The self-aggregation of a series of amphiphilic poly(methyl methacrylate)-block-poly(sulfonated glycidyl methacrylate) (PMMA-b-PSGMA) copolymers in water has been studied by dynamic light scattering (DLS), size exclusion chromatography (SEC) and surface tension measurements. All the copolymers considered in this study form micelles which, however, aggregate into larger structures as shown by DLS and SEC. These larger structures dissociate into smaller ones upon increasing the temperature. The extent of this dissociation process is strongly dependent on the copolymer composition. It is large as the content of the hydrophilic block is high.