Liquid biphase systems formed in ternary mixtures of two organic solvents and ethylene oxide oligomers or polymers

Phase equilibrium data were determined for ternary systems containing ethyl ene oxide oligomers or polymers, heptane and one of three organic solvents (methanol, dichloromethane or chloroform). The effects of temperature, of p olymer molecular weight and of the chemical nature of the organic solvent o n phase equilibrium were investigated. For all the studied systems, the mis cibility region was reduced as temperature decreased, indicating an exother mic phase separation process. For both binary and ternary mixtures, the mis cibility also decreased as the macromolecule size increased, although this effect was less significant for the ternary mixtures. These features sugges t that phase separation is more influenced by enthalpic than entropic contr ibutions. Regarding the different polar solvents investigated, methanol pre sented a much smaller miscibility region, in accordance with its inferior s olvation ability for PEO. The largest miscibility region was observed with chloroform, not much different from the behaviour observed with dichloromet hane. Tie lines were determined for some systems, confirming the strong seg regation between polymer and the hydrocarbon solvent.