Spectroscopic Studies on Photophysical and Photochemical Processes in Associated Water-soluble Polymers

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Block copolymers has been known to form micelles (polymer micelles) in a solvent selective for one of the blocks. Many investigations have been performed on the micelles because they have a variety of properties different from conventional detergent micelles. This study has been undertaken to reveal the characteristics of polymer micelles as a reaction field for photophysical and photochemical processes such as energy transfer. The block copolymers employed are Pluronic F68 (EO_<78>PO_<30>EO_<78>) and Pluronic L64 (EO_<13>PO_<30>EO_<13>). The results obtained are as follows :1.Electronic energy transfer from rhodamine B (donor) to malachite green (acceptor) are examined. The energy transfer is drastically suppressed as the micelles are formed. The decrease of energy transfer is ascribed to that the increase of microviscosity upon micellization dominates other factors such as concentration effect.2.The structures of Pluronic micelles are investigated by the use of rhodamine B and octadecylrhodamine B as fluorescent probes. It is revealed that the micelles undergo a large conformational change from a swollen to a shrunken structure as temperature is increased and that the critical micelle concentrations (CMC's) of the Pluronics are strongly depend on temperature in contrast to those of conventional detergents. Microviscosities of the Pluronic micelles are estimated from the degree of polarization and the fluorescence lifetimes. The CMC's of the Pluronics are also determined.