Synthesis of highly refractive and transparent polyimides derived from 4,4 '-[p-sulfonylbis(phenylenesulfanyl)]diphthalic anhydride and various sulfur-containing aromatic diamines

Highly refractive and transparent polyimides (PIs) have been developed. The PIs were prepared from a para-substituted sulfonyl-bridged dianhydride, 4,4'-[p-sulfonylbis(phenylenesulfanyl)]diphthalic anhydride (p-DPSDA) and various sulfur-containing aromatic diamines including 4,4'-thiobis[(p-phenylenesulfanyl)aniline] (3SDA), 4,4'-sulfonylbis[(p-phenylenesulfanyl)aniline] (BADPS), and 2,7-bis(p-aminophenylenesulfanyl)thianthrene (APTT) by employing a two-step polycondensation procedure. The PIs showed excellent thermal stabilities with 5% weight loss temperatures (T-d(5)) exceeding 470 degrees C in nitrogen and the glass transition temperatures (T-g(s)) higher than 208 degrees C. The PI films exhibited good optical transmittances exceeding 85% at 450 nm and high refractive indices of 1.7169-1.7420 at 632.8 nm that are almost same as those of the PIs derived from 4,4'-[m-sulfonylbis(phenylenesulfanyl)]diplithalic anhydride (mDPSDA). The para-substituted electron-withdrawing sulfonyl moiety improves the transparency but lowers the refractive index. In addition, very small birefringence (Delta n) of 0.0065-0.0093 was obtained for the PIs.