Electrical properties of a novel fluorinated polycarbonate

The relative permittivity, loss and dielectric strength have been measured for a polycarbonate-based material, tetraaryl bisphenol A polycarbonate, that has been fluorine substituted (DiF p-TABPA-PC). The new material has a glass transition temperature, Tg = 489 K, that is higher than that for either conventional bisphenol A polycarbonate (BPA-PC) for which Tg = 421 K or for a copolymer of tetraaryl bisphenol A (TABPA) and bisphenol A (BPA) (TABPA-BPA-PC) for which Tg = 464 K. In addition, the dielectric strength of DiF p-TABPA-PC is almost identical to that for purified BPA-PC and slightly larger than the value for TABPA-BPA-PC. The relative permittivity and loss measurements were carried out from 10 to 105 Hz over a wide temperature range and at pressures up to 0.25 GPa. Variable temperature results for the α relaxation and both temperature and pressure results for the γ relaxation regions are reported. The α relaxation exhibits standard behavior. The γ relaxation exhibits unusual characteristics such as a strong increase in peak height as temperature increases and a strong decrease in peak height with increasing pressure. The data for the γ relaxation have been analyzed using several formulations. Expressions for the peak height and peak position based on a two state (inequivalent well) model and the resulting parameters are discussed in terms of the insight they provide into the molecular mechanisms responsible for the sub-Tg relaxation. Ab initio SCF results for a related model compound are presented. Finally, the real part of the relative permittivity for the new polymer is about 10% higher than for BPA-PC.