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Determination of the Mode of Free Radical Termination from Pulsed Laser Polymerization Experiments
Author(s) -
Nikitin Anatoly N.,
Hutchinson Robin A.
Publication year - 2007
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/mats.200600061
Subject(s) - radical , monomer , polymerization , chain termination , methyl methacrylate , kinetics , radical polymerization , chemistry , chain (unit) , chain propagation , chain transfer , polymer chemistry , analytical chemistry (journal) , materials science , polymer , physics , organic chemistry , quantum mechanics , astronomy
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 $[k_{\rm p}^L = k_{\rm p}^0 (L)^{ - \alpha } ]$ and termination $[k_{\rm t}^{L,L} = k_{\rm t}^0 (L)^{ - \beta } ]$ of long‐chain radicals (where k p 0and k t 0represent 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 ( β − α ) 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 ( β − α ) and 0.75 ± 0.04 for δ .