Synthesis of organosoluble and light‐colored cardo polyimides via aromatic nucleophilic substitution polymerization

A series of cardo polyimides (PIs) containing large‐volume cardo groups were prepared via aromatic nucleophilic substitution polymerization of bisphenols and bis(fluorophthalimide)s. This series of cardo PIs show excellent solubility in a variety of organic solvents. The glass transition temperatures (Tgs) of these PIs are recorded from 217°C to 293°C, the 5% weight loss temperatures (T5%) reach up to 495–536°C in air and 487–531°C in nitrogen, respectively. Flexible films, which could be cast from the polymer solutions, exhibit good mechanical properties with tensile strengths of 118–127 MPa, elongations at break of 10.6–15.4% and tensile moduli of 2.3–2.8 GPa. Their films with cut‐off wavelengths from 342 to 423 nm are essentially colorless, and the transmittance of these cardo polyimide films is over 80% between 450 and 800 nm. It is noted that cardo PIs possess better solubility, higher glass transition temperature, and better optical transparency than linear PIs.