The products of the oxidation of the hydroxyl groups of polyethylene glycol with a mixture of dicyclohexyl carbodiimide, dimethylsulphoxide and o-phosphoric acid in CHCI 3 or CCI 4 at room temperature (Pfitzner-Moffatt reaction) have been studied. Depending on the polymer concentration, the reaction results either in the formation of products of intermolecular condensation or in the formation of intramolecular cyclic semi-acetals. The cyclic structure of this product is proved using GPC data and by study of chemical splitting of the semi-acetal bond. The MWD of products and degrees of cyclization have been determined. The kinetics of cyclization have been studied. The rate constants of this reaction for polymers having various molecular weights were found using an i.r.-spectroscopic method. The rate constant of oxidation of the low-molecular monofunctional analogue (ethyl alcohol) was found by the GPC method. For all cases, the constants were shown to have values in the (4-7) x 10 -6 sec-I range. Oxidation of the hydroxyl group to aldehyde was concluded to be the limiting stage of the oxidation process. A method of synthesis of ~-carboxy, o~-oxypolyethylene oxides by oxidation of the semi-acetal bond in cyclic compounds is proposed.