COSOLVENCY EFFECTS ON COPOLYMER SOLUTIONS AT HIGH-PRESSURE

Cloud-point data to 180-degrees-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 antisolvents. 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.