Kinetics of nitroxide radical trapping. 1. Solvent effects

N-tert-Butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide as counter radical in the controlled free radical polymerization of styrene: kinetic aspects

“…Semi-empirical calculations on the bond dissociation energy have also been carried out and provided useful information on the relative stability of various alkoxyamines 14,17) . Concerning the capture rate constant k c , the kinetics of nitroxide radical trapping, including solvent effects as well as structural effects, have been studied by Beeckwith et al 18,19) and Ingold et al 20) , and the rate constant k c appeared to be lower than the diffusion-controlled limit. In the scope of macromolecular alkoxyamines, Veregin et al 21) have studied the bulk polymerization of styrene with Tempo as counter radical and benzoyl peroxide as initiator.…”

Trapping of photogenerated group IV radicals by TEMPO: Potential new organometallic initiators for ?living? free radical polymerization

“…Thus, some contribution from charge transfer, but not a complete shift to electron transfer quenching, may be possible. In general, the trapping of carbon-centered radicals by TEMPO shows a dependence on the polarity of the solvent, being slower in polar solvents [26]. The rates obtained in this study can be compared directly without concern for the solvent effect, as identical trapping rate constants were obtained for Ph 3 GeD with acetonitrile or cyclohexane as cosolvents for di-tert-butyl peroxide.…”

“…Here, we have expanded upon this knowledge to see whether these metal-centered radicals would exhibit the same reactivity towards persistent nitroxide radicals and be useful for polymer initiation. Persistent nitroxide free radicals, such as TEMPO, are known to trap carbon radicals at rates below diffusion controlled limits [4,5,25,26]. Unfortunately, monitoring some of the generated organometallic radicals cannot be done directly as with carbon-based benzylic initiators [27,28] because aliphatic R 3 MD radicals are only weakly absorbing, with the exception of the R 3 SnD radical [16,19].…”

Supramolecular photochemistry in zeolites: From catalysts to sunscreens

“…In its paramagnetic form, the excited singlet state of the fluorophore is efficiently quenched by the tethered nitroxide moiety corresponding to a free or "off" state. When the nitroxide oxygen couples with a carbon-centered radical (R • in Scheme 8) the resulting species is a diamagnetic alkoxyamine [110][111][112][113]. The quenching mode operative in the paramagnetic probe is lost, and the emission is restored, corresponding to a trapped or "on" state.…”