REVERSE MICELLE FORMATION AND WATER SOLUBILIZATION BY POLYOXYALKYLENEBLOCK-COPOLYMERS IN ORGANIC-SOLVENT

A systematic investigation of the effects of polymer chemical composit ion and molecular mass on (i) the micellization of polyoxyalkylene blo ck copolymers [poly(ethylene oxide)/poly(propylene oxide), PEO/PPO, an d poly(ethylene oxide)/poly(butylene oxide), PEO/PBO] in an organic so lvent(p-xylene: selective solvent for the PPO and PBO blocks) in the p resence of some water and (ii) the solubilization of water (selective solvent for the PEO blocks) in these systems is presented. The ability of the (''reverse'') micelles to solubilize water has been employed f or the detection of the critical micellization concentration (''revers e'' cmc). The ''reverse'' cmc values were in the range 0.01-0.1 m (5-2 0 wt %), while the maximum water solubilization values were 0.3-0.5 g of water per g of copolymer. The cmc decreased with increasing copolym er molecular mass for a given copolymer chemical composition. A notabl e increase (more than doubling) in the water solubilization capacity ( expressed in water molecules per EO segment) was observed when the PEO content of PEO-PPO-PEO copolymers decreased from 40 to 20%. A simple model for the reverse micelles is developed (based on the volume fract ions of the different components and the effective length of a copolym er molecule) that captures experimental trends and allows the estimati on of the (spherical) micelle radius and aggregation number.