Process for the preparation of oxymethylene polymers and apparatus suitable for this purposeA process and an apparatus for the preparation of oxymethylene polymers is described. The process encompasses the polymerization of a monomer that forms oxymethylene groups, if appropriate in the presence of a cyclic acetal, together with an acetal of formaldehyde and with an initiator for cationic polymerization, preferably in a gas-tight kneader or extruder. The temperature profile of the polymerization here is designed in such a way that the polymerization mixture, which is initially heterogeneous by virtue of precipitating polymer, is converted to a homogeneous phase at the end of the polymerization. The homogeneous phase in which the polymer is present in liquid form is stabilized via addition of deactivators.After removal of volatile constituents, oxymethylene polymers are obtained with high thermal stability and with good mechanical properties.The oxymethylene polymers can be prepared at low energy cost and their properties can be adjusted as desired via prescription of the temperature profile during the polymerization.