The patent application relates to a process for preparing polyoxymethylene by polymerization of a reaction mixture (RG) which comprises at least one formaldehyde source and at least one initiator mixture (IG), wherein the initiator mixture (IG) comprises at least one polymerization initiator and at least one solvent of the general formula (I) R1—O—[—R3—O—]m—R2  (I), where m is 1, 2, 3 or 4; R1 and R2 are each, independently of one another, C3-C6-alkyl; R3 is C1-C5-alkylene.