A Two-Dimensional Polymer Synthesized through Topochemical [2 + 2]-Cycloaddition on the Multigram Scale

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 = 464 900, respectively. The sheet size is on the order of
5 × 5 μm2.