It is well-known that fluorinated polymers are very unique polymer materials because of their distinguished properties, such as high electrical resistivities, chemical and thermal stabilities, bio−compatibilities, etc. However, polytetrafluoroethylene (PTFE) is degraded by ionizing radiation with a low dose through main chain scission, and the mechanical properties are seriously deteriorated. In early 1990’s, it was found that irradiation for PTFE at elevating temperature enhances recombination of radicals induced by ionizing radiation. Thus, crosslinked PTFE had been obtained,[1,2],. The crosslinked PTFE shows remarkable improvements for the radiation durability and mechanical properties, etc.