New colorless substrates based on polynorbornene‐chlorinated polyimide copolymers and their application for flexible displays

Novel polynorbornene (PNB)‐polyimide (PI) copolymers were synthesized based on poly(N‐phenyl‐exo‐norbornene‐5,6‐dicarboximide) (PPhNI) and chlorinated PI (BPDA/TCDB). Polynorbornene copolymers (PNCs) with diverse compositions of anhydride were synthesized via ring opening metathesis polymerization (ROMP) of N‐phenyl‐exo‐norbornene‐5,6‐dicarboximide (PhNI) and exo‐7‐oxanorbornene‐5,6‐dicarboxylic anhydride(exo‐NA), followed by copolymerization through a reaction with aromatic dianhydride (3,3′,4,4′‐biphenyltetra‐carboxylic dianhydride, BPDA) and tetrachlorinated diamine (2,2′,5,5′‐tetrachlorobenzidine, TCDB). The copolymer (PNIC) films exhibited good optical transparency with a transmittance of around 70% at 400 nm and a good thermal stability with a glass transition temperature at 276–300 °C. These flexible films also resisted most organic solvents and chemicals, such as methanol, acetone, tetrahydrofuran, N‐methylpyrrolidone, ethyl acetate, hydrochloric acid, sodium hydroxide, and hydrogen peroxide, etc. Indium tin oxide (ITO) coated thin films were prepared at various substrate deposition temperatures with a radio frequency (r.f.) planar magnetron sputtering system. The ITO thin films that were deposited onto the PNIC copolymer substrates had good electrical and optical properties. An organic light‐emitting device (OLED) was fabricated using the PNIC copolymer substrate with a structure of PNIC08/ ITO (anode)/hole‐transporting layer (HTL)/emitting & electron‐transporting layer (EM&ETL)/aluminum (cathode). The flexible OLED fabricated on the ITO‐grown PNIC substrate exhibited a performance that was comparable to corresponding ITO‐grown glass substrates. Therefore, the ITO‐grown PNIC substrate could possibly be a promising candidate as a substrate for flexible displays. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1806–1814, 2010