Stabilized flame retardant additives and their use

A flame retardant additive composition having enhanced thermal stability which comprises a blend formed from (A) tetrabromocyclooctane or dibromoethyl-dibromocyclohexane, or both and (B) halogenated aromatic epoxide and/or halogenated aromatic oligomer in which the halogen atoms are chlorine or bromine, or both, in an (A)/(B) weight ratio in the range of about 95/5 to about 60/40. Components (A) and (B) can be included to provide flame retardancy to various polymers especially styrenic polymers including foamed or foamable styrenic polymers, crystal styrenic polymers, impact-modified styrenic polymers, and blends of crystal styrenic polymers, impact-modified styrenic polymers. In all cases the thermal stability of component (A) is significantly increased by the copresence of component (B).