RESUMEN
2D polymer sheets with six positively charged pyrylium groups at each pore edge in a stacked single crystal can be transformed into a 2D polymer with six pyridines per pore by exposure to gaseous ammonia. This reaction furnishes still a crystalline material with tunable protonation degree at regular nano-sized pores promising as separation membrane. The exfoliation is compared for both 2D polymers with the latter being superior. Its liquid phase exfoliation yields nanosheet dispersions, which can be size-selected using centrifugation cascades. Monolayer contents of ≈30 % are achieved with ≈130â nm sized sheets in mg quantities, corresponding to tens of trillions of monolayers. Quantification of nanosheet sizes, layer number and mass shows that this exfoliation is comparable to graphite. Thus, we expect that recent advances in exfoliation of graphite or inorganic crystals (e.g. scale-up, printing etc.) can be directly applied to this 2D polymer as well as to covalent organic frameworks.
RESUMEN
The single-crystal-to-single-crystal (scsc) synthesis of a 2D polymer based on photochemically triggered [2 + 2]-cycloaddition is reported. Both monomer and polymer single crystals are analyzed by X-ray diffraction, which is the first case of a scsc two-dimensional polymerization based on this cycloaddition and the third ever case for a scsc synthesis of a 2D polymer. The product crystals at quantitative conversion are wet-exfoliated under mild conditions and afford countless features that are single and double layers as judged by their AFM heights of hAFM ≈ 1.2 ± 0.5 and 2.2 ± 0.5 nm, respectively. The X-ray-structure-based molecular weight of the 2D polymers and their degree of polymerization per µm2 are M = 360 MDa and Pn = 464â¯900, respectively. The sheet size is on the order of 5 × 5 µm2.