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)]diphthalic anhydride (DPSDA), and various sulfur-containing aromatic diamines, including 4,4'-thiobis[(p-phenylenesulfanyl)aniline] (3SDA), 4,4'-sulfonylbis[(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 °C and high initial thermal decomposition temperatures (T5%) exceeding 470 °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 μm. 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.