Factors underlying design of a new nitroxide, 2,2,5-trimethyl-4-tert-butyl- 3-azahexane-3-oxyl (TITNO), and its styrene alkoxyamine (Styryl-TITNO) for effecting nitroxide-mediated polymerization (NMP) at temperatures ≥90 °C are described. The rate coefficient, k d, for thermal dissociation of Styryl-TITNO was determined in the range 70-100 °C, giving Arrhenius parameters A d = 2.9 × 10 12 s -1 and E d = 104.1 kJ mol -1. Due to the low value of E d, values of k d and the activation-deactivation equilibrium constant for NMP of n-butyl acrylate (BA) and styrene are much lower at any given temperature than for alkoxyamines of more established nitroxides. Good control of molecular weight and dispersity, with negligible contributions from termination, is achieved at 90 °C for BA and at 70 °C for styrene, thus, eliminating the complicating contributions from styrene thermal initiation. Hence, TITNO and Styryl-TITNO offer new opportunities for controlled NMP at temperatures much lower than has previously been attainable. © 2012 American Chemical Society.