Viscosity of polystyrene solutions expanded with carbon dioxide

The viscosity of solutions of polystyrene (PS) in decahydronaphthalene (DHN) was measured in the presence of carbon dioxide (CO₂) with a moving‐piston viscometer. The effects of the CO₂ pressure (0–21 MPa), polymer concentration (1–15 wt %), temperature (306–423 K), and polymer molecular weight (126 and 412 kDa) on the viscosity were investigated. In the absence of CO₂, the increase in the viscosity with increasing polymer concentration was approximately exponential in concentration and was well described by the Martin equation. All the data fell on a single line when the relative viscosity was plotted against cM^0.50 (where c is the concentration of the polymer in solution and M is the molecular weight of the polymer). The viscosity of the polymer solution decreased with increasing CO₂ pressure under otherwise constant conditions. For a given CO₂ pressure, the viscosity reduction was greatest when the relative viscosity was high in the absence of CO₂, that is, for high‐molecular‐weight polymer, high polymer concentrations, and low temperatures. Reductions in the relative viscosity of almost 2 orders of magnitude were observed in some cases. The viscosity of solutions of PS in DHN also was measured in the presence of sulfur hexafluoride (SF₆). At a given pressure, SF₆ was about as effective as CO₂ in reducing the solution viscosity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 540–549, 2006