Anionic Polymerization by Lewis Bases

On the other hand, lithium mercaptides do not initiate polymerization of the analogous 4-member cyclic sulphides and their reaction with ethyl lithium proceeds in a conventional way  

Neither 5- or 7-membered cyclic sulphides could be polymerized. 

The initiation of propylene sulphide polymerization by a-sulphonyl type carbanions, -S02, CH2Li, proceeds in a conventional way187). 

Anionic polymerization initiated by uncharged nucleophiles has been observed in several systems. The first example of such a reaction probably was furnished by the work of Horner et al.236), who initiated polymerization of nitroethylene and of acrylonitrile by trialkyl phosphines. The following mechanism was postulated  

The same mechanism was postulated by Katchalsky234,235) for polymerization of nitroethylene initiated by pyridine or its derivatives. 

---