Polymerization quinone transfer radical

Co(acac)2 proved also its efficiency in imparting control to the radical polymerization of styrene. This process, coined quinone transfer radical polymerization (QTRP), is carried out in the presence of phenanthroquinone and a catalytic amount of Co(acac)2 . The origin of the control should again be found in an equilibrium between a dormant (1) and... 

A. Debuigne, J. -R. Cadle, R. Jerome, Quinone transfer radical polymerization of styrene synthesis of the actual initiator, J. Polym. Sci., Part A Polym. Chem. 2006, 44, 1233-1244. 

J. -R. Caille, A. Debuigne, R. Jerome, Controlled radical polymerization of styrene by quinone transfer radical polymerization (QTRP), Macromdecides 2005, 38, 27-32. 

Co-2), which is effective for OMRP of VAc and acrylate, could also be used for quinone transfer radical polymerization (QTRP) of styrene, in which the quinone derivatives were employed in place of the halide initiator to produce the pseudohalogen transferring group. The polymerization mechanism became clear when coupled with the monomer addurt of orfho-quinone derivatives, in which the polymerization of styrene smoothly took place in the presence of Co-2 to produce a well-defined polystyrene with narrow MWDs... 

This is similar to the dissociation-combination scheme, but the release and return of the controlling species (X) are catalyzed by an activator (A) which is a transition metal complex. The controlling species is a halide radical in the most common form of this reaction, atom transfer radical polymerization (ATRP), and this technique will be described further in Section 13.5. It is also possible to use a quinone instead of a... 

The catalytic cycle of laccase includes several one-electron transfers between a suitable substrate and the copper atoms, with the concomitant reduction of an oxygen molecule to water during the sequential oxidation of four substrate molecules [66]. With this mechanism, laccases generate phenoxy radicals that undergo non-enzymatic reactions [65]. Multiple reactions lead finally to polymerization, alkyl-aryl cleavage, quinone formation, C> -oxidation or demethoxylation of the phenolic reductant [67]. 

Polymerization inhibitors stop or slow down polymerization by reacting with the initiator or growing-chain radicals. A wide variety of substances can behave as inhibitors quinones, hydroquinones, aromatic nitro compounds, aromatic amines, and so on. In cases where the inhibitor is a hydrogen donor (symbolized here by InH), then for inhibition to occur, the radical resulting from hydrogen transfer (In-) must be too stable to add to monomer. If it does add to monomer and starts a new chain, chain transfer occurs instead of inhibition. For perfect inhibition, the In- radicals must combine with themselves (or initiator radicals) to give inert products ... 

Some vinyl compounds can function as donor molecules because they possess a low ionization potential. The acceptors can be neutral molecules, like quinones, anhydrides, nitrile compounds, etc. They can also be ionic intermediates, such as metal ions, ionized acids, and carbon cations. An interaction of an acceptor with a donor is followed by a subsequent collapse of the charge transfer complex. This can result in formation of cation radicals capable of initiating cationic polymerizations. The exact mechanism of the reaction of cation radicals with olefins is still not completely determined. 

Amines, such as dimethylaniline and triethylamine, are also used as coinitiators for free-radical polymerizations [154,155]. In these cases, initiating radicals are supposedly generated through exciplex formation, followed by proton transfer. The low order of toxicity of camphor quinone and its curability by visible light makes such systems particularly useful for dental applications [152,156,157]. Noteworthy is that the reactivity is relatively low, owing to a comparably low efficiency in hydrogen-abstraction reactions. This circumstance has prevented the use of quinones in other applications. 

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