Kerr effect and wide angle light-scattering studies of a para-aromatic polyamide in dilute solution

The geometric and optical properties of a para-aromatic polyamide are characterized using wide angle light scattering and electric birefringence. The polydispersity correction was applied theoretically by assuming the most probable distribution. The aromatic polyamide studied can be satisfactorily modeled as a Kratky-Porod wormlike chain with a presistence length of 220 ± 50 Å and an optical unit anisotropy ratio of 2.2 ± 0.3 in tetrahydrofuran. The refractive index of 1.67 ± 0.03 is comparable to that of similar polyamides. The high persistence length of the polymer chain and the high inherent optical anisotropy of the repeat unit are found to be responsible for the exceptionally high birefringence observed in the oriented films. It is also conclusively established that there is no aggregation in the absence of moisture.