Bimolecular radical termination: New perspectives and insights

Johnston-Hall, Geoffrey and Monteiro, Michael J. (2008) Bimolecular radical termination: New perspectives and insights. Journal of Polymer Science: Part A: Polymer Chemistry, 46 10: 3155-3173. doi:10.1002/pola.22684


Author Johnston-Hall, Geoffrey
Monteiro, Michael J.
Title Bimolecular radical termination: New perspectives and insights
Journal name Journal of Polymer Science: Part A: Polymer Chemistry   Check publisher's open access policy
ISSN 0887-624X
Publication date 2008-04-10
Year available 2008
Sub-type Article (original research)
DOI 10.1002/pola.22684
Open Access Status
Volume 46
Issue 10
Start page 3155
End page 3173
Total pages 19
Editor Samamoto
Percec
Hawker
Wooley
Meijer
Place of publication USA
Publisher Wiley Inter Science
Language eng
Subject C1
030306 Synthesis of Materials
870303 Polymeric Materials (e.g. Paints)
Abstract The reversible addition-fragmentation chain transfer-chain length dependent termination (RAFT-CLD-T) method has allowed us to answer a number of fundamental questions regarding the mechanism of diffusion-controlled bimolecular termination in free-radical polymerization (FRP). We carried out RAFT-mediated polymerizations of methyl acrylate (MA) in the presence of a star matrix to develop an understanding of the effect of polymer matrix architecture on the termination of linear polyMA radicals and compared this to polystyrene, polymethyl methacrylate, and polyvinyl acetate systems. It was found that the matrix architecture had little or no influence on termination in the dilute regime. However, due to the smaller hydrodynamic volumes of the stars in solution compared to linear polymer of the same molecular weight, the gel onset point occurred at greater conversions, and supported the postulate that chain overlap (or c*) is the main cause for the observed autoacceleration observed in FRP. Other theories based on short-long termination or free-volume should be disregarded. Additionally, since our systems are well below the entanglement molecular weight, entanglements should also be disregarded as the cause of the gel onset. The semidilute regime occurs over a small conversion range and is difficult to quantify. However, we obtain accurate dependencies for termination in the concentrated regime, and observed that the star polymers (through the tethering of the arms) provided constriction points in the matrix that significantly slow the diffusion of linear polymeric radicals. Although, this could at first sight be postulated to be due to reptation, the dependencies showed that reptation could be considered only at very high conversions (close to the glass transition regime). In general, we find from our data that the polymer matrix is much more mobile than what is expected if reptation were to dominate. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3155-3173, 2008
Keyword Polymer Science
Polymer Science
POLYMER SCIENCE
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2009 Higher Education Research Data Collection
Australian Institute for Bioengineering and Nanotechnology Publications
 
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Created: Thu, 09 Apr 2009, 21:14:05 EST by Mrs Jennifer Brown on behalf of Aust Institute for Bioengineering & Nanotechnology