Correlations between the effects of pressure and molecular weight on polymer blend miscibility

We examine the effects of pressure on polymer blend miscibility for two polyolefin blends as well as for blends of polystyrene (PS) and polybutadiene (PB). Each of the blends studied exhibits an upper critical solution temperature (UCST), and for the PS/PB blend we report experimental results on the pressure dependence of the UCST for different molecular weight combinations. We make use of the Born-Green-Yvon integral equation theory to exploit the connection between the pressure dependence of the UCST and the sign of the volume change on mixing, leading us to predict that through judicious choice of polymer molecular weights the response of the UCST to pressure may be controlled.