Amphiphilic diblock copolymers with varying compositions of hydrophilic poly [bis(methoxyethoxyethoxy)phosphazene] and hydrophobic polystyrene were synthesized via the living, cationic polymerization of Cl3P=NSiMe3, using a polystyrenyl-phosphoranimine as a macroterminator. The self-association behavior of the block copolymers in aqueous media was investigated using fluorescence spectroscopy, transmission electron microscopy, and dynamic light scattering. The critical micelle concentrations of PS-MEEP block copolymers with molar block ratios of 1:0.37, 1:0.58, 1:0.70, and 1:0.86 were determined to be 1.8, 2.3, 10.0, and 13.6 mg/L, respectively. The mean diameters of micelles of these block copolymers were measured as 167, 168, 179, and 173 nm through dynamic light scattering. The equilibrium constants of pyrene in these micelles ranged from 5.75 x 10(5) to 7.31 x 10(4).