The electrical conductivity of poly(ethylene terephthalate) in the temperature range 180-290 C

The d.c. conductivity of poly(ethylene terephthalate) in the temperature range 180-290°C, and its variation on annealing the sample, have been obtained from measurements of the conductivity at 50 c/s. The activation energy for conduction appears to be independent of the average molecular weight of the sample over the range 8900 to 17 400 but dependent upon the degree of crystallinity. The values of activation energy obtained for the molten state and the annealed solid above 180°C were 0·62 and 0·90 eV respectively, with a conductivity at 280°C of the order of 5 × 10 -9 mho cm -1 . The results suggest that at high temperatures ions rather than electrons are the dominant charge carriers, whereas at lower temperatures the work of other investigators has sometimes favoured electronic conduction. Both mechanisms may be present but the temperature variation of the relative mobilities causes ionic conduction to predominate at high temperatures.