, its structure is confirmed by FTIR, ¹H NMR, ¹³C NMR, ³¹P NMR and mass spectrometer. Through radical homopolymerization of itself and copolymerization with methyl methacrylate (MMA), a series of optical resins containing cyclotriphosphazene units are obtained. The refractive indices, the visible light transmittance, the density, the water absorption, the thermal and flame-retardant characteristic of the cured resins are studied. Among the tested cured resins, the cyclomatrix homopolymer has the highest refractive index (n _d = 1.596), the highest thermal stability (starting decomposed at 337 °C) and the best halogen-free flame-retardant characteristic (limited oxygen index is 34.33% via the 40.03% char yield data at 850 °C by the semi-empirical formula).