Effects of diffusion control in a compartmentalized atom transfer radical polymerization (ATRP) system have been investigated by modeling and simulations employing modified Smith-Ewart equations in connection with conversion-dependent rate coefficients for the system styrene/polystyrene-Cl/CuCl/4,4'-di(5-nonyl)-2,2'-bipyridine (dNbpy) at 75 degrees C. The effects of conversion-dependent rate coefficients for deactivation (k(deact)) and termination (k(1)) were investigated in detail for the particle diameter 30 nm, i.e., a strongly compartmentalized system. The decrease in k(deact) at high conversion results in an increase in the number of monomer units added per activation-deactivation cycle, thereby causing slight loss of control relative to when k(deact) remains constant. The conversion dependence of k(1) results in a minor increase in livingness at high conversion relative to when k(1) remains constant. The individual compartmentalized rates of deactivation and termination have been analyzed in detail based on the particle distributions N-1' where N-1' is the number of particles containing i propagating radicals and j deactivator species.