MISCIBILITY, DENSITY AND VISCOSITY OF POLYSTYRENE IN N-HEXANE AT HIGH-PRESSURES

The demixing pressures, densities and viscosities of solutions of near ly monodisperse polystyrene samples (M-w/M-n < 1.1) in n-hexane have b een determined. Measurements were conducted with samples of different molecular weights (M-w = 4000-50 000) at concentrations up to 8 mass% over a pressure range from 5 to 70 MPa and a temperature range from 32 3 to 423 K. The demixing pressures were observed to increase with mole cular weight (from about 10 MPa for M-w = 4000 to 50 MPa for M-w = 500 00) and show high sensitivity to temperature (Delta P/Delta T being ab out -1 MPa degrees C-1) in the range investigated. Density and viscosi ty data were collected in the one-phase homogeneous regions, and visco sity was correlated with an equation of the form eta = Aexp{B/(1 - V-0 rho)}, which is based on the free-volume considerations. For a given system, the viscosities increase with solution density (or pressure). At a fixed solution density, viscosity increases with polymer concentr ation or molecular weight. Depending upon the system, viscosities have ranged from 0.15 to 0.45 mPas. Flow activation volumes and flow activ ation energies were about 40 cm(3) mol(-1) and 6 kJ mol(-1), respectiv ely. The demixing and viscosity data have been also compared with the results obtained in n-butane and n-pentane for one sample (M-w = 9000) . In going from n-butane to n-hexane, the demixing pressures decrease while the viscosities become higher. (C) 1997 Elsevier Science Ltd.