Synthesis and characterization of optically transparent semi-aromatic polyimide films with low fluorine content

A series of novel semi-aromatic polyimides with low fluorine content were prepared from alicyclic dianhydrides, i.e. 1,2,4,5-cyclohexane-tetracarboxylic dianhydride (CHDA) and bicyclo[2.2.2]octa-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), and three aromatic diamines containing ortho-substituted methyl and pendent phenyl groups, respectively. These polyimides exhibited excellent solubility even though their fluorine content lower than 10 wt%. Chemical resistance to MEK and aqueous alkali of films was also satisfied for application as flexible substrates. The semi-aromatic polyimides showed outstanding heat resistance with Tg values up to 387 °C and good mechanical strength. These films had excellent optical transparency with cutoff wavelengths of 282–286 nm, transmittance >89% at 500 nm and yellowness indices