Synthesis and characterization of novel fluorinated polyimides derived from 4,4?-[2,2,2-trifluoro-1-(3-trifluoromethylphenyl)ethylidene]diphthalic anhydride and aromatic diamines

A novel fluorinated aromatic dianhydride, 4,4′-[2,2,2-trifluoro-1-(3-trifluoromethyl-phenyl)ethylidene]diphthalic anhydride (TFDA) was synthesized by coupling of 3′-trifluoromethyl-2,2,2-trifluoroacetophenone with o-xylene under the catalysis of trifluoromethanesulfonic acid, followed by oxidation of KMnO4 and dehydration. A series of fluorinated aromatic polyimides derived from the novel fluorinated aromatic dianhydride TFDA with various aromatic diamines, such as p-phenylenediamine (p-PDA), 4,4′-oxydianiline (ODA), 1,4-bis(4-aminophenoxy)benzene (p-APB), 1,3-bis(4-amino-phenoxy)benzene (m-APB), 4-(4-aminophenoxy)-3-trifluoromethylphenylamine (3FODA) and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB), were prepared by polycondensation procedure. All the fluorinated polyimides were soluble in many polar organic solvents such as NMP, DMAc, DMF, and m-cresol, as well as some of low boiling point organic solvents such as CHCl3, THF, and acetone. Homogeneous and stable polyimide solutions with solid content as high as 35–40 wt % could be achieved, which were prepared by strong and flexible polyimide films or coatings. The polymer films have good thermal stability with the glass transition temperature of 232–322 °C, the temperature at 5% weight loss of 500–530 °C in nitrogen, and have outstanding mechanical properties with the tensile strengths of 80.5–133.2 MPa as well as elongations at breakage of 7.1–12.6%. It was also found that the polyimide films derived from TFDA and fluorinated aromatic diamines possess low dielectric constants of 2.75–3.02, a low dissipation factor in the range of 1.27–4.50 × 10−3, and low moisture absorptions