CHEMICAL MODIFICATION PROCESS OF A POLYMERIC ARTICLE WITH A VIEW TO PROVIDE IT WITH FLAME-RETARDANT PROPERTIES OR TO IMPROVE THESE PROPERTIES, COMPRISING A COVALENT REACTION WITH AT LEAST ONE COMPOUND CARRYING AN ISOCYANATE GROUP

A process for chemically modifying a polymeric part in order to impart flame-retardant properties thereto or to improve the properties, the process comprising the following steps: a step of reacting a polymeric part comprising at least one polymer comprising, as reactive groups, amine groups and/or hydroxyl groups, with a functional compound, referred to as first compound, comprising at least one isocyanate group and at least one vinyl type polymerisable group, the isocyanate groups reacting, covalently with all or some of the amine groups and/or hydroxyl groups of the polymer(s), resulting in a polymeric part bonded, covalently, to residues of the functional compound; using the vinyl type polymerisable groups of the residues of the functional compound, a step of polymerising a second compound comprising at least one vinyl type polymerisable group and at least one group comprising at least one phosphorus atom, the reaction step and said polymerisation step being carried out in the presence of at least one supercritical fluid.