ON THE APPLICABILITY OF THE LENNARD-JONES POTENTIAL FUNCTION TO AMORPHOUS HIGH POLYMERS

Pressure-volume-temperature measurements were performed on five amorphous thermoplastics. From these data, first derivatives of internal energy with respect to volume were calculated. These derivatives were cast into the Lennard-Jones form and the two defining parameters were evaluated for each polymer. It was found that, when the polymer is in the glassy state, these parameters correspond to the volume and internal energy of the polymer at absolute zero. For melts, the first derivatives are constant within the accuracy of these experiments regardless of temperature, pressure, or volume. As a result, the Lennard-Jones potential was found to be a good model for the amorphous glassy state and inappropriate above T(g). (C) 1993 John Wiley & Sons, Inc.