Effect of pressure on the segmental dynamics of bisphenol-A-polycarbonate

The segmental dynamics of bisphenol-A-polycarbonate (BPA-PC) are studied as a function of temperature (in the range from 143 to 473 K) and pressure (0.1-300 MPa) within the frequency range from 3 × 10−3 to 1 × 106 Hz using dielectric spectroscopy aiming at extracting the more relevant parameter associated with the liquid-to-glass transition. Rheological measurements are also made in the temperature range from 408 to 513 K for comparison. The dynamic results coupled with the equation of state reveal that both density and thermal energy control the segmental dynamics with density being the most important variable in the vicinity of the transition. This is documented by independent estimates of the value of the dynamic ratio EV∗/H∗ (∼0.44). This low value of the dynamic ratio is discussed in terms of the packing irregularities and large monomer volume of BPA-PC. In addition, the pressure coefficient of Tg (dTg/dP ∼ 0.52 K/MPa) is one of the highest for a polymeric substance.