Structural Characterization of Methylenedianiline Regioisomers by Ion Mobility-Mass Spectrometry and Tandem Mass Spectrometry: IV. 3-Ring and 4-Ring Isomers.

Matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is used to characterize methylenedianiline (MDA) 3-ring and 4-ring species. Building on our previous MALDI-MS 2-ring MDA isomer study, here we compare 3-ring and 4-ring electrospray ionization (ESI) and MALDI results. In ESI, 3-ring and 4-ring MDAs each form one single [M+H]+ parent ion. Whereas in MALDI, each MDA multimer forms three unique precursor ions: [M+H]+, [M.]+, and [M-H]+. In this study, 3-ring and 4-ring MDA precursors are characterized to identify the unique fragment ions formed and their respective fragmentation pathways. In addition to the three possible precursors, the 3-ring and 4-ring species are higher-order oligomer precursors in polyurethane (PUR) production and thus provides additional insight into the polymeric behavior of these PUR hard block precursors. The combination of ion mobility-mass spectrometry (IM-MS) and tandem mass spectrometry (MS/MS) allow the structural characterization of these larger MDA multimers.