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The study of associating polymers is complicated by the fact that at a finite concentration only an a parent molar mass is directly measured. This apparent molar mass deviates From the true one because of thermodynamic interaction. In a good solvent the repulsive interaction can be fully described in terms of the second virial coefficient, which can be measured at very low concentrations, and a correction can be made for the true molar mass. The technique has been successively applied to P-galactosidase in a phosphate buffer and to cellulose 2,Sacetate in acetone. The gel point could be determined, and critical behavior was found in very good agreement with percolation prediction. Two other methods were employed and tested. One is based on the condition that the longest relaxation time must diverge at the gel point, and correspondingly the translational diffusion coefficient should go to zero. The second criterion consists of the prediction that power law behavior should be observed for the time correlation function of dynamic light scattering as well as for the frequency dependent storage and loss moduli.These predictions were indeed found to hold for two polysaccharides which form thermoreversible gels in water at a fairly low salt concentration. The two polysaccharides are the Tamarind seeds polysaccharide in 1M Na,SO and an exopolysaccharide from Rhizobium leguminosarum, strain 8002 in 0.lk NaCl solutions respectively.

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Cellulose and their derivatives only rarely form molecularly dispersed solutions. Colloidal aggregates of yet not fully explored supramolecular structure remain preserved even at the highest dilution. The present contribution is concerned with the determination of the number of aggregated chains per colloid particle. In some cases the aggregation number could be directly determined but for the non‐ionic, partial substituted cellulose‐ethers the degree of polymerization of the non‐aggregated cellulose was not sufficiently well known. A detailed analysis of the angular dependencies of scattered light revealed for the large aggregates a star‐shaped structure. The smaller ones were better described by a worm‐like structure. These observations led to the suggestion of a fringed micelle model where several chains are laterally assembled in a rigid stem leaving at both ends coronas of f/2 dangling chains. Recent SANS experiments support this model. The estimated chain length of a single strand was found with DPw = (4–20)×103 much too high and led to the conclusion that 4–20 chains must be co‐linearly (staggered) associated to form one strand. The obtained overall aggregation numbers are close to those found for cellulose in NMMNO and vary from 10 to 800. The similarity of the supramolecular structures in aggregation numbers and dimensions is interpreted as reminiscent of the semi‐crystalline structure of the parental native cellulose fibers. Much lower aggregation numbers were found for cellulose xanthogenates (viscose) in NaOH solution and for cellulose 2.5‐acetate in acetone than for cellulose in NMMNO.

: The equatorial configuration of the p( 1,4)glycosidic bond predestines a stretched chain conformation. These topological characteristics form the basis for laterally aggregated supramolecular structures in the solid state as well as m the concentrated solution regime. Partially substituted derivatives develop water solubility, but the dissolution process stops at a certain colloidal level. The aggregates show structural properties which are best descnied by a fringed micelle. These objects are built up of laterally aggregated chains forming a stem and have a peripheral shell of dangling chain sections. The striking dynamic properties indicate no segment interpenetration, and the particles lose gradually their shell mobility as the overlap concentration is exceeded.