On free volume of polymers above the glass transition

The magnitude of the activation energy for diffusion, E_D is shown to be inversely dependent on the fractional free volume of the polymer above T_g. From the proportionality of E_D above and below T_g, the magnitude of E_D below T_g is also inversely dependent on the free volume in that temperature range. While this correlation holds very well for our determinations of fractional free volume above T_g it does not correlate with the Simha-Boyer fractional free volume below T_g, contrary to expectations.