Controlled or living radical polymerization

Ruthenium catalysts found many applications in C-C bond formation reactions (selected reviews [157-161]). Ruthenium occurs mostly in oxidation states +2 and +3, but lower as well as higher oxidation states can easily be reached. Thus ruthenium compounds are frequently used in oxidative transformations proceeding by either single or two electron transfer pathways (selected reviews [162-164]). It has long been known that ruthenium complexes can be used for the photoactivation of organic molecules (selected reviews [165, 166]). Ruthenium complexes are applied as catalysts in controlled or living radical polymerizations [167-169]. 

Figure 1.1 Publication rate of journal papers on radical polymerization and on living, controlled or mediated radical polymerization for period 1975-2002 based on SeiFinder search (as of Mar 2005).

Einally, as per Equation 18.27b, if a copolymer has a very narrow composition distribution, will be very close to (M) using a single solvent the same applies to mixed solvents if we follow the procedure mentioned earlier. This can be the case, for instance, of a radical copolymerization in a true azeotrope composition or of a block copolymer synthesized by a controlled anionic or living radical polymerization. 

Jenkins, A.D., Jones, R.G., Moad, G., 2010. Terminology for reversible-deactivation radical polymerization previously called controlled radical or living radical polymerization. Pure Appl. Chem. 82 (2), 483 91. 

Terminology for reversible-deactivation radical polymerization previously called controlled radical or living radical polymerization Pure Appl. Chem. 82 (2010) 483. 

Figure 1 Publication rate of journal papers on radical polymerization and on living, controlled, or mediated radical polymerization for the period 1975-2008 based on SciFinder search (as of March 2010). It does not distinguish forms of controlled radical polymerization. It includes most papers on ATRP, RAFT, and NMP and would also include conventional, non-RDRP, controlled radical polymerizations. It would not include papers, which do not mention the terms living , controlled , or mediated .

Several controlled and living radical polymerization techniques are available today. All are based on the reversible deactivation of growing chains. Consequently, a 2010 lUPAC recommendation proposes the term controlled reversible-deactivation radical polymerization (CRDRP) for polymerizations previously referred to as controlled radical (CRP) or living radical (LRP) polymerization. Nevertheless, due to their widespread acceptance, the terms controlled/living radical polymerization will also be used in this chapter. 

Most radicals are transient species. They (e.%. 1-10) decay by self-reaction with rates at or close to the diffusion-controlled limit (Section 1.4). This situation also pertains in conventional radical polymerization. Certain radicals, however, have thermodynamic stability, kinetic stability (persistence) or both that is conferred by appropriate substitution. Some well-known examples of stable radicals are diphenylpicrylhydrazyl (DPPH), nitroxides such as 2,2,6,6-tetramethylpiperidin-A -oxyl (TEMPO), triphenylniethyl radical (13) and galvinoxyl (14). Some examples of carbon-centered radicals which are persistent but which do not have intrinsic thermodynamic stability are shown in Section 1.4.3.2. These radicals (DPPH, TEMPO, 13, 14) are comparatively stable in isolation as solids or in solution and either do not react or react very slowly with compounds usually thought of as substrates for radical reactions. They may, nonetheless, react with less stable radicals at close to diffusion controlled rates. In polymer synthesis these species find use as inhibitors (to stabilize monomers against polymerization or to quench radical reactions - Section 5,3.1) and as reversible termination agents (in living radical polymerization - Section 9.3). 

It remains a common misconception that radical-radical termination is suppressed in processes such as NMP or ATRP. Another issue, in many people s minds, is whether processes that involve an irreversible termination step, even as a minor side reaction, should be called living. Living radical polymerization appears to be an oxymoron and the heading to this section a contradiction in terms (Section 9.1.1). In any processes that involve propagating radicals, there will be a finite rate of termination commensurate with the concentration of propagating radicals and the reaction conditions. The processes that fall under the heading of living or controlled radical polymerization (e.g. NMP, ATRP, RAFT) provide no exceptions. 

The polymerization of MA with 7 was carried out in the presence of 13, i.e., 7 and 13 were used as two-component iniferters [175]. When an identical amount of 13 to 7 was added to the system, the polymerization proceeded according to a mechanism close to the ideal living radical polymerization mechanism. Similar results were also obtained for the polymerization of VAc. These results indicate that the chain end of the polymer was formed by the competition of primary radical termination and/or chain transfer to bimolecular termination, and that it could be controlled by the addition of 13. 

In contrast to the above polymerizations via anionic and/or coordination anionic mechanisms, radical polymerization initiated with metalloporphyrins remains to be studied. The only example of controlled radical polymerization by metalloporphyrins has been reported by Wayland et al. where the living radical polymerization of acrylic esters initiated with cobalt porphyrins was demonstrated. In this section the radical polymerization of MMA initiated with tin porphyrin is discussed. 

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