Cross-linked polyethylene (XLPE) is an important class of materials with critical applications including pipes and high voltage electric cables. An organic peroxide such as bis(1-methy1-1-phenylethyl) peroxide (BMPEP) is a commonly used radical initiator in the cross-linking process along with a secondary antioxidant such as bis(octadecyloxycarbonylethyl) sulfide (BOCES). Herein is described a detailed investigation into the complex interactions of the radical initiator BMPEP and the secondary antioxidant BOCES in dodecane solvent-a model for the polyethylene polymer. Kinetic and spectroscopic experiments along with DFT calculations provide the foundation for a detailed mechanistic description for the roles of BMPEP, BOCES, atmospheric oxygen, and trace amounts of water in the overall process.