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 equivalent to 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 (B3+) ions, adsorbing up to 312 mg of Li+ (31.2 wt%) and 196 mg of B3+ (19.6 wt%) per 1 g of CMP. This Li+ adsorption capacity is the highest ever record in the area of Li+ adsorption. Polyacetylenes are an important class of conjugated polymers but are generally synthesized via metal-catalyzed coordination polymerization leaving trace metals as impurities. Here the authors demonstrate a free radical polymerization of co-crystalized acetylene monomers without the need of a metal catalyst.

Automated summary

This paper presents the first free-radical solid-phase polymerization (SPP) of acetylenes. The authors co-crystalized acetylene monomers using halogen bonding and polymerized them. The aligned acetylene monomers in the cocrystals allowed for effective radical polymerization, resulting in high-molecular-weight polyacetylenes that cannot be obtained through solution-phase radical polymerizations. Additionally, the SPP of a crosslinkable diacetylene monomer produced networked two-dimensional conjugated microporous polymers (2D CMPs) with excellent adsorption properties for lithium and boronium ions.