‘Living’ radical polymerization of styrene mediated by spiro ring-substituted piperidinyl-N-oxyl radicals. The effect of the spiro rings on the control of polymerization

The bulk radical polymerizations of styrene (St) at 80–120 °C 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 °C, 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 °C showed a good ‘livingness’ of polymerization, but 1 had a poor ability to control the polymerization to give poly(St) with a broad polydispersity of 1.52. The rate constants (kact) for the homolysis of the NO–C bond of the alkoxyamines prepared from 1 and 2 were measured at 333–373 K, and the Aacts and Eacts values were determined to be 2.8×1013 s−1 and 128 kJ mol−1 (1) and 4.0×1013 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.