We describe the synthesis of pH-responsive miktoarm star block terpolymers mu-[polystyrene][poly(ethylene oxide)] [poly(2-(dimethylamino)ethyl acrylate)] (mu-SODA) using a combination of two successive living anionic polymerizations and one reversible addition-fragmentation chain-transfer polymerization. Poly[2-(dimethylamino)ethyl acrylate] (PDMAEA) is a weak polybase that is hydrophilic at low pH and hydrophobic at high pH because of the protonation of the dimethylamino functional group with decreasing pH, In addition, our results suggest that PDMAEA is immiscible with polystyrene (PS),,I feature that is desirable for the formation of multicompartment micelles. Using it combination of dynamic light scattering and cryogenic transmission electron microscopy, we demonstrate that mu-SODA micelles formed in water evolve from mixed corona (PEO + PDMAEA corona; PS core) and predominantly spherical micelles to multicompartment (PEO corona; PS + PDMAEA core) micelles with increasing pH.