CHARACTERIZATION AND FLOW PROPERTIES OF LYOTROPIC ULTRAHIGH-MOLAR-MASS POLYSACCHARIDE MESOPHASES

The occurrence of lyotropic mesophases in solutions of various polysaccharides, such as non-ionic schizophyllan and anionic xanthan, was demonstrated by means of polarizing microscopy. In contrast to synthetic polymers where the formation of liquid-crystalline phases has been attributed to the presence of mesogenic groups in the main- or side-chain, here a helical structure is a prerequisite for the formation of mesophases. It was then shown that the stability of the helix is dependent on the chemical structure and the arrangement of the side groups. Apart from their optical anisotropy, some lyotropic mesophases are distinguished by extraordinary viscous and elastic properties (e.g. maximum behaviour of viscosity). The viscoelastic material functions were determined by rheological methods. A precise characterization of the chemical and steric microstructure should provide information on the ability of polysaccharides to form mesophases. Determination of the chemical microstructure (quaternary polymer) was carried out by H-1 NMR spectroscopy after ultrasonic degradation. Low- and multi-angle laser light scattering were employed for the determination of the steric microstructure which indicates an expanded semi-flexible structure. The experimental results were compared with those from molecular modelling.