The influence of alkali metal salt catalysts and reaction conditions on the oxyethylene units formation in the synthesis of oligocarbonate diols from five-membered cyclic carbonates and aliphatic diols is presented. The reaction mechanism, involving the alkoxide group formation from cyclic carbonate and alkali metal salts has been proposed and discussed. The oligomeric products were analyzed by means of MALDI-TOF mass spectrometry and NMR spectroscopy. (C) 2004 Elsevier Ltd. All rights reserved.