Triptycene Polyimides: Soluble Polymers with High Thermal Stability and Low Refractive Indices

Abstract

A series of soluble, thermally stable aromatic polyimides were synthesized using commercially available five- and six-membered ring anhydrides and 2,6-diaminotriptycene derivatives. All of these triptycene polyimides (TPIs) were soluble in common organic solvents despite their completely aromatic structure due to the three-dimensional triptycene structure that prevents strong interchain interactions. Low solution viscosities (0.07−0.47 dL/g) and versatile solubilities allow for easy solution processing of these polymers. Nanoporosity in the solid state gives rise to high surface areas (up to 430 m2/g) and low refractive indices (1.19−1.79 at 633 nm), which suggest very low dielectric constants at optical frequencies. Polymer films were found to be amorphous. The decomposition temperature (Td) for all of the polymers is above 500 °C, and no glass transition temperatures can be found below 450 °C by differential scanning calorimetry (DSC), indicating excellent prospects for high-temperature applications. This combination of properties makes these polymers candidates for spin-on dielectric materials.