Highly Refractive Polyimides Derived from 2,8‐Bis(p‐aminophenylenesulfanyl)dibenzothiophene and Aromatic Dianhydrides

A series of wholly aromatic PIs were prepared from a newly synthesized sulfur‐containing diamine and various aromatic dianhydrides via a two‐step polycondensation procedure. Flexible and tough PI films were cast from their soluble PAA precursors. The PIs showed good thermal stability with 5% weight loss temperatures above 480 °C and glass transition temperatures above 200 °C. The films showed good optical transparency in the visible region with a transmittance above 80% at 500 nm. The linear thioether linkages and the cyclic dibenzothiophene moiety in the PIs endowed the PIs with high refractive indices ranging from 1.7353 to 1.7578 and low birefringence between 0.0068 and 0.0106. magnified image