Mixtures ofA) 75 to 99.5 wt. % of a high molecular weight, thermoplastic, aromatic polycarbonate with a molecular weight M.sub.w (weight average) of at least 10,000 which contains bifunctional carbonate structural units of the formula (I), ##STR1## in which R.sup.1 and R.sup.2, independently of each other, represent hydrogen, halogen, preferably chlorine or bromine, or a C.sub.1 -C.sub.8 -alkyl, C.sub.5 -C.sub.6 -cycloalkyl, C.sub.6 -C.sub.10 -aryl, preferably phenyl, or C.sub.7 -C.sub.12 -aralkyl, preferably phenyl-C.sub.1 -C.sub.4 -alkyl, in particular a benzyl group,m is an integer from 4 to 7, preferably 4 or 5,R.sup.3 and R.sup.4 can be selected separately for each X and, independently of each other, represent hydrogen or a C.sub.1 -C.sub.6 -alkyl group andX represents carbon,with the proviso that R.sup.3 and R.sup.4 simultaneously represent an alkyl group on at least one X atom.B) 0.5 to 15 wt. % of an aliphatic hydrocarbon with a molecular weight of 300 to 3,000 in particular mineral oil andC) 0 to 11 wt. % of a terpolymer of ethylene, acrylate and a monomer with epoxy groups, and the preparation of these mixtures.