Thermal Stability of Fire Retardants:* V. Decomposition of Haloalkyl Phosphates under Polyurethane Processing Conditions

The thermal decomposition of a series of commercial FR agents used in polyurethane was studied in dilute solution in bibenzyl at temperatures com monly found in the center of large, slab stock buns. At 216°C all of the haloalkyl phosphates containing the XCH₂CYHO- groups, where X is Cl or Br and Y is H or ClCH₂-, decomposed at similar rates, i.e., they all gave first order rate constants between 1.0 and 5.8 x 10 ^-4 min^-1. The addition of toluene diamine to the solution increased the rate of acid evolution from the reacting mixture by a factor of at least ten and in one case by a factor of sixty. The amine is postulated to attack the C-X bond to produce a secondary amine hydrohalide salt which releases hydrogen halide at elevated temperatures.

Pentabromodiphenyl oxide was found to be stable under both sets of condi tions. Tris (2,3-dibromopropyl) phosphate, in contrast, undergoes decomposition via a free radical mechanism similar to that of vicinal dibromoalkanes.

Tribromoneopentyl phosphate was stable at 216°C, though it decomposed slowly at 234 °C. In the presence of the amine, TBNPP decomposed with the liberation of tribromoneopentyl alcohol and minor amounts of HBr.