A highly refractive, transparent, and totally colorless poly(phenylene thioether) (PPT) containing a triazine unit has been developed. A new aromatic dithiol, thianthrene-2,7-dithiol, with a high sulfur content was designed and synthesized in order to develop PPTs with high refractive indices and high glass transition temperatures (T(g)s). These PPTs were prepared by the phase-transfer catalyzed polycondensation of 2,4-dichloro-6-alkylthio-1,3,5-triazines with aromatic dithiols such as 4,4'-thiobisbenzenethiol, benzene-1,3-dithiol, and thianthrene-2,7-dithiol. The PPTs obtained from the 2,4-dichloro-6-methylthio-1,3,5-triazines and aromatic dithiols showed good thermal stabilities such as relatively high T(g)s over 120 degrees C and 5% weight-loss temperatures (T(5%)) around 350 degrees C. The optical transmittance of the polymer films with a 1 gm thickness is around 98% at 400 nm. The combination of the triazine and sulfur-containing thianthrene units provides PPTs with high refractive indices up to 1.7720 at 633 nm and low birefringences (<0.005).