High-Pressure phase behavior of mixtures of poly(ethylene-co-methyl acrylate) with low-molecular weight hydrocarbons

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.