The synthesis of aziridine and azetidine monomers and their ring-opening polymerization via different mechanisms is reviewed.

The anionic ring-opening copolymerization of 1-(methylsulfonyl)aziridine (MsAz) and 1-(sec-butylsulfonyl)aziridine ( s BsAz) produces a soluble random copolymer P(MsAz-r-s BsAz), which can subsequently be converted to linear poly(ethylenimine) (lPEI). The copolymerization of MsAz and s BsAz is living and allows for the synthesis of copolymers with low molecular weight distributions. Sequential anionic polymerization of MsAz and s BsAz with 2-methyl-1-(methylsulfonyl)aziridine (MsMAz) creates P(MsAz-r-s BsAz)-b-P(MeMsAz). Removal of the sulfonyl groups from P(MsAz-r-s BsAz)-b-P(MsMAz) gives lPEI-b-poly(propylenimine). For the first time, lPEI can be synthesized by a controlled anionic polymerization.

The first anionic ring-opening polymerization of an activated azetidine is reported.