AbstractUnsaturated hydrocarbons were prepared from methyl esters of stearic, oleic, linoleic, and linolenic acid, and from linseed oil fatty acid methyl esters, by replacing the ester group by an alkene group (reaction of the esters with alkyl magnesium halide and dehydration of the tertiary alcohols formed).These olefins show the same polymerization phenomena as do the esters from which they are derived. Thermal polymerization of olefins derived from methyl linoleate and methyl linolenate leads to monocyclic and bicyclic dimers, respectively, in accordance with the results of polymerization of the corresponding esters.Copolymerization of tung oil with olefins prepared from linseed oil fatty acid esters only occurs at higher temperatures (275° C); the reaction is promoted by sulphur dioxide. Copolymerization of tung oil and linseed oil is therefore unlikely at temperatures below 250° C.Copolymerization of oleic and elaidic esters with olefins derived from linoleic acid esters does not occur at 300° C; this makes it probable that mono‐unsaturated acids, when present in drying oil glycerides, do not participate in the polymerization.