Phase equilibrium data were determined for ternary systems containing ethylene oxide oligomers or polymers, heptane and one of three organic solvents (methanol, dichloromethane or chloroform). The effects of temperature, of polymer molecular weight and of the chemical nature of the organic solvent on phase equilibrium were investigated. For all the studied systems, the miscibility region was reduced as temperature decreased, indicating an exothermic phase separation process. For both binary and ternary mixtures, the miscibility also decreased as the macromolecule size increased, although this effect was less significant for the ternary mixtures. These features suggest that phase separation is more influenced by enthalpic than entropic contributions. Regarding the different polar solvents investigated, methanol presented a much smaller miscibility region, in accordance with its inferior solvation ability for PEO. The largest miscibility region was observed with chloroform, not much different from the behaviour observed with dichloromethane. Tie lines were determined for some systems, confirming the strong segregation between polymer and the hydrocarbon solvent.
poly(ethylene oxide); liquid-liquid equilibria; polymer solutions; preferential solvation
