POLYMER MICELLE FORMATION .3. POLY(STYRENE-ETHYLENE OXIDE) BLOCK COPOLYMER MICELLE FORMATION IN WATER - A FLUORESCENCE PROBE STUDY

Block copolymer micelle formation was studied by a combination of fluorescent probe and quasi-elastic light scattering (QELS) techniques. The polymers, polystyrene-poly(ethylene oxide) diblock and triblock copolymers, with MBAR(n) values ranging from 8500 to 29 000, form spherical micelles in water over the entire concentration range over which QELS signals can be detected. Pyrene (Py) in water (6 X 10(-7) M) partitions between the aqueous and micellar phases, accompanied by three changes in the pyrene spectroscopy. There is a red shift in the excitation spectrum, a change in the vibrational fine structure of Py fluorescence (I1/I3 decreases from 1.9 to 1.2), and an increase in the fluorescence decay time (from 200 to ca. 350 ns) accompanying transfer of Py from an aqueous to a hydrophobic micellar environment. From these data, critical micelle concentrations (range: 1-5 mg/L) and partition coefficients (3 X 10(5) can be calculated.