We employ temperature
modulated DSC (TMDSC) to determine the dependence of the fictive temperature
on cooling rate for a series of polychlorinated biphenyls (PCB). From the
slopes of semi-logarithmic plots of cooling rate vs.
fictive temperature, the latter normalized by the fictive temperature for
an arbitrary cooling rate, we determine the enthalpic fragilities. Despite
significant differences in glass transition temperature and chemical structure
(specifically chlorine content), the PCB have the same fragility. The value
of the fragility determined using TMDSC is consistent with the fragility previously
determined using dielectric relaxation spectroscopy.