Effects of dissolved gas on viscoelastic scaling and glass transition temperature of polystyrene melts

The free volume theory of Gerhardt et al.(1) (J. Polym. Sci. B: Polym. Phys . 1998, 36, 1911) is used to predict viscoelastic scaling factors describin g the effect of dissolved gas content on the viscosity curves of polystyren e melts swollen with dissolved carbon dioxide and dissolved 1,1-difluoroeth ane. The predictions of the theory are compared to viscoelastic scaling fac tors measured by Kwag et al.(2) (J. Polym. Sci. B: Polym. Phys. 1999, 37, 2 771) for each system at 150 and 175 degreesC, at concentrations up to 10 wt % of dissolved gas, and pressures ranging up to 22 MPa. The agreement betw een the theory and experiments is very good for the polystyrene-CO2 system but only fair for the polystyrene-1,1-difluoroethane system. The experiment al viscoelastic scaling factor values are also interpreted with the WLF equ ation to estimate the change in the underlying glass transition temperature s of the polystyrene-gas mixtures. The glass transition temperatures estima ted from these rheological data are in very good agreement with values dire ctly measured for polystyrene-CO2 mixtures and with the theory of Condo et al.(3) (Macromolecules 1992, 25, 6119).