  Sizable glass formers feature numerous unique properties and potential
applications, but many questions regarding their glass transition dynamics have
not been resolved yet. Here we analyzed structural relaxation times measured as
a function of temperature and pressure in combination with the equation of
state obtained from pressure-volume-temperature (PVT) measurements. Despite
evidence from previous dielectric studies indicating a remarkable sensitivity
of supercooled dynamics to compression, and contrary to intuition, our results
demonstrated the temperate proof for the almost equivalent importance of
thermal energy and free volume fluctuations in controlling reorientation
dynamics of sizable molecules. The found scaling exponent equals 3.0 and Ev/Ep
ratio of 0.6 were typical for glass-forming materials with relaxation dynamics
determined by both effects with a minor advantage of thermal fluctuations
involvement. It shows that the high values of key parameters characterizing the
sensitivity of the glass transition dynamics to pressure changes, i.e.
activation volume and dTg/dP, are not a valid premise for a remarkable
contribution of volume on glass transition dynamics.
