Anionic polymerization of pivalolactone initiated by alkali metal alkoxides

Polymerization of pivalolactone (alpha,alpha-dimethyl-beta-propiolactone) initiated with alkali metal alkoxides has been studied. It has been revealed that after addition of an alkoxide anion, from the initiator, onto the carbonyl carbon atom of the monomer the selective cleavage of the acyl-oxygen bond of the monomer leads to the formation of alkoxide propagating species. Thus, it has been demonstrated that, in contrast to alpha-unsubstituted beta-lactones and higher lactones, the anionic polymerization of pivalolactone proceeds through either alkoxide or carboxylate propagation centers, depending on the nature of initiator used, i.e. an alkoxide or a carboxylate, respectively. In the former case, however, cyclic oligomers are also formed which are unusual in the anionic polymerization of other beta-lactones. This indicates that, whatever the lactone ring size (four-, six-, or seven-membered lactones), intramolecular transesterification reactions can take place if alcoholate ions are propagating species