Preparation and properties of optical acrylate modified with sulfur-containing cyclophosphazene polymer

A new sulfur-containing cyclophosphazene, successfully synthesized by nucleophilic substitution reaction of hexachlorocyclotriphosphazene and allyl mercaptan, was incorporated into the acrylate and acrylate/thiol system to obtain good flame retardant optical resins by UV-curing. The thermal decomposition study showed that phosphazene derivatives can increase the char residues after pyrolysis. The residues after thermal degradation were observed by scanning electron microscopy and it is found that the inside of the residue had numerous porous structure after pyrolysis and the gas generated by the decomposition of phosphorus-nitrogen rings made it expand. The resulting porous expanded carbon layer can play a role of heat insulation, and thus increase the flame retardancy of optical materials. In addition, the introduction of phosphorus-nitrogen rings and sulfur atoms increased refractive index of acrylate materials from 1.5185 to 1.5410 and the optical transmittance was higher than 80 % at 500 nm. These optical resin polymers with high transparency and refractive index, good flame retardancy and glass transition temperature can be promising candidates in optical coatings.