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

The dynamic variation of optical birefringence during solution polycondensation of rigid rodlike molecules in a simple shear flow is obtained. At relatively high shear rates (413 s-1) and late stages of the polymerization the orientation of the molecules is found to be significant. Molecular orientation is important in such reactions since it increases the polymerization rate and alters the molecular weight distribution (Agarwal, U. S.; Khakhar, D. V. Nature 1992, 360, 53). The birefringence at different shear rates (gamma) over the course of the polymerization is found to depend only on gamma/D(r), where D(r) is the rotational diffusivity. The predictions of the theory of Marrucci and Grizzuti (J. Polym. Sci., Polym. Lett. Ed. 1983, 21, 83), however, show large deviations in comparison to the experimental birefringence measurements. The experiments are carried out using terephthaloyl chloride and p-phenylenediamine to produce poly(p-phenyleneterephthalamide) in a mixed solvent at low temperatures. A two-reactor system is used in which the second reactor is designed to give a uniform simple shear flow and to allow for measurement of birefringence during polymerization.