Synthesis and characterization of new soluble polyimides based on pyridine unit with flexible linkages

A series of new polyimides were synthesized by condensation of pyridine-bridged novel diamine monomers, bis(4-aminobenzoyloxy-3,5-dimethyl phenyl)-3-pyridyl methane and 2,6-bis(2-amino-3-pyridyloxy)pyridine, with various aromatic anhydrides. The monomers and precursors were characterized by elemental analysis, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (H-1 NMR), and carbon-13 nuclear magnetic resonance (C-13 NMR) spectroscopic techniques. The structure of the polymers were characterized by FTIR and H-1-NMR spectroscopy, and the physical properties of the polymers, including the glass transition temperature (in the range of 199-319 degrees C), thermal and thermo-oxidative stability (10% weight loss temperature is in the range of 375-539 degrees C in air and 403-542 degrees C in nitrogen atmospheres), the char yield in the range of 37.91-56.65% at 800 degrees C, solubility, solution viscosity (0.81-1.81), molecular weight data, optical properties, crystallinity, mechanical properties like tensile strength (86-102 MPa), elongation at break (12.5-16.5%), tensile modulus (1.2-1.8 GPa), and moisture absorption were also studied.