A novel fluorinated polyimide (PI 3) containing fluorenylene cardo structure, was prepared from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene (1) and 4,4'-(2,2-hexafluoropropylene)bis(phthalic anhydride) (2) via a one-step high-temperature polycondensation. FT-IR, ¹H and ¹⁹F NMR spectra were used to investigate the chemical structure of PI 3. The results confirmed that the structure of PI 3 was in good agreement with the proposed structure and the imidization was conducted completely between 1 and 2. The obtained PI 3 showed high solubility, with the dissolvability higher than 10 wt% in most common solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,N-dimethylformamide, chloroform, dichloromethane and tetrahydrofuran. The resulting PI film exhibited excellent optical transparency and colorlessness, with a UV-Vis absorption edge at 315 nm and the transparency at 400 nm higher than 84%. Furthermore, PI 3 also possessed good thermal and mechanical properties. The temperature at 10% weight loss was beyond 539 ℃in both air and nitrogen atmospheres, and the glass-transition temperature was at 377 ℃. The film had strengths at break of 70～80 MPa, elongations at break of 4%～8%, and initial modulus of 2.6 GPa.

Key words: fluorinated polyimide, solubility, optical transparency