Novel triblock copolymers consisting of end blocks of polyethylene oxide (PEO) and a center block consisting of urethane and carboxylic acid groups constitute an interesting class of polymers that can self-associate to form micelles in water. Micelles of hydrophilic block copolymers are of interest due to their use in the controlled delivery of drugs and other bioactive molecules. Micellization of these block copolymers results from a balance between hydrogen bonding and hydrophobic attraction in the core and repulsion between PEO chains in the corona. The size and mass of these micelles can be tuned by controlling pH and temperature, with ionic strength playing a lesser role. At pH 7 and 25 C, the copolymers are fully soluble unimers with hydrodynamic radius RH ~2 nm whereas at pH 2-3, protonation of the carboxylic acid groups in the core drives assembly of micelles with RH ~10-15 nm over a range of temperatures (25-65 C). These micelles were characterized by static and dynamic light scattering and small angle neutron scattering. The micelle size can be predicted with reasonable accuracy from aggregation number measurements using the Density Distribution model by Vagberg, et.al., that was based on the blob model for star polymers. The second virial coefficients can be predicted semi-quantitatively using a model by Likos, et al., also based on star polymers.