Following our previous paper on the course of the formation of star-polymers from oligo(oxyethylene) alcoholates as arms precursors and diglycidyl ethers as core building units [1], the nature of polymer alcoholate groups formed in this process has been studied. Primary alcoholate groups reacting with diepoxide or epoxide function in polymer give initially predominantly secondary alcoholate groups in the product. However, a small fraction of primary alcoholate groups of polymer is formed from the very beginning. When consumption of epoxide groups increases the contribution of polymer primary groups increases too, reaching eventually from 5 to 15% of total alcoholate groups, depending on reaction conditions. The increase of this proportion with the reaction progress is explained by intramolecular reaction of alcoholate groups with epoxide ones (cyclization) giving a large proportion of primary alcoholate groups. This explanation was supported by the quantum-mechanical calculations of the possible routes of cyclization. (C) 2016 Elsevier Ltd. All rights reserved.