We carried out the suspension polymerization of styrene, initiated with benzoyl peroxide at 80degreesC, in the presence of the simultaneous polymerization of acrylic acid in the water phase, initiated by potassium peroxidisulfate (KPS) at the same temperature. The polymerization in the water phase was started at certain times after the beginning of the polymerization of styrene. Then, a continuous addition of KPS was carried out at a given landing rate and during variable feeding times. The water-phase polymerization actually produced a copolymer of styrene and acrylic acid, which displayed surface-active properties. The particle size distribution depended on the variables mentioned earlier (starting time, KPS feeding rate, and addition time), being controlled by the molecular weight, and on the composition of the copolymer produced and its availability at the increasing conversion of styrene. A second distribution of submicronic particles was produced. Both families of particles had about the same molecular weight.