Water-soluble, SG1 nitroxide-capped poly(methacrylic acid-co-styrene) macroalkoxyamines with similar to 10 mol % of styrene subunits were used as initiators in the surfactant-free, ab initio, batch, emulsion homopolymerization of methyl methacrylate and its copolymerization with a low percentage of styrene, in alkaline conditions at temperatures below 90 degrees C. The polymerizations were well-controlled, with a very high initiating efficiency. due to the high dissociation rate constant of the macroalkoxyamines. It led to the in situ formation of amphiphilic block copolymers that self-assembled into small particles with diameter below 100 nm, according to a polymerization-induced micellization process. The polymerization kinetics, the control over molar mass and molar distribution, and the colloidal characteristics of the so-formed block copolymer micelles were studied in detail. This work represents a breakthrough in controlled/living radical polymerization in aqueous emulsion with the development of new, very efficient macroinitiators used as the sole additive for initiation, stabilization, and chain-growth control. It is also the first development of nitroxide-mediated emulsion polymerization of methyl methacrylate performed at low temperature.