PHASE-EQUILIBRIA OF POLYPROPYLENE WITH COMPRESSED PROPANE AND RELATEDSYSTEMS .1. ISOTACTIC AND ATACTIC POLYPROPYLENE WITH PROPANE AND PROPYLENE

Cloud-point pressures of two isotactic polypropylene samples (iPP-1 an d iPP-2) of different molecular weight and of a high molecular weight atactic polypropylene (aPP) in propane were measured, as well as solid -supercritical fluid (S-SCF) equilibria for the crystalline isotactic samples. The lower critical end point (LCEP) for the aPP sample lies a t 6 degrees C. The second critical endpoint of iPP-1 (M-w = 29 000, M- w/M-n = 2.0), which is defined as the intersection of the 3-phase line starting at the triple-point of the polymer with the liquid-vapor cri tical locus, is estimated to lie at about 109 degrees C, 175 bar, and 15 wt % polymer; that of iPP-2 (M-w = 290 000, M-w/M-n = 4.4) is estim ated to lie at about 130 degrees C, 250 bar, and 7.5 wt % polymer. The pressure-temperature (P-T) phase boundaries separating two fluid phas es from a single supercritical phase (cloud-point isopleths) were dete rmined at several polymer concentrations to 160 degrees C and show a p ositive slope throughout. Pressure-composition plots (cloud-point isot herms) are shown for 135, 145, and 155 degrees C to 20 wt % polymer. A n aPP-propylene-isopleth near the critical composition is roughly para llel to that for aPP-propane, but it occurs at a slightly higher press ure. The locus of lower critical solution temperatures originating at the LCEP of aPP-propane can be made to fit the Sanchez-Lacombe lattice -fluid theory, after allowing both the energy and volume adjustment pa rameters to be temperature-dependent.