Overview of other synthetic methods

It was shown previously that polarisation of some double bonds prevents polymerisation by a free radical mechanism of molecules containing such bonds. Conversely, double bonds that can be opened by ionic mechanisms 

Polymers prepared by opening of double carbon—carbon bonds 

Reactivity in anionic chain polymerisation of monomers possessing a double carbon=carbon bond is increased by the presence of electro-attractive groups on one of these carbon atoms. Depending on the reactivity of the monomer and on the solvent used, different types of initiator can be used. 

The propagation rate depends mainly on dissociation of ion pairs and thus on the polarity of the reaction medium. If the rate of initiation is faster than the rate of propagation, then all the chains are initiated at the same time and grow at a similar rate. In this case, polymeric chains can possess a similar length, i.e. polymolecularity is low M, M ). 

Depending on the reaction medium, termination can be rather slow, and the active site located at the end of the chain can remain active for a few minutes when all of the monomer has been transformed into polymer for this reason, living polymers can be described. This phenomenon can be taken advantage of when preparing block copolymers (see Section 4.1) or for terminating the chains with groups that can be activated in a further step (tele-chelic polymers). Examples of telechelic polymers are given in Equation 3.17. 

---