The invention relates to a process for producing polyoxymethylene block copolymers, comprising the step of activating the DMC catalyst in the presence of an OH-terminated polymeric formaldehyde starter compound by means of a defined amount of alkylene oxide, optionally followed by polymerization with alkylene oxides, if necessary in the presence of other comonomers. The invention further relates to polyoxymethylene block copolymers that can be obtained by means of such a process and to the use of these for producing polyurethane polymers.