Copolymers E96B18, E184B18, E315B17, and E398B19 (E = oxyethylene unit, B = oxybutylene unit) were synthesized and characterized by gel permeation chromatography (for distribution width) and C-13 NMR spectroscopy (for absolute molar mass and composition). Dynamic and static light scattering was used to determine micellar properties in dilute aqueous solution at three temperatures (25, 40, and 50 degrees C): that is, hydrodynamic radius and hydrodynamic expansion factor, mass-average molar mass, and thermodynamic expansion factor. At a given temperature, the values of the radii and expansion factors increased as E-block length was increased, whereas values of the micelle association number decreased. The tube-inversion method was used to define the mobile-immobile (hard gel) phase boundary. At room temperature (20 degrees C), hard gels were formed in the concentration range 3.5-8 wt % copolymer depending on E-block length, the lowest value being for the copolymer with the longest E block (E398B19).