Characterization of Fluorinated Polymers by Atmospheric-Solid-Analysis-Probe High-Resolution Mass Spectrometry (ASAP/HRMS) Combined with Kendrick-Mass-Defect Analysis.

Fluorinated polymers are a diverse and important class of polymers with unique applications. However, characterization of fluorinated polymers by conventional mass spectrometric methods is challenging because (i) their high fluorine contents make them insoluble or only sparingly soluble in most common solvents and (ii) commonly used matrices employed for MALDI do not desorb or ionize them efficiently. In this work, atmospheric-solid-analysis-probe (ASAP) high-resolution orbitrap mass spectrometry (HRMS) was used as a new tool for the molecular characterization of various fluorinated polymers, including polyvinylidene fluoride (PVDF) and fluorinated copolymers containing PVDF and chlorotrifluoroethylene (KEL-F 800) or PVDF and hexafluoropropylene (Viton A and Tecnoflon). The major peaks of the observed distributions were assigned compositions, but the high number of species required the use of an alternative method to treat such complex data. Kendrick-mass defects (KMD) were calculated on the basis of the "common-to-all" vinylidene difluoride repeating unit. By plotting the KMD as a function of the nominal Kendrick masses (NKM), specific patterns based on homologous series emerged. Kendrick maps were therefore drawn to simplify the mass spectra and provide confident peak assignments through homologous-series recognition. A specific fingerprint for each polymer has been identified, and the ability to discern the four species present in a blend through KMD analysis was demonstrated.