aids for the processing of synthetic polymer compositions based on carboxylic esters where the processing aids include partial esters which contain at least 18 carbon atoms have a number average molecular weight of from 300 to 10 000 and can be prepared by the reaction of saturated or unsaturated aliphatic and or cycloaliphatic polycarboxylic acids or anhydrides of these with saturated or unsaturated aliphatic cycloaliphatic and or aromatic monoepoxides and or monoalcohols optionally containing ether groups where at least 10 and not more than 90 of the carboxyl groups of the polycarboxylic acids have been reacted and the polycarboxylic acids and anhydrides of these contain from 8 to 100 carbon atoms the invention further relates to the use of these processing aids in synthetic polymer compositions and also to synthetic polymer compositions which comprise these processing aids application_number US 27464202 A description the processing aids partial esters of the invention can be used either in thermoplastic synthetic polymer compositions or in thermoset synthetic polymer compositions such as those disclosed in din 7724 the processing aids of the invention can be used with many thermoplastic synthetic polymer compositions which include polyolefins such as for example polypropylene polyethylene and the like ethylene vinyl acetate copolymers polyamides polycarbonates polystyrenes polyethylene terephthalates polyesters poly meth acrylates or mixtures thereof a particularly preferred use of the partial esters processing aids is in pvc in.