A series of cyclic nitrones have been tested for their spin-trapping activity in the enhanced spin-capturing polymerization of styrene and in nitrone-mediated radical coupling reactions. rac-2-Isopropyl-2,3-dimethyl-1-oxy- 2,3-dihydro-imidazol-4-one was found to be the most efficient nitrone. The specific polystyrene macroradical addition rate to this nitrone was determined to be 8.010 3Lmol -1s -1, which is by a factor of 10 higher than for previously studied compounds. Via enhanced spin-capturing polymerization, polymers in the range of oligomers to 30000gmol -1 were obtained. A strong dependence of molecular weight on monomer conversion was observed, which can be explained by the high trapping rate. In nitrone-mediated radical coupling, almost ideal coupling of bromine-functional polymers was obtained and the successful introduction of the residual alkoxyamine functionality confirmed.