Thermal Conversion of Acetylene-Containing Cyclotriphosphazene to Graphitic Materials: Controlling Solid-State Morphology through Heating Rates

Abstract

Carbon-rich materials have growing potential for applications ranging from electronics to drug delivery. Traditional methods for preparing these materials often require high temperatures and yield mixtures of products with poor control over structure and properties. To address this, researchers are increasingly using molecular precursors with specific reactive sites that allow for a tunable and well-defined synthesis. This work presents alkyne-terminated cyclotriphosphazenes as promising precursors for synthesizing nitrogen and phosphorus rich graphitic materials with tunable solid-state properties. By applying thermal annealing below 400 °C, it was demonstrated by our groups that precise heating can selectively control ring-opening polymerization of the phosphazene core and crosslinking of terminal acetylenes. Spectroscopic and thermal analysis revealed that slow thermal heating (below 32 °C/min) promotes simultaneous ring-opening polymerization, acetylene crosslinking and graphitization to yield a brittle thin film. In contrast, rapid heating (above 32 °C/min) exclusively induces acetylene crosslinking and graphitization, preserving the cyclotriphosphazene ring and producing a soluble, amorphous black powder. Characterization by electron microscopy and gas absorption analysis confirmed that the fast-heated material has a surface area of 261.03 m²/g, a nitrogen uptake of 822.50 cm³/g, and a significant increase in pore volume. These findings present a new versatile approach for generating carbon-rich, porous graphitic materials for various applications.