Preparation and properties of semi-alicyclic colorless polyimide films and light-colored sheets with low dielectric features for potential applications in optoelectronic integrated circuits

Colorless and transparent polymer films and sheets with good high-temperature resistance and low dielectric constant (low-Dk) and low dissipation factors (low-Df) features are highly desired in advanced optoelectronic integrated circuits (OEIC) fabrications. In the current work, a series of semi-alicyclic polyimide (PI) powders were first prepared by the onestep high-temperature polycondensation of an alicyclic dianhydride, hydrogenated 3,3 ' ,4,4 ' -biphenyl tetracarboxylic dianhydride (HBPDA) and aromatic diamines which were beneficial for endowing the derived PI films with low-Dk features, including 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) for PI-1, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) for PI-2, and 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAOFL) for PI-3. Then, the derived PI powders were fabricated into colorless films and light-colored sheets, respectively. The freestanding flexible and tough PI films showed excellent optical transparency with the ultraviolet (UV) cutoff wavelength (lambda cut) lower than 300 nm, the optical transmittance higher than 85% at the wavelength of 400 nm, yellow indices (b*) lower than 1.0, and haze values lower than 1.2%. The hot-processed PI sheets also exhibited light colors. The PI films and sheets showed good thermal stability with the glass transition temperatures (Tg) higher than 220 degrees C. More importantly, the derived semi-alicyclic PI sheets showed Dk and Df values as low as 2.56 and 0.008 at 1 MHz, respectively.