Small-cell polystyrene foams, and process for producing same

A process for producing a foam from at least one styrene polymer component (S) and at least one additive of the general formula (I), comprising the steps of:

• a. heating at least one styrene polymer component (S) to give a melted polymeric molding compound,
• b. introducing a blowing agent (T) into the melted polymeric molding compound, to form a foamable composition (Z), and
• c. foaming the foamable composition (Z) to give a foamed molding,
• wherein at least one carboxylic bisamide of the general formula (I) is used in the melted polymeric molding compound,
• wherein:
• Z is a C1-C5 alkylene group or an oxygen atom or a sulfur atom;
• R1 and R2 independently of one another are a branched C3-C12 alkyl radical or unbranched C1-C12 alkyl radical, a C3-C12 cycloalkyl radical, or a benzyl radical;
• and
• R3, R4, R5, and R6 each independently of one another are hydrogen, an unbranched C1-C6 alkyl radical, or a branched C3-C6 alkyl radical.