Thermal decomposition study of 1,4-diisobutyl-2,3,5,6-tetrahydroxy-1,4-diphosphorinane 1,4-dioxide

The thermal decomposition behavior of 1,4-diisobutyl-2,3,5,6-tetrahydroxy-1,4-diphosphorinane 1,4-dioxide (Cyagard), a fire retardant additive, was studied by thermogravimetry, differential scanning calorimetry, FT-IR and GC/MS. Cyagard decomposes vigorously exhibiting a strong sharp-exothermic effect. This effect is caused by a phosphine oxide → phosphinate → phosphonate rearrangement. The created POC ester bonds further degrade to form acidic POH and ketone PCOCH3 bonds. The scission of the PC bond yields acetaldehyde which evolves in the gas phase. In high boiling decomposition products, diphosphine dioxides, as well as species containing acidic POH and ester POC bonds are detected.