Formation and melting of solvent crystals in thermoreversible polymer gels

Thermoreversible and cross-linked gels formed from polymer-solvent systems are of fundamental importance in many areas of science, although an understanding of the network structure of these 'diluted solids' is far from complete. One aspect of these systems which merits further study is the relationship between the solvent and the polymer in the gel. We are concerned with thermoreversible gels of isotactic polystyrene (i-PS) in cis-decalin (T_m=230.2 K) and transdecalin (T_m=242.6 K). In this work, we attempt to help resolve the conflicting models of thermoreversible gels of i-PS in decalin. In particular, we test the hypothesis that the lack of solvent freezing in the gel was due to a small crystallite size, to be measured by wide angle x-ray scattering (WAXS) line broadening studies. Because the NMR results indicated that solvent freezing may be occurring at lower temperatures than previously studied, we also conducted DSC measurements down to 140 K to check for further transitions. This includes The possibility of solvent vitrification in the gel, reported for cross-linked gels of poly(2-hydroxyethyl methacrylate) in water.