ON THE INTRINSIC-VISCOSITY OF ANIONIC AND NONIONIC RODLIKE POLYSACCHARIDE SOLUTIONS

The ionic strength dependence of intrinsic viscosity as a function of molecular weight was observed substantially for the anionic xanthan po lyelectrolyte, while the intrinsic viscosity of nonionic schizophyllan does not change with ionic strength. Ultrasonic degradation was appli ed as the best mean of obtaining polymer fractions of different molecu lar weights. It is true, as expected, that schizophyllan has a more ri gid triple helix backbone than that of xanthan. As the molecular weigh t increases, the extension coefficient epsilon of the xanthan chain wi th ionic strength is found empirically to increase by order 1,48 of mo lecular weight. Using the Yamakawa-Fujii theory for worm-like chains, both the persistence length q and the contour length L(c) were determi ned from the best fit of the experimental data of intrinsic viscosity for different ionic strengths to the theoretical curves. The stiffness parameter was established from the ratio of the Kuhn statistical segm ent length (i. e., twice the persistence length) to the contour length . As the molecular weight decreases, stiff chains of short degraded xa nthan become rodlike, while they become gradually worm-like with incre asing molecular weight. It also can be seen that the chain stiffness d epends on the ionic strength.