Soluble polyimides based on a novel pyridine-containing diamine m,p-PAPP and various aromatic dianhydrides

A novel pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-PAPP), was successfully synthesized by a modified Chichibabin reaction of benzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)acetophenone (m,p-NPAP), followed by a reduction of the resulting dinitro compound 4-phenyl-2,6-bis[3-(4-nitrophenoxy)phenyl]pyridine (m,p-PNPP) with Pd/C and hydrazine monohydrate. The aromatic diamine was employed to synthesize a series of pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides in N,N-dimethylformamide (DMF) via the conventional two-step method, and further thermal or chemical imidization forming PIs. The inherent viscosities of the resulting poly(amic acid)s and PIs were 0.59-0.73 and 0.56-0.68 dL/g; most of the PIs obtained by chemical imidization were readily soluble in common organic solvents such as DMF, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), etc. Meanwhile, strong and flexible PI films were obtained, which had good thermal stability, with the glass transition temperature (T (g)) of 204.5-237.4 A degrees C and the temperature at 10% weight loss of 527.7-552.0 A degrees C in nitrogen atmosphere, as well as outstanding mechanical properties with tensile strengths of 88.6-90.4 MPa, a tensile moduli of 1.04-1.56 GPa, and elongations at break of 7.2-8.7%. The PI films also were found to possess low water uptake of 0.89-0.98%.