Anionic Polymerization of Oxiranes and Thiiranes

In this aprotic solvent strongly interacting with cations, termination and chain-transfer were avoided as evident by the relation  

Number average degree of polymerization = [polymerized monomer]/[initiator], 

It seems that the aggregation of ion-pairs is less pronounced in the potassium system than in the sodium, while their direct dissociation into free ions, as well as their capacity to form triple ions, is enhanced. 

Plot of log of bimolecular propagation constant of ethylene oxide polymerization in dimethyl sulphoxide vs. log of concentration of the initiator, QHjOCy OQHtO-, Cs+. Slope 1.9 

The association is avoided by complexing the cations with suitable kryptates. Polymerization of ethylene oxide initiated by potassium carbazyl in THF in the presence of 

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Ionic polymerization of oxiranes and thiiranes is usually divided in three main types anionic, cationic and stereospecific-"coordinated". While anionic and cationic polymerization produce random amorphous polymers, at least when starting from racemic monomers, stereospecific initiators may give isotactic crystalline polymers. 

The ring-opening polymerization of oxiranes, thiiranes, and thietanes can be initiated by both cationic and anionic methods, but thrae are some heterocycUc compounds such as lactones and lactams that are more suited to the anionie technique. 

Olefin derivatives with electron-attracting substituents, such as, for example, acrylic compounds and dienes, as well as lactams, lactones, oxiranes, thiiranes, isocyanates, and A -carboxy anhydrides of a-amino acids, a-hydroxy carboxylic acids, and a-thiol carboxylic acids can be polymerized anionically ... 

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