Process for the production of polyoxymethylene block copolymers

A process for preparing polyoxymethylene block copolymers comprising catalytically adding one or more alkylene oxides and optionally additional comonomers onto at least one polymeric formaldehyde starter compound having at least one terminal hydroxyl group, in the presence of a double metal cyanide (DMC) catalyst, which comprises

• (i) activating the DMC catalyst in the presence of the polymeric formaldehyde starter compound, in which activation of the DMC catalyst is accomplished by adding a portion, based on the totality of the amount of alkylene oxides used in the activation and polymerization, of one or more alkylene oxides,
• and
• (ii) adding one or more alkylene oxides and optionally additional comonomers to the mixture resulting from (i), in which the alkylene oxides used in (ii) may be the same as or different than the alkylene oxides used in (i),
• wherein the activation of the DMC catalyst in (i) is effected at an activation temperature (Tact) of 20 to 120° C.