A cyclic initiator for the nitroxide-mediated controlled radical polymerization (NMP) is a powerful tool for the preparation of macrocyclic polymers via a ring-expansion vinyl polymerization mechanism. For this purpose, we prepared a Hawker-type NMP-initiator that includes an azide and a terminal alkyne as an acyclic precursor, which is subsequently tethered via an intramolecular azide/alkyne-"click"-reaction, producing the final cyclic NMP-initiator. The polymerization reactions of styrene with cyclic initiator were demonstrated and the resultant polymers were characterized by the gel permeation chromatography (GPC) and the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). These results prove that the ring-expansion polymerization of styrene occurred together with the radical ring-crossover reactions originating from the exchange of the inherent nitroxides generating macrocyclic polystyrenes with higher expanded rings. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3402-3416, 2010