Highly transparent and hydrophobic fluorinated polyimide films with ortho-kink structure

This study focuses on the synthesis and characterization of new polyimide films with ortho-kink structures based on trifluoromethyl-containing diamines and hexafluoroisopropylidene-containing dianhydrides. High-temperature solution polycondensation reactions via conventional two-stage process involving the thermal imidization of the poly(amic acid) precursors resulted in polyimides with high molecular weights. The structures of the monomers and the corresponding polymers were fully confirmed by infrared and nuclear magnetic resonance spectroscopy. All polyimides were easily soluble in convenient organic solvents and showed excellent thermal stability, up to 345 °C. Transparent thin films were obtained therefrom, some of them having a porous structure. The polyimides presented good optical properties with high transparency and low cut-off wavelength. Their aggregation behavior followed by fluorescence spectroscopy was discussed in correlation with the chemical structure. The high hydrophobic character of these fluorinated polyimides was evidenced by the values of water contact angle to the polymer film surfaces. All these properties recommend their use in opto-electronic devices as transparent flexible substrates.