Abstract: The present invention relates to a process for the preparation of a peroxyester which can be used in particular in polymerizations, such as the polymerization of vinyl chloride, or in the thermosetting of polyester resins. This process comprises the reaction of a hydroxyhydroperoxide salt with an acid halide or an acid anhydride under the following conditions: the molar ratio Rb of the hydroxyhydroperoxide corresponding to the hydroxyhydroperoxide salt to the acid halide is between 0.5 and 1.5; or alternatively the molar ratio Rb? of the hydroxyhydroperoxide corresponding to the hydroxyhydroperoxide salt to the acid anhydride is between 1.0 and 3.0; the hydroxyhydroperoxide salt was prepared beforehand by reaction of the corresponding hydroxyhydroperoxide with a base according to a molar ratio Ra of the base to the hydroxyhydroperoxide of between 0.5 and 1.5; and this process is carried out in aqueous media.

Abstract: The present invention relates to a process for the preparation of a peroxyester which can be used in particular in polymerizations, such as the polymerization of vinyl chloride, or in the thermosetting of polyester resins.