The micellar properties and solubilization capacity of poorly water soluble drugs of several micellar and gel solutions of diblock and triblock copolymers of styrene oxide/ethylene oxide have been measured and compared with block copolymers of butylene oxide/ethylene oxide, showing that the solubilization capacity of the styrene oxide block is approximately four times that of a butylenes oxide block for dilute solutions. To continue establishing the correlation between micellar characteristics and solubilization capacity, we have found it interesting to compare the micellar and gelation properties of the diblock and triblock copolymers PSO10PEO135 and PEO69PSO8PEO69 (subindexes are the number-average block lengths), with different architecture but similar average block lengths. Surface tension measurements allowed the determination of the critical micelle concentrations at several temperatures and, so, to calculate standard enthalpies of micellization. Static and dynamic light scattering data permitted us to determine micellar parameters and to obtain qualitatively the extent of hydration of the copolymer micelle. A tube inversion method was used to define the mobile-immobile (soft-hard gel) phase boundary. To refine the phase diagram and observe the existence of additional phases, rheological measurements were done. The results are in good agreement with previous values published for PSOnPEOm and PEOmPSOnPEOm copolymers.

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