(151g) Unveiling the Chemical Structure and Barrier Properties of Two-Dimensional Polyaramids for Energy Applications

Two-dimensional (2D) polymers have recently attracted significant attention due to their ability to merge the low density and synthetic versatility of polymeric materials with the in-plane mechanical strength and barrier properties typical of conventional 2D materials. Consequently, these polymers have been investigated 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 a unique class of 2D polymers created via irreversible solution-phase polymerization. Despite advancements in the synthesis of 2D-PAs, critical questions remain regarding the accurate determination of their discoidal size and effective characterization of their growth.

To address the critical questions surrounding 2D polyaramids, we employed ¹H-NMR peak analysis of the aromatic and proton end group regions to monitor the growth of 2D-PAs from monomeric precursors. The ratio of aromatic to end group protons serves as an indicator of molecular weight and discoidal size, while the skewness of the aromatic region provides insights into the balance between dendritic small polycyclic intermediates and larger polycyclic domains. These metrics chart a two-dimensional trajectory that is instrumental in evaluating the effects of various synthetic and processing conditions.

Another critical aspect of 2D polyaramids is their remarkable gas barrier properties. We have found that 2D polyaramid thin films, with a thickness of just 35 nanometers, exhibit nitrogen gas impermeabilities as low as 10^-8 Barrer, which is 1000 times lower than that of existing polymers. Additionally, we have demonstrated that 2D polyaramid thin films can serve as protective layers on MAPbI₃ perovskites, significantly enhancing the stability of these air- and moisture-sensitive materials. These exceptional gas impermeable properties make 2D polyaramids excellent candidates for applications in gas storage, gas separation, and optoelectronics.