Homogeneous bulk atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) was monitored by automatic continuous online monitoring of polymerization reactions (ACOMP). This allowed simultaneous monitoring of conversion, weight-average molar mass M-w, and intrinsic viscosity, from which the viscometric average molar mass M-v, and an index of polydispersity M-w/M-v, were also determined. For ATRP of BA, initiated by methyl 2-bromopropionate and catalyzed by copper bromide complexes with 4,4'-di(5-nonyl)-2,2'-bipyridine, ACOMP yielded an equilibrium constant, K-eq(90 degrees C) = 5.8 x 10(-10). The polymerizations exhibited first-order kinetics with respect to monomer and initiator concentrations, as expected for ATRP. These results set the stage for further detailed understanding of kinetics and mechanisms in ATRP reactions using ACOMP, where temperature and concentration dependences can be readily monitored.