Determination of radii of gyration of particles in the 200 to 70 Å interval by the light scattering method. Polystyrene in toluene and poly(methyl methacrylate) in acetonitrile

First results obtained with an apparatus constructed in our laboratory for precision determination of radii of gyration of particles in solution by the light scattering method are described. The utilized principle of measuring the scattering curves yields a much more exact dependence of the scattering intensity on the angle which permits to solve the problem of applying the light scattering technique for determining the radii of gyration rg for particles of 200 to 70Å. For the example of low molecular weight standard polystyrene samples in toluene (molecular weights 51 000 and 200 000) it is shown that the radii of gyration of such molecules can be determined with an error of no worse than ±2% (rg = 77 Å and 167 Å at 22°C resp.). These values are in exact quantitative accordance with the viscosity data of these samples and also fall on the gradual curve of the rg dependence on the molecular weight, obtained in the range of low molecular weights by Kirste et al., and in the range of high molecular weights by Baumann with standard light scattering methods.