Low temperature dielectric loss spectra of polyolefins

Antioxidants which are 2, 6 di-tert-butyl phenol derivatives exhibit dielectric relaxations at liquid helium temperatures when dispersed in various nondipolar media including polyethylene and polypropylene. Other antioxidants should preferably be used for the insulation tape of AC superconducting power cables. By an appropriate isotopic substitution the effect is shown to be due to tunnelling of the hydroxy hydrogen atoms. These findings prompted further investigations of hydrocarbon media containing phenols and other dipolar additives, from which it appears that the low-temperature dielectric relaxation behaviour can often be understood in terms of the structure and parameters of the additive molecules as revealed by published infrared and microwave spectroscopic data. The low-temperature relaxations of oxidised polyethylene are also summarily reviewed.