Propagation on Macroion Pairs with Different Anions

3 Propagation on Macroion Pairs with Different Anions 

The structure of the cation (counterion) in the anionic polymerization of e, g. styrene is of paramount importance for the kinetics of propagation. This was amply demonstrated by the works of warc Schulz , Bywater a. o. 

Cations used in anionic polymerization markedly differ in their properties. The small Li has an ionic radius equal to 0,60 while Rb or Cs have radii equal to 1.69 A and 1.98 A, respectively 

The choice of counterions (anions) in the cationic polymerization of heterocyclic monomers can be almost as wide as in anionic polymerization, but only for the most nucleophilic monomers (i. e. cyclic amines). Unfortunately, in the polymerization of cyclic ethers, this choice is much more restricted. Thus, the small anions like F or OH cannot be used because, due to their high nucleophilicity and ability to form covalent bonds, they give rise to fast termination. In order to suppress or even to eliminate termination by collapse within an ton pair (cf. Sect. 5.1.), it is necessary to use complexed anions having large ionic radii. These are shown below (rctyst)- 

There are only a few systematic studies of the influence of anions on the propagation rate constant of macroion pairs In the polymerization of THF 

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