The influence of different polyether based diols on the photochemically and thermally induced cationic polymerization of a cycloaliphatic diepoxide is examined. If the polymeric diol is a 1,2-diol based polyether the polymerization is retarded compared to the pure diepoxide, whereas the polymerization is not influenced or even enhanced if the diol is a polyether based on a 1,4-diol or a low molecular weight 1,2-diol. The different behavior is explained by the complexation of protons in a crown ether like structure in the presence of the polyethers based on 1,2-diols. This leads to an effective reduction of the acid concentration available to initiate the polymerization. The model was verified by the addition of a small amount of 12-crown-4. In the presence of the crown ether the polymerization is also strongly retarded. (C) 2003 Elsevier Science Ltd. All rights reserved.