The effects on the molecular weight development of chain segregation in emulsion polymerization are discussed both theoretically and experimentally. A large delay on gel formation induced by carrying out the polymerization reaction in emulsion instead of in bulk is predicted by the model. Two systems of practical interest (polyvinyl acetate and polybutyl acrylate) are then examined. In the first case, literature experimental data are compared with model predictions. The synergic effect of the different branching mechanisms on the molecular weight polydispersity is highlighted. In the second case, original experimental data obtained in a calorimetric reactor are presented. The predicted onset of gel formation at conversion values larger than those expected in bulk polymerization is experimentally verified.