Phosphazene-triazine cyclomatrix network polymers: some aspects of synthesis, thermal- and flame-retardant characteristics

Hydroxy phenyl-substituted cyclotriphosphazenes were synthesized by reacting hexachlorocyclotriphosphazene with sodium phenolate and monosodium bisphenolate. The derivatives, consisting of a mixture of multi-substituted and partly chain-extended cyclophosphazenes, with overall functionality close to the targeted values, were transformed into the cyanatophenyl derivative. Thermal curing of the latter gave phosphazene–triazine cyclomatrix network polymers with varying ratios of phosphazene and triazine rings in the matrix. Although they manifested diminished Tg, the cured polymers were more thermally stable and provided higher char residue in comparison to the polycyanurate derived from bisphenol-A dicyanate. The activation energies for thermal decomposition of the cyclomatrix networks increased with both phosphazene content and crosslink density, and showed a direct relationship with their thermal stability. The presence of phosphazene was conducive for enhancing the flame retardancy of the network. The flame retardancy improved with increase in crosslink density and char-yielding property of the polymer, which implied that the flame-retardant action was operative in the condensed phase.