VISCOELASTIC STUDIES ON STIFF CHAIN POLYMERS

Poly-(gamma)-benzyl-(alpha),L-glutamate (PBLG), a synthetic polypeptide, is well known to molecularly disperse in the (alpha)-helical conformation in various solvents. In low concentrations these solutions are isotropic, in high concentrations liquid crystalline, and at intermediate concentrations a mixture of the two phases. PBLG is also known to aggregate in the (alpha)-helical conformation in various solvents in the isotropic phase. In an aggregating solvent the mechanism of aggregation has been thoroughly analyzed.; A second morphology available to solutions of rigid rod polymers is that of a gel. Gelation occurs upon phase separation, so the gel is actually a biphasic system. Gel structure and kinetics of gelation are studied by measuring rheological properties. The effects of molecular association in the isotropic phase on the rheological properties of the gels are made by comparing results of PBLG in an aggregating solvent with those in a non-aggregating system. It is found that aggregation has little effect on the morphology and rheological properties of the biphasic region. Unlike gels studied so far in literature, rheological properties of these gels showed very little dependence on concentration, temperature and molecular weight. Findings of rheological measurements are explained by the spinodal decomposition mechanism of phase separation. The source of elastic energy in the gels studied is discussed.; Formation of gels by rod-like macromolecules is observed also in biological systems. The non-biological system of PBLG/aggregating solvent is correlated with an aqueous sickle cell deoxyhemoglobin system. Under no or low oxygen pressure, sickle cell hemoglobin (HbS) aggregates to form rod-like molecules, ultimately forming gels. Gel structure is characterized by measuring its viscoelastic properties as functions of concentration, temperature, and kinetics of gelation. Results of gelling HbS with sodium dithionite are compared with those gelled by N(,2). Results point to a unique structure, unstudied so far in literature, in HbS gels.; Phase diagrams are predicted for rod-like systems undergoing a temperature dependent aggregation. Both Flory's model of inflexible rods and Wee and Miller's attached side-chain model are employed to predict the phase diagram. Experimentally determined phase diagrams of PBLG in aggregating and non-aggregating solvents are compared.