Phase behavior of telechelic polyisobutylene in subcritical and supercritical fluids. 4. SAFT association parameters from FTIR for blank, monohydroxy, and dihydroxy PIB 200 in ethane, carbon dioxide, and chlorodifluoromethane

Phase-boundary pressures were measured for binary subcritical and supercrit ical fluid solutions of nonfunctional (referred to as blank), monohydroxy, and dihydroxy polyisobutylenes (200 g/mol) in ethane, carbon dioxide, and c hlorodifluoromethane from -50 to 200 degrees C up to 400 bar. As hydroxy gr oups were added to (blank) polyisobutylene, the phase-boundary pressure was found to increase due to intermolecular self- or cross-association. With c arbon dioxide rather than ethane as the solvent, these boundaries are (1) 2 -3 times lower in pressure and (2) shift differently than those reported in the literature for 2,5-hexanediol [HO-PE-OH (100)]. To examine these diffe rences, the association parameters for the statistical associating fluid th eory model (SAFT) were determined from spectroscopic data and then used to calculate phase boundaries and aggregate size for HO-PIB-OH (200) and HO-PE -OH (100), The SAFT analysis suggests that the steric hindrance due to the methyl branches in PIE decreases the aggregate size and hence lowers the ph ase-boundary pressure.