Anionic oligomerization of acrylic esters

Oligomers of methyl acrylate and of ethyl acrylate were prepared by the use of methanolic and ethanolic solutions (respectively) of the corresponding sodium alkoxides as basic catalysts. Both terminally unsaturated oligomers and oligomers having alkoxyl end-groups were formed. The structure of the dimers was investigated; they were found to be α-methylene-dialkylglutarate and α-alkoxymethyldialkylglutarate. The i.r. and NMR spectra of the dimers are presented and discussed. The molar ratio of unsaturated dimer to saturated dimer was greater for the ethyl acrylate-ethanol system than for the methyl acrylate-methanol system. According to the proposed mechanism, the unsaturated dimers (and higher oligomers) were formed as a result of initiation by monomeric carbanions CH₂C-COOR. These, in turn, were formed by transfer of the acidic α-hydrogen of the monomer to one of the propagating carbanionic species in the oligomerization mixture.