Light scattering and viscosity studies on some branched starch polymers

Preliminary studies are reported regarding the molecular weight of amylopectins and limit dextrins from various sources, using the light scattering method. Apparent molecular weights of all samples are in the millions, and centrifugation studies conclusively demonstrate that the high value determined by light scattering is not due to the presence of relatively insignificant percentages of undispersed material of much larger particle weight. One normal KOH was used as solvent. Since the possibility of air‐alkaline degradation exists using this solvent, some studies designed to determine the importance of this factor are reported. It was found that if air was excluded the particle weights remained in the millions for as long as 54 days, during which time the samples were degraded to less than one hundredth the original weight if air or pure oxygen were present. Further experiments demonstrated that the dispersions were stable during the time necessary for light scattering runs. Intrinsic viscosity data on the amylopectins and their limit dextrins are reported. The intrinsic viscosity of a given amylopectin and the derived limit dextrin are very similar, and in general it is found that there is a very low positive dependence of intrinsic viscosity upon molecular weight for these materials, a result to be expected on the basis of the extensive branching.