abstract a process is provided whereby high trimer content products are obtained by the polymerization of unsaturated fatty acids or lower alkyl esters thereof the process entails heating the fatty acid ester material at a temperature of at least 120 u00b0 c in the presence of a sulphonic acid catalyst which is dissolved therein application_number US 39125882 A description the invention relates to a process for the trimerization of unsaturated fatty materials such as fatty acids and their lower alkyl esters i e monocarboxylic acids which fatty acids contain one or more double bonds these fatty acids can contain 14 22 carbon atoms and in the case of multiple double bonds the unsaturation can be conjugated or random as a rule natural c 18 fatty acids are used which contain oleic acid and especially linoleic acid and linolenic acid preferred are fatty acid mixtures and their esters which contain at least 25 and more preferably at least 35 of a tri or higher unsaturated fatty acid such as linolenic acid linseed oil fatty acids or similar fatty acid mixtures which have been obtained by mixing of fatty acids the reaction products thus obtained usually show relatively low ester contents it.