Transparent semi-aliphatic polyimide films with excellent thermal stabilities for applications in the display technology

A set of colorless polyimide (CPI) films with norbornene-aliphatic ring structures has here been prepared through polycondensation reactions by using cyclopentanone bis-spironorbornane tetracarboxylic dianhydride (CpODA), 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 4,4′-diaminodiphenyl ether (ODA) monomers as raw materials. The transmissivities, dielectric properties and thermal stabilities of CPI films are optimized by adjusting the CpODA-to-6FDA molar ratios. Compared with the aromatic and aliphatic PI films, the thermal stabilities and transmissivities of CPI films are well balanced. Moreover, the CPI films possessed low dielectric constants and low dielectric losses. The thermal expansion coefficients, temperatures at a 5% weight loss and glass-transition temperatures are maintained at 31–41 ppm K−1, 461–484 °C and 348–362 °C, respectively. In addition, the transmittances (86–89%), dielectric constants (2.15–2.47) and dielectric losses (<0.023) are all prominent. In short, the CPI films have been shown to have a high potential for use in the display technology.