Light-colored and transparent polyimide (PI) films with good high-temperature dimensional stability are highly desired for advanced optoelectronic applications. However, in practice, the simultaneous achievement of good optical and thermal properties in one PI film is usually difficult due to the inter-conflicting molecular design of the polymers. In the present work, a series of PI-SiO2 nanocomposite films (ABTFCPI) were developed based on the PI matrix derived from hydrogenated pyromellitic anhydride (HPMDA) and an aromatic diamine containing benzanilide and trifluoromethyl substituents in the structure, 2,2'-bis(trifluoromethyl)-4,4'-bis [4-(4-aminobenzamide)]biphenyl (ABTFMB). The inorganic SiO2 fillers were incorporated into the nanocomposite films in the form of colloidal nanoparticles dispersed in the good solvent of N,N-dimethylacetamide (DMAc) for the PI matrix. The derived ABTFCPI nanocomposite films showed good film-forming ability, flexible and tough nature, good optical transparency, and good thermal properties with loading amounts of SiO2 up to 30 wt% in the system. The ABTFCPI-30 film with a SiO2 content of 30 wt% in the film showed an optical transmittance of 79.6% at the wavelength of 400 nm (T400) with a thickness of 25 μm, yellow index (b*) of 2.15, and 5% weight loss temperatures (T5%) of 491 °C, which are all comparable to those the pristine ABTFCPI-0 matrix without filler (T400 = 81.8%; b* = 1.77; T5% = 492 °C). Meanwhile, the ABTFCPI-30 film exhibited obviously enhanced high-temperature dimensional stability with linear coefficients of thermal expansion (CTE) of 25.4 × 10-6/K in the temperature range of 50 to 250 °C, which is much lower than that of the AMTFCPI-0 film (CTE = 32.7 × 10-6/K).
Keywords: benzanilide; coefficient of thermal expansion (CTE); optical transparency; polyimide film; thermal properties.