Dynamic mechanical spectroscopy, dielectric spectroscopy, and viscosity measurements were carried out on Aroclor 1254 (PCB54), a chlorinated biphenyl. The temperature dependences of both the dielectric relaxation times and the viscosity depart from a single Vogel-Fulcher behavior, at a temperature, T-B, equal to 294 K. The ratio of this characteristic temperature to T-g(=246 K) is close to that found previously for other Aroclors, having different chlorine levels. The shapes of the dielectric and mechanical relaxation functions were equivalent, yielding a value for the Kohlrausch stretch exponent equal to 0.62(5) at T-g. However, the relaxation times for the dielectric modulus were substantially larger than the viscosity and mechanical relaxation times. The respective temperature dependences of the viscosity and the dielectric relaxation times, although similar, deviated from the Debye-Stokes relation with decreasing temperature. The temperature associated with this deviation is somewhat higher than T-B, and coincides with the temperature at which the relaxation function approaches Debye behavior. These phenomena all reflect the alleviation at high temperature of intermolecular constraints on the dynamics. The addition of high molecular weight polystyrene (PS-90k) to the PCB54 had an almost negligible effect on the dielectric relaxation times, notwithstanding that the polystyrene's glass temperature is 130 degrees higher than T-g for PCB54. The PS-90k exerted a more significant effect on the mechanical relaxation times of the PCB54. However, the modification of the Aroclor dynamics is still orders of magnitude less than the effect of the dissolved PS-90k on the relaxation times of an oligomeric PS (PS-o). This low molecular weight PS has a T-g identical to that of the PCB54. The dramatic difference between the effect of added polymer on the dynamics of Aroclor versus PS-o can be ascribed to differences in their capacity for intermolecular coupling with the PS-90k solute.