Initiator efficiencies in high-conversion bulk polymerizations

Russell, G.T., Napper, D.H. and Gilbert, R.G. (1988) Initiator efficiencies in high-conversion bulk polymerizations. Macromolecules, 21 7: 2141-2148. doi:10.1021/ma00185a045


Author Russell, G.T.
Napper, D.H.
Gilbert, R.G.
Title Initiator efficiencies in high-conversion bulk polymerizations
Journal name Macromolecules   Check publisher's open access policy
ISSN 0024-9297
1520-5835
Publication date 1988-07
Sub-type Article (original research)
DOI 10.1021/ma00185a045
Volume 21
Issue 7
Start page 2141
End page 2148
Total pages 8
Place of publication Washington, DC, United States
Publisher American Chemical Society
Language eng
Formatted abstract
By consideration of relative rates of diffusion and of propagation, it is shown that, in some bulk polymerizations, there exists a certain weight fraction of polymer (wp) beyond which initiator efficiency (f) must rapidly decrease. At this critical wp, the two free radicals formed from initiator decomposition are immobilized by propagation faster than they can diffuse apart; consequently, their likely fate is to become trapped in close proximity to each other and undergo geminate recombination. A quantitative theory for the onset of this phenomenon is derived. This effect explains why some bulk polymerizations are extremely slow at high conversions while the corresponding emulsion polymerizations are not; further, it removes apparent discrepancies between kp values directly measured from ESR in emulsion polymerizations and those estimated from bulk kinetics. Bulk kinetic data are employed to give the variation of f with wp for a range of initiator types and concentrations; these f(wp) are shown to be consistent with the proposed theory. This suggests that the common assumption that f is independent of conversion, while kp drops rapidly at the glass transition, is seriously in error. Instead, it appears that kp changes slowly beyond the onset of diffusion-controlled propagation while f drops dramatically beyond a conversion that depends on a number of chemical and physical properties of the system.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemistry and Molecular Biosciences
Centre for Nutrition and Food Sciences Publications
 
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Created: Mon, 07 Mar 2011, 15:57:00 EST