Anionic epoxide polymerization side reactions

Scheme 3 Polymerization of epoxide in an anionic mechanism and a possible side reaction.

Although alkali metal alcoholates are known to initiate living anionic polymerization of epoxyethane (11, R = H), use of these conventional initiators for the polymerization of substituted epoxides results in the concomitant occurrence of side reactions with respect to the substituents.- With 11 (R = Me) as a monomer, a proton transfer from the methyl group of 11 (R = Me) to the growing alcoholate species occurs, to give a polymer having a hydroxyl ter-... 

Monographs and reviews of this subject can be found in Refs. 181-185 and 225-227. The most important polymers from cationic ring-opening polymerization are polyoxyalkylenes with one or four CH2 groups produced by the polymerization of trioxane and tetrahydrofuran. The smaller epoxides, ethylene and propylene oxide, though able to polymerize by a cationic and anionic mechanism, are not polymerized cationically, because of the existence of side reactions leading to dioxane or... 

Detailed studies on the mechanisms of initiation and propagation of epoxide polymerization have been conducted using well-defined and stable initiators. Ethylene oxide (EO) was generally chosen as the reference monomer, owing to the living character of its polymerization, whereas the anionic polymerization of most other epoxides, including propylene oxide (POx), is subject to side reactions. 

Anionic and anionic coordination polymerizations of epoxides are often slow processes that require long reaction times to achieve high monomer conversions. Moreover, as reported in previous sections, a majority of these polymerizations suffer from side reactions, illustrated by the chain transfer reaction to monomer in alkali metal anionic polymerization and by a very low initiation efficiency and the formation of several polyether populations in coordination polymerizations. 

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