Physical Aging of Star-Shaped Macromolecules

Abstract

Time-dependent structural relaxations, physical aging, of films with thicknesses in the range 0.4 μm < <i>H</i> < 2 μm of star-shaped polystyrene (SPS) macromolecules were investigated. Our studies reveal that the aging rates of star-shaped PS macromolecules are appreciably slower than their linear chain analogs. The magnitude of the difference between the aging rates of the linear and star-shaped macromolecules increases with increasing functionality, <i>f</i>, and decreasing molecular weight per arm, <i>M</i>_n^arm, of the stars. Our results are consistent with the notion that constraints imposed due to the architecture of the macromolecule suppress relaxations associated with and accommodate the reduction of the free volume of the system.