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Determination of the Mode of Free Radical Termination from Pulsed Laser Polymerization Experiments
Authors:Anatoly N. Nikitin  Robin A. Hutchinson
Abstract:The molecular‐weight distribution (MWD), obtained by pulsed laser polymerization (PLP) at the high termination rate limit has been considered for investigating termination kinetics. The proposed methodology takes into account both the composite model for termination and the chain‐length dependencies of propagation for short‐chain and long‐chain radicals. Power‐law expressions are used to represent propagation equation image and termination equation image of long‐chain radicals (where kurn:x-wiley:10221344:media:MATS200600061:tex2gif-stack-1 and kurn:x-wiley:10221344:media:MATS200600061:tex2gif-stack-2 represent the maximum “virtual” rate coefficients for monomeric radicals, and α and β capture the chain‐length dependencies for propagation and termination), with the combined value of (βα) evaluated from the MWD, after correcting for the influence of the kinetics of short‐chain radicals. A novel method is also developed for determining the mode of termination, δ, from MWDs produced by PLP at the high termination rate limit. Simulations for methyl methacrylate (MMA) polymerization at 25 °C confirm that the method can be applied robustly in the presence of complicating factors such as chain transfer to monomer and SEC broadening. The analysis of an experimental MWD obtained for MMA polymerization at 25 °C results in estimates of 0.14 ± 0.03 for (βα) and 0.75 ± 0.04 for δ.
image

Keywords:free radical polymerization  mechanistic model  methyl methacrylate  mode of termination  molecular‐weight distribution/molar mass  pulsed laser polymerization  radical polymerization  termination kinetics
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