Dilute solution properties of 13 dextrans with different molar masses in water and 0.5 M NaOH were investigated. Seven of these samples were products of Sigma prepared by bacteria from Leuconostoc mesenteroides, one was obtained by fractionation of the dextran with the highest molar mass, and five samples were obtained by degradation via controlled acid hydrolysis. Static and dynamic light scattering, viscometry and analysis of the reducing end group were applied. The molar mass dependencies of the radius of gyration R g, the hydrodynamic radius Rh, the second virial coefficient A2 and the intrinsic viscosity [η] for the nonfractionated samples were determined. The results are compared with data from the literature. Size exclusion chromatography in on-line combination with multiple-angle laser light scattering and viscosity detection revealed different calibration curves Mi vs Ve for the studied samples. The molar mass dependencies of the radii and intrinsic viscosities could be measured. The data of the radii of gyration from four fractionated samples were found to form one common curve. The intrinsic viscosities, on the other hand, gave two curves, one for the Sigma sample and another one for the aciddegraded samples. These findings are discussed in comparison with the nonfractionated samples. The polydispersity of dextrans, like those for other hyperbranched polysaccharides, increased strongly with Mw but weaker than predicted by theory. Generalized ratios F ) Rg/Rh and Vr ) A2Mw/[η] are considered and discussed in comparison with data from other laboratories and compared with predicted values. The coil-coil interpenetration function Ψ and the solvent-coil draining function Φ were found to increase with the molar mass as a result of increasing branching density. † Dedicated to Professor Cristofor I. Simionescu,"P. Poni" Instiute of Macromolecular Chemistry, Iasi, Romania, on the occasion of his 80th birthday.

Formation and structural transformation of inverse poly(styrene)-block-poly(2-vinylpyridine) micelles whose polyvinylpyridine core was loaded with HAuCl4 or with elementary gold nanoclusters was studied by combined static and dynamic light scattering. A transformation in the morphology from spherical particles (small R g/R h ratio) to large anisomeric objects (large R g/R h ratio) was observed by decreasing the concentration of the block copolymer below the critical micelle concentration. At this point, the polymer chains are molecularly dispersed and no longer able to prevent uncontrolled growth of the gold nanoclusters.

Six starches of different amylose content were studied by static light scattering from very dilute aqueous solutions at 20°C. Reproducible results were obtained after submitting the solutions to a controlled autoclaving step where the solutions were heated up to 135‐155°C. Amylose rich starches exhibited significantly different angular dependences from those with low amylose content. The high experimental accuracy of the angular dependences allowed separate determination of the molar masses Mw and radii of gyration Rg for both components in the mixture. Molar masses of 60‐106 to 110‐ 106 and radii around 220nm were found for the amylopectins from the various starches. Unexpectedly high molar masses between 450‐103 and 2.5‐106 were found for the amylose components but only low radii of gyration. Comparison with synthetic amyloses indicate strong intra and intermolecular aggregation in the form of laterally (side‐by‐side) aligned chains which could contain up to 35 amylose chains. The possibility of a quantitative determination of the degree of branching via the shrinking factor g (=Rg2Ap/Rg2Am I at the same molar mass) is discussed at some length.

Dilute solutions of glycogen from mussels (shellfish) and of different degradation steps were investigated by static and dynamic light scattering, viscometry, and end group analysis of the reducing end. The data were analyzed in comparison with theory for hyperbranched polymers. In the monomer of the A type, the functional group B2 (resulting in α(1, 6) linkages) has a much lower reactivity than that of the B1 group (leading to α(1, 4) linkages and chain growth). Qualitative agreement in behavior was found with the nonfractionated samples, but the effective branching density, derived from the applied physical techniques, was found to be considerably lower than that known from chemical analysis. SEC fractionation in on-line combination with multiple-angle laser light scattering and a viscosity detector revealed molar mass distributions that are composed of two main components. These components differ in their physical properties. The required examination was possible because R g and [η] could be measured for each slice. Shrinking factors g = R g 2 b/R g 2 lin and g‘ = [η]b/[η]lin were determined. The results of quantitative analysis are discussed in relation to current theories.

The solution properties of three dextrans in water with molar masses of 334 000, 506 000 and 2 660 000 g/mol were investigated in a concentration range of 0.1−30%, 0.1−40% and 0.05−65% w/v, respectively. Static and dynamic light scattering, viscometry, and rheological techniques were applied. The forward scattering (at scattering angle θ = 0) could be separated in contributions resulting from repulsive interactions and the true molar mass M w(c) at concentration c. A similar procedure was applied to the apparent radius of gyration to derive the true radius of gyration R g(c). A mean field and a scaling approach were applied, and the difference in the results obtained are discussed. Both molecular parameters remained unchanged up to three times the overlap concentration. At higher concentrations a pronounced increase in M w(c) and R g(c) indicated association. The high M w dextran developed a reversible gel point and critical behavior of percolation theory. The time correlation function of dynamic light scattering displayed fast and slow motions where the slow motion was assigned to clusters. Separating the effect of thermodynamic interactions from the mutual diffusion coefficient allowed the self-diffusion coefficient to be obtained, which is governed by hydrodynamic interactions. The range of this interaction was estimated and compared with the cluster size. The zero shear viscosity showed common behavior with a fairly weak increase in the dilute regime and a steep increase at higher concentrations.