Synthesis and properties of new pyridine-bridged poly(ether-imide)s based on 4-(4-trifluoromethylphenyl)-2,6-bis[4-(4-aminophenoxy)phenyl]pyridine

A novel pyridine-containing aromatic diamine monomer, 4-(4-trifluoromethylphenyl)-2,6-bis[4-(4-aminophenoxy)phenyl]pyridine (FAPP), was synthesized via the modified Chichibabin pyridine synthesis of 4-(4-nitrophenoxy)-acetophenone with 4-trifluoromethyl-benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step process. The resulting polyimides exhibited good solubility in aprotic amide solvents and m-cresol, such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and m-cresol, etc., which possessed the inherent viscosities of 0.76–0.91 dL/g. Strong and flexible poly(ether-imide) films were obtained, which showed excellent thermal properties with the glass transition temperatures of 268–353 °C, the temperature at 5% weight loss of 547–595 °C, and the residue at 700 °C of 65–74% in nitrogen, good mechanical properties with the tensile strengths of 87.6–104.2 MPa and elongations at breakage of 8.9–12.6%, and good optical transparency with the cut-off wavelengths of 357–380 nm, as well as low dielectric constants in the range of 2.49–3.04 at 1 MHz and low water uptake 0.43–0.69%. Furthermore, the resulted polyimides derived from FAPP were compared with non-fluorinated analogous polyimides and fluorinated analogous polyimides with trifluoromethyl groups in different positions, and the effects of substituents were also investigated and discussed.