Synthesis and characterization of novel polyimides derived from 2,6-bis[4-(3,4-dicarboxyphenoxy)benzoyl]pyridine dianhydride and aromatic diamines

A novel pyridine-containing aromatic dianhydride monomer, 2,6-bis[4-(3,4-dicarboxyphenoxy)benzoyl]pyridine dianhydride, was synthesized from the nitro displacement of 4-nitrophthalonitrile by the phenoxide ion of 2,6-bis(4-hydroxybenzoyl)pyridine, followed by acidic hydrolysis of the intermediate tetranitrile and cyclodehydration of the resulting tetraacid. A series of new polyimides holding pyridine moieties in main chain were prepared from the resulting dianhydride monomer with various aromatic diamines via a conventional two-stage process, i.e. ring-opening polycondensation forming the poly(amic acid)s and further thermal or chemical imidization forming polyimides. The inherent viscosities of the resulting polyimides were in the range of 0.51-0.68 dL/g, and most of them were soluble in aprotic amide solvents and cresols, such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and m-cresol, etc. Meanwhile, some strong and flexible polyimide films were obtained, which have good thermal stability with the glass transition temperatures of 221-278 °C, the temperature at 5% weight loss of 512-540 °C, and the residue at 800 °C of 60.4-65.3% in nitrogen, as well as have outstanding mechanical properties with the tensile strengths of 72.8-104.4 MPa and elongations at breakage of 9.1-11.7%. The polyimides also were found to possess low dielectric constants.