We report a ring expansion vinyl polymerization producing cyclic polymers using a tetra(oxyethylene) (TOE) tethered cyclic initiator for the nitroxide-mediated controlled radical polymerization (NMP). Styrene (St) was polymerized with the cyclic NMP initiator 1 in the bulk to produce polymer 2. Structural analyses of 2 were performed by a size exclusion chromatograph equipped with a multiangle laser light scattering (SEC-MALS) detector, focusing on the relationships between the z-averaged root-mean-square radii of gyration (< S-2 >(1/2)(z)) versus the molecular weights. The results proved that 2 would consist of ring components as a result of the ring expansion polymerizations and radical ring crossover reactions together with ring-opened linear components, in which the amount of ring components increased with the increasing molecular weights. The data also enabled the quantification that approximately 13-40 wt% of the final polymer 2 could be identified as the ring species in the M-w range of 1 x 10(5)-5 x 10(5) g mol(-1) (C) 2016 Elsevier B.V. All rights reserved.