WATER-INDUCED MICELLE FORMATION OF BLOCK COPOLY(OXYETHYLENE OXYPROPYLENE OXYETHYLENE) IN O-XYLENE

Static and dynamic light scattering, viscometry, NMR, and vapor pressu re osmometry techniques have been employed to study the water-induced micellization behavior of poly(oxyethylene-oxypropylene-oxyethylene) b lock copolymer, Pluronic L64, in o-xylene solution. Results show that Pluronic L64 does not form polymolecular micelles in the absence of wa ter or in the presence of a small amount of water (molar ratio water/E O < 0.15). Micelles, consisting of a PPO shell and a PEO and H2O core, are formed when the water to EO molar ratio (Z) in the micelle is gre ater than 0.2. For Z < 1.3, spherical micelles with an average hydrody namic radius R(h) of Ca. 9.2 nm are formed, with R(h) almost independe nt of Z. For Z > 1.3, both the aggregation number and the hydrodynamic radius become dependent on the Z value, then the micelle shape could be nonspherical. As experimentally evidenced by NMR spectra, the solub ilized water can be classified into bound water and free water. Most l ikely, water is not evenly distributed in the core, as the environment s of EO units at different positions in the block copolymer are not id entical.