Cloud-point data as a function of polymer molecular weight are presented for polyethylene (PE)-dimethyl ether (DME) and poly(ethylene-co-methyl acrylate) (35 mol % acrylate) (EMA)-butane mixtures to temperatures of 210 °C and pressures of 2700 bar. The cloud-point curves for PE-DME, at temperatures below ~125 °C, and EMA-butane, at temperatures below ~150 °C, order with respect to the weight average molecular weight. The cloud-point behaviors for these two systems along with the poly-(ethylene-co-acrylic acid) (4.1 mol % acid) (EAA)-butene system are modeled with the statistical associating fluid theory (SAFT). For each system, a constant value of the binary interaction parameter, fey, is fit to the parent-solvent cloud-point curve and is used in subsequent calculations. For the EAA system, values for the pure component energy of acid dimerization and the volume of association are obtained from literature spectroscopic data. The SAFT equation, with fey = 0.0405, can only predict the correct qualitative trends observed for the effect of molecular weight on the PE-DME system probably because SAFT does not account for polar DME-DME interactions. A quantitative fit of the EMA-butane system is obtained with fey = 0.026 and a slightly adjusted value of the nonspecific interaction energy for EMA. The calculations for the EAAbutene system with fey = -0.020 are in good agreement with experimental data.
Experimental cloud-point data to 250 °C and 2000 bar are
presented to demonstrate the
impact of dimethyl ether (DME) and ethanol on the phase behavior of
poly(ethylene-co-acrylic acid) (3.9
mol % acrylic acid) (EAA3.9)−butane mixtures. The
addition of 6.4 wt % DME to the EAA−butane system
decreases the cloud-point pressure from 2000 to 650 bar at 165 °C due
to the cross-association of dimethyl
ether and acrylic acid in EAA3.9. At high DME
concentrations, its impact is reduced as the amount of
DME increases since polar interactions between excess DME increase
after the acrylic acid sites are
saturated with DME. Ethanol is a better cosolvent than DME at low
ethanol concentrations. The addition
of 2.2 wt % ethanol decreases the cloud-point pressure from 2000 to
650 bar at 165 °C due to the cross-association of ethanol and acrylic acid in EAA3.9.
Ethanol becomes an “antisolvent” at
concentrations
greater than 16 wt % as excess ethanol self-associates, forming
multimers that increase the polarity of
the mixture. The cloud-point data are modeled with statistical
associating fluid theory (SAFT). The
ternary calculations use temperature-independent, binary mixture
parameters whose values are obtained
by fitting the phase behavior of the three binary pairs that form the
ternary system. SAFT correctly
predicts the trends observed in the cloud-point curves from zero to 100
wt % DME, although quantitatively
it overestimates the effect of DME. SAFT underestimates the effect
of ethanol, as the calculated one-phase region is smaller than that observed. However, SAFT correctly
predicts the decreasing impact of
ethanol with increasing ethanol concentration and that ethanol becomes
an antisolvent at high ethanol
concentrations.
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