Start by Zwitterions

Certain initiators form a zwitterion or an ylid. Formally, the process is representative of a Michael addition, 

An ylid is a zwitterion where the a carbanion is directly bound to the positively charged heteroatom (i.e., N, P, or S). The zwitterion then starts the anionic polymerization  

The presence of these zwitterions has been established by the nitrogen content of the polymer, IR and NMR measurements, the positive charge in esterification, and the mobility of the esterified products in high-voltage electrophoresis. 

In many cases, the addition of such initiators starts a polymerization that is only apparently started by zwitterions. In the polymerization of acrylonitrile by tertiary phosphines, for example, a zwitterion is indeed initially formed  

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