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Kerr effect and wide-angle light scattering studies of a para-aromatic polyamide in dilute solution
Abstract
A series of para-linked aromatic polyamides synthesized with the aim of making optically uniaxial, transparent films and fibers for optical applications, are found to have anomalous properties. Stretched films of these polyamides are highly birefringent and non-crystalline at the same time. These rod-like polyamides do not form lyotropic solutions and are soluble in common solvents like THF, unlike other rod-like polymers. With the goal of understanding this behavior from a molecular standpoint we have quantitatively characterized the geometric, optical and hydrodynamic properties of one of these polyamides. With angle light scattering measurements on polyamide in THF were used in conjunction with electric birefringence measurements to determine the weight average molecular weight, M$\sb{\rm w}$, the root mean square z-averaged radius of gyration, R$\sb{\rm gz}$, the apparent second virial coefficient, A$\sb{\rm 2app}$ and the monomer molecular anisotropy ratio $\varepsilon$. The polydispersity correction was applied theoretically by assuming the most probable distribution. Hydrodynamic and optical properties were determined with viscometry and differential refractometry respectively. The aromatic polyamide studied can be satisfactorily modeled as a Kratky-Porod wormlike chain with a persistence length of 220 $\pm$ 50 A and a monomer optical anisotropy ratio of 2.3 $\pm$ 0.3. The excluded volume effect is found to be negligible in THF at 25$\sp\circ$C. The small axial ratio of 30 may be partly responsible for the non-lyotropic behavior. The refractive index of 1.67 is in good agreement with that of similar polyamides. The repeat unit has a high optical anisotropy leading to highly birefringent films. It is also conclusively established that there is no aggregation due to H-bonding in the absence of moisture. The light scattering theory of Nagai and the hydrodynamic theory adopted for semiflexible chains is found to hold very well for the polyamide studied. Based on the agreement between experiment and theory we infer that the molecular weight distribution is of the most probable type. Our depolarized light scattering data indicate that the straight line behavior observed in Zimm plots even for $\rm R\sb{g}\sp2q\sp2>1$, upto $\rm R\sb{g}\sp2q\sp2$ of 3.5 is due to the combined effect of polydispersity, large size and optical anisotropy of the molecule.
Subject Area
Polymer chemistry|Materials science
Recommended Citation
Shere, Aniruddha Jaywant, "Kerr effect and wide-angle light scattering studies of a para-aromatic polyamide in dilute solution" (1993). Doctoral Dissertations Available from Proquest. AAI9316715.
https://scholarworks.umass.edu/dissertations/AAI9316715