Colorless polyimide films with low birefringence and retardation: Synthesis and characterization

In this study, two series of polyimides (PI) were synthesized from one step solution polycondensation of two diamines containing sulphonyl group with aromatic and aliphatic dianhydrides. These PIs showed good organosolubility and were casted into films with high transparency of T500>86%, and cutoff wavelength in the range of 295–370 nm. Optical birefringence (0.0020–0.0127) of these PIs was lower than that of traditional aromatic PI. PI films demonstrated out-of-plane retardation (Rth) in the range of 42–279 nm, indicating low optical anisotropy of these films. All PIs also exhibited high thermal stability with glass transition temperatures ranging from 200 to 339 °C. PI-1c derived from bis[4-(3-aminophenoxy)phenyl] sulfone (m-BAPS) and 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) showed the lowest birefringence and good transparency.