AQUEOUS-SOLUTIONS OF POLY(ETHYLOXAZOLINE) AND ITS LOWER CONSOLUTE PHASE-TRANSITION

Poly(2-ethyloxazoline) is a tertiary amide polymer that is completely soluble in water at temperatures below 60 °C, above which the system undergoes a liquid–liquid phase segregation. For Mw = 116 000 and Mw/Mn= 2.4, the critical concentration is 0.109 g cm<sp>-3</sp>, and the critical temperature is 65.3 °C. The macroscopic behavior of phase separation is given by the coexistence curve, which in the neighborhood of the critical point shows a cubic dependence on the reduced temperature. The behavior of PEOX in water is expressed in terms of excess thermodynamic functions of dilution derived from osmometry and static light scattering. The low-temperature thermodynamics are shown to be consistent with the phase transition. Static light-scattering experiments show excess scattering at small angles concurrent with the appearance of slow relaxation modes in dynamic scattering. Both are consistent with long-range concentration fluctuations in PEOX–water solutions. The variety of measurements is consistent with the hypothesis that the system can experience partial organization at all temperatures, even well below the LCST, and that the origin of the organization is a specific hydrogen-bonded interaction between the carbonyl oxygen of PEOX and water. © 1990, American Chemical Society. All rights reserved.