Novel Highly Fluorinated Perfluorocyclobutane-Based Phosphazene Polymers for Photonic Applications

Novel cyclophosphazenes containing aryl trifluorovinyl ether functional units together with the corresponding perfluorocyclobutane (PFCB) phosphazene polymers have been synthesized and characterized. These polymers have desirable properties for low optical loss waveguide applications. The monomers used in this study were prepared from sodium 4-(trifluorovinyloxy)phenoxides and cyclophosphazenes with fluorinated alkoxy or aryloxy side groups. The resulting polymers, produced by 2π + 2π cyclopolymerization of the aromatic trifluorovinyl ether moieties, showed good chemical stabilities and high thermal stabilities ( T d up to 330 °C). Tough and transparent thin films of these polymers were readily prepared by solvent-free processes using spin-coating of the monomers. By adjusting the ratio of monomers, the refractive index of the polymers could be controlled from 1.4528 to 1.5187 at 1550 nm, with exceptionally low birefringence of Δ n = 0 to 0.0003 ± 0.0002. A propagation optical loss lower than ∼0.25 dB/cm at 1550 nm was determined from the polymer films, for the TE polarization by measuring the scattered light intensity along the slab waveguide length. Such good thermal and optical properties demonstrate that these novel PFCB-based phosphazene polymers are promising candidates for optical waveguide or optical device materials.