Abstract: For the preparation of hydrophilic polymer resins with functional groups on ligands, one reacts a resin which consists of units of formula I, in which R.sub.1 is hydrogen or an aliphatic residue, with a ligand in the presence of a coupling agent. The reaction is conducted in the presence of a competitive agent which is capable of reacting with the coupling agent at approximately the same rate as the amido group, to achieve a statistical limitation of the reaction of the coupling agent with the polymer. The competitive agent must not react with the resin.The resin is used for the recovery of metal ions from effluents or natural or industrial residual waters.