High refractive index materials: a structural property comparison of sulfide- and sulfoxide-containing polyamides

Abstract

High-refractive-index polyamides (PAs) are developed by incorporation of sulfide- or sulfoxide linkages and chlorine substituents. The PAs are synthesized through the polycondensation of two novel diamine monomers, 2,2'-sulfide-bis(4-chloro-1-(4-aminophenoxy) phenyl ether (3a) and 2,2'-sulfoxide-bis(4-chloro-1-(4-aminophenoxy) phenyl ether (3b), with various aromatic diacids (a-e). The ortho-sulfide or sulfoxide units, pendant chlorine groups, and flexible ether linkages in the diamine monomers endowed the obtained PAs with excellent solubilities in organic solvents. The resulting PAs showed high thermal stability, with 10% weight loss temperatures exceeding 415°C under nitrogen and 399°C in air atmosphere. The combination of chlorine substituents, sulfide or sulfoxide linkages, and ortho-catenated structures provided polymers with high transparency along with high refractive index values of up to 1.7401 at 632.8 nm and low birefringences (<0.0075). The structure-property relationships of the analogous PAs containing sulfide or sulfoxide linkages were also studied in detail by comparing the results