Molecular composition and thermal history of crosslinked polymer networks via mild thermal degradation and in‐situ tandem mass spectrometry

Crosslinked materials have long been utilized to form films of enhanced physical strength and chemical resistance. Unfortunately, their complex structures and insolubility obstruct their characterization by most analytical techniques. Atmospheric solids analysis probe mass spectrometry (ASAP-MS) offers a solution by applying heated nitrogen gas to mildly pyrolyze and desorb material from the polymer film. This results in the observation of oligomeric species that are large enough to reveal the connectivity of the microstructure. The system studied was comprised of a neopentyl glycol terephthalate base polymer crosslinked by a tetrafunctional β-hydroxyalkyl amide crosslinking agent. Base polymer and crosslinking agent were mixed at different weight ratios and cured onto glass capillaries to form networks with varied degrees of crosslinking. ASAP-MS analysis of the individual reactants and crosslinked products led to the observation of signature ions from both the raw materials as well as the resulting network. The relative abundances of these ions provided a full quantitative analysis of the crosslinker loadings, while the time delay between ASAP onset and ion formation permitted estimation of the cure temperature and thermal history. On the other hand, tandem mass spectrometry (MS/MS) experiments on the ions diagnostic of the crosslinked network allowed for identification of the crosslinking bonds formed upon curing. Such ability to reliably evaluate the extent of crosslinker loading, curing conditions, and types of bonds in a network has a significant impact on understanding film performance and defects in industrial coatings.