Semi-batch polymerizations have become increasingly important for the production of a wide variety of copolymers. An important class of copolymers result from polymerizations in which one or both of the comonomers initially reside in the gaseous phase. We report herein on a study of an important copolymer for paint, adhesive and coating applications, namely, ethylene-vinyl acetate (EVA). This study is comprised of two main sections; experimental kinetics and mathematical modelling. Through a series of carefully designed factorial experiments, the effects of twelve process variables on EVA emulsion polymerization were investigated. These included pressure, temperature, emulsifier type and concentration, initiator type and concentration, the addition of stabilizer, the addition of co-solvent, agitation, buffer, vinyl acetate feed rate and reactor configuration. The primary objectives of the research were to increase the amount of ethylene which could be incorporated into the copolymer at reduced temperatures and pressures, to achieve an improved process understanding and to accumulate reliable data for modelling purposes. A copolymer of about 34 weight per cent ethylene has been achieved. In addition to copolymer composition, molecular weight averages, particle size and number, gel content and rates of polymerization were also examined. This study not only offered improved kinetic information but also helped to identify those reaction conditions under which ethylene mass transfer limitations prevail. For this reason a more detailed study of the reactor design itself was also performed. Data showing the effects of impeller design, sparging and agitation on the cumulative copolymer composition have been collected. As a result, one can identify the requirements, with respect to both reaction kinetics and reactor design, for the production of a high solids, homogeneous, high ethylene content copolymer. The partitioning behaviour of ethylene was clarified through the collection of high pressure ethylene solubility data. The monomer partitioning information was incorporated into a mechanistic EVA emulsion polymerization mathematical model. All mechanistic features identified during the experimental portion of the work were integrated into this model. Model predictions were compared with the kinetic data collected and found in satisfactory agreement.