Mesophase Formation and Chain Rigidity in Cellulose and Derivatives. 1. (Hydroxypropyl)cellulose in Dimethylacetamide

The phase diagrams of (hydroxypropyl)cellulose (HPC) in water at 20 °C and in dimethylacetamide (DMAc) between 20 and 130 °C were determined up to concentrations of ~80% polymer. Phase equilibria were determined via optical microscopy, viscosity, ultracentrifugation, and analytical techniques. The molecular weight of the HPC samples investigated varied between 132 000 and 479 000. Fractions of these samples were used to determine the persistence length of HPC in DMAc from intrinsic viscosity measurements at 25 and 70 °C. The critical polymer volume fraction v2* at which a cholesteric mesophase appears is ~0.35 at room temperature and increases, in DMAc, with temperature. v2* is not greatly affected by molecular weight. The ratio of the critical compositions in the biphasic region is considerably smaller than observed for other polydisperse systems. The persistence length of HPC in DMAc was found to be 65 A (±15 A) at 25 °C and 45 A at 70 °C. An approximate correction for excluded volume effects would lower the above figure by ~15 A. The results are discussed in terms of recent theories of liquid crystalline solutions. Provided the axial ratio of the solute is calculated on the basis of the Kuhn statistical segment, the body of the results is satisfactorily described by the Matheson-Flory theory of semirigid mesogens and by the lattice theory of hard rods with anisotropic dispersion forces. © 1983, American Chemical Society. All rights reserved.