Thermal decomposition study of 5,5,5′,5′,5″,5″-hexamethyltris(1,3,2-dioxaphosphorinanemethan)amine 2,2′,2″-trioxide and its mixtures with melamine phosphate

This paper deals with the thermal decomposition behavior of 5,5,5′,5′,5″,5″-hexamethyltris(1,3,2-dioxaphosphorinanemethan)amine 2,2′,2″-trioxide (I), a fire retardant additive, and its mixtures with melamine phosphate. Under nitrogen, (I) exhibits melting followed by an exothermal weight loss process at 260–340 °C. Under air, the temperature of the weight loss process is lowered by about 30 °C. The main volatile pyrolysis products of (I) are 2-methyl-1,3-butadiene, 2-methylbutanal and 5,5-dimethyl-1,3,2-dioxaphosphorinane 2-oxide. Condensed phosphoric acids are accumulated in the solid pyrolysis products. Addition of melamine phosphate decreases the thermal stability of (I) causing its rapid dealkylation followed by the formation of melamine oligophosphates and decomposition of the symm-triazine ring. The structure of the charred products depends on the ratio of the initial components. The main products from pyrolysis of the (I) + melamine phosphate = 1:1 or 2:1 mixtures are cross-linked urea derivatives and imidophosphoric acids.