Process for the foaming of thermoplastics containing ester and/or carbonate groups

A process for the preparation of a foamed moulding comprising using a composition including

• (i) a thermoplastic which is characterized in that its polymer chain contains at least one member selected from the group consisting of an ester group and a carbonate group
• (ii) a compound of the formula ##STR7## in which R.sub.1 -R.sub.4 independently denotes hydrogen, a straight-chain or branched alkyl radical having 1 to 4 carbon atoms, a hydroxyl or nitro group or a halogen atom, and
• R.sub.2 may additionally denote a radical of the following formula ##STR8## wherein n is an integer of from 0 to 4 and
• R.sub.1, R.sub.3 and R.sub.4 have the above-mentioned meaning and
• X denotes hydrogen or straight-chain or branched C.sub.1 -C.sub.4 alkyl radical and
• (iii) a neutral salt of the formula
• A.sub.p EF.sub.q
• wherein
• A denotes an element of the first main group of the Periodic system,
• E denotes an element of the third, fourth or fifth main group or subgroup of the Periodic system,
• F represents a fluorine atom,
• p is 1, 2 or 3 and
• q is 4, 5 or 6 depending on the valence of said E.