General purpose poly(styrene) is a large
volume commodity polymer widely used in a range of applications. For many
of these the presence of an additive to impart some flammability resistance
is required. Most commonly, brominated aromatics are used for this purpose.
As the polymer undergoes combustion these compounds decompose to generate
bromine atoms and/or hydrogen bromide which escape to the gas phase and trap
flame propagating radicals. While these species are effective in inhibiting
flame propagation they present the opportunity for loss of halogen to the
atmosphere. For this reason, the use of these compounds is being limited in
some parts of the world. Phosphorus compounds, on the other had, impart a
flame retarding influence by promoting char formation at the surface of the
burning polymer. This prevents heat feedback to the polymer and consequent
pyrolysis to generate fuel fragments. The combination of both bromine and
phosphorus present in a single compound might generate a superior flame-retarding
additive in that both modes of retardancy might be promoted simultaneously.
Should this be the case smaller amounts of additive might be necessary to
achieve a satisfactory level of flame retardancy. A series of such additives,
brominated aryl phosphates, has been synthesized and fully characterized spectroscopically.
Blends of these additives, at various levels, with poly(styrene) have been
examined by DSC, TG and in the UL-94 flame test. The flammability of the polymer
is dramatically diminished by the presence of the additive.
for more efficient and 'greener' flame retardants for polymeric
materials is ever present and of increasing intensity as regulatory agencies
continue to display concern about the environmental impact of traditional
materials. Compounds capable of multiple modes of action would be particularly
desirable. Compounds containing both bromine (for good gas-phase activity)
and nitrogen (to promote solid-phase activity) should be good candidates for
development as flame retardant agents. A series of 2,4,6-tri[(bromo)xanilino]-1,3,5-triazines
have been synthesized and characterized spectroscopically. The degradation
characteristics of these compounds have been examined using thermogravimetry.
They undergo step-wise decomposition beginning at about 400C.