Synthesis and properties of transparent polyimide films containing amide bonds and trifluoromethyl groups

In this study, two diamine monomers 4,4′-(perfluoro propane-2,2-dial)bis(2-aminophenol)(6FAP) and N, N′-((perfluoro propane-2,2-dial)bis(6-hydroxy-3,1-phenylene))bis(3-aminobenzamide) (HFA) were synthesized and used to prepare polyimide (PI) films. The effects of introducing amide bonds and trifluoromethyl groups into the polymer chains on the film properties were deeply investigated. The prepared PI films have high optical transparency, with a cutoff wavelength ranging from 300 to 330 nm, and a transmittance exceeding 80 % at 500 nm. They also exhibit excellent thermal stability, with a glass transition temperature ( T g ) higher than 300°C, and a 5 % thermal weight loss temperature ranging from T d5 % 482–510°C. Moreover, the films show good mechanical properties. In terms of chemical solubility, they are soluble in common polar aprotic solvents and low-polarity solvents and are resistant to acids and alkalis. The introduction of amide bonds enhances the rigidity of the molecular chains and the intermolecular interactions, further improving the T g without significantly sacrificing optical transparency or thermal stability. This polyimide film with high transparency, good thermal stability, and excellent processing performance is a highly potential candidate material for flexible substrates in flexible displays, advanced electronics, and other photonic applications.