Viscoelastic characteristics of pentane-swollen polystyrene beads

Expansion of pentane-swollen polystyrene beads was followed at and above th e glass transition by using a very simple optical technique. Measurements a llowed a suitable determination of the glass transition temperature and of the viscoelastic characteristics of the pentane-plasticized polystyrene cha ins inside the beads, at different pentane contents. This was achieved by c ombining the well-known Williams, Landel, and Ferry approach and some calcu lations derived from a recent micromechanical modeling of the expanded poly styrene microstructure. The results, analyzed in terms of free volume chara cteristics, revealed the peculiar plasticizing character of pentane, as com pared to the usual polymer diluents. A value of 42 degrees C was found as t he lowest temperature for which the dimensional variation of the beads coul d result from glass transition motions. The relevance of these conclusions was discussed, not just in terms of the changes in dimensions of the indivi dual beads at zero expansion time but also in terms of the dimensional evol ution observed in the expanded polystyrene structures. (C) 1999 John Wiley & Sons, Inc.