The decomposition kinetics of hexabromocyclododecane (HBCD), a flame retardant used in foamed polystyrene, were studied by monitoring the rate of HBr formed at temperatures between 180-240°C. Samples from five suppliers, and from two lots from three of the suppliers, were evaluated. There were significant differences in the decomposition rates, which appeared to be related to the finishing end of the manufacturing process.Samples showing the highest levels of labile bromine containing compounds (probably allylic bromides), as indicated by reactivity towards the silver nitrate, also showed the greatest rates of decomposition.

The thermal decomposition of a series of commercial FR agents used in polyurethane was studied in dilute solution in bibenzyl at temperatures commonly found in the center of large, slab stock buns. At 216°C all of the haloalkyl phosphates containing the XCH 2 CYHOgroups, where X is Cl or Br and Y is H or ClCH 2 -, 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 conditions. Tris (2,3-dibromopropyl) phosphate, in contrast, undergoes decomposition via a free radical mechanism similar to that of vicinal dibromoalkanes.

The thermal decomposition kinetics of several aliphatic FR agents contain ing vicinal bromines were studied under temperature conditions, i.e., 200-226 °C., commonly found in extruders. The reactions were monitored by the rate of HBr evolution and by the formation of trans-stilbene in dilute (1.8-10 wt.% agent) bibenzyl solutions. The measured reaction rate constants ( kHBr) were found to include a free radical component ( kHBr1) and an ionic com ponent ( kHBr2) resulting from the homolytic cleavage of a carbon-bromine bond and from an iron or zinc induced reaction, respectively. Of the primary agents used in polystyrene, pentabromochlorocyclohexane was found to decompose at about three times the rate of hexabromocyclodo decane at any given temperature.

Thermal decomposition kinetics were determined for several brominated phenyl allyl ethers, for several brominated diphenyl oxides, and for several miscellaneous compounds used in the manufacture of fire retardant thermo plastics. The decompositions were carried out using bibenzyl as a model for the polystyrene system and at agent loadings of 10 wt.%. The diphenyl oxide deriv atives were stable at reaction temperature (234 ° C) having reaction rate con stants of < 5 x 10-6 min-1. The phenyl allyl ethers underwent rapid decomposi tions with rate constants of 3 to 4 x 102 min 1. The reaction of these ethers is primarily free radical in nature and generates radicals via the homolytic cleavage of the ether linkage.

The kinetics of the thermal decomposition of pentabromochlorocyclohexane (PBCCH), a flame retardant employed in foamed polystyrene, were determined by monitoring the rate of HBr/Br 2 evolution at temperatures between 195-240°C. The early stage of the decomposition is catalyzed by iron. The acti vation energy for the initial decomposition is approximately 32 Kcal/mole. The principle organic decomposition products are dibromo-, bromochloro-, and tri halobenzenes.