AbstractSome of the distinguishing features of emulsion polymerization kinetics at high conversion are discussed. The apparent anomaly that propagation rate coefficients deduced from bulk and emulsion systems at high conversion are greatly different actually arises because the initiator efficiency in the former is very low. At intermediate and at high conversions, termination kinetics must take account of the length of each terminating chain; data and a new theoretical model for this are found to be in accord. Modelling the reaction‐diffusion equations at high conversion (including new theory to account for polymer migration) shows that large (say,>200 nm radius) particles at high conversion will show strong spatial inhomogeneity (core‐shell structure) even in emulsion homopolymerizations, because of the slow diffusion of monomer and free radic