Preparation of Novel Pyridine-Based Aromatic Polyimides and Effect of Fluorine Functionality.

Novel pyridine-containing linear and branched polyimides (Li-PIs and Br-PIs) were prepared by aromatic diamine and triamine monomers. The fluorinated, non-fluorinated and trifunctional pyridine-based monomers, 4-(4-(trifluoromethylphenyl))-2,6-bis(4-aminophenyl)pyridine (FDAPP), 4-phenyl-2,6-bis(4-aminophenyl)pyridine (DAPP) and 4,4',4"-(pyridine-2,4,6-triyl)tribenzenamine (TAPP) amino compounds were synthesized by a modified Chichibabin reaction of different benzaldehydes and p-nitroacetophenone, followed by a reduction of the resulting nitro compounds with hydrazine monohydrate. Functional amine monomers were used to synthesize a series of pyridine-containing linear and branched polyimides, by polycondensation with aromatic dianhydride in N-Methyl-2-pyrrolidone (NMP) via the conventional two-step method. The obtained novel polyimides (PIs) exhibited good solubility in common organic solvents, such as m-Cresol, NMP, DMF, DMSO and DMAc. Moreover, obtained PI films were flexible and showed excellent thermal stability, with the glass transition temperature (T(g)) of 264-331 degrees C and the temperature at 10% weight loss of 580-620 degrees C in a nitrogen atmosphere. The protonated polymer showed UV-vis absorption in the region of 200-400 nm, good optical transparency with the cut-off wave lengths of 372-392 nm, as well as a low dielectric constant (ε) in the range of 3.897-4.276 at 1 MHz. Moreover, the resulted PIs derived from DAPP, FDAPP and TAPP were compared on the basis of fluorine functionality with non-fluorinated parallels, and the effect of branching units was compared with linear polymers.