Abstract: Process for coating the surface of plastics comprising absorbing the vapor one or more internal reagent(s) in the plastic to be coated, and contacting one or more external reagent(s) with the surface of the plastic, wherein an immobilized coating is formed by a chemical reaction between the internal reagent(s) and the external reagent(s). The internal reagent(s) is(are) selected from substances which do not react with the plastic and the internal reagent(s) diffuse out of the plastic during contacting, wherein the coating is formed at the boundary layer of the plastic towards which the internal reagent(s) and the external reagent(s) diffuse.