NMR-STUDIES OF THE STRUCTURE AND INTERACTIONS OF BLOCK-COPOLYMER MICELLES IN WATER .4. DIFFUSION OF ORGANIC SOLUBILIZATES INTO THE MICELLARCORE

Solubilization of relatively hydrophobic organic compounds (solubiliza tes) by the core of poly(methyl methacrylate)-block-poly(acrylic acid) (PMMA-PAAc) micelles in D2O was theoretically simulated and experimen tally studied for a number of compounds such as chloroform, chlorobenz ene, 4-methylcyclohexanone, benzene, toluene, cyclohexane, and hexane. The experimental results show that (i) the core-captured amount of th e solubilizate as well as its solubilization rate chiefly depend on it s interaction with PMMA (expressed, e.g., by its X-parameter), (ii) th e limiting solubilization degree may also be determined by other therm odynamic factors, in particular the core-water interphase tension, (ii i) the solubilization rate and partly the equilibrium solubilization d egree are also influenced by shell-core interactions, (iv) most solubi lizates, except chloroform, swell the core with a surprisingly narrow front, which could indicate a steep concentration dependence of their diffusion coefficient but also (v) there is morphological inhomogeneit y of the core with more easily accessible domains in the outer part of the core. The last conclusion is also supported by the much lower sol ubilization rates observed with micelles formed by copolymers with lon ger PMMA blocks.