Reaction of cation with monomer

Interaction of a cation with a monomer yields an active centre this is initiation in its most proper sense. The proton and the most simple carboca-tions are attached to the / atom of an alkene. This is documented both by experimental findings and by the corresponding calculations of the localization energies of the respective structures (Hiickel) and of the electron densities on the alkene carbon atoms [264]. 

Also with heterocyclic monomers, simple cations are attached to the atom with the highest electron density in the valence sphere, i. e. to the heteroatoms. The reactions of more complicated carbocations are evidently of greater complexity. The triphenylmethyl cation separates a hydride ion from tetrahydrofuran, producing triphenylmethane and an oxonium ion 

With lactams, a tautomeric equilibrium is assumed to exist between the compounds formed by the addition of a simple primary cation to oxygen or nitrogen. With a proton as the cation, an acyllactam ammonium ion is finally produced [265, 266], 

As for every reaction of ions, even initiation is affected by the medium. It is essentially a rapid process. Of course, in various systems the solvation and desolvation, aggregation and deaggregation, and coordination processes occur to various degrees. Their outward manifestation is a greater or smaller hindrance of the whole process. 

Very rapid initiations are known, manifested by an instantaneous start to the polymerization after which the number of active centres is not further increased. Polymerizations with slow initiation are also quite frequent, starting only after some inhibition and/or induction period. In the course of these polymerizations, the concentration of active centres is not usually constant. A stationary state is not excluded, of course but it occurs much less frequently than with radical polymerizations. 

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