EFFECTS OF TEMPERATURE AND SOLVENT ON THE RHEOOPTICAL BEHAVIOR OF HYDROXYPROPYLCELLULOSE SOLUTIONS

The effects of solvent and temperature on the rheo-optical behavior of hydroxypropylcellulose (HPC) solutions in water and acetic acid have been studied using flow birefringence, quiescent circular birefringenc e, and intrinsic viscosity. Measurements of steady state and transient flow birefringence suggest that the flexibility of the HPC molecule i n water increases with increasing temperature, while it remains relati vely constant in acetic acid. The relatively small temperature-induced changes of HPC are contrasted with the flow birefringence behavior of PBLG (poly(gamma-benzyl L-glutamate)) in the mixed-solvent system, di chloroacetic acid-1,2 dichloroethane, in which it undergoes a coil-hel ix transition. Results indicate that the effects of conformational cha nges on the dynamical behavior of HPC can be described in terms of a w ormlike chain whose rigidity depends on the solvent as well as tempera ture and polymer molecular weight. A discussion of the possible roles of thermodynamic and structural effects on the molecular rigidity lead s to the conclusion that structural effects are more likely.