Influence of chemical structure on the refractive index of imide-type polymers

The influence of different substituents on the optical properties of poly(amide imide)s and polyimides is systematically investigated. All of the polymers exhibit good solubility and film-forming ability, high thermal stability, and glass transition temperatures of 162-209 °C for poly(amide imide)s and of 209-274 °C for polyimides. The optical transmittance of the films at 450 nm is above 80% for all the studied polyimides and poly(amide imide)s containing benzonitrile units linked in the 2,6-position. The values of refractive index for poly(amide imide)s are in the range of 1.623-1.748 and for polyimides in the domain of 1.672-1.768.