1H NMR Trajectories for Analyzing the Growth and Purification of 2D Polyaramids

Abstract

The recent synthesis of two-dimensional (2D) polyaramid (PA) polymers has shown that they exhibit remarkable mechanical and gas barrier properties. However, new methods are necessary to enable the efficient measurement of discoidal sizes of 2D polyaramids and tracking of their growth over time during reaction. Herein, we employ ¹H NMR peak analysis of the aromatic and proton end group regions to characterize 2D-PA growth from monomeric precursors, alongside purification using two-stage filtration and washing steps. The ratio of aromatic to end group protons yields the molecular weight and discoidal size, while the skewness of the NMR peaks in the aromatic region provides a relative weighting between dendritic, small, and larger polycyclic domains. These two metrics delineate a distinct two-dimensional ¹H NMR trajectory that we show to be valuable for analyzing the results of differing synthetic and processing conditions. Theoretical bounds corresponding to dendrimer and polycyclic limits as a function of repeat unit size are derived as an aid in trajectory analysis. These results establish an analytical framework for evaluating 2D-PA and its variants, facilitating the exploration of the synthetic landscape.