Synthesis and Characterization of Some Aromatic Polyimides

摘要

The dian-Line 2-methyl-1,3-bis(4-aminophenyloxy)benzene was prepared via a nucleophilic substitution reaction and was characterized with Fourier transform infrared, elemental analysis, and H-1- and C-13-NMR spectroscopy. The prepared diamine was also characterized with single-crystal analysis. The geometric parameters of C19H18N2O2 were in the usual ranges. The dihedral angles between the central phenyl ring and the two terminal aromatic rings were 88.9 and 91.6 degrees. The crystal structure was stabilized by N-H center dot center dot center dot N hydrogen bonds. The diamine was then polymerized with 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, and pyromellitic dianhydride by either a one-step solution polymerization reaction or a two-step procedure. These polymers had inherent viscosities ranging from 0.61 to 0.85 dL/gm. Some of the polymers were soluble in most common organic solvents even at room temperature, and some were soluble on heating. The degradation temperatures of the resultant polymers fell in the range of 260-500 degrees C in nitrogen (with only 10% weight loss). The specific heat capacity at 200 degrees C ranged from 1.0 to 2.21 J g(-1) K-1. The temperatures at which the maximum degradation of the polymer occurred ranged from 510 to 610 degrees C. The glass-transition temperatures of the polyimides ranged from 182 to 191 degrees C. The activation energy and enthalpy of the polyimides ranged from 44.44 to 73.91 kJ/mol and from 42.58 to 72.08 kJ/mol K, respectively. The moisture absorption was found in the range of 0.23-0.71%.