A radical trapping strategy using a nitroxide free radical was employed to extend the lifetime of polypropylene (PP) reactor powder. It was found that the addition of a radical trapping agent drastically enhanced the stability of PP reactor powder as long as as-synthesized PP was treated with a radical trapping agent before air exposure. These results suggested that the reactor powder was stabilized through the passivation of carbon-centered radicals present as initial radicals. The stabilization of initially formed radicals prevented the chain reactions from proceeding, thus proving the effectiveness of the new stabilization scheme.