Radical reaction kinetics during homolysis of N-alkoxyamines: verification of the persistent radical effect

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

“…The value of the activation energy is in good agreement with known values 13,24,32) . Activation energies for k d and k c of alkoxyamines are typically in the range of 100 -150 kJ N mol -1 and 2 -10 kJ N mol -1 , respectively.…”

“…They found a half-life of 5 -10 min which is in better accordance with polymerization results showing high initiation rate with that alkoxyamine initiator 12) . Such discrepancies can be explained by the Persistant Radical Effect, as described by Fischer et al 13) Moad and Rizzardo 14) measured the disappearance of several alkoxyamines in the presence of an excess of foreign aminoxyl by HPLC. They found a half-life of 65 min for Tempocapped isobutyronitril (AIBN-Tempo) at 60 8C.…”

“…In the same manner, Scaiano et al 16) have obtained some kinetic and thermodynamic data for the decomposition of alkoxyamines derived from Tempo and 4-hydroxy-Tempo involving a primary, secondary or tertiary benzylic site. Recently, Fischer et al 13) determined the rate constants of the individual reactions (dissociation k d , reversible recombination k c , self-termination 2 k t ) under isolation conditions for 2-phenyl-2-(29,29,69,69-tetramethylpiperidine-19-oxyl)propane (cumyl-Tempo). 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) .…”

Microwave-assisted nitroxide-mediated polymerization of alkyl acrylates

“…This kinetic model has been estab-lished on the assumptions that side-reactions do not occur, and that the rate constants are independent of the lengths of the growing polymer chains [31][32][33][34][35]. In such systems, the concentration of the nitroxide (persistent) radicals and the growing polymer chains are not stationary, but depend on time [31][32][33][34][35][36][37]. Consequently, the monomer conversion itself (represented by ln{[M 0 ]/[M t ]}) does not depend linearly on time, but to its 2/3 order, which has been experimentally validated [38].…”

Determination of the activation rate constants of alkyl halide initiators for atom transfer radical polymerization

“…In nitroxide-mediated polymerization, some workers have adopted the nitroxide exchange technique to estimate the k act values of low-molar-mass model alkoxyamines [22][23][24][25] . This method is based on the activation of an alkoxyamine (R-X) in the presence of a large excess of a different kind of nitroxyl radicals (X99), in which either the formation of R-X9 and X9 or the disappearance of R-X is followed by, e. g., high performance liquid chromatography (HPLC) or electron spin resonance (ESR).…”