The Rapid Mechanochemical Synthesis of Microporous Covalent Triazine Networks: Elucidating the Role of Chlorinated Linkers by a Solvent‐Free Approach

Abstract

The mechanochemical synthesis of porous covalent triazine networks (CTNs), exhibiting theoretically ideal C/N ratios and high specific surface areas, is presented. Employing this solvent‐free approach allows to minimize the ecological impact of the synthesis by bypassing hazardous wastes, while simultaneously observing the reactions between the individual starting materials separately for the first time. Especially the role of dichloromethane needs to be reconsidered, functioning as a linker between the nitrogen‐containing node cyanuric chloride and the aromatic monomer 1,3,5‐triphenylbenzene, as proven by X‐ray photoelectron spectroscopy and 1H → 13C Cross‐Polarization magic‐angle‐spinning nuclear magnetic resonance spectroscopy. This results in a drastic enhancement of the reaction rate, reducing the synthesis time down to 1 minute. Additionally, this linkage over a C1 bridge enables the incorporation of nitrogen into already synthesized polymers by post polymerization functionalization. The variation of the synthesis building blocks, namely the linker, node, and monomer, results in a variety of nitrogen‐containing polymers with specific surface areas of up to 1500 m2 g−1. Therefore, the presented approach is capable to target the synthesis of various CTNs with a minimal use of chlorinated linker, rendering the concept as a sustainable alternative to the classical solution‐based synthesis.

Rationalizing the formation of porosity in mechanochemically-synthesized polymers

“…32,[38][39][40][41] Lewis acid-catalyzed polycondensation protocols, such as the Scholl or Friedel-Crafts polymerization, are particularly popular due to their speed, versatility, and cost efficiency. [42][43][44][45][46][47][48] During these reactions, a significant amount of HCl is released into the sealed milling vessels, which has a direct impact on the porosity of the generated polymers. 42 Additionally, the setup of milling parameters and choice of liquid-assisted grinding agents have also been found to be crucial in this regard.…”

“…42 Additionally, the setup of milling parameters and choice of liquid-assisted grinding agents have also been found to be crucial in this regard. 44,47 Despite these developments, ball mills are still considered as ''black boxes'', and a deep understanding of the underlying principles that result in the formation of porous polymers is urgently required.…”

Rationalizing the Formation of Porosity in Mechanochemically-Synthesized Polymers

“…42 Additionally, the setup of milling parameters and choice of liquid-assisted grinding agents have also been found to be crucial in this regard. 44,47 Despite these developments, ball mills are still considered as "black boxes", and a deep understanding of the underlying principles that result in the formation of porous polymers is urgently required. To address the need for a better understanding of mechanochemical synthesis and its impact on the formation of porous polymers, we present a matrix of mechanochemically synthesized polymers based on a Friedel-Crafts reaction.…”