Synthesis and optical properties of sulfur-containing monomers and cyclomatrix polyphosphazenes

Novel cyclotriphosphazenes with sulfur-containing spirocyclic side groups were synthesized and polymerized to cyclomatrix materials for potential optical applications. The cyclotriphosphazenes were designed to give a high content of the phosphazene unit and sulfur atoms, as well as the capability for polymerization by ring- opening of the side groups. The chemical structures of the monomers were confirmed by NMR spectrometry, mass spectrometry, and single-crystal X-ray diffraction. Transparent solids were obtained by thermal bulk polymerization, and these were analyzed by the use of DSC, infrared spectroscopy, and mass spectrometry. One of the resultant cyclomatrix polyphosphazenes had a refractive index at 589 nm of 1.6465 and an Abbe number of 39. The contribution of the phosphazene unit to the refractive index is discussed.