Hybrid systems of acrylic monomers are studied as they undergo miniemulsion free radical polymerization in the presence of unsaturated alkyd resins. The goal of such polymerizations is to induce grafting between the acrylic and alkyd components, which would retard microdomain phase separation, and produce materials with the crosslinking capability of alkyd coatings (normally applied from a solvent system) with the environmental and cost benefits of an aqueous system. In this paper, the observed limiting monomer conversion phenomenon will be explored via simulation studies. Two mathematical models describing the kinetics of bulk hybrid polymerization of an alkyd-acrylate system were developed. The first was a homogenous model in which the kinetics of retardive chain transfer was used to attempt to simulate the observed phenomenon of limiting conversion. The second model was a core-shell model in which polymerization takes place in an acrylic-rich shell, while the alkydrich core serves as a reservoir for acrylic monomer and alkyd. Based on the results from these models, the cause of limiting conversion was attributed to the combined role of the glass effect and the partitioning effect of the monomer into a core-shell system and its subsequent entrapment. Retardive chain transfer was not capable of producing the observed limiting conversion. (C) 2004 Elsevier Ltd. All rights reserved.