FLUORESCENCE STUDIES OF NAPHTHALENE-LABELED DIBLOCK AND TRIBLOCK COPOLYMER MICELLES IN ORGANIC MEDIA

A-B diblock copolymers of polystyrene-block-poly(methyl methacrylate) were prepared by anionic polymerization and labeled with one naphthalene either at the polystyrene block end or at the polystyrene/methyl methacrylate block boundary. B-A-B triblock copolymers of poly(tert-butyl methacrylate)-block-polystyrene-block-poly(tert-butyl methacrylate) were prepared by anionic polymerization and labeled with two naphthalenes in the middle of the polystyrene block. Quasi-elastic light scattering was used to study the transition from unimers to micelles as a function of volume percentage of the solvent system 1,4-dioxane/methanol and the steady-state and time-resolved fluorescence and fluorescence depolarization properties were investigated under the same conditions. Changes in all the fluorescence properties seem to be primarily a function of the collapse of the micelle cores. For end-tagged copolymers, the probe most likely resides in the micellar core and the fluorescence properties change dramatically upon the formation of micelles but change little thereafter. As the center-labeled copolymers undergo the transition from unimers to micelles with increasingly compact cores, the changes in fluorescence properties are more continuous than those observed for the end-tagged copolymers.