Initiation of anionic polymerization

The active centre of anionic polymerization is formed by the addition of an anion to a 

Larger cyclic ethers are more basic and therefore more stable toward anions. Even these can be opened by strongly nucleophilic agents [207] 

Tetrahydrofuran is a frequently used solvent which appears to be not quite inert. The opening of its ring by anions is not infinitely slow. In its presence, polymerization temperatures should be kept below 273 K. 

In polymerizations of cyclic siloxanes, because of the higher coordination number of silicon the active centre can be formed by the decomposition of the transition complex with pentavalent silicon [208] 

The opening of lactam rings by strong bases and their anionic polymerization proceed by means of a complicated disproportionation [173]. The reaction is usually initiated by an organometallic lactam derivative with the alkali 

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Some new initiators soluble in hydrocarbons were described during the last few years. Organo-lithium compounds form 1 1 complexes with alkyls of Mg 134,135), Zn 136) or Cd l36), and their usefulness as initiators of anionic polymerization of styrene and the dienes was established 137). 

B.-A. Feit and M. Frankel Alkoxides as initiators of anionic polymerization of vinyl monomers. Part I. Polymerization of acrylonitrile by use of sodium alkoxides. J. Chem. Soc. 928—933 (1959). 

Similarly, zwitterionic tetramethylenes as initiators of anionic polymerization were also observed. For example, methyl a-cyanoacrylate polymerizes via an anionic mechanism in the presence of n-butyl vinyl ether [90]. A Diels-Alder adduct is also formed. In another example, the reaction of isobutyl vinyl ether and nitroethylene leads to an unstable adduct [91], which is capable of initiating the anionic polymerization of excess nitroethylene, and also the cationic polymerization of added VCZ. 

The initiation of methyl methacrylate polymerization by alkyl- and aryl-lithium compounds is a very complex process which has not been completely elucidated so far. Even less information is available on the efects of or-ganometals not containing lithium. Recently, the interest of some authors has centred on the application of Grignard reagents for the initiation of anionic polymerizations, especially of MMA [171, 172],... 

The classical examples are the polymerization of styrene in NH3, initiated by KNH2 [176], and the polymerization of octamethylcyclotetrasiloxane initiated by alkali metal hydroxides [177]. At the present time, simple strong mineral bases are no longer used for the initiation of anionic polymerizations. 

The initiators of anionic polymerization can also be activated by some types of chelates. Magnon et al. [221] have described ethylene oligomerization with butyllithium activated by tetramethylethylenediamine... 

Klippert and Ringsdorf9-10) tested the activity of a number of phosphoniomethylides as initiators of anionic polymerization. Their findings are summarized in Table 1. 

Initiation. Initiation of anionic polymerization is brought about by species that undergo nucleophilic addition to a monomer. The most typically used anionic initiators can be classified into two basic types ... 

Progress of anionic polymerizations is most favorable with monomers, which have one or more electronegative (electron-withdrawing) groups, such as nitrile or halogen, directly bonded to the vinyl group. Suitable catalysts for initiation of anionic polymerizations fall into one of two classes, according to their mode of action. 

The latter are useful as homogeneous initiators of anionic polymerization. 

Mechanisms of Initiation of Anionic Polymerization by Alkyl Lithiums... 

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