Electron paramagnetic resonance investigation of the nature of the propagating species in methyl methacrylate polymerization

Tonge, Matthew P., Pace, Ronald J. and Gilbert, Robert G. (1994) Electron paramagnetic resonance investigation of the nature of the propagating species in methyl methacrylate polymerization. Macromolecular Chemistry and Physics, 195 9: 3159-3172. doi:10.1002/macp.1994.021950914


Author Tonge, Matthew P.
Pace, Ronald J.
Gilbert, Robert G.
Title Electron paramagnetic resonance investigation of the nature of the propagating species in methyl methacrylate polymerization
Journal name Macromolecular Chemistry and Physics   Check publisher's open access policy
ISSN 1022-1352
Publication date 1994-09
Sub-type Article (original research)
DOI 10.1002/macp.1994.021950914
Volume 195
Issue 9
Start page 3159
End page 3172
Total pages 14
Place of publication Weinheim, Germany
Publisher Wiley
Language eng
Abstract The electron paramagnetic resonance (EPR) spectrum of methyl methacrylate polymerizing in a range of systems is simulated using a consistent set of parameters for two rotamers of a single free radical. The 9-line spectrum observed in bulk and emulsion polymerization was fitted by a superposition of two spectra corresponding to two rotamers of a long-chain species (each a somewhat hindered, non-rotating macroradical), having anisotropic methylene proton hyperfine couplings which can be treated as isotropic to a good approximation. The 13-line spectrum observed at low conversion with very high radical flux was simulated as a superposition of the spectra of two very similar rotamers, the EPR spectra of which are indistinguishable; either rotamer is part of a very short chain (primarily an initiator fragment which has propagated once) undergoing free rotation in a low-viscosity medium. Thus the EPR spectra can be explained without having to invoke earlier suggestions that there are two types of free radicals (“trapped” and “untrapped”) in these systems, corresponding to the 9-line and 13-line spectra. The existence of an enormous proportion of very short free radicals under conditions of high radical flux is supported by quantitative calculations of the radical chain-length distribution. It is suggested that the two rotamers have significantly different propagation rate coefficients because of differences in the hindered rotations in their transition states.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Centre for Nutrition and Food Sciences Publications
 
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Created: Mon, 07 Mar 2011, 15:58:43 EST