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From building units to 3D networks: What’s so magical about the synthesis process of CMPs?
Introduction: Conjugated microporous polymers (CMPs) are an emerging porous material with excellent electrical conductivity and mechanical stability, and their synthesis process has attracted widespread attention in the scientific community. This article will explore the synthesis process of CMPs and its potential applications, revealing the charm of this cutting-edge technology.
What are conjugated microporous polymers (CMPs)?
Conjugated microporous polymers (CMPs) are porous materials related to structures such as zeolites, metal-organic frameworks and covalent organic frameworks, but are characterized by being amorphous rather than crystalline. CMPs are a class of conjugated polymers that possess electrical conductivity, mechanical rigidity, and insolubility. These polymers are constructed by linking multiple units together in a π-conjugated manner to form a three-dimensional network. This conjugation enables CMPs to exhibit excellent conductivity and storage properties.
Design and synthesis of CMPs
Units building CMPs must possess an aromatic system and possess at least two reactive groups. In order to generate the porous structure of CMPs, cross-coupling of units with different geometric shapes must be carried out to form a three-dimensional polymer skeleton. Self-condensation reactions of similar geometric units can promote the formation of isomers. The primitive geometry of CMPs depends on its point group, including C2, C3, C4 and C6 respectively.
Suzuki Coupling
Since 1979, Suzuki coupling has been an effective method of aromatic aromatic bond formation.
Suzuki coupling is suitable for large-scale synthesis of CMPs because of its mild reaction conditions and the availability of commercial organoboron reagents. During the reaction, Suzuki coupling requires the cross-coupling of organic halides and organoboron reagents under the action of some basic catalysts. However, the disadvantages of Suzuki coupling are that it is sensitive to oxygen, often produces by-products, and requires degassing.
Sonogashira Coupling
Sonogashira coupling cross-couples aromatic halides with alkynyl groups, typically using a lithium copper cocatalyst and an appropriate base. This method has the advantages of technical simplicity and functional compatibility, and can realize the three-dimensional formation of CMPs by adjusting the rotation angle of the unit.
Yamamoto Coupling
Yamamoto coupling can form carbon-carbon bonds of aromatic halogenated compounds, and the catalyst used is usually bis(cyclooctadiene)nickel(0). The advantage of this method is that it only requires a single halogen functionalized monomer and the reaction process is simple and convenient. Although current research focuses on controlling porosity and specific surface area, the Yamamoto coupling method has limited flexibility.
Schiff Base Reaction
Schiff's reaction is gradually gaining attention as a method that does not require metal catalysts.
In Schiff's reaction, amine monomers react with aldehyde-containing monomers to form repeating units of CMPs. This approach has attracted attention because it uses polyaldehyde-functional monomers that are inexpensive on an industrial scale and whose nitrogen-generating properties are potentially beneficial for many applications.
Cyano Cyclotrimerization
The cyano cyclotrimerization reaction is carried out at high temperatures, usually under molten zinc chloride conditions. The C3N3 rings formed in this process can be further connected into triangular planes, which serve as auxiliary building blocks. This method can link the properties of tetrahedral monomers, thereby leading to the synthesis of CMPs.
Properties of CMPs
Several physical properties of CMPs can be attributed to their extended conjugation or microporosity.
Electrical Characteristics
Like conducting metals, conjugated polymers exhibit electronic band phenomena. The distribution of electrons in conjugated systems may constitute conductivity and, in many cases, absorption of visible light, paving the way for applications in organic electronics and organic photonics.
Physical properties
CMPs exhibit high tunability in surface area and pore size. By designing the monomer with long rigid sections, the surface area can be effectively increased. However, the inherent insolubility of CMPs is a major obstacle to widespread application.
Application of CMPs
Since their discovery, CMPs have been investigated for a variety of applications and their surface areas can exceed 1000 m2/g in many cases. The porosity of CMP has led to its evaluation as an adsorbent and has shown great potential in the fields of optoelectronics, supercapacitors, catalysis, etc. The versatility of these materials enables them to derive a variety of functions and be used in a wide range of technologies.
With the advancement of science and technology, the synthesis of CMPs will continue to develop, and what kind of breakthroughs may it bring in the future?
