A binder for bituminous compositions including at least one dialkylamide derived from an unsaturated fatty acid; and at least one catalyst for polymerizing the at least one dialkylamide under the action of oxygen is provided. A bituminous composition including (i) 80% b.w. to 94.9% b.w. bitumen; and (ii) a binder, that includes (a) 1% b.w. to 19% b.w. unsaturated fatty acid dialkylamides; and (b) 0.1% b.w. to 1% b.w. of a polymerization catalyst, where the amounts are calculated based on the solids content of the composition, and where the amounts total 100% b.w. is also provided. A method for preparing a binder for a bituminous composition including combining at least one unsaturated dialkylamide derived from an unsaturated fatty acid with at least one catalyst for the polymerization of the at least one dialkylamide under the action of oxygen is also provided.