Highly refractive and transparent polyimides derived from 4,4'-[m-sulfonylbis(phenylenesulfanyl)]diphthalic anhydride and various sulfur-containing aromatic diamines

We have developed highly refractive and transparent polyimides (Pis). The Pis were prepared from a newly developed meta-substituted sulfonyl-bridged dianhydride, 4,4'-[m-sulfonylbis(phenylenesulfanyl)]diplithalic anhydride (DPSDA), and various sulfur-containing aromatic diamines, including 4,4'-thiobis[(p-phenylenesulfanyl)aniline] 3SDA), 4,4'-sulfonyl-bis[(p-phenylenesulfanyl)aniline] (BADPS), 2,8-bis(p-aminophenylenesulfanyl)dibenzothiophene (APDBT), and 2,7-bis(p-aminophenylenesulfanyl)thianthrene (APTT), by, employing a two-step polycondensation procedure. The Pis exhibited good thermal stabilities such as the relatively high glass-transition temperatures in the range of 177-206 degrees C and high initial thermal decomposition temperatures (T-5%) exceeding 470 degrees C. The meta-substituted electron-withdrawing sulfonyl moiety endowed the PI films with good optical transparency. The optical transmittances of the PI films at 450 nm were higher than 85% for the thickness of approximately 10 mu m. Furthermore, the flexible thioether linkages and sulfonyl moiety in the molecular chains of the Pis provided them with high refractive indices of 1.7162-1.7432, relatively small Abbe numbers of 14.1-14.8, and low birefringences of 0.0059-0.0065.