Conjugated Microporous Polymers via Solvent-Free Ionothermal Cyclotrimerization of Methyl Ketones

Abstract

Conjugated microporous polymers (CMPs) are porous organic materials that display (semi)conducting behavior due to their highly π-conjugated structures. As such, they are promising next-generation materials for applications requiring both conductivity and porosity, such as supercapacitive energy storage and electrochemical sensing. However, most CMPs and related porous aromatic frameworks (PAFs) are currently prepared using expensive transition metal-based catalysts under solvothermal conditions, significantly increasing their manufacturing costs. Herein, we demonstrate that the ionothermal cyclotrimerization of methyl ketones via the aldol reaction represents a new strategy for the solvent-free synthesis of CMPs and PAFs. Specifically, we show that 1,3,5-triacetylbenzene and tetrakis(4-acetylphenyl)methane can be polymerized in molten zinc chloride to produce highly conjugated and microporous materials, as confirmed by 77 K N 2 adsorption measurements in conjunction with UV−vis, Raman, and solid-state NMR spectroscopies. The CMP prepared from 1,3,5-triacetylbenzene demonstrates higher charge storage capacities (up to 172 F/g) than a commercially available supercapacitor carbon, reflecting the promise of cyclotrimerized CMPs for electrical energy storage applications.

Synthesis of Porous Organic Polymers Via Catalytic Vapor-Assisted Solvent-Free Method

“…As reported, confirmation of the pore size of amorphous POPs can be complicated due to some factors, such as H−H repulsion and nonplanar structures. 20 Even so, the pore sizes of CPOP1-Vs are similar to that of the previously reported polycarbazole synthesized from TCB via the solvent method, 10,29,31 suggesting the structures of CPOP1-Vs conform to the expected structures of CPOP1. Scanning electron microscopy (SEM) images show the morphologies of CPOP1-V2 as micrometer-scale irregular strips (Figure S1e, Supporting Information).…”

“…At present, the synthesis methods of porous materials mainly include solvent and solvent-free methods. 20 However, the synthesis methods involving chemical vapor are still limitedly reported due to lack of suitable reaction type. The example of trifluoromethanesulfonic acid vapor as catalyst for the preparation of CTFs reflects the potential of catalytic vapor in the preparation of POPs.…”

“…At present, the synthesis methods of porous materials mainly include solvent and solvent-free methods . However, the synthesis methods involving chemical vapor are still limitedly reported due to lack of suitable reaction type.…”

Nanoarchitectured Conjugated Microporous Polymers: State of the Art Synthetic Strategies and Opportunities for Adsorption Science

“…The ionothermal method is also used in the synthesis of CMP; it is not easily interfered with by other ions and has no need of reaction solvents. In 2021, Kim et al 84 synthesized a CMP by using molten ZnCl 2 as the reaction solvent and methyl ketone as the reaction monomer by a C−C bond formation reaction. This CMP was used in the field of supercapacitor energy storage and had better charge storage capacity than the commercial capacitor material (supercapacitor carbon).…”

“…The CMP with the highest content of triazine units could increase the conversion of benzylamine up to 99% with a low catalyst load. Kim et al 84 polymerized tetra-(4-acetyl phenyl)methane and 1,3,5-triacetyl benzene using molten zinc chloride as a solvent through the cyclotrimerization reaction. The synthetic CMP showed a great potential in charge storage.…”