Totally colorless, transparent, and highly refractive poly(phenylene thioether ether)s (PPTEs) containing thianthrene-2,7-disulfanyl moiety were developed in this study. A new 4,4′-diol aromatic compound, 2,7-(4,4′-diphenol)thiothianthrene (DPTT), with a high sulfur content was designed and synthesized to develop polymers with high refractive indices and high thermal stabilities. The PPTEs were prepared by polycondensation of DPTT with organic dihalogen compounds, such as 2,6-difluorobenzonitrile (DFBN) and 4,6-dichloro-2-(methylthio)pyrimidine (DCMP). The obtained polymers showed good thermal stabilities such as relatively high glass transition temperatures (T_gs) in the range of 153–176 °C and 5% weight loss temperatures (T_5%) over 344 °C. The cut-off wavelengths (λ₀) of the PPTE films are shorter than 343 nm, and they have a transmittance higher than 93% at 550 nm. The combination of the pyrimidine and high sulfur-containing thianthrene derivatives provides the PPTEs with a high refractive index of 1.7204 and a small birefringence of 0.0106 at 637 nm.