To provide critical dissociation rate coefficients for different alkoxyamines (TEMPO and SG1 based compounds will be processed first). Data from different techniques (Computational, NMR, ESR, Liquid Chromatography) will be considered. The issue of Arrhenius parameters (Activation factor A and activation energy Ea) will be particularly emphasized.
During the last decade, Nitroxide Mediated Polymerization (NMP) emerged as a promising technique to prepare controlled/living polymers via free radical polymerization.
The NMP has the advantage over the other controlled radical polymerization (CRP) techniques that all the kinetic rate coefficient could be measured and that involves that this technique is the only one with no debate about the mechanism.
A complete kinetic analysis of the NMP process has then been carried out, and the kinetic conditions required for a successful process have been established.
These studies and various experimental results have pointed out the pivotal importance of the equilibrium constant K = kd/kc (with kd for the dissociation rate constant of the macroalkoxyamine and kc for the recombination between the macroradical and nitroxide) for a successful NMP process.
Although a wide range of computational and experimental data is available, the precise knowledge of rate coefficients, was highly insufficient until recently. In particular there is a large discrepancy of Arrhenius parameters for the same compound. The main bias could be due to the Ea – A compensation error effect, which implies that several couples of (Ea, A) values afford the same kd within a short range of temperature.
To limit the effect of this bias, achieving accurate and reliable A values requires compiling data values over the wider range of temperature.
Benchmark values for the dissociation rate coefficient of (macro)alkoxyamines could then be established first for the two more extensively used nitroxide, that is 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO) and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1).The range of alkoxyamines could then be expended if needed.
Secondly, a wide variety of advanced techniques (computational, NMR, ESR, Liquid Chromatography) were applied in the near past to determine the rate coefficients (kd and kc) and there is a need for practical guidelines describing the correct use of these technique to obtain accurate measurements in a similar manner as the work done on termination rate coefficient by the IUPAC Subcommittee on Modeling of Polymerisation Kinetics and Processes.
page last update 14 March 2019