A Commentary on “Role of Initiator-Transfer Agent-Terminator (Iniferter) in Radical Polymerizations: Polymer Design by Organic Disulfides as Iniferters” by T. Otsu, M. Yoshida (Macromol. Rapid Commun. 1982, 3, 127–132)
✍ Scribed by Krzysztof Matyjaszewski
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 304 KB
- Volume
- 26
- Category
- Article
- ISSN
- 1022-1336
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✦ Synopsis
Controlled or living radical polymerization (CRP/LRP) is now one of the most rapidly developing areas of chemistry with many forthcoming commercial applications. [1] The desire to control radical polymerization has its roots in the success of living anionic polymerization, [2] and CRP can now offer similar control over the synthetic process, [3] although with somewhat lower precision. On the other hand, CRP has the advantage in that its procedures can be conducted under much milder and less restricted reaction conditions and for a larger range of monomers. [1] In contrast to living anionic polymerization, control over cationic and radical polymerizations depend on creating a dynamic equilibrium between active and dormant species. In this way, the strong contribution of transfer and fast propagation in carbocationic systems [4] as well as bimolecular termination reactions, which were previously considered unavoidable in radical systems, could be overcome.
The very important papers on radical polymerization published by Otsu in 1982 [5] followed the equally significant reports on cationic polymerization by Kennedy, [6] in which he developed the concept of inifers and iniferters, i.e. compounds which concurrently INitiate, transFER and TERminate. The system on which Otsu primarily focused, was controlled by the addition of dithiocarbamates (DTC) compounds that were previously used in the rubber industry. [5,7] Otsu discovered that in the presence of light, there was a reversible dissociation of dithiocarbamate end groups from polystyrene and poly(methyl methacrylate) chains. Despite the fact that the molecular weight distributions of the resulting polymers were quite broad, this approach resulted in molecular weights that increased with conversion, which was in contrast to all previously known radical polymerizations. [5] We now recognize that an increase of molecular weight with conversion (even linear) barely means that the total number of chains is constant. Molecular weights increase linearly with conversion if initiation is complete and transfer is absent, even if termination occurs. [1] How does the original system described by Otsu compare with the systems currently used for CRP that include degenerative transfer with alkyl iodidies, [8] dithioesters (RAFT) [9] or xanthates (MADIX); [10] nitroxide mediated systems (NMP or SFRP); [11,12] and atom transfer radical polymerization (ATRP)? [13]