Light-colored and soluble fluorinated polyimides based on 2-trifluoromethyl-4,4′-diaminodiphenyl ether and various aromatic dianhydrides

A series of soluble and light-colored fluorinated polyimides and copolyimides (5) were synthesized from 2-trifluoromethyl-4,4′-diaminodiphenyl ether (2) and various aromatic dianhydrides via thermal or chemical imidization. Diamine 2 was prepared starting from 2-chloro-5-nitrobenzotrifluoride and 4-nitrophenol to yield the intermediate dinitro compound, followed by catalytic reduction with hydrazine and Pd/C. These polymers had inherent viscosities ranging from 0.56 to 1.29 dl/g. Polyimides 5d–f and all copolyimides were soluble in amide polar solvents and even in less polar m-cresol. Polyimide films 5a–f had tensile strengths of 111–141 MPa, elongations at break of 12–27%, and initial moduli of 2.0–2.7 GPa. The glass-transition temperatures of these polymers were in the range 259–314 °C, and the 10% weight loss temperatures were above 534 °C. Compared with polyimides based on 4,4′-diaminodiphenyl ether, polyimides 5 showed better solubility and lower color intensity, dielectric constant, and moisture absorption. Their films had cutoff wavelengths between 369 and 421 nm, b* values ranging from 14 to 75, dielectric constants of 2.79–3.87 (40 MHz), and moisture absorptions in the range 0.21–0.45 wt%.