The preparation of ABA-type block copolymers via tandem enhanced spin capturing polymerization (ESCP) and nitroxide-mediated polymerization (NMP) processes is explored in-depth. Midchain alkoxyamine functional polystyrenes (M-n = 6200, 12,500 and 19,900 g mol(-1)) were chain extended with styrene as well as tert-butyl acrylate at elevated temperature NMP conditions (T = 110 degrees C) generating a tandem ESCP-NMP sequence. Although the chain extensions and thus the block copolymer formation processes function well (yielding in the case of the chain extension with styrene number average molecular weights of up to 20,800 g mol(-1) (PDI = 1.22) when the 6200 g mol(-1) precursor is used and up to 67,500 g mol(-1) (PDI = 1.36) when the 19,900 g mol(-1) precursor is used and 21,600 g mol(-1) (PDI = 1.17) as well as 37,100 g mol(-1) (PDI = 1.21) for the tert-butyl acrylate chain extensions for the 6200 and 12,500 g mol(-1) precursors, respectively), it is also evident that the efficiency of the block copolymer formation process decreases with an increasing chain length of the ESCP precursor macromolecules (i.e., for the 19,900 g mol(-1) ESCP precursor no efficient chain extension with tert-butyl acrylate can be observed). For the polystyrene-block-tert-butyl acrylate-block-polystyrene polymers, the molecular weights were determined via triple detection SEC using light scattering and small-angle X-ray scattering. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4841-4850, 2011