Activation Thermodynamics and Concentration Scaling of the Viscosity of Unimeric and Aggregated Poloxamer EO93PO54EO93 in Water

Abstract

The viscosity of the aqueous solutions of Poloxamer EO93PO54EO93 (a triblock copolymer of ethylene oxide, EO, and propylene oxide, PO) was determined at concentrations ranging from 0.002 to 0.12 g·mL–1 at 0.9, 8.9, and 20.0 °C where only unimers are present, at 24.9 and 30.3 °C where the unimers are in equilibrium with aggregates and at 39.8 and 49.8 °C where only aggregates are present. The reciprocal of the intrinsic viscosity derived from Huggins, Kraemer, Martin and Phillies’s models is compared to the experimentally determined overlap concentration. A simple model that accounts for intermolecular interactions provides better estimates of the experimental overlap concentration. The concentration scaling exponents of the viscosity at low and high concentrations are compared to the predictions for entangled polymer chains. It is suggested that at low temperature, the Poloxamer molecules evolve from dilute unimers to semidilute unentangled unimers. At high temperature, Poloxamer molecules evolve from dil...