(660d) NMR Trajectories for Analyzing the Growth and Purification of 2D Polyaramids

Two-dimensional (2D) polymers have attracted significant attention due to their unique combination of low density, synthetic processability, and the mechanical strength and barrier properties typical of conventional 2D materials. These attributes make 2D polymers promising for various applications, including separation membranes, composite structures, and organic electronics. Unlike most 2D crystalline polymers synthesized through reversible methods, 2D polyaramids (2D-PAs) are produced via irreversible solution-phase polymerization, eliminating the need for lengthy crystallization processes. Synthesized through polycondensation reactions under ambient conditions, 2D-PAs offer a streamlined approach to polymer creation.

Despite advancements in 2D-PA synthesis, critical questions remain regarding their characterization, such as determining the discoidal size, understanding growth patterns, and distinguishing between dendritic intermediates and larger polycyclic domains. Unlike many 2D polymers with poor solubility in common solvents, 2D-PAs dissolve well in trifluoracetic acid (TFA) and dimethyl sulfoxide (DMSO), making them suitable for nuclear magnetic resonance (NMR) analysis. This study utilizes ¹H-NMR peak analysis of aromatic and proton end group regions to characterize the growth of 2D-PAs from monomeric precursors. The ratio of aromatic-to-end group protons provides metrics for molecular weight and discoidal size, while the skewness of the aromatic region offers insights into the balance between dendritic intermediates and larger polycyclic domains. These metrics chart a two-dimensional trajectory useful for analyzing synthetic and processing conditions. Additionally, a novel purification method employing two-stage filtration and washing steps effectively separates samples into distinct size regions, consistent with size-dependent separation. Theoretical analysis of ideal dendrimer and polycyclic limits based on repeat unit size further aids in trajectory analysis.