Highly optically transparent/low color polyimide films prepared from hydroquinone- or resorcinol-based bis(ether anhydride) and trifluoromethyl-containing bis(ether amine)s

Two series of novel polyimides (5a–g and 6a–g) containing flexible ether linkages and pendent trifluoromethyl (CF3) groups were synthesized from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (3a) and 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride (3b) with various CF3-substituted aromatic bis(ether amine)s (4a–g) via ring-opening polyaddition to poly(amic acid)s, followed by thermal or chemical imidization. These polyimides were readily soluble in a variety of organic solvents and could be solution-cast into flexible and tough films. The cast films exhibited high optical transparency and almost no color, with a UV–vis absorption edge of 368–382 nm and a very low b∗ value (a yellowness index) of 6.2–15.5. They had good thermal stability with glass-transition temperatures of 186–288 °C, and most of them did not show significant decomposition before 500 °C. Moreover, these polyimide films also possessed low dielectric constants of 2.79–3.49 (at 1 MHz) and low water uptakes (<0.65 wt%).