Termination by Irreversible Collapse of the Macroion Pair

The quantitative studies of the termination by recombination of ions within a macro-ion pair and determination of the corresponding rate constants became possible by application of the end-capping method .  

The dependence of concentration of active species in the polymerization of THF as a function of monomer convCTsion is shown in Fig. 14a,b for two different initiators C2HsAlCl2-a-epiclilorohydrin (a) and (C2Hs)30 BF4 (b). These curves are calculated on the basis of the original data given in Ref. 232. 

The termination reactions, responsible for the decrease of [P ], involve attack of the complex anion on the growing species followed by decomposition of the anion and formation of the haloalkyl end group  

This and similar reactions have been treated as the irreversible ones however, the reversible process carmot be excluded at least for some MtX which are strong enough electrophEes. The mechanism of this opposing reaction can be presented as follows for the polymerization of THF  

In the case of MtX unable to react directly with THF (e.g. BF3), Eq. (118) describes a real equilibrium which can be reached either after or before the monomer-polymer equilibrium is established. 

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