Fully crosslinked, stable poly(styrene-co-divinylbenzene) microspheres were prepared by precipitation polymerization, and a new mechanism is proposed, based on the morphology, circularity, and specific surface area. Once the stable particles were generated by aggregation of the primary nucleus particles, they grew in size by absorbing oligomeric species without generating substantial pores. The investigation was carried out characterizing the particles in the polymerization time and in various concentrations of the polymerization ingredients. Particle size continuously grew, but the uniformity and circularity of the microspheres were reduced with polymerization time because of the higher reactivity of divinylbenzene. The measured specific surface areas of the microspheres all were less than 10 m(2)/g, which showed good agreement with calculated values under an assumption of no pores on the surface of the microspheres. Thus, the specific surface area of the microspheres supported the proposed mechanism. (C) 2004 Wiley Periodicals, Inc.