Highly Refractive Aromatic Polybenzoxazoles Derived from Sulfur-Containing Dibenzoyl Chlorides

A series of aromatic polybenzoxazoles (PBOs) containing sulfur atoms in their main chains were developed. All of the PBOs were prepared from synthesized hydroxyl-diamine 4,4′-bis­(4-amino-3-hydroxyphenylthio)­diphenylsulfide (3SDA) and aromatic diacyl chlorides, such as 4,4′-((thiobis­(4,1-phenylene))­bis­(sulfanediyl))­dibenzoyl chloride (3SDBC), trans-1,4-cyclohexanedicarbonyl dichloride (trans-CHDC), isophthaloyl dichloride (IPC), and 4,4′-oxybis­(benzoyl chloride) (OBC), via a conventional two-step procedure. The PBOs exhibited high thermal stability, thermal decomposition temperature (>430 °C), and glass-transition temperature (204–255 °C). The PBO derived from 3SDA and 3SDBC exhibited a very high refractive index, i.e., 1.7862 at 637 nm due to the high sulfur content (21.79%).