| The phase-boundary pressures for non-associating and associating systems containing model polymers were measured in a variable-volume optical cell up to 200{dollar}spcirc{dollar}C and 2000 bar. The binaries of C{dollar}sb{lcub}20{rcub}{dollar} +, C{dollar}sb{lcub}30{rcub}{dollar} +, C{dollar}sb{lcub}40{rcub}{dollar} + ethylene, C{dollar}sb{lcub}26{rcub}{dollar} + 1-butene, C{dollar}sb{lcub}36{rcub}{dollar} + (ethylene/1-butene), ethylene-propylene copolymer (PEP) + ethylene, and PEP + propylene, represent non-associating systems and they establish the polymer-size effect on phase behavior. In these systems, as the size difference between the solvent and polymer increases, the LCST (Lower Critical Solution Temperature) behavior merges with the UCST (Upper Critical Solution Temperature) to form U-LCST behavior.; The monohydroxy (one terminal hydroxy group) and dihydroxy (two terminal hydroxy groups) telechelic polyisobutylenes (PIB) in ethane, propane, chlorodifluoromethane, dimethylether, and carbon dioxide solutions, represent associating systems and they establish the hydrogen bonding effect on phase behavior. This effect is described by self-(polymer/polymer), cross-(polymer/solvent), or intramolecular (polymer) association and depends strongly on the PIB-size, solvent polarity, and hydroxy-group density. (1) For low PIB-size and high hydroxy-group density, as in PIB (200 g/mol) solutions, an increase in hydroxy groups results in an increase in phase-boundary pressure if self-association prevails, or no change in phase-boundary pressures if cross-association prevails. (2) For moderate PIB-size and moderate hydroxy-group density, as in PIB (1k) solutions, either self-association prevails, which increases the phase-boundary pressures above those for a model three-arm-star-PIB (4k) trimer, or solvent-polarity induces intramolecular association, which decreases the phase-boundary pressures. (3) For high PIB-size and low hydroxy-group density, such as PIB (11k) solutions, either cross-association prevails, which lowers the phase-boundary pressures, or solvent-polarity induces intramolecular association, which tends to increase phase-boundary pressures.; The statistical associating fluid theory (SAFT) neatly accounts for these phase-boundary shifts, if they are due to intermolecular association. If they are due to intramolecular association, effective SAFT sites and association parameters are needed to correlate the data. |
