A highly refractive and transparent poly(arylene sulfide sulfone) (PASS) containing pyrimidine (or pyridazine) unit has been developed. The polymer was prepared by a polycondensation reaction of 4,4'-dimercaptodiphenyl sulfone (DMDPS) and 4,6-dichloropyrimidine (DCPM) (or 3,6-dichloropyridazine (DCPD)). They showed good thermal stabilities such as a relatively high glass transition temperature of 193-202 degrees C and a 5% weight loss temperature (T-5%) of 370-372 degrees C. The optical transmittance of the polymer at 450 nm is higher than 81%. The heterocycles unit and plural -S- linkages provides the polymer with a high refractive index of 1.737-1.743 at 633 nm and a low birefringence of 0.003-0.004. (C) 2012 Elsevier Ltd. All rights reserved.