Synthesis and characterization of soluble polyimides derived from a novel unsymmetrical diamine monomer:: 1,4-(2′,4-diaminodiphenoxy)benzene

A new aromatic unsymmetrical diamine monomer, 1,4-(2',4-diaminodiphenoxy)benzene (OAPB), was successfully synthesized in three steps using hydroquinone as starting material and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4'-oxydiphthatic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 2,2'-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) and pyromellitic dianhydride (PMDA) via the conventional two-step thermal or chemical imidization method to produce a series of the unsymmetrical aromatic polyimides. The polyimides were characterized by solubility tests, viscosity measurements, IR, H-1 NMR, and C-13 NMR spectroscopy, X-ray diffraction studies, and thermogravimetric analysis. The polyimides obtained had inherent viscosities ranged of 0.38-0.58 dL/g, and were easily dissolved in common organic solvents. The resulting strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 505 degrees C and the glass transition temperature in the range of 230-299 degrees C. Moreover, the polymer films showed outstanding mechanical properties with the tensile strengths of 41.4-108.5 MPa, elongation at breaks of 5-9% and initial moduli of 1.15-1.68 GPa. (C) 2007 Elsevier Ltd. All rights reserved.