Phase Diagrams and Aggregation Behavior of Poly(oxyethylene)-Poly(oxypropylene)-Poly(oxyethylene) Triblock Copolymers in Aqueous Solutions

The aggregation and phase behavior in water of several triblock copolymers of poly(oxethylene)poly(oxypropylene)-poly(oxyethylene) [(EO) x (PO) y (EO) x ] has been studied. The y-values of the compounds ranged from 16 to 70 and the x:y ratios from 0.1 to 2.5. All studied compounds form micelles and lyotropic liquid crystalline phases. Fow constant temperature the critical micelle concentrations (cmc) of the compounds decrease exponentially with y. The energy increment for the transfer of a PO group from the aqueous to the micellar state is about (0.25±0.05) kT. The cmc values for all compounds decrease strongly with increasing temperature. As a consequence the solutions undergo a monomermicelle transition for constant concentration and increasing temperature