Design of Optimized Reaction Conditions for the Efficient Living Anionic Polymerization of Cyclopropane-1,1-Dicarboxylates

A reinvestigation of the experimental parameters used when polymerizing anionically a cyclopropane-1,1-dicarboxylate indicates that several key steps have to be considered, but that other steps-including some routinely used up to now-although not harmful, are nevertheless useless. A robust protocol is thus designed whose implementation allows us to routinely control the polymerization of di-n-propyl cyclopropane-1,1-dicarboxylate, used as a model monomer for the entire family of cyclopropyl monomers geminally activated by two ester groups. Degrees of polymerization of up to 200 can be routinely obtained, with polydispersity indexes lower than 1.05. In some cases, a small shoulder can be identified in the size exclusion chromatography (SEC) chromatogram, although not systematically. The close proximity between the two distributions affects the polydispersity index only marginally (M-w/M-n still in the 1.01-1.05 range), and highly resolutive SEC columns are needed in order to identify the issue. Finally, attempts to use organic super-bases other than tBuP(4) have failed thus far.