3-Ethyl-3-hydroxymethyloxetane (EOX) polymerizes readily to branched multihydroxyl polyethers. Molecular weights of the polymers are, however, limited, and macromolecules are predominantly cyclic. This indicates that intramolecular chain transfer to polymer (back-biting) proceeds in the system. Repeating units in poly-EOX contain two nucleophilic sites that may participate in back-biting, namely ether groups and hydroxyl groups. Analysis of matrix-assisted laser desorption/ionization time-offlight (MALDI-TOF) mass spectra of poly-EOX prepared in the presence of analogous polyether that does not contain HO- groups (poly(3,3-dimethyloxetane)-poly-DMOX) shows that the ether group in the repeating unit of poly-DMOX does not participate in chain transfer to the polymer. However, when DMOX was polymerized in the presence of poly-EOX, clear evidence of participation of 110-groups in intramolecular chain transfer was obtained. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym. Chem 42: 245-252,2004