AbstractThe stabilizing efficiency of a variety of amphipathic copolymers was studied in aqueous emulsion polymerizations of styrene, methyl methacrylate and acrylonitrile. Using the number, and size of the particles as the criterion of stability, it was found that the availability for anchoring of the backbone in the amphipathic graft copolymers was crucial for stability. Within a system, a change in the backbone chain length with the same percent hydrophilic grafts had no effect on the outcome of the reaction: the latices stabilized to the same number of particles of the same size.The results with the polystyrene‐block‐poly(ethylene oxide) copolymers as stabilizers in styrene polymerization gave indication that for efficient anchoring the block length need not be more than 10 monomeric units, and that a poly(ethylene oxide) (PEO) with weight‐average molecular weight Mw = 3000 is just as effective stabilizer as is a block with PEO of Mn = 9000.