Phase equilibria of polypropylene samples with hydrocarbon solvents at high pressures

The objective of this work is to provide high-pressure phase equilibrium da ta for polypropylene (PP) samples (two commercial and one metallocenic grad es) with some hydrocarbon solvents (propane, propylene, n-butane and 1-bute ne). The experiments were carried out in a high-pressure variable-volume vi ew cell in the temperature range of 75-150 degreesC, for polymer compositio ns ranging from 0.3 to 10 wt %. Phase transitions were recorded visually as cloud points and identified as liquid-liquid and vapor-liquid transitions. When pressure transition data obtained for olefins and paraffins of simila r chain length and at similar temperatures and polymer compositions are com pared, it may be observed that paraffins lead to the decrease of the pressu re transition values. Therefore, the one-phase region is larger for paraffi ns than for olefins. In the range of commercial interest analyzed, it is al so observed that the influence of polymer average molecular weight upon the cloud points is negligible. Experimental data are then used to build the P -T diagrams for these systems, allowing the identification of the LCST (Low er Critical Solution Temperatures) and LCEP (Lower Critical End Points) cur ves. Finally, the original SAFT equation of state (SAFT-EOS) is used to mod el the experimental data. It is shown that the SAFT-EOS provides an excelle nt description of the solution behavior in the whole experimental range ana lyzed. (C) 2001 John Wiley & Sons, Inc.