matic hydrocarbons over straight-chain hydrocarbons (1-Micelle structural properties were determined for five poly-3). These surfactants have also been investigated in areas of (ethylene oxide) -poly(propylene oxide) -poly(ethylene oxide) drug delivery (4-11). Advantages of using these surfactants triblock copolymer solutions at 25ЊC by using light scattering techinclude their low toxicity, the commercial availability of niques. Size distributions for the Pluronic series P103, P104, P105, many varieties, and their unique micellization behavior. F108, and P123 were found from dynamic light scattering. Aggre-The micelle-forming properties of the PEO-PPO-PEO gation numbers from both dynamic light scattering and static light copolymers are of considerable interest, in part because of scattering were determined, and the results are interpreted using the importance of these properties in applications involving fundamental hydrodynamic and statistical thermodynamic modsolute extraction or delivery (12,13). Critical micelle conels. The trends in aggregation behavior are discussed in terms of the surfactant composition. For a fixed poly(propylene oxide) centrations (CMC) for several of the PEO-PPO-PEO cocontent, surfactants with a higher poly(ethylene oxide) content polymers have recently been measured as a function of temwere found to be less aggregated. For a fixed poly(ethylene oxide)/ perature and polymer molecular structure ( 14). Studies of poly(propylene oxide) ratio, surfactants with a higher molecular the structure (size, shape, or aggregation number) of the weight were more aggregated. These results are shown to be in micelles above the CMC have largely focused on the effects agreement with previous self-consistent mean-field calculations for of temperature and concentration for individual polymer the same series of polymers and are compared with ''star'' and types; these studies are reviewed in a recent article by Alex-''brush'' model predictions for the effect of poly(ethylene oxide) andridis and Hatton (15). Less understood is the influence chain length on the thickness of the micelle corona. ᭧ 1997 Academic