The ability of atom transfer radical polymerization (ATRP) in the sequential synthesis of triblock copolymers was examined using Cu(I)Cl/2,2 ' -bipyridine catalysis at 110 degreesC in toluene, starting from PMMA macroinitiators terminated with the C-Br group. The PMMAs were prepared by living anionic or group transfer polymerization (GTP), followed by bromination of the respective active site with Br, or N-bromosuccinimide (NBS). The yield of the terminal bromination in the products of both living polymerizations was 60-64% at best, compared with the yield of the bromination of 1-methoxy-(1-trimethylsilyloxy)prop-1-ene (a model of the GTP active site) with NBS, as found by H-1-NMR. The PMMA macroinitiators prepared were utilized to start the sequential ATRP, finally affording PMMA-b-PBuA-b-PSt (M-n 69,100), PMMA-6-PStb-PBuA (M-n 21,300) and PMMA-b-PSt-b-PMMA (M-n 35,200), which have not yet been synthesized by ATRP. After the second block has been formed, the Br-unterminated part of PMMA macroinitiator was removed by extraction or repeated precipitation. In the third (last) sequence polymerization, induction periods were observed. The first two triblock copolymers were free of precursors and have M-w/M-n values 1.5-1.6 (SEC). In the course of the last step of PMMA-b-PSt-b-PMMA synthesis, the content of the PMMA-b-PSt precursor slowly decreased with increasing MMA conversion. Still, at approximate to 90% MMA conversion, about 10-15% of the precursor remained in the product.