A dynamic model for a system containing a semi-batchwise operating reaction vessel connected to a distillation unit was developed. The approach consisted of kinetic equations for the reactions as well as a dynamic model for the distillation unit. As an example reaction, the catalyzed polyesterification of maleic acid with propylene glycol was used. The kinetic and the mass transfer parameters at 170 degrees C were estimated from experimental data. The fit of the model to the data indicated that the approach is suitable for the description of semibatch liquid phase reaction-separation systems.