Synthesis and characterization of novel polyimides derived from 4-phenyl-2, 6-bis [3-(4-aminophenoxy)-phenyl]-pyridine diamine and aromatic dianhydrides

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2, 6-bis [3-(4-aminophenoxy)phenyl]-pyridine(m-PAPP),was synthesized by a modified Chichibabin reaction of benzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)-acetophenone(m-NPAP), and a reduction of the resulting dinitro compound 4-phenyl-2, 6-bis[3-(4-nitrophenoxy)phenyl]-pyridine (m-PNPP) with Pd/C and hydrazine monohydrate, successively. A series of novel aromatic polyimides were prepared from the diamine with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities of the resulting poly (amic acid) precursors were 1.37-1.56 dL/g, and these polymers could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The glass transition temperatures of these polymers were recorded at 180-264 °C. All of these novel polyimides held 10% weight loss at the temperature above 430 °C and left more than 50% residue even at 800 °C in air, as well as have outstanding mechanical properties with the tensile strengths of 91.6-114.1 MPa and elongations at breakage of 10.1-15.7%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.