An N-alkoxyamine macroinitiator bearing a polymeric nitroxide cap was synthesized and used to investigate the effect of nitroxide size on the rate of nitroxide-mediated radical polymerization (NMRP). This macroinitiator was prepared from asymmetric double-headed initiator 9, which contains both an alpha-bromoester and an N-alkoxyamine functionality. Poly(methyl methacrylate) was grown by atom transfer radical polymerization from the a-bromoester end of this initiator, resulting in a macroinitiator (M-n = 31,000; PDI = 1.34) bearing a nitroxide cap permanently attached to a polymer chain. The polymerization kinetics of this macroinitiator in NMRP were compared with known N-alkoxyamine initiator 1. It was found that the rate of polymerization was unaffected by the size of the macromolecular nitroxide cap. It was confirmed that NMRP using this macroinitiator is a "living" process. (c) 2007 Wiley Periodicals, Inc.