Abstract
Highly refractive and transparent polyimides (PIs) based on 2,5-bis(4-aminophenylsulfanyl)-1,4-dithiane (BASDT) have been developed. BASDT was polymerized with two dianhhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 4,4'-[p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) to afford two PIs. The PI of 3SDEA/BASDT exhibited the glass transition temperature at 156 °C and the 5% weight loss temperatures (T5%) at 310 °C. The 1,4-dithiane moiety endowed the PI films with good optical transparency with high refractive indices. The optical transmittance of the PI film from CBDA and BASDT at 400 nm was higher than 90% for the thickness of 1.0 μm. Furthermore, the 1,4-dithiane moiety and flexible thioether linkages in the molecular chains of the PIs provided them with high refractive indices of 1.6929?1.7455 and small birefringence of 0.0056-0.0299.
