Spiro-cyclotriphosphazene with three functional end groups: Synthesis and structural characterization of new polycyclotriphosphazenes with Schiff-base groups

Abstract

A new tris-spiro-(3, 4-dioxybenzaldehyde)cyclotriphosphazene [PNCHO] was synthesized from the condensation of hexachlorocyclotriphosphazene with 3, 4-dihydroxybenzaldehyde in the presence of strong base. Further reaction of the trialdehydic cyclotriphosphazene based molecules [PNCHO] with three different dianilines (benzidine, 4, 4'-methylenedianiline and 4, 4'-Sulfonyldianiline) resulted in creation of a new poly(tris-spiro-3, 4-dioxbenzene)cyclotriphosphazenes with Schiff-base groups [PNSB1-3]. The structures of [PNCHO] and the polycyclotriphosphazenes-schiff base derivatives were characterized by means of FTIR, 1H, 13C NMR and C.H.N elemental analysis. Differential scanning calorimetery (DSC) revealed a relatively high glass transition temperature (135-175°C) of obtained polymers. Thermal gravimetric analysis (TGA) exhibited their good thermal stability (up to 375°C). The char yield was about 36-42% at 700°C. All polymers were self-extinguishable as the LOI (Limiting Oxygen Index) values were above 26% and this meets with the V-0 and V-1, classification (UL-94). No fumes, soot, or toxic gases emission were observed during burning. The polymers obtained can be used as environmentally friendly, flame-retardant materials.