Thermally stable hybrid foams based on cyclophosphazenes and polyurethanes

Two cyclotriphosphazenes, containing OH groups, have been synthesized: hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene (PN6), with six hydroxyl groups, and 2,2-di-[p-(hydroxymethyl)phenoxy]-4,4,6,6,-bis[spiro(2',2" -dioxy-1',1"-biphenyl)cyclotriphosphazene (PN2) with two hydroxyl groups. They were used in the preparation of modified rigid polyurethane foams as OH containing compounds, alone or in mixtures with polyol components. The thermal stabilities of the resultant hybrid foams were analysed using thermogravimetric analysis (TGA), in inert (nitrogen) and oxidizing (air) atmosphere. The fire behaviour has been investigated by means of oxygen index (LOI) tests. The results showed that the introduction of increasing amount of cyclotriphosphazene in foams leads to a significant improvement of the thermal stability, both in nitrogen and in air. Improvement has also been observed in the fire behaviour of modified foams, particularly for the foams containing cyclotriphosphazene PN2.