In addition to associating into (''normal'') micelles in aqueous blocks (1). Many of these copolymers associate in aqueous solutions, amphiphilic polyoxyalkylene block copolymers can form solutions to form spherical micelles (with a ''core'' made ''reverse'' micelles in organic solvents at sufficiently high copolyup from the water-insoluble PPO or PBO blocks and a ''comer concentrations (above the critical micellization concentration rona'' composed by the water-soluble PEO blocks) (2-4);
(CMC)) and in the presence of some water. The effects of solvent at higher concentrations, polyoxyalkylene block copolymers quality on the copolymer micellization in an organic solvent and can also self-assemble into lyotropic liquid crystals (5-7). on the solubilization of water in such systems are examined here A strongly endothermic micellization (and temperature-defor representative poly(ethylene oxide)-b-poly(propylene oxide)pendent CMC) in water is one of the salient features of b-poly(ethylene oxide) (PEO-PPO-PEO) and poly(butylene ox-PEO-PPO-PEO copolymers (8, 9).
ide)-b-poly(ethylene oxide) (PBO-PEO) copolymers. The solvent quality is modulated by the addition of cosolutes and by a change
Following the reports (10-13) on the water-induced miin the temperature. A number of notable observations are reported: celle formation of a PEO-PPO-PEO copolymer (Pluronic Worsening the aqueous solvent conditions by the addition of NaCl L64: EO 13 PO 30 EO 13 ) in o-xylene and our study (14) of the (10 wt% with respect to water) almost doubles the CMC and the ternary EO 13 PO 30 EO 13 -water-p-xylene phase diagram at water solubilization capacity (WS) of a PEO-PPO-PEO copoly-25ะC, where we showed that EO 13 PO 30 EO 13 was completely mer in p-xylene. An increase in temperature makes water a worse miscible with p-xylene and formed an isotropic solution (L 2 and xylene a better solvent for the copolymer. The combined result region) along the copolymer-oil axis which could solubilize of heating is an increase of the CMC for all three copolymers up to approximately two water molecules per EO segment, studied. This indicates that the formation of reverse micelles is we undertook a systematic investigation of the polyoxyalkyexothermic, which is opposite to what has been observed for norlene block copolymer solution behavior in organic solvents mal micelles. The effects of temperature on the water uptake are (selective for the PPO and PBO blocks) and of the solubilinonmonotonic: WS increased with temperature for a PEO-PPOzation of water (selective solvent for the PEO blocks) in PEO copolymer with 40% PEO but decreased for a copolymer with 20% PEO. An increase in WS with temperature, followed by such solutions. We detected the formation of ''reverse'' a decrease, with the maximum WS efficiency occurring at the (PEO core and PPO or PBO corona) micelles in organic ''effective'' cloud point of the copolymer is proposed in order to solvents upon increasing the copolymer concentration explain this observation.