Synergistic Effect of Sulfur and Chalcogen Atoms on the Enhanced Refractive Indices of Polyimides in the Visible and Near-Infrared Regions

Abstract

To develop thermally stable optical polymers for visible and near-infrared sensor applications, a series of sulfur containing polyimides (PIs) with chalcogen atoms were successfully synthesized via conventional two-step polycondensation of 4,4'-[p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) with four diamines: 4,4'-oxidianiline (ODA), 4,4'-thiodianiline (TDA), 4,4'-selenodianiline (SEDA), and 4,4'-tellurodianiline (TEDA). Because of the large atomic polarizabilities of the sulfur, selenium, and tellurium atoms, the resultant PIs exhibited significantly high refractive indices in the 1.738-1.778 range at 637 nm along with a transmittance >90% at 650-1500 nm. In addition, the PIs exhibited good thermal stability, with high thermal decomposition and glass transition temperatures (T-ds% > 390 degrees C and T-g = 183-217 degrees C, respectively). Owing to the good affinity of SEDA-3SDEA for TiO2 nanoparticles, a nanocomposite film with a 3.0 wt % loading of TiO2 nanoparticles exhibited a refractive index of 1.774 at 637 nm.