PHASE-EQUILIBRIUM AND CONFORMATION OF A POLYMER IN A BINARY SOLVENT

The phase equilibrium behavior of a dilute high molecular weight polym er (poly-ethylene oxide PEG, molecular weight 9x10(5), concentration 0 .001 g/cc) solution in a two-component liquid mixture (isobutyric acid + water, IBAW) is studied experimentally. Far above the critical temp erature T-c of IBAW, we found that although PEO dissolved in pure isob utyric acid (IBA) and pure water, mixtures of IBA and water with 0.1% PEO became cloudy within a certain composition range. Far below T-c, w hen the binary mixture phase separates in two coexisting phases, the p resence of PEO which dissolved in both phases did not affect the coexi stence curve of the binary mixture, Around T-c, three phases in coexis tence were observed in a narrow composition range near the critical co mposition of IBAW. At high temperature (similar to 24 degrees C above T-c) the size of PEO in IBAW was measured by light scattering method a t different IBAW compositions, We observed expansion of PEO molecules in the mixed solvent,which can be explained using the single liquid ap proximation by Scott. Such an expansion caused the macromolecules to o verlap and separate from the solvent.