Controlled refractive index polymers: Polyphosphazenes with chlorinated- and fluorinated-, aryloxy- and alkoxy- side-groups

A series of novel halogenated alkoxy and aryloxy polyphosphazenes have been synthesized via macromolecular substitution reactions carried out on poly(dichlorophosphazene). These polymers showed good film-forming properties and tunability of refractive index. Moreover, several examples combined low glass transition temperatures with high refractive index changes as a function of temperature - a prerequisite for optical switching applications. The refractive indices could be controlled over the range of 1.3889-1.5610 by alterations to the side-groups or side-group ratios. The birefringence (n_TE - n_TM) of these polyphosphazenes was shown to be highly dependent on the amount of aryloxy side-group attached to the polyphosphazene backbone. They showed evidence of thermal stability up to 400 °C. These properties, combined with the tailorability of the polyphosphazene system make chlorinatedand fluorinated-, alkoxy- and aryloxy-substituted polyphosphazenes possible candidates for optical waveguide and optical switching applications.