SOME PREVIOUSLY UNEXPECTED PHENOMENA OF VOLUME RECOVERY

We have extensively studied the nonequilibrium behavior of atactic polystyrenes in a broad range of temperatures. Depending on the conditions of the initial temperature (T0) and the aging temperature (T), the shapes of isotherms plotted in the form of total fractional free volume (viz., delta) versus logarithmic aging time can be linear or nonlinear. At a T in the vicinity of T(g), the isotherms converge together. When the T is lowered, the isotherms become increasingly nonlinear; eventually, these isotherms intersect one another at various points, forming a newly discovered crossing phenomenon. Differences in volume contraction persist throughout further aging, regardless of the equality in delta right at the moment of crossing. In a further case, the nonlinear isotherms between the two polystyrenes may be superposable by a simple delta shift, despite their substantial differences in delta. As none of these phenomena can be justified by kinetic arguments, this study seriously questions the validity of the existing kinetic theories as well as the existence of the extrapolated underlying equilibrium state.