Theoretical Study On Reaction Of Polar Molecules Grafted To Polyethylene By UV Radiation

Cross-linked polyethylene has become the most widely used polymer material in high voltage insulation cable due to its excellent electrical and mechanical properties.However,there is problem of space charge accumulation in the cross-linked polyethylene insulation material during a continuous direct current electric field.The problem will limit the development of the rated voltage level for high voltage direct current cables.Further study and solution of space charge accumulation has become a difficult problem in the field of cross-linked polyethylene insulation material development.By UV radiation,based on theoretical study on the grafting reaction of polar molecules to polyethylene,molecules with polar functional groups can be grafted to polyethylene chains at the atomic and molecular level.The reaction behavior of polar molecules grafted polyethylene successfully explained the experimental phenomenon of the suppress space charge and and clarified the reaction mechanism,which provided a reliable theory for the screening and design of cross-linked polyethylene space charge inhibitors.In this paper,the Gaussian 09 calculation program is used.At B3LYP/6-311+G(d,p)level,the main materials for preparing cross-linked polyethylene include cross-linked polyethylene,photoinitiator benzophenone,hindered phenol antioxidant,cross-linking agent polar molecules as space inhibitors and transition state.All stable point geometries are optimized.At the same level,the harmonic resonance frequency is calculated.The ionization potentials,electron affinities and HOMO-LUMO energy gaps are obtained.The excited states of maleimide and bismaleimide were calculated using time-dependent density functional theory and the charge distribution of bismaleimide is obtained by using the natural bond orbital theory.The potential energy surface information of polar molecules maleic anhydride,maleimide and bismaleimide grafted polyethylene are obtained by UV radiation.The results show that the reaction of maleic anhydride grafted polyethylene is initiated by in the excited triplet state benzophenone during the UV radiation.Benzophenone can also sensitize maleic anhydride and make maleic anhydride at the excited triplet state to complete the reaction of maleic anhydride grafted polyethylene.By analyzing the excited state energy of the maleimide and its derivatives show that by UV radiation the maleimide and its derivatives can be directly excited to its excited singlet state without photoinitiator.Maleimide and its derivatives are excited to triple state by intersystem crossing.The reaction of maleimide and its derivative grafted polyethylene is completed.In the cross-linked polyethylene system grafted with polar molecules.These polar molecules of contain carbonyl group can suppress space charge aggregation.In addition,the bismaleimide has two vinyl groups,both ends of which can be grafted to polyethylene chains.There,bismaleimide can be used as space charge inhibitor as well as cross-linking agent of polyethylene.The reaction potential energy information of polar molecules grafted polyethylene can provide a theoretical basis for further research and development of cross-linked polyethylene insulation materials,optimizing UV radiation cross-linking process,and improving the industrialization of HVDC cable materials.