Phosphonium Bromide Salts as Potential Flame Retardants for Polymeric Materials

Abstract

Highly halogenated compounds. particularly multiply brominated aromatics, continue to be effective and widely uKd flame retardants for a vOricty of applications Phosphorus compounds, although somewhat more expensive than the brominated aromatics are effective at lower levels and function in both the solid and gas phase. The combination ofboth halogen and phosphorus in the m e compound can lead to a synergy of action and superior performance w a flame retardant.[1] The preparation of flame retardant compounds containing both halogen and phosphorous requires. first, the synthcsk of a hdogrmtcd compound that would dlow for a rusonable mount of phosphine to be incorpomtcd into the compound and. second, a compound that would also contain a rusonable percentage of hrlogen after phosphrus incorporation The halogenated compound rlccIed was 1,3,5-tri(bromomethyl)benzene. 1,3,5-Tri(bromomethy)benzene is a crystalline, tri-functional compound that is emnomid to produce and has a relatively high percentage of bromine (67.2%). Treatment of this cornpound with a variety of phosphines (which were generally available from reaction of the appropriate Grignard or orgrnolithium reagent with phosphorus trichloride) in dimcthylfomumide, usually at reflux, afforded the corresponding phosphonium bromides in excellent yields. [2] These salts are granular powders which should make excellent additives. The decomposition behavior of these materials as demonstrated by thermogravimctry suggest that they should be uxful in high temperature applications. Several of them have decompostion temperatures in excess of 300 C.