The essence of our work in Friedel-Crafts chemistry is the discovery that one can use this reaction to cross-link polystyrene, at a temperature above that at which the polymer is processed, i.e., under fire conditions, and this cross-linked material shows a much reduced rate of heat release in a cone calorimeter. The identification of the most suitable catalyst, which will not effect reaction under processing conditions but will under fir conditions is at the heart of this work. The catalyst of choice is a material which will undergo a decomposition reaction at elevated temperature and be converted from a benign, non-catalytic material, into the catalyst. The compound of choice is an alkyl, diarylphosphate ester; depending upon the substitutions on the aromatic ring and the structure of the alkyl group, decomposition can occur in the range of 200 to 300EC to give a diaryl phosphoric acid. This acid will effectively catalyze the reaction and leads to cross-linking. From a radiative gasification experiment one can warch the formation of char in this system; it should be noted that in the degradation of polystyrene no char is formed.
Our initial work began using a copolymer of styrene and vinylbenzyl alcohol and this proved to be very effective. We now use polystyrene with a difunctional Friedel-Crafts alkylating agent which will give a functionalized polymer under processing conditions and will cross-link under fire conditions. The same reduced rate of heat release is seen in this system. A scheme showing the details of the reaction available. We have applied this technology to polystyrene and co- and ter-polymers of polystyrene, such as ABS, HIPS and commercial copolymers of styrene and butadiene. Current work is directed towards optimizing this work to make it more useful for societal purposes.