A scale-down study of an industrial reactor for the production of polyvinyl chloride (PVC) via an emulsion polymerization process was carried out in order to understand the source of batch-to-batch variations in product quality. In Part 1, an analysis of the plant is presented and the industrial recipe scaled down to a pilot-scale reactor. In the following Parts 2 and 3 a systematic analysis of the main process parameters revealed that particle generation and stabilization actually occurred in a manner slightly different from what was thought at the production site.