The bulk radical polymerizations of styrene (St) at 80-120 degreesC in the presence of 6-aza-7,7-dimethyl-9-hydroxyspiro[4.5]decane-6-yloxyl (1) and 1-aza-2,2-dimethyl-4-hydroxy[5.5]undecane-1-yloxyl (2) were studied. At 100 and 120 degreesC, the polymerizations were well controlled by those nitroxides to give poly(St)s with narrow polydispersities. On the other hand, the polymerization mediated by 2 at 80 degreesC showed a good 'livingness' of polymerization, but I had a poor ability to control the polymerization to give poly(St) with a broad polydispersity of 1.52. The rate constants (k(act)) for the homolysis of the NO-C bond of the alkoxyamines prepared from 1 and 2 were measured at 333-373 K, and the A(act)s and E(act)s values were determined to be 2.8 X 10(13) s(-1) and 128 kJ mol(-1) (1) and 4.0 X 10(13) s(-1) and 125 kJ mol(-1) (2), respectively, from the Arrhenius plots. These results are compared with those for the structurally related piperidinyl-N-yloxyl radicals including TEMPO. (C) 2003 Elsevier Ltd. All rights reserved.