Functional materials containing chemically or physically crosslinked (co)polymer networks with high molecular weight (&gt;100,000 Da), such as polyurethanes, rubber copolymers, and hydrogels, cannot be analyzed in intact form by mass spectrometry (MS) and are also challenging to characterize by other spectroscopic methods of analysis. Information about the molecular composition and structure of this class of materials and about their additive and stabilizer content can be obtained by utilizing mild thermal desorption/degradation followed by analysis of the resulting products by mass spectrometry (MS dimension) and, if needed, tandem mass spectrometry (MS2 dimension). Mild thermal degradation is efficiently performed with an atmospheric solids analysis probe (ASAP) located within an atmospheric pressure chemical ionization ion source for immediate in-situ ionization of the desorption and degradation products. The ASAP source is operated at low temperatures (&lt;600 oC), ensuring the formation of oligomeric species that provide molecular connectivity detail, since low temperatures preferentially break the weakest bonds within the crosslinked network; often these are highly substituted bonds or weak carbon-heteroatom bonds (like C-S or C-P). Combining ASAP-MS/MS2 with ion mobility separation capabilities (IM dimension) creates an effective top-down technique for the molecular characterization of crosslinked functional materials. This methodology has been successfully applied to chemically crosslinked polyether hydrogels designed for biomedical applications. The spectra acquired reveal the crosslink chemistry (oxime bonds) and star-like architecture of the gels and verify the presence of defects ("loose" or unreacted ends). Parallel experiments on copolymeric polyether/polyester hydrogels unveil comparably important microstructure detail. The ASAP-IM-MS/MS2 method is currently extended to rubbery industrial copolymers doped with additives, dispersants, and stabilizers; slowly increasing the ASAP temperature gradually volatilizes the latter constituents based on their size and polarity, before the crosslinked network starts to degrade. Such gradient desorption/degradation yields substantial molecular insight that can help to differentiate apparently similar samples.

Top-down mass spectrometry of crosslinked functional materials

256th National Meeting (2018)

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