PREBREAKDOWN FREE-RADICAL STATES IN POLYETHYLENE.

Two types of free radical have been observed in polyethylene subjected to a strong electric field, which arise from local heating and from collisional ionization. The radicals of the first type are localized in the pyrolized layers near the electrodes, while the second type occurs in the dendritic formations along the incomplete-breakdown tracks. The two types enhance the damage to the insulator, with the first type producing highly conducting regions due to the delocalized pi electrons in the thermally modified macromolecules, and the second type by involvement in an oxidative destructive chain reaction. The thermodynamic free volume plays a decisive part in the development of the ionization processes and radical formation in polyethylene in strong electric fields.