ANOMALOUS MICELLIZATION BEHAVIOR AND COMPOSITION HETEROGENEITY OF A TRIBLOCK ABA COPOLYMER OF (A) ETHYLENE-OXIDE AND (B) PROPYLENE-OXIDE IN AQUEOUS-SOLUTION

Dynamic light scattering in combination with time-averaged scattered light intensity measurements has been employed to study the temperature-induced micellization behavior of poly(oxyethylene-oxypropylene-oxyethylene) block copolymer, poloxamer 184, in aqueous solution. As experimentally evidenced, there exist three temperature regions, namely, the unimer and micelle regions at the two extremes and an anomalous association behavior in the middle region which manifests itself with a milky opalescent appearance and a large angular dissymetry in the scattered intensity before the onset of micellization. When filtration experiments are carried out to remove the 'opalescent' minor components, the anomalous region is replaced by a normal transition region, where an equilibrium mixture of unimers and micelles occurs. Results of the composition analysis by NMR spectroscopy strongly support the composition heterogeneity mechanism for the anomalous association behavior.