(245c) Density and Viscosity of Star/Linear Polystyrene + Toluene Mixtures at Temperatures to 523 K and Pressures to 200 Mpa: Experiments and Modeling

High-pressure, high-temperature (HPHT) densities and viscosities of polymer solutions are important for many industrial applications. For example, high molecular weight polymers are used as viscosity modifiers or performance enhancers in the design and development of advanced lubricants. There is an increasing interest in the use of star polymers for a variety of industrial applications, because of their unusual flow and viscosity properties compared to their linear analogues. At present there are virtually no HPHT data available for the density and viscosity of star polymers. This study reports the mixture, high-pressure densities and viscosities of three, symmetric, 3-arm star polystyrenes (s-PS) (M_w = 45, 120, and 305 kg/mol) and three, linear polystyrenes (l-PS) (M_w = 15, 33, and 120 kg/mol), each at 2 wt% in toluene. An interesting feature of this study is that the molecular weight of each of the l-PS polymers is approximately equal to the molecular weight of the arms of the three s-PS polymers. The measurements are performed at temperatures from 313 to 523 K and at pressures from 5 to 200 MPa using a windowed, rolling-ball viscometer equipped with a linear variable differential transformer for simultaneous density measurements. The results show that the viscosity of l-PS is higher than that of s-PS for polymers of the same molecular weight. The experimental density and viscosity data are correlated with the modified Tait equation which facilitates the interpolation of data within the experimental conditions investigated in this study. In this talk calculations are presented for the solution viscosity using the free volume theory (FVT) model.