Process for the production of an alpha olefin polymer and a process for the treatment of the alpha olefin polymer. A polymerization feed containing an alpha olefin, such as propylene, is supplied to the reactor to produce a thermoplastic polymer product involving a homopolymer or a copolymer. A product stream containing the polymer is withdrawn from the polymerization reactor and the polymer product is recovered from the product stream. The polymer product is then processed to produce the polymer product in a granular or pelletized form. A hindered amine light stabilizer is oxidized with an oxidizing agent under conditions to convert at least a portion of the amine groups to nitroxyl groups. The oxidized hindered amine light stabilizer is then supplied to the polymer product prior to heating and processing of the polymer product.