Block Copolymerization of 3, 3-Dimethyl-2-oxetanone. 1. About the Mechanism of a, a-Disubstituted β-Propiolactones Block Copolymerization

Block copolymerization of 3, 3-dimethyl-2-oxetanone (or pivalolactone, PVL) has been reported by different authors by applying an anionic process initiated by carboxylate salt end groups. A living (co)polymerization of PVL is observed, and the mechanism could be assume as being of wide application. However, in every successful block PVL copolymerization described, a polarizable group is present in the vicinity of the initiating carboxylate salt. From our observations, it is concluded that the absence of such a structural feature is responsible for PVL homopolymerization. Accordingly, the initiating carboxylate end group cannot be free but must be interacting with a neighboring polarizable group to avoid this unexpectedly drastic limitation. The extension of this requirement to the PVL grafting processes has not been ascertained. © 1979, American Chemical Society. All rights reserved.