Changes in yield and deformation of polycarbonates caused by physical aging

Change in yield and deformation associated with physical aging was studied on a series of polycarbonates (bisphenol‐A polycarbonate, polyestercarbonates, and phenolphthalein‐bisphenol‐A copolycarbonates) and a polysulfone. A combination of tensile and biaxial yield measurements, dynamical mechanical analysis, and high‐resolution density measurements were performed. These data indicate that both free volume arguments and molecular entanglement arguments are inadequate for explaining the differences in large‐scale deformation associated with physical aging for the polymers and the superiority of polyestercarbonates over the other resins. The local intramolecular and intermolecular conformation in the glassy state, as predicated by molecular structure, is apparently an important key to understanding physical aging in polycarbonate‐type polymers.