  The experimental fact that relaxation times, tau, of supercooled liquids and
polymers are uniquely defined by the quantity TV^g, where T is temperature, V
specific volume, and g a material constant, leads to a number of
interpretations and predictions concerning the dynamics of vitrification.
Herein we examine means to determine the scaling exponent g apart from the
usual superpositioning of relaxation data. If the intermolecular potential can
be approximated by an inverse power law, as implied by the TV^g scaling,
various equations are derived relating g to the Gruneisen parameter and to a
common expression for the pressure derivative of the glass temperature. In
addition, without assumptions, g can be obtained directly from
pressure-volume-temperature data. These methods for determining g from
molecular or thermodynamic properties are useful because they enable the P- and
V-dependences of tau to be obtained, and thereby various analyses of the
dynamics to be explored, without the need to carry out relaxation measurements
beyond ambient pressure.
