| Autor: |
Willemse, Robin X. E., van Herk, Alex M., Panchenko, Elena, Junkers, Tanja, Buback, Michael |
| Zdroj: |
Macromolecules; June 2005, Vol. 38 Issue: 12 p5098-5103, 6p |
| Abstrakt: |
The percentage of two types of free radicals occurring within n-butyl acrylate pulsed laser polymerization (PLP) has been measured via ESR spectroscopy. Polymerization in solution of toluene, at monomer concentrations between 0.50 and 2.53 mol L-1and temperatures between −50 and 70 °C, was induced by 351 nm excimer laser pulses applied at a repetition rate of 20 Hz. The ESR spectra obtained at low degrees of monomer conversion may be adequately represented by superimposing a six-component four-line spectrum assigned to secondary propagating radicals (SPRs) and a nine-line spectrum assigned to tertiary midchain radicals produced by backbiting (MCR1s). The percentage contribution to total radical concentration of the latter species, which is produced from an SPR by a 1,5-H shift backbiting reaction, is negligible at −50 °C and is close to 80% at 70 °C. The transition of an SPR to a MCR1 species invalidates the linear correlation of time tafter applying a laser pulse with the size of the growing radical. The observed high concentration of MCR1 species explains the known severe limitations met in acrylate PLP−SEC experiments directed toward measuring the propagation rate of acrylate radicals with chain-end functionality. |
| Databáze: |
Supplemental Index |
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