Cyclotriphosphazene-containing polymeric nanotubes: synthesis, properties, and formation mechanism

Highly crosslinked, cyclotriphosphazene-containing polymer nanotubes have been successfully synthesized by polycondensation between hexachlorocyclotriphosphazene and melamine with pyridine as solution and acid-acceptor. The obtained nanotubes with rough surface, closed at one end, of lengths in several micrometers range, outer diameter in the range of 50–250 nm, and two ends of inner diameters in the range of 50–100 and 100–200 nm, respectively have been investigated by SEM and TEM. The formation mechanism has been proposed and named as self-template directing approach. In order to verify this mechanism, the products at variable stages of polymerization were traced by SEM. In addition, the melamine played a crucial role during the polymerization, guiding the formation of nanotube’s structure. The nanotubes showed remarkable thermal performance with the initial decomposition temperature at 220 °C and the residual is more than 40 % at 800 °C. Also, the morphology of nanotubes has undergone a progress from monodispersed nanotubes, to aggregation state, and to sponge-like structure at 220, 350, and 800 °C, respectively.