To investigate the process for the preparation of well-defined poly-dimethylsiloxane-b-2,2,3,3,4,4,4-heptafluorobutylmetharylate block copolymers via a macroinitiator initiated atom transfer radical polymerization (ATRP), a model for the batch and semi-batch ATRP process was presented based on the method of moments. The ATRP mechanism, the diffusion limitation, and the reactor choice were considered in the model. Besides, the polymer molecular weight, monomer conversion, and polymer polydispersity index as a function of polymerization time were described by this model. The model was validated by comparing simulated results with experimental data and was also used to investigate the effects of diffusion limitation and reactor choice (i.e., batch and semi-batch reactors). (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3473-3481, 2013