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SYNOPSISStatistical associating fluid theory (SAFT) is used to calculate the cloud-point behavior of poly(ethy1ene-co-methyl acrylate) (EMA) copolymers (0-41 mol % methyl acrylate) in ethane, propane, butane, ethylene, propylene, 1-butene, chlorodifluoromethane, and dimethy1 ether a t temperatures to 250°C and pressures to 2,600 bar. Poor agreement is obtained between calculated and experimental data if the pure component EMA parameters used in SAFT are calculated using mixing rules that average polyethylene (PE) and poly(methy1 acrylate) (PMA) parameters. Therefore, two of the three pure component parameters for all of the EMA copolymers are fixed to the values reported for P E and the third parameter, u"/k, for the copolymer containing 31 mol % methyl acrylate (EMASI) is determined by fitting the EMA3,-butane cloud-point curve. The value for (uo/k)pMA is then obtained using a mixing rule and the values of uo/k for all of the EMA copolymers are calculated. A good fit of all of the copolymer-solvent cloud-point curves is obtained using a temperature-independent mixture parameter, 12, . With this method of calculation it is possible to correlate cloud-point data with the SAFT equation of state if a small amount of experimental data are available.

Cloud‐point data to 180°C and 2,800 bar are presented for three poly(ethylene‐co‐methyl acrylate) copolymers [10, 31, and 41 mol % methyl acrylate (MA)] and for polyethylene in ethylene, ethane, propylene, and propane. At low concentrations of MA in the backbone of the copolymer, the saturated hydrocarbons are better solvents for the copolymer than their olefinic analogs because polarizability drives the phase behavior. For the higher MA‐content copolymers, which have more polar repeat units, the unsaturated hydrocarbons are better solvents owing to favorable quadrupolar interactions between the solvent and the polymer segments. The cloud‐point curves of the high MA‐content copolymers in the unsaturated hydrocarbons are shifted to very high temperatures to overcome strong acrylate‐acrylate interactions in the polymer. In fact, the 41 mol % MA copolymer cannot be dissolved in propane at temperatures to 180°C and pressures to 2,800 bar even though the copolymer is predominantly ethylene, while the same copolymer dissolves in propylene at 40°C and at pressures as low as 1,400 bar. Although the Sanchez‐Lacombe equation of state is used to model the cloud‐point curves, two temperature‐dependent mixture parameters are needed for a good fit of the data. © 1992 John Wiley & Sons, Inc.

Cloud‐point data to 180°C and 2800 bar are presented for polyethylene, poly(methyl acrylate), and two poly(ethylene‐co‐methyl acrylate) copolymers (10 and 31 mol % methyl acrylate) in propane and chlorodifluoromethane with two cosolvents, acetone and ethanol. The addition of small amounts of either cosolvent to the copolymer–solvent mixtures shifts the cloud‐point curve to lower pressures and temperatures, as both cosolvents provide favorable polar interactions with the acrylate group in the backbone of the copolymer. Ethanol has a larger effect than acetone since ethanol hydrogen bonds to the acrylate group. However, if the concentration of ethanol is increased above ca. 10 wt %, it self‐associates and reverts to antisolvent behavior, forcing the copolymer out of solution. For nonpolar polyethylene–propane mixtures, the polar cosolvents behave as traditional an‐tisolvents. In poly(methyl acrylate)–chlorodifluoromethane mixtures, both polar cosolvents enlarge the single‐phase region. The cloud‐point curves for the (co)polymer–propane–acetone mixtures are modeled reasonably well using the Sanchez–Lacombe equation of state with two adjustable mixture parameters. No attempt is made to model the mixtures that exhibit hydrogen bonding. © 1993 John Wiley & Sons, Inc.