Synthesis and Performance of Cyclomatrix Polyphosphazene Derived from Trispiro-Cyclotriphosphazene as a Halogen-Free Nonflammable Material

Novel cyclomatrix polyphosphazene was designed as a halogen-free nonflammable material and was successfully synthesized through ring-opening and ring expansion of trispiro-cyclotriphosphazene as a precursor. The chemical structure and composition of the synthesized trispiro-cyclotriphosphazene were characterized by 1H, 13C, and 31P NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, mass spectroscopy, and elemental analysis. The polymerization of the cyclomatrix polyphosphazene was dynamically monitored by FTIR spectroscopy. The synthesized cyclomatrix polyphosphazene exhibits a highly rigid and brittle nature as well as a high decomposition temperature over 350 °C due to its densely cyclic structure. This polyphosphazene material also shows a high limiting oxygen index and a V-0 classification in a UL-94 burning experiment. Such an excellent flame-retardant property is attributed to the construction of trispiro-cyclotriphosphazene on the backbone of the cross-linking system, which can lead to a synergistically flame-retardant effect resulting from the unique combination of phosphorus and nitrogen. With the characteristics of more safety and excellent performance, the cyclomatrix polyphosphazene designed by this work exhibits a broad prospect for electronic and microelectronic applications as a sustainable nonflammable polymeric material.