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synopsisThe role of mixtures of reactive bromine and phosphorus flameretardant polyol intermediates as well as the individual bromine and phosphorus reagents in suppressing combustion of flexible polyurethane foams was investigated by means of the oxygen index flame test and charring techniques. Bromine alone appears to contribute to flame retardancy in the solid as well as the vapor phase. A substantid portion of the bromine from both aliphatic and aromatic bromide flame retardants w q accounted for in the char, and this is also true when phosphorus is preseqt. Ionic bromine appears to be the most effective elemental form. Like phosphorus, bromine alone in foams is also observed to increase the yield of char. Aliphatic bromide in mixture with phosphonate or phosphate gave enhanced flame retardancy, whereas, mixtures with phosphite are not beneficial. Maximum flame retardancy and char yields correlate well for bromine mixed with phosphate and phosphonate, whereas' the relationship does not hold with phosphites. Charring experiments at 500°C with foams containing both phosphorus and bromine generdy afforded a constant P/Br ratio, suggesting a specific chemical interaction for flame retardancy. Phosphate flame-retardant efficiency was sensitive to concentration of phosphorus in the foams. On the other hand, phosphonate and phosphite exhibited a constant level of fire resistance at phosphorus levels greater than 0.3%.

synopsisA chemical model is outlined which gives a simple description of flameretardant &-ciency of organic bromides in flexible polyurethane foam systems. The mechanism suggests dehydrobromination by an interplay of S N~ and SN2 reactions in intramolecular and intermolecular processes. Evidence is presented to demonstrate that flameretardant efficiency is directly related to the facility of dehydrohalogenation by an intramolecular process in which cyclic urethanes (five to ten membered rings) are formed by either S N~ and/or sN2 reactions. The requirement for a nucleophile, such as carbamate nitrogen, in halogen systems is suggested. In other mechanistic aspects, it was shown that flame retardancy passes through a maximum as a function of bromide content in the foam. It is believed that this behavior reflects certain undefined combustion aspects in the solid phase. It is also shown that unlike additive flame retardants, the TGA's of neither the starting brominecontaining alcohols nor their model N-phenylcarbamates correlate with the weight loas cuwes of the control foam. Instead, the TGA's of both flame retardant and nonflameretarded foams from the reactive bromide alcohols all fall in about the decomposition range of the control foam. As a practical consequence of the rwults reported herein, it is now possible to correlate flame retardancy and structure as well as formulate new flame retardants with greater assurance of success.

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