Fabrication of polyimide copolymer films for controlled optical retardation

Poly(amic acid)s were successfully synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) or 4,4'-hexafluoroisopropylidene diphthalic dianhydride (6FDA) with different molar fractions of 4,4'-oxyaniline (ODA) and 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane diamine (AHHFP). Stepwise thermal imidization method were used for preparing polyimide copolymer fdms. Two-axis out-of-plane retardations were detected for optical retardation (R0 and R&) measurement using an LCD panel measuring device. The optical transparency and yellow index were measured by a ultraviolet-visible (UV-vis) spectrophotometer and a color-difference meter. Their thermal properties were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The physical properties of PI copolymer films were found to be strongly dependent upon the morphological structure and composition. After all, RA of PI copolymer films were possibly controlled.