Multiple dielectric relaxation processes in an unequilibrated bisphenol-A polycarbonate

Complex relative permittivity data within the ranges 0.1 Hz-3 MHz and -175 degrees C to +200 degrees C are presented for an unequilibrated compression-moulded bisphenol-A polycarbonate of commercial origin (LEXAN 141). Comparisons are drawn with the nitrogen-equilibrated material in which eight distinct absorption regions have been identified. One low-frequency region common to both materials at low temperature is shown to be caused directly by a processing stabiliser. A second at high temperature is thought to originate in part from an interfacial polarisation associated with a second phase of polycarbonate. An absorption observed only in the unequilibrated polycarbonate is attributed to bound water. Two intermediate-temperature losses are differentiated and delineated for the first time. Their origins and reason for diminution by annealing are examined. The multiplicity of overlapping absorptions, including a low-temperature loss region which is almost continuous at higher frequencies, is consistent with the high impact strength of polycarbonate over an extended temperature range.