Micellization of polyoxyethylene-polyoxypropylene block copolymers in aqueous polyol solutions

The micellization of a representative polyoxyethylene-polyoxypropylene-polyoxyethylene (POE-POP-POE) amphiphilic block copolymer (Pluronic P105, EO37PO58EO37) in aqueous solutions of the common excipients glucose, glycerol or ethanol, has been investigated as a function of solute (solvent) concentration, block copolymer concentration, and temperature. The formation of POE-POP-POE micelles is favored in the presence of glucose or glycerol, while ethanol has the opposite effect. ΔH° and ΔS° values derived from analysis of critical micellization concentration (CMC) data are both positive in all mixed aqueous polyol systems. ΔH° and ΔS° decrease slightly with increasing glucose or glycerol content, but increase significantly in the presence of ethanol. A 10- to 100-fold increase of the amphiphilic block copolymer solution viscosity was observed in the presence of glucose or glycerol above a certain temperature. This viscosity increase is indicative of micelle shape changes from spherical to elongated. The CMC and viscosity changes caused by glucose and glycerol are attributed to the enhanced dehydration of the POE block of the polymeric amphiphile. Glucose is more effective than glycerol, apparently due to its higher hydration number.