Di-tert-butylnitroxide

The photochemistry of di-terf-butyl nitroxide was studied149. When di-tert-butylnitroxide (DTBN) is excited at 254 nm to the rnt state in pentane solution, it is cleaved to terf-butyl radical and 2-methyl-2-nitrosopropane (with quantum yield of 0.21). The tert-butyl radical is scavenged by DTBN to give di-ferf-butyl-terf-butoxyamine150 (equation 129). 

Reactions that convert the alkoxyamines to hy-droxylamines and alkenes can strongly limit the monomer conversion. These are either usual radical disproportionations between the nitroxide and the propagating radicals or concerted alkoxyamine decays. Both pathways lead to an exponential decrease of the concentration of the dormant chains with rate constant kdec = f)kd, where fn is the fraction of the side reaction concurring with radical coupling of alkoxyamine decay.57 kdec can be measured from the decay of the dormant alkoxyamine chains under nonscavenging conditions, and its relation with kd provides fn. From data of Fukuda et al. one can deduce fn = 0.4% for a TEMPO-polystyryl compound and fn = 1.1% for a di-tert-butylnitroxide-poly-terf-butylacrylate macroinitiator both at 120 °C.53,55 Similar small values of fn hold for TEMPO-cumyl (Scheme 10),22 TEMPO-1-phenylethyl,112 and a better mimetic compound for TEMPO-polystyryl.113 In these cases, fn probably represents the usual radical disproportionation. A much larger fn 25% holds for TEMPO—... 

Encinas, M. V. and Scaiano, J. C., Interaction between photogenerated biradicals and free radicals di-tert-butylnitroxide,/. Photochem., 11,241, 1979. 

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