Foamed styrenic polymers containing a brominated styrene-butadiene copolymer and having enhanced cell size homogeneity

A monolithic foamed polymer composition having a polymeric phase which contains gas-filled cells, wherein the polymer phase comprises:

• (a) one or more thermoplastic, non-brominated styrenic polymers containing no more than 1% polymerized diene monomers,
• (b) a thermoplastic brominated vinyl aromatic/butadiene copolymer having a molecular weight of at least 1000 g/mol in an amount sufficient to provide 0.25 to 5% by weight bromine based on the combined weights of components (a), (b) and (c), and
• (c) from 0.1 to 5 parts by weight, per part by weight of component (b) of at least one thermoplastic unbrominated vinyl aromatic/butadiene block copolymer selected from the group consisting of a thermoplastic unbrominated styrene-butadiene-styrene triblock copolymer containing a central poly(butadiene) block of 30,000 to 100,000 g/mol and terminal polystyrene blocks each having a molecular weight of 20,000 to 100,000 g/mol and a thermoplastic unbrominated styrene-butadiene diblock copolymer in which the polystyrene block has a molecular weight of 30,000 to 75,000 g/mol and the poly(butadiene) block has a molecular weight of 40,000 to 100,000 g/mol.