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

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