STRUCTURAL RELAXATION INVESTIGATIONS OF GLASSY POLYSTYRENE BY RADIAL-DISTRIBUTION FUNCTIONS

The structural relaxation of an atactic polystyrene under sub-T(g) ann ealing at 50-degrees-C and at 70-degrees-C was investigated by the rad ial distribution function (RDF) derived from its wide-angle x-ray scat tering (WAXS). By recording the changes in RDF (i.e., DELTAH(r), where r is the radial distance from an arbitrary reference atom) after it h ad been annealed for a certain period of days, and taking the integrat ion of integral0r DELTAH(r)2dr, we found that the atom density within structural domains in a size below 15 was changed dramatically, but th at the tendency leveled off as annealing proceeded. However, the atom density outside the domains is barely changed by sub-T(g) annealing. T he size of the domain is similar to the statistical segment length rep orted in the literature. The behavior of the domains-that the segmenta l relaxation inside the domains in the initial sub-T(g) annealing is u nconstrained by their neighbors outside the domains-is also similar to the behavior of the statistical segments. The domains are believed to be composed of a statistical segment across the center, which has abo ut 6 styrene repeat units, and 6 equal-distanced parallel segments tan gent to the edge of the domain. On the other hand, as the annealing te mperature is closer to the glass transition temperature, the frozen un stable chain segments reach equilibrium sooner and with less disturban ce in their conformation.