Novel soluble and optically active polyimides containing axially asymmetric 9,9′-spirobifluorene units: Synthesis, thermal, optical and chiral properties

A new optically active spirobifluorene-based diamine monomer, (R)-2,2′-bis(4-amino-2-trifluorom-ethylphenoxy)-9,9′-spirobifluorene, was synthesized using (R)-2,2′-dihydroxy-9,9′-spirobifluorene as starting material. The absolute stereochemistry of the chiral diamine was determined by single crystal X-ray diffraction. A series of novel chiral polyimides were prepared from the diamine with various aromatic dianhydrides via a two-stage process with chemical imidization method. All these optically active polyimides were readily soluble in many organic solvents and could afford flexible, tough and transparent films with an UV–vis absorption cutoff wavelength at 351–375 nm. The glass transition temperatures of these polyimides were recorded between 262 and 281 °C by differential scanning calorimetry, and the 5% weight loss occurred at temperatures above 510 °C. The specific rotations of these chiral polyimides ranged from −48.5° to +73.0° depending on the structures of the aromatic dianhydrides. All the optically active polyimides exhibited high chiral stability in solid state or in DMAc solvent at high temperature due to introduction of chiral spirobifluorone group into polymer backbones. The circular dichroism (CD) spectroscopic properties of these chiral polyimides in tetrahydrofuran solutions were also studied.