2D conjugated microporous polyacetylenes synthesized via halogen-bond-assisted radical solid-phase polymerization for high-performance metal-ion absorbents.

The paper reports the first free-radical solid-phase polymerization (SPP) of acetylenes. Acetylene monomers were co-crystalized using halogen bonding, and the obtained cocrystals were polymerized. Notably, because of the alignment of acetylene monomers in the cocrystals, the adjacent C≡C groups were close enough to undergo radical polymerization effectively, enabling the radically low-reactive acetylene monomers to generate high-molecular-weight polyacetylenes that are unattainable in solution-phase radical polymerizations. Furthermore, the SPP of a crosslinkable diacetylene monomer yielded networked two-dimensional conjugated microporous polymers (2D CMPs), where 2D porous polyacetylene nanosheets were cumulated in layer-by-layer manners. Because of the porous structures, the obtained 2D CMPs worked as highly efficient and selective adsorbents of lithium (Li) and boronium (B) ions, adsorbing up to 312 mg of Li (31.2 wt%) and 196 mg of B (19.6 wt%) per 1 g of CMP. This Li adsorption capacity is the highest ever record in the area of Li adsorption.