Transfer Complexes in Ionic Initiations

Formations of copolymers by charge transfer mechanisms in free-radical polymerizations are discussed in Chapter 2. Reactions between donor and acceptor molecules, however, can also result in some charge transfers that yield ion radicals and subsequent ionic polymerizations. 

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. 

One example is a combination of an alkyl vinyl ether (donor) with vinylidine cyanide (acceptor) that results in ionic polymerizations. The reaction actually contains the ingredients of both cationic-and anionic-type polymerizations  

Solvations of the charged species accelerate the transfer of electrons and the ionizations are enhanced by polar solvents.Charge transfer reaction studies with tetracyanoethylene, an acceptor, and A -vinyl carbazole, a donor, in benzene solution demonstrated that both cation radicals and anion radicals form. This can be used in a subsequent cationic polymerizations  

A similar reaction takes place between chloranil and A -vinyl carbazole  

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