AbstractThe polymerizations of 2,3‐epoxypropanal (glycidaldehyde) (1a) and its 2‐methyl and 2,3‐dimethyl derivatives (1b, 1c) were studied in the temperature range of 20–50°C in the presence of aluminum 2‐propoxide as catalyst.The polymerization of these epoxyaldehydes was found to proceed in two stages. A Tishchenko reaction leading to the formation of the corresponding esters2was found to be predominant in the first stage of polymerization. In the case of aldehydes having a methyl group in the 2‐position, the β‐lactones3are formed.Polymer chain growth takes place in the second stage of the polymerization reaction with the participation of the epoxide groups of the dimers2produced in the first stage, which leads to the formation of non‐crosslinked polyethers having short ester side chains with epoxide groups or side chains with β‐lactone rings.The structure of the starting monomer was shown to determine directly the differences in polymerization rates and in the structure of the polymers and i