The present invention relates to a method for post-modification of a porous polymeric polysaccharide support comprising one or more unreacted double bonds, which method includes to contact the polymeric support with a liquid phase comprising at least one grafting compound and to initiate a free radical reaction in the mixture obtained, wherein the grafting compound is comprised of a double bond as a reactive group coupled to a linear or cyclic chain of carbon, which optionally comprises one or more heteroatoms. An advantageous grafting compound is a vinyl ether or a hydroxyvinyl ether. The invention also encompasses a polymeric support that has been post-modified by the method according to the invention as well as the use of such a support, e.g. in chromatography.