Synthesis and characterization of novel fluorinated pyridine-based polyimides derived from 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine and dianhydrides

A series of new fluorinated pyridine-based polyimides (PIs) was synthesized by polycondensation of 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine with various aromatic dianhydrides in N,N-dimethylacetamide (DMAc) via the conventional two-step method. The inherent viscosities of the resulting poly(amic acid)s and PIs were 0.54-0.94 and 0.58-0.88 dLg(-1), respectively. The obtained PIs were predominantly amorphous and soluble in polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, and DMAc at room temperature or upon heating at 70 degrees C. They also displayed good thermal stability with the glass transition temperature of 324-416(degrees)C, the temperature at 5% weight loss of 546-584(degrees)C, and the residue of 58-69% at 750(degrees)C under nitrogen, as well as outstanding mechanical properties with tensile strengths of 69132 MPa, tensile moduli of 1.1-2.0 GPa, and elongations at break of 7-27%. Meanwhile, these PI films had dielectric constants of 2.95-3.22 (1 MHz), low water uptake 0.44-0.71%, and high optical transparency with the ultraviolet cutoff wavelength in the 388-406 nm range and the wavelength of 80% transparency in the range of 550-680 nm.