Study on the preparation of novel transparent UV- barrier polyimide films via regulating molecular chain Configuration and electronic orbital Arrangement by –CF3 and their application properties

In order to prepare polyimide materials with excellent optical transparency and UV barrier, the effects of the number and substitution position of −CF 3 groups on polyimide properties were investigated. Researchers synthesized four novel diamine monomers (BPA-O, BPA-NH 2 , BPAF-O, BPAF-NH 2 ) and synthesized eight high-performance colorless polyimides (PI-1 ∼ PI-8). On the one hand, the strong electron-withdrawing effect of −CF 3 restricts electron movement within the molecular chain, weakening the CTC effect of the molecular chain and thereby enhancing the transparency of the film. On the other hand, the ortho -substitution of −CF 3 on the imide ring induces greater twisting of molecular chains, disrupts their close packing, and thereby exerts a positive effect on enhancing the optical transparency of the film. The high bond energy of the C-F bond and the introduction of the flexible group −O- act as an “energy buffer,” suppressing UV-induced main chain breakage and achieving high UV barrier. All CPI films exhibit excellent transparency and thermal stability, with a cut-off wavelength range of 325 nm-381 nm and a transmittance range of 78.7 %-88 % at 550 nm. They have good optical properties, with T d5% distributed in the range of 511.5 °C − 533.7 °C, and the glass transition temperature ( T g ) distributed in the range of 197.3 °C-234.4 °C, demonstrating good thermal stability. Additionally, the cut-off wavelength is at a relatively high level, reaching up to 381 nm.