Thermally Stable, Hydrophobic Colorless Polyimides With High Strength and Excellent Dimensional Stability for Flexible Optoelectronics and Electronics
Zhengsheng Yang, Huanyong Liu, Peiheng Zhou, Haolan Li, Zhiheng Zou, Guang Yang
Abstract
ABSTRACT Concurrently achieving excellent optical properties, thermal stability, mechanical properties, dimensional stability as well as low dielectric constant of colorless polyimides (CPI) is urgently needed for flexible display and electronics. Here, CPI named PI‐5 was designed and synthesized from 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′‐bis(trifluoromethyl) benzidine (TFMB), polyhedral oligomeric silsesquioxane (POSS) based micro‐crosslinker and chain end tethered units. For comparison, other PI samples are synthesized by adjusting reactants. PI‐5 film has excellent transmittance at 450 nm (92.8%) and yellowness index of 2.43. All PI samples are soluble in organic solvents showing good processability. POSS micro‐crosslinker reduces the CTE of PI and POSS termination unit further decreases it to 17.4 ppm K −1 . Meanwhile, PI‐5 has glass transition temperature ( T g ) of 356°C, 5 wt% weight‐loss temperature of 522°C, tensile strength ( δ max ) of 265 MPa, Young's modulus ( E ) of 7.2 GPa. Additionally, PI‐5 shows low dielectric constant ( D k ) and dielectric loss ( D f ) of 2.61 and 0.0072 at 1 MHz, as well as low water absorption value (0.39%). This work provides a new strategy to prepare mechanically robust CPI with enhanced general properties for flexible substrate, optoelectronic and related applications.