Method for functionalising a thermoset, crosslinked isocyanate-based polymeric solid material

A method for functionalising a thermoset, crosslinked isocyanate-based polymeric solid material, which material is made of isocyanate and isocyanate reactive components, at least one of which comprises an anchor component which has at least one anchor group, in which method the solid material is brought in contact with a liquid containing at least one functional component which is allowed to bind covalently to this solid material by a heterogeneous reaction between the functional component contained in said liquid and the anchor groups on undissolved, solid material, characterized in that the anchor groups on said solid material comprise terminal alkene and/or alkyne groups and said functional component comprises at least one thiol group, said functional component being allowed to bind covalently to said solid material by a heterogeneous, free-radical addition reaction between the thiol groups on the functional component and the terminal alkene and/or alkyne anchor groups on the undissolved, solid material.