Thermogravimetric Analysis and Mass Spectrometry of 2D Polyaramid Nanoplatelets.

Abstract

Two-dimensional (2D) polyaramids (2DPAs) have recently emerged as a class of organic 2D nanomaterials exhibiting high mechanical strength and gas barrier properties. However, their characterization remains challenging due to their hybrid molecular structure, combining features of conventional 2D inorganic materials with those of organic polymers, which results in limited solvent dispersibility. Herein, we elucidate how thermal degradation, monitored by thermogravimetric analysis coupled with mass spectroscopy (TGA-MS), can provide chemical insights into the end group and discoidal molecular structure of 2DPAs. We find that distinct thermogravimetric loss regimes correlate with the ratio of aromatic-to-end group proton peak integrations from ¹H NMR, referred to as the <i>r</i> value. This informs the end group chemical composition, which can be linked to a consistent set of mechanistic steps for thermal degradation. For instance, isopropyl-ester-terminated 2DPA-1 decomposes first through a six-centered intermediate formed from the intramolecular methyl hydrogen interaction with the carbonyl, yielding 1-propene after cleavage of the C-O bond, consistent with mass spectrometry. Kinetic parameters, including activation energies, are determined using the Coats-Redfern method from TGA data, with values spanning 11.8 to 63.6 kJ/mol. The analysis is extended to ethyl-ester- and carboxyl-terminated 2DPA-1 for comparison. This study establishes the utility of TGA and TGA-MS as versatile characterization tools for 2D polyaramids with distinct terminal groups, allowing measurement and therefore control of nanoplatelet functionalization and molecular weight.