One Electron Transposition Initiation Reactions

Some radical sources will, in the presence of oxidizing agents, or light or heat energy, initiate cationic polymerizations of monomers, like n-butyl vinyl ether. Those that are most readily oxidized are carbon atom centered radicals that have substituents like benzyl, allyl, alkoxy, or structures with nitrogen or sulfur. Also, radicals that are formed by addition of other radicals to alkyl vinyl ethers are particularly reactive. 

Oxidants that can be used in these reactions are salts, like (C6H5)2l PF6 . Such salts oxidize the radical and also supply the counterions, as shown below  

What happens to the final radical is uncertain. High conversions were reported in polymerizations of n-butyl vinyl ether in the presence of azobisisobutyronitrile (as a source of radicals) with (p-tolyl)2-I PF6 at 50 °C 

The above is a thetmal process. Free radicals can also be generated with the aid of UV light. This, for instance, was done with a UV light decomposition of benzoin methyl ether in the presence of an oxidizing salt  

What happens to the final radical is uncertain. High conversions were reported in polymerizations of n-butyl vinyl ether in the presence of azobisisobutyronitrile (as a source of radicals) with ip - tolyl)2—I PFe at 50°C [55]. The above is an illustration of a thermal process [12]. Free radicals can also be generated with the aid of UV light. This, for instance, was done with a UV light decomposition of benzoin methyl ether in the presence of an oxidizing salt [56]  

Formations of copolymers by charge transfer mechanisms in free-radical polymerizations are discussed in Chap. 3. Reactions between donor and acceptor molecules, however, can also result in some charge transfers that yield ion-radicals and subsequent polymerization by ionic mechanism  

Some vinyl compounds, i.e., vinyl ethers, can function as donor molecules because they possess a low ionization potential. The acceptors can be neutral molecules Uke, 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 results in formation of cation-radicals that are capable of initiating cationic polymerizations [57], The exact mechanism of the reaction of cation-radicals with olefins is still not completely determined. 

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