SHEAR-FLOW INDUCED ORIENTATION DEVELOPMENT DURING HOMOGENEOUS SOLUTION POLYMERIZATION OF RIGID RODLIKE MOLECULES

The dynamic variation of optical birefringence during solution polycon densation of rigid rodlike molecules in a simple shear flow is obtaine d. At relatively high shear rates (413 s-1) and late stages of the pol ymerization the orientation of the molecules is found to be significan t. Molecular orientation is important in such reactions since it incre ases the polymerization rate and alters the molecular weight distribut ion (Agarwal, U. S.; Khakhar, D. V. Nature 1992, 360, 53). The birefri ngence at different shear rates (gamma) over the course of the polymer ization is found to depend only on gamma/D(r), where D(r) is the rotat ional diffusivity. The predictions of the theory of Marrucci and Grizz uti (J. Polym. Sci., Polym. Lett. Ed. 1983, 21, 83), however, show lar ge deviations in comparison to the experimental birefringence measurem ents. The experiments are carried out using terephthaloyl chloride and p-phenylenediamine to produce poly(p-phenyleneterephthalamide) in a m ixed solvent at low temperatures. A two-reactor system is used in whic h the second reactor is designed to give a uniform simple shear flow a nd to allow for measurement of birefringence during polymerization.