VISCOELASTICITY AND BIREFRINGENCE OF BISPHENOL-A POLYCARBONATE

The dynamic Young's modulus, E*, and birefringence of bisphenol A polycarbonate were measured over the glassy to rubbery plateau zone. Measurements were performed over the frequency range of 1 to 130 Hz at various temperatures between 148 and 170-degrees-C. A modified stress-optical rule was applied in characteristic analysis of the glassy and glass transition regions. It was earlier proposed to replace the stress-optical rule which, generally, was valid only at relatively low frequencies corresponding to rubbery plateau and rubbery flow regions. E* could be separated into two component functions, E(R)* and E(G)*. The stress-optical coefficients,C(R) and C(G), associated with the respective components were 5.0 x 10(-9) and 3.5 x 10(-11) Pa-1. In constructing master curves of E(R)* and E(G)* with the method of reduced variables, an unlike temperature dependence was found. This result could account for the breakdown of the time-temperature superposition principle for E* reported by several investigators.