Ultra-fast supercritically solvothermal polymerization for large single-crystalline covalent organic frameworks

Area of Science:

• Materials Science
• Polymer Chemistry
• Crystallography

Background:

• Crystalline polymer materials like covalent organic frameworks (COFs) are crucial for applications in catalysis, electronics, and separations.
• Achieving high crystallinity and large grain sizes in polymers via polymerization is challenging, often resulting in amorphous or poorly crystalline products.
• Precise control over molecular assembly into single crystals during polymerization is essential for structure-property relationship studies and practical applications.

Purpose of the Study:

• To develop an efficient and rapid polymerization strategy for synthesizing highly or single-crystalline polymer materials.
• To overcome the limitations of traditional polymerization methods that yield amorphous or small-grained crystalline products.
• To demonstrate a novel method for the precise assembly of organic molecules into single crystals through polymerization.

Main Methods:

• A supercritically solvothermal method utilizing supercritical carbon dioxide (sc-CO2) as the reaction medium for polymerization.
• Employing sc-CO2, which offers high diffusivity and low viscosity to accelerate crystal growth compared to conventional organic solvents.
• Detailed step-by-step procedures for monomer dispersion preparation, polymerization in sc-CO2, and subsequent purification and characterization of single crystals.

Main Results:

• Successfully synthesized six covalent organic frameworks with diverse topologies, linkages, and crystal structures using the sc-CO2 method.
• The synthesized single crystals exhibited polarized photoluminescence and second-harmonic generation, confirming their high-quality crystalline nature.
• Achieved rapid growth of sub-millimeter-sized single crystals within 1-5 minutes of polymerization, with the overall procedure completed in approximately 4 hours.

Conclusions:

• The supercritically solvothermal method provides an efficient, rapid, and environmentally friendly approach for synthesizing high-quality crystalline polymer materials.
• This technique offers advantages including high productivity, industrial compatibility, and ease of accessibility, making it suitable for both research and potential industrial applications.
• The ability to rapidly produce single crystals via polymerization opens new avenues for advanced materials development and structure-property investigations.