Structural characterization of polyoxymethylenes by matrix-assisted laser desorption/ionization mass spectrometry

Several polyoxymethylene (POM) model compounds with relatively low molecular weights were characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using dithranol matrix, 1,1,1,3,3,3-hexafluoro-2-propanol solvent for matrix/analyte solution, and sodium iodide as cationization reagent. For POM oligomers with thermally unstable hydroxyl end-groups (paraformaldehyde), a series of sodium-cationized molecular ions up to MW ca. 2000 was observed at good sensitivity with little or no fragmentation. The MALDI mass spectra of the trimethylsilylated and acetylated POM samples were interpreted in terms of their end-group structures and molecular weight distributions. Furthermore, the formation mechanisms of the macrocyclic POM oligomers (Mn = 1500–2000), isolated by alkaline degradation of raw bulk POM obtained by cationic polymerization, are discussed by relating them to their lamellar structures on the basis of their MALDI mass spectra.