Synthesis and Characterization of Aromatic Polyamides Obtained from 4-4'-(9-Fluorenylidene)Diamine, 4-4'-(Hexafluoro-Isopropylidene)Dianiline and 4-4'-Diamine-Benzophenone

Abstract

Nine aromatic polyamides were synthesized from three different diamines by high-temperature polycondensation using three different aromatic diacid chlorides. A comparison of the effect that structural modifications afforded by the substitutions at the diacid chloride phenyl position and the introduction of bulky side groups in the diamine contribution were evaluated. Polyamide properties were characterized by DSC, TGA, wide angle x-ray scattering, density, light scattering and solubility. Differential scanning calorimetry measurements indicated that all polymers have high glass transition temperatures ranging from 236 to 319 'C, while thermogravimetrical measurements show that the onset of decomposition of these polymers is above 460 'C and that they are thermally stable. It was also found that almost all polymers were soluble in polar aprotic solvents. The results indicate that introduction of bulky side groups in the structure of the aromatic polyamides increases the Tg, while packing efficiency is lowered by these aromatic groups. Furthermore, the hexafluoro substitution in the polyamides raises their thermal stability, which may be attributed to the strong C-F bond. A relationship between Tg and the conformational entropy determined by structure was found, indicating that the higher the rigidity of the polyamide the higher the Tg. Moreover, the incorporation of bulky side groups on the structure increases the Tg more than an increase on rigidity, which indicates that the effect of intermolecular interactions is more important for an increase in Tg than the effect of chain stiffniess.