The preparation of functional copolymers based on allyl methacrylate (AMA) and butyl acrylate (BA) without gel formation via atom transfer radical polymerization is described. The gelation-free controlled radical copolymerizations were carried out in benzonitrile solution at 70 degrees C using ethyl 2-bromoisobutyrate as initiator and mixed halogen technique, copper chloride along with N,N,N '',N ''-pentamethyldiethylenetriamine as the catalyst system. Kinetic analyses have demonstrated that all the copolymerizations showed a general behaviour characterized by two clearly differentiated stages. Thus, in an initial stage, the polymerizations presented first order kinetic with respect to the monomer concentration. In the subsequent stage, at low-intermediate conversions, a deceleration in the rate copolymerization leads to limit conversions, which decrease as the initial concentration of BA in the feed increases. The reactivity ratios values were calculated from the copolymer composition determined by H-1 NMR, and using the extended Kelen-Tudos method. Values of 2.70 +/- 0.21 and 0.49 +/- 0.04 were obtained for AMA and BA, respectively. The cumulative copolymer compositions as a function of conversion degree for the different monomer molar fractions in the feed showed gradient character of the copolymers obtained. (c) 2006 Elsevier Ltd. All rights reserved.