Method of preparing a polymer substance which is insoluble in aqueous media and bears substrates having nucleophilic properties, ion exchange properties, catalytic properties or biological properties characterized in that it comprises causing one or more difunctional substrates bearing on the one hand a reactive function and on the other hand a nucleophilic group or groups or having ion exchange properties, catalytic properties or biological properties to react with the reactive sites of a polymer material which is insoluble in aqueous media and comprises a chemically inert polymer selected from polyolefins, copolyolefins, polyamides, copolyamides and fluorinated polyolefins, wherein said polymer is insoluble in aqueous media, and sufficiently reticulated to be usable in a defined configuration, said chemically inert polymer having grafted thereon a monomer having one or more carboxyl groups and/or a polymer of said monomer, at least a portion of said carboxyl groups having been chemically reacted to form one or more condensed groups selected from an acid anhydride group, an active ester group and an active thioester group, said substrates being selected from mono- and diamines, amino acids, polypeptides, proteins and enzymes.