Effect of composition on the width of the calorimetric glass transition in polymer-solvent and solvent-solvent mixtures

The calorimetric glass-transition temperature (T-g) and transition width were measured over the full composition range for solvent-solvent mixtures of o-terphenyl with tricresyl phosphate and with dibutyl phthalate and for polymer-solvent mixtures of polystyrene with three dialkyl phthalates. T-g shifted smoothly to higher temperatures with the addition of the component. with the higher T-g for both sets of solvent-solvent mixtures. The superposition of the differential scanning calorimetry traces showed almost no composition dependence for the width of the transition region. In contrast, the composition dependence of T-g in polymer-solvent mixtures was different at high and low polymer concentrations, and two distinct T-g' s were observed at intermediate compositions. These results were interpreted in terms of the local length scale and associated local composition variations affecting T-g. The possible implications of these results for the dynamics of miscible polymer blends were examined. (C) 2004 Wiley Periodicals, Inc.