Theoretical Study of the Grafting Reaction of a New Antioxidant to Cross-Linked Polyethylene and the Antioxidation Mechanism

Cross-linked polyethylene (XLPE) insulation has been used in most advanced power cable technology. Strategies for decreasing the amount of antioxidants have been proposed to reduce conductivity further. In this study, the structural design of a new dual-functional antioxidant has been established. Theoretical investigation of the antioxidative behavior and grafting reaction of the new antioxidant by ultraviolet (UV) radiation was performed using the density functional theory (DFT) method. The reaction potential energy information of the six reaction channels at the B3LYP/6-311+G (d,p) level was obtained. Frontier molecular orbitals (MOs) and natural bond orbital (NBO) charge populations of the designed antioxidant molecule were analyzed. The calculation results indicate that the reaction Gibbs energy barrier of the designed antioxidant and O₂ required to achieve the antioxidative effect is about 0.8 eV lower than that of the polyethylene chain. Moreover, due to the lower reaction Gibbs energy barrier, the reaction active site of the designed antioxidant accepting H is located on the O of the C-O groups. The proposed mechanism would be beneficial to understanding the molecular functions of antioxidants and further broadening the design ideas of thermoplastic insulation materials for future advanced power cables.