Side-reactions in the transesterification of oligoethylene glycols by methacrylates

Transesterifications of di-, tri-, and tetra-ethylene glycols with methyl methacrylate or corresponding dimethacrylates were carried out in different conditions using potassium carbonate as a catalyst. The resulting monomethacrylates of glycols were separated from the reaction mixtures by extraction and vacuum-distilled. The reaction mixtures as well as the crude and purified products were examined by 1H-NMR spectroscopy. The formation of a considerable amount of side-products by Michael-type addition of hydroxyl-bearing species to C=C double bonds was observed. Possible structures of the addition products are proposed, including higher oligomers of oligo(ether-ester) type.