The Cu(0)/Me-6-TREN-catalyzed polymerization of methyl acrylate (MA) initiated by methyl 2-bromopropionate (MBP) in DMSO at 25 degrees C was performed in a UV cuvette, and the absorbance of CuBr2 was monitored online in a UV-vis spectrophotometer as a function of the monomer conversion. A continuous increase of CuBr2 absorbance throughout the reaction demonstrated no reduction of CuBr2 concentration during the entire polymerization process. In addition, the 100% chain-end functionality of the polymer observed from 10% to 95% monomer bimolecular termination required to provide the persistent radical effect in ATRP was not responsible for the production of CuBr2.