Synthesis of High Refractive Index Polyimides Derived from 1,6-Bis(p-aminophenylsulfanyl)-3,4,8,9-tetrahydro-2,5,7,10-tetrathiaanthracene and Aromatic Dianhydrides

Highly refractive and transparent polyimides (PIs) containing a 3,4,8,9-tetrahydro-2,5,7,10-tetrathiaanthracene moiety in their main chains have been developed. These PIs were prepared from several dianhydrides such as 4,4′-[ p -thiobis(phenylsulfanyl)]diphthalic anhydride (3SDEA), 4,4′-[(9 H -fluorene-9-ylidene)bis( p -phenylsulfanyl)]diphthalic anhydride (FPSP), 4,4′-oxidiphthalic anhydride (ODPA), and a new sulfur-containing aromatic diamine, 1,6-bis( p -aminophenylsulfanyl)-3,4,8,9-tetrahydro-2,5,7,10-tetrathiaanthracene (BTTA), by a two-step polycondensation procedure. The PIs exhibit good thermal and optical properties such as glass transition temperatures higher than 213 °C, thermal decomposition temperatures ( T 10% ) in the range of 390−443 °C, and optical transparency higher than 80% at 500 nm for a thickness of ca. 10 μm. Because of the very high sulfur content (28.4%) in the polymer main chain, the PI derived from BTTA and 3SDEA exhibits the highest refractive index, i.e., 1.769 at 633 nm.