Summary: The structure of polyacetal copolymers with respect to their end groups is investigated. Several techniques, such as liquid chromatography, MALDI‐TOF MS, IR and NMR spectroscopy, as well as combined techniques like 2D chromatography have been applied. Cyclic oligomers and polymers with formyl, hydroxy, and aliphatic end groups are identified. 2D chromatography shows that all the separated species are homogenously distributed with respect to their molar mass.2D chromatograms of sample F97B3.magnified image2D chromatograms of sample F97B3.