The stabilized substance is assigned by name to UN No. 2618.
For the unstabilized substance, see 2.2.3.2.2 of the RID:

"Chemically unstable substances of Class 3 shall not be accepted for carriage unless the necessary precau-tions have been taken to prevent the possibility of a dangerous decomposition or polymerization under normal conditions of carriage. For the precautions necessary to prevent polymerization, see special provision 386 of Chapter 3.3. To this end particular care shall be taken to ensure that receptacles and tanks do not contain any substances liable to promote these reactions. If temperature control is required to prevent polymerization of a substance (i.e. for a substance in a packaging or IBC with an SAPT of 50 °C or less, or in a tank with an SAPT of 45 °C or less), the substance shall not be accepted for carriage."