Ethylene oxide and styrene oxide were sequentially polymerized to form the diblock copolymer E(17)S(8) (E = oxyethylene, OCH(2)CH(2); S = oxyphenylethylene, OCH(2)CH(C(6)H(5)); subscripts denote number-average block lengths in repeat units). Light scattering was used to investigate the properties of the micelles formed in dilute solution in the temperature range 15-30 degrees C. The micelles are elongated (probably spheroidal) at the lower temperature and highly elongated (cylindrical, probably wormlike) at the higher temperature. Comparison with results reported for the copolymer E(11)B(8) (B = oxybutylene, OCH(2)CH(C(2)H(5))) allowed exploration of the effect of changing the hydrophobic block. The results provide useful indicators toward the design of ES copolymers with optimal solubilization properties.