Abstract: It comprises reacting, both continuously and discontinuously, acrylic acid and 1-butene in the presence of an ionic exchange resin that contains sulfonic acid groups, carrying out the reaction at a temperature between 50.degree. and 120.degree. C., at a pressure between 10 and 30 kg/cm.sup.2, for a reaction or contact time between 0.5 and 4 hours and using a olefin/acrylic acid molar ratio between 0.3 and 10.The sec-butyl acrylate obtained is useful in polymerization processes yielding very hard polymers with a high thermal resistance and high resistance to hydrolysis.FIG. 1 represents a graph of the effect of the olefin/acrylic acid ratio over the conversion of acrylic acid.