A reactive polymeric surfactant that contains: (a) at least two hydrophilic monomeric units per molecule, each independently according to formula (I): wherein R1 is alkylene or oxyalkylene, R2 is H, methyl, or ethyl, R3 is H, and n is greater than about 5, (b) one or more hydrophobic monomeric units per molecule, each independently according to formula (II) wherein R4 is H or methyl, R5 is a hydrophobic group, is useful in stabilizing aqueous emulsions and aqueous dispersions.